Slide 1

Electronics
Principles & Applications
Sixth Edition

Charles A. Schuler
Chapter 5

Transistors
(student version)
©2003

Glencoe/McGraw-Hill

INTRODUCTION
• Amplification
• Transistors
• Characteristic Curves
• Transistor Testing
• Other Transistor Types
• Transistors as Switches

Dear Student:
This presentation is arranged in segments.
Each segment is preceded by a Concept
Preview slide and is followed by a Concept
Review slide. When you reach a Concept
Review slide, you can return to the
beginning of that segment by clicking on the
Repeat Segment button. This will allow you
to view that segment again, if you want to.

Concept Preview
• Amplifiers provide gain (the output is larger
than the input).
• Transistors have gain.
• Transistors have a collector, a base, and an
emitter.
• The C-B junction is reverse biased.
• The B-E junction is forward biased.
• Most of the emitter carriers reach the collector.
• The base current is relatively small but controls
the larger currents.

In

Gain =

Amplifier

Out

In

Out

NPN Transistor Structure

The collector is lightly doped.

N

C

The base is thin and
is lightly doped.

P

B

The emitter is heavily doped.

N

E

NPN Transistor Bias
No current flows.
The C-B junction
is reverse biased.

N

C

P

B

N

E

NPN Transistor Bias

The B-E junction
is forward biased.

Current flows.

N

C

P

B

N

E

NPN Transistor Bias
IC
Current flows
everywhere.
Most of the emitter carriers
diffuse through the thin base
When
both
junctions
region since they are attracted
biased....
by are
the collector.

Note that IB is smaller
than IE or IC.

N

C

P

B

N

E

IB

IE

Note: when the
switch opens, all
currents go to zero.
Although IB is smaller
it controls IE and IC.

Gain is something small
controlling something large
(IB is small).

IC
N

C

P

B

N

E

IB

IE

Transistor Structure and Bias Quiz
The heaviest doping is found in
the ___________ region.

emitter

The thinnest of all three regions
is called the ____________.

base

The collector-base junction is
___________ biased.

reverse

The base-emitter junction is
____________ biased.

forward

The majority of the emitter
carriers flow to the ___________.

collector

Concept Review
• Amplifiers provide gain (the output is larger than
the input).
• Transistors have gain.

• Transistors have a collector, a base, and an emitter.
• The C-B junction is reverse biased.
• The B-E junction is forward biased.

• Most of the emitter carriers reach the collector.
• The base current is relatively small but controls the
larger currents.
Repeat Segment

Concept Preview
• The base to collector gain is called b (beta).
• To find b, divide the collector current by the
base current.
• The emitter current is the largest since it is the
sum of the base and collector currents.
• PNP transistors have opposite polarity from
NPN transistors.

• In an NPN transistor, the major flow is made
up of electrons.
• In a PNP transistor, the major flow is made up
of holes.

IC = 99 mA

The current gain from
base to collector
is called b.
IB = 1 mA

b =

99
ICmA
1IBmA

= 99

IE = 100 mA

C
P

B

N

E

IC = 99 mA
Kirchhoff’s
current law:

IB = 1 mA

C
P

B

N

E

IE = I B + I C

= 1 mA + 99 mA
= 100 mA
IE = 100 mA

IC = 99 mA
In a PNP transistor,
holes flow from
emitter to collector.

IB = 1 mA
Notice the PNP
bias voltages.

C
B

E

IE = 100 mA

Transistor Currents Quiz
b is the ratio of collector current to
______ current.

base

The sum of the base and collector
currents is the __________ current.

emitter

In NPN transistors, the flow from emitter
to collector is composed of _______.

electrons

In PNP transistors, the flow from emitter
to collector is composed of _______.

holes

Both NPN and PNP transistors show
__________ gain.

current

Concept Review
• The base to collector gain is called b (beta).
• To find b, divide the collector current by the
base current.
• The emitter current is the largest since it is the
sum of the base and collector currents.
• PNP transistors have opposite polarity from
NPN transistors.
• In an NPN transistor, the major flow is made
up of electrons.
• In a PNP transistor, the major flow is made up
of holes.
Repeat Segment

Concept Preview
• The NPN schematic symbol shows the emitter
arrow as Not Pointing iN.
• The collector curves are a graph of collector
voltage versus collector current.
• Both dc beta (bdc) and ac beta (bac) can be
determined from the collector curves.
• The collector circuit of a transistor can be
modeled as a resistor, as a closed switch or as
an open switch.
• The amount of base current determines which
of the three models applies.

NPN Schematic Symbol
Collector

Base

C
B E

Emitter
Memory aid: NPN
means Not Pointing iN.

PNP Schematic Symbol
Collector

Base

C
B E

Emitter

IC

This circuit is used to
collect IC versus
VCE data for
several values of IB.
C

IB
B

E

VCE

When graphed, the data provide an
NPN collector family of curves.
100 mA

14
12
10
IC in mA 8
6
4
2

80 mA
60 mA
40 mA
20 mA

0 2 4 6

8 10 12 14 16 18

VCE in Volts

0 mA

100 mA

14
12
10
IC in mA 8
6
4
2

80 mA
60 mA

40 mA
20 mA

0 2 4 6

8 10 12 14 16 18

0 mA

VCE in Volts

b =

14
mA
6ICmA
40
IB mA
100
mA

150
== 140

This type of gain
is called bdc or hFE.

100 mA

14
12
10
IC in mA 8
6
4
2

80 mA
60 mA

40 mA
20 mA

0 2 4 6

bac =

2.5DImA
C
20DImA
B

8 10 12 14 16 18

0 mA

VCE in Volts
= 125

Another type of gain
is called bac or hfe.

100 mA

14
12
10
IC in mA 8
6
4
2

80 mA
60 mA

40 mA
20 mA

0 2 4 6
IB

C

8 10 12 14 16 18
VCE in Volts

0 mA

With these values of IB:
The C-E model is a resistor.
E

100 mA

14
12
10
IC in mA 8
6
4
2
0 2 4 6
IB

80 mA
60 mA

40 mA
20 mA
8 10 12 14 16 18
VCE in Volts

0 mA

When IB >> 100 mA
VCE @ 0
The model is a closed switch.

100 mA

14
12
10
IC in mA 8
6
4
2
0 2 4 6
IB

80 mA
60 mA

40 mA
20 mA
8 10 12 14 16 18
VCE in Volts

0 mA

When IB = 0
IC = 0
The model is an open switch.

Transistor Operating Conditions Quiz
When IB is large and VCE @ 0, the transistor
acts as a ___________ switch.
closed
When IB = 0 and IC = 0, the transistor
acts as an ___________ switch.

open

When IB > 0 and VCE > 0, the transistor
acts as a ___________.

resistor

Two current gain measures are bdc and
__________.

bac

The symbol hfe is the same as _________.

bac

Concept Review
• The NPN schematic symbol shows the emitter
arrow as Not Pointing iN.
• The collector curves are a graph of collector
voltage versus collector current.
• Both dc beta (bdc) and ac beta (bac) can be
determined from the collector curves.
• The collector circuit of a transistor can be
modeled as a resistor, as a closed switch or as
an open switch.
• The amount of base current determines which
of the three models applies.
Repeat Segment

Concept Preview
• It is possible to test transistors out-of-circuit
using an ohmmeter.
• The E-B and C-B junctions act as diodes
during ohmmeter testing.

• The C-E test shows a high resistance because
two junctions are involved; one of which is
reverse biased by the ohmmeter.
• Gain can be verified by using a resistor in
conjunction with the ohmmeter test.

NPN

V

mA

E
B
C

The E-B junction is forward biased by the ohmmeter.

NPN

V

mA

E
B
C

The C-E resistance is very high.

NPN

V

mA

E
B
C
100 kW

The meter reading is < 100 kW due to gain.

Concept Review
• It is possible to test transistors out-of-circuit
using an ohmmeter.
• The E-B and C-B junctions act as diodes
during ohmmeter testing.
• The C-E test shows a high resistance because
two junctions are involved; one of which is
reverse biased by the ohmmeter.
• Gain can be verified by using a resistor in
conjunction with the ohmmeter test.
Repeat Segment

Concept Preview
• Bipolar junction transistors (BJTs) are controlled by
base current.
• Junction field effect transistors (JFETs) are controlled
by gate voltage.

• JFETs operate in the depletion mode (as normally on
devices).
• Metal oxide semiconductor field effect transistors
(MOSFETs) usually operate in the enhancement mode
(as normally off devices).
• Insulated gate bipolar transistors (IGBTs) are modified
MOSFETs and have very low on-resistance.
• Unijunction transistors (UJTs) are not used as
amplifiers.

Current In

The BJT is
a current
amplifier.

Current
Amplifier

Current Out

Voltage In

The JFET is
a voltage
controlled
amplifier.

Voltage
Amplifier

Current Out

Source

Gate

Drain

P

N-channel
P-type substrate
Structure of an
N-channel JFET

The channel has carriers so it
conducts from source to drain.

Drain

Gate
Source

Source

Gate

Drain

P

N-channel
P-type substrate

A negative gate voltage
can push the carriers from
the channel and turn
the JFET off.

Drain

Gate
Source

0V
-1 V
-2 V

ID in mA

-3 V

VGS

-4 V

0

-5 V
VDS in Volts

This is known as a depletion-mode device.
N-channel JFET drain family of characteristic curves

It’s possible to make enhancement
type field effect transistors as well.
Metal
oxide
insulator

Drain

n

Gate

VGG

D

VDD

p

G

n

S
N-channel
MOSFET

Source

Gate bias enhances the channel and turns the device on.

5V
4V
3V

ID in mA

2V

VGS

1V

0

0V
Drain

VDS in Volts

Enhancement mode
MOSFET drain family of
characteristic curves

Gate
Source

The IGBT (insulated gate bipolar transistor)
Operation and structure
similar to a MOSFET
Voltage controlled
(like the MOSFET)
Has one more junction
than a MOSFET
Hole injection reduces
the collector resistance

Faster turn off than
BJTs but not as fast
as MOSFETS

RCE = 8.33 mW

Three major device technologies

hole injection
Extra
junction

Courtesy of Powerex, Inc.

Typical IGBT Driver Circuit
Typically +15 V for turn on
Typically - 5 to -15 V for turn off

Control signal

IGBT

Powerex IGBT Module Structure

Powerex high voltage IGBT package

Emitter voltage

The unijunction transistor fires
when its emitter voltage reaches VP.
VP

Then, the emitter voltage
drops due to its negative
resistance characteristic.
Base 2

Emitter current
Emitter

The UJT is not useful as an amplifier.
It is used in timing and control applications.

Base 1

Other Transistor Types Quiz
BJTs are _________-controlled
amplifiers.

current

FETs are __________-controlled
amplifiers.

voltage

JFETs operate in the __________ mode. depletion
MOSFETs operate in the __________
mode.

enhancement

IGBTs are __________-controlled
amplifiers.

voltage

UJTs are not useful as __________.

amplifiers

Concept Review
• Bipolar junction transistors (BJTs) are controlled by
base current.
• Junction field effect transistors (JFETs) are controlled
by gate voltage.
• JFETs operate in the depletion mode (as normally on
devices).
• Metal oxide semiconductor field effect transistors
(MOSFETs) usually operate in the enhancement mode
(as normally off devices).
• Insulated gate bipolar transistors (IGBTs) are modified
MOSFETs and have very low on-resistance.
• Unijunction transistors (UJTs) are not used as
amplifiers.
Repeat Segment

Concept Preview
• BJTs can be used as switches.
• No base current = switch is off.
• High base current = switch is on.
• The dissipation is always zero in an ideal
switch: off = no current flow and on = no
voltage drop.

• MOSFETs can also be used as switches: no
gate voltage = switch is off and high gate
voltage = switch is on.

How do transistor switches work?
Can be viewed as solid state relays:
they are either ON or they are OFF.
BJT switches are characterized by:
high base current (switch is on)
(or no base current … off)

low resistance from collector to emitter (on)
(or very high resistance … off)
low collector dissipation (on or off)
PC = VCE x IC
PC = 0 x IC = 0 W
(on)
(or PC = VCE x 0 = 0 W … off)

NPN SWITCH
LOAD

RCE @ 
W
0W
DRIVER

The
The
driver
driver
output
output
isiszero
positive,
volts,
IIBB>=I0
0and
andthe
theload
loadis
ison
off
The
driver
output
is
zero
volts,
B = 0 and ILOAD = 0

PNP SWITCH
DRIVER

LOAD

The
Z):
Thedriver
driveroutput
outputisgoes
isoff
off(high
(highthe
Z):the
theresistor
resistor
low:
voltage
drop
pulls
the
base
voltage
up
that
VV
pulls
thethe
base
voltage
upso
soV
that
across
resistor
makes
BE
BE==00
BE negative

PNP SWITCH WITH NPN DRIVER

LOAD

NPN SWITCH WITH PNP DRIVER
(NEGATIVE POWER SUPPLY)

VV
0VV
BE
BE@ @+0.7

VVBE
0 VV
BE@@-0.7

LOAD

STEPPER MOTOR

A

B

C

A

Enhancement mode
power MOSFETs
used as switches

B

C
D

D

Concept Review
• BJTs can be used as switches.
• No base current = switch is off.
• High base current = switch is on.
• The dissipation is always zero in an ideal
switch: off = no current flow and on = no
voltage drop.
• MOSFETs can also be used as switches: no
gate voltage = switch is off and high gate
voltage = switch is on.
Repeat Segment

REVIEW
• Amplification
• Transistors
• Characteristic Curves
• Transistor Testing
• Other Transistor Types
• Transistors as Switches


Slide 2

Electronics
Principles & Applications
Sixth Edition

Charles A. Schuler
Chapter 5

Transistors
(student version)
©2003

Glencoe/McGraw-Hill

INTRODUCTION
• Amplification
• Transistors
• Characteristic Curves
• Transistor Testing
• Other Transistor Types
• Transistors as Switches

Dear Student:
This presentation is arranged in segments.
Each segment is preceded by a Concept
Preview slide and is followed by a Concept
Review slide. When you reach a Concept
Review slide, you can return to the
beginning of that segment by clicking on the
Repeat Segment button. This will allow you
to view that segment again, if you want to.

Concept Preview
• Amplifiers provide gain (the output is larger
than the input).
• Transistors have gain.
• Transistors have a collector, a base, and an
emitter.
• The C-B junction is reverse biased.
• The B-E junction is forward biased.
• Most of the emitter carriers reach the collector.
• The base current is relatively small but controls
the larger currents.

In

Gain =

Amplifier

Out

In

Out

NPN Transistor Structure

The collector is lightly doped.

N

C

The base is thin and
is lightly doped.

P

B

The emitter is heavily doped.

N

E

NPN Transistor Bias
No current flows.
The C-B junction
is reverse biased.

N

C

P

B

N

E

NPN Transistor Bias

The B-E junction
is forward biased.

Current flows.

N

C

P

B

N

E

NPN Transistor Bias
IC
Current flows
everywhere.
Most of the emitter carriers
diffuse through the thin base
When
both
junctions
region since they are attracted
biased....
by are
the collector.

Note that IB is smaller
than IE or IC.

N

C

P

B

N

E

IB

IE

Note: when the
switch opens, all
currents go to zero.
Although IB is smaller
it controls IE and IC.

Gain is something small
controlling something large
(IB is small).

IC
N

C

P

B

N

E

IB

IE

Transistor Structure and Bias Quiz
The heaviest doping is found in
the ___________ region.

emitter

The thinnest of all three regions
is called the ____________.

base

The collector-base junction is
___________ biased.

reverse

The base-emitter junction is
____________ biased.

forward

The majority of the emitter
carriers flow to the ___________.

collector

Concept Review
• Amplifiers provide gain (the output is larger than
the input).
• Transistors have gain.

• Transistors have a collector, a base, and an emitter.
• The C-B junction is reverse biased.
• The B-E junction is forward biased.

• Most of the emitter carriers reach the collector.
• The base current is relatively small but controls the
larger currents.
Repeat Segment

Concept Preview
• The base to collector gain is called b (beta).
• To find b, divide the collector current by the
base current.
• The emitter current is the largest since it is the
sum of the base and collector currents.
• PNP transistors have opposite polarity from
NPN transistors.

• In an NPN transistor, the major flow is made
up of electrons.
• In a PNP transistor, the major flow is made up
of holes.

IC = 99 mA

The current gain from
base to collector
is called b.
IB = 1 mA

b =

99
ICmA
1IBmA

= 99

IE = 100 mA

C
P

B

N

E

IC = 99 mA
Kirchhoff’s
current law:

IB = 1 mA

C
P

B

N

E

IE = I B + I C

= 1 mA + 99 mA
= 100 mA
IE = 100 mA

IC = 99 mA
In a PNP transistor,
holes flow from
emitter to collector.

IB = 1 mA
Notice the PNP
bias voltages.

C
B

E

IE = 100 mA

Transistor Currents Quiz
b is the ratio of collector current to
______ current.

base

The sum of the base and collector
currents is the __________ current.

emitter

In NPN transistors, the flow from emitter
to collector is composed of _______.

electrons

In PNP transistors, the flow from emitter
to collector is composed of _______.

holes

Both NPN and PNP transistors show
__________ gain.

current

Concept Review
• The base to collector gain is called b (beta).
• To find b, divide the collector current by the
base current.
• The emitter current is the largest since it is the
sum of the base and collector currents.
• PNP transistors have opposite polarity from
NPN transistors.
• In an NPN transistor, the major flow is made
up of electrons.
• In a PNP transistor, the major flow is made up
of holes.
Repeat Segment

Concept Preview
• The NPN schematic symbol shows the emitter
arrow as Not Pointing iN.
• The collector curves are a graph of collector
voltage versus collector current.
• Both dc beta (bdc) and ac beta (bac) can be
determined from the collector curves.
• The collector circuit of a transistor can be
modeled as a resistor, as a closed switch or as
an open switch.
• The amount of base current determines which
of the three models applies.

NPN Schematic Symbol
Collector

Base

C
B E

Emitter
Memory aid: NPN
means Not Pointing iN.

PNP Schematic Symbol
Collector

Base

C
B E

Emitter

IC

This circuit is used to
collect IC versus
VCE data for
several values of IB.
C

IB
B

E

VCE

When graphed, the data provide an
NPN collector family of curves.
100 mA

14
12
10
IC in mA 8
6
4
2

80 mA
60 mA
40 mA
20 mA

0 2 4 6

8 10 12 14 16 18

VCE in Volts

0 mA

100 mA

14
12
10
IC in mA 8
6
4
2

80 mA
60 mA

40 mA
20 mA

0 2 4 6

8 10 12 14 16 18

0 mA

VCE in Volts

b =

14
mA
6ICmA
40
IB mA
100
mA

150
== 140

This type of gain
is called bdc or hFE.

100 mA

14
12
10
IC in mA 8
6
4
2

80 mA
60 mA

40 mA
20 mA

0 2 4 6

bac =

2.5DImA
C
20DImA
B

8 10 12 14 16 18

0 mA

VCE in Volts
= 125

Another type of gain
is called bac or hfe.

100 mA

14
12
10
IC in mA 8
6
4
2

80 mA
60 mA

40 mA
20 mA

0 2 4 6
IB

C

8 10 12 14 16 18
VCE in Volts

0 mA

With these values of IB:
The C-E model is a resistor.
E

100 mA

14
12
10
IC in mA 8
6
4
2
0 2 4 6
IB

80 mA
60 mA

40 mA
20 mA
8 10 12 14 16 18
VCE in Volts

0 mA

When IB >> 100 mA
VCE @ 0
The model is a closed switch.

100 mA

14
12
10
IC in mA 8
6
4
2
0 2 4 6
IB

80 mA
60 mA

40 mA
20 mA
8 10 12 14 16 18
VCE in Volts

0 mA

When IB = 0
IC = 0
The model is an open switch.

Transistor Operating Conditions Quiz
When IB is large and VCE @ 0, the transistor
acts as a ___________ switch.
closed
When IB = 0 and IC = 0, the transistor
acts as an ___________ switch.

open

When IB > 0 and VCE > 0, the transistor
acts as a ___________.

resistor

Two current gain measures are bdc and
__________.

bac

The symbol hfe is the same as _________.

bac

Concept Review
• The NPN schematic symbol shows the emitter
arrow as Not Pointing iN.
• The collector curves are a graph of collector
voltage versus collector current.
• Both dc beta (bdc) and ac beta (bac) can be
determined from the collector curves.
• The collector circuit of a transistor can be
modeled as a resistor, as a closed switch or as
an open switch.
• The amount of base current determines which
of the three models applies.
Repeat Segment

Concept Preview
• It is possible to test transistors out-of-circuit
using an ohmmeter.
• The E-B and C-B junctions act as diodes
during ohmmeter testing.

• The C-E test shows a high resistance because
two junctions are involved; one of which is
reverse biased by the ohmmeter.
• Gain can be verified by using a resistor in
conjunction with the ohmmeter test.

NPN

V

mA

E
B
C

The E-B junction is forward biased by the ohmmeter.

NPN

V

mA

E
B
C

The C-E resistance is very high.

NPN

V

mA

E
B
C
100 kW

The meter reading is < 100 kW due to gain.

Concept Review
• It is possible to test transistors out-of-circuit
using an ohmmeter.
• The E-B and C-B junctions act as diodes
during ohmmeter testing.
• The C-E test shows a high resistance because
two junctions are involved; one of which is
reverse biased by the ohmmeter.
• Gain can be verified by using a resistor in
conjunction with the ohmmeter test.
Repeat Segment

Concept Preview
• Bipolar junction transistors (BJTs) are controlled by
base current.
• Junction field effect transistors (JFETs) are controlled
by gate voltage.

• JFETs operate in the depletion mode (as normally on
devices).
• Metal oxide semiconductor field effect transistors
(MOSFETs) usually operate in the enhancement mode
(as normally off devices).
• Insulated gate bipolar transistors (IGBTs) are modified
MOSFETs and have very low on-resistance.
• Unijunction transistors (UJTs) are not used as
amplifiers.

Current In

The BJT is
a current
amplifier.

Current
Amplifier

Current Out

Voltage In

The JFET is
a voltage
controlled
amplifier.

Voltage
Amplifier

Current Out

Source

Gate

Drain

P

N-channel
P-type substrate
Structure of an
N-channel JFET

The channel has carriers so it
conducts from source to drain.

Drain

Gate
Source

Source

Gate

Drain

P

N-channel
P-type substrate

A negative gate voltage
can push the carriers from
the channel and turn
the JFET off.

Drain

Gate
Source

0V
-1 V
-2 V

ID in mA

-3 V

VGS

-4 V

0

-5 V
VDS in Volts

This is known as a depletion-mode device.
N-channel JFET drain family of characteristic curves

It’s possible to make enhancement
type field effect transistors as well.
Metal
oxide
insulator

Drain

n

Gate

VGG

D

VDD

p

G

n

S
N-channel
MOSFET

Source

Gate bias enhances the channel and turns the device on.

5V
4V
3V

ID in mA

2V

VGS

1V

0

0V
Drain

VDS in Volts

Enhancement mode
MOSFET drain family of
characteristic curves

Gate
Source

The IGBT (insulated gate bipolar transistor)
Operation and structure
similar to a MOSFET
Voltage controlled
(like the MOSFET)
Has one more junction
than a MOSFET
Hole injection reduces
the collector resistance

Faster turn off than
BJTs but not as fast
as MOSFETS

RCE = 8.33 mW

Three major device technologies

hole injection
Extra
junction

Courtesy of Powerex, Inc.

Typical IGBT Driver Circuit
Typically +15 V for turn on
Typically - 5 to -15 V for turn off

Control signal

IGBT

Powerex IGBT Module Structure

Powerex high voltage IGBT package

Emitter voltage

The unijunction transistor fires
when its emitter voltage reaches VP.
VP

Then, the emitter voltage
drops due to its negative
resistance characteristic.
Base 2

Emitter current
Emitter

The UJT is not useful as an amplifier.
It is used in timing and control applications.

Base 1

Other Transistor Types Quiz
BJTs are _________-controlled
amplifiers.

current

FETs are __________-controlled
amplifiers.

voltage

JFETs operate in the __________ mode. depletion
MOSFETs operate in the __________
mode.

enhancement

IGBTs are __________-controlled
amplifiers.

voltage

UJTs are not useful as __________.

amplifiers

Concept Review
• Bipolar junction transistors (BJTs) are controlled by
base current.
• Junction field effect transistors (JFETs) are controlled
by gate voltage.
• JFETs operate in the depletion mode (as normally on
devices).
• Metal oxide semiconductor field effect transistors
(MOSFETs) usually operate in the enhancement mode
(as normally off devices).
• Insulated gate bipolar transistors (IGBTs) are modified
MOSFETs and have very low on-resistance.
• Unijunction transistors (UJTs) are not used as
amplifiers.
Repeat Segment

Concept Preview
• BJTs can be used as switches.
• No base current = switch is off.
• High base current = switch is on.
• The dissipation is always zero in an ideal
switch: off = no current flow and on = no
voltage drop.

• MOSFETs can also be used as switches: no
gate voltage = switch is off and high gate
voltage = switch is on.

How do transistor switches work?
Can be viewed as solid state relays:
they are either ON or they are OFF.
BJT switches are characterized by:
high base current (switch is on)
(or no base current … off)

low resistance from collector to emitter (on)
(or very high resistance … off)
low collector dissipation (on or off)
PC = VCE x IC
PC = 0 x IC = 0 W
(on)
(or PC = VCE x 0 = 0 W … off)

NPN SWITCH
LOAD

RCE @ 
W
0W
DRIVER

The
The
driver
driver
output
output
isiszero
positive,
volts,
IIBB>=I0
0and
andthe
theload
loadis
ison
off
The
driver
output
is
zero
volts,
B = 0 and ILOAD = 0

PNP SWITCH
DRIVER

LOAD

The
Z):
Thedriver
driveroutput
outputisgoes
isoff
off(high
(highthe
Z):the
theresistor
resistor
low:
voltage
drop
pulls
the
base
voltage
up
that
VV
pulls
thethe
base
voltage
upso
soV
that
across
resistor
makes
BE
BE==00
BE negative

PNP SWITCH WITH NPN DRIVER

LOAD

NPN SWITCH WITH PNP DRIVER
(NEGATIVE POWER SUPPLY)

VV
0VV
BE
BE@ @+0.7

VVBE
0 VV
BE@@-0.7

LOAD

STEPPER MOTOR

A

B

C

A

Enhancement mode
power MOSFETs
used as switches

B

C
D

D

Concept Review
• BJTs can be used as switches.
• No base current = switch is off.
• High base current = switch is on.
• The dissipation is always zero in an ideal
switch: off = no current flow and on = no
voltage drop.
• MOSFETs can also be used as switches: no
gate voltage = switch is off and high gate
voltage = switch is on.
Repeat Segment

REVIEW
• Amplification
• Transistors
• Characteristic Curves
• Transistor Testing
• Other Transistor Types
• Transistors as Switches


Slide 3

Electronics
Principles & Applications
Sixth Edition

Charles A. Schuler
Chapter 5

Transistors
(student version)
©2003

Glencoe/McGraw-Hill

INTRODUCTION
• Amplification
• Transistors
• Characteristic Curves
• Transistor Testing
• Other Transistor Types
• Transistors as Switches

Dear Student:
This presentation is arranged in segments.
Each segment is preceded by a Concept
Preview slide and is followed by a Concept
Review slide. When you reach a Concept
Review slide, you can return to the
beginning of that segment by clicking on the
Repeat Segment button. This will allow you
to view that segment again, if you want to.

Concept Preview
• Amplifiers provide gain (the output is larger
than the input).
• Transistors have gain.
• Transistors have a collector, a base, and an
emitter.
• The C-B junction is reverse biased.
• The B-E junction is forward biased.
• Most of the emitter carriers reach the collector.
• The base current is relatively small but controls
the larger currents.

In

Gain =

Amplifier

Out

In

Out

NPN Transistor Structure

The collector is lightly doped.

N

C

The base is thin and
is lightly doped.

P

B

The emitter is heavily doped.

N

E

NPN Transistor Bias
No current flows.
The C-B junction
is reverse biased.

N

C

P

B

N

E

NPN Transistor Bias

The B-E junction
is forward biased.

Current flows.

N

C

P

B

N

E

NPN Transistor Bias
IC
Current flows
everywhere.
Most of the emitter carriers
diffuse through the thin base
When
both
junctions
region since they are attracted
biased....
by are
the collector.

Note that IB is smaller
than IE or IC.

N

C

P

B

N

E

IB

IE

Note: when the
switch opens, all
currents go to zero.
Although IB is smaller
it controls IE and IC.

Gain is something small
controlling something large
(IB is small).

IC
N

C

P

B

N

E

IB

IE

Transistor Structure and Bias Quiz
The heaviest doping is found in
the ___________ region.

emitter

The thinnest of all three regions
is called the ____________.

base

The collector-base junction is
___________ biased.

reverse

The base-emitter junction is
____________ biased.

forward

The majority of the emitter
carriers flow to the ___________.

collector

Concept Review
• Amplifiers provide gain (the output is larger than
the input).
• Transistors have gain.

• Transistors have a collector, a base, and an emitter.
• The C-B junction is reverse biased.
• The B-E junction is forward biased.

• Most of the emitter carriers reach the collector.
• The base current is relatively small but controls the
larger currents.
Repeat Segment

Concept Preview
• The base to collector gain is called b (beta).
• To find b, divide the collector current by the
base current.
• The emitter current is the largest since it is the
sum of the base and collector currents.
• PNP transistors have opposite polarity from
NPN transistors.

• In an NPN transistor, the major flow is made
up of electrons.
• In a PNP transistor, the major flow is made up
of holes.

IC = 99 mA

The current gain from
base to collector
is called b.
IB = 1 mA

b =

99
ICmA
1IBmA

= 99

IE = 100 mA

C
P

B

N

E

IC = 99 mA
Kirchhoff’s
current law:

IB = 1 mA

C
P

B

N

E

IE = I B + I C

= 1 mA + 99 mA
= 100 mA
IE = 100 mA

IC = 99 mA
In a PNP transistor,
holes flow from
emitter to collector.

IB = 1 mA
Notice the PNP
bias voltages.

C
B

E

IE = 100 mA

Transistor Currents Quiz
b is the ratio of collector current to
______ current.

base

The sum of the base and collector
currents is the __________ current.

emitter

In NPN transistors, the flow from emitter
to collector is composed of _______.

electrons

In PNP transistors, the flow from emitter
to collector is composed of _______.

holes

Both NPN and PNP transistors show
__________ gain.

current

Concept Review
• The base to collector gain is called b (beta).
• To find b, divide the collector current by the
base current.
• The emitter current is the largest since it is the
sum of the base and collector currents.
• PNP transistors have opposite polarity from
NPN transistors.
• In an NPN transistor, the major flow is made
up of electrons.
• In a PNP transistor, the major flow is made up
of holes.
Repeat Segment

Concept Preview
• The NPN schematic symbol shows the emitter
arrow as Not Pointing iN.
• The collector curves are a graph of collector
voltage versus collector current.
• Both dc beta (bdc) and ac beta (bac) can be
determined from the collector curves.
• The collector circuit of a transistor can be
modeled as a resistor, as a closed switch or as
an open switch.
• The amount of base current determines which
of the three models applies.

NPN Schematic Symbol
Collector

Base

C
B E

Emitter
Memory aid: NPN
means Not Pointing iN.

PNP Schematic Symbol
Collector

Base

C
B E

Emitter

IC

This circuit is used to
collect IC versus
VCE data for
several values of IB.
C

IB
B

E

VCE

When graphed, the data provide an
NPN collector family of curves.
100 mA

14
12
10
IC in mA 8
6
4
2

80 mA
60 mA
40 mA
20 mA

0 2 4 6

8 10 12 14 16 18

VCE in Volts

0 mA

100 mA

14
12
10
IC in mA 8
6
4
2

80 mA
60 mA

40 mA
20 mA

0 2 4 6

8 10 12 14 16 18

0 mA

VCE in Volts

b =

14
mA
6ICmA
40
IB mA
100
mA

150
== 140

This type of gain
is called bdc or hFE.

100 mA

14
12
10
IC in mA 8
6
4
2

80 mA
60 mA

40 mA
20 mA

0 2 4 6

bac =

2.5DImA
C
20DImA
B

8 10 12 14 16 18

0 mA

VCE in Volts
= 125

Another type of gain
is called bac or hfe.

100 mA

14
12
10
IC in mA 8
6
4
2

80 mA
60 mA

40 mA
20 mA

0 2 4 6
IB

C

8 10 12 14 16 18
VCE in Volts

0 mA

With these values of IB:
The C-E model is a resistor.
E

100 mA

14
12
10
IC in mA 8
6
4
2
0 2 4 6
IB

80 mA
60 mA

40 mA
20 mA
8 10 12 14 16 18
VCE in Volts

0 mA

When IB >> 100 mA
VCE @ 0
The model is a closed switch.

100 mA

14
12
10
IC in mA 8
6
4
2
0 2 4 6
IB

80 mA
60 mA

40 mA
20 mA
8 10 12 14 16 18
VCE in Volts

0 mA

When IB = 0
IC = 0
The model is an open switch.

Transistor Operating Conditions Quiz
When IB is large and VCE @ 0, the transistor
acts as a ___________ switch.
closed
When IB = 0 and IC = 0, the transistor
acts as an ___________ switch.

open

When IB > 0 and VCE > 0, the transistor
acts as a ___________.

resistor

Two current gain measures are bdc and
__________.

bac

The symbol hfe is the same as _________.

bac

Concept Review
• The NPN schematic symbol shows the emitter
arrow as Not Pointing iN.
• The collector curves are a graph of collector
voltage versus collector current.
• Both dc beta (bdc) and ac beta (bac) can be
determined from the collector curves.
• The collector circuit of a transistor can be
modeled as a resistor, as a closed switch or as
an open switch.
• The amount of base current determines which
of the three models applies.
Repeat Segment

Concept Preview
• It is possible to test transistors out-of-circuit
using an ohmmeter.
• The E-B and C-B junctions act as diodes
during ohmmeter testing.

• The C-E test shows a high resistance because
two junctions are involved; one of which is
reverse biased by the ohmmeter.
• Gain can be verified by using a resistor in
conjunction with the ohmmeter test.

NPN

V

mA

E
B
C

The E-B junction is forward biased by the ohmmeter.

NPN

V

mA

E
B
C

The C-E resistance is very high.

NPN

V

mA

E
B
C
100 kW

The meter reading is < 100 kW due to gain.

Concept Review
• It is possible to test transistors out-of-circuit
using an ohmmeter.
• The E-B and C-B junctions act as diodes
during ohmmeter testing.
• The C-E test shows a high resistance because
two junctions are involved; one of which is
reverse biased by the ohmmeter.
• Gain can be verified by using a resistor in
conjunction with the ohmmeter test.
Repeat Segment

Concept Preview
• Bipolar junction transistors (BJTs) are controlled by
base current.
• Junction field effect transistors (JFETs) are controlled
by gate voltage.

• JFETs operate in the depletion mode (as normally on
devices).
• Metal oxide semiconductor field effect transistors
(MOSFETs) usually operate in the enhancement mode
(as normally off devices).
• Insulated gate bipolar transistors (IGBTs) are modified
MOSFETs and have very low on-resistance.
• Unijunction transistors (UJTs) are not used as
amplifiers.

Current In

The BJT is
a current
amplifier.

Current
Amplifier

Current Out

Voltage In

The JFET is
a voltage
controlled
amplifier.

Voltage
Amplifier

Current Out

Source

Gate

Drain

P

N-channel
P-type substrate
Structure of an
N-channel JFET

The channel has carriers so it
conducts from source to drain.

Drain

Gate
Source

Source

Gate

Drain

P

N-channel
P-type substrate

A negative gate voltage
can push the carriers from
the channel and turn
the JFET off.

Drain

Gate
Source

0V
-1 V
-2 V

ID in mA

-3 V

VGS

-4 V

0

-5 V
VDS in Volts

This is known as a depletion-mode device.
N-channel JFET drain family of characteristic curves

It’s possible to make enhancement
type field effect transistors as well.
Metal
oxide
insulator

Drain

n

Gate

VGG

D

VDD

p

G

n

S
N-channel
MOSFET

Source

Gate bias enhances the channel and turns the device on.

5V
4V
3V

ID in mA

2V

VGS

1V

0

0V
Drain

VDS in Volts

Enhancement mode
MOSFET drain family of
characteristic curves

Gate
Source

The IGBT (insulated gate bipolar transistor)
Operation and structure
similar to a MOSFET
Voltage controlled
(like the MOSFET)
Has one more junction
than a MOSFET
Hole injection reduces
the collector resistance

Faster turn off than
BJTs but not as fast
as MOSFETS

RCE = 8.33 mW

Three major device technologies

hole injection
Extra
junction

Courtesy of Powerex, Inc.

Typical IGBT Driver Circuit
Typically +15 V for turn on
Typically - 5 to -15 V for turn off

Control signal

IGBT

Powerex IGBT Module Structure

Powerex high voltage IGBT package

Emitter voltage

The unijunction transistor fires
when its emitter voltage reaches VP.
VP

Then, the emitter voltage
drops due to its negative
resistance characteristic.
Base 2

Emitter current
Emitter

The UJT is not useful as an amplifier.
It is used in timing and control applications.

Base 1

Other Transistor Types Quiz
BJTs are _________-controlled
amplifiers.

current

FETs are __________-controlled
amplifiers.

voltage

JFETs operate in the __________ mode. depletion
MOSFETs operate in the __________
mode.

enhancement

IGBTs are __________-controlled
amplifiers.

voltage

UJTs are not useful as __________.

amplifiers

Concept Review
• Bipolar junction transistors (BJTs) are controlled by
base current.
• Junction field effect transistors (JFETs) are controlled
by gate voltage.
• JFETs operate in the depletion mode (as normally on
devices).
• Metal oxide semiconductor field effect transistors
(MOSFETs) usually operate in the enhancement mode
(as normally off devices).
• Insulated gate bipolar transistors (IGBTs) are modified
MOSFETs and have very low on-resistance.
• Unijunction transistors (UJTs) are not used as
amplifiers.
Repeat Segment

Concept Preview
• BJTs can be used as switches.
• No base current = switch is off.
• High base current = switch is on.
• The dissipation is always zero in an ideal
switch: off = no current flow and on = no
voltage drop.

• MOSFETs can also be used as switches: no
gate voltage = switch is off and high gate
voltage = switch is on.

How do transistor switches work?
Can be viewed as solid state relays:
they are either ON or they are OFF.
BJT switches are characterized by:
high base current (switch is on)
(or no base current … off)

low resistance from collector to emitter (on)
(or very high resistance … off)
low collector dissipation (on or off)
PC = VCE x IC
PC = 0 x IC = 0 W
(on)
(or PC = VCE x 0 = 0 W … off)

NPN SWITCH
LOAD

RCE @ 
W
0W
DRIVER

The
The
driver
driver
output
output
isiszero
positive,
volts,
IIBB>=I0
0and
andthe
theload
loadis
ison
off
The
driver
output
is
zero
volts,
B = 0 and ILOAD = 0

PNP SWITCH
DRIVER

LOAD

The
Z):
Thedriver
driveroutput
outputisgoes
isoff
off(high
(highthe
Z):the
theresistor
resistor
low:
voltage
drop
pulls
the
base
voltage
up
that
VV
pulls
thethe
base
voltage
upso
soV
that
across
resistor
makes
BE
BE==00
BE negative

PNP SWITCH WITH NPN DRIVER

LOAD

NPN SWITCH WITH PNP DRIVER
(NEGATIVE POWER SUPPLY)

VV
0VV
BE
BE@ @+0.7

VVBE
0 VV
BE@@-0.7

LOAD

STEPPER MOTOR

A

B

C

A

Enhancement mode
power MOSFETs
used as switches

B

C
D

D

Concept Review
• BJTs can be used as switches.
• No base current = switch is off.
• High base current = switch is on.
• The dissipation is always zero in an ideal
switch: off = no current flow and on = no
voltage drop.
• MOSFETs can also be used as switches: no
gate voltage = switch is off and high gate
voltage = switch is on.
Repeat Segment

REVIEW
• Amplification
• Transistors
• Characteristic Curves
• Transistor Testing
• Other Transistor Types
• Transistors as Switches


Slide 4

Electronics
Principles & Applications
Sixth Edition

Charles A. Schuler
Chapter 5

Transistors
(student version)
©2003

Glencoe/McGraw-Hill

INTRODUCTION
• Amplification
• Transistors
• Characteristic Curves
• Transistor Testing
• Other Transistor Types
• Transistors as Switches

Dear Student:
This presentation is arranged in segments.
Each segment is preceded by a Concept
Preview slide and is followed by a Concept
Review slide. When you reach a Concept
Review slide, you can return to the
beginning of that segment by clicking on the
Repeat Segment button. This will allow you
to view that segment again, if you want to.

Concept Preview
• Amplifiers provide gain (the output is larger
than the input).
• Transistors have gain.
• Transistors have a collector, a base, and an
emitter.
• The C-B junction is reverse biased.
• The B-E junction is forward biased.
• Most of the emitter carriers reach the collector.
• The base current is relatively small but controls
the larger currents.

In

Gain =

Amplifier

Out

In

Out

NPN Transistor Structure

The collector is lightly doped.

N

C

The base is thin and
is lightly doped.

P

B

The emitter is heavily doped.

N

E

NPN Transistor Bias
No current flows.
The C-B junction
is reverse biased.

N

C

P

B

N

E

NPN Transistor Bias

The B-E junction
is forward biased.

Current flows.

N

C

P

B

N

E

NPN Transistor Bias
IC
Current flows
everywhere.
Most of the emitter carriers
diffuse through the thin base
When
both
junctions
region since they are attracted
biased....
by are
the collector.

Note that IB is smaller
than IE or IC.

N

C

P

B

N

E

IB

IE

Note: when the
switch opens, all
currents go to zero.
Although IB is smaller
it controls IE and IC.

Gain is something small
controlling something large
(IB is small).

IC
N

C

P

B

N

E

IB

IE

Transistor Structure and Bias Quiz
The heaviest doping is found in
the ___________ region.

emitter

The thinnest of all three regions
is called the ____________.

base

The collector-base junction is
___________ biased.

reverse

The base-emitter junction is
____________ biased.

forward

The majority of the emitter
carriers flow to the ___________.

collector

Concept Review
• Amplifiers provide gain (the output is larger than
the input).
• Transistors have gain.

• Transistors have a collector, a base, and an emitter.
• The C-B junction is reverse biased.
• The B-E junction is forward biased.

• Most of the emitter carriers reach the collector.
• The base current is relatively small but controls the
larger currents.
Repeat Segment

Concept Preview
• The base to collector gain is called b (beta).
• To find b, divide the collector current by the
base current.
• The emitter current is the largest since it is the
sum of the base and collector currents.
• PNP transistors have opposite polarity from
NPN transistors.

• In an NPN transistor, the major flow is made
up of electrons.
• In a PNP transistor, the major flow is made up
of holes.

IC = 99 mA

The current gain from
base to collector
is called b.
IB = 1 mA

b =

99
ICmA
1IBmA

= 99

IE = 100 mA

C
P

B

N

E

IC = 99 mA
Kirchhoff’s
current law:

IB = 1 mA

C
P

B

N

E

IE = I B + I C

= 1 mA + 99 mA
= 100 mA
IE = 100 mA

IC = 99 mA
In a PNP transistor,
holes flow from
emitter to collector.

IB = 1 mA
Notice the PNP
bias voltages.

C
B

E

IE = 100 mA

Transistor Currents Quiz
b is the ratio of collector current to
______ current.

base

The sum of the base and collector
currents is the __________ current.

emitter

In NPN transistors, the flow from emitter
to collector is composed of _______.

electrons

In PNP transistors, the flow from emitter
to collector is composed of _______.

holes

Both NPN and PNP transistors show
__________ gain.

current

Concept Review
• The base to collector gain is called b (beta).
• To find b, divide the collector current by the
base current.
• The emitter current is the largest since it is the
sum of the base and collector currents.
• PNP transistors have opposite polarity from
NPN transistors.
• In an NPN transistor, the major flow is made
up of electrons.
• In a PNP transistor, the major flow is made up
of holes.
Repeat Segment

Concept Preview
• The NPN schematic symbol shows the emitter
arrow as Not Pointing iN.
• The collector curves are a graph of collector
voltage versus collector current.
• Both dc beta (bdc) and ac beta (bac) can be
determined from the collector curves.
• The collector circuit of a transistor can be
modeled as a resistor, as a closed switch or as
an open switch.
• The amount of base current determines which
of the three models applies.

NPN Schematic Symbol
Collector

Base

C
B E

Emitter
Memory aid: NPN
means Not Pointing iN.

PNP Schematic Symbol
Collector

Base

C
B E

Emitter

IC

This circuit is used to
collect IC versus
VCE data for
several values of IB.
C

IB
B

E

VCE

When graphed, the data provide an
NPN collector family of curves.
100 mA

14
12
10
IC in mA 8
6
4
2

80 mA
60 mA
40 mA
20 mA

0 2 4 6

8 10 12 14 16 18

VCE in Volts

0 mA

100 mA

14
12
10
IC in mA 8
6
4
2

80 mA
60 mA

40 mA
20 mA

0 2 4 6

8 10 12 14 16 18

0 mA

VCE in Volts

b =

14
mA
6ICmA
40
IB mA
100
mA

150
== 140

This type of gain
is called bdc or hFE.

100 mA

14
12
10
IC in mA 8
6
4
2

80 mA
60 mA

40 mA
20 mA

0 2 4 6

bac =

2.5DImA
C
20DImA
B

8 10 12 14 16 18

0 mA

VCE in Volts
= 125

Another type of gain
is called bac or hfe.

100 mA

14
12
10
IC in mA 8
6
4
2

80 mA
60 mA

40 mA
20 mA

0 2 4 6
IB

C

8 10 12 14 16 18
VCE in Volts

0 mA

With these values of IB:
The C-E model is a resistor.
E

100 mA

14
12
10
IC in mA 8
6
4
2
0 2 4 6
IB

80 mA
60 mA

40 mA
20 mA
8 10 12 14 16 18
VCE in Volts

0 mA

When IB >> 100 mA
VCE @ 0
The model is a closed switch.

100 mA

14
12
10
IC in mA 8
6
4
2
0 2 4 6
IB

80 mA
60 mA

40 mA
20 mA
8 10 12 14 16 18
VCE in Volts

0 mA

When IB = 0
IC = 0
The model is an open switch.

Transistor Operating Conditions Quiz
When IB is large and VCE @ 0, the transistor
acts as a ___________ switch.
closed
When IB = 0 and IC = 0, the transistor
acts as an ___________ switch.

open

When IB > 0 and VCE > 0, the transistor
acts as a ___________.

resistor

Two current gain measures are bdc and
__________.

bac

The symbol hfe is the same as _________.

bac

Concept Review
• The NPN schematic symbol shows the emitter
arrow as Not Pointing iN.
• The collector curves are a graph of collector
voltage versus collector current.
• Both dc beta (bdc) and ac beta (bac) can be
determined from the collector curves.
• The collector circuit of a transistor can be
modeled as a resistor, as a closed switch or as
an open switch.
• The amount of base current determines which
of the three models applies.
Repeat Segment

Concept Preview
• It is possible to test transistors out-of-circuit
using an ohmmeter.
• The E-B and C-B junctions act as diodes
during ohmmeter testing.

• The C-E test shows a high resistance because
two junctions are involved; one of which is
reverse biased by the ohmmeter.
• Gain can be verified by using a resistor in
conjunction with the ohmmeter test.

NPN

V

mA

E
B
C

The E-B junction is forward biased by the ohmmeter.

NPN

V

mA

E
B
C

The C-E resistance is very high.

NPN

V

mA

E
B
C
100 kW

The meter reading is < 100 kW due to gain.

Concept Review
• It is possible to test transistors out-of-circuit
using an ohmmeter.
• The E-B and C-B junctions act as diodes
during ohmmeter testing.
• The C-E test shows a high resistance because
two junctions are involved; one of which is
reverse biased by the ohmmeter.
• Gain can be verified by using a resistor in
conjunction with the ohmmeter test.
Repeat Segment

Concept Preview
• Bipolar junction transistors (BJTs) are controlled by
base current.
• Junction field effect transistors (JFETs) are controlled
by gate voltage.

• JFETs operate in the depletion mode (as normally on
devices).
• Metal oxide semiconductor field effect transistors
(MOSFETs) usually operate in the enhancement mode
(as normally off devices).
• Insulated gate bipolar transistors (IGBTs) are modified
MOSFETs and have very low on-resistance.
• Unijunction transistors (UJTs) are not used as
amplifiers.

Current In

The BJT is
a current
amplifier.

Current
Amplifier

Current Out

Voltage In

The JFET is
a voltage
controlled
amplifier.

Voltage
Amplifier

Current Out

Source

Gate

Drain

P

N-channel
P-type substrate
Structure of an
N-channel JFET

The channel has carriers so it
conducts from source to drain.

Drain

Gate
Source

Source

Gate

Drain

P

N-channel
P-type substrate

A negative gate voltage
can push the carriers from
the channel and turn
the JFET off.

Drain

Gate
Source

0V
-1 V
-2 V

ID in mA

-3 V

VGS

-4 V

0

-5 V
VDS in Volts

This is known as a depletion-mode device.
N-channel JFET drain family of characteristic curves

It’s possible to make enhancement
type field effect transistors as well.
Metal
oxide
insulator

Drain

n

Gate

VGG

D

VDD

p

G

n

S
N-channel
MOSFET

Source

Gate bias enhances the channel and turns the device on.

5V
4V
3V

ID in mA

2V

VGS

1V

0

0V
Drain

VDS in Volts

Enhancement mode
MOSFET drain family of
characteristic curves

Gate
Source

The IGBT (insulated gate bipolar transistor)
Operation and structure
similar to a MOSFET
Voltage controlled
(like the MOSFET)
Has one more junction
than a MOSFET
Hole injection reduces
the collector resistance

Faster turn off than
BJTs but not as fast
as MOSFETS

RCE = 8.33 mW

Three major device technologies

hole injection
Extra
junction

Courtesy of Powerex, Inc.

Typical IGBT Driver Circuit
Typically +15 V for turn on
Typically - 5 to -15 V for turn off

Control signal

IGBT

Powerex IGBT Module Structure

Powerex high voltage IGBT package

Emitter voltage

The unijunction transistor fires
when its emitter voltage reaches VP.
VP

Then, the emitter voltage
drops due to its negative
resistance characteristic.
Base 2

Emitter current
Emitter

The UJT is not useful as an amplifier.
It is used in timing and control applications.

Base 1

Other Transistor Types Quiz
BJTs are _________-controlled
amplifiers.

current

FETs are __________-controlled
amplifiers.

voltage

JFETs operate in the __________ mode. depletion
MOSFETs operate in the __________
mode.

enhancement

IGBTs are __________-controlled
amplifiers.

voltage

UJTs are not useful as __________.

amplifiers

Concept Review
• Bipolar junction transistors (BJTs) are controlled by
base current.
• Junction field effect transistors (JFETs) are controlled
by gate voltage.
• JFETs operate in the depletion mode (as normally on
devices).
• Metal oxide semiconductor field effect transistors
(MOSFETs) usually operate in the enhancement mode
(as normally off devices).
• Insulated gate bipolar transistors (IGBTs) are modified
MOSFETs and have very low on-resistance.
• Unijunction transistors (UJTs) are not used as
amplifiers.
Repeat Segment

Concept Preview
• BJTs can be used as switches.
• No base current = switch is off.
• High base current = switch is on.
• The dissipation is always zero in an ideal
switch: off = no current flow and on = no
voltage drop.

• MOSFETs can also be used as switches: no
gate voltage = switch is off and high gate
voltage = switch is on.

How do transistor switches work?
Can be viewed as solid state relays:
they are either ON or they are OFF.
BJT switches are characterized by:
high base current (switch is on)
(or no base current … off)

low resistance from collector to emitter (on)
(or very high resistance … off)
low collector dissipation (on or off)
PC = VCE x IC
PC = 0 x IC = 0 W
(on)
(or PC = VCE x 0 = 0 W … off)

NPN SWITCH
LOAD

RCE @ 
W
0W
DRIVER

The
The
driver
driver
output
output
isiszero
positive,
volts,
IIBB>=I0
0and
andthe
theload
loadis
ison
off
The
driver
output
is
zero
volts,
B = 0 and ILOAD = 0

PNP SWITCH
DRIVER

LOAD

The
Z):
Thedriver
driveroutput
outputisgoes
isoff
off(high
(highthe
Z):the
theresistor
resistor
low:
voltage
drop
pulls
the
base
voltage
up
that
VV
pulls
thethe
base
voltage
upso
soV
that
across
resistor
makes
BE
BE==00
BE negative

PNP SWITCH WITH NPN DRIVER

LOAD

NPN SWITCH WITH PNP DRIVER
(NEGATIVE POWER SUPPLY)

VV
0VV
BE
BE@ @+0.7

VVBE
0 VV
BE@@-0.7

LOAD

STEPPER MOTOR

A

B

C

A

Enhancement mode
power MOSFETs
used as switches

B

C
D

D

Concept Review
• BJTs can be used as switches.
• No base current = switch is off.
• High base current = switch is on.
• The dissipation is always zero in an ideal
switch: off = no current flow and on = no
voltage drop.
• MOSFETs can also be used as switches: no
gate voltage = switch is off and high gate
voltage = switch is on.
Repeat Segment

REVIEW
• Amplification
• Transistors
• Characteristic Curves
• Transistor Testing
• Other Transistor Types
• Transistors as Switches


Slide 5

Electronics
Principles & Applications
Sixth Edition

Charles A. Schuler
Chapter 5

Transistors
(student version)
©2003

Glencoe/McGraw-Hill

INTRODUCTION
• Amplification
• Transistors
• Characteristic Curves
• Transistor Testing
• Other Transistor Types
• Transistors as Switches

Dear Student:
This presentation is arranged in segments.
Each segment is preceded by a Concept
Preview slide and is followed by a Concept
Review slide. When you reach a Concept
Review slide, you can return to the
beginning of that segment by clicking on the
Repeat Segment button. This will allow you
to view that segment again, if you want to.

Concept Preview
• Amplifiers provide gain (the output is larger
than the input).
• Transistors have gain.
• Transistors have a collector, a base, and an
emitter.
• The C-B junction is reverse biased.
• The B-E junction is forward biased.
• Most of the emitter carriers reach the collector.
• The base current is relatively small but controls
the larger currents.

In

Gain =

Amplifier

Out

In

Out

NPN Transistor Structure

The collector is lightly doped.

N

C

The base is thin and
is lightly doped.

P

B

The emitter is heavily doped.

N

E

NPN Transistor Bias
No current flows.
The C-B junction
is reverse biased.

N

C

P

B

N

E

NPN Transistor Bias

The B-E junction
is forward biased.

Current flows.

N

C

P

B

N

E

NPN Transistor Bias
IC
Current flows
everywhere.
Most of the emitter carriers
diffuse through the thin base
When
both
junctions
region since they are attracted
biased....
by are
the collector.

Note that IB is smaller
than IE or IC.

N

C

P

B

N

E

IB

IE

Note: when the
switch opens, all
currents go to zero.
Although IB is smaller
it controls IE and IC.

Gain is something small
controlling something large
(IB is small).

IC
N

C

P

B

N

E

IB

IE

Transistor Structure and Bias Quiz
The heaviest doping is found in
the ___________ region.

emitter

The thinnest of all three regions
is called the ____________.

base

The collector-base junction is
___________ biased.

reverse

The base-emitter junction is
____________ biased.

forward

The majority of the emitter
carriers flow to the ___________.

collector

Concept Review
• Amplifiers provide gain (the output is larger than
the input).
• Transistors have gain.

• Transistors have a collector, a base, and an emitter.
• The C-B junction is reverse biased.
• The B-E junction is forward biased.

• Most of the emitter carriers reach the collector.
• The base current is relatively small but controls the
larger currents.
Repeat Segment

Concept Preview
• The base to collector gain is called b (beta).
• To find b, divide the collector current by the
base current.
• The emitter current is the largest since it is the
sum of the base and collector currents.
• PNP transistors have opposite polarity from
NPN transistors.

• In an NPN transistor, the major flow is made
up of electrons.
• In a PNP transistor, the major flow is made up
of holes.

IC = 99 mA

The current gain from
base to collector
is called b.
IB = 1 mA

b =

99
ICmA
1IBmA

= 99

IE = 100 mA

C
P

B

N

E

IC = 99 mA
Kirchhoff’s
current law:

IB = 1 mA

C
P

B

N

E

IE = I B + I C

= 1 mA + 99 mA
= 100 mA
IE = 100 mA

IC = 99 mA
In a PNP transistor,
holes flow from
emitter to collector.

IB = 1 mA
Notice the PNP
bias voltages.

C
B

E

IE = 100 mA

Transistor Currents Quiz
b is the ratio of collector current to
______ current.

base

The sum of the base and collector
currents is the __________ current.

emitter

In NPN transistors, the flow from emitter
to collector is composed of _______.

electrons

In PNP transistors, the flow from emitter
to collector is composed of _______.

holes

Both NPN and PNP transistors show
__________ gain.

current

Concept Review
• The base to collector gain is called b (beta).
• To find b, divide the collector current by the
base current.
• The emitter current is the largest since it is the
sum of the base and collector currents.
• PNP transistors have opposite polarity from
NPN transistors.
• In an NPN transistor, the major flow is made
up of electrons.
• In a PNP transistor, the major flow is made up
of holes.
Repeat Segment

Concept Preview
• The NPN schematic symbol shows the emitter
arrow as Not Pointing iN.
• The collector curves are a graph of collector
voltage versus collector current.
• Both dc beta (bdc) and ac beta (bac) can be
determined from the collector curves.
• The collector circuit of a transistor can be
modeled as a resistor, as a closed switch or as
an open switch.
• The amount of base current determines which
of the three models applies.

NPN Schematic Symbol
Collector

Base

C
B E

Emitter
Memory aid: NPN
means Not Pointing iN.

PNP Schematic Symbol
Collector

Base

C
B E

Emitter

IC

This circuit is used to
collect IC versus
VCE data for
several values of IB.
C

IB
B

E

VCE

When graphed, the data provide an
NPN collector family of curves.
100 mA

14
12
10
IC in mA 8
6
4
2

80 mA
60 mA
40 mA
20 mA

0 2 4 6

8 10 12 14 16 18

VCE in Volts

0 mA

100 mA

14
12
10
IC in mA 8
6
4
2

80 mA
60 mA

40 mA
20 mA

0 2 4 6

8 10 12 14 16 18

0 mA

VCE in Volts

b =

14
mA
6ICmA
40
IB mA
100
mA

150
== 140

This type of gain
is called bdc or hFE.

100 mA

14
12
10
IC in mA 8
6
4
2

80 mA
60 mA

40 mA
20 mA

0 2 4 6

bac =

2.5DImA
C
20DImA
B

8 10 12 14 16 18

0 mA

VCE in Volts
= 125

Another type of gain
is called bac or hfe.

100 mA

14
12
10
IC in mA 8
6
4
2

80 mA
60 mA

40 mA
20 mA

0 2 4 6
IB

C

8 10 12 14 16 18
VCE in Volts

0 mA

With these values of IB:
The C-E model is a resistor.
E

100 mA

14
12
10
IC in mA 8
6
4
2
0 2 4 6
IB

80 mA
60 mA

40 mA
20 mA
8 10 12 14 16 18
VCE in Volts

0 mA

When IB >> 100 mA
VCE @ 0
The model is a closed switch.

100 mA

14
12
10
IC in mA 8
6
4
2
0 2 4 6
IB

80 mA
60 mA

40 mA
20 mA
8 10 12 14 16 18
VCE in Volts

0 mA

When IB = 0
IC = 0
The model is an open switch.

Transistor Operating Conditions Quiz
When IB is large and VCE @ 0, the transistor
acts as a ___________ switch.
closed
When IB = 0 and IC = 0, the transistor
acts as an ___________ switch.

open

When IB > 0 and VCE > 0, the transistor
acts as a ___________.

resistor

Two current gain measures are bdc and
__________.

bac

The symbol hfe is the same as _________.

bac

Concept Review
• The NPN schematic symbol shows the emitter
arrow as Not Pointing iN.
• The collector curves are a graph of collector
voltage versus collector current.
• Both dc beta (bdc) and ac beta (bac) can be
determined from the collector curves.
• The collector circuit of a transistor can be
modeled as a resistor, as a closed switch or as
an open switch.
• The amount of base current determines which
of the three models applies.
Repeat Segment

Concept Preview
• It is possible to test transistors out-of-circuit
using an ohmmeter.
• The E-B and C-B junctions act as diodes
during ohmmeter testing.

• The C-E test shows a high resistance because
two junctions are involved; one of which is
reverse biased by the ohmmeter.
• Gain can be verified by using a resistor in
conjunction with the ohmmeter test.

NPN

V

mA

E
B
C

The E-B junction is forward biased by the ohmmeter.

NPN

V

mA

E
B
C

The C-E resistance is very high.

NPN

V

mA

E
B
C
100 kW

The meter reading is < 100 kW due to gain.

Concept Review
• It is possible to test transistors out-of-circuit
using an ohmmeter.
• The E-B and C-B junctions act as diodes
during ohmmeter testing.
• The C-E test shows a high resistance because
two junctions are involved; one of which is
reverse biased by the ohmmeter.
• Gain can be verified by using a resistor in
conjunction with the ohmmeter test.
Repeat Segment

Concept Preview
• Bipolar junction transistors (BJTs) are controlled by
base current.
• Junction field effect transistors (JFETs) are controlled
by gate voltage.

• JFETs operate in the depletion mode (as normally on
devices).
• Metal oxide semiconductor field effect transistors
(MOSFETs) usually operate in the enhancement mode
(as normally off devices).
• Insulated gate bipolar transistors (IGBTs) are modified
MOSFETs and have very low on-resistance.
• Unijunction transistors (UJTs) are not used as
amplifiers.

Current In

The BJT is
a current
amplifier.

Current
Amplifier

Current Out

Voltage In

The JFET is
a voltage
controlled
amplifier.

Voltage
Amplifier

Current Out

Source

Gate

Drain

P

N-channel
P-type substrate
Structure of an
N-channel JFET

The channel has carriers so it
conducts from source to drain.

Drain

Gate
Source

Source

Gate

Drain

P

N-channel
P-type substrate

A negative gate voltage
can push the carriers from
the channel and turn
the JFET off.

Drain

Gate
Source

0V
-1 V
-2 V

ID in mA

-3 V

VGS

-4 V

0

-5 V
VDS in Volts

This is known as a depletion-mode device.
N-channel JFET drain family of characteristic curves

It’s possible to make enhancement
type field effect transistors as well.
Metal
oxide
insulator

Drain

n

Gate

VGG

D

VDD

p

G

n

S
N-channel
MOSFET

Source

Gate bias enhances the channel and turns the device on.

5V
4V
3V

ID in mA

2V

VGS

1V

0

0V
Drain

VDS in Volts

Enhancement mode
MOSFET drain family of
characteristic curves

Gate
Source

The IGBT (insulated gate bipolar transistor)
Operation and structure
similar to a MOSFET
Voltage controlled
(like the MOSFET)
Has one more junction
than a MOSFET
Hole injection reduces
the collector resistance

Faster turn off than
BJTs but not as fast
as MOSFETS

RCE = 8.33 mW

Three major device technologies

hole injection
Extra
junction

Courtesy of Powerex, Inc.

Typical IGBT Driver Circuit
Typically +15 V for turn on
Typically - 5 to -15 V for turn off

Control signal

IGBT

Powerex IGBT Module Structure

Powerex high voltage IGBT package

Emitter voltage

The unijunction transistor fires
when its emitter voltage reaches VP.
VP

Then, the emitter voltage
drops due to its negative
resistance characteristic.
Base 2

Emitter current
Emitter

The UJT is not useful as an amplifier.
It is used in timing and control applications.

Base 1

Other Transistor Types Quiz
BJTs are _________-controlled
amplifiers.

current

FETs are __________-controlled
amplifiers.

voltage

JFETs operate in the __________ mode. depletion
MOSFETs operate in the __________
mode.

enhancement

IGBTs are __________-controlled
amplifiers.

voltage

UJTs are not useful as __________.

amplifiers

Concept Review
• Bipolar junction transistors (BJTs) are controlled by
base current.
• Junction field effect transistors (JFETs) are controlled
by gate voltage.
• JFETs operate in the depletion mode (as normally on
devices).
• Metal oxide semiconductor field effect transistors
(MOSFETs) usually operate in the enhancement mode
(as normally off devices).
• Insulated gate bipolar transistors (IGBTs) are modified
MOSFETs and have very low on-resistance.
• Unijunction transistors (UJTs) are not used as
amplifiers.
Repeat Segment

Concept Preview
• BJTs can be used as switches.
• No base current = switch is off.
• High base current = switch is on.
• The dissipation is always zero in an ideal
switch: off = no current flow and on = no
voltage drop.

• MOSFETs can also be used as switches: no
gate voltage = switch is off and high gate
voltage = switch is on.

How do transistor switches work?
Can be viewed as solid state relays:
they are either ON or they are OFF.
BJT switches are characterized by:
high base current (switch is on)
(or no base current … off)

low resistance from collector to emitter (on)
(or very high resistance … off)
low collector dissipation (on or off)
PC = VCE x IC
PC = 0 x IC = 0 W
(on)
(or PC = VCE x 0 = 0 W … off)

NPN SWITCH
LOAD

RCE @ 
W
0W
DRIVER

The
The
driver
driver
output
output
isiszero
positive,
volts,
IIBB>=I0
0and
andthe
theload
loadis
ison
off
The
driver
output
is
zero
volts,
B = 0 and ILOAD = 0

PNP SWITCH
DRIVER

LOAD

The
Z):
Thedriver
driveroutput
outputisgoes
isoff
off(high
(highthe
Z):the
theresistor
resistor
low:
voltage
drop
pulls
the
base
voltage
up
that
VV
pulls
thethe
base
voltage
upso
soV
that
across
resistor
makes
BE
BE==00
BE negative

PNP SWITCH WITH NPN DRIVER

LOAD

NPN SWITCH WITH PNP DRIVER
(NEGATIVE POWER SUPPLY)

VV
0VV
BE
BE@ @+0.7

VVBE
0 VV
BE@@-0.7

LOAD

STEPPER MOTOR

A

B

C

A

Enhancement mode
power MOSFETs
used as switches

B

C
D

D

Concept Review
• BJTs can be used as switches.
• No base current = switch is off.
• High base current = switch is on.
• The dissipation is always zero in an ideal
switch: off = no current flow and on = no
voltage drop.
• MOSFETs can also be used as switches: no
gate voltage = switch is off and high gate
voltage = switch is on.
Repeat Segment

REVIEW
• Amplification
• Transistors
• Characteristic Curves
• Transistor Testing
• Other Transistor Types
• Transistors as Switches


Slide 6

Electronics
Principles & Applications
Sixth Edition

Charles A. Schuler
Chapter 5

Transistors
(student version)
©2003

Glencoe/McGraw-Hill

INTRODUCTION
• Amplification
• Transistors
• Characteristic Curves
• Transistor Testing
• Other Transistor Types
• Transistors as Switches

Dear Student:
This presentation is arranged in segments.
Each segment is preceded by a Concept
Preview slide and is followed by a Concept
Review slide. When you reach a Concept
Review slide, you can return to the
beginning of that segment by clicking on the
Repeat Segment button. This will allow you
to view that segment again, if you want to.

Concept Preview
• Amplifiers provide gain (the output is larger
than the input).
• Transistors have gain.
• Transistors have a collector, a base, and an
emitter.
• The C-B junction is reverse biased.
• The B-E junction is forward biased.
• Most of the emitter carriers reach the collector.
• The base current is relatively small but controls
the larger currents.

In

Gain =

Amplifier

Out

In

Out

NPN Transistor Structure

The collector is lightly doped.

N

C

The base is thin and
is lightly doped.

P

B

The emitter is heavily doped.

N

E

NPN Transistor Bias
No current flows.
The C-B junction
is reverse biased.

N

C

P

B

N

E

NPN Transistor Bias

The B-E junction
is forward biased.

Current flows.

N

C

P

B

N

E

NPN Transistor Bias
IC
Current flows
everywhere.
Most of the emitter carriers
diffuse through the thin base
When
both
junctions
region since they are attracted
biased....
by are
the collector.

Note that IB is smaller
than IE or IC.

N

C

P

B

N

E

IB

IE

Note: when the
switch opens, all
currents go to zero.
Although IB is smaller
it controls IE and IC.

Gain is something small
controlling something large
(IB is small).

IC
N

C

P

B

N

E

IB

IE

Transistor Structure and Bias Quiz
The heaviest doping is found in
the ___________ region.

emitter

The thinnest of all three regions
is called the ____________.

base

The collector-base junction is
___________ biased.

reverse

The base-emitter junction is
____________ biased.

forward

The majority of the emitter
carriers flow to the ___________.

collector

Concept Review
• Amplifiers provide gain (the output is larger than
the input).
• Transistors have gain.

• Transistors have a collector, a base, and an emitter.
• The C-B junction is reverse biased.
• The B-E junction is forward biased.

• Most of the emitter carriers reach the collector.
• The base current is relatively small but controls the
larger currents.
Repeat Segment

Concept Preview
• The base to collector gain is called b (beta).
• To find b, divide the collector current by the
base current.
• The emitter current is the largest since it is the
sum of the base and collector currents.
• PNP transistors have opposite polarity from
NPN transistors.

• In an NPN transistor, the major flow is made
up of electrons.
• In a PNP transistor, the major flow is made up
of holes.

IC = 99 mA

The current gain from
base to collector
is called b.
IB = 1 mA

b =

99
ICmA
1IBmA

= 99

IE = 100 mA

C
P

B

N

E

IC = 99 mA
Kirchhoff’s
current law:

IB = 1 mA

C
P

B

N

E

IE = I B + I C

= 1 mA + 99 mA
= 100 mA
IE = 100 mA

IC = 99 mA
In a PNP transistor,
holes flow from
emitter to collector.

IB = 1 mA
Notice the PNP
bias voltages.

C
B

E

IE = 100 mA

Transistor Currents Quiz
b is the ratio of collector current to
______ current.

base

The sum of the base and collector
currents is the __________ current.

emitter

In NPN transistors, the flow from emitter
to collector is composed of _______.

electrons

In PNP transistors, the flow from emitter
to collector is composed of _______.

holes

Both NPN and PNP transistors show
__________ gain.

current

Concept Review
• The base to collector gain is called b (beta).
• To find b, divide the collector current by the
base current.
• The emitter current is the largest since it is the
sum of the base and collector currents.
• PNP transistors have opposite polarity from
NPN transistors.
• In an NPN transistor, the major flow is made
up of electrons.
• In a PNP transistor, the major flow is made up
of holes.
Repeat Segment

Concept Preview
• The NPN schematic symbol shows the emitter
arrow as Not Pointing iN.
• The collector curves are a graph of collector
voltage versus collector current.
• Both dc beta (bdc) and ac beta (bac) can be
determined from the collector curves.
• The collector circuit of a transistor can be
modeled as a resistor, as a closed switch or as
an open switch.
• The amount of base current determines which
of the three models applies.

NPN Schematic Symbol
Collector

Base

C
B E

Emitter
Memory aid: NPN
means Not Pointing iN.

PNP Schematic Symbol
Collector

Base

C
B E

Emitter

IC

This circuit is used to
collect IC versus
VCE data for
several values of IB.
C

IB
B

E

VCE

When graphed, the data provide an
NPN collector family of curves.
100 mA

14
12
10
IC in mA 8
6
4
2

80 mA
60 mA
40 mA
20 mA

0 2 4 6

8 10 12 14 16 18

VCE in Volts

0 mA

100 mA

14
12
10
IC in mA 8
6
4
2

80 mA
60 mA

40 mA
20 mA

0 2 4 6

8 10 12 14 16 18

0 mA

VCE in Volts

b =

14
mA
6ICmA
40
IB mA
100
mA

150
== 140

This type of gain
is called bdc or hFE.

100 mA

14
12
10
IC in mA 8
6
4
2

80 mA
60 mA

40 mA
20 mA

0 2 4 6

bac =

2.5DImA
C
20DImA
B

8 10 12 14 16 18

0 mA

VCE in Volts
= 125

Another type of gain
is called bac or hfe.

100 mA

14
12
10
IC in mA 8
6
4
2

80 mA
60 mA

40 mA
20 mA

0 2 4 6
IB

C

8 10 12 14 16 18
VCE in Volts

0 mA

With these values of IB:
The C-E model is a resistor.
E

100 mA

14
12
10
IC in mA 8
6
4
2
0 2 4 6
IB

80 mA
60 mA

40 mA
20 mA
8 10 12 14 16 18
VCE in Volts

0 mA

When IB >> 100 mA
VCE @ 0
The model is a closed switch.

100 mA

14
12
10
IC in mA 8
6
4
2
0 2 4 6
IB

80 mA
60 mA

40 mA
20 mA
8 10 12 14 16 18
VCE in Volts

0 mA

When IB = 0
IC = 0
The model is an open switch.

Transistor Operating Conditions Quiz
When IB is large and VCE @ 0, the transistor
acts as a ___________ switch.
closed
When IB = 0 and IC = 0, the transistor
acts as an ___________ switch.

open

When IB > 0 and VCE > 0, the transistor
acts as a ___________.

resistor

Two current gain measures are bdc and
__________.

bac

The symbol hfe is the same as _________.

bac

Concept Review
• The NPN schematic symbol shows the emitter
arrow as Not Pointing iN.
• The collector curves are a graph of collector
voltage versus collector current.
• Both dc beta (bdc) and ac beta (bac) can be
determined from the collector curves.
• The collector circuit of a transistor can be
modeled as a resistor, as a closed switch or as
an open switch.
• The amount of base current determines which
of the three models applies.
Repeat Segment

Concept Preview
• It is possible to test transistors out-of-circuit
using an ohmmeter.
• The E-B and C-B junctions act as diodes
during ohmmeter testing.

• The C-E test shows a high resistance because
two junctions are involved; one of which is
reverse biased by the ohmmeter.
• Gain can be verified by using a resistor in
conjunction with the ohmmeter test.

NPN

V

mA

E
B
C

The E-B junction is forward biased by the ohmmeter.

NPN

V

mA

E
B
C

The C-E resistance is very high.

NPN

V

mA

E
B
C
100 kW

The meter reading is < 100 kW due to gain.

Concept Review
• It is possible to test transistors out-of-circuit
using an ohmmeter.
• The E-B and C-B junctions act as diodes
during ohmmeter testing.
• The C-E test shows a high resistance because
two junctions are involved; one of which is
reverse biased by the ohmmeter.
• Gain can be verified by using a resistor in
conjunction with the ohmmeter test.
Repeat Segment

Concept Preview
• Bipolar junction transistors (BJTs) are controlled by
base current.
• Junction field effect transistors (JFETs) are controlled
by gate voltage.

• JFETs operate in the depletion mode (as normally on
devices).
• Metal oxide semiconductor field effect transistors
(MOSFETs) usually operate in the enhancement mode
(as normally off devices).
• Insulated gate bipolar transistors (IGBTs) are modified
MOSFETs and have very low on-resistance.
• Unijunction transistors (UJTs) are not used as
amplifiers.

Current In

The BJT is
a current
amplifier.

Current
Amplifier

Current Out

Voltage In

The JFET is
a voltage
controlled
amplifier.

Voltage
Amplifier

Current Out

Source

Gate

Drain

P

N-channel
P-type substrate
Structure of an
N-channel JFET

The channel has carriers so it
conducts from source to drain.

Drain

Gate
Source

Source

Gate

Drain

P

N-channel
P-type substrate

A negative gate voltage
can push the carriers from
the channel and turn
the JFET off.

Drain

Gate
Source

0V
-1 V
-2 V

ID in mA

-3 V

VGS

-4 V

0

-5 V
VDS in Volts

This is known as a depletion-mode device.
N-channel JFET drain family of characteristic curves

It’s possible to make enhancement
type field effect transistors as well.
Metal
oxide
insulator

Drain

n

Gate

VGG

D

VDD

p

G

n

S
N-channel
MOSFET

Source

Gate bias enhances the channel and turns the device on.

5V
4V
3V

ID in mA

2V

VGS

1V

0

0V
Drain

VDS in Volts

Enhancement mode
MOSFET drain family of
characteristic curves

Gate
Source

The IGBT (insulated gate bipolar transistor)
Operation and structure
similar to a MOSFET
Voltage controlled
(like the MOSFET)
Has one more junction
than a MOSFET
Hole injection reduces
the collector resistance

Faster turn off than
BJTs but not as fast
as MOSFETS

RCE = 8.33 mW

Three major device technologies

hole injection
Extra
junction

Courtesy of Powerex, Inc.

Typical IGBT Driver Circuit
Typically +15 V for turn on
Typically - 5 to -15 V for turn off

Control signal

IGBT

Powerex IGBT Module Structure

Powerex high voltage IGBT package

Emitter voltage

The unijunction transistor fires
when its emitter voltage reaches VP.
VP

Then, the emitter voltage
drops due to its negative
resistance characteristic.
Base 2

Emitter current
Emitter

The UJT is not useful as an amplifier.
It is used in timing and control applications.

Base 1

Other Transistor Types Quiz
BJTs are _________-controlled
amplifiers.

current

FETs are __________-controlled
amplifiers.

voltage

JFETs operate in the __________ mode. depletion
MOSFETs operate in the __________
mode.

enhancement

IGBTs are __________-controlled
amplifiers.

voltage

UJTs are not useful as __________.

amplifiers

Concept Review
• Bipolar junction transistors (BJTs) are controlled by
base current.
• Junction field effect transistors (JFETs) are controlled
by gate voltage.
• JFETs operate in the depletion mode (as normally on
devices).
• Metal oxide semiconductor field effect transistors
(MOSFETs) usually operate in the enhancement mode
(as normally off devices).
• Insulated gate bipolar transistors (IGBTs) are modified
MOSFETs and have very low on-resistance.
• Unijunction transistors (UJTs) are not used as
amplifiers.
Repeat Segment

Concept Preview
• BJTs can be used as switches.
• No base current = switch is off.
• High base current = switch is on.
• The dissipation is always zero in an ideal
switch: off = no current flow and on = no
voltage drop.

• MOSFETs can also be used as switches: no
gate voltage = switch is off and high gate
voltage = switch is on.

How do transistor switches work?
Can be viewed as solid state relays:
they are either ON or they are OFF.
BJT switches are characterized by:
high base current (switch is on)
(or no base current … off)

low resistance from collector to emitter (on)
(or very high resistance … off)
low collector dissipation (on or off)
PC = VCE x IC
PC = 0 x IC = 0 W
(on)
(or PC = VCE x 0 = 0 W … off)

NPN SWITCH
LOAD

RCE @ 
W
0W
DRIVER

The
The
driver
driver
output
output
isiszero
positive,
volts,
IIBB>=I0
0and
andthe
theload
loadis
ison
off
The
driver
output
is
zero
volts,
B = 0 and ILOAD = 0

PNP SWITCH
DRIVER

LOAD

The
Z):
Thedriver
driveroutput
outputisgoes
isoff
off(high
(highthe
Z):the
theresistor
resistor
low:
voltage
drop
pulls
the
base
voltage
up
that
VV
pulls
thethe
base
voltage
upso
soV
that
across
resistor
makes
BE
BE==00
BE negative

PNP SWITCH WITH NPN DRIVER

LOAD

NPN SWITCH WITH PNP DRIVER
(NEGATIVE POWER SUPPLY)

VV
0VV
BE
BE@ @+0.7

VVBE
0 VV
BE@@-0.7

LOAD

STEPPER MOTOR

A

B

C

A

Enhancement mode
power MOSFETs
used as switches

B

C
D

D

Concept Review
• BJTs can be used as switches.
• No base current = switch is off.
• High base current = switch is on.
• The dissipation is always zero in an ideal
switch: off = no current flow and on = no
voltage drop.
• MOSFETs can also be used as switches: no
gate voltage = switch is off and high gate
voltage = switch is on.
Repeat Segment

REVIEW
• Amplification
• Transistors
• Characteristic Curves
• Transistor Testing
• Other Transistor Types
• Transistors as Switches


Slide 7

Electronics
Principles & Applications
Sixth Edition

Charles A. Schuler
Chapter 5

Transistors
(student version)
©2003

Glencoe/McGraw-Hill

INTRODUCTION
• Amplification
• Transistors
• Characteristic Curves
• Transistor Testing
• Other Transistor Types
• Transistors as Switches

Dear Student:
This presentation is arranged in segments.
Each segment is preceded by a Concept
Preview slide and is followed by a Concept
Review slide. When you reach a Concept
Review slide, you can return to the
beginning of that segment by clicking on the
Repeat Segment button. This will allow you
to view that segment again, if you want to.

Concept Preview
• Amplifiers provide gain (the output is larger
than the input).
• Transistors have gain.
• Transistors have a collector, a base, and an
emitter.
• The C-B junction is reverse biased.
• The B-E junction is forward biased.
• Most of the emitter carriers reach the collector.
• The base current is relatively small but controls
the larger currents.

In

Gain =

Amplifier

Out

In

Out

NPN Transistor Structure

The collector is lightly doped.

N

C

The base is thin and
is lightly doped.

P

B

The emitter is heavily doped.

N

E

NPN Transistor Bias
No current flows.
The C-B junction
is reverse biased.

N

C

P

B

N

E

NPN Transistor Bias

The B-E junction
is forward biased.

Current flows.

N

C

P

B

N

E

NPN Transistor Bias
IC
Current flows
everywhere.
Most of the emitter carriers
diffuse through the thin base
When
both
junctions
region since they are attracted
biased....
by are
the collector.

Note that IB is smaller
than IE or IC.

N

C

P

B

N

E

IB

IE

Note: when the
switch opens, all
currents go to zero.
Although IB is smaller
it controls IE and IC.

Gain is something small
controlling something large
(IB is small).

IC
N

C

P

B

N

E

IB

IE

Transistor Structure and Bias Quiz
The heaviest doping is found in
the ___________ region.

emitter

The thinnest of all three regions
is called the ____________.

base

The collector-base junction is
___________ biased.

reverse

The base-emitter junction is
____________ biased.

forward

The majority of the emitter
carriers flow to the ___________.

collector

Concept Review
• Amplifiers provide gain (the output is larger than
the input).
• Transistors have gain.

• Transistors have a collector, a base, and an emitter.
• The C-B junction is reverse biased.
• The B-E junction is forward biased.

• Most of the emitter carriers reach the collector.
• The base current is relatively small but controls the
larger currents.
Repeat Segment

Concept Preview
• The base to collector gain is called b (beta).
• To find b, divide the collector current by the
base current.
• The emitter current is the largest since it is the
sum of the base and collector currents.
• PNP transistors have opposite polarity from
NPN transistors.

• In an NPN transistor, the major flow is made
up of electrons.
• In a PNP transistor, the major flow is made up
of holes.

IC = 99 mA

The current gain from
base to collector
is called b.
IB = 1 mA

b =

99
ICmA
1IBmA

= 99

IE = 100 mA

C
P

B

N

E

IC = 99 mA
Kirchhoff’s
current law:

IB = 1 mA

C
P

B

N

E

IE = I B + I C

= 1 mA + 99 mA
= 100 mA
IE = 100 mA

IC = 99 mA
In a PNP transistor,
holes flow from
emitter to collector.

IB = 1 mA
Notice the PNP
bias voltages.

C
B

E

IE = 100 mA

Transistor Currents Quiz
b is the ratio of collector current to
______ current.

base

The sum of the base and collector
currents is the __________ current.

emitter

In NPN transistors, the flow from emitter
to collector is composed of _______.

electrons

In PNP transistors, the flow from emitter
to collector is composed of _______.

holes

Both NPN and PNP transistors show
__________ gain.

current

Concept Review
• The base to collector gain is called b (beta).
• To find b, divide the collector current by the
base current.
• The emitter current is the largest since it is the
sum of the base and collector currents.
• PNP transistors have opposite polarity from
NPN transistors.
• In an NPN transistor, the major flow is made
up of electrons.
• In a PNP transistor, the major flow is made up
of holes.
Repeat Segment

Concept Preview
• The NPN schematic symbol shows the emitter
arrow as Not Pointing iN.
• The collector curves are a graph of collector
voltage versus collector current.
• Both dc beta (bdc) and ac beta (bac) can be
determined from the collector curves.
• The collector circuit of a transistor can be
modeled as a resistor, as a closed switch or as
an open switch.
• The amount of base current determines which
of the three models applies.

NPN Schematic Symbol
Collector

Base

C
B E

Emitter
Memory aid: NPN
means Not Pointing iN.

PNP Schematic Symbol
Collector

Base

C
B E

Emitter

IC

This circuit is used to
collect IC versus
VCE data for
several values of IB.
C

IB
B

E

VCE

When graphed, the data provide an
NPN collector family of curves.
100 mA

14
12
10
IC in mA 8
6
4
2

80 mA
60 mA
40 mA
20 mA

0 2 4 6

8 10 12 14 16 18

VCE in Volts

0 mA

100 mA

14
12
10
IC in mA 8
6
4
2

80 mA
60 mA

40 mA
20 mA

0 2 4 6

8 10 12 14 16 18

0 mA

VCE in Volts

b =

14
mA
6ICmA
40
IB mA
100
mA

150
== 140

This type of gain
is called bdc or hFE.

100 mA

14
12
10
IC in mA 8
6
4
2

80 mA
60 mA

40 mA
20 mA

0 2 4 6

bac =

2.5DImA
C
20DImA
B

8 10 12 14 16 18

0 mA

VCE in Volts
= 125

Another type of gain
is called bac or hfe.

100 mA

14
12
10
IC in mA 8
6
4
2

80 mA
60 mA

40 mA
20 mA

0 2 4 6
IB

C

8 10 12 14 16 18
VCE in Volts

0 mA

With these values of IB:
The C-E model is a resistor.
E

100 mA

14
12
10
IC in mA 8
6
4
2
0 2 4 6
IB

80 mA
60 mA

40 mA
20 mA
8 10 12 14 16 18
VCE in Volts

0 mA

When IB >> 100 mA
VCE @ 0
The model is a closed switch.

100 mA

14
12
10
IC in mA 8
6
4
2
0 2 4 6
IB

80 mA
60 mA

40 mA
20 mA
8 10 12 14 16 18
VCE in Volts

0 mA

When IB = 0
IC = 0
The model is an open switch.

Transistor Operating Conditions Quiz
When IB is large and VCE @ 0, the transistor
acts as a ___________ switch.
closed
When IB = 0 and IC = 0, the transistor
acts as an ___________ switch.

open

When IB > 0 and VCE > 0, the transistor
acts as a ___________.

resistor

Two current gain measures are bdc and
__________.

bac

The symbol hfe is the same as _________.

bac

Concept Review
• The NPN schematic symbol shows the emitter
arrow as Not Pointing iN.
• The collector curves are a graph of collector
voltage versus collector current.
• Both dc beta (bdc) and ac beta (bac) can be
determined from the collector curves.
• The collector circuit of a transistor can be
modeled as a resistor, as a closed switch or as
an open switch.
• The amount of base current determines which
of the three models applies.
Repeat Segment

Concept Preview
• It is possible to test transistors out-of-circuit
using an ohmmeter.
• The E-B and C-B junctions act as diodes
during ohmmeter testing.

• The C-E test shows a high resistance because
two junctions are involved; one of which is
reverse biased by the ohmmeter.
• Gain can be verified by using a resistor in
conjunction with the ohmmeter test.

NPN

V

mA

E
B
C

The E-B junction is forward biased by the ohmmeter.

NPN

V

mA

E
B
C

The C-E resistance is very high.

NPN

V

mA

E
B
C
100 kW

The meter reading is < 100 kW due to gain.

Concept Review
• It is possible to test transistors out-of-circuit
using an ohmmeter.
• The E-B and C-B junctions act as diodes
during ohmmeter testing.
• The C-E test shows a high resistance because
two junctions are involved; one of which is
reverse biased by the ohmmeter.
• Gain can be verified by using a resistor in
conjunction with the ohmmeter test.
Repeat Segment

Concept Preview
• Bipolar junction transistors (BJTs) are controlled by
base current.
• Junction field effect transistors (JFETs) are controlled
by gate voltage.

• JFETs operate in the depletion mode (as normally on
devices).
• Metal oxide semiconductor field effect transistors
(MOSFETs) usually operate in the enhancement mode
(as normally off devices).
• Insulated gate bipolar transistors (IGBTs) are modified
MOSFETs and have very low on-resistance.
• Unijunction transistors (UJTs) are not used as
amplifiers.

Current In

The BJT is
a current
amplifier.

Current
Amplifier

Current Out

Voltage In

The JFET is
a voltage
controlled
amplifier.

Voltage
Amplifier

Current Out

Source

Gate

Drain

P

N-channel
P-type substrate
Structure of an
N-channel JFET

The channel has carriers so it
conducts from source to drain.

Drain

Gate
Source

Source

Gate

Drain

P

N-channel
P-type substrate

A negative gate voltage
can push the carriers from
the channel and turn
the JFET off.

Drain

Gate
Source

0V
-1 V
-2 V

ID in mA

-3 V

VGS

-4 V

0

-5 V
VDS in Volts

This is known as a depletion-mode device.
N-channel JFET drain family of characteristic curves

It’s possible to make enhancement
type field effect transistors as well.
Metal
oxide
insulator

Drain

n

Gate

VGG

D

VDD

p

G

n

S
N-channel
MOSFET

Source

Gate bias enhances the channel and turns the device on.

5V
4V
3V

ID in mA

2V

VGS

1V

0

0V
Drain

VDS in Volts

Enhancement mode
MOSFET drain family of
characteristic curves

Gate
Source

The IGBT (insulated gate bipolar transistor)
Operation and structure
similar to a MOSFET
Voltage controlled
(like the MOSFET)
Has one more junction
than a MOSFET
Hole injection reduces
the collector resistance

Faster turn off than
BJTs but not as fast
as MOSFETS

RCE = 8.33 mW

Three major device technologies

hole injection
Extra
junction

Courtesy of Powerex, Inc.

Typical IGBT Driver Circuit
Typically +15 V for turn on
Typically - 5 to -15 V for turn off

Control signal

IGBT

Powerex IGBT Module Structure

Powerex high voltage IGBT package

Emitter voltage

The unijunction transistor fires
when its emitter voltage reaches VP.
VP

Then, the emitter voltage
drops due to its negative
resistance characteristic.
Base 2

Emitter current
Emitter

The UJT is not useful as an amplifier.
It is used in timing and control applications.

Base 1

Other Transistor Types Quiz
BJTs are _________-controlled
amplifiers.

current

FETs are __________-controlled
amplifiers.

voltage

JFETs operate in the __________ mode. depletion
MOSFETs operate in the __________
mode.

enhancement

IGBTs are __________-controlled
amplifiers.

voltage

UJTs are not useful as __________.

amplifiers

Concept Review
• Bipolar junction transistors (BJTs) are controlled by
base current.
• Junction field effect transistors (JFETs) are controlled
by gate voltage.
• JFETs operate in the depletion mode (as normally on
devices).
• Metal oxide semiconductor field effect transistors
(MOSFETs) usually operate in the enhancement mode
(as normally off devices).
• Insulated gate bipolar transistors (IGBTs) are modified
MOSFETs and have very low on-resistance.
• Unijunction transistors (UJTs) are not used as
amplifiers.
Repeat Segment

Concept Preview
• BJTs can be used as switches.
• No base current = switch is off.
• High base current = switch is on.
• The dissipation is always zero in an ideal
switch: off = no current flow and on = no
voltage drop.

• MOSFETs can also be used as switches: no
gate voltage = switch is off and high gate
voltage = switch is on.

How do transistor switches work?
Can be viewed as solid state relays:
they are either ON or they are OFF.
BJT switches are characterized by:
high base current (switch is on)
(or no base current … off)

low resistance from collector to emitter (on)
(or very high resistance … off)
low collector dissipation (on or off)
PC = VCE x IC
PC = 0 x IC = 0 W
(on)
(or PC = VCE x 0 = 0 W … off)

NPN SWITCH
LOAD

RCE @ 
W
0W
DRIVER

The
The
driver
driver
output
output
isiszero
positive,
volts,
IIBB>=I0
0and
andthe
theload
loadis
ison
off
The
driver
output
is
zero
volts,
B = 0 and ILOAD = 0

PNP SWITCH
DRIVER

LOAD

The
Z):
Thedriver
driveroutput
outputisgoes
isoff
off(high
(highthe
Z):the
theresistor
resistor
low:
voltage
drop
pulls
the
base
voltage
up
that
VV
pulls
thethe
base
voltage
upso
soV
that
across
resistor
makes
BE
BE==00
BE negative

PNP SWITCH WITH NPN DRIVER

LOAD

NPN SWITCH WITH PNP DRIVER
(NEGATIVE POWER SUPPLY)

VV
0VV
BE
BE@ @+0.7

VVBE
0 VV
BE@@-0.7

LOAD

STEPPER MOTOR

A

B

C

A

Enhancement mode
power MOSFETs
used as switches

B

C
D

D

Concept Review
• BJTs can be used as switches.
• No base current = switch is off.
• High base current = switch is on.
• The dissipation is always zero in an ideal
switch: off = no current flow and on = no
voltage drop.
• MOSFETs can also be used as switches: no
gate voltage = switch is off and high gate
voltage = switch is on.
Repeat Segment

REVIEW
• Amplification
• Transistors
• Characteristic Curves
• Transistor Testing
• Other Transistor Types
• Transistors as Switches


Slide 8

Electronics
Principles & Applications
Sixth Edition

Charles A. Schuler
Chapter 5

Transistors
(student version)
©2003

Glencoe/McGraw-Hill

INTRODUCTION
• Amplification
• Transistors
• Characteristic Curves
• Transistor Testing
• Other Transistor Types
• Transistors as Switches

Dear Student:
This presentation is arranged in segments.
Each segment is preceded by a Concept
Preview slide and is followed by a Concept
Review slide. When you reach a Concept
Review slide, you can return to the
beginning of that segment by clicking on the
Repeat Segment button. This will allow you
to view that segment again, if you want to.

Concept Preview
• Amplifiers provide gain (the output is larger
than the input).
• Transistors have gain.
• Transistors have a collector, a base, and an
emitter.
• The C-B junction is reverse biased.
• The B-E junction is forward biased.
• Most of the emitter carriers reach the collector.
• The base current is relatively small but controls
the larger currents.

In

Gain =

Amplifier

Out

In

Out

NPN Transistor Structure

The collector is lightly doped.

N

C

The base is thin and
is lightly doped.

P

B

The emitter is heavily doped.

N

E

NPN Transistor Bias
No current flows.
The C-B junction
is reverse biased.

N

C

P

B

N

E

NPN Transistor Bias

The B-E junction
is forward biased.

Current flows.

N

C

P

B

N

E

NPN Transistor Bias
IC
Current flows
everywhere.
Most of the emitter carriers
diffuse through the thin base
When
both
junctions
region since they are attracted
biased....
by are
the collector.

Note that IB is smaller
than IE or IC.

N

C

P

B

N

E

IB

IE

Note: when the
switch opens, all
currents go to zero.
Although IB is smaller
it controls IE and IC.

Gain is something small
controlling something large
(IB is small).

IC
N

C

P

B

N

E

IB

IE

Transistor Structure and Bias Quiz
The heaviest doping is found in
the ___________ region.

emitter

The thinnest of all three regions
is called the ____________.

base

The collector-base junction is
___________ biased.

reverse

The base-emitter junction is
____________ biased.

forward

The majority of the emitter
carriers flow to the ___________.

collector

Concept Review
• Amplifiers provide gain (the output is larger than
the input).
• Transistors have gain.

• Transistors have a collector, a base, and an emitter.
• The C-B junction is reverse biased.
• The B-E junction is forward biased.

• Most of the emitter carriers reach the collector.
• The base current is relatively small but controls the
larger currents.
Repeat Segment

Concept Preview
• The base to collector gain is called b (beta).
• To find b, divide the collector current by the
base current.
• The emitter current is the largest since it is the
sum of the base and collector currents.
• PNP transistors have opposite polarity from
NPN transistors.

• In an NPN transistor, the major flow is made
up of electrons.
• In a PNP transistor, the major flow is made up
of holes.

IC = 99 mA

The current gain from
base to collector
is called b.
IB = 1 mA

b =

99
ICmA
1IBmA

= 99

IE = 100 mA

C
P

B

N

E

IC = 99 mA
Kirchhoff’s
current law:

IB = 1 mA

C
P

B

N

E

IE = I B + I C

= 1 mA + 99 mA
= 100 mA
IE = 100 mA

IC = 99 mA
In a PNP transistor,
holes flow from
emitter to collector.

IB = 1 mA
Notice the PNP
bias voltages.

C
B

E

IE = 100 mA

Transistor Currents Quiz
b is the ratio of collector current to
______ current.

base

The sum of the base and collector
currents is the __________ current.

emitter

In NPN transistors, the flow from emitter
to collector is composed of _______.

electrons

In PNP transistors, the flow from emitter
to collector is composed of _______.

holes

Both NPN and PNP transistors show
__________ gain.

current

Concept Review
• The base to collector gain is called b (beta).
• To find b, divide the collector current by the
base current.
• The emitter current is the largest since it is the
sum of the base and collector currents.
• PNP transistors have opposite polarity from
NPN transistors.
• In an NPN transistor, the major flow is made
up of electrons.
• In a PNP transistor, the major flow is made up
of holes.
Repeat Segment

Concept Preview
• The NPN schematic symbol shows the emitter
arrow as Not Pointing iN.
• The collector curves are a graph of collector
voltage versus collector current.
• Both dc beta (bdc) and ac beta (bac) can be
determined from the collector curves.
• The collector circuit of a transistor can be
modeled as a resistor, as a closed switch or as
an open switch.
• The amount of base current determines which
of the three models applies.

NPN Schematic Symbol
Collector

Base

C
B E

Emitter
Memory aid: NPN
means Not Pointing iN.

PNP Schematic Symbol
Collector

Base

C
B E

Emitter

IC

This circuit is used to
collect IC versus
VCE data for
several values of IB.
C

IB
B

E

VCE

When graphed, the data provide an
NPN collector family of curves.
100 mA

14
12
10
IC in mA 8
6
4
2

80 mA
60 mA
40 mA
20 mA

0 2 4 6

8 10 12 14 16 18

VCE in Volts

0 mA

100 mA

14
12
10
IC in mA 8
6
4
2

80 mA
60 mA

40 mA
20 mA

0 2 4 6

8 10 12 14 16 18

0 mA

VCE in Volts

b =

14
mA
6ICmA
40
IB mA
100
mA

150
== 140

This type of gain
is called bdc or hFE.

100 mA

14
12
10
IC in mA 8
6
4
2

80 mA
60 mA

40 mA
20 mA

0 2 4 6

bac =

2.5DImA
C
20DImA
B

8 10 12 14 16 18

0 mA

VCE in Volts
= 125

Another type of gain
is called bac or hfe.

100 mA

14
12
10
IC in mA 8
6
4
2

80 mA
60 mA

40 mA
20 mA

0 2 4 6
IB

C

8 10 12 14 16 18
VCE in Volts

0 mA

With these values of IB:
The C-E model is a resistor.
E

100 mA

14
12
10
IC in mA 8
6
4
2
0 2 4 6
IB

80 mA
60 mA

40 mA
20 mA
8 10 12 14 16 18
VCE in Volts

0 mA

When IB >> 100 mA
VCE @ 0
The model is a closed switch.

100 mA

14
12
10
IC in mA 8
6
4
2
0 2 4 6
IB

80 mA
60 mA

40 mA
20 mA
8 10 12 14 16 18
VCE in Volts

0 mA

When IB = 0
IC = 0
The model is an open switch.

Transistor Operating Conditions Quiz
When IB is large and VCE @ 0, the transistor
acts as a ___________ switch.
closed
When IB = 0 and IC = 0, the transistor
acts as an ___________ switch.

open

When IB > 0 and VCE > 0, the transistor
acts as a ___________.

resistor

Two current gain measures are bdc and
__________.

bac

The symbol hfe is the same as _________.

bac

Concept Review
• The NPN schematic symbol shows the emitter
arrow as Not Pointing iN.
• The collector curves are a graph of collector
voltage versus collector current.
• Both dc beta (bdc) and ac beta (bac) can be
determined from the collector curves.
• The collector circuit of a transistor can be
modeled as a resistor, as a closed switch or as
an open switch.
• The amount of base current determines which
of the three models applies.
Repeat Segment

Concept Preview
• It is possible to test transistors out-of-circuit
using an ohmmeter.
• The E-B and C-B junctions act as diodes
during ohmmeter testing.

• The C-E test shows a high resistance because
two junctions are involved; one of which is
reverse biased by the ohmmeter.
• Gain can be verified by using a resistor in
conjunction with the ohmmeter test.

NPN

V

mA

E
B
C

The E-B junction is forward biased by the ohmmeter.

NPN

V

mA

E
B
C

The C-E resistance is very high.

NPN

V

mA

E
B
C
100 kW

The meter reading is < 100 kW due to gain.

Concept Review
• It is possible to test transistors out-of-circuit
using an ohmmeter.
• The E-B and C-B junctions act as diodes
during ohmmeter testing.
• The C-E test shows a high resistance because
two junctions are involved; one of which is
reverse biased by the ohmmeter.
• Gain can be verified by using a resistor in
conjunction with the ohmmeter test.
Repeat Segment

Concept Preview
• Bipolar junction transistors (BJTs) are controlled by
base current.
• Junction field effect transistors (JFETs) are controlled
by gate voltage.

• JFETs operate in the depletion mode (as normally on
devices).
• Metal oxide semiconductor field effect transistors
(MOSFETs) usually operate in the enhancement mode
(as normally off devices).
• Insulated gate bipolar transistors (IGBTs) are modified
MOSFETs and have very low on-resistance.
• Unijunction transistors (UJTs) are not used as
amplifiers.

Current In

The BJT is
a current
amplifier.

Current
Amplifier

Current Out

Voltage In

The JFET is
a voltage
controlled
amplifier.

Voltage
Amplifier

Current Out

Source

Gate

Drain

P

N-channel
P-type substrate
Structure of an
N-channel JFET

The channel has carriers so it
conducts from source to drain.

Drain

Gate
Source

Source

Gate

Drain

P

N-channel
P-type substrate

A negative gate voltage
can push the carriers from
the channel and turn
the JFET off.

Drain

Gate
Source

0V
-1 V
-2 V

ID in mA

-3 V

VGS

-4 V

0

-5 V
VDS in Volts

This is known as a depletion-mode device.
N-channel JFET drain family of characteristic curves

It’s possible to make enhancement
type field effect transistors as well.
Metal
oxide
insulator

Drain

n

Gate

VGG

D

VDD

p

G

n

S
N-channel
MOSFET

Source

Gate bias enhances the channel and turns the device on.

5V
4V
3V

ID in mA

2V

VGS

1V

0

0V
Drain

VDS in Volts

Enhancement mode
MOSFET drain family of
characteristic curves

Gate
Source

The IGBT (insulated gate bipolar transistor)
Operation and structure
similar to a MOSFET
Voltage controlled
(like the MOSFET)
Has one more junction
than a MOSFET
Hole injection reduces
the collector resistance

Faster turn off than
BJTs but not as fast
as MOSFETS

RCE = 8.33 mW

Three major device technologies

hole injection
Extra
junction

Courtesy of Powerex, Inc.

Typical IGBT Driver Circuit
Typically +15 V for turn on
Typically - 5 to -15 V for turn off

Control signal

IGBT

Powerex IGBT Module Structure

Powerex high voltage IGBT package

Emitter voltage

The unijunction transistor fires
when its emitter voltage reaches VP.
VP

Then, the emitter voltage
drops due to its negative
resistance characteristic.
Base 2

Emitter current
Emitter

The UJT is not useful as an amplifier.
It is used in timing and control applications.

Base 1

Other Transistor Types Quiz
BJTs are _________-controlled
amplifiers.

current

FETs are __________-controlled
amplifiers.

voltage

JFETs operate in the __________ mode. depletion
MOSFETs operate in the __________
mode.

enhancement

IGBTs are __________-controlled
amplifiers.

voltage

UJTs are not useful as __________.

amplifiers

Concept Review
• Bipolar junction transistors (BJTs) are controlled by
base current.
• Junction field effect transistors (JFETs) are controlled
by gate voltage.
• JFETs operate in the depletion mode (as normally on
devices).
• Metal oxide semiconductor field effect transistors
(MOSFETs) usually operate in the enhancement mode
(as normally off devices).
• Insulated gate bipolar transistors (IGBTs) are modified
MOSFETs and have very low on-resistance.
• Unijunction transistors (UJTs) are not used as
amplifiers.
Repeat Segment

Concept Preview
• BJTs can be used as switches.
• No base current = switch is off.
• High base current = switch is on.
• The dissipation is always zero in an ideal
switch: off = no current flow and on = no
voltage drop.

• MOSFETs can also be used as switches: no
gate voltage = switch is off and high gate
voltage = switch is on.

How do transistor switches work?
Can be viewed as solid state relays:
they are either ON or they are OFF.
BJT switches are characterized by:
high base current (switch is on)
(or no base current … off)

low resistance from collector to emitter (on)
(or very high resistance … off)
low collector dissipation (on or off)
PC = VCE x IC
PC = 0 x IC = 0 W
(on)
(or PC = VCE x 0 = 0 W … off)

NPN SWITCH
LOAD

RCE @ 
W
0W
DRIVER

The
The
driver
driver
output
output
isiszero
positive,
volts,
IIBB>=I0
0and
andthe
theload
loadis
ison
off
The
driver
output
is
zero
volts,
B = 0 and ILOAD = 0

PNP SWITCH
DRIVER

LOAD

The
Z):
Thedriver
driveroutput
outputisgoes
isoff
off(high
(highthe
Z):the
theresistor
resistor
low:
voltage
drop
pulls
the
base
voltage
up
that
VV
pulls
thethe
base
voltage
upso
soV
that
across
resistor
makes
BE
BE==00
BE negative

PNP SWITCH WITH NPN DRIVER

LOAD

NPN SWITCH WITH PNP DRIVER
(NEGATIVE POWER SUPPLY)

VV
0VV
BE
BE@ @+0.7

VVBE
0 VV
BE@@-0.7

LOAD

STEPPER MOTOR

A

B

C

A

Enhancement mode
power MOSFETs
used as switches

B

C
D

D

Concept Review
• BJTs can be used as switches.
• No base current = switch is off.
• High base current = switch is on.
• The dissipation is always zero in an ideal
switch: off = no current flow and on = no
voltage drop.
• MOSFETs can also be used as switches: no
gate voltage = switch is off and high gate
voltage = switch is on.
Repeat Segment

REVIEW
• Amplification
• Transistors
• Characteristic Curves
• Transistor Testing
• Other Transistor Types
• Transistors as Switches


Slide 9

Electronics
Principles & Applications
Sixth Edition

Charles A. Schuler
Chapter 5

Transistors
(student version)
©2003

Glencoe/McGraw-Hill

INTRODUCTION
• Amplification
• Transistors
• Characteristic Curves
• Transistor Testing
• Other Transistor Types
• Transistors as Switches

Dear Student:
This presentation is arranged in segments.
Each segment is preceded by a Concept
Preview slide and is followed by a Concept
Review slide. When you reach a Concept
Review slide, you can return to the
beginning of that segment by clicking on the
Repeat Segment button. This will allow you
to view that segment again, if you want to.

Concept Preview
• Amplifiers provide gain (the output is larger
than the input).
• Transistors have gain.
• Transistors have a collector, a base, and an
emitter.
• The C-B junction is reverse biased.
• The B-E junction is forward biased.
• Most of the emitter carriers reach the collector.
• The base current is relatively small but controls
the larger currents.

In

Gain =

Amplifier

Out

In

Out

NPN Transistor Structure

The collector is lightly doped.

N

C

The base is thin and
is lightly doped.

P

B

The emitter is heavily doped.

N

E

NPN Transistor Bias
No current flows.
The C-B junction
is reverse biased.

N

C

P

B

N

E

NPN Transistor Bias

The B-E junction
is forward biased.

Current flows.

N

C

P

B

N

E

NPN Transistor Bias
IC
Current flows
everywhere.
Most of the emitter carriers
diffuse through the thin base
When
both
junctions
region since they are attracted
biased....
by are
the collector.

Note that IB is smaller
than IE or IC.

N

C

P

B

N

E

IB

IE

Note: when the
switch opens, all
currents go to zero.
Although IB is smaller
it controls IE and IC.

Gain is something small
controlling something large
(IB is small).

IC
N

C

P

B

N

E

IB

IE

Transistor Structure and Bias Quiz
The heaviest doping is found in
the ___________ region.

emitter

The thinnest of all three regions
is called the ____________.

base

The collector-base junction is
___________ biased.

reverse

The base-emitter junction is
____________ biased.

forward

The majority of the emitter
carriers flow to the ___________.

collector

Concept Review
• Amplifiers provide gain (the output is larger than
the input).
• Transistors have gain.

• Transistors have a collector, a base, and an emitter.
• The C-B junction is reverse biased.
• The B-E junction is forward biased.

• Most of the emitter carriers reach the collector.
• The base current is relatively small but controls the
larger currents.
Repeat Segment

Concept Preview
• The base to collector gain is called b (beta).
• To find b, divide the collector current by the
base current.
• The emitter current is the largest since it is the
sum of the base and collector currents.
• PNP transistors have opposite polarity from
NPN transistors.

• In an NPN transistor, the major flow is made
up of electrons.
• In a PNP transistor, the major flow is made up
of holes.

IC = 99 mA

The current gain from
base to collector
is called b.
IB = 1 mA

b =

99
ICmA
1IBmA

= 99

IE = 100 mA

C
P

B

N

E

IC = 99 mA
Kirchhoff’s
current law:

IB = 1 mA

C
P

B

N

E

IE = I B + I C

= 1 mA + 99 mA
= 100 mA
IE = 100 mA

IC = 99 mA
In a PNP transistor,
holes flow from
emitter to collector.

IB = 1 mA
Notice the PNP
bias voltages.

C
B

E

IE = 100 mA

Transistor Currents Quiz
b is the ratio of collector current to
______ current.

base

The sum of the base and collector
currents is the __________ current.

emitter

In NPN transistors, the flow from emitter
to collector is composed of _______.

electrons

In PNP transistors, the flow from emitter
to collector is composed of _______.

holes

Both NPN and PNP transistors show
__________ gain.

current

Concept Review
• The base to collector gain is called b (beta).
• To find b, divide the collector current by the
base current.
• The emitter current is the largest since it is the
sum of the base and collector currents.
• PNP transistors have opposite polarity from
NPN transistors.
• In an NPN transistor, the major flow is made
up of electrons.
• In a PNP transistor, the major flow is made up
of holes.
Repeat Segment

Concept Preview
• The NPN schematic symbol shows the emitter
arrow as Not Pointing iN.
• The collector curves are a graph of collector
voltage versus collector current.
• Both dc beta (bdc) and ac beta (bac) can be
determined from the collector curves.
• The collector circuit of a transistor can be
modeled as a resistor, as a closed switch or as
an open switch.
• The amount of base current determines which
of the three models applies.

NPN Schematic Symbol
Collector

Base

C
B E

Emitter
Memory aid: NPN
means Not Pointing iN.

PNP Schematic Symbol
Collector

Base

C
B E

Emitter

IC

This circuit is used to
collect IC versus
VCE data for
several values of IB.
C

IB
B

E

VCE

When graphed, the data provide an
NPN collector family of curves.
100 mA

14
12
10
IC in mA 8
6
4
2

80 mA
60 mA
40 mA
20 mA

0 2 4 6

8 10 12 14 16 18

VCE in Volts

0 mA

100 mA

14
12
10
IC in mA 8
6
4
2

80 mA
60 mA

40 mA
20 mA

0 2 4 6

8 10 12 14 16 18

0 mA

VCE in Volts

b =

14
mA
6ICmA
40
IB mA
100
mA

150
== 140

This type of gain
is called bdc or hFE.

100 mA

14
12
10
IC in mA 8
6
4
2

80 mA
60 mA

40 mA
20 mA

0 2 4 6

bac =

2.5DImA
C
20DImA
B

8 10 12 14 16 18

0 mA

VCE in Volts
= 125

Another type of gain
is called bac or hfe.

100 mA

14
12
10
IC in mA 8
6
4
2

80 mA
60 mA

40 mA
20 mA

0 2 4 6
IB

C

8 10 12 14 16 18
VCE in Volts

0 mA

With these values of IB:
The C-E model is a resistor.
E

100 mA

14
12
10
IC in mA 8
6
4
2
0 2 4 6
IB

80 mA
60 mA

40 mA
20 mA
8 10 12 14 16 18
VCE in Volts

0 mA

When IB >> 100 mA
VCE @ 0
The model is a closed switch.

100 mA

14
12
10
IC in mA 8
6
4
2
0 2 4 6
IB

80 mA
60 mA

40 mA
20 mA
8 10 12 14 16 18
VCE in Volts

0 mA

When IB = 0
IC = 0
The model is an open switch.

Transistor Operating Conditions Quiz
When IB is large and VCE @ 0, the transistor
acts as a ___________ switch.
closed
When IB = 0 and IC = 0, the transistor
acts as an ___________ switch.

open

When IB > 0 and VCE > 0, the transistor
acts as a ___________.

resistor

Two current gain measures are bdc and
__________.

bac

The symbol hfe is the same as _________.

bac

Concept Review
• The NPN schematic symbol shows the emitter
arrow as Not Pointing iN.
• The collector curves are a graph of collector
voltage versus collector current.
• Both dc beta (bdc) and ac beta (bac) can be
determined from the collector curves.
• The collector circuit of a transistor can be
modeled as a resistor, as a closed switch or as
an open switch.
• The amount of base current determines which
of the three models applies.
Repeat Segment

Concept Preview
• It is possible to test transistors out-of-circuit
using an ohmmeter.
• The E-B and C-B junctions act as diodes
during ohmmeter testing.

• The C-E test shows a high resistance because
two junctions are involved; one of which is
reverse biased by the ohmmeter.
• Gain can be verified by using a resistor in
conjunction with the ohmmeter test.

NPN

V

mA

E
B
C

The E-B junction is forward biased by the ohmmeter.

NPN

V

mA

E
B
C

The C-E resistance is very high.

NPN

V

mA

E
B
C
100 kW

The meter reading is < 100 kW due to gain.

Concept Review
• It is possible to test transistors out-of-circuit
using an ohmmeter.
• The E-B and C-B junctions act as diodes
during ohmmeter testing.
• The C-E test shows a high resistance because
two junctions are involved; one of which is
reverse biased by the ohmmeter.
• Gain can be verified by using a resistor in
conjunction with the ohmmeter test.
Repeat Segment

Concept Preview
• Bipolar junction transistors (BJTs) are controlled by
base current.
• Junction field effect transistors (JFETs) are controlled
by gate voltage.

• JFETs operate in the depletion mode (as normally on
devices).
• Metal oxide semiconductor field effect transistors
(MOSFETs) usually operate in the enhancement mode
(as normally off devices).
• Insulated gate bipolar transistors (IGBTs) are modified
MOSFETs and have very low on-resistance.
• Unijunction transistors (UJTs) are not used as
amplifiers.

Current In

The BJT is
a current
amplifier.

Current
Amplifier

Current Out

Voltage In

The JFET is
a voltage
controlled
amplifier.

Voltage
Amplifier

Current Out

Source

Gate

Drain

P

N-channel
P-type substrate
Structure of an
N-channel JFET

The channel has carriers so it
conducts from source to drain.

Drain

Gate
Source

Source

Gate

Drain

P

N-channel
P-type substrate

A negative gate voltage
can push the carriers from
the channel and turn
the JFET off.

Drain

Gate
Source

0V
-1 V
-2 V

ID in mA

-3 V

VGS

-4 V

0

-5 V
VDS in Volts

This is known as a depletion-mode device.
N-channel JFET drain family of characteristic curves

It’s possible to make enhancement
type field effect transistors as well.
Metal
oxide
insulator

Drain

n

Gate

VGG

D

VDD

p

G

n

S
N-channel
MOSFET

Source

Gate bias enhances the channel and turns the device on.

5V
4V
3V

ID in mA

2V

VGS

1V

0

0V
Drain

VDS in Volts

Enhancement mode
MOSFET drain family of
characteristic curves

Gate
Source

The IGBT (insulated gate bipolar transistor)
Operation and structure
similar to a MOSFET
Voltage controlled
(like the MOSFET)
Has one more junction
than a MOSFET
Hole injection reduces
the collector resistance

Faster turn off than
BJTs but not as fast
as MOSFETS

RCE = 8.33 mW

Three major device technologies

hole injection
Extra
junction

Courtesy of Powerex, Inc.

Typical IGBT Driver Circuit
Typically +15 V for turn on
Typically - 5 to -15 V for turn off

Control signal

IGBT

Powerex IGBT Module Structure

Powerex high voltage IGBT package

Emitter voltage

The unijunction transistor fires
when its emitter voltage reaches VP.
VP

Then, the emitter voltage
drops due to its negative
resistance characteristic.
Base 2

Emitter current
Emitter

The UJT is not useful as an amplifier.
It is used in timing and control applications.

Base 1

Other Transistor Types Quiz
BJTs are _________-controlled
amplifiers.

current

FETs are __________-controlled
amplifiers.

voltage

JFETs operate in the __________ mode. depletion
MOSFETs operate in the __________
mode.

enhancement

IGBTs are __________-controlled
amplifiers.

voltage

UJTs are not useful as __________.

amplifiers

Concept Review
• Bipolar junction transistors (BJTs) are controlled by
base current.
• Junction field effect transistors (JFETs) are controlled
by gate voltage.
• JFETs operate in the depletion mode (as normally on
devices).
• Metal oxide semiconductor field effect transistors
(MOSFETs) usually operate in the enhancement mode
(as normally off devices).
• Insulated gate bipolar transistors (IGBTs) are modified
MOSFETs and have very low on-resistance.
• Unijunction transistors (UJTs) are not used as
amplifiers.
Repeat Segment

Concept Preview
• BJTs can be used as switches.
• No base current = switch is off.
• High base current = switch is on.
• The dissipation is always zero in an ideal
switch: off = no current flow and on = no
voltage drop.

• MOSFETs can also be used as switches: no
gate voltage = switch is off and high gate
voltage = switch is on.

How do transistor switches work?
Can be viewed as solid state relays:
they are either ON or they are OFF.
BJT switches are characterized by:
high base current (switch is on)
(or no base current … off)

low resistance from collector to emitter (on)
(or very high resistance … off)
low collector dissipation (on or off)
PC = VCE x IC
PC = 0 x IC = 0 W
(on)
(or PC = VCE x 0 = 0 W … off)

NPN SWITCH
LOAD

RCE @ 
W
0W
DRIVER

The
The
driver
driver
output
output
isiszero
positive,
volts,
IIBB>=I0
0and
andthe
theload
loadis
ison
off
The
driver
output
is
zero
volts,
B = 0 and ILOAD = 0

PNP SWITCH
DRIVER

LOAD

The
Z):
Thedriver
driveroutput
outputisgoes
isoff
off(high
(highthe
Z):the
theresistor
resistor
low:
voltage
drop
pulls
the
base
voltage
up
that
VV
pulls
thethe
base
voltage
upso
soV
that
across
resistor
makes
BE
BE==00
BE negative

PNP SWITCH WITH NPN DRIVER

LOAD

NPN SWITCH WITH PNP DRIVER
(NEGATIVE POWER SUPPLY)

VV
0VV
BE
BE@ @+0.7

VVBE
0 VV
BE@@-0.7

LOAD

STEPPER MOTOR

A

B

C

A

Enhancement mode
power MOSFETs
used as switches

B

C
D

D

Concept Review
• BJTs can be used as switches.
• No base current = switch is off.
• High base current = switch is on.
• The dissipation is always zero in an ideal
switch: off = no current flow and on = no
voltage drop.
• MOSFETs can also be used as switches: no
gate voltage = switch is off and high gate
voltage = switch is on.
Repeat Segment

REVIEW
• Amplification
• Transistors
• Characteristic Curves
• Transistor Testing
• Other Transistor Types
• Transistors as Switches


Slide 10

Electronics
Principles & Applications
Sixth Edition

Charles A. Schuler
Chapter 5

Transistors
(student version)
©2003

Glencoe/McGraw-Hill

INTRODUCTION
• Amplification
• Transistors
• Characteristic Curves
• Transistor Testing
• Other Transistor Types
• Transistors as Switches

Dear Student:
This presentation is arranged in segments.
Each segment is preceded by a Concept
Preview slide and is followed by a Concept
Review slide. When you reach a Concept
Review slide, you can return to the
beginning of that segment by clicking on the
Repeat Segment button. This will allow you
to view that segment again, if you want to.

Concept Preview
• Amplifiers provide gain (the output is larger
than the input).
• Transistors have gain.
• Transistors have a collector, a base, and an
emitter.
• The C-B junction is reverse biased.
• The B-E junction is forward biased.
• Most of the emitter carriers reach the collector.
• The base current is relatively small but controls
the larger currents.

In

Gain =

Amplifier

Out

In

Out

NPN Transistor Structure

The collector is lightly doped.

N

C

The base is thin and
is lightly doped.

P

B

The emitter is heavily doped.

N

E

NPN Transistor Bias
No current flows.
The C-B junction
is reverse biased.

N

C

P

B

N

E

NPN Transistor Bias

The B-E junction
is forward biased.

Current flows.

N

C

P

B

N

E

NPN Transistor Bias
IC
Current flows
everywhere.
Most of the emitter carriers
diffuse through the thin base
When
both
junctions
region since they are attracted
biased....
by are
the collector.

Note that IB is smaller
than IE or IC.

N

C

P

B

N

E

IB

IE

Note: when the
switch opens, all
currents go to zero.
Although IB is smaller
it controls IE and IC.

Gain is something small
controlling something large
(IB is small).

IC
N

C

P

B

N

E

IB

IE

Transistor Structure and Bias Quiz
The heaviest doping is found in
the ___________ region.

emitter

The thinnest of all three regions
is called the ____________.

base

The collector-base junction is
___________ biased.

reverse

The base-emitter junction is
____________ biased.

forward

The majority of the emitter
carriers flow to the ___________.

collector

Concept Review
• Amplifiers provide gain (the output is larger than
the input).
• Transistors have gain.

• Transistors have a collector, a base, and an emitter.
• The C-B junction is reverse biased.
• The B-E junction is forward biased.

• Most of the emitter carriers reach the collector.
• The base current is relatively small but controls the
larger currents.
Repeat Segment

Concept Preview
• The base to collector gain is called b (beta).
• To find b, divide the collector current by the
base current.
• The emitter current is the largest since it is the
sum of the base and collector currents.
• PNP transistors have opposite polarity from
NPN transistors.

• In an NPN transistor, the major flow is made
up of electrons.
• In a PNP transistor, the major flow is made up
of holes.

IC = 99 mA

The current gain from
base to collector
is called b.
IB = 1 mA

b =

99
ICmA
1IBmA

= 99

IE = 100 mA

C
P

B

N

E

IC = 99 mA
Kirchhoff’s
current law:

IB = 1 mA

C
P

B

N

E

IE = I B + I C

= 1 mA + 99 mA
= 100 mA
IE = 100 mA

IC = 99 mA
In a PNP transistor,
holes flow from
emitter to collector.

IB = 1 mA
Notice the PNP
bias voltages.

C
B

E

IE = 100 mA

Transistor Currents Quiz
b is the ratio of collector current to
______ current.

base

The sum of the base and collector
currents is the __________ current.

emitter

In NPN transistors, the flow from emitter
to collector is composed of _______.

electrons

In PNP transistors, the flow from emitter
to collector is composed of _______.

holes

Both NPN and PNP transistors show
__________ gain.

current

Concept Review
• The base to collector gain is called b (beta).
• To find b, divide the collector current by the
base current.
• The emitter current is the largest since it is the
sum of the base and collector currents.
• PNP transistors have opposite polarity from
NPN transistors.
• In an NPN transistor, the major flow is made
up of electrons.
• In a PNP transistor, the major flow is made up
of holes.
Repeat Segment

Concept Preview
• The NPN schematic symbol shows the emitter
arrow as Not Pointing iN.
• The collector curves are a graph of collector
voltage versus collector current.
• Both dc beta (bdc) and ac beta (bac) can be
determined from the collector curves.
• The collector circuit of a transistor can be
modeled as a resistor, as a closed switch or as
an open switch.
• The amount of base current determines which
of the three models applies.

NPN Schematic Symbol
Collector

Base

C
B E

Emitter
Memory aid: NPN
means Not Pointing iN.

PNP Schematic Symbol
Collector

Base

C
B E

Emitter

IC

This circuit is used to
collect IC versus
VCE data for
several values of IB.
C

IB
B

E

VCE

When graphed, the data provide an
NPN collector family of curves.
100 mA

14
12
10
IC in mA 8
6
4
2

80 mA
60 mA
40 mA
20 mA

0 2 4 6

8 10 12 14 16 18

VCE in Volts

0 mA

100 mA

14
12
10
IC in mA 8
6
4
2

80 mA
60 mA

40 mA
20 mA

0 2 4 6

8 10 12 14 16 18

0 mA

VCE in Volts

b =

14
mA
6ICmA
40
IB mA
100
mA

150
== 140

This type of gain
is called bdc or hFE.

100 mA

14
12
10
IC in mA 8
6
4
2

80 mA
60 mA

40 mA
20 mA

0 2 4 6

bac =

2.5DImA
C
20DImA
B

8 10 12 14 16 18

0 mA

VCE in Volts
= 125

Another type of gain
is called bac or hfe.

100 mA

14
12
10
IC in mA 8
6
4
2

80 mA
60 mA

40 mA
20 mA

0 2 4 6
IB

C

8 10 12 14 16 18
VCE in Volts

0 mA

With these values of IB:
The C-E model is a resistor.
E

100 mA

14
12
10
IC in mA 8
6
4
2
0 2 4 6
IB

80 mA
60 mA

40 mA
20 mA
8 10 12 14 16 18
VCE in Volts

0 mA

When IB >> 100 mA
VCE @ 0
The model is a closed switch.

100 mA

14
12
10
IC in mA 8
6
4
2
0 2 4 6
IB

80 mA
60 mA

40 mA
20 mA
8 10 12 14 16 18
VCE in Volts

0 mA

When IB = 0
IC = 0
The model is an open switch.

Transistor Operating Conditions Quiz
When IB is large and VCE @ 0, the transistor
acts as a ___________ switch.
closed
When IB = 0 and IC = 0, the transistor
acts as an ___________ switch.

open

When IB > 0 and VCE > 0, the transistor
acts as a ___________.

resistor

Two current gain measures are bdc and
__________.

bac

The symbol hfe is the same as _________.

bac

Concept Review
• The NPN schematic symbol shows the emitter
arrow as Not Pointing iN.
• The collector curves are a graph of collector
voltage versus collector current.
• Both dc beta (bdc) and ac beta (bac) can be
determined from the collector curves.
• The collector circuit of a transistor can be
modeled as a resistor, as a closed switch or as
an open switch.
• The amount of base current determines which
of the three models applies.
Repeat Segment

Concept Preview
• It is possible to test transistors out-of-circuit
using an ohmmeter.
• The E-B and C-B junctions act as diodes
during ohmmeter testing.

• The C-E test shows a high resistance because
two junctions are involved; one of which is
reverse biased by the ohmmeter.
• Gain can be verified by using a resistor in
conjunction with the ohmmeter test.

NPN

V

mA

E
B
C

The E-B junction is forward biased by the ohmmeter.

NPN

V

mA

E
B
C

The C-E resistance is very high.

NPN

V

mA

E
B
C
100 kW

The meter reading is < 100 kW due to gain.

Concept Review
• It is possible to test transistors out-of-circuit
using an ohmmeter.
• The E-B and C-B junctions act as diodes
during ohmmeter testing.
• The C-E test shows a high resistance because
two junctions are involved; one of which is
reverse biased by the ohmmeter.
• Gain can be verified by using a resistor in
conjunction with the ohmmeter test.
Repeat Segment

Concept Preview
• Bipolar junction transistors (BJTs) are controlled by
base current.
• Junction field effect transistors (JFETs) are controlled
by gate voltage.

• JFETs operate in the depletion mode (as normally on
devices).
• Metal oxide semiconductor field effect transistors
(MOSFETs) usually operate in the enhancement mode
(as normally off devices).
• Insulated gate bipolar transistors (IGBTs) are modified
MOSFETs and have very low on-resistance.
• Unijunction transistors (UJTs) are not used as
amplifiers.

Current In

The BJT is
a current
amplifier.

Current
Amplifier

Current Out

Voltage In

The JFET is
a voltage
controlled
amplifier.

Voltage
Amplifier

Current Out

Source

Gate

Drain

P

N-channel
P-type substrate
Structure of an
N-channel JFET

The channel has carriers so it
conducts from source to drain.

Drain

Gate
Source

Source

Gate

Drain

P

N-channel
P-type substrate

A negative gate voltage
can push the carriers from
the channel and turn
the JFET off.

Drain

Gate
Source

0V
-1 V
-2 V

ID in mA

-3 V

VGS

-4 V

0

-5 V
VDS in Volts

This is known as a depletion-mode device.
N-channel JFET drain family of characteristic curves

It’s possible to make enhancement
type field effect transistors as well.
Metal
oxide
insulator

Drain

n

Gate

VGG

D

VDD

p

G

n

S
N-channel
MOSFET

Source

Gate bias enhances the channel and turns the device on.

5V
4V
3V

ID in mA

2V

VGS

1V

0

0V
Drain

VDS in Volts

Enhancement mode
MOSFET drain family of
characteristic curves

Gate
Source

The IGBT (insulated gate bipolar transistor)
Operation and structure
similar to a MOSFET
Voltage controlled
(like the MOSFET)
Has one more junction
than a MOSFET
Hole injection reduces
the collector resistance

Faster turn off than
BJTs but not as fast
as MOSFETS

RCE = 8.33 mW

Three major device technologies

hole injection
Extra
junction

Courtesy of Powerex, Inc.

Typical IGBT Driver Circuit
Typically +15 V for turn on
Typically - 5 to -15 V for turn off

Control signal

IGBT

Powerex IGBT Module Structure

Powerex high voltage IGBT package

Emitter voltage

The unijunction transistor fires
when its emitter voltage reaches VP.
VP

Then, the emitter voltage
drops due to its negative
resistance characteristic.
Base 2

Emitter current
Emitter

The UJT is not useful as an amplifier.
It is used in timing and control applications.

Base 1

Other Transistor Types Quiz
BJTs are _________-controlled
amplifiers.

current

FETs are __________-controlled
amplifiers.

voltage

JFETs operate in the __________ mode. depletion
MOSFETs operate in the __________
mode.

enhancement

IGBTs are __________-controlled
amplifiers.

voltage

UJTs are not useful as __________.

amplifiers

Concept Review
• Bipolar junction transistors (BJTs) are controlled by
base current.
• Junction field effect transistors (JFETs) are controlled
by gate voltage.
• JFETs operate in the depletion mode (as normally on
devices).
• Metal oxide semiconductor field effect transistors
(MOSFETs) usually operate in the enhancement mode
(as normally off devices).
• Insulated gate bipolar transistors (IGBTs) are modified
MOSFETs and have very low on-resistance.
• Unijunction transistors (UJTs) are not used as
amplifiers.
Repeat Segment

Concept Preview
• BJTs can be used as switches.
• No base current = switch is off.
• High base current = switch is on.
• The dissipation is always zero in an ideal
switch: off = no current flow and on = no
voltage drop.

• MOSFETs can also be used as switches: no
gate voltage = switch is off and high gate
voltage = switch is on.

How do transistor switches work?
Can be viewed as solid state relays:
they are either ON or they are OFF.
BJT switches are characterized by:
high base current (switch is on)
(or no base current … off)

low resistance from collector to emitter (on)
(or very high resistance … off)
low collector dissipation (on or off)
PC = VCE x IC
PC = 0 x IC = 0 W
(on)
(or PC = VCE x 0 = 0 W … off)

NPN SWITCH
LOAD

RCE @ 
W
0W
DRIVER

The
The
driver
driver
output
output
isiszero
positive,
volts,
IIBB>=I0
0and
andthe
theload
loadis
ison
off
The
driver
output
is
zero
volts,
B = 0 and ILOAD = 0

PNP SWITCH
DRIVER

LOAD

The
Z):
Thedriver
driveroutput
outputisgoes
isoff
off(high
(highthe
Z):the
theresistor
resistor
low:
voltage
drop
pulls
the
base
voltage
up
that
VV
pulls
thethe
base
voltage
upso
soV
that
across
resistor
makes
BE
BE==00
BE negative

PNP SWITCH WITH NPN DRIVER

LOAD

NPN SWITCH WITH PNP DRIVER
(NEGATIVE POWER SUPPLY)

VV
0VV
BE
BE@ @+0.7

VVBE
0 VV
BE@@-0.7

LOAD

STEPPER MOTOR

A

B

C

A

Enhancement mode
power MOSFETs
used as switches

B

C
D

D

Concept Review
• BJTs can be used as switches.
• No base current = switch is off.
• High base current = switch is on.
• The dissipation is always zero in an ideal
switch: off = no current flow and on = no
voltage drop.
• MOSFETs can also be used as switches: no
gate voltage = switch is off and high gate
voltage = switch is on.
Repeat Segment

REVIEW
• Amplification
• Transistors
• Characteristic Curves
• Transistor Testing
• Other Transistor Types
• Transistors as Switches


Slide 11

Electronics
Principles & Applications
Sixth Edition

Charles A. Schuler
Chapter 5

Transistors
(student version)
©2003

Glencoe/McGraw-Hill

INTRODUCTION
• Amplification
• Transistors
• Characteristic Curves
• Transistor Testing
• Other Transistor Types
• Transistors as Switches

Dear Student:
This presentation is arranged in segments.
Each segment is preceded by a Concept
Preview slide and is followed by a Concept
Review slide. When you reach a Concept
Review slide, you can return to the
beginning of that segment by clicking on the
Repeat Segment button. This will allow you
to view that segment again, if you want to.

Concept Preview
• Amplifiers provide gain (the output is larger
than the input).
• Transistors have gain.
• Transistors have a collector, a base, and an
emitter.
• The C-B junction is reverse biased.
• The B-E junction is forward biased.
• Most of the emitter carriers reach the collector.
• The base current is relatively small but controls
the larger currents.

In

Gain =

Amplifier

Out

In

Out

NPN Transistor Structure

The collector is lightly doped.

N

C

The base is thin and
is lightly doped.

P

B

The emitter is heavily doped.

N

E

NPN Transistor Bias
No current flows.
The C-B junction
is reverse biased.

N

C

P

B

N

E

NPN Transistor Bias

The B-E junction
is forward biased.

Current flows.

N

C

P

B

N

E

NPN Transistor Bias
IC
Current flows
everywhere.
Most of the emitter carriers
diffuse through the thin base
When
both
junctions
region since they are attracted
biased....
by are
the collector.

Note that IB is smaller
than IE or IC.

N

C

P

B

N

E

IB

IE

Note: when the
switch opens, all
currents go to zero.
Although IB is smaller
it controls IE and IC.

Gain is something small
controlling something large
(IB is small).

IC
N

C

P

B

N

E

IB

IE

Transistor Structure and Bias Quiz
The heaviest doping is found in
the ___________ region.

emitter

The thinnest of all three regions
is called the ____________.

base

The collector-base junction is
___________ biased.

reverse

The base-emitter junction is
____________ biased.

forward

The majority of the emitter
carriers flow to the ___________.

collector

Concept Review
• Amplifiers provide gain (the output is larger than
the input).
• Transistors have gain.

• Transistors have a collector, a base, and an emitter.
• The C-B junction is reverse biased.
• The B-E junction is forward biased.

• Most of the emitter carriers reach the collector.
• The base current is relatively small but controls the
larger currents.
Repeat Segment

Concept Preview
• The base to collector gain is called b (beta).
• To find b, divide the collector current by the
base current.
• The emitter current is the largest since it is the
sum of the base and collector currents.
• PNP transistors have opposite polarity from
NPN transistors.

• In an NPN transistor, the major flow is made
up of electrons.
• In a PNP transistor, the major flow is made up
of holes.

IC = 99 mA

The current gain from
base to collector
is called b.
IB = 1 mA

b =

99
ICmA
1IBmA

= 99

IE = 100 mA

C
P

B

N

E

IC = 99 mA
Kirchhoff’s
current law:

IB = 1 mA

C
P

B

N

E

IE = I B + I C

= 1 mA + 99 mA
= 100 mA
IE = 100 mA

IC = 99 mA
In a PNP transistor,
holes flow from
emitter to collector.

IB = 1 mA
Notice the PNP
bias voltages.

C
B

E

IE = 100 mA

Transistor Currents Quiz
b is the ratio of collector current to
______ current.

base

The sum of the base and collector
currents is the __________ current.

emitter

In NPN transistors, the flow from emitter
to collector is composed of _______.

electrons

In PNP transistors, the flow from emitter
to collector is composed of _______.

holes

Both NPN and PNP transistors show
__________ gain.

current

Concept Review
• The base to collector gain is called b (beta).
• To find b, divide the collector current by the
base current.
• The emitter current is the largest since it is the
sum of the base and collector currents.
• PNP transistors have opposite polarity from
NPN transistors.
• In an NPN transistor, the major flow is made
up of electrons.
• In a PNP transistor, the major flow is made up
of holes.
Repeat Segment

Concept Preview
• The NPN schematic symbol shows the emitter
arrow as Not Pointing iN.
• The collector curves are a graph of collector
voltage versus collector current.
• Both dc beta (bdc) and ac beta (bac) can be
determined from the collector curves.
• The collector circuit of a transistor can be
modeled as a resistor, as a closed switch or as
an open switch.
• The amount of base current determines which
of the three models applies.

NPN Schematic Symbol
Collector

Base

C
B E

Emitter
Memory aid: NPN
means Not Pointing iN.

PNP Schematic Symbol
Collector

Base

C
B E

Emitter

IC

This circuit is used to
collect IC versus
VCE data for
several values of IB.
C

IB
B

E

VCE

When graphed, the data provide an
NPN collector family of curves.
100 mA

14
12
10
IC in mA 8
6
4
2

80 mA
60 mA
40 mA
20 mA

0 2 4 6

8 10 12 14 16 18

VCE in Volts

0 mA

100 mA

14
12
10
IC in mA 8
6
4
2

80 mA
60 mA

40 mA
20 mA

0 2 4 6

8 10 12 14 16 18

0 mA

VCE in Volts

b =

14
mA
6ICmA
40
IB mA
100
mA

150
== 140

This type of gain
is called bdc or hFE.

100 mA

14
12
10
IC in mA 8
6
4
2

80 mA
60 mA

40 mA
20 mA

0 2 4 6

bac =

2.5DImA
C
20DImA
B

8 10 12 14 16 18

0 mA

VCE in Volts
= 125

Another type of gain
is called bac or hfe.

100 mA

14
12
10
IC in mA 8
6
4
2

80 mA
60 mA

40 mA
20 mA

0 2 4 6
IB

C

8 10 12 14 16 18
VCE in Volts

0 mA

With these values of IB:
The C-E model is a resistor.
E

100 mA

14
12
10
IC in mA 8
6
4
2
0 2 4 6
IB

80 mA
60 mA

40 mA
20 mA
8 10 12 14 16 18
VCE in Volts

0 mA

When IB >> 100 mA
VCE @ 0
The model is a closed switch.

100 mA

14
12
10
IC in mA 8
6
4
2
0 2 4 6
IB

80 mA
60 mA

40 mA
20 mA
8 10 12 14 16 18
VCE in Volts

0 mA

When IB = 0
IC = 0
The model is an open switch.

Transistor Operating Conditions Quiz
When IB is large and VCE @ 0, the transistor
acts as a ___________ switch.
closed
When IB = 0 and IC = 0, the transistor
acts as an ___________ switch.

open

When IB > 0 and VCE > 0, the transistor
acts as a ___________.

resistor

Two current gain measures are bdc and
__________.

bac

The symbol hfe is the same as _________.

bac

Concept Review
• The NPN schematic symbol shows the emitter
arrow as Not Pointing iN.
• The collector curves are a graph of collector
voltage versus collector current.
• Both dc beta (bdc) and ac beta (bac) can be
determined from the collector curves.
• The collector circuit of a transistor can be
modeled as a resistor, as a closed switch or as
an open switch.
• The amount of base current determines which
of the three models applies.
Repeat Segment

Concept Preview
• It is possible to test transistors out-of-circuit
using an ohmmeter.
• The E-B and C-B junctions act as diodes
during ohmmeter testing.

• The C-E test shows a high resistance because
two junctions are involved; one of which is
reverse biased by the ohmmeter.
• Gain can be verified by using a resistor in
conjunction with the ohmmeter test.

NPN

V

mA

E
B
C

The E-B junction is forward biased by the ohmmeter.

NPN

V

mA

E
B
C

The C-E resistance is very high.

NPN

V

mA

E
B
C
100 kW

The meter reading is < 100 kW due to gain.

Concept Review
• It is possible to test transistors out-of-circuit
using an ohmmeter.
• The E-B and C-B junctions act as diodes
during ohmmeter testing.
• The C-E test shows a high resistance because
two junctions are involved; one of which is
reverse biased by the ohmmeter.
• Gain can be verified by using a resistor in
conjunction with the ohmmeter test.
Repeat Segment

Concept Preview
• Bipolar junction transistors (BJTs) are controlled by
base current.
• Junction field effect transistors (JFETs) are controlled
by gate voltage.

• JFETs operate in the depletion mode (as normally on
devices).
• Metal oxide semiconductor field effect transistors
(MOSFETs) usually operate in the enhancement mode
(as normally off devices).
• Insulated gate bipolar transistors (IGBTs) are modified
MOSFETs and have very low on-resistance.
• Unijunction transistors (UJTs) are not used as
amplifiers.

Current In

The BJT is
a current
amplifier.

Current
Amplifier

Current Out

Voltage In

The JFET is
a voltage
controlled
amplifier.

Voltage
Amplifier

Current Out

Source

Gate

Drain

P

N-channel
P-type substrate
Structure of an
N-channel JFET

The channel has carriers so it
conducts from source to drain.

Drain

Gate
Source

Source

Gate

Drain

P

N-channel
P-type substrate

A negative gate voltage
can push the carriers from
the channel and turn
the JFET off.

Drain

Gate
Source

0V
-1 V
-2 V

ID in mA

-3 V

VGS

-4 V

0

-5 V
VDS in Volts

This is known as a depletion-mode device.
N-channel JFET drain family of characteristic curves

It’s possible to make enhancement
type field effect transistors as well.
Metal
oxide
insulator

Drain

n

Gate

VGG

D

VDD

p

G

n

S
N-channel
MOSFET

Source

Gate bias enhances the channel and turns the device on.

5V
4V
3V

ID in mA

2V

VGS

1V

0

0V
Drain

VDS in Volts

Enhancement mode
MOSFET drain family of
characteristic curves

Gate
Source

The IGBT (insulated gate bipolar transistor)
Operation and structure
similar to a MOSFET
Voltage controlled
(like the MOSFET)
Has one more junction
than a MOSFET
Hole injection reduces
the collector resistance

Faster turn off than
BJTs but not as fast
as MOSFETS

RCE = 8.33 mW

Three major device technologies

hole injection
Extra
junction

Courtesy of Powerex, Inc.

Typical IGBT Driver Circuit
Typically +15 V for turn on
Typically - 5 to -15 V for turn off

Control signal

IGBT

Powerex IGBT Module Structure

Powerex high voltage IGBT package

Emitter voltage

The unijunction transistor fires
when its emitter voltage reaches VP.
VP

Then, the emitter voltage
drops due to its negative
resistance characteristic.
Base 2

Emitter current
Emitter

The UJT is not useful as an amplifier.
It is used in timing and control applications.

Base 1

Other Transistor Types Quiz
BJTs are _________-controlled
amplifiers.

current

FETs are __________-controlled
amplifiers.

voltage

JFETs operate in the __________ mode. depletion
MOSFETs operate in the __________
mode.

enhancement

IGBTs are __________-controlled
amplifiers.

voltage

UJTs are not useful as __________.

amplifiers

Concept Review
• Bipolar junction transistors (BJTs) are controlled by
base current.
• Junction field effect transistors (JFETs) are controlled
by gate voltage.
• JFETs operate in the depletion mode (as normally on
devices).
• Metal oxide semiconductor field effect transistors
(MOSFETs) usually operate in the enhancement mode
(as normally off devices).
• Insulated gate bipolar transistors (IGBTs) are modified
MOSFETs and have very low on-resistance.
• Unijunction transistors (UJTs) are not used as
amplifiers.
Repeat Segment

Concept Preview
• BJTs can be used as switches.
• No base current = switch is off.
• High base current = switch is on.
• The dissipation is always zero in an ideal
switch: off = no current flow and on = no
voltage drop.

• MOSFETs can also be used as switches: no
gate voltage = switch is off and high gate
voltage = switch is on.

How do transistor switches work?
Can be viewed as solid state relays:
they are either ON or they are OFF.
BJT switches are characterized by:
high base current (switch is on)
(or no base current … off)

low resistance from collector to emitter (on)
(or very high resistance … off)
low collector dissipation (on or off)
PC = VCE x IC
PC = 0 x IC = 0 W
(on)
(or PC = VCE x 0 = 0 W … off)

NPN SWITCH
LOAD

RCE @ 
W
0W
DRIVER

The
The
driver
driver
output
output
isiszero
positive,
volts,
IIBB>=I0
0and
andthe
theload
loadis
ison
off
The
driver
output
is
zero
volts,
B = 0 and ILOAD = 0

PNP SWITCH
DRIVER

LOAD

The
Z):
Thedriver
driveroutput
outputisgoes
isoff
off(high
(highthe
Z):the
theresistor
resistor
low:
voltage
drop
pulls
the
base
voltage
up
that
VV
pulls
thethe
base
voltage
upso
soV
that
across
resistor
makes
BE
BE==00
BE negative

PNP SWITCH WITH NPN DRIVER

LOAD

NPN SWITCH WITH PNP DRIVER
(NEGATIVE POWER SUPPLY)

VV
0VV
BE
BE@ @+0.7

VVBE
0 VV
BE@@-0.7

LOAD

STEPPER MOTOR

A

B

C

A

Enhancement mode
power MOSFETs
used as switches

B

C
D

D

Concept Review
• BJTs can be used as switches.
• No base current = switch is off.
• High base current = switch is on.
• The dissipation is always zero in an ideal
switch: off = no current flow and on = no
voltage drop.
• MOSFETs can also be used as switches: no
gate voltage = switch is off and high gate
voltage = switch is on.
Repeat Segment

REVIEW
• Amplification
• Transistors
• Characteristic Curves
• Transistor Testing
• Other Transistor Types
• Transistors as Switches


Slide 12

Electronics
Principles & Applications
Sixth Edition

Charles A. Schuler
Chapter 5

Transistors
(student version)
©2003

Glencoe/McGraw-Hill

INTRODUCTION
• Amplification
• Transistors
• Characteristic Curves
• Transistor Testing
• Other Transistor Types
• Transistors as Switches

Dear Student:
This presentation is arranged in segments.
Each segment is preceded by a Concept
Preview slide and is followed by a Concept
Review slide. When you reach a Concept
Review slide, you can return to the
beginning of that segment by clicking on the
Repeat Segment button. This will allow you
to view that segment again, if you want to.

Concept Preview
• Amplifiers provide gain (the output is larger
than the input).
• Transistors have gain.
• Transistors have a collector, a base, and an
emitter.
• The C-B junction is reverse biased.
• The B-E junction is forward biased.
• Most of the emitter carriers reach the collector.
• The base current is relatively small but controls
the larger currents.

In

Gain =

Amplifier

Out

In

Out

NPN Transistor Structure

The collector is lightly doped.

N

C

The base is thin and
is lightly doped.

P

B

The emitter is heavily doped.

N

E

NPN Transistor Bias
No current flows.
The C-B junction
is reverse biased.

N

C

P

B

N

E

NPN Transistor Bias

The B-E junction
is forward biased.

Current flows.

N

C

P

B

N

E

NPN Transistor Bias
IC
Current flows
everywhere.
Most of the emitter carriers
diffuse through the thin base
When
both
junctions
region since they are attracted
biased....
by are
the collector.

Note that IB is smaller
than IE or IC.

N

C

P

B

N

E

IB

IE

Note: when the
switch opens, all
currents go to zero.
Although IB is smaller
it controls IE and IC.

Gain is something small
controlling something large
(IB is small).

IC
N

C

P

B

N

E

IB

IE

Transistor Structure and Bias Quiz
The heaviest doping is found in
the ___________ region.

emitter

The thinnest of all three regions
is called the ____________.

base

The collector-base junction is
___________ biased.

reverse

The base-emitter junction is
____________ biased.

forward

The majority of the emitter
carriers flow to the ___________.

collector

Concept Review
• Amplifiers provide gain (the output is larger than
the input).
• Transistors have gain.

• Transistors have a collector, a base, and an emitter.
• The C-B junction is reverse biased.
• The B-E junction is forward biased.

• Most of the emitter carriers reach the collector.
• The base current is relatively small but controls the
larger currents.
Repeat Segment

Concept Preview
• The base to collector gain is called b (beta).
• To find b, divide the collector current by the
base current.
• The emitter current is the largest since it is the
sum of the base and collector currents.
• PNP transistors have opposite polarity from
NPN transistors.

• In an NPN transistor, the major flow is made
up of electrons.
• In a PNP transistor, the major flow is made up
of holes.

IC = 99 mA

The current gain from
base to collector
is called b.
IB = 1 mA

b =

99
ICmA
1IBmA

= 99

IE = 100 mA

C
P

B

N

E

IC = 99 mA
Kirchhoff’s
current law:

IB = 1 mA

C
P

B

N

E

IE = I B + I C

= 1 mA + 99 mA
= 100 mA
IE = 100 mA

IC = 99 mA
In a PNP transistor,
holes flow from
emitter to collector.

IB = 1 mA
Notice the PNP
bias voltages.

C
B

E

IE = 100 mA

Transistor Currents Quiz
b is the ratio of collector current to
______ current.

base

The sum of the base and collector
currents is the __________ current.

emitter

In NPN transistors, the flow from emitter
to collector is composed of _______.

electrons

In PNP transistors, the flow from emitter
to collector is composed of _______.

holes

Both NPN and PNP transistors show
__________ gain.

current

Concept Review
• The base to collector gain is called b (beta).
• To find b, divide the collector current by the
base current.
• The emitter current is the largest since it is the
sum of the base and collector currents.
• PNP transistors have opposite polarity from
NPN transistors.
• In an NPN transistor, the major flow is made
up of electrons.
• In a PNP transistor, the major flow is made up
of holes.
Repeat Segment

Concept Preview
• The NPN schematic symbol shows the emitter
arrow as Not Pointing iN.
• The collector curves are a graph of collector
voltage versus collector current.
• Both dc beta (bdc) and ac beta (bac) can be
determined from the collector curves.
• The collector circuit of a transistor can be
modeled as a resistor, as a closed switch or as
an open switch.
• The amount of base current determines which
of the three models applies.

NPN Schematic Symbol
Collector

Base

C
B E

Emitter
Memory aid: NPN
means Not Pointing iN.

PNP Schematic Symbol
Collector

Base

C
B E

Emitter

IC

This circuit is used to
collect IC versus
VCE data for
several values of IB.
C

IB
B

E

VCE

When graphed, the data provide an
NPN collector family of curves.
100 mA

14
12
10
IC in mA 8
6
4
2

80 mA
60 mA
40 mA
20 mA

0 2 4 6

8 10 12 14 16 18

VCE in Volts

0 mA

100 mA

14
12
10
IC in mA 8
6
4
2

80 mA
60 mA

40 mA
20 mA

0 2 4 6

8 10 12 14 16 18

0 mA

VCE in Volts

b =

14
mA
6ICmA
40
IB mA
100
mA

150
== 140

This type of gain
is called bdc or hFE.

100 mA

14
12
10
IC in mA 8
6
4
2

80 mA
60 mA

40 mA
20 mA

0 2 4 6

bac =

2.5DImA
C
20DImA
B

8 10 12 14 16 18

0 mA

VCE in Volts
= 125

Another type of gain
is called bac or hfe.

100 mA

14
12
10
IC in mA 8
6
4
2

80 mA
60 mA

40 mA
20 mA

0 2 4 6
IB

C

8 10 12 14 16 18
VCE in Volts

0 mA

With these values of IB:
The C-E model is a resistor.
E

100 mA

14
12
10
IC in mA 8
6
4
2
0 2 4 6
IB

80 mA
60 mA

40 mA
20 mA
8 10 12 14 16 18
VCE in Volts

0 mA

When IB >> 100 mA
VCE @ 0
The model is a closed switch.

100 mA

14
12
10
IC in mA 8
6
4
2
0 2 4 6
IB

80 mA
60 mA

40 mA
20 mA
8 10 12 14 16 18
VCE in Volts

0 mA

When IB = 0
IC = 0
The model is an open switch.

Transistor Operating Conditions Quiz
When IB is large and VCE @ 0, the transistor
acts as a ___________ switch.
closed
When IB = 0 and IC = 0, the transistor
acts as an ___________ switch.

open

When IB > 0 and VCE > 0, the transistor
acts as a ___________.

resistor

Two current gain measures are bdc and
__________.

bac

The symbol hfe is the same as _________.

bac

Concept Review
• The NPN schematic symbol shows the emitter
arrow as Not Pointing iN.
• The collector curves are a graph of collector
voltage versus collector current.
• Both dc beta (bdc) and ac beta (bac) can be
determined from the collector curves.
• The collector circuit of a transistor can be
modeled as a resistor, as a closed switch or as
an open switch.
• The amount of base current determines which
of the three models applies.
Repeat Segment

Concept Preview
• It is possible to test transistors out-of-circuit
using an ohmmeter.
• The E-B and C-B junctions act as diodes
during ohmmeter testing.

• The C-E test shows a high resistance because
two junctions are involved; one of which is
reverse biased by the ohmmeter.
• Gain can be verified by using a resistor in
conjunction with the ohmmeter test.

NPN

V

mA

E
B
C

The E-B junction is forward biased by the ohmmeter.

NPN

V

mA

E
B
C

The C-E resistance is very high.

NPN

V

mA

E
B
C
100 kW

The meter reading is < 100 kW due to gain.

Concept Review
• It is possible to test transistors out-of-circuit
using an ohmmeter.
• The E-B and C-B junctions act as diodes
during ohmmeter testing.
• The C-E test shows a high resistance because
two junctions are involved; one of which is
reverse biased by the ohmmeter.
• Gain can be verified by using a resistor in
conjunction with the ohmmeter test.
Repeat Segment

Concept Preview
• Bipolar junction transistors (BJTs) are controlled by
base current.
• Junction field effect transistors (JFETs) are controlled
by gate voltage.

• JFETs operate in the depletion mode (as normally on
devices).
• Metal oxide semiconductor field effect transistors
(MOSFETs) usually operate in the enhancement mode
(as normally off devices).
• Insulated gate bipolar transistors (IGBTs) are modified
MOSFETs and have very low on-resistance.
• Unijunction transistors (UJTs) are not used as
amplifiers.

Current In

The BJT is
a current
amplifier.

Current
Amplifier

Current Out

Voltage In

The JFET is
a voltage
controlled
amplifier.

Voltage
Amplifier

Current Out

Source

Gate

Drain

P

N-channel
P-type substrate
Structure of an
N-channel JFET

The channel has carriers so it
conducts from source to drain.

Drain

Gate
Source

Source

Gate

Drain

P

N-channel
P-type substrate

A negative gate voltage
can push the carriers from
the channel and turn
the JFET off.

Drain

Gate
Source

0V
-1 V
-2 V

ID in mA

-3 V

VGS

-4 V

0

-5 V
VDS in Volts

This is known as a depletion-mode device.
N-channel JFET drain family of characteristic curves

It’s possible to make enhancement
type field effect transistors as well.
Metal
oxide
insulator

Drain

n

Gate

VGG

D

VDD

p

G

n

S
N-channel
MOSFET

Source

Gate bias enhances the channel and turns the device on.

5V
4V
3V

ID in mA

2V

VGS

1V

0

0V
Drain

VDS in Volts

Enhancement mode
MOSFET drain family of
characteristic curves

Gate
Source

The IGBT (insulated gate bipolar transistor)
Operation and structure
similar to a MOSFET
Voltage controlled
(like the MOSFET)
Has one more junction
than a MOSFET
Hole injection reduces
the collector resistance

Faster turn off than
BJTs but not as fast
as MOSFETS

RCE = 8.33 mW

Three major device technologies

hole injection
Extra
junction

Courtesy of Powerex, Inc.

Typical IGBT Driver Circuit
Typically +15 V for turn on
Typically - 5 to -15 V for turn off

Control signal

IGBT

Powerex IGBT Module Structure

Powerex high voltage IGBT package

Emitter voltage

The unijunction transistor fires
when its emitter voltage reaches VP.
VP

Then, the emitter voltage
drops due to its negative
resistance characteristic.
Base 2

Emitter current
Emitter

The UJT is not useful as an amplifier.
It is used in timing and control applications.

Base 1

Other Transistor Types Quiz
BJTs are _________-controlled
amplifiers.

current

FETs are __________-controlled
amplifiers.

voltage

JFETs operate in the __________ mode. depletion
MOSFETs operate in the __________
mode.

enhancement

IGBTs are __________-controlled
amplifiers.

voltage

UJTs are not useful as __________.

amplifiers

Concept Review
• Bipolar junction transistors (BJTs) are controlled by
base current.
• Junction field effect transistors (JFETs) are controlled
by gate voltage.
• JFETs operate in the depletion mode (as normally on
devices).
• Metal oxide semiconductor field effect transistors
(MOSFETs) usually operate in the enhancement mode
(as normally off devices).
• Insulated gate bipolar transistors (IGBTs) are modified
MOSFETs and have very low on-resistance.
• Unijunction transistors (UJTs) are not used as
amplifiers.
Repeat Segment

Concept Preview
• BJTs can be used as switches.
• No base current = switch is off.
• High base current = switch is on.
• The dissipation is always zero in an ideal
switch: off = no current flow and on = no
voltage drop.

• MOSFETs can also be used as switches: no
gate voltage = switch is off and high gate
voltage = switch is on.

How do transistor switches work?
Can be viewed as solid state relays:
they are either ON or they are OFF.
BJT switches are characterized by:
high base current (switch is on)
(or no base current … off)

low resistance from collector to emitter (on)
(or very high resistance … off)
low collector dissipation (on or off)
PC = VCE x IC
PC = 0 x IC = 0 W
(on)
(or PC = VCE x 0 = 0 W … off)

NPN SWITCH
LOAD

RCE @ 
W
0W
DRIVER

The
The
driver
driver
output
output
isiszero
positive,
volts,
IIBB>=I0
0and
andthe
theload
loadis
ison
off
The
driver
output
is
zero
volts,
B = 0 and ILOAD = 0

PNP SWITCH
DRIVER

LOAD

The
Z):
Thedriver
driveroutput
outputisgoes
isoff
off(high
(highthe
Z):the
theresistor
resistor
low:
voltage
drop
pulls
the
base
voltage
up
that
VV
pulls
thethe
base
voltage
upso
soV
that
across
resistor
makes
BE
BE==00
BE negative

PNP SWITCH WITH NPN DRIVER

LOAD

NPN SWITCH WITH PNP DRIVER
(NEGATIVE POWER SUPPLY)

VV
0VV
BE
BE@ @+0.7

VVBE
0 VV
BE@@-0.7

LOAD

STEPPER MOTOR

A

B

C

A

Enhancement mode
power MOSFETs
used as switches

B

C
D

D

Concept Review
• BJTs can be used as switches.
• No base current = switch is off.
• High base current = switch is on.
• The dissipation is always zero in an ideal
switch: off = no current flow and on = no
voltage drop.
• MOSFETs can also be used as switches: no
gate voltage = switch is off and high gate
voltage = switch is on.
Repeat Segment

REVIEW
• Amplification
• Transistors
• Characteristic Curves
• Transistor Testing
• Other Transistor Types
• Transistors as Switches


Slide 13

Electronics
Principles & Applications
Sixth Edition

Charles A. Schuler
Chapter 5

Transistors
(student version)
©2003

Glencoe/McGraw-Hill

INTRODUCTION
• Amplification
• Transistors
• Characteristic Curves
• Transistor Testing
• Other Transistor Types
• Transistors as Switches

Dear Student:
This presentation is arranged in segments.
Each segment is preceded by a Concept
Preview slide and is followed by a Concept
Review slide. When you reach a Concept
Review slide, you can return to the
beginning of that segment by clicking on the
Repeat Segment button. This will allow you
to view that segment again, if you want to.

Concept Preview
• Amplifiers provide gain (the output is larger
than the input).
• Transistors have gain.
• Transistors have a collector, a base, and an
emitter.
• The C-B junction is reverse biased.
• The B-E junction is forward biased.
• Most of the emitter carriers reach the collector.
• The base current is relatively small but controls
the larger currents.

In

Gain =

Amplifier

Out

In

Out

NPN Transistor Structure

The collector is lightly doped.

N

C

The base is thin and
is lightly doped.

P

B

The emitter is heavily doped.

N

E

NPN Transistor Bias
No current flows.
The C-B junction
is reverse biased.

N

C

P

B

N

E

NPN Transistor Bias

The B-E junction
is forward biased.

Current flows.

N

C

P

B

N

E

NPN Transistor Bias
IC
Current flows
everywhere.
Most of the emitter carriers
diffuse through the thin base
When
both
junctions
region since they are attracted
biased....
by are
the collector.

Note that IB is smaller
than IE or IC.

N

C

P

B

N

E

IB

IE

Note: when the
switch opens, all
currents go to zero.
Although IB is smaller
it controls IE and IC.

Gain is something small
controlling something large
(IB is small).

IC
N

C

P

B

N

E

IB

IE

Transistor Structure and Bias Quiz
The heaviest doping is found in
the ___________ region.

emitter

The thinnest of all three regions
is called the ____________.

base

The collector-base junction is
___________ biased.

reverse

The base-emitter junction is
____________ biased.

forward

The majority of the emitter
carriers flow to the ___________.

collector

Concept Review
• Amplifiers provide gain (the output is larger than
the input).
• Transistors have gain.

• Transistors have a collector, a base, and an emitter.
• The C-B junction is reverse biased.
• The B-E junction is forward biased.

• Most of the emitter carriers reach the collector.
• The base current is relatively small but controls the
larger currents.
Repeat Segment

Concept Preview
• The base to collector gain is called b (beta).
• To find b, divide the collector current by the
base current.
• The emitter current is the largest since it is the
sum of the base and collector currents.
• PNP transistors have opposite polarity from
NPN transistors.

• In an NPN transistor, the major flow is made
up of electrons.
• In a PNP transistor, the major flow is made up
of holes.

IC = 99 mA

The current gain from
base to collector
is called b.
IB = 1 mA

b =

99
ICmA
1IBmA

= 99

IE = 100 mA

C
P

B

N

E

IC = 99 mA
Kirchhoff’s
current law:

IB = 1 mA

C
P

B

N

E

IE = I B + I C

= 1 mA + 99 mA
= 100 mA
IE = 100 mA

IC = 99 mA
In a PNP transistor,
holes flow from
emitter to collector.

IB = 1 mA
Notice the PNP
bias voltages.

C
B

E

IE = 100 mA

Transistor Currents Quiz
b is the ratio of collector current to
______ current.

base

The sum of the base and collector
currents is the __________ current.

emitter

In NPN transistors, the flow from emitter
to collector is composed of _______.

electrons

In PNP transistors, the flow from emitter
to collector is composed of _______.

holes

Both NPN and PNP transistors show
__________ gain.

current

Concept Review
• The base to collector gain is called b (beta).
• To find b, divide the collector current by the
base current.
• The emitter current is the largest since it is the
sum of the base and collector currents.
• PNP transistors have opposite polarity from
NPN transistors.
• In an NPN transistor, the major flow is made
up of electrons.
• In a PNP transistor, the major flow is made up
of holes.
Repeat Segment

Concept Preview
• The NPN schematic symbol shows the emitter
arrow as Not Pointing iN.
• The collector curves are a graph of collector
voltage versus collector current.
• Both dc beta (bdc) and ac beta (bac) can be
determined from the collector curves.
• The collector circuit of a transistor can be
modeled as a resistor, as a closed switch or as
an open switch.
• The amount of base current determines which
of the three models applies.

NPN Schematic Symbol
Collector

Base

C
B E

Emitter
Memory aid: NPN
means Not Pointing iN.

PNP Schematic Symbol
Collector

Base

C
B E

Emitter

IC

This circuit is used to
collect IC versus
VCE data for
several values of IB.
C

IB
B

E

VCE

When graphed, the data provide an
NPN collector family of curves.
100 mA

14
12
10
IC in mA 8
6
4
2

80 mA
60 mA
40 mA
20 mA

0 2 4 6

8 10 12 14 16 18

VCE in Volts

0 mA

100 mA

14
12
10
IC in mA 8
6
4
2

80 mA
60 mA

40 mA
20 mA

0 2 4 6

8 10 12 14 16 18

0 mA

VCE in Volts

b =

14
mA
6ICmA
40
IB mA
100
mA

150
== 140

This type of gain
is called bdc or hFE.

100 mA

14
12
10
IC in mA 8
6
4
2

80 mA
60 mA

40 mA
20 mA

0 2 4 6

bac =

2.5DImA
C
20DImA
B

8 10 12 14 16 18

0 mA

VCE in Volts
= 125

Another type of gain
is called bac or hfe.

100 mA

14
12
10
IC in mA 8
6
4
2

80 mA
60 mA

40 mA
20 mA

0 2 4 6
IB

C

8 10 12 14 16 18
VCE in Volts

0 mA

With these values of IB:
The C-E model is a resistor.
E

100 mA

14
12
10
IC in mA 8
6
4
2
0 2 4 6
IB

80 mA
60 mA

40 mA
20 mA
8 10 12 14 16 18
VCE in Volts

0 mA

When IB >> 100 mA
VCE @ 0
The model is a closed switch.

100 mA

14
12
10
IC in mA 8
6
4
2
0 2 4 6
IB

80 mA
60 mA

40 mA
20 mA
8 10 12 14 16 18
VCE in Volts

0 mA

When IB = 0
IC = 0
The model is an open switch.

Transistor Operating Conditions Quiz
When IB is large and VCE @ 0, the transistor
acts as a ___________ switch.
closed
When IB = 0 and IC = 0, the transistor
acts as an ___________ switch.

open

When IB > 0 and VCE > 0, the transistor
acts as a ___________.

resistor

Two current gain measures are bdc and
__________.

bac

The symbol hfe is the same as _________.

bac

Concept Review
• The NPN schematic symbol shows the emitter
arrow as Not Pointing iN.
• The collector curves are a graph of collector
voltage versus collector current.
• Both dc beta (bdc) and ac beta (bac) can be
determined from the collector curves.
• The collector circuit of a transistor can be
modeled as a resistor, as a closed switch or as
an open switch.
• The amount of base current determines which
of the three models applies.
Repeat Segment

Concept Preview
• It is possible to test transistors out-of-circuit
using an ohmmeter.
• The E-B and C-B junctions act as diodes
during ohmmeter testing.

• The C-E test shows a high resistance because
two junctions are involved; one of which is
reverse biased by the ohmmeter.
• Gain can be verified by using a resistor in
conjunction with the ohmmeter test.

NPN

V

mA

E
B
C

The E-B junction is forward biased by the ohmmeter.

NPN

V

mA

E
B
C

The C-E resistance is very high.

NPN

V

mA

E
B
C
100 kW

The meter reading is < 100 kW due to gain.

Concept Review
• It is possible to test transistors out-of-circuit
using an ohmmeter.
• The E-B and C-B junctions act as diodes
during ohmmeter testing.
• The C-E test shows a high resistance because
two junctions are involved; one of which is
reverse biased by the ohmmeter.
• Gain can be verified by using a resistor in
conjunction with the ohmmeter test.
Repeat Segment

Concept Preview
• Bipolar junction transistors (BJTs) are controlled by
base current.
• Junction field effect transistors (JFETs) are controlled
by gate voltage.

• JFETs operate in the depletion mode (as normally on
devices).
• Metal oxide semiconductor field effect transistors
(MOSFETs) usually operate in the enhancement mode
(as normally off devices).
• Insulated gate bipolar transistors (IGBTs) are modified
MOSFETs and have very low on-resistance.
• Unijunction transistors (UJTs) are not used as
amplifiers.

Current In

The BJT is
a current
amplifier.

Current
Amplifier

Current Out

Voltage In

The JFET is
a voltage
controlled
amplifier.

Voltage
Amplifier

Current Out

Source

Gate

Drain

P

N-channel
P-type substrate
Structure of an
N-channel JFET

The channel has carriers so it
conducts from source to drain.

Drain

Gate
Source

Source

Gate

Drain

P

N-channel
P-type substrate

A negative gate voltage
can push the carriers from
the channel and turn
the JFET off.

Drain

Gate
Source

0V
-1 V
-2 V

ID in mA

-3 V

VGS

-4 V

0

-5 V
VDS in Volts

This is known as a depletion-mode device.
N-channel JFET drain family of characteristic curves

It’s possible to make enhancement
type field effect transistors as well.
Metal
oxide
insulator

Drain

n

Gate

VGG

D

VDD

p

G

n

S
N-channel
MOSFET

Source

Gate bias enhances the channel and turns the device on.

5V
4V
3V

ID in mA

2V

VGS

1V

0

0V
Drain

VDS in Volts

Enhancement mode
MOSFET drain family of
characteristic curves

Gate
Source

The IGBT (insulated gate bipolar transistor)
Operation and structure
similar to a MOSFET
Voltage controlled
(like the MOSFET)
Has one more junction
than a MOSFET
Hole injection reduces
the collector resistance

Faster turn off than
BJTs but not as fast
as MOSFETS

RCE = 8.33 mW

Three major device technologies

hole injection
Extra
junction

Courtesy of Powerex, Inc.

Typical IGBT Driver Circuit
Typically +15 V for turn on
Typically - 5 to -15 V for turn off

Control signal

IGBT

Powerex IGBT Module Structure

Powerex high voltage IGBT package

Emitter voltage

The unijunction transistor fires
when its emitter voltage reaches VP.
VP

Then, the emitter voltage
drops due to its negative
resistance characteristic.
Base 2

Emitter current
Emitter

The UJT is not useful as an amplifier.
It is used in timing and control applications.

Base 1

Other Transistor Types Quiz
BJTs are _________-controlled
amplifiers.

current

FETs are __________-controlled
amplifiers.

voltage

JFETs operate in the __________ mode. depletion
MOSFETs operate in the __________
mode.

enhancement

IGBTs are __________-controlled
amplifiers.

voltage

UJTs are not useful as __________.

amplifiers

Concept Review
• Bipolar junction transistors (BJTs) are controlled by
base current.
• Junction field effect transistors (JFETs) are controlled
by gate voltage.
• JFETs operate in the depletion mode (as normally on
devices).
• Metal oxide semiconductor field effect transistors
(MOSFETs) usually operate in the enhancement mode
(as normally off devices).
• Insulated gate bipolar transistors (IGBTs) are modified
MOSFETs and have very low on-resistance.
• Unijunction transistors (UJTs) are not used as
amplifiers.
Repeat Segment

Concept Preview
• BJTs can be used as switches.
• No base current = switch is off.
• High base current = switch is on.
• The dissipation is always zero in an ideal
switch: off = no current flow and on = no
voltage drop.

• MOSFETs can also be used as switches: no
gate voltage = switch is off and high gate
voltage = switch is on.

How do transistor switches work?
Can be viewed as solid state relays:
they are either ON or they are OFF.
BJT switches are characterized by:
high base current (switch is on)
(or no base current … off)

low resistance from collector to emitter (on)
(or very high resistance … off)
low collector dissipation (on or off)
PC = VCE x IC
PC = 0 x IC = 0 W
(on)
(or PC = VCE x 0 = 0 W … off)

NPN SWITCH
LOAD

RCE @ 
W
0W
DRIVER

The
The
driver
driver
output
output
isiszero
positive,
volts,
IIBB>=I0
0and
andthe
theload
loadis
ison
off
The
driver
output
is
zero
volts,
B = 0 and ILOAD = 0

PNP SWITCH
DRIVER

LOAD

The
Z):
Thedriver
driveroutput
outputisgoes
isoff
off(high
(highthe
Z):the
theresistor
resistor
low:
voltage
drop
pulls
the
base
voltage
up
that
VV
pulls
thethe
base
voltage
upso
soV
that
across
resistor
makes
BE
BE==00
BE negative

PNP SWITCH WITH NPN DRIVER

LOAD

NPN SWITCH WITH PNP DRIVER
(NEGATIVE POWER SUPPLY)

VV
0VV
BE
BE@ @+0.7

VVBE
0 VV
BE@@-0.7

LOAD

STEPPER MOTOR

A

B

C

A

Enhancement mode
power MOSFETs
used as switches

B

C
D

D

Concept Review
• BJTs can be used as switches.
• No base current = switch is off.
• High base current = switch is on.
• The dissipation is always zero in an ideal
switch: off = no current flow and on = no
voltage drop.
• MOSFETs can also be used as switches: no
gate voltage = switch is off and high gate
voltage = switch is on.
Repeat Segment

REVIEW
• Amplification
• Transistors
• Characteristic Curves
• Transistor Testing
• Other Transistor Types
• Transistors as Switches


Slide 14

Electronics
Principles & Applications
Sixth Edition

Charles A. Schuler
Chapter 5

Transistors
(student version)
©2003

Glencoe/McGraw-Hill

INTRODUCTION
• Amplification
• Transistors
• Characteristic Curves
• Transistor Testing
• Other Transistor Types
• Transistors as Switches

Dear Student:
This presentation is arranged in segments.
Each segment is preceded by a Concept
Preview slide and is followed by a Concept
Review slide. When you reach a Concept
Review slide, you can return to the
beginning of that segment by clicking on the
Repeat Segment button. This will allow you
to view that segment again, if you want to.

Concept Preview
• Amplifiers provide gain (the output is larger
than the input).
• Transistors have gain.
• Transistors have a collector, a base, and an
emitter.
• The C-B junction is reverse biased.
• The B-E junction is forward biased.
• Most of the emitter carriers reach the collector.
• The base current is relatively small but controls
the larger currents.

In

Gain =

Amplifier

Out

In

Out

NPN Transistor Structure

The collector is lightly doped.

N

C

The base is thin and
is lightly doped.

P

B

The emitter is heavily doped.

N

E

NPN Transistor Bias
No current flows.
The C-B junction
is reverse biased.

N

C

P

B

N

E

NPN Transistor Bias

The B-E junction
is forward biased.

Current flows.

N

C

P

B

N

E

NPN Transistor Bias
IC
Current flows
everywhere.
Most of the emitter carriers
diffuse through the thin base
When
both
junctions
region since they are attracted
biased....
by are
the collector.

Note that IB is smaller
than IE or IC.

N

C

P

B

N

E

IB

IE

Note: when the
switch opens, all
currents go to zero.
Although IB is smaller
it controls IE and IC.

Gain is something small
controlling something large
(IB is small).

IC
N

C

P

B

N

E

IB

IE

Transistor Structure and Bias Quiz
The heaviest doping is found in
the ___________ region.

emitter

The thinnest of all three regions
is called the ____________.

base

The collector-base junction is
___________ biased.

reverse

The base-emitter junction is
____________ biased.

forward

The majority of the emitter
carriers flow to the ___________.

collector

Concept Review
• Amplifiers provide gain (the output is larger than
the input).
• Transistors have gain.

• Transistors have a collector, a base, and an emitter.
• The C-B junction is reverse biased.
• The B-E junction is forward biased.

• Most of the emitter carriers reach the collector.
• The base current is relatively small but controls the
larger currents.
Repeat Segment

Concept Preview
• The base to collector gain is called b (beta).
• To find b, divide the collector current by the
base current.
• The emitter current is the largest since it is the
sum of the base and collector currents.
• PNP transistors have opposite polarity from
NPN transistors.

• In an NPN transistor, the major flow is made
up of electrons.
• In a PNP transistor, the major flow is made up
of holes.

IC = 99 mA

The current gain from
base to collector
is called b.
IB = 1 mA

b =

99
ICmA
1IBmA

= 99

IE = 100 mA

C
P

B

N

E

IC = 99 mA
Kirchhoff’s
current law:

IB = 1 mA

C
P

B

N

E

IE = I B + I C

= 1 mA + 99 mA
= 100 mA
IE = 100 mA

IC = 99 mA
In a PNP transistor,
holes flow from
emitter to collector.

IB = 1 mA
Notice the PNP
bias voltages.

C
B

E

IE = 100 mA

Transistor Currents Quiz
b is the ratio of collector current to
______ current.

base

The sum of the base and collector
currents is the __________ current.

emitter

In NPN transistors, the flow from emitter
to collector is composed of _______.

electrons

In PNP transistors, the flow from emitter
to collector is composed of _______.

holes

Both NPN and PNP transistors show
__________ gain.

current

Concept Review
• The base to collector gain is called b (beta).
• To find b, divide the collector current by the
base current.
• The emitter current is the largest since it is the
sum of the base and collector currents.
• PNP transistors have opposite polarity from
NPN transistors.
• In an NPN transistor, the major flow is made
up of electrons.
• In a PNP transistor, the major flow is made up
of holes.
Repeat Segment

Concept Preview
• The NPN schematic symbol shows the emitter
arrow as Not Pointing iN.
• The collector curves are a graph of collector
voltage versus collector current.
• Both dc beta (bdc) and ac beta (bac) can be
determined from the collector curves.
• The collector circuit of a transistor can be
modeled as a resistor, as a closed switch or as
an open switch.
• The amount of base current determines which
of the three models applies.

NPN Schematic Symbol
Collector

Base

C
B E

Emitter
Memory aid: NPN
means Not Pointing iN.

PNP Schematic Symbol
Collector

Base

C
B E

Emitter

IC

This circuit is used to
collect IC versus
VCE data for
several values of IB.
C

IB
B

E

VCE

When graphed, the data provide an
NPN collector family of curves.
100 mA

14
12
10
IC in mA 8
6
4
2

80 mA
60 mA
40 mA
20 mA

0 2 4 6

8 10 12 14 16 18

VCE in Volts

0 mA

100 mA

14
12
10
IC in mA 8
6
4
2

80 mA
60 mA

40 mA
20 mA

0 2 4 6

8 10 12 14 16 18

0 mA

VCE in Volts

b =

14
mA
6ICmA
40
IB mA
100
mA

150
== 140

This type of gain
is called bdc or hFE.

100 mA

14
12
10
IC in mA 8
6
4
2

80 mA
60 mA

40 mA
20 mA

0 2 4 6

bac =

2.5DImA
C
20DImA
B

8 10 12 14 16 18

0 mA

VCE in Volts
= 125

Another type of gain
is called bac or hfe.

100 mA

14
12
10
IC in mA 8
6
4
2

80 mA
60 mA

40 mA
20 mA

0 2 4 6
IB

C

8 10 12 14 16 18
VCE in Volts

0 mA

With these values of IB:
The C-E model is a resistor.
E

100 mA

14
12
10
IC in mA 8
6
4
2
0 2 4 6
IB

80 mA
60 mA

40 mA
20 mA
8 10 12 14 16 18
VCE in Volts

0 mA

When IB >> 100 mA
VCE @ 0
The model is a closed switch.

100 mA

14
12
10
IC in mA 8
6
4
2
0 2 4 6
IB

80 mA
60 mA

40 mA
20 mA
8 10 12 14 16 18
VCE in Volts

0 mA

When IB = 0
IC = 0
The model is an open switch.

Transistor Operating Conditions Quiz
When IB is large and VCE @ 0, the transistor
acts as a ___________ switch.
closed
When IB = 0 and IC = 0, the transistor
acts as an ___________ switch.

open

When IB > 0 and VCE > 0, the transistor
acts as a ___________.

resistor

Two current gain measures are bdc and
__________.

bac

The symbol hfe is the same as _________.

bac

Concept Review
• The NPN schematic symbol shows the emitter
arrow as Not Pointing iN.
• The collector curves are a graph of collector
voltage versus collector current.
• Both dc beta (bdc) and ac beta (bac) can be
determined from the collector curves.
• The collector circuit of a transistor can be
modeled as a resistor, as a closed switch or as
an open switch.
• The amount of base current determines which
of the three models applies.
Repeat Segment

Concept Preview
• It is possible to test transistors out-of-circuit
using an ohmmeter.
• The E-B and C-B junctions act as diodes
during ohmmeter testing.

• The C-E test shows a high resistance because
two junctions are involved; one of which is
reverse biased by the ohmmeter.
• Gain can be verified by using a resistor in
conjunction with the ohmmeter test.

NPN

V

mA

E
B
C

The E-B junction is forward biased by the ohmmeter.

NPN

V

mA

E
B
C

The C-E resistance is very high.

NPN

V

mA

E
B
C
100 kW

The meter reading is < 100 kW due to gain.

Concept Review
• It is possible to test transistors out-of-circuit
using an ohmmeter.
• The E-B and C-B junctions act as diodes
during ohmmeter testing.
• The C-E test shows a high resistance because
two junctions are involved; one of which is
reverse biased by the ohmmeter.
• Gain can be verified by using a resistor in
conjunction with the ohmmeter test.
Repeat Segment

Concept Preview
• Bipolar junction transistors (BJTs) are controlled by
base current.
• Junction field effect transistors (JFETs) are controlled
by gate voltage.

• JFETs operate in the depletion mode (as normally on
devices).
• Metal oxide semiconductor field effect transistors
(MOSFETs) usually operate in the enhancement mode
(as normally off devices).
• Insulated gate bipolar transistors (IGBTs) are modified
MOSFETs and have very low on-resistance.
• Unijunction transistors (UJTs) are not used as
amplifiers.

Current In

The BJT is
a current
amplifier.

Current
Amplifier

Current Out

Voltage In

The JFET is
a voltage
controlled
amplifier.

Voltage
Amplifier

Current Out

Source

Gate

Drain

P

N-channel
P-type substrate
Structure of an
N-channel JFET

The channel has carriers so it
conducts from source to drain.

Drain

Gate
Source

Source

Gate

Drain

P

N-channel
P-type substrate

A negative gate voltage
can push the carriers from
the channel and turn
the JFET off.

Drain

Gate
Source

0V
-1 V
-2 V

ID in mA

-3 V

VGS

-4 V

0

-5 V
VDS in Volts

This is known as a depletion-mode device.
N-channel JFET drain family of characteristic curves

It’s possible to make enhancement
type field effect transistors as well.
Metal
oxide
insulator

Drain

n

Gate

VGG

D

VDD

p

G

n

S
N-channel
MOSFET

Source

Gate bias enhances the channel and turns the device on.

5V
4V
3V

ID in mA

2V

VGS

1V

0

0V
Drain

VDS in Volts

Enhancement mode
MOSFET drain family of
characteristic curves

Gate
Source

The IGBT (insulated gate bipolar transistor)
Operation and structure
similar to a MOSFET
Voltage controlled
(like the MOSFET)
Has one more junction
than a MOSFET
Hole injection reduces
the collector resistance

Faster turn off than
BJTs but not as fast
as MOSFETS

RCE = 8.33 mW

Three major device technologies

hole injection
Extra
junction

Courtesy of Powerex, Inc.

Typical IGBT Driver Circuit
Typically +15 V for turn on
Typically - 5 to -15 V for turn off

Control signal

IGBT

Powerex IGBT Module Structure

Powerex high voltage IGBT package

Emitter voltage

The unijunction transistor fires
when its emitter voltage reaches VP.
VP

Then, the emitter voltage
drops due to its negative
resistance characteristic.
Base 2

Emitter current
Emitter

The UJT is not useful as an amplifier.
It is used in timing and control applications.

Base 1

Other Transistor Types Quiz
BJTs are _________-controlled
amplifiers.

current

FETs are __________-controlled
amplifiers.

voltage

JFETs operate in the __________ mode. depletion
MOSFETs operate in the __________
mode.

enhancement

IGBTs are __________-controlled
amplifiers.

voltage

UJTs are not useful as __________.

amplifiers

Concept Review
• Bipolar junction transistors (BJTs) are controlled by
base current.
• Junction field effect transistors (JFETs) are controlled
by gate voltage.
• JFETs operate in the depletion mode (as normally on
devices).
• Metal oxide semiconductor field effect transistors
(MOSFETs) usually operate in the enhancement mode
(as normally off devices).
• Insulated gate bipolar transistors (IGBTs) are modified
MOSFETs and have very low on-resistance.
• Unijunction transistors (UJTs) are not used as
amplifiers.
Repeat Segment

Concept Preview
• BJTs can be used as switches.
• No base current = switch is off.
• High base current = switch is on.
• The dissipation is always zero in an ideal
switch: off = no current flow and on = no
voltage drop.

• MOSFETs can also be used as switches: no
gate voltage = switch is off and high gate
voltage = switch is on.

How do transistor switches work?
Can be viewed as solid state relays:
they are either ON or they are OFF.
BJT switches are characterized by:
high base current (switch is on)
(or no base current … off)

low resistance from collector to emitter (on)
(or very high resistance … off)
low collector dissipation (on or off)
PC = VCE x IC
PC = 0 x IC = 0 W
(on)
(or PC = VCE x 0 = 0 W … off)

NPN SWITCH
LOAD

RCE @ 
W
0W
DRIVER

The
The
driver
driver
output
output
isiszero
positive,
volts,
IIBB>=I0
0and
andthe
theload
loadis
ison
off
The
driver
output
is
zero
volts,
B = 0 and ILOAD = 0

PNP SWITCH
DRIVER

LOAD

The
Z):
Thedriver
driveroutput
outputisgoes
isoff
off(high
(highthe
Z):the
theresistor
resistor
low:
voltage
drop
pulls
the
base
voltage
up
that
VV
pulls
thethe
base
voltage
upso
soV
that
across
resistor
makes
BE
BE==00
BE negative

PNP SWITCH WITH NPN DRIVER

LOAD

NPN SWITCH WITH PNP DRIVER
(NEGATIVE POWER SUPPLY)

VV
0VV
BE
BE@ @+0.7

VVBE
0 VV
BE@@-0.7

LOAD

STEPPER MOTOR

A

B

C

A

Enhancement mode
power MOSFETs
used as switches

B

C
D

D

Concept Review
• BJTs can be used as switches.
• No base current = switch is off.
• High base current = switch is on.
• The dissipation is always zero in an ideal
switch: off = no current flow and on = no
voltage drop.
• MOSFETs can also be used as switches: no
gate voltage = switch is off and high gate
voltage = switch is on.
Repeat Segment

REVIEW
• Amplification
• Transistors
• Characteristic Curves
• Transistor Testing
• Other Transistor Types
• Transistors as Switches


Slide 15

Electronics
Principles & Applications
Sixth Edition

Charles A. Schuler
Chapter 5

Transistors
(student version)
©2003

Glencoe/McGraw-Hill

INTRODUCTION
• Amplification
• Transistors
• Characteristic Curves
• Transistor Testing
• Other Transistor Types
• Transistors as Switches

Dear Student:
This presentation is arranged in segments.
Each segment is preceded by a Concept
Preview slide and is followed by a Concept
Review slide. When you reach a Concept
Review slide, you can return to the
beginning of that segment by clicking on the
Repeat Segment button. This will allow you
to view that segment again, if you want to.

Concept Preview
• Amplifiers provide gain (the output is larger
than the input).
• Transistors have gain.
• Transistors have a collector, a base, and an
emitter.
• The C-B junction is reverse biased.
• The B-E junction is forward biased.
• Most of the emitter carriers reach the collector.
• The base current is relatively small but controls
the larger currents.

In

Gain =

Amplifier

Out

In

Out

NPN Transistor Structure

The collector is lightly doped.

N

C

The base is thin and
is lightly doped.

P

B

The emitter is heavily doped.

N

E

NPN Transistor Bias
No current flows.
The C-B junction
is reverse biased.

N

C

P

B

N

E

NPN Transistor Bias

The B-E junction
is forward biased.

Current flows.

N

C

P

B

N

E

NPN Transistor Bias
IC
Current flows
everywhere.
Most of the emitter carriers
diffuse through the thin base
When
both
junctions
region since they are attracted
biased....
by are
the collector.

Note that IB is smaller
than IE or IC.

N

C

P

B

N

E

IB

IE

Note: when the
switch opens, all
currents go to zero.
Although IB is smaller
it controls IE and IC.

Gain is something small
controlling something large
(IB is small).

IC
N

C

P

B

N

E

IB

IE

Transistor Structure and Bias Quiz
The heaviest doping is found in
the ___________ region.

emitter

The thinnest of all three regions
is called the ____________.

base

The collector-base junction is
___________ biased.

reverse

The base-emitter junction is
____________ biased.

forward

The majority of the emitter
carriers flow to the ___________.

collector

Concept Review
• Amplifiers provide gain (the output is larger than
the input).
• Transistors have gain.

• Transistors have a collector, a base, and an emitter.
• The C-B junction is reverse biased.
• The B-E junction is forward biased.

• Most of the emitter carriers reach the collector.
• The base current is relatively small but controls the
larger currents.
Repeat Segment

Concept Preview
• The base to collector gain is called b (beta).
• To find b, divide the collector current by the
base current.
• The emitter current is the largest since it is the
sum of the base and collector currents.
• PNP transistors have opposite polarity from
NPN transistors.

• In an NPN transistor, the major flow is made
up of electrons.
• In a PNP transistor, the major flow is made up
of holes.

IC = 99 mA

The current gain from
base to collector
is called b.
IB = 1 mA

b =

99
ICmA
1IBmA

= 99

IE = 100 mA

C
P

B

N

E

IC = 99 mA
Kirchhoff’s
current law:

IB = 1 mA

C
P

B

N

E

IE = I B + I C

= 1 mA + 99 mA
= 100 mA
IE = 100 mA

IC = 99 mA
In a PNP transistor,
holes flow from
emitter to collector.

IB = 1 mA
Notice the PNP
bias voltages.

C
B

E

IE = 100 mA

Transistor Currents Quiz
b is the ratio of collector current to
______ current.

base

The sum of the base and collector
currents is the __________ current.

emitter

In NPN transistors, the flow from emitter
to collector is composed of _______.

electrons

In PNP transistors, the flow from emitter
to collector is composed of _______.

holes

Both NPN and PNP transistors show
__________ gain.

current

Concept Review
• The base to collector gain is called b (beta).
• To find b, divide the collector current by the
base current.
• The emitter current is the largest since it is the
sum of the base and collector currents.
• PNP transistors have opposite polarity from
NPN transistors.
• In an NPN transistor, the major flow is made
up of electrons.
• In a PNP transistor, the major flow is made up
of holes.
Repeat Segment

Concept Preview
• The NPN schematic symbol shows the emitter
arrow as Not Pointing iN.
• The collector curves are a graph of collector
voltage versus collector current.
• Both dc beta (bdc) and ac beta (bac) can be
determined from the collector curves.
• The collector circuit of a transistor can be
modeled as a resistor, as a closed switch or as
an open switch.
• The amount of base current determines which
of the three models applies.

NPN Schematic Symbol
Collector

Base

C
B E

Emitter
Memory aid: NPN
means Not Pointing iN.

PNP Schematic Symbol
Collector

Base

C
B E

Emitter

IC

This circuit is used to
collect IC versus
VCE data for
several values of IB.
C

IB
B

E

VCE

When graphed, the data provide an
NPN collector family of curves.
100 mA

14
12
10
IC in mA 8
6
4
2

80 mA
60 mA
40 mA
20 mA

0 2 4 6

8 10 12 14 16 18

VCE in Volts

0 mA

100 mA

14
12
10
IC in mA 8
6
4
2

80 mA
60 mA

40 mA
20 mA

0 2 4 6

8 10 12 14 16 18

0 mA

VCE in Volts

b =

14
mA
6ICmA
40
IB mA
100
mA

150
== 140

This type of gain
is called bdc or hFE.

100 mA

14
12
10
IC in mA 8
6
4
2

80 mA
60 mA

40 mA
20 mA

0 2 4 6

bac =

2.5DImA
C
20DImA
B

8 10 12 14 16 18

0 mA

VCE in Volts
= 125

Another type of gain
is called bac or hfe.

100 mA

14
12
10
IC in mA 8
6
4
2

80 mA
60 mA

40 mA
20 mA

0 2 4 6
IB

C

8 10 12 14 16 18
VCE in Volts

0 mA

With these values of IB:
The C-E model is a resistor.
E

100 mA

14
12
10
IC in mA 8
6
4
2
0 2 4 6
IB

80 mA
60 mA

40 mA
20 mA
8 10 12 14 16 18
VCE in Volts

0 mA

When IB >> 100 mA
VCE @ 0
The model is a closed switch.

100 mA

14
12
10
IC in mA 8
6
4
2
0 2 4 6
IB

80 mA
60 mA

40 mA
20 mA
8 10 12 14 16 18
VCE in Volts

0 mA

When IB = 0
IC = 0
The model is an open switch.

Transistor Operating Conditions Quiz
When IB is large and VCE @ 0, the transistor
acts as a ___________ switch.
closed
When IB = 0 and IC = 0, the transistor
acts as an ___________ switch.

open

When IB > 0 and VCE > 0, the transistor
acts as a ___________.

resistor

Two current gain measures are bdc and
__________.

bac

The symbol hfe is the same as _________.

bac

Concept Review
• The NPN schematic symbol shows the emitter
arrow as Not Pointing iN.
• The collector curves are a graph of collector
voltage versus collector current.
• Both dc beta (bdc) and ac beta (bac) can be
determined from the collector curves.
• The collector circuit of a transistor can be
modeled as a resistor, as a closed switch or as
an open switch.
• The amount of base current determines which
of the three models applies.
Repeat Segment

Concept Preview
• It is possible to test transistors out-of-circuit
using an ohmmeter.
• The E-B and C-B junctions act as diodes
during ohmmeter testing.

• The C-E test shows a high resistance because
two junctions are involved; one of which is
reverse biased by the ohmmeter.
• Gain can be verified by using a resistor in
conjunction with the ohmmeter test.

NPN

V

mA

E
B
C

The E-B junction is forward biased by the ohmmeter.

NPN

V

mA

E
B
C

The C-E resistance is very high.

NPN

V

mA

E
B
C
100 kW

The meter reading is < 100 kW due to gain.

Concept Review
• It is possible to test transistors out-of-circuit
using an ohmmeter.
• The E-B and C-B junctions act as diodes
during ohmmeter testing.
• The C-E test shows a high resistance because
two junctions are involved; one of which is
reverse biased by the ohmmeter.
• Gain can be verified by using a resistor in
conjunction with the ohmmeter test.
Repeat Segment

Concept Preview
• Bipolar junction transistors (BJTs) are controlled by
base current.
• Junction field effect transistors (JFETs) are controlled
by gate voltage.

• JFETs operate in the depletion mode (as normally on
devices).
• Metal oxide semiconductor field effect transistors
(MOSFETs) usually operate in the enhancement mode
(as normally off devices).
• Insulated gate bipolar transistors (IGBTs) are modified
MOSFETs and have very low on-resistance.
• Unijunction transistors (UJTs) are not used as
amplifiers.

Current In

The BJT is
a current
amplifier.

Current
Amplifier

Current Out

Voltage In

The JFET is
a voltage
controlled
amplifier.

Voltage
Amplifier

Current Out

Source

Gate

Drain

P

N-channel
P-type substrate
Structure of an
N-channel JFET

The channel has carriers so it
conducts from source to drain.

Drain

Gate
Source

Source

Gate

Drain

P

N-channel
P-type substrate

A negative gate voltage
can push the carriers from
the channel and turn
the JFET off.

Drain

Gate
Source

0V
-1 V
-2 V

ID in mA

-3 V

VGS

-4 V

0

-5 V
VDS in Volts

This is known as a depletion-mode device.
N-channel JFET drain family of characteristic curves

It’s possible to make enhancement
type field effect transistors as well.
Metal
oxide
insulator

Drain

n

Gate

VGG

D

VDD

p

G

n

S
N-channel
MOSFET

Source

Gate bias enhances the channel and turns the device on.

5V
4V
3V

ID in mA

2V

VGS

1V

0

0V
Drain

VDS in Volts

Enhancement mode
MOSFET drain family of
characteristic curves

Gate
Source

The IGBT (insulated gate bipolar transistor)
Operation and structure
similar to a MOSFET
Voltage controlled
(like the MOSFET)
Has one more junction
than a MOSFET
Hole injection reduces
the collector resistance

Faster turn off than
BJTs but not as fast
as MOSFETS

RCE = 8.33 mW

Three major device technologies

hole injection
Extra
junction

Courtesy of Powerex, Inc.

Typical IGBT Driver Circuit
Typically +15 V for turn on
Typically - 5 to -15 V for turn off

Control signal

IGBT

Powerex IGBT Module Structure

Powerex high voltage IGBT package

Emitter voltage

The unijunction transistor fires
when its emitter voltage reaches VP.
VP

Then, the emitter voltage
drops due to its negative
resistance characteristic.
Base 2

Emitter current
Emitter

The UJT is not useful as an amplifier.
It is used in timing and control applications.

Base 1

Other Transistor Types Quiz
BJTs are _________-controlled
amplifiers.

current

FETs are __________-controlled
amplifiers.

voltage

JFETs operate in the __________ mode. depletion
MOSFETs operate in the __________
mode.

enhancement

IGBTs are __________-controlled
amplifiers.

voltage

UJTs are not useful as __________.

amplifiers

Concept Review
• Bipolar junction transistors (BJTs) are controlled by
base current.
• Junction field effect transistors (JFETs) are controlled
by gate voltage.
• JFETs operate in the depletion mode (as normally on
devices).
• Metal oxide semiconductor field effect transistors
(MOSFETs) usually operate in the enhancement mode
(as normally off devices).
• Insulated gate bipolar transistors (IGBTs) are modified
MOSFETs and have very low on-resistance.
• Unijunction transistors (UJTs) are not used as
amplifiers.
Repeat Segment

Concept Preview
• BJTs can be used as switches.
• No base current = switch is off.
• High base current = switch is on.
• The dissipation is always zero in an ideal
switch: off = no current flow and on = no
voltage drop.

• MOSFETs can also be used as switches: no
gate voltage = switch is off and high gate
voltage = switch is on.

How do transistor switches work?
Can be viewed as solid state relays:
they are either ON or they are OFF.
BJT switches are characterized by:
high base current (switch is on)
(or no base current … off)

low resistance from collector to emitter (on)
(or very high resistance … off)
low collector dissipation (on or off)
PC = VCE x IC
PC = 0 x IC = 0 W
(on)
(or PC = VCE x 0 = 0 W … off)

NPN SWITCH
LOAD

RCE @ 
W
0W
DRIVER

The
The
driver
driver
output
output
isiszero
positive,
volts,
IIBB>=I0
0and
andthe
theload
loadis
ison
off
The
driver
output
is
zero
volts,
B = 0 and ILOAD = 0

PNP SWITCH
DRIVER

LOAD

The
Z):
Thedriver
driveroutput
outputisgoes
isoff
off(high
(highthe
Z):the
theresistor
resistor
low:
voltage
drop
pulls
the
base
voltage
up
that
VV
pulls
thethe
base
voltage
upso
soV
that
across
resistor
makes
BE
BE==00
BE negative

PNP SWITCH WITH NPN DRIVER

LOAD

NPN SWITCH WITH PNP DRIVER
(NEGATIVE POWER SUPPLY)

VV
0VV
BE
BE@ @+0.7

VVBE
0 VV
BE@@-0.7

LOAD

STEPPER MOTOR

A

B

C

A

Enhancement mode
power MOSFETs
used as switches

B

C
D

D

Concept Review
• BJTs can be used as switches.
• No base current = switch is off.
• High base current = switch is on.
• The dissipation is always zero in an ideal
switch: off = no current flow and on = no
voltage drop.
• MOSFETs can also be used as switches: no
gate voltage = switch is off and high gate
voltage = switch is on.
Repeat Segment

REVIEW
• Amplification
• Transistors
• Characteristic Curves
• Transistor Testing
• Other Transistor Types
• Transistors as Switches


Slide 16

Electronics
Principles & Applications
Sixth Edition

Charles A. Schuler
Chapter 5

Transistors
(student version)
©2003

Glencoe/McGraw-Hill

INTRODUCTION
• Amplification
• Transistors
• Characteristic Curves
• Transistor Testing
• Other Transistor Types
• Transistors as Switches

Dear Student:
This presentation is arranged in segments.
Each segment is preceded by a Concept
Preview slide and is followed by a Concept
Review slide. When you reach a Concept
Review slide, you can return to the
beginning of that segment by clicking on the
Repeat Segment button. This will allow you
to view that segment again, if you want to.

Concept Preview
• Amplifiers provide gain (the output is larger
than the input).
• Transistors have gain.
• Transistors have a collector, a base, and an
emitter.
• The C-B junction is reverse biased.
• The B-E junction is forward biased.
• Most of the emitter carriers reach the collector.
• The base current is relatively small but controls
the larger currents.

In

Gain =

Amplifier

Out

In

Out

NPN Transistor Structure

The collector is lightly doped.

N

C

The base is thin and
is lightly doped.

P

B

The emitter is heavily doped.

N

E

NPN Transistor Bias
No current flows.
The C-B junction
is reverse biased.

N

C

P

B

N

E

NPN Transistor Bias

The B-E junction
is forward biased.

Current flows.

N

C

P

B

N

E

NPN Transistor Bias
IC
Current flows
everywhere.
Most of the emitter carriers
diffuse through the thin base
When
both
junctions
region since they are attracted
biased....
by are
the collector.

Note that IB is smaller
than IE or IC.

N

C

P

B

N

E

IB

IE

Note: when the
switch opens, all
currents go to zero.
Although IB is smaller
it controls IE and IC.

Gain is something small
controlling something large
(IB is small).

IC
N

C

P

B

N

E

IB

IE

Transistor Structure and Bias Quiz
The heaviest doping is found in
the ___________ region.

emitter

The thinnest of all three regions
is called the ____________.

base

The collector-base junction is
___________ biased.

reverse

The base-emitter junction is
____________ biased.

forward

The majority of the emitter
carriers flow to the ___________.

collector

Concept Review
• Amplifiers provide gain (the output is larger than
the input).
• Transistors have gain.

• Transistors have a collector, a base, and an emitter.
• The C-B junction is reverse biased.
• The B-E junction is forward biased.

• Most of the emitter carriers reach the collector.
• The base current is relatively small but controls the
larger currents.
Repeat Segment

Concept Preview
• The base to collector gain is called b (beta).
• To find b, divide the collector current by the
base current.
• The emitter current is the largest since it is the
sum of the base and collector currents.
• PNP transistors have opposite polarity from
NPN transistors.

• In an NPN transistor, the major flow is made
up of electrons.
• In a PNP transistor, the major flow is made up
of holes.

IC = 99 mA

The current gain from
base to collector
is called b.
IB = 1 mA

b =

99
ICmA
1IBmA

= 99

IE = 100 mA

C
P

B

N

E

IC = 99 mA
Kirchhoff’s
current law:

IB = 1 mA

C
P

B

N

E

IE = I B + I C

= 1 mA + 99 mA
= 100 mA
IE = 100 mA

IC = 99 mA
In a PNP transistor,
holes flow from
emitter to collector.

IB = 1 mA
Notice the PNP
bias voltages.

C
B

E

IE = 100 mA

Transistor Currents Quiz
b is the ratio of collector current to
______ current.

base

The sum of the base and collector
currents is the __________ current.

emitter

In NPN transistors, the flow from emitter
to collector is composed of _______.

electrons

In PNP transistors, the flow from emitter
to collector is composed of _______.

holes

Both NPN and PNP transistors show
__________ gain.

current

Concept Review
• The base to collector gain is called b (beta).
• To find b, divide the collector current by the
base current.
• The emitter current is the largest since it is the
sum of the base and collector currents.
• PNP transistors have opposite polarity from
NPN transistors.
• In an NPN transistor, the major flow is made
up of electrons.
• In a PNP transistor, the major flow is made up
of holes.
Repeat Segment

Concept Preview
• The NPN schematic symbol shows the emitter
arrow as Not Pointing iN.
• The collector curves are a graph of collector
voltage versus collector current.
• Both dc beta (bdc) and ac beta (bac) can be
determined from the collector curves.
• The collector circuit of a transistor can be
modeled as a resistor, as a closed switch or as
an open switch.
• The amount of base current determines which
of the three models applies.

NPN Schematic Symbol
Collector

Base

C
B E

Emitter
Memory aid: NPN
means Not Pointing iN.

PNP Schematic Symbol
Collector

Base

C
B E

Emitter

IC

This circuit is used to
collect IC versus
VCE data for
several values of IB.
C

IB
B

E

VCE

When graphed, the data provide an
NPN collector family of curves.
100 mA

14
12
10
IC in mA 8
6
4
2

80 mA
60 mA
40 mA
20 mA

0 2 4 6

8 10 12 14 16 18

VCE in Volts

0 mA

100 mA

14
12
10
IC in mA 8
6
4
2

80 mA
60 mA

40 mA
20 mA

0 2 4 6

8 10 12 14 16 18

0 mA

VCE in Volts

b =

14
mA
6ICmA
40
IB mA
100
mA

150
== 140

This type of gain
is called bdc or hFE.

100 mA

14
12
10
IC in mA 8
6
4
2

80 mA
60 mA

40 mA
20 mA

0 2 4 6

bac =

2.5DImA
C
20DImA
B

8 10 12 14 16 18

0 mA

VCE in Volts
= 125

Another type of gain
is called bac or hfe.

100 mA

14
12
10
IC in mA 8
6
4
2

80 mA
60 mA

40 mA
20 mA

0 2 4 6
IB

C

8 10 12 14 16 18
VCE in Volts

0 mA

With these values of IB:
The C-E model is a resistor.
E

100 mA

14
12
10
IC in mA 8
6
4
2
0 2 4 6
IB

80 mA
60 mA

40 mA
20 mA
8 10 12 14 16 18
VCE in Volts

0 mA

When IB >> 100 mA
VCE @ 0
The model is a closed switch.

100 mA

14
12
10
IC in mA 8
6
4
2
0 2 4 6
IB

80 mA
60 mA

40 mA
20 mA
8 10 12 14 16 18
VCE in Volts

0 mA

When IB = 0
IC = 0
The model is an open switch.

Transistor Operating Conditions Quiz
When IB is large and VCE @ 0, the transistor
acts as a ___________ switch.
closed
When IB = 0 and IC = 0, the transistor
acts as an ___________ switch.

open

When IB > 0 and VCE > 0, the transistor
acts as a ___________.

resistor

Two current gain measures are bdc and
__________.

bac

The symbol hfe is the same as _________.

bac

Concept Review
• The NPN schematic symbol shows the emitter
arrow as Not Pointing iN.
• The collector curves are a graph of collector
voltage versus collector current.
• Both dc beta (bdc) and ac beta (bac) can be
determined from the collector curves.
• The collector circuit of a transistor can be
modeled as a resistor, as a closed switch or as
an open switch.
• The amount of base current determines which
of the three models applies.
Repeat Segment

Concept Preview
• It is possible to test transistors out-of-circuit
using an ohmmeter.
• The E-B and C-B junctions act as diodes
during ohmmeter testing.

• The C-E test shows a high resistance because
two junctions are involved; one of which is
reverse biased by the ohmmeter.
• Gain can be verified by using a resistor in
conjunction with the ohmmeter test.

NPN

V

mA

E
B
C

The E-B junction is forward biased by the ohmmeter.

NPN

V

mA

E
B
C

The C-E resistance is very high.

NPN

V

mA

E
B
C
100 kW

The meter reading is < 100 kW due to gain.

Concept Review
• It is possible to test transistors out-of-circuit
using an ohmmeter.
• The E-B and C-B junctions act as diodes
during ohmmeter testing.
• The C-E test shows a high resistance because
two junctions are involved; one of which is
reverse biased by the ohmmeter.
• Gain can be verified by using a resistor in
conjunction with the ohmmeter test.
Repeat Segment

Concept Preview
• Bipolar junction transistors (BJTs) are controlled by
base current.
• Junction field effect transistors (JFETs) are controlled
by gate voltage.

• JFETs operate in the depletion mode (as normally on
devices).
• Metal oxide semiconductor field effect transistors
(MOSFETs) usually operate in the enhancement mode
(as normally off devices).
• Insulated gate bipolar transistors (IGBTs) are modified
MOSFETs and have very low on-resistance.
• Unijunction transistors (UJTs) are not used as
amplifiers.

Current In

The BJT is
a current
amplifier.

Current
Amplifier

Current Out

Voltage In

The JFET is
a voltage
controlled
amplifier.

Voltage
Amplifier

Current Out

Source

Gate

Drain

P

N-channel
P-type substrate
Structure of an
N-channel JFET

The channel has carriers so it
conducts from source to drain.

Drain

Gate
Source

Source

Gate

Drain

P

N-channel
P-type substrate

A negative gate voltage
can push the carriers from
the channel and turn
the JFET off.

Drain

Gate
Source

0V
-1 V
-2 V

ID in mA

-3 V

VGS

-4 V

0

-5 V
VDS in Volts

This is known as a depletion-mode device.
N-channel JFET drain family of characteristic curves

It’s possible to make enhancement
type field effect transistors as well.
Metal
oxide
insulator

Drain

n

Gate

VGG

D

VDD

p

G

n

S
N-channel
MOSFET

Source

Gate bias enhances the channel and turns the device on.

5V
4V
3V

ID in mA

2V

VGS

1V

0

0V
Drain

VDS in Volts

Enhancement mode
MOSFET drain family of
characteristic curves

Gate
Source

The IGBT (insulated gate bipolar transistor)
Operation and structure
similar to a MOSFET
Voltage controlled
(like the MOSFET)
Has one more junction
than a MOSFET
Hole injection reduces
the collector resistance

Faster turn off than
BJTs but not as fast
as MOSFETS

RCE = 8.33 mW

Three major device technologies

hole injection
Extra
junction

Courtesy of Powerex, Inc.

Typical IGBT Driver Circuit
Typically +15 V for turn on
Typically - 5 to -15 V for turn off

Control signal

IGBT

Powerex IGBT Module Structure

Powerex high voltage IGBT package

Emitter voltage

The unijunction transistor fires
when its emitter voltage reaches VP.
VP

Then, the emitter voltage
drops due to its negative
resistance characteristic.
Base 2

Emitter current
Emitter

The UJT is not useful as an amplifier.
It is used in timing and control applications.

Base 1

Other Transistor Types Quiz
BJTs are _________-controlled
amplifiers.

current

FETs are __________-controlled
amplifiers.

voltage

JFETs operate in the __________ mode. depletion
MOSFETs operate in the __________
mode.

enhancement

IGBTs are __________-controlled
amplifiers.

voltage

UJTs are not useful as __________.

amplifiers

Concept Review
• Bipolar junction transistors (BJTs) are controlled by
base current.
• Junction field effect transistors (JFETs) are controlled
by gate voltage.
• JFETs operate in the depletion mode (as normally on
devices).
• Metal oxide semiconductor field effect transistors
(MOSFETs) usually operate in the enhancement mode
(as normally off devices).
• Insulated gate bipolar transistors (IGBTs) are modified
MOSFETs and have very low on-resistance.
• Unijunction transistors (UJTs) are not used as
amplifiers.
Repeat Segment

Concept Preview
• BJTs can be used as switches.
• No base current = switch is off.
• High base current = switch is on.
• The dissipation is always zero in an ideal
switch: off = no current flow and on = no
voltage drop.

• MOSFETs can also be used as switches: no
gate voltage = switch is off and high gate
voltage = switch is on.

How do transistor switches work?
Can be viewed as solid state relays:
they are either ON or they are OFF.
BJT switches are characterized by:
high base current (switch is on)
(or no base current … off)

low resistance from collector to emitter (on)
(or very high resistance … off)
low collector dissipation (on or off)
PC = VCE x IC
PC = 0 x IC = 0 W
(on)
(or PC = VCE x 0 = 0 W … off)

NPN SWITCH
LOAD

RCE @ 
W
0W
DRIVER

The
The
driver
driver
output
output
isiszero
positive,
volts,
IIBB>=I0
0and
andthe
theload
loadis
ison
off
The
driver
output
is
zero
volts,
B = 0 and ILOAD = 0

PNP SWITCH
DRIVER

LOAD

The
Z):
Thedriver
driveroutput
outputisgoes
isoff
off(high
(highthe
Z):the
theresistor
resistor
low:
voltage
drop
pulls
the
base
voltage
up
that
VV
pulls
thethe
base
voltage
upso
soV
that
across
resistor
makes
BE
BE==00
BE negative

PNP SWITCH WITH NPN DRIVER

LOAD

NPN SWITCH WITH PNP DRIVER
(NEGATIVE POWER SUPPLY)

VV
0VV
BE
BE@ @+0.7

VVBE
0 VV
BE@@-0.7

LOAD

STEPPER MOTOR

A

B

C

A

Enhancement mode
power MOSFETs
used as switches

B

C
D

D

Concept Review
• BJTs can be used as switches.
• No base current = switch is off.
• High base current = switch is on.
• The dissipation is always zero in an ideal
switch: off = no current flow and on = no
voltage drop.
• MOSFETs can also be used as switches: no
gate voltage = switch is off and high gate
voltage = switch is on.
Repeat Segment

REVIEW
• Amplification
• Transistors
• Characteristic Curves
• Transistor Testing
• Other Transistor Types
• Transistors as Switches


Slide 17

Electronics
Principles & Applications
Sixth Edition

Charles A. Schuler
Chapter 5

Transistors
(student version)
©2003

Glencoe/McGraw-Hill

INTRODUCTION
• Amplification
• Transistors
• Characteristic Curves
• Transistor Testing
• Other Transistor Types
• Transistors as Switches

Dear Student:
This presentation is arranged in segments.
Each segment is preceded by a Concept
Preview slide and is followed by a Concept
Review slide. When you reach a Concept
Review slide, you can return to the
beginning of that segment by clicking on the
Repeat Segment button. This will allow you
to view that segment again, if you want to.

Concept Preview
• Amplifiers provide gain (the output is larger
than the input).
• Transistors have gain.
• Transistors have a collector, a base, and an
emitter.
• The C-B junction is reverse biased.
• The B-E junction is forward biased.
• Most of the emitter carriers reach the collector.
• The base current is relatively small but controls
the larger currents.

In

Gain =

Amplifier

Out

In

Out

NPN Transistor Structure

The collector is lightly doped.

N

C

The base is thin and
is lightly doped.

P

B

The emitter is heavily doped.

N

E

NPN Transistor Bias
No current flows.
The C-B junction
is reverse biased.

N

C

P

B

N

E

NPN Transistor Bias

The B-E junction
is forward biased.

Current flows.

N

C

P

B

N

E

NPN Transistor Bias
IC
Current flows
everywhere.
Most of the emitter carriers
diffuse through the thin base
When
both
junctions
region since they are attracted
biased....
by are
the collector.

Note that IB is smaller
than IE or IC.

N

C

P

B

N

E

IB

IE

Note: when the
switch opens, all
currents go to zero.
Although IB is smaller
it controls IE and IC.

Gain is something small
controlling something large
(IB is small).

IC
N

C

P

B

N

E

IB

IE

Transistor Structure and Bias Quiz
The heaviest doping is found in
the ___________ region.

emitter

The thinnest of all three regions
is called the ____________.

base

The collector-base junction is
___________ biased.

reverse

The base-emitter junction is
____________ biased.

forward

The majority of the emitter
carriers flow to the ___________.

collector

Concept Review
• Amplifiers provide gain (the output is larger than
the input).
• Transistors have gain.

• Transistors have a collector, a base, and an emitter.
• The C-B junction is reverse biased.
• The B-E junction is forward biased.

• Most of the emitter carriers reach the collector.
• The base current is relatively small but controls the
larger currents.
Repeat Segment

Concept Preview
• The base to collector gain is called b (beta).
• To find b, divide the collector current by the
base current.
• The emitter current is the largest since it is the
sum of the base and collector currents.
• PNP transistors have opposite polarity from
NPN transistors.

• In an NPN transistor, the major flow is made
up of electrons.
• In a PNP transistor, the major flow is made up
of holes.

IC = 99 mA

The current gain from
base to collector
is called b.
IB = 1 mA

b =

99
ICmA
1IBmA

= 99

IE = 100 mA

C
P

B

N

E

IC = 99 mA
Kirchhoff’s
current law:

IB = 1 mA

C
P

B

N

E

IE = I B + I C

= 1 mA + 99 mA
= 100 mA
IE = 100 mA

IC = 99 mA
In a PNP transistor,
holes flow from
emitter to collector.

IB = 1 mA
Notice the PNP
bias voltages.

C
B

E

IE = 100 mA

Transistor Currents Quiz
b is the ratio of collector current to
______ current.

base

The sum of the base and collector
currents is the __________ current.

emitter

In NPN transistors, the flow from emitter
to collector is composed of _______.

electrons

In PNP transistors, the flow from emitter
to collector is composed of _______.

holes

Both NPN and PNP transistors show
__________ gain.

current

Concept Review
• The base to collector gain is called b (beta).
• To find b, divide the collector current by the
base current.
• The emitter current is the largest since it is the
sum of the base and collector currents.
• PNP transistors have opposite polarity from
NPN transistors.
• In an NPN transistor, the major flow is made
up of electrons.
• In a PNP transistor, the major flow is made up
of holes.
Repeat Segment

Concept Preview
• The NPN schematic symbol shows the emitter
arrow as Not Pointing iN.
• The collector curves are a graph of collector
voltage versus collector current.
• Both dc beta (bdc) and ac beta (bac) can be
determined from the collector curves.
• The collector circuit of a transistor can be
modeled as a resistor, as a closed switch or as
an open switch.
• The amount of base current determines which
of the three models applies.

NPN Schematic Symbol
Collector

Base

C
B E

Emitter
Memory aid: NPN
means Not Pointing iN.

PNP Schematic Symbol
Collector

Base

C
B E

Emitter

IC

This circuit is used to
collect IC versus
VCE data for
several values of IB.
C

IB
B

E

VCE

When graphed, the data provide an
NPN collector family of curves.
100 mA

14
12
10
IC in mA 8
6
4
2

80 mA
60 mA
40 mA
20 mA

0 2 4 6

8 10 12 14 16 18

VCE in Volts

0 mA

100 mA

14
12
10
IC in mA 8
6
4
2

80 mA
60 mA

40 mA
20 mA

0 2 4 6

8 10 12 14 16 18

0 mA

VCE in Volts

b =

14
mA
6ICmA
40
IB mA
100
mA

150
== 140

This type of gain
is called bdc or hFE.

100 mA

14
12
10
IC in mA 8
6
4
2

80 mA
60 mA

40 mA
20 mA

0 2 4 6

bac =

2.5DImA
C
20DImA
B

8 10 12 14 16 18

0 mA

VCE in Volts
= 125

Another type of gain
is called bac or hfe.

100 mA

14
12
10
IC in mA 8
6
4
2

80 mA
60 mA

40 mA
20 mA

0 2 4 6
IB

C

8 10 12 14 16 18
VCE in Volts

0 mA

With these values of IB:
The C-E model is a resistor.
E

100 mA

14
12
10
IC in mA 8
6
4
2
0 2 4 6
IB

80 mA
60 mA

40 mA
20 mA
8 10 12 14 16 18
VCE in Volts

0 mA

When IB >> 100 mA
VCE @ 0
The model is a closed switch.

100 mA

14
12
10
IC in mA 8
6
4
2
0 2 4 6
IB

80 mA
60 mA

40 mA
20 mA
8 10 12 14 16 18
VCE in Volts

0 mA

When IB = 0
IC = 0
The model is an open switch.

Transistor Operating Conditions Quiz
When IB is large and VCE @ 0, the transistor
acts as a ___________ switch.
closed
When IB = 0 and IC = 0, the transistor
acts as an ___________ switch.

open

When IB > 0 and VCE > 0, the transistor
acts as a ___________.

resistor

Two current gain measures are bdc and
__________.

bac

The symbol hfe is the same as _________.

bac

Concept Review
• The NPN schematic symbol shows the emitter
arrow as Not Pointing iN.
• The collector curves are a graph of collector
voltage versus collector current.
• Both dc beta (bdc) and ac beta (bac) can be
determined from the collector curves.
• The collector circuit of a transistor can be
modeled as a resistor, as a closed switch or as
an open switch.
• The amount of base current determines which
of the three models applies.
Repeat Segment

Concept Preview
• It is possible to test transistors out-of-circuit
using an ohmmeter.
• The E-B and C-B junctions act as diodes
during ohmmeter testing.

• The C-E test shows a high resistance because
two junctions are involved; one of which is
reverse biased by the ohmmeter.
• Gain can be verified by using a resistor in
conjunction with the ohmmeter test.

NPN

V

mA

E
B
C

The E-B junction is forward biased by the ohmmeter.

NPN

V

mA

E
B
C

The C-E resistance is very high.

NPN

V

mA

E
B
C
100 kW

The meter reading is < 100 kW due to gain.

Concept Review
• It is possible to test transistors out-of-circuit
using an ohmmeter.
• The E-B and C-B junctions act as diodes
during ohmmeter testing.
• The C-E test shows a high resistance because
two junctions are involved; one of which is
reverse biased by the ohmmeter.
• Gain can be verified by using a resistor in
conjunction with the ohmmeter test.
Repeat Segment

Concept Preview
• Bipolar junction transistors (BJTs) are controlled by
base current.
• Junction field effect transistors (JFETs) are controlled
by gate voltage.

• JFETs operate in the depletion mode (as normally on
devices).
• Metal oxide semiconductor field effect transistors
(MOSFETs) usually operate in the enhancement mode
(as normally off devices).
• Insulated gate bipolar transistors (IGBTs) are modified
MOSFETs and have very low on-resistance.
• Unijunction transistors (UJTs) are not used as
amplifiers.

Current In

The BJT is
a current
amplifier.

Current
Amplifier

Current Out

Voltage In

The JFET is
a voltage
controlled
amplifier.

Voltage
Amplifier

Current Out

Source

Gate

Drain

P

N-channel
P-type substrate
Structure of an
N-channel JFET

The channel has carriers so it
conducts from source to drain.

Drain

Gate
Source

Source

Gate

Drain

P

N-channel
P-type substrate

A negative gate voltage
can push the carriers from
the channel and turn
the JFET off.

Drain

Gate
Source

0V
-1 V
-2 V

ID in mA

-3 V

VGS

-4 V

0

-5 V
VDS in Volts

This is known as a depletion-mode device.
N-channel JFET drain family of characteristic curves

It’s possible to make enhancement
type field effect transistors as well.
Metal
oxide
insulator

Drain

n

Gate

VGG

D

VDD

p

G

n

S
N-channel
MOSFET

Source

Gate bias enhances the channel and turns the device on.

5V
4V
3V

ID in mA

2V

VGS

1V

0

0V
Drain

VDS in Volts

Enhancement mode
MOSFET drain family of
characteristic curves

Gate
Source

The IGBT (insulated gate bipolar transistor)
Operation and structure
similar to a MOSFET
Voltage controlled
(like the MOSFET)
Has one more junction
than a MOSFET
Hole injection reduces
the collector resistance

Faster turn off than
BJTs but not as fast
as MOSFETS

RCE = 8.33 mW

Three major device technologies

hole injection
Extra
junction

Courtesy of Powerex, Inc.

Typical IGBT Driver Circuit
Typically +15 V for turn on
Typically - 5 to -15 V for turn off

Control signal

IGBT

Powerex IGBT Module Structure

Powerex high voltage IGBT package

Emitter voltage

The unijunction transistor fires
when its emitter voltage reaches VP.
VP

Then, the emitter voltage
drops due to its negative
resistance characteristic.
Base 2

Emitter current
Emitter

The UJT is not useful as an amplifier.
It is used in timing and control applications.

Base 1

Other Transistor Types Quiz
BJTs are _________-controlled
amplifiers.

current

FETs are __________-controlled
amplifiers.

voltage

JFETs operate in the __________ mode. depletion
MOSFETs operate in the __________
mode.

enhancement

IGBTs are __________-controlled
amplifiers.

voltage

UJTs are not useful as __________.

amplifiers

Concept Review
• Bipolar junction transistors (BJTs) are controlled by
base current.
• Junction field effect transistors (JFETs) are controlled
by gate voltage.
• JFETs operate in the depletion mode (as normally on
devices).
• Metal oxide semiconductor field effect transistors
(MOSFETs) usually operate in the enhancement mode
(as normally off devices).
• Insulated gate bipolar transistors (IGBTs) are modified
MOSFETs and have very low on-resistance.
• Unijunction transistors (UJTs) are not used as
amplifiers.
Repeat Segment

Concept Preview
• BJTs can be used as switches.
• No base current = switch is off.
• High base current = switch is on.
• The dissipation is always zero in an ideal
switch: off = no current flow and on = no
voltage drop.

• MOSFETs can also be used as switches: no
gate voltage = switch is off and high gate
voltage = switch is on.

How do transistor switches work?
Can be viewed as solid state relays:
they are either ON or they are OFF.
BJT switches are characterized by:
high base current (switch is on)
(or no base current … off)

low resistance from collector to emitter (on)
(or very high resistance … off)
low collector dissipation (on or off)
PC = VCE x IC
PC = 0 x IC = 0 W
(on)
(or PC = VCE x 0 = 0 W … off)

NPN SWITCH
LOAD

RCE @ 
W
0W
DRIVER

The
The
driver
driver
output
output
isiszero
positive,
volts,
IIBB>=I0
0and
andthe
theload
loadis
ison
off
The
driver
output
is
zero
volts,
B = 0 and ILOAD = 0

PNP SWITCH
DRIVER

LOAD

The
Z):
Thedriver
driveroutput
outputisgoes
isoff
off(high
(highthe
Z):the
theresistor
resistor
low:
voltage
drop
pulls
the
base
voltage
up
that
VV
pulls
thethe
base
voltage
upso
soV
that
across
resistor
makes
BE
BE==00
BE negative

PNP SWITCH WITH NPN DRIVER

LOAD

NPN SWITCH WITH PNP DRIVER
(NEGATIVE POWER SUPPLY)

VV
0VV
BE
BE@ @+0.7

VVBE
0 VV
BE@@-0.7

LOAD

STEPPER MOTOR

A

B

C

A

Enhancement mode
power MOSFETs
used as switches

B

C
D

D

Concept Review
• BJTs can be used as switches.
• No base current = switch is off.
• High base current = switch is on.
• The dissipation is always zero in an ideal
switch: off = no current flow and on = no
voltage drop.
• MOSFETs can also be used as switches: no
gate voltage = switch is off and high gate
voltage = switch is on.
Repeat Segment

REVIEW
• Amplification
• Transistors
• Characteristic Curves
• Transistor Testing
• Other Transistor Types
• Transistors as Switches


Slide 18

Electronics
Principles & Applications
Sixth Edition

Charles A. Schuler
Chapter 5

Transistors
(student version)
©2003

Glencoe/McGraw-Hill

INTRODUCTION
• Amplification
• Transistors
• Characteristic Curves
• Transistor Testing
• Other Transistor Types
• Transistors as Switches

Dear Student:
This presentation is arranged in segments.
Each segment is preceded by a Concept
Preview slide and is followed by a Concept
Review slide. When you reach a Concept
Review slide, you can return to the
beginning of that segment by clicking on the
Repeat Segment button. This will allow you
to view that segment again, if you want to.

Concept Preview
• Amplifiers provide gain (the output is larger
than the input).
• Transistors have gain.
• Transistors have a collector, a base, and an
emitter.
• The C-B junction is reverse biased.
• The B-E junction is forward biased.
• Most of the emitter carriers reach the collector.
• The base current is relatively small but controls
the larger currents.

In

Gain =

Amplifier

Out

In

Out

NPN Transistor Structure

The collector is lightly doped.

N

C

The base is thin and
is lightly doped.

P

B

The emitter is heavily doped.

N

E

NPN Transistor Bias
No current flows.
The C-B junction
is reverse biased.

N

C

P

B

N

E

NPN Transistor Bias

The B-E junction
is forward biased.

Current flows.

N

C

P

B

N

E

NPN Transistor Bias
IC
Current flows
everywhere.
Most of the emitter carriers
diffuse through the thin base
When
both
junctions
region since they are attracted
biased....
by are
the collector.

Note that IB is smaller
than IE or IC.

N

C

P

B

N

E

IB

IE

Note: when the
switch opens, all
currents go to zero.
Although IB is smaller
it controls IE and IC.

Gain is something small
controlling something large
(IB is small).

IC
N

C

P

B

N

E

IB

IE

Transistor Structure and Bias Quiz
The heaviest doping is found in
the ___________ region.

emitter

The thinnest of all three regions
is called the ____________.

base

The collector-base junction is
___________ biased.

reverse

The base-emitter junction is
____________ biased.

forward

The majority of the emitter
carriers flow to the ___________.

collector

Concept Review
• Amplifiers provide gain (the output is larger than
the input).
• Transistors have gain.

• Transistors have a collector, a base, and an emitter.
• The C-B junction is reverse biased.
• The B-E junction is forward biased.

• Most of the emitter carriers reach the collector.
• The base current is relatively small but controls the
larger currents.
Repeat Segment

Concept Preview
• The base to collector gain is called b (beta).
• To find b, divide the collector current by the
base current.
• The emitter current is the largest since it is the
sum of the base and collector currents.
• PNP transistors have opposite polarity from
NPN transistors.

• In an NPN transistor, the major flow is made
up of electrons.
• In a PNP transistor, the major flow is made up
of holes.

IC = 99 mA

The current gain from
base to collector
is called b.
IB = 1 mA

b =

99
ICmA
1IBmA

= 99

IE = 100 mA

C
P

B

N

E

IC = 99 mA
Kirchhoff’s
current law:

IB = 1 mA

C
P

B

N

E

IE = I B + I C

= 1 mA + 99 mA
= 100 mA
IE = 100 mA

IC = 99 mA
In a PNP transistor,
holes flow from
emitter to collector.

IB = 1 mA
Notice the PNP
bias voltages.

C
B

E

IE = 100 mA

Transistor Currents Quiz
b is the ratio of collector current to
______ current.

base

The sum of the base and collector
currents is the __________ current.

emitter

In NPN transistors, the flow from emitter
to collector is composed of _______.

electrons

In PNP transistors, the flow from emitter
to collector is composed of _______.

holes

Both NPN and PNP transistors show
__________ gain.

current

Concept Review
• The base to collector gain is called b (beta).
• To find b, divide the collector current by the
base current.
• The emitter current is the largest since it is the
sum of the base and collector currents.
• PNP transistors have opposite polarity from
NPN transistors.
• In an NPN transistor, the major flow is made
up of electrons.
• In a PNP transistor, the major flow is made up
of holes.
Repeat Segment

Concept Preview
• The NPN schematic symbol shows the emitter
arrow as Not Pointing iN.
• The collector curves are a graph of collector
voltage versus collector current.
• Both dc beta (bdc) and ac beta (bac) can be
determined from the collector curves.
• The collector circuit of a transistor can be
modeled as a resistor, as a closed switch or as
an open switch.
• The amount of base current determines which
of the three models applies.

NPN Schematic Symbol
Collector

Base

C
B E

Emitter
Memory aid: NPN
means Not Pointing iN.

PNP Schematic Symbol
Collector

Base

C
B E

Emitter

IC

This circuit is used to
collect IC versus
VCE data for
several values of IB.
C

IB
B

E

VCE

When graphed, the data provide an
NPN collector family of curves.
100 mA

14
12
10
IC in mA 8
6
4
2

80 mA
60 mA
40 mA
20 mA

0 2 4 6

8 10 12 14 16 18

VCE in Volts

0 mA

100 mA

14
12
10
IC in mA 8
6
4
2

80 mA
60 mA

40 mA
20 mA

0 2 4 6

8 10 12 14 16 18

0 mA

VCE in Volts

b =

14
mA
6ICmA
40
IB mA
100
mA

150
== 140

This type of gain
is called bdc or hFE.

100 mA

14
12
10
IC in mA 8
6
4
2

80 mA
60 mA

40 mA
20 mA

0 2 4 6

bac =

2.5DImA
C
20DImA
B

8 10 12 14 16 18

0 mA

VCE in Volts
= 125

Another type of gain
is called bac or hfe.

100 mA

14
12
10
IC in mA 8
6
4
2

80 mA
60 mA

40 mA
20 mA

0 2 4 6
IB

C

8 10 12 14 16 18
VCE in Volts

0 mA

With these values of IB:
The C-E model is a resistor.
E

100 mA

14
12
10
IC in mA 8
6
4
2
0 2 4 6
IB

80 mA
60 mA

40 mA
20 mA
8 10 12 14 16 18
VCE in Volts

0 mA

When IB >> 100 mA
VCE @ 0
The model is a closed switch.

100 mA

14
12
10
IC in mA 8
6
4
2
0 2 4 6
IB

80 mA
60 mA

40 mA
20 mA
8 10 12 14 16 18
VCE in Volts

0 mA

When IB = 0
IC = 0
The model is an open switch.

Transistor Operating Conditions Quiz
When IB is large and VCE @ 0, the transistor
acts as a ___________ switch.
closed
When IB = 0 and IC = 0, the transistor
acts as an ___________ switch.

open

When IB > 0 and VCE > 0, the transistor
acts as a ___________.

resistor

Two current gain measures are bdc and
__________.

bac

The symbol hfe is the same as _________.

bac

Concept Review
• The NPN schematic symbol shows the emitter
arrow as Not Pointing iN.
• The collector curves are a graph of collector
voltage versus collector current.
• Both dc beta (bdc) and ac beta (bac) can be
determined from the collector curves.
• The collector circuit of a transistor can be
modeled as a resistor, as a closed switch or as
an open switch.
• The amount of base current determines which
of the three models applies.
Repeat Segment

Concept Preview
• It is possible to test transistors out-of-circuit
using an ohmmeter.
• The E-B and C-B junctions act as diodes
during ohmmeter testing.

• The C-E test shows a high resistance because
two junctions are involved; one of which is
reverse biased by the ohmmeter.
• Gain can be verified by using a resistor in
conjunction with the ohmmeter test.

NPN

V

mA

E
B
C

The E-B junction is forward biased by the ohmmeter.

NPN

V

mA

E
B
C

The C-E resistance is very high.

NPN

V

mA

E
B
C
100 kW

The meter reading is < 100 kW due to gain.

Concept Review
• It is possible to test transistors out-of-circuit
using an ohmmeter.
• The E-B and C-B junctions act as diodes
during ohmmeter testing.
• The C-E test shows a high resistance because
two junctions are involved; one of which is
reverse biased by the ohmmeter.
• Gain can be verified by using a resistor in
conjunction with the ohmmeter test.
Repeat Segment

Concept Preview
• Bipolar junction transistors (BJTs) are controlled by
base current.
• Junction field effect transistors (JFETs) are controlled
by gate voltage.

• JFETs operate in the depletion mode (as normally on
devices).
• Metal oxide semiconductor field effect transistors
(MOSFETs) usually operate in the enhancement mode
(as normally off devices).
• Insulated gate bipolar transistors (IGBTs) are modified
MOSFETs and have very low on-resistance.
• Unijunction transistors (UJTs) are not used as
amplifiers.

Current In

The BJT is
a current
amplifier.

Current
Amplifier

Current Out

Voltage In

The JFET is
a voltage
controlled
amplifier.

Voltage
Amplifier

Current Out

Source

Gate

Drain

P

N-channel
P-type substrate
Structure of an
N-channel JFET

The channel has carriers so it
conducts from source to drain.

Drain

Gate
Source

Source

Gate

Drain

P

N-channel
P-type substrate

A negative gate voltage
can push the carriers from
the channel and turn
the JFET off.

Drain

Gate
Source

0V
-1 V
-2 V

ID in mA

-3 V

VGS

-4 V

0

-5 V
VDS in Volts

This is known as a depletion-mode device.
N-channel JFET drain family of characteristic curves

It’s possible to make enhancement
type field effect transistors as well.
Metal
oxide
insulator

Drain

n

Gate

VGG

D

VDD

p

G

n

S
N-channel
MOSFET

Source

Gate bias enhances the channel and turns the device on.

5V
4V
3V

ID in mA

2V

VGS

1V

0

0V
Drain

VDS in Volts

Enhancement mode
MOSFET drain family of
characteristic curves

Gate
Source

The IGBT (insulated gate bipolar transistor)
Operation and structure
similar to a MOSFET
Voltage controlled
(like the MOSFET)
Has one more junction
than a MOSFET
Hole injection reduces
the collector resistance

Faster turn off than
BJTs but not as fast
as MOSFETS

RCE = 8.33 mW

Three major device technologies

hole injection
Extra
junction

Courtesy of Powerex, Inc.

Typical IGBT Driver Circuit
Typically +15 V for turn on
Typically - 5 to -15 V for turn off

Control signal

IGBT

Powerex IGBT Module Structure

Powerex high voltage IGBT package

Emitter voltage

The unijunction transistor fires
when its emitter voltage reaches VP.
VP

Then, the emitter voltage
drops due to its negative
resistance characteristic.
Base 2

Emitter current
Emitter

The UJT is not useful as an amplifier.
It is used in timing and control applications.

Base 1

Other Transistor Types Quiz
BJTs are _________-controlled
amplifiers.

current

FETs are __________-controlled
amplifiers.

voltage

JFETs operate in the __________ mode. depletion
MOSFETs operate in the __________
mode.

enhancement

IGBTs are __________-controlled
amplifiers.

voltage

UJTs are not useful as __________.

amplifiers

Concept Review
• Bipolar junction transistors (BJTs) are controlled by
base current.
• Junction field effect transistors (JFETs) are controlled
by gate voltage.
• JFETs operate in the depletion mode (as normally on
devices).
• Metal oxide semiconductor field effect transistors
(MOSFETs) usually operate in the enhancement mode
(as normally off devices).
• Insulated gate bipolar transistors (IGBTs) are modified
MOSFETs and have very low on-resistance.
• Unijunction transistors (UJTs) are not used as
amplifiers.
Repeat Segment

Concept Preview
• BJTs can be used as switches.
• No base current = switch is off.
• High base current = switch is on.
• The dissipation is always zero in an ideal
switch: off = no current flow and on = no
voltage drop.

• MOSFETs can also be used as switches: no
gate voltage = switch is off and high gate
voltage = switch is on.

How do transistor switches work?
Can be viewed as solid state relays:
they are either ON or they are OFF.
BJT switches are characterized by:
high base current (switch is on)
(or no base current … off)

low resistance from collector to emitter (on)
(or very high resistance … off)
low collector dissipation (on or off)
PC = VCE x IC
PC = 0 x IC = 0 W
(on)
(or PC = VCE x 0 = 0 W … off)

NPN SWITCH
LOAD

RCE @ 
W
0W
DRIVER

The
The
driver
driver
output
output
isiszero
positive,
volts,
IIBB>=I0
0and
andthe
theload
loadis
ison
off
The
driver
output
is
zero
volts,
B = 0 and ILOAD = 0

PNP SWITCH
DRIVER

LOAD

The
Z):
Thedriver
driveroutput
outputisgoes
isoff
off(high
(highthe
Z):the
theresistor
resistor
low:
voltage
drop
pulls
the
base
voltage
up
that
VV
pulls
thethe
base
voltage
upso
soV
that
across
resistor
makes
BE
BE==00
BE negative

PNP SWITCH WITH NPN DRIVER

LOAD

NPN SWITCH WITH PNP DRIVER
(NEGATIVE POWER SUPPLY)

VV
0VV
BE
BE@ @+0.7

VVBE
0 VV
BE@@-0.7

LOAD

STEPPER MOTOR

A

B

C

A

Enhancement mode
power MOSFETs
used as switches

B

C
D

D

Concept Review
• BJTs can be used as switches.
• No base current = switch is off.
• High base current = switch is on.
• The dissipation is always zero in an ideal
switch: off = no current flow and on = no
voltage drop.
• MOSFETs can also be used as switches: no
gate voltage = switch is off and high gate
voltage = switch is on.
Repeat Segment

REVIEW
• Amplification
• Transistors
• Characteristic Curves
• Transistor Testing
• Other Transistor Types
• Transistors as Switches


Slide 19

Electronics
Principles & Applications
Sixth Edition

Charles A. Schuler
Chapter 5

Transistors
(student version)
©2003

Glencoe/McGraw-Hill

INTRODUCTION
• Amplification
• Transistors
• Characteristic Curves
• Transistor Testing
• Other Transistor Types
• Transistors as Switches

Dear Student:
This presentation is arranged in segments.
Each segment is preceded by a Concept
Preview slide and is followed by a Concept
Review slide. When you reach a Concept
Review slide, you can return to the
beginning of that segment by clicking on the
Repeat Segment button. This will allow you
to view that segment again, if you want to.

Concept Preview
• Amplifiers provide gain (the output is larger
than the input).
• Transistors have gain.
• Transistors have a collector, a base, and an
emitter.
• The C-B junction is reverse biased.
• The B-E junction is forward biased.
• Most of the emitter carriers reach the collector.
• The base current is relatively small but controls
the larger currents.

In

Gain =

Amplifier

Out

In

Out

NPN Transistor Structure

The collector is lightly doped.

N

C

The base is thin and
is lightly doped.

P

B

The emitter is heavily doped.

N

E

NPN Transistor Bias
No current flows.
The C-B junction
is reverse biased.

N

C

P

B

N

E

NPN Transistor Bias

The B-E junction
is forward biased.

Current flows.

N

C

P

B

N

E

NPN Transistor Bias
IC
Current flows
everywhere.
Most of the emitter carriers
diffuse through the thin base
When
both
junctions
region since they are attracted
biased....
by are
the collector.

Note that IB is smaller
than IE or IC.

N

C

P

B

N

E

IB

IE

Note: when the
switch opens, all
currents go to zero.
Although IB is smaller
it controls IE and IC.

Gain is something small
controlling something large
(IB is small).

IC
N

C

P

B

N

E

IB

IE

Transistor Structure and Bias Quiz
The heaviest doping is found in
the ___________ region.

emitter

The thinnest of all three regions
is called the ____________.

base

The collector-base junction is
___________ biased.

reverse

The base-emitter junction is
____________ biased.

forward

The majority of the emitter
carriers flow to the ___________.

collector

Concept Review
• Amplifiers provide gain (the output is larger than
the input).
• Transistors have gain.

• Transistors have a collector, a base, and an emitter.
• The C-B junction is reverse biased.
• The B-E junction is forward biased.

• Most of the emitter carriers reach the collector.
• The base current is relatively small but controls the
larger currents.
Repeat Segment

Concept Preview
• The base to collector gain is called b (beta).
• To find b, divide the collector current by the
base current.
• The emitter current is the largest since it is the
sum of the base and collector currents.
• PNP transistors have opposite polarity from
NPN transistors.

• In an NPN transistor, the major flow is made
up of electrons.
• In a PNP transistor, the major flow is made up
of holes.

IC = 99 mA

The current gain from
base to collector
is called b.
IB = 1 mA

b =

99
ICmA
1IBmA

= 99

IE = 100 mA

C
P

B

N

E

IC = 99 mA
Kirchhoff’s
current law:

IB = 1 mA

C
P

B

N

E

IE = I B + I C

= 1 mA + 99 mA
= 100 mA
IE = 100 mA

IC = 99 mA
In a PNP transistor,
holes flow from
emitter to collector.

IB = 1 mA
Notice the PNP
bias voltages.

C
B

E

IE = 100 mA

Transistor Currents Quiz
b is the ratio of collector current to
______ current.

base

The sum of the base and collector
currents is the __________ current.

emitter

In NPN transistors, the flow from emitter
to collector is composed of _______.

electrons

In PNP transistors, the flow from emitter
to collector is composed of _______.

holes

Both NPN and PNP transistors show
__________ gain.

current

Concept Review
• The base to collector gain is called b (beta).
• To find b, divide the collector current by the
base current.
• The emitter current is the largest since it is the
sum of the base and collector currents.
• PNP transistors have opposite polarity from
NPN transistors.
• In an NPN transistor, the major flow is made
up of electrons.
• In a PNP transistor, the major flow is made up
of holes.
Repeat Segment

Concept Preview
• The NPN schematic symbol shows the emitter
arrow as Not Pointing iN.
• The collector curves are a graph of collector
voltage versus collector current.
• Both dc beta (bdc) and ac beta (bac) can be
determined from the collector curves.
• The collector circuit of a transistor can be
modeled as a resistor, as a closed switch or as
an open switch.
• The amount of base current determines which
of the three models applies.

NPN Schematic Symbol
Collector

Base

C
B E

Emitter
Memory aid: NPN
means Not Pointing iN.

PNP Schematic Symbol
Collector

Base

C
B E

Emitter

IC

This circuit is used to
collect IC versus
VCE data for
several values of IB.
C

IB
B

E

VCE

When graphed, the data provide an
NPN collector family of curves.
100 mA

14
12
10
IC in mA 8
6
4
2

80 mA
60 mA
40 mA
20 mA

0 2 4 6

8 10 12 14 16 18

VCE in Volts

0 mA

100 mA

14
12
10
IC in mA 8
6
4
2

80 mA
60 mA

40 mA
20 mA

0 2 4 6

8 10 12 14 16 18

0 mA

VCE in Volts

b =

14
mA
6ICmA
40
IB mA
100
mA

150
== 140

This type of gain
is called bdc or hFE.

100 mA

14
12
10
IC in mA 8
6
4
2

80 mA
60 mA

40 mA
20 mA

0 2 4 6

bac =

2.5DImA
C
20DImA
B

8 10 12 14 16 18

0 mA

VCE in Volts
= 125

Another type of gain
is called bac or hfe.

100 mA

14
12
10
IC in mA 8
6
4
2

80 mA
60 mA

40 mA
20 mA

0 2 4 6
IB

C

8 10 12 14 16 18
VCE in Volts

0 mA

With these values of IB:
The C-E model is a resistor.
E

100 mA

14
12
10
IC in mA 8
6
4
2
0 2 4 6
IB

80 mA
60 mA

40 mA
20 mA
8 10 12 14 16 18
VCE in Volts

0 mA

When IB >> 100 mA
VCE @ 0
The model is a closed switch.

100 mA

14
12
10
IC in mA 8
6
4
2
0 2 4 6
IB

80 mA
60 mA

40 mA
20 mA
8 10 12 14 16 18
VCE in Volts

0 mA

When IB = 0
IC = 0
The model is an open switch.

Transistor Operating Conditions Quiz
When IB is large and VCE @ 0, the transistor
acts as a ___________ switch.
closed
When IB = 0 and IC = 0, the transistor
acts as an ___________ switch.

open

When IB > 0 and VCE > 0, the transistor
acts as a ___________.

resistor

Two current gain measures are bdc and
__________.

bac

The symbol hfe is the same as _________.

bac

Concept Review
• The NPN schematic symbol shows the emitter
arrow as Not Pointing iN.
• The collector curves are a graph of collector
voltage versus collector current.
• Both dc beta (bdc) and ac beta (bac) can be
determined from the collector curves.
• The collector circuit of a transistor can be
modeled as a resistor, as a closed switch or as
an open switch.
• The amount of base current determines which
of the three models applies.
Repeat Segment

Concept Preview
• It is possible to test transistors out-of-circuit
using an ohmmeter.
• The E-B and C-B junctions act as diodes
during ohmmeter testing.

• The C-E test shows a high resistance because
two junctions are involved; one of which is
reverse biased by the ohmmeter.
• Gain can be verified by using a resistor in
conjunction with the ohmmeter test.

NPN

V

mA

E
B
C

The E-B junction is forward biased by the ohmmeter.

NPN

V

mA

E
B
C

The C-E resistance is very high.

NPN

V

mA

E
B
C
100 kW

The meter reading is < 100 kW due to gain.

Concept Review
• It is possible to test transistors out-of-circuit
using an ohmmeter.
• The E-B and C-B junctions act as diodes
during ohmmeter testing.
• The C-E test shows a high resistance because
two junctions are involved; one of which is
reverse biased by the ohmmeter.
• Gain can be verified by using a resistor in
conjunction with the ohmmeter test.
Repeat Segment

Concept Preview
• Bipolar junction transistors (BJTs) are controlled by
base current.
• Junction field effect transistors (JFETs) are controlled
by gate voltage.

• JFETs operate in the depletion mode (as normally on
devices).
• Metal oxide semiconductor field effect transistors
(MOSFETs) usually operate in the enhancement mode
(as normally off devices).
• Insulated gate bipolar transistors (IGBTs) are modified
MOSFETs and have very low on-resistance.
• Unijunction transistors (UJTs) are not used as
amplifiers.

Current In

The BJT is
a current
amplifier.

Current
Amplifier

Current Out

Voltage In

The JFET is
a voltage
controlled
amplifier.

Voltage
Amplifier

Current Out

Source

Gate

Drain

P

N-channel
P-type substrate
Structure of an
N-channel JFET

The channel has carriers so it
conducts from source to drain.

Drain

Gate
Source

Source

Gate

Drain

P

N-channel
P-type substrate

A negative gate voltage
can push the carriers from
the channel and turn
the JFET off.

Drain

Gate
Source

0V
-1 V
-2 V

ID in mA

-3 V

VGS

-4 V

0

-5 V
VDS in Volts

This is known as a depletion-mode device.
N-channel JFET drain family of characteristic curves

It’s possible to make enhancement
type field effect transistors as well.
Metal
oxide
insulator

Drain

n

Gate

VGG

D

VDD

p

G

n

S
N-channel
MOSFET

Source

Gate bias enhances the channel and turns the device on.

5V
4V
3V

ID in mA

2V

VGS

1V

0

0V
Drain

VDS in Volts

Enhancement mode
MOSFET drain family of
characteristic curves

Gate
Source

The IGBT (insulated gate bipolar transistor)
Operation and structure
similar to a MOSFET
Voltage controlled
(like the MOSFET)
Has one more junction
than a MOSFET
Hole injection reduces
the collector resistance

Faster turn off than
BJTs but not as fast
as MOSFETS

RCE = 8.33 mW

Three major device technologies

hole injection
Extra
junction

Courtesy of Powerex, Inc.

Typical IGBT Driver Circuit
Typically +15 V for turn on
Typically - 5 to -15 V for turn off

Control signal

IGBT

Powerex IGBT Module Structure

Powerex high voltage IGBT package

Emitter voltage

The unijunction transistor fires
when its emitter voltage reaches VP.
VP

Then, the emitter voltage
drops due to its negative
resistance characteristic.
Base 2

Emitter current
Emitter

The UJT is not useful as an amplifier.
It is used in timing and control applications.

Base 1

Other Transistor Types Quiz
BJTs are _________-controlled
amplifiers.

current

FETs are __________-controlled
amplifiers.

voltage

JFETs operate in the __________ mode. depletion
MOSFETs operate in the __________
mode.

enhancement

IGBTs are __________-controlled
amplifiers.

voltage

UJTs are not useful as __________.

amplifiers

Concept Review
• Bipolar junction transistors (BJTs) are controlled by
base current.
• Junction field effect transistors (JFETs) are controlled
by gate voltage.
• JFETs operate in the depletion mode (as normally on
devices).
• Metal oxide semiconductor field effect transistors
(MOSFETs) usually operate in the enhancement mode
(as normally off devices).
• Insulated gate bipolar transistors (IGBTs) are modified
MOSFETs and have very low on-resistance.
• Unijunction transistors (UJTs) are not used as
amplifiers.
Repeat Segment

Concept Preview
• BJTs can be used as switches.
• No base current = switch is off.
• High base current = switch is on.
• The dissipation is always zero in an ideal
switch: off = no current flow and on = no
voltage drop.

• MOSFETs can also be used as switches: no
gate voltage = switch is off and high gate
voltage = switch is on.

How do transistor switches work?
Can be viewed as solid state relays:
they are either ON or they are OFF.
BJT switches are characterized by:
high base current (switch is on)
(or no base current … off)

low resistance from collector to emitter (on)
(or very high resistance … off)
low collector dissipation (on or off)
PC = VCE x IC
PC = 0 x IC = 0 W
(on)
(or PC = VCE x 0 = 0 W … off)

NPN SWITCH
LOAD

RCE @ 
W
0W
DRIVER

The
The
driver
driver
output
output
isiszero
positive,
volts,
IIBB>=I0
0and
andthe
theload
loadis
ison
off
The
driver
output
is
zero
volts,
B = 0 and ILOAD = 0

PNP SWITCH
DRIVER

LOAD

The
Z):
Thedriver
driveroutput
outputisgoes
isoff
off(high
(highthe
Z):the
theresistor
resistor
low:
voltage
drop
pulls
the
base
voltage
up
that
VV
pulls
thethe
base
voltage
upso
soV
that
across
resistor
makes
BE
BE==00
BE negative

PNP SWITCH WITH NPN DRIVER

LOAD

NPN SWITCH WITH PNP DRIVER
(NEGATIVE POWER SUPPLY)

VV
0VV
BE
BE@ @+0.7

VVBE
0 VV
BE@@-0.7

LOAD

STEPPER MOTOR

A

B

C

A

Enhancement mode
power MOSFETs
used as switches

B

C
D

D

Concept Review
• BJTs can be used as switches.
• No base current = switch is off.
• High base current = switch is on.
• The dissipation is always zero in an ideal
switch: off = no current flow and on = no
voltage drop.
• MOSFETs can also be used as switches: no
gate voltage = switch is off and high gate
voltage = switch is on.
Repeat Segment

REVIEW
• Amplification
• Transistors
• Characteristic Curves
• Transistor Testing
• Other Transistor Types
• Transistors as Switches


Slide 20

Electronics
Principles & Applications
Sixth Edition

Charles A. Schuler
Chapter 5

Transistors
(student version)
©2003

Glencoe/McGraw-Hill

INTRODUCTION
• Amplification
• Transistors
• Characteristic Curves
• Transistor Testing
• Other Transistor Types
• Transistors as Switches

Dear Student:
This presentation is arranged in segments.
Each segment is preceded by a Concept
Preview slide and is followed by a Concept
Review slide. When you reach a Concept
Review slide, you can return to the
beginning of that segment by clicking on the
Repeat Segment button. This will allow you
to view that segment again, if you want to.

Concept Preview
• Amplifiers provide gain (the output is larger
than the input).
• Transistors have gain.
• Transistors have a collector, a base, and an
emitter.
• The C-B junction is reverse biased.
• The B-E junction is forward biased.
• Most of the emitter carriers reach the collector.
• The base current is relatively small but controls
the larger currents.

In

Gain =

Amplifier

Out

In

Out

NPN Transistor Structure

The collector is lightly doped.

N

C

The base is thin and
is lightly doped.

P

B

The emitter is heavily doped.

N

E

NPN Transistor Bias
No current flows.
The C-B junction
is reverse biased.

N

C

P

B

N

E

NPN Transistor Bias

The B-E junction
is forward biased.

Current flows.

N

C

P

B

N

E

NPN Transistor Bias
IC
Current flows
everywhere.
Most of the emitter carriers
diffuse through the thin base
When
both
junctions
region since they are attracted
biased....
by are
the collector.

Note that IB is smaller
than IE or IC.

N

C

P

B

N

E

IB

IE

Note: when the
switch opens, all
currents go to zero.
Although IB is smaller
it controls IE and IC.

Gain is something small
controlling something large
(IB is small).

IC
N

C

P

B

N

E

IB

IE

Transistor Structure and Bias Quiz
The heaviest doping is found in
the ___________ region.

emitter

The thinnest of all three regions
is called the ____________.

base

The collector-base junction is
___________ biased.

reverse

The base-emitter junction is
____________ biased.

forward

The majority of the emitter
carriers flow to the ___________.

collector

Concept Review
• Amplifiers provide gain (the output is larger than
the input).
• Transistors have gain.

• Transistors have a collector, a base, and an emitter.
• The C-B junction is reverse biased.
• The B-E junction is forward biased.

• Most of the emitter carriers reach the collector.
• The base current is relatively small but controls the
larger currents.
Repeat Segment

Concept Preview
• The base to collector gain is called b (beta).
• To find b, divide the collector current by the
base current.
• The emitter current is the largest since it is the
sum of the base and collector currents.
• PNP transistors have opposite polarity from
NPN transistors.

• In an NPN transistor, the major flow is made
up of electrons.
• In a PNP transistor, the major flow is made up
of holes.

IC = 99 mA

The current gain from
base to collector
is called b.
IB = 1 mA

b =

99
ICmA
1IBmA

= 99

IE = 100 mA

C
P

B

N

E

IC = 99 mA
Kirchhoff’s
current law:

IB = 1 mA

C
P

B

N

E

IE = I B + I C

= 1 mA + 99 mA
= 100 mA
IE = 100 mA

IC = 99 mA
In a PNP transistor,
holes flow from
emitter to collector.

IB = 1 mA
Notice the PNP
bias voltages.

C
B

E

IE = 100 mA

Transistor Currents Quiz
b is the ratio of collector current to
______ current.

base

The sum of the base and collector
currents is the __________ current.

emitter

In NPN transistors, the flow from emitter
to collector is composed of _______.

electrons

In PNP transistors, the flow from emitter
to collector is composed of _______.

holes

Both NPN and PNP transistors show
__________ gain.

current

Concept Review
• The base to collector gain is called b (beta).
• To find b, divide the collector current by the
base current.
• The emitter current is the largest since it is the
sum of the base and collector currents.
• PNP transistors have opposite polarity from
NPN transistors.
• In an NPN transistor, the major flow is made
up of electrons.
• In a PNP transistor, the major flow is made up
of holes.
Repeat Segment

Concept Preview
• The NPN schematic symbol shows the emitter
arrow as Not Pointing iN.
• The collector curves are a graph of collector
voltage versus collector current.
• Both dc beta (bdc) and ac beta (bac) can be
determined from the collector curves.
• The collector circuit of a transistor can be
modeled as a resistor, as a closed switch or as
an open switch.
• The amount of base current determines which
of the three models applies.

NPN Schematic Symbol
Collector

Base

C
B E

Emitter
Memory aid: NPN
means Not Pointing iN.

PNP Schematic Symbol
Collector

Base

C
B E

Emitter

IC

This circuit is used to
collect IC versus
VCE data for
several values of IB.
C

IB
B

E

VCE

When graphed, the data provide an
NPN collector family of curves.
100 mA

14
12
10
IC in mA 8
6
4
2

80 mA
60 mA
40 mA
20 mA

0 2 4 6

8 10 12 14 16 18

VCE in Volts

0 mA

100 mA

14
12
10
IC in mA 8
6
4
2

80 mA
60 mA

40 mA
20 mA

0 2 4 6

8 10 12 14 16 18

0 mA

VCE in Volts

b =

14
mA
6ICmA
40
IB mA
100
mA

150
== 140

This type of gain
is called bdc or hFE.

100 mA

14
12
10
IC in mA 8
6
4
2

80 mA
60 mA

40 mA
20 mA

0 2 4 6

bac =

2.5DImA
C
20DImA
B

8 10 12 14 16 18

0 mA

VCE in Volts
= 125

Another type of gain
is called bac or hfe.

100 mA

14
12
10
IC in mA 8
6
4
2

80 mA
60 mA

40 mA
20 mA

0 2 4 6
IB

C

8 10 12 14 16 18
VCE in Volts

0 mA

With these values of IB:
The C-E model is a resistor.
E

100 mA

14
12
10
IC in mA 8
6
4
2
0 2 4 6
IB

80 mA
60 mA

40 mA
20 mA
8 10 12 14 16 18
VCE in Volts

0 mA

When IB >> 100 mA
VCE @ 0
The model is a closed switch.

100 mA

14
12
10
IC in mA 8
6
4
2
0 2 4 6
IB

80 mA
60 mA

40 mA
20 mA
8 10 12 14 16 18
VCE in Volts

0 mA

When IB = 0
IC = 0
The model is an open switch.

Transistor Operating Conditions Quiz
When IB is large and VCE @ 0, the transistor
acts as a ___________ switch.
closed
When IB = 0 and IC = 0, the transistor
acts as an ___________ switch.

open

When IB > 0 and VCE > 0, the transistor
acts as a ___________.

resistor

Two current gain measures are bdc and
__________.

bac

The symbol hfe is the same as _________.

bac

Concept Review
• The NPN schematic symbol shows the emitter
arrow as Not Pointing iN.
• The collector curves are a graph of collector
voltage versus collector current.
• Both dc beta (bdc) and ac beta (bac) can be
determined from the collector curves.
• The collector circuit of a transistor can be
modeled as a resistor, as a closed switch or as
an open switch.
• The amount of base current determines which
of the three models applies.
Repeat Segment

Concept Preview
• It is possible to test transistors out-of-circuit
using an ohmmeter.
• The E-B and C-B junctions act as diodes
during ohmmeter testing.

• The C-E test shows a high resistance because
two junctions are involved; one of which is
reverse biased by the ohmmeter.
• Gain can be verified by using a resistor in
conjunction with the ohmmeter test.

NPN

V

mA

E
B
C

The E-B junction is forward biased by the ohmmeter.

NPN

V

mA

E
B
C

The C-E resistance is very high.

NPN

V

mA

E
B
C
100 kW

The meter reading is < 100 kW due to gain.

Concept Review
• It is possible to test transistors out-of-circuit
using an ohmmeter.
• The E-B and C-B junctions act as diodes
during ohmmeter testing.
• The C-E test shows a high resistance because
two junctions are involved; one of which is
reverse biased by the ohmmeter.
• Gain can be verified by using a resistor in
conjunction with the ohmmeter test.
Repeat Segment

Concept Preview
• Bipolar junction transistors (BJTs) are controlled by
base current.
• Junction field effect transistors (JFETs) are controlled
by gate voltage.

• JFETs operate in the depletion mode (as normally on
devices).
• Metal oxide semiconductor field effect transistors
(MOSFETs) usually operate in the enhancement mode
(as normally off devices).
• Insulated gate bipolar transistors (IGBTs) are modified
MOSFETs and have very low on-resistance.
• Unijunction transistors (UJTs) are not used as
amplifiers.

Current In

The BJT is
a current
amplifier.

Current
Amplifier

Current Out

Voltage In

The JFET is
a voltage
controlled
amplifier.

Voltage
Amplifier

Current Out

Source

Gate

Drain

P

N-channel
P-type substrate
Structure of an
N-channel JFET

The channel has carriers so it
conducts from source to drain.

Drain

Gate
Source

Source

Gate

Drain

P

N-channel
P-type substrate

A negative gate voltage
can push the carriers from
the channel and turn
the JFET off.

Drain

Gate
Source

0V
-1 V
-2 V

ID in mA

-3 V

VGS

-4 V

0

-5 V
VDS in Volts

This is known as a depletion-mode device.
N-channel JFET drain family of characteristic curves

It’s possible to make enhancement
type field effect transistors as well.
Metal
oxide
insulator

Drain

n

Gate

VGG

D

VDD

p

G

n

S
N-channel
MOSFET

Source

Gate bias enhances the channel and turns the device on.

5V
4V
3V

ID in mA

2V

VGS

1V

0

0V
Drain

VDS in Volts

Enhancement mode
MOSFET drain family of
characteristic curves

Gate
Source

The IGBT (insulated gate bipolar transistor)
Operation and structure
similar to a MOSFET
Voltage controlled
(like the MOSFET)
Has one more junction
than a MOSFET
Hole injection reduces
the collector resistance

Faster turn off than
BJTs but not as fast
as MOSFETS

RCE = 8.33 mW

Three major device technologies

hole injection
Extra
junction

Courtesy of Powerex, Inc.

Typical IGBT Driver Circuit
Typically +15 V for turn on
Typically - 5 to -15 V for turn off

Control signal

IGBT

Powerex IGBT Module Structure

Powerex high voltage IGBT package

Emitter voltage

The unijunction transistor fires
when its emitter voltage reaches VP.
VP

Then, the emitter voltage
drops due to its negative
resistance characteristic.
Base 2

Emitter current
Emitter

The UJT is not useful as an amplifier.
It is used in timing and control applications.

Base 1

Other Transistor Types Quiz
BJTs are _________-controlled
amplifiers.

current

FETs are __________-controlled
amplifiers.

voltage

JFETs operate in the __________ mode. depletion
MOSFETs operate in the __________
mode.

enhancement

IGBTs are __________-controlled
amplifiers.

voltage

UJTs are not useful as __________.

amplifiers

Concept Review
• Bipolar junction transistors (BJTs) are controlled by
base current.
• Junction field effect transistors (JFETs) are controlled
by gate voltage.
• JFETs operate in the depletion mode (as normally on
devices).
• Metal oxide semiconductor field effect transistors
(MOSFETs) usually operate in the enhancement mode
(as normally off devices).
• Insulated gate bipolar transistors (IGBTs) are modified
MOSFETs and have very low on-resistance.
• Unijunction transistors (UJTs) are not used as
amplifiers.
Repeat Segment

Concept Preview
• BJTs can be used as switches.
• No base current = switch is off.
• High base current = switch is on.
• The dissipation is always zero in an ideal
switch: off = no current flow and on = no
voltage drop.

• MOSFETs can also be used as switches: no
gate voltage = switch is off and high gate
voltage = switch is on.

How do transistor switches work?
Can be viewed as solid state relays:
they are either ON or they are OFF.
BJT switches are characterized by:
high base current (switch is on)
(or no base current … off)

low resistance from collector to emitter (on)
(or very high resistance … off)
low collector dissipation (on or off)
PC = VCE x IC
PC = 0 x IC = 0 W
(on)
(or PC = VCE x 0 = 0 W … off)

NPN SWITCH
LOAD

RCE @ 
W
0W
DRIVER

The
The
driver
driver
output
output
isiszero
positive,
volts,
IIBB>=I0
0and
andthe
theload
loadis
ison
off
The
driver
output
is
zero
volts,
B = 0 and ILOAD = 0

PNP SWITCH
DRIVER

LOAD

The
Z):
Thedriver
driveroutput
outputisgoes
isoff
off(high
(highthe
Z):the
theresistor
resistor
low:
voltage
drop
pulls
the
base
voltage
up
that
VV
pulls
thethe
base
voltage
upso
soV
that
across
resistor
makes
BE
BE==00
BE negative

PNP SWITCH WITH NPN DRIVER

LOAD

NPN SWITCH WITH PNP DRIVER
(NEGATIVE POWER SUPPLY)

VV
0VV
BE
BE@ @+0.7

VVBE
0 VV
BE@@-0.7

LOAD

STEPPER MOTOR

A

B

C

A

Enhancement mode
power MOSFETs
used as switches

B

C
D

D

Concept Review
• BJTs can be used as switches.
• No base current = switch is off.
• High base current = switch is on.
• The dissipation is always zero in an ideal
switch: off = no current flow and on = no
voltage drop.
• MOSFETs can also be used as switches: no
gate voltage = switch is off and high gate
voltage = switch is on.
Repeat Segment

REVIEW
• Amplification
• Transistors
• Characteristic Curves
• Transistor Testing
• Other Transistor Types
• Transistors as Switches


Slide 21

Electronics
Principles & Applications
Sixth Edition

Charles A. Schuler
Chapter 5

Transistors
(student version)
©2003

Glencoe/McGraw-Hill

INTRODUCTION
• Amplification
• Transistors
• Characteristic Curves
• Transistor Testing
• Other Transistor Types
• Transistors as Switches

Dear Student:
This presentation is arranged in segments.
Each segment is preceded by a Concept
Preview slide and is followed by a Concept
Review slide. When you reach a Concept
Review slide, you can return to the
beginning of that segment by clicking on the
Repeat Segment button. This will allow you
to view that segment again, if you want to.

Concept Preview
• Amplifiers provide gain (the output is larger
than the input).
• Transistors have gain.
• Transistors have a collector, a base, and an
emitter.
• The C-B junction is reverse biased.
• The B-E junction is forward biased.
• Most of the emitter carriers reach the collector.
• The base current is relatively small but controls
the larger currents.

In

Gain =

Amplifier

Out

In

Out

NPN Transistor Structure

The collector is lightly doped.

N

C

The base is thin and
is lightly doped.

P

B

The emitter is heavily doped.

N

E

NPN Transistor Bias
No current flows.
The C-B junction
is reverse biased.

N

C

P

B

N

E

NPN Transistor Bias

The B-E junction
is forward biased.

Current flows.

N

C

P

B

N

E

NPN Transistor Bias
IC
Current flows
everywhere.
Most of the emitter carriers
diffuse through the thin base
When
both
junctions
region since they are attracted
biased....
by are
the collector.

Note that IB is smaller
than IE or IC.

N

C

P

B

N

E

IB

IE

Note: when the
switch opens, all
currents go to zero.
Although IB is smaller
it controls IE and IC.

Gain is something small
controlling something large
(IB is small).

IC
N

C

P

B

N

E

IB

IE

Transistor Structure and Bias Quiz
The heaviest doping is found in
the ___________ region.

emitter

The thinnest of all three regions
is called the ____________.

base

The collector-base junction is
___________ biased.

reverse

The base-emitter junction is
____________ biased.

forward

The majority of the emitter
carriers flow to the ___________.

collector

Concept Review
• Amplifiers provide gain (the output is larger than
the input).
• Transistors have gain.

• Transistors have a collector, a base, and an emitter.
• The C-B junction is reverse biased.
• The B-E junction is forward biased.

• Most of the emitter carriers reach the collector.
• The base current is relatively small but controls the
larger currents.
Repeat Segment

Concept Preview
• The base to collector gain is called b (beta).
• To find b, divide the collector current by the
base current.
• The emitter current is the largest since it is the
sum of the base and collector currents.
• PNP transistors have opposite polarity from
NPN transistors.

• In an NPN transistor, the major flow is made
up of electrons.
• In a PNP transistor, the major flow is made up
of holes.

IC = 99 mA

The current gain from
base to collector
is called b.
IB = 1 mA

b =

99
ICmA
1IBmA

= 99

IE = 100 mA

C
P

B

N

E

IC = 99 mA
Kirchhoff’s
current law:

IB = 1 mA

C
P

B

N

E

IE = I B + I C

= 1 mA + 99 mA
= 100 mA
IE = 100 mA

IC = 99 mA
In a PNP transistor,
holes flow from
emitter to collector.

IB = 1 mA
Notice the PNP
bias voltages.

C
B

E

IE = 100 mA

Transistor Currents Quiz
b is the ratio of collector current to
______ current.

base

The sum of the base and collector
currents is the __________ current.

emitter

In NPN transistors, the flow from emitter
to collector is composed of _______.

electrons

In PNP transistors, the flow from emitter
to collector is composed of _______.

holes

Both NPN and PNP transistors show
__________ gain.

current

Concept Review
• The base to collector gain is called b (beta).
• To find b, divide the collector current by the
base current.
• The emitter current is the largest since it is the
sum of the base and collector currents.
• PNP transistors have opposite polarity from
NPN transistors.
• In an NPN transistor, the major flow is made
up of electrons.
• In a PNP transistor, the major flow is made up
of holes.
Repeat Segment

Concept Preview
• The NPN schematic symbol shows the emitter
arrow as Not Pointing iN.
• The collector curves are a graph of collector
voltage versus collector current.
• Both dc beta (bdc) and ac beta (bac) can be
determined from the collector curves.
• The collector circuit of a transistor can be
modeled as a resistor, as a closed switch or as
an open switch.
• The amount of base current determines which
of the three models applies.

NPN Schematic Symbol
Collector

Base

C
B E

Emitter
Memory aid: NPN
means Not Pointing iN.

PNP Schematic Symbol
Collector

Base

C
B E

Emitter

IC

This circuit is used to
collect IC versus
VCE data for
several values of IB.
C

IB
B

E

VCE

When graphed, the data provide an
NPN collector family of curves.
100 mA

14
12
10
IC in mA 8
6
4
2

80 mA
60 mA
40 mA
20 mA

0 2 4 6

8 10 12 14 16 18

VCE in Volts

0 mA

100 mA

14
12
10
IC in mA 8
6
4
2

80 mA
60 mA

40 mA
20 mA

0 2 4 6

8 10 12 14 16 18

0 mA

VCE in Volts

b =

14
mA
6ICmA
40
IB mA
100
mA

150
== 140

This type of gain
is called bdc or hFE.

100 mA

14
12
10
IC in mA 8
6
4
2

80 mA
60 mA

40 mA
20 mA

0 2 4 6

bac =

2.5DImA
C
20DImA
B

8 10 12 14 16 18

0 mA

VCE in Volts
= 125

Another type of gain
is called bac or hfe.

100 mA

14
12
10
IC in mA 8
6
4
2

80 mA
60 mA

40 mA
20 mA

0 2 4 6
IB

C

8 10 12 14 16 18
VCE in Volts

0 mA

With these values of IB:
The C-E model is a resistor.
E

100 mA

14
12
10
IC in mA 8
6
4
2
0 2 4 6
IB

80 mA
60 mA

40 mA
20 mA
8 10 12 14 16 18
VCE in Volts

0 mA

When IB >> 100 mA
VCE @ 0
The model is a closed switch.

100 mA

14
12
10
IC in mA 8
6
4
2
0 2 4 6
IB

80 mA
60 mA

40 mA
20 mA
8 10 12 14 16 18
VCE in Volts

0 mA

When IB = 0
IC = 0
The model is an open switch.

Transistor Operating Conditions Quiz
When IB is large and VCE @ 0, the transistor
acts as a ___________ switch.
closed
When IB = 0 and IC = 0, the transistor
acts as an ___________ switch.

open

When IB > 0 and VCE > 0, the transistor
acts as a ___________.

resistor

Two current gain measures are bdc and
__________.

bac

The symbol hfe is the same as _________.

bac

Concept Review
• The NPN schematic symbol shows the emitter
arrow as Not Pointing iN.
• The collector curves are a graph of collector
voltage versus collector current.
• Both dc beta (bdc) and ac beta (bac) can be
determined from the collector curves.
• The collector circuit of a transistor can be
modeled as a resistor, as a closed switch or as
an open switch.
• The amount of base current determines which
of the three models applies.
Repeat Segment

Concept Preview
• It is possible to test transistors out-of-circuit
using an ohmmeter.
• The E-B and C-B junctions act as diodes
during ohmmeter testing.

• The C-E test shows a high resistance because
two junctions are involved; one of which is
reverse biased by the ohmmeter.
• Gain can be verified by using a resistor in
conjunction with the ohmmeter test.

NPN

V

mA

E
B
C

The E-B junction is forward biased by the ohmmeter.

NPN

V

mA

E
B
C

The C-E resistance is very high.

NPN

V

mA

E
B
C
100 kW

The meter reading is < 100 kW due to gain.

Concept Review
• It is possible to test transistors out-of-circuit
using an ohmmeter.
• The E-B and C-B junctions act as diodes
during ohmmeter testing.
• The C-E test shows a high resistance because
two junctions are involved; one of which is
reverse biased by the ohmmeter.
• Gain can be verified by using a resistor in
conjunction with the ohmmeter test.
Repeat Segment

Concept Preview
• Bipolar junction transistors (BJTs) are controlled by
base current.
• Junction field effect transistors (JFETs) are controlled
by gate voltage.

• JFETs operate in the depletion mode (as normally on
devices).
• Metal oxide semiconductor field effect transistors
(MOSFETs) usually operate in the enhancement mode
(as normally off devices).
• Insulated gate bipolar transistors (IGBTs) are modified
MOSFETs and have very low on-resistance.
• Unijunction transistors (UJTs) are not used as
amplifiers.

Current In

The BJT is
a current
amplifier.

Current
Amplifier

Current Out

Voltage In

The JFET is
a voltage
controlled
amplifier.

Voltage
Amplifier

Current Out

Source

Gate

Drain

P

N-channel
P-type substrate
Structure of an
N-channel JFET

The channel has carriers so it
conducts from source to drain.

Drain

Gate
Source

Source

Gate

Drain

P

N-channel
P-type substrate

A negative gate voltage
can push the carriers from
the channel and turn
the JFET off.

Drain

Gate
Source

0V
-1 V
-2 V

ID in mA

-3 V

VGS

-4 V

0

-5 V
VDS in Volts

This is known as a depletion-mode device.
N-channel JFET drain family of characteristic curves

It’s possible to make enhancement
type field effect transistors as well.
Metal
oxide
insulator

Drain

n

Gate

VGG

D

VDD

p

G

n

S
N-channel
MOSFET

Source

Gate bias enhances the channel and turns the device on.

5V
4V
3V

ID in mA

2V

VGS

1V

0

0V
Drain

VDS in Volts

Enhancement mode
MOSFET drain family of
characteristic curves

Gate
Source

The IGBT (insulated gate bipolar transistor)
Operation and structure
similar to a MOSFET
Voltage controlled
(like the MOSFET)
Has one more junction
than a MOSFET
Hole injection reduces
the collector resistance

Faster turn off than
BJTs but not as fast
as MOSFETS

RCE = 8.33 mW

Three major device technologies

hole injection
Extra
junction

Courtesy of Powerex, Inc.

Typical IGBT Driver Circuit
Typically +15 V for turn on
Typically - 5 to -15 V for turn off

Control signal

IGBT

Powerex IGBT Module Structure

Powerex high voltage IGBT package

Emitter voltage

The unijunction transistor fires
when its emitter voltage reaches VP.
VP

Then, the emitter voltage
drops due to its negative
resistance characteristic.
Base 2

Emitter current
Emitter

The UJT is not useful as an amplifier.
It is used in timing and control applications.

Base 1

Other Transistor Types Quiz
BJTs are _________-controlled
amplifiers.

current

FETs are __________-controlled
amplifiers.

voltage

JFETs operate in the __________ mode. depletion
MOSFETs operate in the __________
mode.

enhancement

IGBTs are __________-controlled
amplifiers.

voltage

UJTs are not useful as __________.

amplifiers

Concept Review
• Bipolar junction transistors (BJTs) are controlled by
base current.
• Junction field effect transistors (JFETs) are controlled
by gate voltage.
• JFETs operate in the depletion mode (as normally on
devices).
• Metal oxide semiconductor field effect transistors
(MOSFETs) usually operate in the enhancement mode
(as normally off devices).
• Insulated gate bipolar transistors (IGBTs) are modified
MOSFETs and have very low on-resistance.
• Unijunction transistors (UJTs) are not used as
amplifiers.
Repeat Segment

Concept Preview
• BJTs can be used as switches.
• No base current = switch is off.
• High base current = switch is on.
• The dissipation is always zero in an ideal
switch: off = no current flow and on = no
voltage drop.

• MOSFETs can also be used as switches: no
gate voltage = switch is off and high gate
voltage = switch is on.

How do transistor switches work?
Can be viewed as solid state relays:
they are either ON or they are OFF.
BJT switches are characterized by:
high base current (switch is on)
(or no base current … off)

low resistance from collector to emitter (on)
(or very high resistance … off)
low collector dissipation (on or off)
PC = VCE x IC
PC = 0 x IC = 0 W
(on)
(or PC = VCE x 0 = 0 W … off)

NPN SWITCH
LOAD

RCE @ 
W
0W
DRIVER

The
The
driver
driver
output
output
isiszero
positive,
volts,
IIBB>=I0
0and
andthe
theload
loadis
ison
off
The
driver
output
is
zero
volts,
B = 0 and ILOAD = 0

PNP SWITCH
DRIVER

LOAD

The
Z):
Thedriver
driveroutput
outputisgoes
isoff
off(high
(highthe
Z):the
theresistor
resistor
low:
voltage
drop
pulls
the
base
voltage
up
that
VV
pulls
thethe
base
voltage
upso
soV
that
across
resistor
makes
BE
BE==00
BE negative

PNP SWITCH WITH NPN DRIVER

LOAD

NPN SWITCH WITH PNP DRIVER
(NEGATIVE POWER SUPPLY)

VV
0VV
BE
BE@ @+0.7

VVBE
0 VV
BE@@-0.7

LOAD

STEPPER MOTOR

A

B

C

A

Enhancement mode
power MOSFETs
used as switches

B

C
D

D

Concept Review
• BJTs can be used as switches.
• No base current = switch is off.
• High base current = switch is on.
• The dissipation is always zero in an ideal
switch: off = no current flow and on = no
voltage drop.
• MOSFETs can also be used as switches: no
gate voltage = switch is off and high gate
voltage = switch is on.
Repeat Segment

REVIEW
• Amplification
• Transistors
• Characteristic Curves
• Transistor Testing
• Other Transistor Types
• Transistors as Switches


Slide 22

Electronics
Principles & Applications
Sixth Edition

Charles A. Schuler
Chapter 5

Transistors
(student version)
©2003

Glencoe/McGraw-Hill

INTRODUCTION
• Amplification
• Transistors
• Characteristic Curves
• Transistor Testing
• Other Transistor Types
• Transistors as Switches

Dear Student:
This presentation is arranged in segments.
Each segment is preceded by a Concept
Preview slide and is followed by a Concept
Review slide. When you reach a Concept
Review slide, you can return to the
beginning of that segment by clicking on the
Repeat Segment button. This will allow you
to view that segment again, if you want to.

Concept Preview
• Amplifiers provide gain (the output is larger
than the input).
• Transistors have gain.
• Transistors have a collector, a base, and an
emitter.
• The C-B junction is reverse biased.
• The B-E junction is forward biased.
• Most of the emitter carriers reach the collector.
• The base current is relatively small but controls
the larger currents.

In

Gain =

Amplifier

Out

In

Out

NPN Transistor Structure

The collector is lightly doped.

N

C

The base is thin and
is lightly doped.

P

B

The emitter is heavily doped.

N

E

NPN Transistor Bias
No current flows.
The C-B junction
is reverse biased.

N

C

P

B

N

E

NPN Transistor Bias

The B-E junction
is forward biased.

Current flows.

N

C

P

B

N

E

NPN Transistor Bias
IC
Current flows
everywhere.
Most of the emitter carriers
diffuse through the thin base
When
both
junctions
region since they are attracted
biased....
by are
the collector.

Note that IB is smaller
than IE or IC.

N

C

P

B

N

E

IB

IE

Note: when the
switch opens, all
currents go to zero.
Although IB is smaller
it controls IE and IC.

Gain is something small
controlling something large
(IB is small).

IC
N

C

P

B

N

E

IB

IE

Transistor Structure and Bias Quiz
The heaviest doping is found in
the ___________ region.

emitter

The thinnest of all three regions
is called the ____________.

base

The collector-base junction is
___________ biased.

reverse

The base-emitter junction is
____________ biased.

forward

The majority of the emitter
carriers flow to the ___________.

collector

Concept Review
• Amplifiers provide gain (the output is larger than
the input).
• Transistors have gain.

• Transistors have a collector, a base, and an emitter.
• The C-B junction is reverse biased.
• The B-E junction is forward biased.

• Most of the emitter carriers reach the collector.
• The base current is relatively small but controls the
larger currents.
Repeat Segment

Concept Preview
• The base to collector gain is called b (beta).
• To find b, divide the collector current by the
base current.
• The emitter current is the largest since it is the
sum of the base and collector currents.
• PNP transistors have opposite polarity from
NPN transistors.

• In an NPN transistor, the major flow is made
up of electrons.
• In a PNP transistor, the major flow is made up
of holes.

IC = 99 mA

The current gain from
base to collector
is called b.
IB = 1 mA

b =

99
ICmA
1IBmA

= 99

IE = 100 mA

C
P

B

N

E

IC = 99 mA
Kirchhoff’s
current law:

IB = 1 mA

C
P

B

N

E

IE = I B + I C

= 1 mA + 99 mA
= 100 mA
IE = 100 mA

IC = 99 mA
In a PNP transistor,
holes flow from
emitter to collector.

IB = 1 mA
Notice the PNP
bias voltages.

C
B

E

IE = 100 mA

Transistor Currents Quiz
b is the ratio of collector current to
______ current.

base

The sum of the base and collector
currents is the __________ current.

emitter

In NPN transistors, the flow from emitter
to collector is composed of _______.

electrons

In PNP transistors, the flow from emitter
to collector is composed of _______.

holes

Both NPN and PNP transistors show
__________ gain.

current

Concept Review
• The base to collector gain is called b (beta).
• To find b, divide the collector current by the
base current.
• The emitter current is the largest since it is the
sum of the base and collector currents.
• PNP transistors have opposite polarity from
NPN transistors.
• In an NPN transistor, the major flow is made
up of electrons.
• In a PNP transistor, the major flow is made up
of holes.
Repeat Segment

Concept Preview
• The NPN schematic symbol shows the emitter
arrow as Not Pointing iN.
• The collector curves are a graph of collector
voltage versus collector current.
• Both dc beta (bdc) and ac beta (bac) can be
determined from the collector curves.
• The collector circuit of a transistor can be
modeled as a resistor, as a closed switch or as
an open switch.
• The amount of base current determines which
of the three models applies.

NPN Schematic Symbol
Collector

Base

C
B E

Emitter
Memory aid: NPN
means Not Pointing iN.

PNP Schematic Symbol
Collector

Base

C
B E

Emitter

IC

This circuit is used to
collect IC versus
VCE data for
several values of IB.
C

IB
B

E

VCE

When graphed, the data provide an
NPN collector family of curves.
100 mA

14
12
10
IC in mA 8
6
4
2

80 mA
60 mA
40 mA
20 mA

0 2 4 6

8 10 12 14 16 18

VCE in Volts

0 mA

100 mA

14
12
10
IC in mA 8
6
4
2

80 mA
60 mA

40 mA
20 mA

0 2 4 6

8 10 12 14 16 18

0 mA

VCE in Volts

b =

14
mA
6ICmA
40
IB mA
100
mA

150
== 140

This type of gain
is called bdc or hFE.

100 mA

14
12
10
IC in mA 8
6
4
2

80 mA
60 mA

40 mA
20 mA

0 2 4 6

bac =

2.5DImA
C
20DImA
B

8 10 12 14 16 18

0 mA

VCE in Volts
= 125

Another type of gain
is called bac or hfe.

100 mA

14
12
10
IC in mA 8
6
4
2

80 mA
60 mA

40 mA
20 mA

0 2 4 6
IB

C

8 10 12 14 16 18
VCE in Volts

0 mA

With these values of IB:
The C-E model is a resistor.
E

100 mA

14
12
10
IC in mA 8
6
4
2
0 2 4 6
IB

80 mA
60 mA

40 mA
20 mA
8 10 12 14 16 18
VCE in Volts

0 mA

When IB >> 100 mA
VCE @ 0
The model is a closed switch.

100 mA

14
12
10
IC in mA 8
6
4
2
0 2 4 6
IB

80 mA
60 mA

40 mA
20 mA
8 10 12 14 16 18
VCE in Volts

0 mA

When IB = 0
IC = 0
The model is an open switch.

Transistor Operating Conditions Quiz
When IB is large and VCE @ 0, the transistor
acts as a ___________ switch.
closed
When IB = 0 and IC = 0, the transistor
acts as an ___________ switch.

open

When IB > 0 and VCE > 0, the transistor
acts as a ___________.

resistor

Two current gain measures are bdc and
__________.

bac

The symbol hfe is the same as _________.

bac

Concept Review
• The NPN schematic symbol shows the emitter
arrow as Not Pointing iN.
• The collector curves are a graph of collector
voltage versus collector current.
• Both dc beta (bdc) and ac beta (bac) can be
determined from the collector curves.
• The collector circuit of a transistor can be
modeled as a resistor, as a closed switch or as
an open switch.
• The amount of base current determines which
of the three models applies.
Repeat Segment

Concept Preview
• It is possible to test transistors out-of-circuit
using an ohmmeter.
• The E-B and C-B junctions act as diodes
during ohmmeter testing.

• The C-E test shows a high resistance because
two junctions are involved; one of which is
reverse biased by the ohmmeter.
• Gain can be verified by using a resistor in
conjunction with the ohmmeter test.

NPN

V

mA

E
B
C

The E-B junction is forward biased by the ohmmeter.

NPN

V

mA

E
B
C

The C-E resistance is very high.

NPN

V

mA

E
B
C
100 kW

The meter reading is < 100 kW due to gain.

Concept Review
• It is possible to test transistors out-of-circuit
using an ohmmeter.
• The E-B and C-B junctions act as diodes
during ohmmeter testing.
• The C-E test shows a high resistance because
two junctions are involved; one of which is
reverse biased by the ohmmeter.
• Gain can be verified by using a resistor in
conjunction with the ohmmeter test.
Repeat Segment

Concept Preview
• Bipolar junction transistors (BJTs) are controlled by
base current.
• Junction field effect transistors (JFETs) are controlled
by gate voltage.

• JFETs operate in the depletion mode (as normally on
devices).
• Metal oxide semiconductor field effect transistors
(MOSFETs) usually operate in the enhancement mode
(as normally off devices).
• Insulated gate bipolar transistors (IGBTs) are modified
MOSFETs and have very low on-resistance.
• Unijunction transistors (UJTs) are not used as
amplifiers.

Current In

The BJT is
a current
amplifier.

Current
Amplifier

Current Out

Voltage In

The JFET is
a voltage
controlled
amplifier.

Voltage
Amplifier

Current Out

Source

Gate

Drain

P

N-channel
P-type substrate
Structure of an
N-channel JFET

The channel has carriers so it
conducts from source to drain.

Drain

Gate
Source

Source

Gate

Drain

P

N-channel
P-type substrate

A negative gate voltage
can push the carriers from
the channel and turn
the JFET off.

Drain

Gate
Source

0V
-1 V
-2 V

ID in mA

-3 V

VGS

-4 V

0

-5 V
VDS in Volts

This is known as a depletion-mode device.
N-channel JFET drain family of characteristic curves

It’s possible to make enhancement
type field effect transistors as well.
Metal
oxide
insulator

Drain

n

Gate

VGG

D

VDD

p

G

n

S
N-channel
MOSFET

Source

Gate bias enhances the channel and turns the device on.

5V
4V
3V

ID in mA

2V

VGS

1V

0

0V
Drain

VDS in Volts

Enhancement mode
MOSFET drain family of
characteristic curves

Gate
Source

The IGBT (insulated gate bipolar transistor)
Operation and structure
similar to a MOSFET
Voltage controlled
(like the MOSFET)
Has one more junction
than a MOSFET
Hole injection reduces
the collector resistance

Faster turn off than
BJTs but not as fast
as MOSFETS

RCE = 8.33 mW

Three major device technologies

hole injection
Extra
junction

Courtesy of Powerex, Inc.

Typical IGBT Driver Circuit
Typically +15 V for turn on
Typically - 5 to -15 V for turn off

Control signal

IGBT

Powerex IGBT Module Structure

Powerex high voltage IGBT package

Emitter voltage

The unijunction transistor fires
when its emitter voltage reaches VP.
VP

Then, the emitter voltage
drops due to its negative
resistance characteristic.
Base 2

Emitter current
Emitter

The UJT is not useful as an amplifier.
It is used in timing and control applications.

Base 1

Other Transistor Types Quiz
BJTs are _________-controlled
amplifiers.

current

FETs are __________-controlled
amplifiers.

voltage

JFETs operate in the __________ mode. depletion
MOSFETs operate in the __________
mode.

enhancement

IGBTs are __________-controlled
amplifiers.

voltage

UJTs are not useful as __________.

amplifiers

Concept Review
• Bipolar junction transistors (BJTs) are controlled by
base current.
• Junction field effect transistors (JFETs) are controlled
by gate voltage.
• JFETs operate in the depletion mode (as normally on
devices).
• Metal oxide semiconductor field effect transistors
(MOSFETs) usually operate in the enhancement mode
(as normally off devices).
• Insulated gate bipolar transistors (IGBTs) are modified
MOSFETs and have very low on-resistance.
• Unijunction transistors (UJTs) are not used as
amplifiers.
Repeat Segment

Concept Preview
• BJTs can be used as switches.
• No base current = switch is off.
• High base current = switch is on.
• The dissipation is always zero in an ideal
switch: off = no current flow and on = no
voltage drop.

• MOSFETs can also be used as switches: no
gate voltage = switch is off and high gate
voltage = switch is on.

How do transistor switches work?
Can be viewed as solid state relays:
they are either ON or they are OFF.
BJT switches are characterized by:
high base current (switch is on)
(or no base current … off)

low resistance from collector to emitter (on)
(or very high resistance … off)
low collector dissipation (on or off)
PC = VCE x IC
PC = 0 x IC = 0 W
(on)
(or PC = VCE x 0 = 0 W … off)

NPN SWITCH
LOAD

RCE @ 
W
0W
DRIVER

The
The
driver
driver
output
output
isiszero
positive,
volts,
IIBB>=I0
0and
andthe
theload
loadis
ison
off
The
driver
output
is
zero
volts,
B = 0 and ILOAD = 0

PNP SWITCH
DRIVER

LOAD

The
Z):
Thedriver
driveroutput
outputisgoes
isoff
off(high
(highthe
Z):the
theresistor
resistor
low:
voltage
drop
pulls
the
base
voltage
up
that
VV
pulls
thethe
base
voltage
upso
soV
that
across
resistor
makes
BE
BE==00
BE negative

PNP SWITCH WITH NPN DRIVER

LOAD

NPN SWITCH WITH PNP DRIVER
(NEGATIVE POWER SUPPLY)

VV
0VV
BE
BE@ @+0.7

VVBE
0 VV
BE@@-0.7

LOAD

STEPPER MOTOR

A

B

C

A

Enhancement mode
power MOSFETs
used as switches

B

C
D

D

Concept Review
• BJTs can be used as switches.
• No base current = switch is off.
• High base current = switch is on.
• The dissipation is always zero in an ideal
switch: off = no current flow and on = no
voltage drop.
• MOSFETs can also be used as switches: no
gate voltage = switch is off and high gate
voltage = switch is on.
Repeat Segment

REVIEW
• Amplification
• Transistors
• Characteristic Curves
• Transistor Testing
• Other Transistor Types
• Transistors as Switches


Slide 23

Electronics
Principles & Applications
Sixth Edition

Charles A. Schuler
Chapter 5

Transistors
(student version)
©2003

Glencoe/McGraw-Hill

INTRODUCTION
• Amplification
• Transistors
• Characteristic Curves
• Transistor Testing
• Other Transistor Types
• Transistors as Switches

Dear Student:
This presentation is arranged in segments.
Each segment is preceded by a Concept
Preview slide and is followed by a Concept
Review slide. When you reach a Concept
Review slide, you can return to the
beginning of that segment by clicking on the
Repeat Segment button. This will allow you
to view that segment again, if you want to.

Concept Preview
• Amplifiers provide gain (the output is larger
than the input).
• Transistors have gain.
• Transistors have a collector, a base, and an
emitter.
• The C-B junction is reverse biased.
• The B-E junction is forward biased.
• Most of the emitter carriers reach the collector.
• The base current is relatively small but controls
the larger currents.

In

Gain =

Amplifier

Out

In

Out

NPN Transistor Structure

The collector is lightly doped.

N

C

The base is thin and
is lightly doped.

P

B

The emitter is heavily doped.

N

E

NPN Transistor Bias
No current flows.
The C-B junction
is reverse biased.

N

C

P

B

N

E

NPN Transistor Bias

The B-E junction
is forward biased.

Current flows.

N

C

P

B

N

E

NPN Transistor Bias
IC
Current flows
everywhere.
Most of the emitter carriers
diffuse through the thin base
When
both
junctions
region since they are attracted
biased....
by are
the collector.

Note that IB is smaller
than IE or IC.

N

C

P

B

N

E

IB

IE

Note: when the
switch opens, all
currents go to zero.
Although IB is smaller
it controls IE and IC.

Gain is something small
controlling something large
(IB is small).

IC
N

C

P

B

N

E

IB

IE

Transistor Structure and Bias Quiz
The heaviest doping is found in
the ___________ region.

emitter

The thinnest of all three regions
is called the ____________.

base

The collector-base junction is
___________ biased.

reverse

The base-emitter junction is
____________ biased.

forward

The majority of the emitter
carriers flow to the ___________.

collector

Concept Review
• Amplifiers provide gain (the output is larger than
the input).
• Transistors have gain.

• Transistors have a collector, a base, and an emitter.
• The C-B junction is reverse biased.
• The B-E junction is forward biased.

• Most of the emitter carriers reach the collector.
• The base current is relatively small but controls the
larger currents.
Repeat Segment

Concept Preview
• The base to collector gain is called b (beta).
• To find b, divide the collector current by the
base current.
• The emitter current is the largest since it is the
sum of the base and collector currents.
• PNP transistors have opposite polarity from
NPN transistors.

• In an NPN transistor, the major flow is made
up of electrons.
• In a PNP transistor, the major flow is made up
of holes.

IC = 99 mA

The current gain from
base to collector
is called b.
IB = 1 mA

b =

99
ICmA
1IBmA

= 99

IE = 100 mA

C
P

B

N

E

IC = 99 mA
Kirchhoff’s
current law:

IB = 1 mA

C
P

B

N

E

IE = I B + I C

= 1 mA + 99 mA
= 100 mA
IE = 100 mA

IC = 99 mA
In a PNP transistor,
holes flow from
emitter to collector.

IB = 1 mA
Notice the PNP
bias voltages.

C
B

E

IE = 100 mA

Transistor Currents Quiz
b is the ratio of collector current to
______ current.

base

The sum of the base and collector
currents is the __________ current.

emitter

In NPN transistors, the flow from emitter
to collector is composed of _______.

electrons

In PNP transistors, the flow from emitter
to collector is composed of _______.

holes

Both NPN and PNP transistors show
__________ gain.

current

Concept Review
• The base to collector gain is called b (beta).
• To find b, divide the collector current by the
base current.
• The emitter current is the largest since it is the
sum of the base and collector currents.
• PNP transistors have opposite polarity from
NPN transistors.
• In an NPN transistor, the major flow is made
up of electrons.
• In a PNP transistor, the major flow is made up
of holes.
Repeat Segment

Concept Preview
• The NPN schematic symbol shows the emitter
arrow as Not Pointing iN.
• The collector curves are a graph of collector
voltage versus collector current.
• Both dc beta (bdc) and ac beta (bac) can be
determined from the collector curves.
• The collector circuit of a transistor can be
modeled as a resistor, as a closed switch or as
an open switch.
• The amount of base current determines which
of the three models applies.

NPN Schematic Symbol
Collector

Base

C
B E

Emitter
Memory aid: NPN
means Not Pointing iN.

PNP Schematic Symbol
Collector

Base

C
B E

Emitter

IC

This circuit is used to
collect IC versus
VCE data for
several values of IB.
C

IB
B

E

VCE

When graphed, the data provide an
NPN collector family of curves.
100 mA

14
12
10
IC in mA 8
6
4
2

80 mA
60 mA
40 mA
20 mA

0 2 4 6

8 10 12 14 16 18

VCE in Volts

0 mA

100 mA

14
12
10
IC in mA 8
6
4
2

80 mA
60 mA

40 mA
20 mA

0 2 4 6

8 10 12 14 16 18

0 mA

VCE in Volts

b =

14
mA
6ICmA
40
IB mA
100
mA

150
== 140

This type of gain
is called bdc or hFE.

100 mA

14
12
10
IC in mA 8
6
4
2

80 mA
60 mA

40 mA
20 mA

0 2 4 6

bac =

2.5DImA
C
20DImA
B

8 10 12 14 16 18

0 mA

VCE in Volts
= 125

Another type of gain
is called bac or hfe.

100 mA

14
12
10
IC in mA 8
6
4
2

80 mA
60 mA

40 mA
20 mA

0 2 4 6
IB

C

8 10 12 14 16 18
VCE in Volts

0 mA

With these values of IB:
The C-E model is a resistor.
E

100 mA

14
12
10
IC in mA 8
6
4
2
0 2 4 6
IB

80 mA
60 mA

40 mA
20 mA
8 10 12 14 16 18
VCE in Volts

0 mA

When IB >> 100 mA
VCE @ 0
The model is a closed switch.

100 mA

14
12
10
IC in mA 8
6
4
2
0 2 4 6
IB

80 mA
60 mA

40 mA
20 mA
8 10 12 14 16 18
VCE in Volts

0 mA

When IB = 0
IC = 0
The model is an open switch.

Transistor Operating Conditions Quiz
When IB is large and VCE @ 0, the transistor
acts as a ___________ switch.
closed
When IB = 0 and IC = 0, the transistor
acts as an ___________ switch.

open

When IB > 0 and VCE > 0, the transistor
acts as a ___________.

resistor

Two current gain measures are bdc and
__________.

bac

The symbol hfe is the same as _________.

bac

Concept Review
• The NPN schematic symbol shows the emitter
arrow as Not Pointing iN.
• The collector curves are a graph of collector
voltage versus collector current.
• Both dc beta (bdc) and ac beta (bac) can be
determined from the collector curves.
• The collector circuit of a transistor can be
modeled as a resistor, as a closed switch or as
an open switch.
• The amount of base current determines which
of the three models applies.
Repeat Segment

Concept Preview
• It is possible to test transistors out-of-circuit
using an ohmmeter.
• The E-B and C-B junctions act as diodes
during ohmmeter testing.

• The C-E test shows a high resistance because
two junctions are involved; one of which is
reverse biased by the ohmmeter.
• Gain can be verified by using a resistor in
conjunction with the ohmmeter test.

NPN

V

mA

E
B
C

The E-B junction is forward biased by the ohmmeter.

NPN

V

mA

E
B
C

The C-E resistance is very high.

NPN

V

mA

E
B
C
100 kW

The meter reading is < 100 kW due to gain.

Concept Review
• It is possible to test transistors out-of-circuit
using an ohmmeter.
• The E-B and C-B junctions act as diodes
during ohmmeter testing.
• The C-E test shows a high resistance because
two junctions are involved; one of which is
reverse biased by the ohmmeter.
• Gain can be verified by using a resistor in
conjunction with the ohmmeter test.
Repeat Segment

Concept Preview
• Bipolar junction transistors (BJTs) are controlled by
base current.
• Junction field effect transistors (JFETs) are controlled
by gate voltage.

• JFETs operate in the depletion mode (as normally on
devices).
• Metal oxide semiconductor field effect transistors
(MOSFETs) usually operate in the enhancement mode
(as normally off devices).
• Insulated gate bipolar transistors (IGBTs) are modified
MOSFETs and have very low on-resistance.
• Unijunction transistors (UJTs) are not used as
amplifiers.

Current In

The BJT is
a current
amplifier.

Current
Amplifier

Current Out

Voltage In

The JFET is
a voltage
controlled
amplifier.

Voltage
Amplifier

Current Out

Source

Gate

Drain

P

N-channel
P-type substrate
Structure of an
N-channel JFET

The channel has carriers so it
conducts from source to drain.

Drain

Gate
Source

Source

Gate

Drain

P

N-channel
P-type substrate

A negative gate voltage
can push the carriers from
the channel and turn
the JFET off.

Drain

Gate
Source

0V
-1 V
-2 V

ID in mA

-3 V

VGS

-4 V

0

-5 V
VDS in Volts

This is known as a depletion-mode device.
N-channel JFET drain family of characteristic curves

It’s possible to make enhancement
type field effect transistors as well.
Metal
oxide
insulator

Drain

n

Gate

VGG

D

VDD

p

G

n

S
N-channel
MOSFET

Source

Gate bias enhances the channel and turns the device on.

5V
4V
3V

ID in mA

2V

VGS

1V

0

0V
Drain

VDS in Volts

Enhancement mode
MOSFET drain family of
characteristic curves

Gate
Source

The IGBT (insulated gate bipolar transistor)
Operation and structure
similar to a MOSFET
Voltage controlled
(like the MOSFET)
Has one more junction
than a MOSFET
Hole injection reduces
the collector resistance

Faster turn off than
BJTs but not as fast
as MOSFETS

RCE = 8.33 mW

Three major device technologies

hole injection
Extra
junction

Courtesy of Powerex, Inc.

Typical IGBT Driver Circuit
Typically +15 V for turn on
Typically - 5 to -15 V for turn off

Control signal

IGBT

Powerex IGBT Module Structure

Powerex high voltage IGBT package

Emitter voltage

The unijunction transistor fires
when its emitter voltage reaches VP.
VP

Then, the emitter voltage
drops due to its negative
resistance characteristic.
Base 2

Emitter current
Emitter

The UJT is not useful as an amplifier.
It is used in timing and control applications.

Base 1

Other Transistor Types Quiz
BJTs are _________-controlled
amplifiers.

current

FETs are __________-controlled
amplifiers.

voltage

JFETs operate in the __________ mode. depletion
MOSFETs operate in the __________
mode.

enhancement

IGBTs are __________-controlled
amplifiers.

voltage

UJTs are not useful as __________.

amplifiers

Concept Review
• Bipolar junction transistors (BJTs) are controlled by
base current.
• Junction field effect transistors (JFETs) are controlled
by gate voltage.
• JFETs operate in the depletion mode (as normally on
devices).
• Metal oxide semiconductor field effect transistors
(MOSFETs) usually operate in the enhancement mode
(as normally off devices).
• Insulated gate bipolar transistors (IGBTs) are modified
MOSFETs and have very low on-resistance.
• Unijunction transistors (UJTs) are not used as
amplifiers.
Repeat Segment

Concept Preview
• BJTs can be used as switches.
• No base current = switch is off.
• High base current = switch is on.
• The dissipation is always zero in an ideal
switch: off = no current flow and on = no
voltage drop.

• MOSFETs can also be used as switches: no
gate voltage = switch is off and high gate
voltage = switch is on.

How do transistor switches work?
Can be viewed as solid state relays:
they are either ON or they are OFF.
BJT switches are characterized by:
high base current (switch is on)
(or no base current … off)

low resistance from collector to emitter (on)
(or very high resistance … off)
low collector dissipation (on or off)
PC = VCE x IC
PC = 0 x IC = 0 W
(on)
(or PC = VCE x 0 = 0 W … off)

NPN SWITCH
LOAD

RCE @ 
W
0W
DRIVER

The
The
driver
driver
output
output
isiszero
positive,
volts,
IIBB>=I0
0and
andthe
theload
loadis
ison
off
The
driver
output
is
zero
volts,
B = 0 and ILOAD = 0

PNP SWITCH
DRIVER

LOAD

The
Z):
Thedriver
driveroutput
outputisgoes
isoff
off(high
(highthe
Z):the
theresistor
resistor
low:
voltage
drop
pulls
the
base
voltage
up
that
VV
pulls
thethe
base
voltage
upso
soV
that
across
resistor
makes
BE
BE==00
BE negative

PNP SWITCH WITH NPN DRIVER

LOAD

NPN SWITCH WITH PNP DRIVER
(NEGATIVE POWER SUPPLY)

VV
0VV
BE
BE@ @+0.7

VVBE
0 VV
BE@@-0.7

LOAD

STEPPER MOTOR

A

B

C

A

Enhancement mode
power MOSFETs
used as switches

B

C
D

D

Concept Review
• BJTs can be used as switches.
• No base current = switch is off.
• High base current = switch is on.
• The dissipation is always zero in an ideal
switch: off = no current flow and on = no
voltage drop.
• MOSFETs can also be used as switches: no
gate voltage = switch is off and high gate
voltage = switch is on.
Repeat Segment

REVIEW
• Amplification
• Transistors
• Characteristic Curves
• Transistor Testing
• Other Transistor Types
• Transistors as Switches


Slide 24

Electronics
Principles & Applications
Sixth Edition

Charles A. Schuler
Chapter 5

Transistors
(student version)
©2003

Glencoe/McGraw-Hill

INTRODUCTION
• Amplification
• Transistors
• Characteristic Curves
• Transistor Testing
• Other Transistor Types
• Transistors as Switches

Dear Student:
This presentation is arranged in segments.
Each segment is preceded by a Concept
Preview slide and is followed by a Concept
Review slide. When you reach a Concept
Review slide, you can return to the
beginning of that segment by clicking on the
Repeat Segment button. This will allow you
to view that segment again, if you want to.

Concept Preview
• Amplifiers provide gain (the output is larger
than the input).
• Transistors have gain.
• Transistors have a collector, a base, and an
emitter.
• The C-B junction is reverse biased.
• The B-E junction is forward biased.
• Most of the emitter carriers reach the collector.
• The base current is relatively small but controls
the larger currents.

In

Gain =

Amplifier

Out

In

Out

NPN Transistor Structure

The collector is lightly doped.

N

C

The base is thin and
is lightly doped.

P

B

The emitter is heavily doped.

N

E

NPN Transistor Bias
No current flows.
The C-B junction
is reverse biased.

N

C

P

B

N

E

NPN Transistor Bias

The B-E junction
is forward biased.

Current flows.

N

C

P

B

N

E

NPN Transistor Bias
IC
Current flows
everywhere.
Most of the emitter carriers
diffuse through the thin base
When
both
junctions
region since they are attracted
biased....
by are
the collector.

Note that IB is smaller
than IE or IC.

N

C

P

B

N

E

IB

IE

Note: when the
switch opens, all
currents go to zero.
Although IB is smaller
it controls IE and IC.

Gain is something small
controlling something large
(IB is small).

IC
N

C

P

B

N

E

IB

IE

Transistor Structure and Bias Quiz
The heaviest doping is found in
the ___________ region.

emitter

The thinnest of all three regions
is called the ____________.

base

The collector-base junction is
___________ biased.

reverse

The base-emitter junction is
____________ biased.

forward

The majority of the emitter
carriers flow to the ___________.

collector

Concept Review
• Amplifiers provide gain (the output is larger than
the input).
• Transistors have gain.

• Transistors have a collector, a base, and an emitter.
• The C-B junction is reverse biased.
• The B-E junction is forward biased.

• Most of the emitter carriers reach the collector.
• The base current is relatively small but controls the
larger currents.
Repeat Segment

Concept Preview
• The base to collector gain is called b (beta).
• To find b, divide the collector current by the
base current.
• The emitter current is the largest since it is the
sum of the base and collector currents.
• PNP transistors have opposite polarity from
NPN transistors.

• In an NPN transistor, the major flow is made
up of electrons.
• In a PNP transistor, the major flow is made up
of holes.

IC = 99 mA

The current gain from
base to collector
is called b.
IB = 1 mA

b =

99
ICmA
1IBmA

= 99

IE = 100 mA

C
P

B

N

E

IC = 99 mA
Kirchhoff’s
current law:

IB = 1 mA

C
P

B

N

E

IE = I B + I C

= 1 mA + 99 mA
= 100 mA
IE = 100 mA

IC = 99 mA
In a PNP transistor,
holes flow from
emitter to collector.

IB = 1 mA
Notice the PNP
bias voltages.

C
B

E

IE = 100 mA

Transistor Currents Quiz
b is the ratio of collector current to
______ current.

base

The sum of the base and collector
currents is the __________ current.

emitter

In NPN transistors, the flow from emitter
to collector is composed of _______.

electrons

In PNP transistors, the flow from emitter
to collector is composed of _______.

holes

Both NPN and PNP transistors show
__________ gain.

current

Concept Review
• The base to collector gain is called b (beta).
• To find b, divide the collector current by the
base current.
• The emitter current is the largest since it is the
sum of the base and collector currents.
• PNP transistors have opposite polarity from
NPN transistors.
• In an NPN transistor, the major flow is made
up of electrons.
• In a PNP transistor, the major flow is made up
of holes.
Repeat Segment

Concept Preview
• The NPN schematic symbol shows the emitter
arrow as Not Pointing iN.
• The collector curves are a graph of collector
voltage versus collector current.
• Both dc beta (bdc) and ac beta (bac) can be
determined from the collector curves.
• The collector circuit of a transistor can be
modeled as a resistor, as a closed switch or as
an open switch.
• The amount of base current determines which
of the three models applies.

NPN Schematic Symbol
Collector

Base

C
B E

Emitter
Memory aid: NPN
means Not Pointing iN.

PNP Schematic Symbol
Collector

Base

C
B E

Emitter

IC

This circuit is used to
collect IC versus
VCE data for
several values of IB.
C

IB
B

E

VCE

When graphed, the data provide an
NPN collector family of curves.
100 mA

14
12
10
IC in mA 8
6
4
2

80 mA
60 mA
40 mA
20 mA

0 2 4 6

8 10 12 14 16 18

VCE in Volts

0 mA

100 mA

14
12
10
IC in mA 8
6
4
2

80 mA
60 mA

40 mA
20 mA

0 2 4 6

8 10 12 14 16 18

0 mA

VCE in Volts

b =

14
mA
6ICmA
40
IB mA
100
mA

150
== 140

This type of gain
is called bdc or hFE.

100 mA

14
12
10
IC in mA 8
6
4
2

80 mA
60 mA

40 mA
20 mA

0 2 4 6

bac =

2.5DImA
C
20DImA
B

8 10 12 14 16 18

0 mA

VCE in Volts
= 125

Another type of gain
is called bac or hfe.

100 mA

14
12
10
IC in mA 8
6
4
2

80 mA
60 mA

40 mA
20 mA

0 2 4 6
IB

C

8 10 12 14 16 18
VCE in Volts

0 mA

With these values of IB:
The C-E model is a resistor.
E

100 mA

14
12
10
IC in mA 8
6
4
2
0 2 4 6
IB

80 mA
60 mA

40 mA
20 mA
8 10 12 14 16 18
VCE in Volts

0 mA

When IB >> 100 mA
VCE @ 0
The model is a closed switch.

100 mA

14
12
10
IC in mA 8
6
4
2
0 2 4 6
IB

80 mA
60 mA

40 mA
20 mA
8 10 12 14 16 18
VCE in Volts

0 mA

When IB = 0
IC = 0
The model is an open switch.

Transistor Operating Conditions Quiz
When IB is large and VCE @ 0, the transistor
acts as a ___________ switch.
closed
When IB = 0 and IC = 0, the transistor
acts as an ___________ switch.

open

When IB > 0 and VCE > 0, the transistor
acts as a ___________.

resistor

Two current gain measures are bdc and
__________.

bac

The symbol hfe is the same as _________.

bac

Concept Review
• The NPN schematic symbol shows the emitter
arrow as Not Pointing iN.
• The collector curves are a graph of collector
voltage versus collector current.
• Both dc beta (bdc) and ac beta (bac) can be
determined from the collector curves.
• The collector circuit of a transistor can be
modeled as a resistor, as a closed switch or as
an open switch.
• The amount of base current determines which
of the three models applies.
Repeat Segment

Concept Preview
• It is possible to test transistors out-of-circuit
using an ohmmeter.
• The E-B and C-B junctions act as diodes
during ohmmeter testing.

• The C-E test shows a high resistance because
two junctions are involved; one of which is
reverse biased by the ohmmeter.
• Gain can be verified by using a resistor in
conjunction with the ohmmeter test.

NPN

V

mA

E
B
C

The E-B junction is forward biased by the ohmmeter.

NPN

V

mA

E
B
C

The C-E resistance is very high.

NPN

V

mA

E
B
C
100 kW

The meter reading is < 100 kW due to gain.

Concept Review
• It is possible to test transistors out-of-circuit
using an ohmmeter.
• The E-B and C-B junctions act as diodes
during ohmmeter testing.
• The C-E test shows a high resistance because
two junctions are involved; one of which is
reverse biased by the ohmmeter.
• Gain can be verified by using a resistor in
conjunction with the ohmmeter test.
Repeat Segment

Concept Preview
• Bipolar junction transistors (BJTs) are controlled by
base current.
• Junction field effect transistors (JFETs) are controlled
by gate voltage.

• JFETs operate in the depletion mode (as normally on
devices).
• Metal oxide semiconductor field effect transistors
(MOSFETs) usually operate in the enhancement mode
(as normally off devices).
• Insulated gate bipolar transistors (IGBTs) are modified
MOSFETs and have very low on-resistance.
• Unijunction transistors (UJTs) are not used as
amplifiers.

Current In

The BJT is
a current
amplifier.

Current
Amplifier

Current Out

Voltage In

The JFET is
a voltage
controlled
amplifier.

Voltage
Amplifier

Current Out

Source

Gate

Drain

P

N-channel
P-type substrate
Structure of an
N-channel JFET

The channel has carriers so it
conducts from source to drain.

Drain

Gate
Source

Source

Gate

Drain

P

N-channel
P-type substrate

A negative gate voltage
can push the carriers from
the channel and turn
the JFET off.

Drain

Gate
Source

0V
-1 V
-2 V

ID in mA

-3 V

VGS

-4 V

0

-5 V
VDS in Volts

This is known as a depletion-mode device.
N-channel JFET drain family of characteristic curves

It’s possible to make enhancement
type field effect transistors as well.
Metal
oxide
insulator

Drain

n

Gate

VGG

D

VDD

p

G

n

S
N-channel
MOSFET

Source

Gate bias enhances the channel and turns the device on.

5V
4V
3V

ID in mA

2V

VGS

1V

0

0V
Drain

VDS in Volts

Enhancement mode
MOSFET drain family of
characteristic curves

Gate
Source

The IGBT (insulated gate bipolar transistor)
Operation and structure
similar to a MOSFET
Voltage controlled
(like the MOSFET)
Has one more junction
than a MOSFET
Hole injection reduces
the collector resistance

Faster turn off than
BJTs but not as fast
as MOSFETS

RCE = 8.33 mW

Three major device technologies

hole injection
Extra
junction

Courtesy of Powerex, Inc.

Typical IGBT Driver Circuit
Typically +15 V for turn on
Typically - 5 to -15 V for turn off

Control signal

IGBT

Powerex IGBT Module Structure

Powerex high voltage IGBT package

Emitter voltage

The unijunction transistor fires
when its emitter voltage reaches VP.
VP

Then, the emitter voltage
drops due to its negative
resistance characteristic.
Base 2

Emitter current
Emitter

The UJT is not useful as an amplifier.
It is used in timing and control applications.

Base 1

Other Transistor Types Quiz
BJTs are _________-controlled
amplifiers.

current

FETs are __________-controlled
amplifiers.

voltage

JFETs operate in the __________ mode. depletion
MOSFETs operate in the __________
mode.

enhancement

IGBTs are __________-controlled
amplifiers.

voltage

UJTs are not useful as __________.

amplifiers

Concept Review
• Bipolar junction transistors (BJTs) are controlled by
base current.
• Junction field effect transistors (JFETs) are controlled
by gate voltage.
• JFETs operate in the depletion mode (as normally on
devices).
• Metal oxide semiconductor field effect transistors
(MOSFETs) usually operate in the enhancement mode
(as normally off devices).
• Insulated gate bipolar transistors (IGBTs) are modified
MOSFETs and have very low on-resistance.
• Unijunction transistors (UJTs) are not used as
amplifiers.
Repeat Segment

Concept Preview
• BJTs can be used as switches.
• No base current = switch is off.
• High base current = switch is on.
• The dissipation is always zero in an ideal
switch: off = no current flow and on = no
voltage drop.

• MOSFETs can also be used as switches: no
gate voltage = switch is off and high gate
voltage = switch is on.

How do transistor switches work?
Can be viewed as solid state relays:
they are either ON or they are OFF.
BJT switches are characterized by:
high base current (switch is on)
(or no base current … off)

low resistance from collector to emitter (on)
(or very high resistance … off)
low collector dissipation (on or off)
PC = VCE x IC
PC = 0 x IC = 0 W
(on)
(or PC = VCE x 0 = 0 W … off)

NPN SWITCH
LOAD

RCE @ 
W
0W
DRIVER

The
The
driver
driver
output
output
isiszero
positive,
volts,
IIBB>=I0
0and
andthe
theload
loadis
ison
off
The
driver
output
is
zero
volts,
B = 0 and ILOAD = 0

PNP SWITCH
DRIVER

LOAD

The
Z):
Thedriver
driveroutput
outputisgoes
isoff
off(high
(highthe
Z):the
theresistor
resistor
low:
voltage
drop
pulls
the
base
voltage
up
that
VV
pulls
thethe
base
voltage
upso
soV
that
across
resistor
makes
BE
BE==00
BE negative

PNP SWITCH WITH NPN DRIVER

LOAD

NPN SWITCH WITH PNP DRIVER
(NEGATIVE POWER SUPPLY)

VV
0VV
BE
BE@ @+0.7

VVBE
0 VV
BE@@-0.7

LOAD

STEPPER MOTOR

A

B

C

A

Enhancement mode
power MOSFETs
used as switches

B

C
D

D

Concept Review
• BJTs can be used as switches.
• No base current = switch is off.
• High base current = switch is on.
• The dissipation is always zero in an ideal
switch: off = no current flow and on = no
voltage drop.
• MOSFETs can also be used as switches: no
gate voltage = switch is off and high gate
voltage = switch is on.
Repeat Segment

REVIEW
• Amplification
• Transistors
• Characteristic Curves
• Transistor Testing
• Other Transistor Types
• Transistors as Switches


Slide 25

Electronics
Principles & Applications
Sixth Edition

Charles A. Schuler
Chapter 5

Transistors
(student version)
©2003

Glencoe/McGraw-Hill

INTRODUCTION
• Amplification
• Transistors
• Characteristic Curves
• Transistor Testing
• Other Transistor Types
• Transistors as Switches

Dear Student:
This presentation is arranged in segments.
Each segment is preceded by a Concept
Preview slide and is followed by a Concept
Review slide. When you reach a Concept
Review slide, you can return to the
beginning of that segment by clicking on the
Repeat Segment button. This will allow you
to view that segment again, if you want to.

Concept Preview
• Amplifiers provide gain (the output is larger
than the input).
• Transistors have gain.
• Transistors have a collector, a base, and an
emitter.
• The C-B junction is reverse biased.
• The B-E junction is forward biased.
• Most of the emitter carriers reach the collector.
• The base current is relatively small but controls
the larger currents.

In

Gain =

Amplifier

Out

In

Out

NPN Transistor Structure

The collector is lightly doped.

N

C

The base is thin and
is lightly doped.

P

B

The emitter is heavily doped.

N

E

NPN Transistor Bias
No current flows.
The C-B junction
is reverse biased.

N

C

P

B

N

E

NPN Transistor Bias

The B-E junction
is forward biased.

Current flows.

N

C

P

B

N

E

NPN Transistor Bias
IC
Current flows
everywhere.
Most of the emitter carriers
diffuse through the thin base
When
both
junctions
region since they are attracted
biased....
by are
the collector.

Note that IB is smaller
than IE or IC.

N

C

P

B

N

E

IB

IE

Note: when the
switch opens, all
currents go to zero.
Although IB is smaller
it controls IE and IC.

Gain is something small
controlling something large
(IB is small).

IC
N

C

P

B

N

E

IB

IE

Transistor Structure and Bias Quiz
The heaviest doping is found in
the ___________ region.

emitter

The thinnest of all three regions
is called the ____________.

base

The collector-base junction is
___________ biased.

reverse

The base-emitter junction is
____________ biased.

forward

The majority of the emitter
carriers flow to the ___________.

collector

Concept Review
• Amplifiers provide gain (the output is larger than
the input).
• Transistors have gain.

• Transistors have a collector, a base, and an emitter.
• The C-B junction is reverse biased.
• The B-E junction is forward biased.

• Most of the emitter carriers reach the collector.
• The base current is relatively small but controls the
larger currents.
Repeat Segment

Concept Preview
• The base to collector gain is called b (beta).
• To find b, divide the collector current by the
base current.
• The emitter current is the largest since it is the
sum of the base and collector currents.
• PNP transistors have opposite polarity from
NPN transistors.

• In an NPN transistor, the major flow is made
up of electrons.
• In a PNP transistor, the major flow is made up
of holes.

IC = 99 mA

The current gain from
base to collector
is called b.
IB = 1 mA

b =

99
ICmA
1IBmA

= 99

IE = 100 mA

C
P

B

N

E

IC = 99 mA
Kirchhoff’s
current law:

IB = 1 mA

C
P

B

N

E

IE = I B + I C

= 1 mA + 99 mA
= 100 mA
IE = 100 mA

IC = 99 mA
In a PNP transistor,
holes flow from
emitter to collector.

IB = 1 mA
Notice the PNP
bias voltages.

C
B

E

IE = 100 mA

Transistor Currents Quiz
b is the ratio of collector current to
______ current.

base

The sum of the base and collector
currents is the __________ current.

emitter

In NPN transistors, the flow from emitter
to collector is composed of _______.

electrons

In PNP transistors, the flow from emitter
to collector is composed of _______.

holes

Both NPN and PNP transistors show
__________ gain.

current

Concept Review
• The base to collector gain is called b (beta).
• To find b, divide the collector current by the
base current.
• The emitter current is the largest since it is the
sum of the base and collector currents.
• PNP transistors have opposite polarity from
NPN transistors.
• In an NPN transistor, the major flow is made
up of electrons.
• In a PNP transistor, the major flow is made up
of holes.
Repeat Segment

Concept Preview
• The NPN schematic symbol shows the emitter
arrow as Not Pointing iN.
• The collector curves are a graph of collector
voltage versus collector current.
• Both dc beta (bdc) and ac beta (bac) can be
determined from the collector curves.
• The collector circuit of a transistor can be
modeled as a resistor, as a closed switch or as
an open switch.
• The amount of base current determines which
of the three models applies.

NPN Schematic Symbol
Collector

Base

C
B E

Emitter
Memory aid: NPN
means Not Pointing iN.

PNP Schematic Symbol
Collector

Base

C
B E

Emitter

IC

This circuit is used to
collect IC versus
VCE data for
several values of IB.
C

IB
B

E

VCE

When graphed, the data provide an
NPN collector family of curves.
100 mA

14
12
10
IC in mA 8
6
4
2

80 mA
60 mA
40 mA
20 mA

0 2 4 6

8 10 12 14 16 18

VCE in Volts

0 mA

100 mA

14
12
10
IC in mA 8
6
4
2

80 mA
60 mA

40 mA
20 mA

0 2 4 6

8 10 12 14 16 18

0 mA

VCE in Volts

b =

14
mA
6ICmA
40
IB mA
100
mA

150
== 140

This type of gain
is called bdc or hFE.

100 mA

14
12
10
IC in mA 8
6
4
2

80 mA
60 mA

40 mA
20 mA

0 2 4 6

bac =

2.5DImA
C
20DImA
B

8 10 12 14 16 18

0 mA

VCE in Volts
= 125

Another type of gain
is called bac or hfe.

100 mA

14
12
10
IC in mA 8
6
4
2

80 mA
60 mA

40 mA
20 mA

0 2 4 6
IB

C

8 10 12 14 16 18
VCE in Volts

0 mA

With these values of IB:
The C-E model is a resistor.
E

100 mA

14
12
10
IC in mA 8
6
4
2
0 2 4 6
IB

80 mA
60 mA

40 mA
20 mA
8 10 12 14 16 18
VCE in Volts

0 mA

When IB >> 100 mA
VCE @ 0
The model is a closed switch.

100 mA

14
12
10
IC in mA 8
6
4
2
0 2 4 6
IB

80 mA
60 mA

40 mA
20 mA
8 10 12 14 16 18
VCE in Volts

0 mA

When IB = 0
IC = 0
The model is an open switch.

Transistor Operating Conditions Quiz
When IB is large and VCE @ 0, the transistor
acts as a ___________ switch.
closed
When IB = 0 and IC = 0, the transistor
acts as an ___________ switch.

open

When IB > 0 and VCE > 0, the transistor
acts as a ___________.

resistor

Two current gain measures are bdc and
__________.

bac

The symbol hfe is the same as _________.

bac

Concept Review
• The NPN schematic symbol shows the emitter
arrow as Not Pointing iN.
• The collector curves are a graph of collector
voltage versus collector current.
• Both dc beta (bdc) and ac beta (bac) can be
determined from the collector curves.
• The collector circuit of a transistor can be
modeled as a resistor, as a closed switch or as
an open switch.
• The amount of base current determines which
of the three models applies.
Repeat Segment

Concept Preview
• It is possible to test transistors out-of-circuit
using an ohmmeter.
• The E-B and C-B junctions act as diodes
during ohmmeter testing.

• The C-E test shows a high resistance because
two junctions are involved; one of which is
reverse biased by the ohmmeter.
• Gain can be verified by using a resistor in
conjunction with the ohmmeter test.

NPN

V

mA

E
B
C

The E-B junction is forward biased by the ohmmeter.

NPN

V

mA

E
B
C

The C-E resistance is very high.

NPN

V

mA

E
B
C
100 kW

The meter reading is < 100 kW due to gain.

Concept Review
• It is possible to test transistors out-of-circuit
using an ohmmeter.
• The E-B and C-B junctions act as diodes
during ohmmeter testing.
• The C-E test shows a high resistance because
two junctions are involved; one of which is
reverse biased by the ohmmeter.
• Gain can be verified by using a resistor in
conjunction with the ohmmeter test.
Repeat Segment

Concept Preview
• Bipolar junction transistors (BJTs) are controlled by
base current.
• Junction field effect transistors (JFETs) are controlled
by gate voltage.

• JFETs operate in the depletion mode (as normally on
devices).
• Metal oxide semiconductor field effect transistors
(MOSFETs) usually operate in the enhancement mode
(as normally off devices).
• Insulated gate bipolar transistors (IGBTs) are modified
MOSFETs and have very low on-resistance.
• Unijunction transistors (UJTs) are not used as
amplifiers.

Current In

The BJT is
a current
amplifier.

Current
Amplifier

Current Out

Voltage In

The JFET is
a voltage
controlled
amplifier.

Voltage
Amplifier

Current Out

Source

Gate

Drain

P

N-channel
P-type substrate
Structure of an
N-channel JFET

The channel has carriers so it
conducts from source to drain.

Drain

Gate
Source

Source

Gate

Drain

P

N-channel
P-type substrate

A negative gate voltage
can push the carriers from
the channel and turn
the JFET off.

Drain

Gate
Source

0V
-1 V
-2 V

ID in mA

-3 V

VGS

-4 V

0

-5 V
VDS in Volts

This is known as a depletion-mode device.
N-channel JFET drain family of characteristic curves

It’s possible to make enhancement
type field effect transistors as well.
Metal
oxide
insulator

Drain

n

Gate

VGG

D

VDD

p

G

n

S
N-channel
MOSFET

Source

Gate bias enhances the channel and turns the device on.

5V
4V
3V

ID in mA

2V

VGS

1V

0

0V
Drain

VDS in Volts

Enhancement mode
MOSFET drain family of
characteristic curves

Gate
Source

The IGBT (insulated gate bipolar transistor)
Operation and structure
similar to a MOSFET
Voltage controlled
(like the MOSFET)
Has one more junction
than a MOSFET
Hole injection reduces
the collector resistance

Faster turn off than
BJTs but not as fast
as MOSFETS

RCE = 8.33 mW

Three major device technologies

hole injection
Extra
junction

Courtesy of Powerex, Inc.

Typical IGBT Driver Circuit
Typically +15 V for turn on
Typically - 5 to -15 V for turn off

Control signal

IGBT

Powerex IGBT Module Structure

Powerex high voltage IGBT package

Emitter voltage

The unijunction transistor fires
when its emitter voltage reaches VP.
VP

Then, the emitter voltage
drops due to its negative
resistance characteristic.
Base 2

Emitter current
Emitter

The UJT is not useful as an amplifier.
It is used in timing and control applications.

Base 1

Other Transistor Types Quiz
BJTs are _________-controlled
amplifiers.

current

FETs are __________-controlled
amplifiers.

voltage

JFETs operate in the __________ mode. depletion
MOSFETs operate in the __________
mode.

enhancement

IGBTs are __________-controlled
amplifiers.

voltage

UJTs are not useful as __________.

amplifiers

Concept Review
• Bipolar junction transistors (BJTs) are controlled by
base current.
• Junction field effect transistors (JFETs) are controlled
by gate voltage.
• JFETs operate in the depletion mode (as normally on
devices).
• Metal oxide semiconductor field effect transistors
(MOSFETs) usually operate in the enhancement mode
(as normally off devices).
• Insulated gate bipolar transistors (IGBTs) are modified
MOSFETs and have very low on-resistance.
• Unijunction transistors (UJTs) are not used as
amplifiers.
Repeat Segment

Concept Preview
• BJTs can be used as switches.
• No base current = switch is off.
• High base current = switch is on.
• The dissipation is always zero in an ideal
switch: off = no current flow and on = no
voltage drop.

• MOSFETs can also be used as switches: no
gate voltage = switch is off and high gate
voltage = switch is on.

How do transistor switches work?
Can be viewed as solid state relays:
they are either ON or they are OFF.
BJT switches are characterized by:
high base current (switch is on)
(or no base current … off)

low resistance from collector to emitter (on)
(or very high resistance … off)
low collector dissipation (on or off)
PC = VCE x IC
PC = 0 x IC = 0 W
(on)
(or PC = VCE x 0 = 0 W … off)

NPN SWITCH
LOAD

RCE @ 
W
0W
DRIVER

The
The
driver
driver
output
output
isiszero
positive,
volts,
IIBB>=I0
0and
andthe
theload
loadis
ison
off
The
driver
output
is
zero
volts,
B = 0 and ILOAD = 0

PNP SWITCH
DRIVER

LOAD

The
Z):
Thedriver
driveroutput
outputisgoes
isoff
off(high
(highthe
Z):the
theresistor
resistor
low:
voltage
drop
pulls
the
base
voltage
up
that
VV
pulls
thethe
base
voltage
upso
soV
that
across
resistor
makes
BE
BE==00
BE negative

PNP SWITCH WITH NPN DRIVER

LOAD

NPN SWITCH WITH PNP DRIVER
(NEGATIVE POWER SUPPLY)

VV
0VV
BE
BE@ @+0.7

VVBE
0 VV
BE@@-0.7

LOAD

STEPPER MOTOR

A

B

C

A

Enhancement mode
power MOSFETs
used as switches

B

C
D

D

Concept Review
• BJTs can be used as switches.
• No base current = switch is off.
• High base current = switch is on.
• The dissipation is always zero in an ideal
switch: off = no current flow and on = no
voltage drop.
• MOSFETs can also be used as switches: no
gate voltage = switch is off and high gate
voltage = switch is on.
Repeat Segment

REVIEW
• Amplification
• Transistors
• Characteristic Curves
• Transistor Testing
• Other Transistor Types
• Transistors as Switches


Slide 26

Electronics
Principles & Applications
Sixth Edition

Charles A. Schuler
Chapter 5

Transistors
(student version)
©2003

Glencoe/McGraw-Hill

INTRODUCTION
• Amplification
• Transistors
• Characteristic Curves
• Transistor Testing
• Other Transistor Types
• Transistors as Switches

Dear Student:
This presentation is arranged in segments.
Each segment is preceded by a Concept
Preview slide and is followed by a Concept
Review slide. When you reach a Concept
Review slide, you can return to the
beginning of that segment by clicking on the
Repeat Segment button. This will allow you
to view that segment again, if you want to.

Concept Preview
• Amplifiers provide gain (the output is larger
than the input).
• Transistors have gain.
• Transistors have a collector, a base, and an
emitter.
• The C-B junction is reverse biased.
• The B-E junction is forward biased.
• Most of the emitter carriers reach the collector.
• The base current is relatively small but controls
the larger currents.

In

Gain =

Amplifier

Out

In

Out

NPN Transistor Structure

The collector is lightly doped.

N

C

The base is thin and
is lightly doped.

P

B

The emitter is heavily doped.

N

E

NPN Transistor Bias
No current flows.
The C-B junction
is reverse biased.

N

C

P

B

N

E

NPN Transistor Bias

The B-E junction
is forward biased.

Current flows.

N

C

P

B

N

E

NPN Transistor Bias
IC
Current flows
everywhere.
Most of the emitter carriers
diffuse through the thin base
When
both
junctions
region since they are attracted
biased....
by are
the collector.

Note that IB is smaller
than IE or IC.

N

C

P

B

N

E

IB

IE

Note: when the
switch opens, all
currents go to zero.
Although IB is smaller
it controls IE and IC.

Gain is something small
controlling something large
(IB is small).

IC
N

C

P

B

N

E

IB

IE

Transistor Structure and Bias Quiz
The heaviest doping is found in
the ___________ region.

emitter

The thinnest of all three regions
is called the ____________.

base

The collector-base junction is
___________ biased.

reverse

The base-emitter junction is
____________ biased.

forward

The majority of the emitter
carriers flow to the ___________.

collector

Concept Review
• Amplifiers provide gain (the output is larger than
the input).
• Transistors have gain.

• Transistors have a collector, a base, and an emitter.
• The C-B junction is reverse biased.
• The B-E junction is forward biased.

• Most of the emitter carriers reach the collector.
• The base current is relatively small but controls the
larger currents.
Repeat Segment

Concept Preview
• The base to collector gain is called b (beta).
• To find b, divide the collector current by the
base current.
• The emitter current is the largest since it is the
sum of the base and collector currents.
• PNP transistors have opposite polarity from
NPN transistors.

• In an NPN transistor, the major flow is made
up of electrons.
• In a PNP transistor, the major flow is made up
of holes.

IC = 99 mA

The current gain from
base to collector
is called b.
IB = 1 mA

b =

99
ICmA
1IBmA

= 99

IE = 100 mA

C
P

B

N

E

IC = 99 mA
Kirchhoff’s
current law:

IB = 1 mA

C
P

B

N

E

IE = I B + I C

= 1 mA + 99 mA
= 100 mA
IE = 100 mA

IC = 99 mA
In a PNP transistor,
holes flow from
emitter to collector.

IB = 1 mA
Notice the PNP
bias voltages.

C
B

E

IE = 100 mA

Transistor Currents Quiz
b is the ratio of collector current to
______ current.

base

The sum of the base and collector
currents is the __________ current.

emitter

In NPN transistors, the flow from emitter
to collector is composed of _______.

electrons

In PNP transistors, the flow from emitter
to collector is composed of _______.

holes

Both NPN and PNP transistors show
__________ gain.

current

Concept Review
• The base to collector gain is called b (beta).
• To find b, divide the collector current by the
base current.
• The emitter current is the largest since it is the
sum of the base and collector currents.
• PNP transistors have opposite polarity from
NPN transistors.
• In an NPN transistor, the major flow is made
up of electrons.
• In a PNP transistor, the major flow is made up
of holes.
Repeat Segment

Concept Preview
• The NPN schematic symbol shows the emitter
arrow as Not Pointing iN.
• The collector curves are a graph of collector
voltage versus collector current.
• Both dc beta (bdc) and ac beta (bac) can be
determined from the collector curves.
• The collector circuit of a transistor can be
modeled as a resistor, as a closed switch or as
an open switch.
• The amount of base current determines which
of the three models applies.

NPN Schematic Symbol
Collector

Base

C
B E

Emitter
Memory aid: NPN
means Not Pointing iN.

PNP Schematic Symbol
Collector

Base

C
B E

Emitter

IC

This circuit is used to
collect IC versus
VCE data for
several values of IB.
C

IB
B

E

VCE

When graphed, the data provide an
NPN collector family of curves.
100 mA

14
12
10
IC in mA 8
6
4
2

80 mA
60 mA
40 mA
20 mA

0 2 4 6

8 10 12 14 16 18

VCE in Volts

0 mA

100 mA

14
12
10
IC in mA 8
6
4
2

80 mA
60 mA

40 mA
20 mA

0 2 4 6

8 10 12 14 16 18

0 mA

VCE in Volts

b =

14
mA
6ICmA
40
IB mA
100
mA

150
== 140

This type of gain
is called bdc or hFE.

100 mA

14
12
10
IC in mA 8
6
4
2

80 mA
60 mA

40 mA
20 mA

0 2 4 6

bac =

2.5DImA
C
20DImA
B

8 10 12 14 16 18

0 mA

VCE in Volts
= 125

Another type of gain
is called bac or hfe.

100 mA

14
12
10
IC in mA 8
6
4
2

80 mA
60 mA

40 mA
20 mA

0 2 4 6
IB

C

8 10 12 14 16 18
VCE in Volts

0 mA

With these values of IB:
The C-E model is a resistor.
E

100 mA

14
12
10
IC in mA 8
6
4
2
0 2 4 6
IB

80 mA
60 mA

40 mA
20 mA
8 10 12 14 16 18
VCE in Volts

0 mA

When IB >> 100 mA
VCE @ 0
The model is a closed switch.

100 mA

14
12
10
IC in mA 8
6
4
2
0 2 4 6
IB

80 mA
60 mA

40 mA
20 mA
8 10 12 14 16 18
VCE in Volts

0 mA

When IB = 0
IC = 0
The model is an open switch.

Transistor Operating Conditions Quiz
When IB is large and VCE @ 0, the transistor
acts as a ___________ switch.
closed
When IB = 0 and IC = 0, the transistor
acts as an ___________ switch.

open

When IB > 0 and VCE > 0, the transistor
acts as a ___________.

resistor

Two current gain measures are bdc and
__________.

bac

The symbol hfe is the same as _________.

bac

Concept Review
• The NPN schematic symbol shows the emitter
arrow as Not Pointing iN.
• The collector curves are a graph of collector
voltage versus collector current.
• Both dc beta (bdc) and ac beta (bac) can be
determined from the collector curves.
• The collector circuit of a transistor can be
modeled as a resistor, as a closed switch or as
an open switch.
• The amount of base current determines which
of the three models applies.
Repeat Segment

Concept Preview
• It is possible to test transistors out-of-circuit
using an ohmmeter.
• The E-B and C-B junctions act as diodes
during ohmmeter testing.

• The C-E test shows a high resistance because
two junctions are involved; one of which is
reverse biased by the ohmmeter.
• Gain can be verified by using a resistor in
conjunction with the ohmmeter test.

NPN

V

mA

E
B
C

The E-B junction is forward biased by the ohmmeter.

NPN

V

mA

E
B
C

The C-E resistance is very high.

NPN

V

mA

E
B
C
100 kW

The meter reading is < 100 kW due to gain.

Concept Review
• It is possible to test transistors out-of-circuit
using an ohmmeter.
• The E-B and C-B junctions act as diodes
during ohmmeter testing.
• The C-E test shows a high resistance because
two junctions are involved; one of which is
reverse biased by the ohmmeter.
• Gain can be verified by using a resistor in
conjunction with the ohmmeter test.
Repeat Segment

Concept Preview
• Bipolar junction transistors (BJTs) are controlled by
base current.
• Junction field effect transistors (JFETs) are controlled
by gate voltage.

• JFETs operate in the depletion mode (as normally on
devices).
• Metal oxide semiconductor field effect transistors
(MOSFETs) usually operate in the enhancement mode
(as normally off devices).
• Insulated gate bipolar transistors (IGBTs) are modified
MOSFETs and have very low on-resistance.
• Unijunction transistors (UJTs) are not used as
amplifiers.

Current In

The BJT is
a current
amplifier.

Current
Amplifier

Current Out

Voltage In

The JFET is
a voltage
controlled
amplifier.

Voltage
Amplifier

Current Out

Source

Gate

Drain

P

N-channel
P-type substrate
Structure of an
N-channel JFET

The channel has carriers so it
conducts from source to drain.

Drain

Gate
Source

Source

Gate

Drain

P

N-channel
P-type substrate

A negative gate voltage
can push the carriers from
the channel and turn
the JFET off.

Drain

Gate
Source

0V
-1 V
-2 V

ID in mA

-3 V

VGS

-4 V

0

-5 V
VDS in Volts

This is known as a depletion-mode device.
N-channel JFET drain family of characteristic curves

It’s possible to make enhancement
type field effect transistors as well.
Metal
oxide
insulator

Drain

n

Gate

VGG

D

VDD

p

G

n

S
N-channel
MOSFET

Source

Gate bias enhances the channel and turns the device on.

5V
4V
3V

ID in mA

2V

VGS

1V

0

0V
Drain

VDS in Volts

Enhancement mode
MOSFET drain family of
characteristic curves

Gate
Source

The IGBT (insulated gate bipolar transistor)
Operation and structure
similar to a MOSFET
Voltage controlled
(like the MOSFET)
Has one more junction
than a MOSFET
Hole injection reduces
the collector resistance

Faster turn off than
BJTs but not as fast
as MOSFETS

RCE = 8.33 mW

Three major device technologies

hole injection
Extra
junction

Courtesy of Powerex, Inc.

Typical IGBT Driver Circuit
Typically +15 V for turn on
Typically - 5 to -15 V for turn off

Control signal

IGBT

Powerex IGBT Module Structure

Powerex high voltage IGBT package

Emitter voltage

The unijunction transistor fires
when its emitter voltage reaches VP.
VP

Then, the emitter voltage
drops due to its negative
resistance characteristic.
Base 2

Emitter current
Emitter

The UJT is not useful as an amplifier.
It is used in timing and control applications.

Base 1

Other Transistor Types Quiz
BJTs are _________-controlled
amplifiers.

current

FETs are __________-controlled
amplifiers.

voltage

JFETs operate in the __________ mode. depletion
MOSFETs operate in the __________
mode.

enhancement

IGBTs are __________-controlled
amplifiers.

voltage

UJTs are not useful as __________.

amplifiers

Concept Review
• Bipolar junction transistors (BJTs) are controlled by
base current.
• Junction field effect transistors (JFETs) are controlled
by gate voltage.
• JFETs operate in the depletion mode (as normally on
devices).
• Metal oxide semiconductor field effect transistors
(MOSFETs) usually operate in the enhancement mode
(as normally off devices).
• Insulated gate bipolar transistors (IGBTs) are modified
MOSFETs and have very low on-resistance.
• Unijunction transistors (UJTs) are not used as
amplifiers.
Repeat Segment

Concept Preview
• BJTs can be used as switches.
• No base current = switch is off.
• High base current = switch is on.
• The dissipation is always zero in an ideal
switch: off = no current flow and on = no
voltage drop.

• MOSFETs can also be used as switches: no
gate voltage = switch is off and high gate
voltage = switch is on.

How do transistor switches work?
Can be viewed as solid state relays:
they are either ON or they are OFF.
BJT switches are characterized by:
high base current (switch is on)
(or no base current … off)

low resistance from collector to emitter (on)
(or very high resistance … off)
low collector dissipation (on or off)
PC = VCE x IC
PC = 0 x IC = 0 W
(on)
(or PC = VCE x 0 = 0 W … off)

NPN SWITCH
LOAD

RCE @ 
W
0W
DRIVER

The
The
driver
driver
output
output
isiszero
positive,
volts,
IIBB>=I0
0and
andthe
theload
loadis
ison
off
The
driver
output
is
zero
volts,
B = 0 and ILOAD = 0

PNP SWITCH
DRIVER

LOAD

The
Z):
Thedriver
driveroutput
outputisgoes
isoff
off(high
(highthe
Z):the
theresistor
resistor
low:
voltage
drop
pulls
the
base
voltage
up
that
VV
pulls
thethe
base
voltage
upso
soV
that
across
resistor
makes
BE
BE==00
BE negative

PNP SWITCH WITH NPN DRIVER

LOAD

NPN SWITCH WITH PNP DRIVER
(NEGATIVE POWER SUPPLY)

VV
0VV
BE
BE@ @+0.7

VVBE
0 VV
BE@@-0.7

LOAD

STEPPER MOTOR

A

B

C

A

Enhancement mode
power MOSFETs
used as switches

B

C
D

D

Concept Review
• BJTs can be used as switches.
• No base current = switch is off.
• High base current = switch is on.
• The dissipation is always zero in an ideal
switch: off = no current flow and on = no
voltage drop.
• MOSFETs can also be used as switches: no
gate voltage = switch is off and high gate
voltage = switch is on.
Repeat Segment

REVIEW
• Amplification
• Transistors
• Characteristic Curves
• Transistor Testing
• Other Transistor Types
• Transistors as Switches


Slide 27

Electronics
Principles & Applications
Sixth Edition

Charles A. Schuler
Chapter 5

Transistors
(student version)
©2003

Glencoe/McGraw-Hill

INTRODUCTION
• Amplification
• Transistors
• Characteristic Curves
• Transistor Testing
• Other Transistor Types
• Transistors as Switches

Dear Student:
This presentation is arranged in segments.
Each segment is preceded by a Concept
Preview slide and is followed by a Concept
Review slide. When you reach a Concept
Review slide, you can return to the
beginning of that segment by clicking on the
Repeat Segment button. This will allow you
to view that segment again, if you want to.

Concept Preview
• Amplifiers provide gain (the output is larger
than the input).
• Transistors have gain.
• Transistors have a collector, a base, and an
emitter.
• The C-B junction is reverse biased.
• The B-E junction is forward biased.
• Most of the emitter carriers reach the collector.
• The base current is relatively small but controls
the larger currents.

In

Gain =

Amplifier

Out

In

Out

NPN Transistor Structure

The collector is lightly doped.

N

C

The base is thin and
is lightly doped.

P

B

The emitter is heavily doped.

N

E

NPN Transistor Bias
No current flows.
The C-B junction
is reverse biased.

N

C

P

B

N

E

NPN Transistor Bias

The B-E junction
is forward biased.

Current flows.

N

C

P

B

N

E

NPN Transistor Bias
IC
Current flows
everywhere.
Most of the emitter carriers
diffuse through the thin base
When
both
junctions
region since they are attracted
biased....
by are
the collector.

Note that IB is smaller
than IE or IC.

N

C

P

B

N

E

IB

IE

Note: when the
switch opens, all
currents go to zero.
Although IB is smaller
it controls IE and IC.

Gain is something small
controlling something large
(IB is small).

IC
N

C

P

B

N

E

IB

IE

Transistor Structure and Bias Quiz
The heaviest doping is found in
the ___________ region.

emitter

The thinnest of all three regions
is called the ____________.

base

The collector-base junction is
___________ biased.

reverse

The base-emitter junction is
____________ biased.

forward

The majority of the emitter
carriers flow to the ___________.

collector

Concept Review
• Amplifiers provide gain (the output is larger than
the input).
• Transistors have gain.

• Transistors have a collector, a base, and an emitter.
• The C-B junction is reverse biased.
• The B-E junction is forward biased.

• Most of the emitter carriers reach the collector.
• The base current is relatively small but controls the
larger currents.
Repeat Segment

Concept Preview
• The base to collector gain is called b (beta).
• To find b, divide the collector current by the
base current.
• The emitter current is the largest since it is the
sum of the base and collector currents.
• PNP transistors have opposite polarity from
NPN transistors.

• In an NPN transistor, the major flow is made
up of electrons.
• In a PNP transistor, the major flow is made up
of holes.

IC = 99 mA

The current gain from
base to collector
is called b.
IB = 1 mA

b =

99
ICmA
1IBmA

= 99

IE = 100 mA

C
P

B

N

E

IC = 99 mA
Kirchhoff’s
current law:

IB = 1 mA

C
P

B

N

E

IE = I B + I C

= 1 mA + 99 mA
= 100 mA
IE = 100 mA

IC = 99 mA
In a PNP transistor,
holes flow from
emitter to collector.

IB = 1 mA
Notice the PNP
bias voltages.

C
B

E

IE = 100 mA

Transistor Currents Quiz
b is the ratio of collector current to
______ current.

base

The sum of the base and collector
currents is the __________ current.

emitter

In NPN transistors, the flow from emitter
to collector is composed of _______.

electrons

In PNP transistors, the flow from emitter
to collector is composed of _______.

holes

Both NPN and PNP transistors show
__________ gain.

current

Concept Review
• The base to collector gain is called b (beta).
• To find b, divide the collector current by the
base current.
• The emitter current is the largest since it is the
sum of the base and collector currents.
• PNP transistors have opposite polarity from
NPN transistors.
• In an NPN transistor, the major flow is made
up of electrons.
• In a PNP transistor, the major flow is made up
of holes.
Repeat Segment

Concept Preview
• The NPN schematic symbol shows the emitter
arrow as Not Pointing iN.
• The collector curves are a graph of collector
voltage versus collector current.
• Both dc beta (bdc) and ac beta (bac) can be
determined from the collector curves.
• The collector circuit of a transistor can be
modeled as a resistor, as a closed switch or as
an open switch.
• The amount of base current determines which
of the three models applies.

NPN Schematic Symbol
Collector

Base

C
B E

Emitter
Memory aid: NPN
means Not Pointing iN.

PNP Schematic Symbol
Collector

Base

C
B E

Emitter

IC

This circuit is used to
collect IC versus
VCE data for
several values of IB.
C

IB
B

E

VCE

When graphed, the data provide an
NPN collector family of curves.
100 mA

14
12
10
IC in mA 8
6
4
2

80 mA
60 mA
40 mA
20 mA

0 2 4 6

8 10 12 14 16 18

VCE in Volts

0 mA

100 mA

14
12
10
IC in mA 8
6
4
2

80 mA
60 mA

40 mA
20 mA

0 2 4 6

8 10 12 14 16 18

0 mA

VCE in Volts

b =

14
mA
6ICmA
40
IB mA
100
mA

150
== 140

This type of gain
is called bdc or hFE.

100 mA

14
12
10
IC in mA 8
6
4
2

80 mA
60 mA

40 mA
20 mA

0 2 4 6

bac =

2.5DImA
C
20DImA
B

8 10 12 14 16 18

0 mA

VCE in Volts
= 125

Another type of gain
is called bac or hfe.

100 mA

14
12
10
IC in mA 8
6
4
2

80 mA
60 mA

40 mA
20 mA

0 2 4 6
IB

C

8 10 12 14 16 18
VCE in Volts

0 mA

With these values of IB:
The C-E model is a resistor.
E

100 mA

14
12
10
IC in mA 8
6
4
2
0 2 4 6
IB

80 mA
60 mA

40 mA
20 mA
8 10 12 14 16 18
VCE in Volts

0 mA

When IB >> 100 mA
VCE @ 0
The model is a closed switch.

100 mA

14
12
10
IC in mA 8
6
4
2
0 2 4 6
IB

80 mA
60 mA

40 mA
20 mA
8 10 12 14 16 18
VCE in Volts

0 mA

When IB = 0
IC = 0
The model is an open switch.

Transistor Operating Conditions Quiz
When IB is large and VCE @ 0, the transistor
acts as a ___________ switch.
closed
When IB = 0 and IC = 0, the transistor
acts as an ___________ switch.

open

When IB > 0 and VCE > 0, the transistor
acts as a ___________.

resistor

Two current gain measures are bdc and
__________.

bac

The symbol hfe is the same as _________.

bac

Concept Review
• The NPN schematic symbol shows the emitter
arrow as Not Pointing iN.
• The collector curves are a graph of collector
voltage versus collector current.
• Both dc beta (bdc) and ac beta (bac) can be
determined from the collector curves.
• The collector circuit of a transistor can be
modeled as a resistor, as a closed switch or as
an open switch.
• The amount of base current determines which
of the three models applies.
Repeat Segment

Concept Preview
• It is possible to test transistors out-of-circuit
using an ohmmeter.
• The E-B and C-B junctions act as diodes
during ohmmeter testing.

• The C-E test shows a high resistance because
two junctions are involved; one of which is
reverse biased by the ohmmeter.
• Gain can be verified by using a resistor in
conjunction with the ohmmeter test.

NPN

V

mA

E
B
C

The E-B junction is forward biased by the ohmmeter.

NPN

V

mA

E
B
C

The C-E resistance is very high.

NPN

V

mA

E
B
C
100 kW

The meter reading is < 100 kW due to gain.

Concept Review
• It is possible to test transistors out-of-circuit
using an ohmmeter.
• The E-B and C-B junctions act as diodes
during ohmmeter testing.
• The C-E test shows a high resistance because
two junctions are involved; one of which is
reverse biased by the ohmmeter.
• Gain can be verified by using a resistor in
conjunction with the ohmmeter test.
Repeat Segment

Concept Preview
• Bipolar junction transistors (BJTs) are controlled by
base current.
• Junction field effect transistors (JFETs) are controlled
by gate voltage.

• JFETs operate in the depletion mode (as normally on
devices).
• Metal oxide semiconductor field effect transistors
(MOSFETs) usually operate in the enhancement mode
(as normally off devices).
• Insulated gate bipolar transistors (IGBTs) are modified
MOSFETs and have very low on-resistance.
• Unijunction transistors (UJTs) are not used as
amplifiers.

Current In

The BJT is
a current
amplifier.

Current
Amplifier

Current Out

Voltage In

The JFET is
a voltage
controlled
amplifier.

Voltage
Amplifier

Current Out

Source

Gate

Drain

P

N-channel
P-type substrate
Structure of an
N-channel JFET

The channel has carriers so it
conducts from source to drain.

Drain

Gate
Source

Source

Gate

Drain

P

N-channel
P-type substrate

A negative gate voltage
can push the carriers from
the channel and turn
the JFET off.

Drain

Gate
Source

0V
-1 V
-2 V

ID in mA

-3 V

VGS

-4 V

0

-5 V
VDS in Volts

This is known as a depletion-mode device.
N-channel JFET drain family of characteristic curves

It’s possible to make enhancement
type field effect transistors as well.
Metal
oxide
insulator

Drain

n

Gate

VGG

D

VDD

p

G

n

S
N-channel
MOSFET

Source

Gate bias enhances the channel and turns the device on.

5V
4V
3V

ID in mA

2V

VGS

1V

0

0V
Drain

VDS in Volts

Enhancement mode
MOSFET drain family of
characteristic curves

Gate
Source

The IGBT (insulated gate bipolar transistor)
Operation and structure
similar to a MOSFET
Voltage controlled
(like the MOSFET)
Has one more junction
than a MOSFET
Hole injection reduces
the collector resistance

Faster turn off than
BJTs but not as fast
as MOSFETS

RCE = 8.33 mW

Three major device technologies

hole injection
Extra
junction

Courtesy of Powerex, Inc.

Typical IGBT Driver Circuit
Typically +15 V for turn on
Typically - 5 to -15 V for turn off

Control signal

IGBT

Powerex IGBT Module Structure

Powerex high voltage IGBT package

Emitter voltage

The unijunction transistor fires
when its emitter voltage reaches VP.
VP

Then, the emitter voltage
drops due to its negative
resistance characteristic.
Base 2

Emitter current
Emitter

The UJT is not useful as an amplifier.
It is used in timing and control applications.

Base 1

Other Transistor Types Quiz
BJTs are _________-controlled
amplifiers.

current

FETs are __________-controlled
amplifiers.

voltage

JFETs operate in the __________ mode. depletion
MOSFETs operate in the __________
mode.

enhancement

IGBTs are __________-controlled
amplifiers.

voltage

UJTs are not useful as __________.

amplifiers

Concept Review
• Bipolar junction transistors (BJTs) are controlled by
base current.
• Junction field effect transistors (JFETs) are controlled
by gate voltage.
• JFETs operate in the depletion mode (as normally on
devices).
• Metal oxide semiconductor field effect transistors
(MOSFETs) usually operate in the enhancement mode
(as normally off devices).
• Insulated gate bipolar transistors (IGBTs) are modified
MOSFETs and have very low on-resistance.
• Unijunction transistors (UJTs) are not used as
amplifiers.
Repeat Segment

Concept Preview
• BJTs can be used as switches.
• No base current = switch is off.
• High base current = switch is on.
• The dissipation is always zero in an ideal
switch: off = no current flow and on = no
voltage drop.

• MOSFETs can also be used as switches: no
gate voltage = switch is off and high gate
voltage = switch is on.

How do transistor switches work?
Can be viewed as solid state relays:
they are either ON or they are OFF.
BJT switches are characterized by:
high base current (switch is on)
(or no base current … off)

low resistance from collector to emitter (on)
(or very high resistance … off)
low collector dissipation (on or off)
PC = VCE x IC
PC = 0 x IC = 0 W
(on)
(or PC = VCE x 0 = 0 W … off)

NPN SWITCH
LOAD

RCE @ 
W
0W
DRIVER

The
The
driver
driver
output
output
isiszero
positive,
volts,
IIBB>=I0
0and
andthe
theload
loadis
ison
off
The
driver
output
is
zero
volts,
B = 0 and ILOAD = 0

PNP SWITCH
DRIVER

LOAD

The
Z):
Thedriver
driveroutput
outputisgoes
isoff
off(high
(highthe
Z):the
theresistor
resistor
low:
voltage
drop
pulls
the
base
voltage
up
that
VV
pulls
thethe
base
voltage
upso
soV
that
across
resistor
makes
BE
BE==00
BE negative

PNP SWITCH WITH NPN DRIVER

LOAD

NPN SWITCH WITH PNP DRIVER
(NEGATIVE POWER SUPPLY)

VV
0VV
BE
BE@ @+0.7

VVBE
0 VV
BE@@-0.7

LOAD

STEPPER MOTOR

A

B

C

A

Enhancement mode
power MOSFETs
used as switches

B

C
D

D

Concept Review
• BJTs can be used as switches.
• No base current = switch is off.
• High base current = switch is on.
• The dissipation is always zero in an ideal
switch: off = no current flow and on = no
voltage drop.
• MOSFETs can also be used as switches: no
gate voltage = switch is off and high gate
voltage = switch is on.
Repeat Segment

REVIEW
• Amplification
• Transistors
• Characteristic Curves
• Transistor Testing
• Other Transistor Types
• Transistors as Switches


Slide 28

Electronics
Principles & Applications
Sixth Edition

Charles A. Schuler
Chapter 5

Transistors
(student version)
©2003

Glencoe/McGraw-Hill

INTRODUCTION
• Amplification
• Transistors
• Characteristic Curves
• Transistor Testing
• Other Transistor Types
• Transistors as Switches

Dear Student:
This presentation is arranged in segments.
Each segment is preceded by a Concept
Preview slide and is followed by a Concept
Review slide. When you reach a Concept
Review slide, you can return to the
beginning of that segment by clicking on the
Repeat Segment button. This will allow you
to view that segment again, if you want to.

Concept Preview
• Amplifiers provide gain (the output is larger
than the input).
• Transistors have gain.
• Transistors have a collector, a base, and an
emitter.
• The C-B junction is reverse biased.
• The B-E junction is forward biased.
• Most of the emitter carriers reach the collector.
• The base current is relatively small but controls
the larger currents.

In

Gain =

Amplifier

Out

In

Out

NPN Transistor Structure

The collector is lightly doped.

N

C

The base is thin and
is lightly doped.

P

B

The emitter is heavily doped.

N

E

NPN Transistor Bias
No current flows.
The C-B junction
is reverse biased.

N

C

P

B

N

E

NPN Transistor Bias

The B-E junction
is forward biased.

Current flows.

N

C

P

B

N

E

NPN Transistor Bias
IC
Current flows
everywhere.
Most of the emitter carriers
diffuse through the thin base
When
both
junctions
region since they are attracted
biased....
by are
the collector.

Note that IB is smaller
than IE or IC.

N

C

P

B

N

E

IB

IE

Note: when the
switch opens, all
currents go to zero.
Although IB is smaller
it controls IE and IC.

Gain is something small
controlling something large
(IB is small).

IC
N

C

P

B

N

E

IB

IE

Transistor Structure and Bias Quiz
The heaviest doping is found in
the ___________ region.

emitter

The thinnest of all three regions
is called the ____________.

base

The collector-base junction is
___________ biased.

reverse

The base-emitter junction is
____________ biased.

forward

The majority of the emitter
carriers flow to the ___________.

collector

Concept Review
• Amplifiers provide gain (the output is larger than
the input).
• Transistors have gain.

• Transistors have a collector, a base, and an emitter.
• The C-B junction is reverse biased.
• The B-E junction is forward biased.

• Most of the emitter carriers reach the collector.
• The base current is relatively small but controls the
larger currents.
Repeat Segment

Concept Preview
• The base to collector gain is called b (beta).
• To find b, divide the collector current by the
base current.
• The emitter current is the largest since it is the
sum of the base and collector currents.
• PNP transistors have opposite polarity from
NPN transistors.

• In an NPN transistor, the major flow is made
up of electrons.
• In a PNP transistor, the major flow is made up
of holes.

IC = 99 mA

The current gain from
base to collector
is called b.
IB = 1 mA

b =

99
ICmA
1IBmA

= 99

IE = 100 mA

C
P

B

N

E

IC = 99 mA
Kirchhoff’s
current law:

IB = 1 mA

C
P

B

N

E

IE = I B + I C

= 1 mA + 99 mA
= 100 mA
IE = 100 mA

IC = 99 mA
In a PNP transistor,
holes flow from
emitter to collector.

IB = 1 mA
Notice the PNP
bias voltages.

C
B

E

IE = 100 mA

Transistor Currents Quiz
b is the ratio of collector current to
______ current.

base

The sum of the base and collector
currents is the __________ current.

emitter

In NPN transistors, the flow from emitter
to collector is composed of _______.

electrons

In PNP transistors, the flow from emitter
to collector is composed of _______.

holes

Both NPN and PNP transistors show
__________ gain.

current

Concept Review
• The base to collector gain is called b (beta).
• To find b, divide the collector current by the
base current.
• The emitter current is the largest since it is the
sum of the base and collector currents.
• PNP transistors have opposite polarity from
NPN transistors.
• In an NPN transistor, the major flow is made
up of electrons.
• In a PNP transistor, the major flow is made up
of holes.
Repeat Segment

Concept Preview
• The NPN schematic symbol shows the emitter
arrow as Not Pointing iN.
• The collector curves are a graph of collector
voltage versus collector current.
• Both dc beta (bdc) and ac beta (bac) can be
determined from the collector curves.
• The collector circuit of a transistor can be
modeled as a resistor, as a closed switch or as
an open switch.
• The amount of base current determines which
of the three models applies.

NPN Schematic Symbol
Collector

Base

C
B E

Emitter
Memory aid: NPN
means Not Pointing iN.

PNP Schematic Symbol
Collector

Base

C
B E

Emitter

IC

This circuit is used to
collect IC versus
VCE data for
several values of IB.
C

IB
B

E

VCE

When graphed, the data provide an
NPN collector family of curves.
100 mA

14
12
10
IC in mA 8
6
4
2

80 mA
60 mA
40 mA
20 mA

0 2 4 6

8 10 12 14 16 18

VCE in Volts

0 mA

100 mA

14
12
10
IC in mA 8
6
4
2

80 mA
60 mA

40 mA
20 mA

0 2 4 6

8 10 12 14 16 18

0 mA

VCE in Volts

b =

14
mA
6ICmA
40
IB mA
100
mA

150
== 140

This type of gain
is called bdc or hFE.

100 mA

14
12
10
IC in mA 8
6
4
2

80 mA
60 mA

40 mA
20 mA

0 2 4 6

bac =

2.5DImA
C
20DImA
B

8 10 12 14 16 18

0 mA

VCE in Volts
= 125

Another type of gain
is called bac or hfe.

100 mA

14
12
10
IC in mA 8
6
4
2

80 mA
60 mA

40 mA
20 mA

0 2 4 6
IB

C

8 10 12 14 16 18
VCE in Volts

0 mA

With these values of IB:
The C-E model is a resistor.
E

100 mA

14
12
10
IC in mA 8
6
4
2
0 2 4 6
IB

80 mA
60 mA

40 mA
20 mA
8 10 12 14 16 18
VCE in Volts

0 mA

When IB >> 100 mA
VCE @ 0
The model is a closed switch.

100 mA

14
12
10
IC in mA 8
6
4
2
0 2 4 6
IB

80 mA
60 mA

40 mA
20 mA
8 10 12 14 16 18
VCE in Volts

0 mA

When IB = 0
IC = 0
The model is an open switch.

Transistor Operating Conditions Quiz
When IB is large and VCE @ 0, the transistor
acts as a ___________ switch.
closed
When IB = 0 and IC = 0, the transistor
acts as an ___________ switch.

open

When IB > 0 and VCE > 0, the transistor
acts as a ___________.

resistor

Two current gain measures are bdc and
__________.

bac

The symbol hfe is the same as _________.

bac

Concept Review
• The NPN schematic symbol shows the emitter
arrow as Not Pointing iN.
• The collector curves are a graph of collector
voltage versus collector current.
• Both dc beta (bdc) and ac beta (bac) can be
determined from the collector curves.
• The collector circuit of a transistor can be
modeled as a resistor, as a closed switch or as
an open switch.
• The amount of base current determines which
of the three models applies.
Repeat Segment

Concept Preview
• It is possible to test transistors out-of-circuit
using an ohmmeter.
• The E-B and C-B junctions act as diodes
during ohmmeter testing.

• The C-E test shows a high resistance because
two junctions are involved; one of which is
reverse biased by the ohmmeter.
• Gain can be verified by using a resistor in
conjunction with the ohmmeter test.

NPN

V

mA

E
B
C

The E-B junction is forward biased by the ohmmeter.

NPN

V

mA

E
B
C

The C-E resistance is very high.

NPN

V

mA

E
B
C
100 kW

The meter reading is < 100 kW due to gain.

Concept Review
• It is possible to test transistors out-of-circuit
using an ohmmeter.
• The E-B and C-B junctions act as diodes
during ohmmeter testing.
• The C-E test shows a high resistance because
two junctions are involved; one of which is
reverse biased by the ohmmeter.
• Gain can be verified by using a resistor in
conjunction with the ohmmeter test.
Repeat Segment

Concept Preview
• Bipolar junction transistors (BJTs) are controlled by
base current.
• Junction field effect transistors (JFETs) are controlled
by gate voltage.

• JFETs operate in the depletion mode (as normally on
devices).
• Metal oxide semiconductor field effect transistors
(MOSFETs) usually operate in the enhancement mode
(as normally off devices).
• Insulated gate bipolar transistors (IGBTs) are modified
MOSFETs and have very low on-resistance.
• Unijunction transistors (UJTs) are not used as
amplifiers.

Current In

The BJT is
a current
amplifier.

Current
Amplifier

Current Out

Voltage In

The JFET is
a voltage
controlled
amplifier.

Voltage
Amplifier

Current Out

Source

Gate

Drain

P

N-channel
P-type substrate
Structure of an
N-channel JFET

The channel has carriers so it
conducts from source to drain.

Drain

Gate
Source

Source

Gate

Drain

P

N-channel
P-type substrate

A negative gate voltage
can push the carriers from
the channel and turn
the JFET off.

Drain

Gate
Source

0V
-1 V
-2 V

ID in mA

-3 V

VGS

-4 V

0

-5 V
VDS in Volts

This is known as a depletion-mode device.
N-channel JFET drain family of characteristic curves

It’s possible to make enhancement
type field effect transistors as well.
Metal
oxide
insulator

Drain

n

Gate

VGG

D

VDD

p

G

n

S
N-channel
MOSFET

Source

Gate bias enhances the channel and turns the device on.

5V
4V
3V

ID in mA

2V

VGS

1V

0

0V
Drain

VDS in Volts

Enhancement mode
MOSFET drain family of
characteristic curves

Gate
Source

The IGBT (insulated gate bipolar transistor)
Operation and structure
similar to a MOSFET
Voltage controlled
(like the MOSFET)
Has one more junction
than a MOSFET
Hole injection reduces
the collector resistance

Faster turn off than
BJTs but not as fast
as MOSFETS

RCE = 8.33 mW

Three major device technologies

hole injection
Extra
junction

Courtesy of Powerex, Inc.

Typical IGBT Driver Circuit
Typically +15 V for turn on
Typically - 5 to -15 V for turn off

Control signal

IGBT

Powerex IGBT Module Structure

Powerex high voltage IGBT package

Emitter voltage

The unijunction transistor fires
when its emitter voltage reaches VP.
VP

Then, the emitter voltage
drops due to its negative
resistance characteristic.
Base 2

Emitter current
Emitter

The UJT is not useful as an amplifier.
It is used in timing and control applications.

Base 1

Other Transistor Types Quiz
BJTs are _________-controlled
amplifiers.

current

FETs are __________-controlled
amplifiers.

voltage

JFETs operate in the __________ mode. depletion
MOSFETs operate in the __________
mode.

enhancement

IGBTs are __________-controlled
amplifiers.

voltage

UJTs are not useful as __________.

amplifiers

Concept Review
• Bipolar junction transistors (BJTs) are controlled by
base current.
• Junction field effect transistors (JFETs) are controlled
by gate voltage.
• JFETs operate in the depletion mode (as normally on
devices).
• Metal oxide semiconductor field effect transistors
(MOSFETs) usually operate in the enhancement mode
(as normally off devices).
• Insulated gate bipolar transistors (IGBTs) are modified
MOSFETs and have very low on-resistance.
• Unijunction transistors (UJTs) are not used as
amplifiers.
Repeat Segment

Concept Preview
• BJTs can be used as switches.
• No base current = switch is off.
• High base current = switch is on.
• The dissipation is always zero in an ideal
switch: off = no current flow and on = no
voltage drop.

• MOSFETs can also be used as switches: no
gate voltage = switch is off and high gate
voltage = switch is on.

How do transistor switches work?
Can be viewed as solid state relays:
they are either ON or they are OFF.
BJT switches are characterized by:
high base current (switch is on)
(or no base current … off)

low resistance from collector to emitter (on)
(or very high resistance … off)
low collector dissipation (on or off)
PC = VCE x IC
PC = 0 x IC = 0 W
(on)
(or PC = VCE x 0 = 0 W … off)

NPN SWITCH
LOAD

RCE @ 
W
0W
DRIVER

The
The
driver
driver
output
output
isiszero
positive,
volts,
IIBB>=I0
0and
andthe
theload
loadis
ison
off
The
driver
output
is
zero
volts,
B = 0 and ILOAD = 0

PNP SWITCH
DRIVER

LOAD

The
Z):
Thedriver
driveroutput
outputisgoes
isoff
off(high
(highthe
Z):the
theresistor
resistor
low:
voltage
drop
pulls
the
base
voltage
up
that
VV
pulls
thethe
base
voltage
upso
soV
that
across
resistor
makes
BE
BE==00
BE negative

PNP SWITCH WITH NPN DRIVER

LOAD

NPN SWITCH WITH PNP DRIVER
(NEGATIVE POWER SUPPLY)

VV
0VV
BE
BE@ @+0.7

VVBE
0 VV
BE@@-0.7

LOAD

STEPPER MOTOR

A

B

C

A

Enhancement mode
power MOSFETs
used as switches

B

C
D

D

Concept Review
• BJTs can be used as switches.
• No base current = switch is off.
• High base current = switch is on.
• The dissipation is always zero in an ideal
switch: off = no current flow and on = no
voltage drop.
• MOSFETs can also be used as switches: no
gate voltage = switch is off and high gate
voltage = switch is on.
Repeat Segment

REVIEW
• Amplification
• Transistors
• Characteristic Curves
• Transistor Testing
• Other Transistor Types
• Transistors as Switches


Slide 29

Electronics
Principles & Applications
Sixth Edition

Charles A. Schuler
Chapter 5

Transistors
(student version)
©2003

Glencoe/McGraw-Hill

INTRODUCTION
• Amplification
• Transistors
• Characteristic Curves
• Transistor Testing
• Other Transistor Types
• Transistors as Switches

Dear Student:
This presentation is arranged in segments.
Each segment is preceded by a Concept
Preview slide and is followed by a Concept
Review slide. When you reach a Concept
Review slide, you can return to the
beginning of that segment by clicking on the
Repeat Segment button. This will allow you
to view that segment again, if you want to.

Concept Preview
• Amplifiers provide gain (the output is larger
than the input).
• Transistors have gain.
• Transistors have a collector, a base, and an
emitter.
• The C-B junction is reverse biased.
• The B-E junction is forward biased.
• Most of the emitter carriers reach the collector.
• The base current is relatively small but controls
the larger currents.

In

Gain =

Amplifier

Out

In

Out

NPN Transistor Structure

The collector is lightly doped.

N

C

The base is thin and
is lightly doped.

P

B

The emitter is heavily doped.

N

E

NPN Transistor Bias
No current flows.
The C-B junction
is reverse biased.

N

C

P

B

N

E

NPN Transistor Bias

The B-E junction
is forward biased.

Current flows.

N

C

P

B

N

E

NPN Transistor Bias
IC
Current flows
everywhere.
Most of the emitter carriers
diffuse through the thin base
When
both
junctions
region since they are attracted
biased....
by are
the collector.

Note that IB is smaller
than IE or IC.

N

C

P

B

N

E

IB

IE

Note: when the
switch opens, all
currents go to zero.
Although IB is smaller
it controls IE and IC.

Gain is something small
controlling something large
(IB is small).

IC
N

C

P

B

N

E

IB

IE

Transistor Structure and Bias Quiz
The heaviest doping is found in
the ___________ region.

emitter

The thinnest of all three regions
is called the ____________.

base

The collector-base junction is
___________ biased.

reverse

The base-emitter junction is
____________ biased.

forward

The majority of the emitter
carriers flow to the ___________.

collector

Concept Review
• Amplifiers provide gain (the output is larger than
the input).
• Transistors have gain.

• Transistors have a collector, a base, and an emitter.
• The C-B junction is reverse biased.
• The B-E junction is forward biased.

• Most of the emitter carriers reach the collector.
• The base current is relatively small but controls the
larger currents.
Repeat Segment

Concept Preview
• The base to collector gain is called b (beta).
• To find b, divide the collector current by the
base current.
• The emitter current is the largest since it is the
sum of the base and collector currents.
• PNP transistors have opposite polarity from
NPN transistors.

• In an NPN transistor, the major flow is made
up of electrons.
• In a PNP transistor, the major flow is made up
of holes.

IC = 99 mA

The current gain from
base to collector
is called b.
IB = 1 mA

b =

99
ICmA
1IBmA

= 99

IE = 100 mA

C
P

B

N

E

IC = 99 mA
Kirchhoff’s
current law:

IB = 1 mA

C
P

B

N

E

IE = I B + I C

= 1 mA + 99 mA
= 100 mA
IE = 100 mA

IC = 99 mA
In a PNP transistor,
holes flow from
emitter to collector.

IB = 1 mA
Notice the PNP
bias voltages.

C
B

E

IE = 100 mA

Transistor Currents Quiz
b is the ratio of collector current to
______ current.

base

The sum of the base and collector
currents is the __________ current.

emitter

In NPN transistors, the flow from emitter
to collector is composed of _______.

electrons

In PNP transistors, the flow from emitter
to collector is composed of _______.

holes

Both NPN and PNP transistors show
__________ gain.

current

Concept Review
• The base to collector gain is called b (beta).
• To find b, divide the collector current by the
base current.
• The emitter current is the largest since it is the
sum of the base and collector currents.
• PNP transistors have opposite polarity from
NPN transistors.
• In an NPN transistor, the major flow is made
up of electrons.
• In a PNP transistor, the major flow is made up
of holes.
Repeat Segment

Concept Preview
• The NPN schematic symbol shows the emitter
arrow as Not Pointing iN.
• The collector curves are a graph of collector
voltage versus collector current.
• Both dc beta (bdc) and ac beta (bac) can be
determined from the collector curves.
• The collector circuit of a transistor can be
modeled as a resistor, as a closed switch or as
an open switch.
• The amount of base current determines which
of the three models applies.

NPN Schematic Symbol
Collector

Base

C
B E

Emitter
Memory aid: NPN
means Not Pointing iN.

PNP Schematic Symbol
Collector

Base

C
B E

Emitter

IC

This circuit is used to
collect IC versus
VCE data for
several values of IB.
C

IB
B

E

VCE

When graphed, the data provide an
NPN collector family of curves.
100 mA

14
12
10
IC in mA 8
6
4
2

80 mA
60 mA
40 mA
20 mA

0 2 4 6

8 10 12 14 16 18

VCE in Volts

0 mA

100 mA

14
12
10
IC in mA 8
6
4
2

80 mA
60 mA

40 mA
20 mA

0 2 4 6

8 10 12 14 16 18

0 mA

VCE in Volts

b =

14
mA
6ICmA
40
IB mA
100
mA

150
== 140

This type of gain
is called bdc or hFE.

100 mA

14
12
10
IC in mA 8
6
4
2

80 mA
60 mA

40 mA
20 mA

0 2 4 6

bac =

2.5DImA
C
20DImA
B

8 10 12 14 16 18

0 mA

VCE in Volts
= 125

Another type of gain
is called bac or hfe.

100 mA

14
12
10
IC in mA 8
6
4
2

80 mA
60 mA

40 mA
20 mA

0 2 4 6
IB

C

8 10 12 14 16 18
VCE in Volts

0 mA

With these values of IB:
The C-E model is a resistor.
E

100 mA

14
12
10
IC in mA 8
6
4
2
0 2 4 6
IB

80 mA
60 mA

40 mA
20 mA
8 10 12 14 16 18
VCE in Volts

0 mA

When IB >> 100 mA
VCE @ 0
The model is a closed switch.

100 mA

14
12
10
IC in mA 8
6
4
2
0 2 4 6
IB

80 mA
60 mA

40 mA
20 mA
8 10 12 14 16 18
VCE in Volts

0 mA

When IB = 0
IC = 0
The model is an open switch.

Transistor Operating Conditions Quiz
When IB is large and VCE @ 0, the transistor
acts as a ___________ switch.
closed
When IB = 0 and IC = 0, the transistor
acts as an ___________ switch.

open

When IB > 0 and VCE > 0, the transistor
acts as a ___________.

resistor

Two current gain measures are bdc and
__________.

bac

The symbol hfe is the same as _________.

bac

Concept Review
• The NPN schematic symbol shows the emitter
arrow as Not Pointing iN.
• The collector curves are a graph of collector
voltage versus collector current.
• Both dc beta (bdc) and ac beta (bac) can be
determined from the collector curves.
• The collector circuit of a transistor can be
modeled as a resistor, as a closed switch or as
an open switch.
• The amount of base current determines which
of the three models applies.
Repeat Segment

Concept Preview
• It is possible to test transistors out-of-circuit
using an ohmmeter.
• The E-B and C-B junctions act as diodes
during ohmmeter testing.

• The C-E test shows a high resistance because
two junctions are involved; one of which is
reverse biased by the ohmmeter.
• Gain can be verified by using a resistor in
conjunction with the ohmmeter test.

NPN

V

mA

E
B
C

The E-B junction is forward biased by the ohmmeter.

NPN

V

mA

E
B
C

The C-E resistance is very high.

NPN

V

mA

E
B
C
100 kW

The meter reading is < 100 kW due to gain.

Concept Review
• It is possible to test transistors out-of-circuit
using an ohmmeter.
• The E-B and C-B junctions act as diodes
during ohmmeter testing.
• The C-E test shows a high resistance because
two junctions are involved; one of which is
reverse biased by the ohmmeter.
• Gain can be verified by using a resistor in
conjunction with the ohmmeter test.
Repeat Segment

Concept Preview
• Bipolar junction transistors (BJTs) are controlled by
base current.
• Junction field effect transistors (JFETs) are controlled
by gate voltage.

• JFETs operate in the depletion mode (as normally on
devices).
• Metal oxide semiconductor field effect transistors
(MOSFETs) usually operate in the enhancement mode
(as normally off devices).
• Insulated gate bipolar transistors (IGBTs) are modified
MOSFETs and have very low on-resistance.
• Unijunction transistors (UJTs) are not used as
amplifiers.

Current In

The BJT is
a current
amplifier.

Current
Amplifier

Current Out

Voltage In

The JFET is
a voltage
controlled
amplifier.

Voltage
Amplifier

Current Out

Source

Gate

Drain

P

N-channel
P-type substrate
Structure of an
N-channel JFET

The channel has carriers so it
conducts from source to drain.

Drain

Gate
Source

Source

Gate

Drain

P

N-channel
P-type substrate

A negative gate voltage
can push the carriers from
the channel and turn
the JFET off.

Drain

Gate
Source

0V
-1 V
-2 V

ID in mA

-3 V

VGS

-4 V

0

-5 V
VDS in Volts

This is known as a depletion-mode device.
N-channel JFET drain family of characteristic curves

It’s possible to make enhancement
type field effect transistors as well.
Metal
oxide
insulator

Drain

n

Gate

VGG

D

VDD

p

G

n

S
N-channel
MOSFET

Source

Gate bias enhances the channel and turns the device on.

5V
4V
3V

ID in mA

2V

VGS

1V

0

0V
Drain

VDS in Volts

Enhancement mode
MOSFET drain family of
characteristic curves

Gate
Source

The IGBT (insulated gate bipolar transistor)
Operation and structure
similar to a MOSFET
Voltage controlled
(like the MOSFET)
Has one more junction
than a MOSFET
Hole injection reduces
the collector resistance

Faster turn off than
BJTs but not as fast
as MOSFETS

RCE = 8.33 mW

Three major device technologies

hole injection
Extra
junction

Courtesy of Powerex, Inc.

Typical IGBT Driver Circuit
Typically +15 V for turn on
Typically - 5 to -15 V for turn off

Control signal

IGBT

Powerex IGBT Module Structure

Powerex high voltage IGBT package

Emitter voltage

The unijunction transistor fires
when its emitter voltage reaches VP.
VP

Then, the emitter voltage
drops due to its negative
resistance characteristic.
Base 2

Emitter current
Emitter

The UJT is not useful as an amplifier.
It is used in timing and control applications.

Base 1

Other Transistor Types Quiz
BJTs are _________-controlled
amplifiers.

current

FETs are __________-controlled
amplifiers.

voltage

JFETs operate in the __________ mode. depletion
MOSFETs operate in the __________
mode.

enhancement

IGBTs are __________-controlled
amplifiers.

voltage

UJTs are not useful as __________.

amplifiers

Concept Review
• Bipolar junction transistors (BJTs) are controlled by
base current.
• Junction field effect transistors (JFETs) are controlled
by gate voltage.
• JFETs operate in the depletion mode (as normally on
devices).
• Metal oxide semiconductor field effect transistors
(MOSFETs) usually operate in the enhancement mode
(as normally off devices).
• Insulated gate bipolar transistors (IGBTs) are modified
MOSFETs and have very low on-resistance.
• Unijunction transistors (UJTs) are not used as
amplifiers.
Repeat Segment

Concept Preview
• BJTs can be used as switches.
• No base current = switch is off.
• High base current = switch is on.
• The dissipation is always zero in an ideal
switch: off = no current flow and on = no
voltage drop.

• MOSFETs can also be used as switches: no
gate voltage = switch is off and high gate
voltage = switch is on.

How do transistor switches work?
Can be viewed as solid state relays:
they are either ON or they are OFF.
BJT switches are characterized by:
high base current (switch is on)
(or no base current … off)

low resistance from collector to emitter (on)
(or very high resistance … off)
low collector dissipation (on or off)
PC = VCE x IC
PC = 0 x IC = 0 W
(on)
(or PC = VCE x 0 = 0 W … off)

NPN SWITCH
LOAD

RCE @ 
W
0W
DRIVER

The
The
driver
driver
output
output
isiszero
positive,
volts,
IIBB>=I0
0and
andthe
theload
loadis
ison
off
The
driver
output
is
zero
volts,
B = 0 and ILOAD = 0

PNP SWITCH
DRIVER

LOAD

The
Z):
Thedriver
driveroutput
outputisgoes
isoff
off(high
(highthe
Z):the
theresistor
resistor
low:
voltage
drop
pulls
the
base
voltage
up
that
VV
pulls
thethe
base
voltage
upso
soV
that
across
resistor
makes
BE
BE==00
BE negative

PNP SWITCH WITH NPN DRIVER

LOAD

NPN SWITCH WITH PNP DRIVER
(NEGATIVE POWER SUPPLY)

VV
0VV
BE
BE@ @+0.7

VVBE
0 VV
BE@@-0.7

LOAD

STEPPER MOTOR

A

B

C

A

Enhancement mode
power MOSFETs
used as switches

B

C
D

D

Concept Review
• BJTs can be used as switches.
• No base current = switch is off.
• High base current = switch is on.
• The dissipation is always zero in an ideal
switch: off = no current flow and on = no
voltage drop.
• MOSFETs can also be used as switches: no
gate voltage = switch is off and high gate
voltage = switch is on.
Repeat Segment

REVIEW
• Amplification
• Transistors
• Characteristic Curves
• Transistor Testing
• Other Transistor Types
• Transistors as Switches


Slide 30

Electronics
Principles & Applications
Sixth Edition

Charles A. Schuler
Chapter 5

Transistors
(student version)
©2003

Glencoe/McGraw-Hill

INTRODUCTION
• Amplification
• Transistors
• Characteristic Curves
• Transistor Testing
• Other Transistor Types
• Transistors as Switches

Dear Student:
This presentation is arranged in segments.
Each segment is preceded by a Concept
Preview slide and is followed by a Concept
Review slide. When you reach a Concept
Review slide, you can return to the
beginning of that segment by clicking on the
Repeat Segment button. This will allow you
to view that segment again, if you want to.

Concept Preview
• Amplifiers provide gain (the output is larger
than the input).
• Transistors have gain.
• Transistors have a collector, a base, and an
emitter.
• The C-B junction is reverse biased.
• The B-E junction is forward biased.
• Most of the emitter carriers reach the collector.
• The base current is relatively small but controls
the larger currents.

In

Gain =

Amplifier

Out

In

Out

NPN Transistor Structure

The collector is lightly doped.

N

C

The base is thin and
is lightly doped.

P

B

The emitter is heavily doped.

N

E

NPN Transistor Bias
No current flows.
The C-B junction
is reverse biased.

N

C

P

B

N

E

NPN Transistor Bias

The B-E junction
is forward biased.

Current flows.

N

C

P

B

N

E

NPN Transistor Bias
IC
Current flows
everywhere.
Most of the emitter carriers
diffuse through the thin base
When
both
junctions
region since they are attracted
biased....
by are
the collector.

Note that IB is smaller
than IE or IC.

N

C

P

B

N

E

IB

IE

Note: when the
switch opens, all
currents go to zero.
Although IB is smaller
it controls IE and IC.

Gain is something small
controlling something large
(IB is small).

IC
N

C

P

B

N

E

IB

IE

Transistor Structure and Bias Quiz
The heaviest doping is found in
the ___________ region.

emitter

The thinnest of all three regions
is called the ____________.

base

The collector-base junction is
___________ biased.

reverse

The base-emitter junction is
____________ biased.

forward

The majority of the emitter
carriers flow to the ___________.

collector

Concept Review
• Amplifiers provide gain (the output is larger than
the input).
• Transistors have gain.

• Transistors have a collector, a base, and an emitter.
• The C-B junction is reverse biased.
• The B-E junction is forward biased.

• Most of the emitter carriers reach the collector.
• The base current is relatively small but controls the
larger currents.
Repeat Segment

Concept Preview
• The base to collector gain is called b (beta).
• To find b, divide the collector current by the
base current.
• The emitter current is the largest since it is the
sum of the base and collector currents.
• PNP transistors have opposite polarity from
NPN transistors.

• In an NPN transistor, the major flow is made
up of electrons.
• In a PNP transistor, the major flow is made up
of holes.

IC = 99 mA

The current gain from
base to collector
is called b.
IB = 1 mA

b =

99
ICmA
1IBmA

= 99

IE = 100 mA

C
P

B

N

E

IC = 99 mA
Kirchhoff’s
current law:

IB = 1 mA

C
P

B

N

E

IE = I B + I C

= 1 mA + 99 mA
= 100 mA
IE = 100 mA

IC = 99 mA
In a PNP transistor,
holes flow from
emitter to collector.

IB = 1 mA
Notice the PNP
bias voltages.

C
B

E

IE = 100 mA

Transistor Currents Quiz
b is the ratio of collector current to
______ current.

base

The sum of the base and collector
currents is the __________ current.

emitter

In NPN transistors, the flow from emitter
to collector is composed of _______.

electrons

In PNP transistors, the flow from emitter
to collector is composed of _______.

holes

Both NPN and PNP transistors show
__________ gain.

current

Concept Review
• The base to collector gain is called b (beta).
• To find b, divide the collector current by the
base current.
• The emitter current is the largest since it is the
sum of the base and collector currents.
• PNP transistors have opposite polarity from
NPN transistors.
• In an NPN transistor, the major flow is made
up of electrons.
• In a PNP transistor, the major flow is made up
of holes.
Repeat Segment

Concept Preview
• The NPN schematic symbol shows the emitter
arrow as Not Pointing iN.
• The collector curves are a graph of collector
voltage versus collector current.
• Both dc beta (bdc) and ac beta (bac) can be
determined from the collector curves.
• The collector circuit of a transistor can be
modeled as a resistor, as a closed switch or as
an open switch.
• The amount of base current determines which
of the three models applies.

NPN Schematic Symbol
Collector

Base

C
B E

Emitter
Memory aid: NPN
means Not Pointing iN.

PNP Schematic Symbol
Collector

Base

C
B E

Emitter

IC

This circuit is used to
collect IC versus
VCE data for
several values of IB.
C

IB
B

E

VCE

When graphed, the data provide an
NPN collector family of curves.
100 mA

14
12
10
IC in mA 8
6
4
2

80 mA
60 mA
40 mA
20 mA

0 2 4 6

8 10 12 14 16 18

VCE in Volts

0 mA

100 mA

14
12
10
IC in mA 8
6
4
2

80 mA
60 mA

40 mA
20 mA

0 2 4 6

8 10 12 14 16 18

0 mA

VCE in Volts

b =

14
mA
6ICmA
40
IB mA
100
mA

150
== 140

This type of gain
is called bdc or hFE.

100 mA

14
12
10
IC in mA 8
6
4
2

80 mA
60 mA

40 mA
20 mA

0 2 4 6

bac =

2.5DImA
C
20DImA
B

8 10 12 14 16 18

0 mA

VCE in Volts
= 125

Another type of gain
is called bac or hfe.

100 mA

14
12
10
IC in mA 8
6
4
2

80 mA
60 mA

40 mA
20 mA

0 2 4 6
IB

C

8 10 12 14 16 18
VCE in Volts

0 mA

With these values of IB:
The C-E model is a resistor.
E

100 mA

14
12
10
IC in mA 8
6
4
2
0 2 4 6
IB

80 mA
60 mA

40 mA
20 mA
8 10 12 14 16 18
VCE in Volts

0 mA

When IB >> 100 mA
VCE @ 0
The model is a closed switch.

100 mA

14
12
10
IC in mA 8
6
4
2
0 2 4 6
IB

80 mA
60 mA

40 mA
20 mA
8 10 12 14 16 18
VCE in Volts

0 mA

When IB = 0
IC = 0
The model is an open switch.

Transistor Operating Conditions Quiz
When IB is large and VCE @ 0, the transistor
acts as a ___________ switch.
closed
When IB = 0 and IC = 0, the transistor
acts as an ___________ switch.

open

When IB > 0 and VCE > 0, the transistor
acts as a ___________.

resistor

Two current gain measures are bdc and
__________.

bac

The symbol hfe is the same as _________.

bac

Concept Review
• The NPN schematic symbol shows the emitter
arrow as Not Pointing iN.
• The collector curves are a graph of collector
voltage versus collector current.
• Both dc beta (bdc) and ac beta (bac) can be
determined from the collector curves.
• The collector circuit of a transistor can be
modeled as a resistor, as a closed switch or as
an open switch.
• The amount of base current determines which
of the three models applies.
Repeat Segment

Concept Preview
• It is possible to test transistors out-of-circuit
using an ohmmeter.
• The E-B and C-B junctions act as diodes
during ohmmeter testing.

• The C-E test shows a high resistance because
two junctions are involved; one of which is
reverse biased by the ohmmeter.
• Gain can be verified by using a resistor in
conjunction with the ohmmeter test.

NPN

V

mA

E
B
C

The E-B junction is forward biased by the ohmmeter.

NPN

V

mA

E
B
C

The C-E resistance is very high.

NPN

V

mA

E
B
C
100 kW

The meter reading is < 100 kW due to gain.

Concept Review
• It is possible to test transistors out-of-circuit
using an ohmmeter.
• The E-B and C-B junctions act as diodes
during ohmmeter testing.
• The C-E test shows a high resistance because
two junctions are involved; one of which is
reverse biased by the ohmmeter.
• Gain can be verified by using a resistor in
conjunction with the ohmmeter test.
Repeat Segment

Concept Preview
• Bipolar junction transistors (BJTs) are controlled by
base current.
• Junction field effect transistors (JFETs) are controlled
by gate voltage.

• JFETs operate in the depletion mode (as normally on
devices).
• Metal oxide semiconductor field effect transistors
(MOSFETs) usually operate in the enhancement mode
(as normally off devices).
• Insulated gate bipolar transistors (IGBTs) are modified
MOSFETs and have very low on-resistance.
• Unijunction transistors (UJTs) are not used as
amplifiers.

Current In

The BJT is
a current
amplifier.

Current
Amplifier

Current Out

Voltage In

The JFET is
a voltage
controlled
amplifier.

Voltage
Amplifier

Current Out

Source

Gate

Drain

P

N-channel
P-type substrate
Structure of an
N-channel JFET

The channel has carriers so it
conducts from source to drain.

Drain

Gate
Source

Source

Gate

Drain

P

N-channel
P-type substrate

A negative gate voltage
can push the carriers from
the channel and turn
the JFET off.

Drain

Gate
Source

0V
-1 V
-2 V

ID in mA

-3 V

VGS

-4 V

0

-5 V
VDS in Volts

This is known as a depletion-mode device.
N-channel JFET drain family of characteristic curves

It’s possible to make enhancement
type field effect transistors as well.
Metal
oxide
insulator

Drain

n

Gate

VGG

D

VDD

p

G

n

S
N-channel
MOSFET

Source

Gate bias enhances the channel and turns the device on.

5V
4V
3V

ID in mA

2V

VGS

1V

0

0V
Drain

VDS in Volts

Enhancement mode
MOSFET drain family of
characteristic curves

Gate
Source

The IGBT (insulated gate bipolar transistor)
Operation and structure
similar to a MOSFET
Voltage controlled
(like the MOSFET)
Has one more junction
than a MOSFET
Hole injection reduces
the collector resistance

Faster turn off than
BJTs but not as fast
as MOSFETS

RCE = 8.33 mW

Three major device technologies

hole injection
Extra
junction

Courtesy of Powerex, Inc.

Typical IGBT Driver Circuit
Typically +15 V for turn on
Typically - 5 to -15 V for turn off

Control signal

IGBT

Powerex IGBT Module Structure

Powerex high voltage IGBT package

Emitter voltage

The unijunction transistor fires
when its emitter voltage reaches VP.
VP

Then, the emitter voltage
drops due to its negative
resistance characteristic.
Base 2

Emitter current
Emitter

The UJT is not useful as an amplifier.
It is used in timing and control applications.

Base 1

Other Transistor Types Quiz
BJTs are _________-controlled
amplifiers.

current

FETs are __________-controlled
amplifiers.

voltage

JFETs operate in the __________ mode. depletion
MOSFETs operate in the __________
mode.

enhancement

IGBTs are __________-controlled
amplifiers.

voltage

UJTs are not useful as __________.

amplifiers

Concept Review
• Bipolar junction transistors (BJTs) are controlled by
base current.
• Junction field effect transistors (JFETs) are controlled
by gate voltage.
• JFETs operate in the depletion mode (as normally on
devices).
• Metal oxide semiconductor field effect transistors
(MOSFETs) usually operate in the enhancement mode
(as normally off devices).
• Insulated gate bipolar transistors (IGBTs) are modified
MOSFETs and have very low on-resistance.
• Unijunction transistors (UJTs) are not used as
amplifiers.
Repeat Segment

Concept Preview
• BJTs can be used as switches.
• No base current = switch is off.
• High base current = switch is on.
• The dissipation is always zero in an ideal
switch: off = no current flow and on = no
voltage drop.

• MOSFETs can also be used as switches: no
gate voltage = switch is off and high gate
voltage = switch is on.

How do transistor switches work?
Can be viewed as solid state relays:
they are either ON or they are OFF.
BJT switches are characterized by:
high base current (switch is on)
(or no base current … off)

low resistance from collector to emitter (on)
(or very high resistance … off)
low collector dissipation (on or off)
PC = VCE x IC
PC = 0 x IC = 0 W
(on)
(or PC = VCE x 0 = 0 W … off)

NPN SWITCH
LOAD

RCE @ 
W
0W
DRIVER

The
The
driver
driver
output
output
isiszero
positive,
volts,
IIBB>=I0
0and
andthe
theload
loadis
ison
off
The
driver
output
is
zero
volts,
B = 0 and ILOAD = 0

PNP SWITCH
DRIVER

LOAD

The
Z):
Thedriver
driveroutput
outputisgoes
isoff
off(high
(highthe
Z):the
theresistor
resistor
low:
voltage
drop
pulls
the
base
voltage
up
that
VV
pulls
thethe
base
voltage
upso
soV
that
across
resistor
makes
BE
BE==00
BE negative

PNP SWITCH WITH NPN DRIVER

LOAD

NPN SWITCH WITH PNP DRIVER
(NEGATIVE POWER SUPPLY)

VV
0VV
BE
BE@ @+0.7

VVBE
0 VV
BE@@-0.7

LOAD

STEPPER MOTOR

A

B

C

A

Enhancement mode
power MOSFETs
used as switches

B

C
D

D

Concept Review
• BJTs can be used as switches.
• No base current = switch is off.
• High base current = switch is on.
• The dissipation is always zero in an ideal
switch: off = no current flow and on = no
voltage drop.
• MOSFETs can also be used as switches: no
gate voltage = switch is off and high gate
voltage = switch is on.
Repeat Segment

REVIEW
• Amplification
• Transistors
• Characteristic Curves
• Transistor Testing
• Other Transistor Types
• Transistors as Switches


Slide 31

Electronics
Principles & Applications
Sixth Edition

Charles A. Schuler
Chapter 5

Transistors
(student version)
©2003

Glencoe/McGraw-Hill

INTRODUCTION
• Amplification
• Transistors
• Characteristic Curves
• Transistor Testing
• Other Transistor Types
• Transistors as Switches

Dear Student:
This presentation is arranged in segments.
Each segment is preceded by a Concept
Preview slide and is followed by a Concept
Review slide. When you reach a Concept
Review slide, you can return to the
beginning of that segment by clicking on the
Repeat Segment button. This will allow you
to view that segment again, if you want to.

Concept Preview
• Amplifiers provide gain (the output is larger
than the input).
• Transistors have gain.
• Transistors have a collector, a base, and an
emitter.
• The C-B junction is reverse biased.
• The B-E junction is forward biased.
• Most of the emitter carriers reach the collector.
• The base current is relatively small but controls
the larger currents.

In

Gain =

Amplifier

Out

In

Out

NPN Transistor Structure

The collector is lightly doped.

N

C

The base is thin and
is lightly doped.

P

B

The emitter is heavily doped.

N

E

NPN Transistor Bias
No current flows.
The C-B junction
is reverse biased.

N

C

P

B

N

E

NPN Transistor Bias

The B-E junction
is forward biased.

Current flows.

N

C

P

B

N

E

NPN Transistor Bias
IC
Current flows
everywhere.
Most of the emitter carriers
diffuse through the thin base
When
both
junctions
region since they are attracted
biased....
by are
the collector.

Note that IB is smaller
than IE or IC.

N

C

P

B

N

E

IB

IE

Note: when the
switch opens, all
currents go to zero.
Although IB is smaller
it controls IE and IC.

Gain is something small
controlling something large
(IB is small).

IC
N

C

P

B

N

E

IB

IE

Transistor Structure and Bias Quiz
The heaviest doping is found in
the ___________ region.

emitter

The thinnest of all three regions
is called the ____________.

base

The collector-base junction is
___________ biased.

reverse

The base-emitter junction is
____________ biased.

forward

The majority of the emitter
carriers flow to the ___________.

collector

Concept Review
• Amplifiers provide gain (the output is larger than
the input).
• Transistors have gain.

• Transistors have a collector, a base, and an emitter.
• The C-B junction is reverse biased.
• The B-E junction is forward biased.

• Most of the emitter carriers reach the collector.
• The base current is relatively small but controls the
larger currents.
Repeat Segment

Concept Preview
• The base to collector gain is called b (beta).
• To find b, divide the collector current by the
base current.
• The emitter current is the largest since it is the
sum of the base and collector currents.
• PNP transistors have opposite polarity from
NPN transistors.

• In an NPN transistor, the major flow is made
up of electrons.
• In a PNP transistor, the major flow is made up
of holes.

IC = 99 mA

The current gain from
base to collector
is called b.
IB = 1 mA

b =

99
ICmA
1IBmA

= 99

IE = 100 mA

C
P

B

N

E

IC = 99 mA
Kirchhoff’s
current law:

IB = 1 mA

C
P

B

N

E

IE = I B + I C

= 1 mA + 99 mA
= 100 mA
IE = 100 mA

IC = 99 mA
In a PNP transistor,
holes flow from
emitter to collector.

IB = 1 mA
Notice the PNP
bias voltages.

C
B

E

IE = 100 mA

Transistor Currents Quiz
b is the ratio of collector current to
______ current.

base

The sum of the base and collector
currents is the __________ current.

emitter

In NPN transistors, the flow from emitter
to collector is composed of _______.

electrons

In PNP transistors, the flow from emitter
to collector is composed of _______.

holes

Both NPN and PNP transistors show
__________ gain.

current

Concept Review
• The base to collector gain is called b (beta).
• To find b, divide the collector current by the
base current.
• The emitter current is the largest since it is the
sum of the base and collector currents.
• PNP transistors have opposite polarity from
NPN transistors.
• In an NPN transistor, the major flow is made
up of electrons.
• In a PNP transistor, the major flow is made up
of holes.
Repeat Segment

Concept Preview
• The NPN schematic symbol shows the emitter
arrow as Not Pointing iN.
• The collector curves are a graph of collector
voltage versus collector current.
• Both dc beta (bdc) and ac beta (bac) can be
determined from the collector curves.
• The collector circuit of a transistor can be
modeled as a resistor, as a closed switch or as
an open switch.
• The amount of base current determines which
of the three models applies.

NPN Schematic Symbol
Collector

Base

C
B E

Emitter
Memory aid: NPN
means Not Pointing iN.

PNP Schematic Symbol
Collector

Base

C
B E

Emitter

IC

This circuit is used to
collect IC versus
VCE data for
several values of IB.
C

IB
B

E

VCE

When graphed, the data provide an
NPN collector family of curves.
100 mA

14
12
10
IC in mA 8
6
4
2

80 mA
60 mA
40 mA
20 mA

0 2 4 6

8 10 12 14 16 18

VCE in Volts

0 mA

100 mA

14
12
10
IC in mA 8
6
4
2

80 mA
60 mA

40 mA
20 mA

0 2 4 6

8 10 12 14 16 18

0 mA

VCE in Volts

b =

14
mA
6ICmA
40
IB mA
100
mA

150
== 140

This type of gain
is called bdc or hFE.

100 mA

14
12
10
IC in mA 8
6
4
2

80 mA
60 mA

40 mA
20 mA

0 2 4 6

bac =

2.5DImA
C
20DImA
B

8 10 12 14 16 18

0 mA

VCE in Volts
= 125

Another type of gain
is called bac or hfe.

100 mA

14
12
10
IC in mA 8
6
4
2

80 mA
60 mA

40 mA
20 mA

0 2 4 6
IB

C

8 10 12 14 16 18
VCE in Volts

0 mA

With these values of IB:
The C-E model is a resistor.
E

100 mA

14
12
10
IC in mA 8
6
4
2
0 2 4 6
IB

80 mA
60 mA

40 mA
20 mA
8 10 12 14 16 18
VCE in Volts

0 mA

When IB >> 100 mA
VCE @ 0
The model is a closed switch.

100 mA

14
12
10
IC in mA 8
6
4
2
0 2 4 6
IB

80 mA
60 mA

40 mA
20 mA
8 10 12 14 16 18
VCE in Volts

0 mA

When IB = 0
IC = 0
The model is an open switch.

Transistor Operating Conditions Quiz
When IB is large and VCE @ 0, the transistor
acts as a ___________ switch.
closed
When IB = 0 and IC = 0, the transistor
acts as an ___________ switch.

open

When IB > 0 and VCE > 0, the transistor
acts as a ___________.

resistor

Two current gain measures are bdc and
__________.

bac

The symbol hfe is the same as _________.

bac

Concept Review
• The NPN schematic symbol shows the emitter
arrow as Not Pointing iN.
• The collector curves are a graph of collector
voltage versus collector current.
• Both dc beta (bdc) and ac beta (bac) can be
determined from the collector curves.
• The collector circuit of a transistor can be
modeled as a resistor, as a closed switch or as
an open switch.
• The amount of base current determines which
of the three models applies.
Repeat Segment

Concept Preview
• It is possible to test transistors out-of-circuit
using an ohmmeter.
• The E-B and C-B junctions act as diodes
during ohmmeter testing.

• The C-E test shows a high resistance because
two junctions are involved; one of which is
reverse biased by the ohmmeter.
• Gain can be verified by using a resistor in
conjunction with the ohmmeter test.

NPN

V

mA

E
B
C

The E-B junction is forward biased by the ohmmeter.

NPN

V

mA

E
B
C

The C-E resistance is very high.

NPN

V

mA

E
B
C
100 kW

The meter reading is < 100 kW due to gain.

Concept Review
• It is possible to test transistors out-of-circuit
using an ohmmeter.
• The E-B and C-B junctions act as diodes
during ohmmeter testing.
• The C-E test shows a high resistance because
two junctions are involved; one of which is
reverse biased by the ohmmeter.
• Gain can be verified by using a resistor in
conjunction with the ohmmeter test.
Repeat Segment

Concept Preview
• Bipolar junction transistors (BJTs) are controlled by
base current.
• Junction field effect transistors (JFETs) are controlled
by gate voltage.

• JFETs operate in the depletion mode (as normally on
devices).
• Metal oxide semiconductor field effect transistors
(MOSFETs) usually operate in the enhancement mode
(as normally off devices).
• Insulated gate bipolar transistors (IGBTs) are modified
MOSFETs and have very low on-resistance.
• Unijunction transistors (UJTs) are not used as
amplifiers.

Current In

The BJT is
a current
amplifier.

Current
Amplifier

Current Out

Voltage In

The JFET is
a voltage
controlled
amplifier.

Voltage
Amplifier

Current Out

Source

Gate

Drain

P

N-channel
P-type substrate
Structure of an
N-channel JFET

The channel has carriers so it
conducts from source to drain.

Drain

Gate
Source

Source

Gate

Drain

P

N-channel
P-type substrate

A negative gate voltage
can push the carriers from
the channel and turn
the JFET off.

Drain

Gate
Source

0V
-1 V
-2 V

ID in mA

-3 V

VGS

-4 V

0

-5 V
VDS in Volts

This is known as a depletion-mode device.
N-channel JFET drain family of characteristic curves

It’s possible to make enhancement
type field effect transistors as well.
Metal
oxide
insulator

Drain

n

Gate

VGG

D

VDD

p

G

n

S
N-channel
MOSFET

Source

Gate bias enhances the channel and turns the device on.

5V
4V
3V

ID in mA

2V

VGS

1V

0

0V
Drain

VDS in Volts

Enhancement mode
MOSFET drain family of
characteristic curves

Gate
Source

The IGBT (insulated gate bipolar transistor)
Operation and structure
similar to a MOSFET
Voltage controlled
(like the MOSFET)
Has one more junction
than a MOSFET
Hole injection reduces
the collector resistance

Faster turn off than
BJTs but not as fast
as MOSFETS

RCE = 8.33 mW

Three major device technologies

hole injection
Extra
junction

Courtesy of Powerex, Inc.

Typical IGBT Driver Circuit
Typically +15 V for turn on
Typically - 5 to -15 V for turn off

Control signal

IGBT

Powerex IGBT Module Structure

Powerex high voltage IGBT package

Emitter voltage

The unijunction transistor fires
when its emitter voltage reaches VP.
VP

Then, the emitter voltage
drops due to its negative
resistance characteristic.
Base 2

Emitter current
Emitter

The UJT is not useful as an amplifier.
It is used in timing and control applications.

Base 1

Other Transistor Types Quiz
BJTs are _________-controlled
amplifiers.

current

FETs are __________-controlled
amplifiers.

voltage

JFETs operate in the __________ mode. depletion
MOSFETs operate in the __________
mode.

enhancement

IGBTs are __________-controlled
amplifiers.

voltage

UJTs are not useful as __________.

amplifiers

Concept Review
• Bipolar junction transistors (BJTs) are controlled by
base current.
• Junction field effect transistors (JFETs) are controlled
by gate voltage.
• JFETs operate in the depletion mode (as normally on
devices).
• Metal oxide semiconductor field effect transistors
(MOSFETs) usually operate in the enhancement mode
(as normally off devices).
• Insulated gate bipolar transistors (IGBTs) are modified
MOSFETs and have very low on-resistance.
• Unijunction transistors (UJTs) are not used as
amplifiers.
Repeat Segment

Concept Preview
• BJTs can be used as switches.
• No base current = switch is off.
• High base current = switch is on.
• The dissipation is always zero in an ideal
switch: off = no current flow and on = no
voltage drop.

• MOSFETs can also be used as switches: no
gate voltage = switch is off and high gate
voltage = switch is on.

How do transistor switches work?
Can be viewed as solid state relays:
they are either ON or they are OFF.
BJT switches are characterized by:
high base current (switch is on)
(or no base current … off)

low resistance from collector to emitter (on)
(or very high resistance … off)
low collector dissipation (on or off)
PC = VCE x IC
PC = 0 x IC = 0 W
(on)
(or PC = VCE x 0 = 0 W … off)

NPN SWITCH
LOAD

RCE @ 
W
0W
DRIVER

The
The
driver
driver
output
output
isiszero
positive,
volts,
IIBB>=I0
0and
andthe
theload
loadis
ison
off
The
driver
output
is
zero
volts,
B = 0 and ILOAD = 0

PNP SWITCH
DRIVER

LOAD

The
Z):
Thedriver
driveroutput
outputisgoes
isoff
off(high
(highthe
Z):the
theresistor
resistor
low:
voltage
drop
pulls
the
base
voltage
up
that
VV
pulls
thethe
base
voltage
upso
soV
that
across
resistor
makes
BE
BE==00
BE negative

PNP SWITCH WITH NPN DRIVER

LOAD

NPN SWITCH WITH PNP DRIVER
(NEGATIVE POWER SUPPLY)

VV
0VV
BE
BE@ @+0.7

VVBE
0 VV
BE@@-0.7

LOAD

STEPPER MOTOR

A

B

C

A

Enhancement mode
power MOSFETs
used as switches

B

C
D

D

Concept Review
• BJTs can be used as switches.
• No base current = switch is off.
• High base current = switch is on.
• The dissipation is always zero in an ideal
switch: off = no current flow and on = no
voltage drop.
• MOSFETs can also be used as switches: no
gate voltage = switch is off and high gate
voltage = switch is on.
Repeat Segment

REVIEW
• Amplification
• Transistors
• Characteristic Curves
• Transistor Testing
• Other Transistor Types
• Transistors as Switches


Slide 32

Electronics
Principles & Applications
Sixth Edition

Charles A. Schuler
Chapter 5

Transistors
(student version)
©2003

Glencoe/McGraw-Hill

INTRODUCTION
• Amplification
• Transistors
• Characteristic Curves
• Transistor Testing
• Other Transistor Types
• Transistors as Switches

Dear Student:
This presentation is arranged in segments.
Each segment is preceded by a Concept
Preview slide and is followed by a Concept
Review slide. When you reach a Concept
Review slide, you can return to the
beginning of that segment by clicking on the
Repeat Segment button. This will allow you
to view that segment again, if you want to.

Concept Preview
• Amplifiers provide gain (the output is larger
than the input).
• Transistors have gain.
• Transistors have a collector, a base, and an
emitter.
• The C-B junction is reverse biased.
• The B-E junction is forward biased.
• Most of the emitter carriers reach the collector.
• The base current is relatively small but controls
the larger currents.

In

Gain =

Amplifier

Out

In

Out

NPN Transistor Structure

The collector is lightly doped.

N

C

The base is thin and
is lightly doped.

P

B

The emitter is heavily doped.

N

E

NPN Transistor Bias
No current flows.
The C-B junction
is reverse biased.

N

C

P

B

N

E

NPN Transistor Bias

The B-E junction
is forward biased.

Current flows.

N

C

P

B

N

E

NPN Transistor Bias
IC
Current flows
everywhere.
Most of the emitter carriers
diffuse through the thin base
When
both
junctions
region since they are attracted
biased....
by are
the collector.

Note that IB is smaller
than IE or IC.

N

C

P

B

N

E

IB

IE

Note: when the
switch opens, all
currents go to zero.
Although IB is smaller
it controls IE and IC.

Gain is something small
controlling something large
(IB is small).

IC
N

C

P

B

N

E

IB

IE

Transistor Structure and Bias Quiz
The heaviest doping is found in
the ___________ region.

emitter

The thinnest of all three regions
is called the ____________.

base

The collector-base junction is
___________ biased.

reverse

The base-emitter junction is
____________ biased.

forward

The majority of the emitter
carriers flow to the ___________.

collector

Concept Review
• Amplifiers provide gain (the output is larger than
the input).
• Transistors have gain.

• Transistors have a collector, a base, and an emitter.
• The C-B junction is reverse biased.
• The B-E junction is forward biased.

• Most of the emitter carriers reach the collector.
• The base current is relatively small but controls the
larger currents.
Repeat Segment

Concept Preview
• The base to collector gain is called b (beta).
• To find b, divide the collector current by the
base current.
• The emitter current is the largest since it is the
sum of the base and collector currents.
• PNP transistors have opposite polarity from
NPN transistors.

• In an NPN transistor, the major flow is made
up of electrons.
• In a PNP transistor, the major flow is made up
of holes.

IC = 99 mA

The current gain from
base to collector
is called b.
IB = 1 mA

b =

99
ICmA
1IBmA

= 99

IE = 100 mA

C
P

B

N

E

IC = 99 mA
Kirchhoff’s
current law:

IB = 1 mA

C
P

B

N

E

IE = I B + I C

= 1 mA + 99 mA
= 100 mA
IE = 100 mA

IC = 99 mA
In a PNP transistor,
holes flow from
emitter to collector.

IB = 1 mA
Notice the PNP
bias voltages.

C
B

E

IE = 100 mA

Transistor Currents Quiz
b is the ratio of collector current to
______ current.

base

The sum of the base and collector
currents is the __________ current.

emitter

In NPN transistors, the flow from emitter
to collector is composed of _______.

electrons

In PNP transistors, the flow from emitter
to collector is composed of _______.

holes

Both NPN and PNP transistors show
__________ gain.

current

Concept Review
• The base to collector gain is called b (beta).
• To find b, divide the collector current by the
base current.
• The emitter current is the largest since it is the
sum of the base and collector currents.
• PNP transistors have opposite polarity from
NPN transistors.
• In an NPN transistor, the major flow is made
up of electrons.
• In a PNP transistor, the major flow is made up
of holes.
Repeat Segment

Concept Preview
• The NPN schematic symbol shows the emitter
arrow as Not Pointing iN.
• The collector curves are a graph of collector
voltage versus collector current.
• Both dc beta (bdc) and ac beta (bac) can be
determined from the collector curves.
• The collector circuit of a transistor can be
modeled as a resistor, as a closed switch or as
an open switch.
• The amount of base current determines which
of the three models applies.

NPN Schematic Symbol
Collector

Base

C
B E

Emitter
Memory aid: NPN
means Not Pointing iN.

PNP Schematic Symbol
Collector

Base

C
B E

Emitter

IC

This circuit is used to
collect IC versus
VCE data for
several values of IB.
C

IB
B

E

VCE

When graphed, the data provide an
NPN collector family of curves.
100 mA

14
12
10
IC in mA 8
6
4
2

80 mA
60 mA
40 mA
20 mA

0 2 4 6

8 10 12 14 16 18

VCE in Volts

0 mA

100 mA

14
12
10
IC in mA 8
6
4
2

80 mA
60 mA

40 mA
20 mA

0 2 4 6

8 10 12 14 16 18

0 mA

VCE in Volts

b =

14
mA
6ICmA
40
IB mA
100
mA

150
== 140

This type of gain
is called bdc or hFE.

100 mA

14
12
10
IC in mA 8
6
4
2

80 mA
60 mA

40 mA
20 mA

0 2 4 6

bac =

2.5DImA
C
20DImA
B

8 10 12 14 16 18

0 mA

VCE in Volts
= 125

Another type of gain
is called bac or hfe.

100 mA

14
12
10
IC in mA 8
6
4
2

80 mA
60 mA

40 mA
20 mA

0 2 4 6
IB

C

8 10 12 14 16 18
VCE in Volts

0 mA

With these values of IB:
The C-E model is a resistor.
E

100 mA

14
12
10
IC in mA 8
6
4
2
0 2 4 6
IB

80 mA
60 mA

40 mA
20 mA
8 10 12 14 16 18
VCE in Volts

0 mA

When IB >> 100 mA
VCE @ 0
The model is a closed switch.

100 mA

14
12
10
IC in mA 8
6
4
2
0 2 4 6
IB

80 mA
60 mA

40 mA
20 mA
8 10 12 14 16 18
VCE in Volts

0 mA

When IB = 0
IC = 0
The model is an open switch.

Transistor Operating Conditions Quiz
When IB is large and VCE @ 0, the transistor
acts as a ___________ switch.
closed
When IB = 0 and IC = 0, the transistor
acts as an ___________ switch.

open

When IB > 0 and VCE > 0, the transistor
acts as a ___________.

resistor

Two current gain measures are bdc and
__________.

bac

The symbol hfe is the same as _________.

bac

Concept Review
• The NPN schematic symbol shows the emitter
arrow as Not Pointing iN.
• The collector curves are a graph of collector
voltage versus collector current.
• Both dc beta (bdc) and ac beta (bac) can be
determined from the collector curves.
• The collector circuit of a transistor can be
modeled as a resistor, as a closed switch or as
an open switch.
• The amount of base current determines which
of the three models applies.
Repeat Segment

Concept Preview
• It is possible to test transistors out-of-circuit
using an ohmmeter.
• The E-B and C-B junctions act as diodes
during ohmmeter testing.

• The C-E test shows a high resistance because
two junctions are involved; one of which is
reverse biased by the ohmmeter.
• Gain can be verified by using a resistor in
conjunction with the ohmmeter test.

NPN

V

mA

E
B
C

The E-B junction is forward biased by the ohmmeter.

NPN

V

mA

E
B
C

The C-E resistance is very high.

NPN

V

mA

E
B
C
100 kW

The meter reading is < 100 kW due to gain.

Concept Review
• It is possible to test transistors out-of-circuit
using an ohmmeter.
• The E-B and C-B junctions act as diodes
during ohmmeter testing.
• The C-E test shows a high resistance because
two junctions are involved; one of which is
reverse biased by the ohmmeter.
• Gain can be verified by using a resistor in
conjunction with the ohmmeter test.
Repeat Segment

Concept Preview
• Bipolar junction transistors (BJTs) are controlled by
base current.
• Junction field effect transistors (JFETs) are controlled
by gate voltage.

• JFETs operate in the depletion mode (as normally on
devices).
• Metal oxide semiconductor field effect transistors
(MOSFETs) usually operate in the enhancement mode
(as normally off devices).
• Insulated gate bipolar transistors (IGBTs) are modified
MOSFETs and have very low on-resistance.
• Unijunction transistors (UJTs) are not used as
amplifiers.

Current In

The BJT is
a current
amplifier.

Current
Amplifier

Current Out

Voltage In

The JFET is
a voltage
controlled
amplifier.

Voltage
Amplifier

Current Out

Source

Gate

Drain

P

N-channel
P-type substrate
Structure of an
N-channel JFET

The channel has carriers so it
conducts from source to drain.

Drain

Gate
Source

Source

Gate

Drain

P

N-channel
P-type substrate

A negative gate voltage
can push the carriers from
the channel and turn
the JFET off.

Drain

Gate
Source

0V
-1 V
-2 V

ID in mA

-3 V

VGS

-4 V

0

-5 V
VDS in Volts

This is known as a depletion-mode device.
N-channel JFET drain family of characteristic curves

It’s possible to make enhancement
type field effect transistors as well.
Metal
oxide
insulator

Drain

n

Gate

VGG

D

VDD

p

G

n

S
N-channel
MOSFET

Source

Gate bias enhances the channel and turns the device on.

5V
4V
3V

ID in mA

2V

VGS

1V

0

0V
Drain

VDS in Volts

Enhancement mode
MOSFET drain family of
characteristic curves

Gate
Source

The IGBT (insulated gate bipolar transistor)
Operation and structure
similar to a MOSFET
Voltage controlled
(like the MOSFET)
Has one more junction
than a MOSFET
Hole injection reduces
the collector resistance

Faster turn off than
BJTs but not as fast
as MOSFETS

RCE = 8.33 mW

Three major device technologies

hole injection
Extra
junction

Courtesy of Powerex, Inc.

Typical IGBT Driver Circuit
Typically +15 V for turn on
Typically - 5 to -15 V for turn off

Control signal

IGBT

Powerex IGBT Module Structure

Powerex high voltage IGBT package

Emitter voltage

The unijunction transistor fires
when its emitter voltage reaches VP.
VP

Then, the emitter voltage
drops due to its negative
resistance characteristic.
Base 2

Emitter current
Emitter

The UJT is not useful as an amplifier.
It is used in timing and control applications.

Base 1

Other Transistor Types Quiz
BJTs are _________-controlled
amplifiers.

current

FETs are __________-controlled
amplifiers.

voltage

JFETs operate in the __________ mode. depletion
MOSFETs operate in the __________
mode.

enhancement

IGBTs are __________-controlled
amplifiers.

voltage

UJTs are not useful as __________.

amplifiers

Concept Review
• Bipolar junction transistors (BJTs) are controlled by
base current.
• Junction field effect transistors (JFETs) are controlled
by gate voltage.
• JFETs operate in the depletion mode (as normally on
devices).
• Metal oxide semiconductor field effect transistors
(MOSFETs) usually operate in the enhancement mode
(as normally off devices).
• Insulated gate bipolar transistors (IGBTs) are modified
MOSFETs and have very low on-resistance.
• Unijunction transistors (UJTs) are not used as
amplifiers.
Repeat Segment

Concept Preview
• BJTs can be used as switches.
• No base current = switch is off.
• High base current = switch is on.
• The dissipation is always zero in an ideal
switch: off = no current flow and on = no
voltage drop.

• MOSFETs can also be used as switches: no
gate voltage = switch is off and high gate
voltage = switch is on.

How do transistor switches work?
Can be viewed as solid state relays:
they are either ON or they are OFF.
BJT switches are characterized by:
high base current (switch is on)
(or no base current … off)

low resistance from collector to emitter (on)
(or very high resistance … off)
low collector dissipation (on or off)
PC = VCE x IC
PC = 0 x IC = 0 W
(on)
(or PC = VCE x 0 = 0 W … off)

NPN SWITCH
LOAD

RCE @ 
W
0W
DRIVER

The
The
driver
driver
output
output
isiszero
positive,
volts,
IIBB>=I0
0and
andthe
theload
loadis
ison
off
The
driver
output
is
zero
volts,
B = 0 and ILOAD = 0

PNP SWITCH
DRIVER

LOAD

The
Z):
Thedriver
driveroutput
outputisgoes
isoff
off(high
(highthe
Z):the
theresistor
resistor
low:
voltage
drop
pulls
the
base
voltage
up
that
VV
pulls
thethe
base
voltage
upso
soV
that
across
resistor
makes
BE
BE==00
BE negative

PNP SWITCH WITH NPN DRIVER

LOAD

NPN SWITCH WITH PNP DRIVER
(NEGATIVE POWER SUPPLY)

VV
0VV
BE
BE@ @+0.7

VVBE
0 VV
BE@@-0.7

LOAD

STEPPER MOTOR

A

B

C

A

Enhancement mode
power MOSFETs
used as switches

B

C
D

D

Concept Review
• BJTs can be used as switches.
• No base current = switch is off.
• High base current = switch is on.
• The dissipation is always zero in an ideal
switch: off = no current flow and on = no
voltage drop.
• MOSFETs can also be used as switches: no
gate voltage = switch is off and high gate
voltage = switch is on.
Repeat Segment

REVIEW
• Amplification
• Transistors
• Characteristic Curves
• Transistor Testing
• Other Transistor Types
• Transistors as Switches


Slide 33

Electronics
Principles & Applications
Sixth Edition

Charles A. Schuler
Chapter 5

Transistors
(student version)
©2003

Glencoe/McGraw-Hill

INTRODUCTION
• Amplification
• Transistors
• Characteristic Curves
• Transistor Testing
• Other Transistor Types
• Transistors as Switches

Dear Student:
This presentation is arranged in segments.
Each segment is preceded by a Concept
Preview slide and is followed by a Concept
Review slide. When you reach a Concept
Review slide, you can return to the
beginning of that segment by clicking on the
Repeat Segment button. This will allow you
to view that segment again, if you want to.

Concept Preview
• Amplifiers provide gain (the output is larger
than the input).
• Transistors have gain.
• Transistors have a collector, a base, and an
emitter.
• The C-B junction is reverse biased.
• The B-E junction is forward biased.
• Most of the emitter carriers reach the collector.
• The base current is relatively small but controls
the larger currents.

In

Gain =

Amplifier

Out

In

Out

NPN Transistor Structure

The collector is lightly doped.

N

C

The base is thin and
is lightly doped.

P

B

The emitter is heavily doped.

N

E

NPN Transistor Bias
No current flows.
The C-B junction
is reverse biased.

N

C

P

B

N

E

NPN Transistor Bias

The B-E junction
is forward biased.

Current flows.

N

C

P

B

N

E

NPN Transistor Bias
IC
Current flows
everywhere.
Most of the emitter carriers
diffuse through the thin base
When
both
junctions
region since they are attracted
biased....
by are
the collector.

Note that IB is smaller
than IE or IC.

N

C

P

B

N

E

IB

IE

Note: when the
switch opens, all
currents go to zero.
Although IB is smaller
it controls IE and IC.

Gain is something small
controlling something large
(IB is small).

IC
N

C

P

B

N

E

IB

IE

Transistor Structure and Bias Quiz
The heaviest doping is found in
the ___________ region.

emitter

The thinnest of all three regions
is called the ____________.

base

The collector-base junction is
___________ biased.

reverse

The base-emitter junction is
____________ biased.

forward

The majority of the emitter
carriers flow to the ___________.

collector

Concept Review
• Amplifiers provide gain (the output is larger than
the input).
• Transistors have gain.

• Transistors have a collector, a base, and an emitter.
• The C-B junction is reverse biased.
• The B-E junction is forward biased.

• Most of the emitter carriers reach the collector.
• The base current is relatively small but controls the
larger currents.
Repeat Segment

Concept Preview
• The base to collector gain is called b (beta).
• To find b, divide the collector current by the
base current.
• The emitter current is the largest since it is the
sum of the base and collector currents.
• PNP transistors have opposite polarity from
NPN transistors.

• In an NPN transistor, the major flow is made
up of electrons.
• In a PNP transistor, the major flow is made up
of holes.

IC = 99 mA

The current gain from
base to collector
is called b.
IB = 1 mA

b =

99
ICmA
1IBmA

= 99

IE = 100 mA

C
P

B

N

E

IC = 99 mA
Kirchhoff’s
current law:

IB = 1 mA

C
P

B

N

E

IE = I B + I C

= 1 mA + 99 mA
= 100 mA
IE = 100 mA

IC = 99 mA
In a PNP transistor,
holes flow from
emitter to collector.

IB = 1 mA
Notice the PNP
bias voltages.

C
B

E

IE = 100 mA

Transistor Currents Quiz
b is the ratio of collector current to
______ current.

base

The sum of the base and collector
currents is the __________ current.

emitter

In NPN transistors, the flow from emitter
to collector is composed of _______.

electrons

In PNP transistors, the flow from emitter
to collector is composed of _______.

holes

Both NPN and PNP transistors show
__________ gain.

current

Concept Review
• The base to collector gain is called b (beta).
• To find b, divide the collector current by the
base current.
• The emitter current is the largest since it is the
sum of the base and collector currents.
• PNP transistors have opposite polarity from
NPN transistors.
• In an NPN transistor, the major flow is made
up of electrons.
• In a PNP transistor, the major flow is made up
of holes.
Repeat Segment

Concept Preview
• The NPN schematic symbol shows the emitter
arrow as Not Pointing iN.
• The collector curves are a graph of collector
voltage versus collector current.
• Both dc beta (bdc) and ac beta (bac) can be
determined from the collector curves.
• The collector circuit of a transistor can be
modeled as a resistor, as a closed switch or as
an open switch.
• The amount of base current determines which
of the three models applies.

NPN Schematic Symbol
Collector

Base

C
B E

Emitter
Memory aid: NPN
means Not Pointing iN.

PNP Schematic Symbol
Collector

Base

C
B E

Emitter

IC

This circuit is used to
collect IC versus
VCE data for
several values of IB.
C

IB
B

E

VCE

When graphed, the data provide an
NPN collector family of curves.
100 mA

14
12
10
IC in mA 8
6
4
2

80 mA
60 mA
40 mA
20 mA

0 2 4 6

8 10 12 14 16 18

VCE in Volts

0 mA

100 mA

14
12
10
IC in mA 8
6
4
2

80 mA
60 mA

40 mA
20 mA

0 2 4 6

8 10 12 14 16 18

0 mA

VCE in Volts

b =

14
mA
6ICmA
40
IB mA
100
mA

150
== 140

This type of gain
is called bdc or hFE.

100 mA

14
12
10
IC in mA 8
6
4
2

80 mA
60 mA

40 mA
20 mA

0 2 4 6

bac =

2.5DImA
C
20DImA
B

8 10 12 14 16 18

0 mA

VCE in Volts
= 125

Another type of gain
is called bac or hfe.

100 mA

14
12
10
IC in mA 8
6
4
2

80 mA
60 mA

40 mA
20 mA

0 2 4 6
IB

C

8 10 12 14 16 18
VCE in Volts

0 mA

With these values of IB:
The C-E model is a resistor.
E

100 mA

14
12
10
IC in mA 8
6
4
2
0 2 4 6
IB

80 mA
60 mA

40 mA
20 mA
8 10 12 14 16 18
VCE in Volts

0 mA

When IB >> 100 mA
VCE @ 0
The model is a closed switch.

100 mA

14
12
10
IC in mA 8
6
4
2
0 2 4 6
IB

80 mA
60 mA

40 mA
20 mA
8 10 12 14 16 18
VCE in Volts

0 mA

When IB = 0
IC = 0
The model is an open switch.

Transistor Operating Conditions Quiz
When IB is large and VCE @ 0, the transistor
acts as a ___________ switch.
closed
When IB = 0 and IC = 0, the transistor
acts as an ___________ switch.

open

When IB > 0 and VCE > 0, the transistor
acts as a ___________.

resistor

Two current gain measures are bdc and
__________.

bac

The symbol hfe is the same as _________.

bac

Concept Review
• The NPN schematic symbol shows the emitter
arrow as Not Pointing iN.
• The collector curves are a graph of collector
voltage versus collector current.
• Both dc beta (bdc) and ac beta (bac) can be
determined from the collector curves.
• The collector circuit of a transistor can be
modeled as a resistor, as a closed switch or as
an open switch.
• The amount of base current determines which
of the three models applies.
Repeat Segment

Concept Preview
• It is possible to test transistors out-of-circuit
using an ohmmeter.
• The E-B and C-B junctions act as diodes
during ohmmeter testing.

• The C-E test shows a high resistance because
two junctions are involved; one of which is
reverse biased by the ohmmeter.
• Gain can be verified by using a resistor in
conjunction with the ohmmeter test.

NPN

V

mA

E
B
C

The E-B junction is forward biased by the ohmmeter.

NPN

V

mA

E
B
C

The C-E resistance is very high.

NPN

V

mA

E
B
C
100 kW

The meter reading is < 100 kW due to gain.

Concept Review
• It is possible to test transistors out-of-circuit
using an ohmmeter.
• The E-B and C-B junctions act as diodes
during ohmmeter testing.
• The C-E test shows a high resistance because
two junctions are involved; one of which is
reverse biased by the ohmmeter.
• Gain can be verified by using a resistor in
conjunction with the ohmmeter test.
Repeat Segment

Concept Preview
• Bipolar junction transistors (BJTs) are controlled by
base current.
• Junction field effect transistors (JFETs) are controlled
by gate voltage.

• JFETs operate in the depletion mode (as normally on
devices).
• Metal oxide semiconductor field effect transistors
(MOSFETs) usually operate in the enhancement mode
(as normally off devices).
• Insulated gate bipolar transistors (IGBTs) are modified
MOSFETs and have very low on-resistance.
• Unijunction transistors (UJTs) are not used as
amplifiers.

Current In

The BJT is
a current
amplifier.

Current
Amplifier

Current Out

Voltage In

The JFET is
a voltage
controlled
amplifier.

Voltage
Amplifier

Current Out

Source

Gate

Drain

P

N-channel
P-type substrate
Structure of an
N-channel JFET

The channel has carriers so it
conducts from source to drain.

Drain

Gate
Source

Source

Gate

Drain

P

N-channel
P-type substrate

A negative gate voltage
can push the carriers from
the channel and turn
the JFET off.

Drain

Gate
Source

0V
-1 V
-2 V

ID in mA

-3 V

VGS

-4 V

0

-5 V
VDS in Volts

This is known as a depletion-mode device.
N-channel JFET drain family of characteristic curves

It’s possible to make enhancement
type field effect transistors as well.
Metal
oxide
insulator

Drain

n

Gate

VGG

D

VDD

p

G

n

S
N-channel
MOSFET

Source

Gate bias enhances the channel and turns the device on.

5V
4V
3V

ID in mA

2V

VGS

1V

0

0V
Drain

VDS in Volts

Enhancement mode
MOSFET drain family of
characteristic curves

Gate
Source

The IGBT (insulated gate bipolar transistor)
Operation and structure
similar to a MOSFET
Voltage controlled
(like the MOSFET)
Has one more junction
than a MOSFET
Hole injection reduces
the collector resistance

Faster turn off than
BJTs but not as fast
as MOSFETS

RCE = 8.33 mW

Three major device technologies

hole injection
Extra
junction

Courtesy of Powerex, Inc.

Typical IGBT Driver Circuit
Typically +15 V for turn on
Typically - 5 to -15 V for turn off

Control signal

IGBT

Powerex IGBT Module Structure

Powerex high voltage IGBT package

Emitter voltage

The unijunction transistor fires
when its emitter voltage reaches VP.
VP

Then, the emitter voltage
drops due to its negative
resistance characteristic.
Base 2

Emitter current
Emitter

The UJT is not useful as an amplifier.
It is used in timing and control applications.

Base 1

Other Transistor Types Quiz
BJTs are _________-controlled
amplifiers.

current

FETs are __________-controlled
amplifiers.

voltage

JFETs operate in the __________ mode. depletion
MOSFETs operate in the __________
mode.

enhancement

IGBTs are __________-controlled
amplifiers.

voltage

UJTs are not useful as __________.

amplifiers

Concept Review
• Bipolar junction transistors (BJTs) are controlled by
base current.
• Junction field effect transistors (JFETs) are controlled
by gate voltage.
• JFETs operate in the depletion mode (as normally on
devices).
• Metal oxide semiconductor field effect transistors
(MOSFETs) usually operate in the enhancement mode
(as normally off devices).
• Insulated gate bipolar transistors (IGBTs) are modified
MOSFETs and have very low on-resistance.
• Unijunction transistors (UJTs) are not used as
amplifiers.
Repeat Segment

Concept Preview
• BJTs can be used as switches.
• No base current = switch is off.
• High base current = switch is on.
• The dissipation is always zero in an ideal
switch: off = no current flow and on = no
voltage drop.

• MOSFETs can also be used as switches: no
gate voltage = switch is off and high gate
voltage = switch is on.

How do transistor switches work?
Can be viewed as solid state relays:
they are either ON or they are OFF.
BJT switches are characterized by:
high base current (switch is on)
(or no base current … off)

low resistance from collector to emitter (on)
(or very high resistance … off)
low collector dissipation (on or off)
PC = VCE x IC
PC = 0 x IC = 0 W
(on)
(or PC = VCE x 0 = 0 W … off)

NPN SWITCH
LOAD

RCE @ 
W
0W
DRIVER

The
The
driver
driver
output
output
isiszero
positive,
volts,
IIBB>=I0
0and
andthe
theload
loadis
ison
off
The
driver
output
is
zero
volts,
B = 0 and ILOAD = 0

PNP SWITCH
DRIVER

LOAD

The
Z):
Thedriver
driveroutput
outputisgoes
isoff
off(high
(highthe
Z):the
theresistor
resistor
low:
voltage
drop
pulls
the
base
voltage
up
that
VV
pulls
thethe
base
voltage
upso
soV
that
across
resistor
makes
BE
BE==00
BE negative

PNP SWITCH WITH NPN DRIVER

LOAD

NPN SWITCH WITH PNP DRIVER
(NEGATIVE POWER SUPPLY)

VV
0VV
BE
BE@ @+0.7

VVBE
0 VV
BE@@-0.7

LOAD

STEPPER MOTOR

A

B

C

A

Enhancement mode
power MOSFETs
used as switches

B

C
D

D

Concept Review
• BJTs can be used as switches.
• No base current = switch is off.
• High base current = switch is on.
• The dissipation is always zero in an ideal
switch: off = no current flow and on = no
voltage drop.
• MOSFETs can also be used as switches: no
gate voltage = switch is off and high gate
voltage = switch is on.
Repeat Segment

REVIEW
• Amplification
• Transistors
• Characteristic Curves
• Transistor Testing
• Other Transistor Types
• Transistors as Switches


Slide 34

Electronics
Principles & Applications
Sixth Edition

Charles A. Schuler
Chapter 5

Transistors
(student version)
©2003

Glencoe/McGraw-Hill

INTRODUCTION
• Amplification
• Transistors
• Characteristic Curves
• Transistor Testing
• Other Transistor Types
• Transistors as Switches

Dear Student:
This presentation is arranged in segments.
Each segment is preceded by a Concept
Preview slide and is followed by a Concept
Review slide. When you reach a Concept
Review slide, you can return to the
beginning of that segment by clicking on the
Repeat Segment button. This will allow you
to view that segment again, if you want to.

Concept Preview
• Amplifiers provide gain (the output is larger
than the input).
• Transistors have gain.
• Transistors have a collector, a base, and an
emitter.
• The C-B junction is reverse biased.
• The B-E junction is forward biased.
• Most of the emitter carriers reach the collector.
• The base current is relatively small but controls
the larger currents.

In

Gain =

Amplifier

Out

In

Out

NPN Transistor Structure

The collector is lightly doped.

N

C

The base is thin and
is lightly doped.

P

B

The emitter is heavily doped.

N

E

NPN Transistor Bias
No current flows.
The C-B junction
is reverse biased.

N

C

P

B

N

E

NPN Transistor Bias

The B-E junction
is forward biased.

Current flows.

N

C

P

B

N

E

NPN Transistor Bias
IC
Current flows
everywhere.
Most of the emitter carriers
diffuse through the thin base
When
both
junctions
region since they are attracted
biased....
by are
the collector.

Note that IB is smaller
than IE or IC.

N

C

P

B

N

E

IB

IE

Note: when the
switch opens, all
currents go to zero.
Although IB is smaller
it controls IE and IC.

Gain is something small
controlling something large
(IB is small).

IC
N

C

P

B

N

E

IB

IE

Transistor Structure and Bias Quiz
The heaviest doping is found in
the ___________ region.

emitter

The thinnest of all three regions
is called the ____________.

base

The collector-base junction is
___________ biased.

reverse

The base-emitter junction is
____________ biased.

forward

The majority of the emitter
carriers flow to the ___________.

collector

Concept Review
• Amplifiers provide gain (the output is larger than
the input).
• Transistors have gain.

• Transistors have a collector, a base, and an emitter.
• The C-B junction is reverse biased.
• The B-E junction is forward biased.

• Most of the emitter carriers reach the collector.
• The base current is relatively small but controls the
larger currents.
Repeat Segment

Concept Preview
• The base to collector gain is called b (beta).
• To find b, divide the collector current by the
base current.
• The emitter current is the largest since it is the
sum of the base and collector currents.
• PNP transistors have opposite polarity from
NPN transistors.

• In an NPN transistor, the major flow is made
up of electrons.
• In a PNP transistor, the major flow is made up
of holes.

IC = 99 mA

The current gain from
base to collector
is called b.
IB = 1 mA

b =

99
ICmA
1IBmA

= 99

IE = 100 mA

C
P

B

N

E

IC = 99 mA
Kirchhoff’s
current law:

IB = 1 mA

C
P

B

N

E

IE = I B + I C

= 1 mA + 99 mA
= 100 mA
IE = 100 mA

IC = 99 mA
In a PNP transistor,
holes flow from
emitter to collector.

IB = 1 mA
Notice the PNP
bias voltages.

C
B

E

IE = 100 mA

Transistor Currents Quiz
b is the ratio of collector current to
______ current.

base

The sum of the base and collector
currents is the __________ current.

emitter

In NPN transistors, the flow from emitter
to collector is composed of _______.

electrons

In PNP transistors, the flow from emitter
to collector is composed of _______.

holes

Both NPN and PNP transistors show
__________ gain.

current

Concept Review
• The base to collector gain is called b (beta).
• To find b, divide the collector current by the
base current.
• The emitter current is the largest since it is the
sum of the base and collector currents.
• PNP transistors have opposite polarity from
NPN transistors.
• In an NPN transistor, the major flow is made
up of electrons.
• In a PNP transistor, the major flow is made up
of holes.
Repeat Segment

Concept Preview
• The NPN schematic symbol shows the emitter
arrow as Not Pointing iN.
• The collector curves are a graph of collector
voltage versus collector current.
• Both dc beta (bdc) and ac beta (bac) can be
determined from the collector curves.
• The collector circuit of a transistor can be
modeled as a resistor, as a closed switch or as
an open switch.
• The amount of base current determines which
of the three models applies.

NPN Schematic Symbol
Collector

Base

C
B E

Emitter
Memory aid: NPN
means Not Pointing iN.

PNP Schematic Symbol
Collector

Base

C
B E

Emitter

IC

This circuit is used to
collect IC versus
VCE data for
several values of IB.
C

IB
B

E

VCE

When graphed, the data provide an
NPN collector family of curves.
100 mA

14
12
10
IC in mA 8
6
4
2

80 mA
60 mA
40 mA
20 mA

0 2 4 6

8 10 12 14 16 18

VCE in Volts

0 mA

100 mA

14
12
10
IC in mA 8
6
4
2

80 mA
60 mA

40 mA
20 mA

0 2 4 6

8 10 12 14 16 18

0 mA

VCE in Volts

b =

14
mA
6ICmA
40
IB mA
100
mA

150
== 140

This type of gain
is called bdc or hFE.

100 mA

14
12
10
IC in mA 8
6
4
2

80 mA
60 mA

40 mA
20 mA

0 2 4 6

bac =

2.5DImA
C
20DImA
B

8 10 12 14 16 18

0 mA

VCE in Volts
= 125

Another type of gain
is called bac or hfe.

100 mA

14
12
10
IC in mA 8
6
4
2

80 mA
60 mA

40 mA
20 mA

0 2 4 6
IB

C

8 10 12 14 16 18
VCE in Volts

0 mA

With these values of IB:
The C-E model is a resistor.
E

100 mA

14
12
10
IC in mA 8
6
4
2
0 2 4 6
IB

80 mA
60 mA

40 mA
20 mA
8 10 12 14 16 18
VCE in Volts

0 mA

When IB >> 100 mA
VCE @ 0
The model is a closed switch.

100 mA

14
12
10
IC in mA 8
6
4
2
0 2 4 6
IB

80 mA
60 mA

40 mA
20 mA
8 10 12 14 16 18
VCE in Volts

0 mA

When IB = 0
IC = 0
The model is an open switch.

Transistor Operating Conditions Quiz
When IB is large and VCE @ 0, the transistor
acts as a ___________ switch.
closed
When IB = 0 and IC = 0, the transistor
acts as an ___________ switch.

open

When IB > 0 and VCE > 0, the transistor
acts as a ___________.

resistor

Two current gain measures are bdc and
__________.

bac

The symbol hfe is the same as _________.

bac

Concept Review
• The NPN schematic symbol shows the emitter
arrow as Not Pointing iN.
• The collector curves are a graph of collector
voltage versus collector current.
• Both dc beta (bdc) and ac beta (bac) can be
determined from the collector curves.
• The collector circuit of a transistor can be
modeled as a resistor, as a closed switch or as
an open switch.
• The amount of base current determines which
of the three models applies.
Repeat Segment

Concept Preview
• It is possible to test transistors out-of-circuit
using an ohmmeter.
• The E-B and C-B junctions act as diodes
during ohmmeter testing.

• The C-E test shows a high resistance because
two junctions are involved; one of which is
reverse biased by the ohmmeter.
• Gain can be verified by using a resistor in
conjunction with the ohmmeter test.

NPN

V

mA

E
B
C

The E-B junction is forward biased by the ohmmeter.

NPN

V

mA

E
B
C

The C-E resistance is very high.

NPN

V

mA

E
B
C
100 kW

The meter reading is < 100 kW due to gain.

Concept Review
• It is possible to test transistors out-of-circuit
using an ohmmeter.
• The E-B and C-B junctions act as diodes
during ohmmeter testing.
• The C-E test shows a high resistance because
two junctions are involved; one of which is
reverse biased by the ohmmeter.
• Gain can be verified by using a resistor in
conjunction with the ohmmeter test.
Repeat Segment

Concept Preview
• Bipolar junction transistors (BJTs) are controlled by
base current.
• Junction field effect transistors (JFETs) are controlled
by gate voltage.

• JFETs operate in the depletion mode (as normally on
devices).
• Metal oxide semiconductor field effect transistors
(MOSFETs) usually operate in the enhancement mode
(as normally off devices).
• Insulated gate bipolar transistors (IGBTs) are modified
MOSFETs and have very low on-resistance.
• Unijunction transistors (UJTs) are not used as
amplifiers.

Current In

The BJT is
a current
amplifier.

Current
Amplifier

Current Out

Voltage In

The JFET is
a voltage
controlled
amplifier.

Voltage
Amplifier

Current Out

Source

Gate

Drain

P

N-channel
P-type substrate
Structure of an
N-channel JFET

The channel has carriers so it
conducts from source to drain.

Drain

Gate
Source

Source

Gate

Drain

P

N-channel
P-type substrate

A negative gate voltage
can push the carriers from
the channel and turn
the JFET off.

Drain

Gate
Source

0V
-1 V
-2 V

ID in mA

-3 V

VGS

-4 V

0

-5 V
VDS in Volts

This is known as a depletion-mode device.
N-channel JFET drain family of characteristic curves

It’s possible to make enhancement
type field effect transistors as well.
Metal
oxide
insulator

Drain

n

Gate

VGG

D

VDD

p

G

n

S
N-channel
MOSFET

Source

Gate bias enhances the channel and turns the device on.

5V
4V
3V

ID in mA

2V

VGS

1V

0

0V
Drain

VDS in Volts

Enhancement mode
MOSFET drain family of
characteristic curves

Gate
Source

The IGBT (insulated gate bipolar transistor)
Operation and structure
similar to a MOSFET
Voltage controlled
(like the MOSFET)
Has one more junction
than a MOSFET
Hole injection reduces
the collector resistance

Faster turn off than
BJTs but not as fast
as MOSFETS

RCE = 8.33 mW

Three major device technologies

hole injection
Extra
junction

Courtesy of Powerex, Inc.

Typical IGBT Driver Circuit
Typically +15 V for turn on
Typically - 5 to -15 V for turn off

Control signal

IGBT

Powerex IGBT Module Structure

Powerex high voltage IGBT package

Emitter voltage

The unijunction transistor fires
when its emitter voltage reaches VP.
VP

Then, the emitter voltage
drops due to its negative
resistance characteristic.
Base 2

Emitter current
Emitter

The UJT is not useful as an amplifier.
It is used in timing and control applications.

Base 1

Other Transistor Types Quiz
BJTs are _________-controlled
amplifiers.

current

FETs are __________-controlled
amplifiers.

voltage

JFETs operate in the __________ mode. depletion
MOSFETs operate in the __________
mode.

enhancement

IGBTs are __________-controlled
amplifiers.

voltage

UJTs are not useful as __________.

amplifiers

Concept Review
• Bipolar junction transistors (BJTs) are controlled by
base current.
• Junction field effect transistors (JFETs) are controlled
by gate voltage.
• JFETs operate in the depletion mode (as normally on
devices).
• Metal oxide semiconductor field effect transistors
(MOSFETs) usually operate in the enhancement mode
(as normally off devices).
• Insulated gate bipolar transistors (IGBTs) are modified
MOSFETs and have very low on-resistance.
• Unijunction transistors (UJTs) are not used as
amplifiers.
Repeat Segment

Concept Preview
• BJTs can be used as switches.
• No base current = switch is off.
• High base current = switch is on.
• The dissipation is always zero in an ideal
switch: off = no current flow and on = no
voltage drop.

• MOSFETs can also be used as switches: no
gate voltage = switch is off and high gate
voltage = switch is on.

How do transistor switches work?
Can be viewed as solid state relays:
they are either ON or they are OFF.
BJT switches are characterized by:
high base current (switch is on)
(or no base current … off)

low resistance from collector to emitter (on)
(or very high resistance … off)
low collector dissipation (on or off)
PC = VCE x IC
PC = 0 x IC = 0 W
(on)
(or PC = VCE x 0 = 0 W … off)

NPN SWITCH
LOAD

RCE @ 
W
0W
DRIVER

The
The
driver
driver
output
output
isiszero
positive,
volts,
IIBB>=I0
0and
andthe
theload
loadis
ison
off
The
driver
output
is
zero
volts,
B = 0 and ILOAD = 0

PNP SWITCH
DRIVER

LOAD

The
Z):
Thedriver
driveroutput
outputisgoes
isoff
off(high
(highthe
Z):the
theresistor
resistor
low:
voltage
drop
pulls
the
base
voltage
up
that
VV
pulls
thethe
base
voltage
upso
soV
that
across
resistor
makes
BE
BE==00
BE negative

PNP SWITCH WITH NPN DRIVER

LOAD

NPN SWITCH WITH PNP DRIVER
(NEGATIVE POWER SUPPLY)

VV
0VV
BE
BE@ @+0.7

VVBE
0 VV
BE@@-0.7

LOAD

STEPPER MOTOR

A

B

C

A

Enhancement mode
power MOSFETs
used as switches

B

C
D

D

Concept Review
• BJTs can be used as switches.
• No base current = switch is off.
• High base current = switch is on.
• The dissipation is always zero in an ideal
switch: off = no current flow and on = no
voltage drop.
• MOSFETs can also be used as switches: no
gate voltage = switch is off and high gate
voltage = switch is on.
Repeat Segment

REVIEW
• Amplification
• Transistors
• Characteristic Curves
• Transistor Testing
• Other Transistor Types
• Transistors as Switches


Slide 35

Electronics
Principles & Applications
Sixth Edition

Charles A. Schuler
Chapter 5

Transistors
(student version)
©2003

Glencoe/McGraw-Hill

INTRODUCTION
• Amplification
• Transistors
• Characteristic Curves
• Transistor Testing
• Other Transistor Types
• Transistors as Switches

Dear Student:
This presentation is arranged in segments.
Each segment is preceded by a Concept
Preview slide and is followed by a Concept
Review slide. When you reach a Concept
Review slide, you can return to the
beginning of that segment by clicking on the
Repeat Segment button. This will allow you
to view that segment again, if you want to.

Concept Preview
• Amplifiers provide gain (the output is larger
than the input).
• Transistors have gain.
• Transistors have a collector, a base, and an
emitter.
• The C-B junction is reverse biased.
• The B-E junction is forward biased.
• Most of the emitter carriers reach the collector.
• The base current is relatively small but controls
the larger currents.

In

Gain =

Amplifier

Out

In

Out

NPN Transistor Structure

The collector is lightly doped.

N

C

The base is thin and
is lightly doped.

P

B

The emitter is heavily doped.

N

E

NPN Transistor Bias
No current flows.
The C-B junction
is reverse biased.

N

C

P

B

N

E

NPN Transistor Bias

The B-E junction
is forward biased.

Current flows.

N

C

P

B

N

E

NPN Transistor Bias
IC
Current flows
everywhere.
Most of the emitter carriers
diffuse through the thin base
When
both
junctions
region since they are attracted
biased....
by are
the collector.

Note that IB is smaller
than IE or IC.

N

C

P

B

N

E

IB

IE

Note: when the
switch opens, all
currents go to zero.
Although IB is smaller
it controls IE and IC.

Gain is something small
controlling something large
(IB is small).

IC
N

C

P

B

N

E

IB

IE

Transistor Structure and Bias Quiz
The heaviest doping is found in
the ___________ region.

emitter

The thinnest of all three regions
is called the ____________.

base

The collector-base junction is
___________ biased.

reverse

The base-emitter junction is
____________ biased.

forward

The majority of the emitter
carriers flow to the ___________.

collector

Concept Review
• Amplifiers provide gain (the output is larger than
the input).
• Transistors have gain.

• Transistors have a collector, a base, and an emitter.
• The C-B junction is reverse biased.
• The B-E junction is forward biased.

• Most of the emitter carriers reach the collector.
• The base current is relatively small but controls the
larger currents.
Repeat Segment

Concept Preview
• The base to collector gain is called b (beta).
• To find b, divide the collector current by the
base current.
• The emitter current is the largest since it is the
sum of the base and collector currents.
• PNP transistors have opposite polarity from
NPN transistors.

• In an NPN transistor, the major flow is made
up of electrons.
• In a PNP transistor, the major flow is made up
of holes.

IC = 99 mA

The current gain from
base to collector
is called b.
IB = 1 mA

b =

99
ICmA
1IBmA

= 99

IE = 100 mA

C
P

B

N

E

IC = 99 mA
Kirchhoff’s
current law:

IB = 1 mA

C
P

B

N

E

IE = I B + I C

= 1 mA + 99 mA
= 100 mA
IE = 100 mA

IC = 99 mA
In a PNP transistor,
holes flow from
emitter to collector.

IB = 1 mA
Notice the PNP
bias voltages.

C
B

E

IE = 100 mA

Transistor Currents Quiz
b is the ratio of collector current to
______ current.

base

The sum of the base and collector
currents is the __________ current.

emitter

In NPN transistors, the flow from emitter
to collector is composed of _______.

electrons

In PNP transistors, the flow from emitter
to collector is composed of _______.

holes

Both NPN and PNP transistors show
__________ gain.

current

Concept Review
• The base to collector gain is called b (beta).
• To find b, divide the collector current by the
base current.
• The emitter current is the largest since it is the
sum of the base and collector currents.
• PNP transistors have opposite polarity from
NPN transistors.
• In an NPN transistor, the major flow is made
up of electrons.
• In a PNP transistor, the major flow is made up
of holes.
Repeat Segment

Concept Preview
• The NPN schematic symbol shows the emitter
arrow as Not Pointing iN.
• The collector curves are a graph of collector
voltage versus collector current.
• Both dc beta (bdc) and ac beta (bac) can be
determined from the collector curves.
• The collector circuit of a transistor can be
modeled as a resistor, as a closed switch or as
an open switch.
• The amount of base current determines which
of the three models applies.

NPN Schematic Symbol
Collector

Base

C
B E

Emitter
Memory aid: NPN
means Not Pointing iN.

PNP Schematic Symbol
Collector

Base

C
B E

Emitter

IC

This circuit is used to
collect IC versus
VCE data for
several values of IB.
C

IB
B

E

VCE

When graphed, the data provide an
NPN collector family of curves.
100 mA

14
12
10
IC in mA 8
6
4
2

80 mA
60 mA
40 mA
20 mA

0 2 4 6

8 10 12 14 16 18

VCE in Volts

0 mA

100 mA

14
12
10
IC in mA 8
6
4
2

80 mA
60 mA

40 mA
20 mA

0 2 4 6

8 10 12 14 16 18

0 mA

VCE in Volts

b =

14
mA
6ICmA
40
IB mA
100
mA

150
== 140

This type of gain
is called bdc or hFE.

100 mA

14
12
10
IC in mA 8
6
4
2

80 mA
60 mA

40 mA
20 mA

0 2 4 6

bac =

2.5DImA
C
20DImA
B

8 10 12 14 16 18

0 mA

VCE in Volts
= 125

Another type of gain
is called bac or hfe.

100 mA

14
12
10
IC in mA 8
6
4
2

80 mA
60 mA

40 mA
20 mA

0 2 4 6
IB

C

8 10 12 14 16 18
VCE in Volts

0 mA

With these values of IB:
The C-E model is a resistor.
E

100 mA

14
12
10
IC in mA 8
6
4
2
0 2 4 6
IB

80 mA
60 mA

40 mA
20 mA
8 10 12 14 16 18
VCE in Volts

0 mA

When IB >> 100 mA
VCE @ 0
The model is a closed switch.

100 mA

14
12
10
IC in mA 8
6
4
2
0 2 4 6
IB

80 mA
60 mA

40 mA
20 mA
8 10 12 14 16 18
VCE in Volts

0 mA

When IB = 0
IC = 0
The model is an open switch.

Transistor Operating Conditions Quiz
When IB is large and VCE @ 0, the transistor
acts as a ___________ switch.
closed
When IB = 0 and IC = 0, the transistor
acts as an ___________ switch.

open

When IB > 0 and VCE > 0, the transistor
acts as a ___________.

resistor

Two current gain measures are bdc and
__________.

bac

The symbol hfe is the same as _________.

bac

Concept Review
• The NPN schematic symbol shows the emitter
arrow as Not Pointing iN.
• The collector curves are a graph of collector
voltage versus collector current.
• Both dc beta (bdc) and ac beta (bac) can be
determined from the collector curves.
• The collector circuit of a transistor can be
modeled as a resistor, as a closed switch or as
an open switch.
• The amount of base current determines which
of the three models applies.
Repeat Segment

Concept Preview
• It is possible to test transistors out-of-circuit
using an ohmmeter.
• The E-B and C-B junctions act as diodes
during ohmmeter testing.

• The C-E test shows a high resistance because
two junctions are involved; one of which is
reverse biased by the ohmmeter.
• Gain can be verified by using a resistor in
conjunction with the ohmmeter test.

NPN

V

mA

E
B
C

The E-B junction is forward biased by the ohmmeter.

NPN

V

mA

E
B
C

The C-E resistance is very high.

NPN

V

mA

E
B
C
100 kW

The meter reading is < 100 kW due to gain.

Concept Review
• It is possible to test transistors out-of-circuit
using an ohmmeter.
• The E-B and C-B junctions act as diodes
during ohmmeter testing.
• The C-E test shows a high resistance because
two junctions are involved; one of which is
reverse biased by the ohmmeter.
• Gain can be verified by using a resistor in
conjunction with the ohmmeter test.
Repeat Segment

Concept Preview
• Bipolar junction transistors (BJTs) are controlled by
base current.
• Junction field effect transistors (JFETs) are controlled
by gate voltage.

• JFETs operate in the depletion mode (as normally on
devices).
• Metal oxide semiconductor field effect transistors
(MOSFETs) usually operate in the enhancement mode
(as normally off devices).
• Insulated gate bipolar transistors (IGBTs) are modified
MOSFETs and have very low on-resistance.
• Unijunction transistors (UJTs) are not used as
amplifiers.

Current In

The BJT is
a current
amplifier.

Current
Amplifier

Current Out

Voltage In

The JFET is
a voltage
controlled
amplifier.

Voltage
Amplifier

Current Out

Source

Gate

Drain

P

N-channel
P-type substrate
Structure of an
N-channel JFET

The channel has carriers so it
conducts from source to drain.

Drain

Gate
Source

Source

Gate

Drain

P

N-channel
P-type substrate

A negative gate voltage
can push the carriers from
the channel and turn
the JFET off.

Drain

Gate
Source

0V
-1 V
-2 V

ID in mA

-3 V

VGS

-4 V

0

-5 V
VDS in Volts

This is known as a depletion-mode device.
N-channel JFET drain family of characteristic curves

It’s possible to make enhancement
type field effect transistors as well.
Metal
oxide
insulator

Drain

n

Gate

VGG

D

VDD

p

G

n

S
N-channel
MOSFET

Source

Gate bias enhances the channel and turns the device on.

5V
4V
3V

ID in mA

2V

VGS

1V

0

0V
Drain

VDS in Volts

Enhancement mode
MOSFET drain family of
characteristic curves

Gate
Source

The IGBT (insulated gate bipolar transistor)
Operation and structure
similar to a MOSFET
Voltage controlled
(like the MOSFET)
Has one more junction
than a MOSFET
Hole injection reduces
the collector resistance

Faster turn off than
BJTs but not as fast
as MOSFETS

RCE = 8.33 mW

Three major device technologies

hole injection
Extra
junction

Courtesy of Powerex, Inc.

Typical IGBT Driver Circuit
Typically +15 V for turn on
Typically - 5 to -15 V for turn off

Control signal

IGBT

Powerex IGBT Module Structure

Powerex high voltage IGBT package

Emitter voltage

The unijunction transistor fires
when its emitter voltage reaches VP.
VP

Then, the emitter voltage
drops due to its negative
resistance characteristic.
Base 2

Emitter current
Emitter

The UJT is not useful as an amplifier.
It is used in timing and control applications.

Base 1

Other Transistor Types Quiz
BJTs are _________-controlled
amplifiers.

current

FETs are __________-controlled
amplifiers.

voltage

JFETs operate in the __________ mode. depletion
MOSFETs operate in the __________
mode.

enhancement

IGBTs are __________-controlled
amplifiers.

voltage

UJTs are not useful as __________.

amplifiers

Concept Review
• Bipolar junction transistors (BJTs) are controlled by
base current.
• Junction field effect transistors (JFETs) are controlled
by gate voltage.
• JFETs operate in the depletion mode (as normally on
devices).
• Metal oxide semiconductor field effect transistors
(MOSFETs) usually operate in the enhancement mode
(as normally off devices).
• Insulated gate bipolar transistors (IGBTs) are modified
MOSFETs and have very low on-resistance.
• Unijunction transistors (UJTs) are not used as
amplifiers.
Repeat Segment

Concept Preview
• BJTs can be used as switches.
• No base current = switch is off.
• High base current = switch is on.
• The dissipation is always zero in an ideal
switch: off = no current flow and on = no
voltage drop.

• MOSFETs can also be used as switches: no
gate voltage = switch is off and high gate
voltage = switch is on.

How do transistor switches work?
Can be viewed as solid state relays:
they are either ON or they are OFF.
BJT switches are characterized by:
high base current (switch is on)
(or no base current … off)

low resistance from collector to emitter (on)
(or very high resistance … off)
low collector dissipation (on or off)
PC = VCE x IC
PC = 0 x IC = 0 W
(on)
(or PC = VCE x 0 = 0 W … off)

NPN SWITCH
LOAD

RCE @ 
W
0W
DRIVER

The
The
driver
driver
output
output
isiszero
positive,
volts,
IIBB>=I0
0and
andthe
theload
loadis
ison
off
The
driver
output
is
zero
volts,
B = 0 and ILOAD = 0

PNP SWITCH
DRIVER

LOAD

The
Z):
Thedriver
driveroutput
outputisgoes
isoff
off(high
(highthe
Z):the
theresistor
resistor
low:
voltage
drop
pulls
the
base
voltage
up
that
VV
pulls
thethe
base
voltage
upso
soV
that
across
resistor
makes
BE
BE==00
BE negative

PNP SWITCH WITH NPN DRIVER

LOAD

NPN SWITCH WITH PNP DRIVER
(NEGATIVE POWER SUPPLY)

VV
0VV
BE
BE@ @+0.7

VVBE
0 VV
BE@@-0.7

LOAD

STEPPER MOTOR

A

B

C

A

Enhancement mode
power MOSFETs
used as switches

B

C
D

D

Concept Review
• BJTs can be used as switches.
• No base current = switch is off.
• High base current = switch is on.
• The dissipation is always zero in an ideal
switch: off = no current flow and on = no
voltage drop.
• MOSFETs can also be used as switches: no
gate voltage = switch is off and high gate
voltage = switch is on.
Repeat Segment

REVIEW
• Amplification
• Transistors
• Characteristic Curves
• Transistor Testing
• Other Transistor Types
• Transistors as Switches


Slide 36

Electronics
Principles & Applications
Sixth Edition

Charles A. Schuler
Chapter 5

Transistors
(student version)
©2003

Glencoe/McGraw-Hill

INTRODUCTION
• Amplification
• Transistors
• Characteristic Curves
• Transistor Testing
• Other Transistor Types
• Transistors as Switches

Dear Student:
This presentation is arranged in segments.
Each segment is preceded by a Concept
Preview slide and is followed by a Concept
Review slide. When you reach a Concept
Review slide, you can return to the
beginning of that segment by clicking on the
Repeat Segment button. This will allow you
to view that segment again, if you want to.

Concept Preview
• Amplifiers provide gain (the output is larger
than the input).
• Transistors have gain.
• Transistors have a collector, a base, and an
emitter.
• The C-B junction is reverse biased.
• The B-E junction is forward biased.
• Most of the emitter carriers reach the collector.
• The base current is relatively small but controls
the larger currents.

In

Gain =

Amplifier

Out

In

Out

NPN Transistor Structure

The collector is lightly doped.

N

C

The base is thin and
is lightly doped.

P

B

The emitter is heavily doped.

N

E

NPN Transistor Bias
No current flows.
The C-B junction
is reverse biased.

N

C

P

B

N

E

NPN Transistor Bias

The B-E junction
is forward biased.

Current flows.

N

C

P

B

N

E

NPN Transistor Bias
IC
Current flows
everywhere.
Most of the emitter carriers
diffuse through the thin base
When
both
junctions
region since they are attracted
biased....
by are
the collector.

Note that IB is smaller
than IE or IC.

N

C

P

B

N

E

IB

IE

Note: when the
switch opens, all
currents go to zero.
Although IB is smaller
it controls IE and IC.

Gain is something small
controlling something large
(IB is small).

IC
N

C

P

B

N

E

IB

IE

Transistor Structure and Bias Quiz
The heaviest doping is found in
the ___________ region.

emitter

The thinnest of all three regions
is called the ____________.

base

The collector-base junction is
___________ biased.

reverse

The base-emitter junction is
____________ biased.

forward

The majority of the emitter
carriers flow to the ___________.

collector

Concept Review
• Amplifiers provide gain (the output is larger than
the input).
• Transistors have gain.

• Transistors have a collector, a base, and an emitter.
• The C-B junction is reverse biased.
• The B-E junction is forward biased.

• Most of the emitter carriers reach the collector.
• The base current is relatively small but controls the
larger currents.
Repeat Segment

Concept Preview
• The base to collector gain is called b (beta).
• To find b, divide the collector current by the
base current.
• The emitter current is the largest since it is the
sum of the base and collector currents.
• PNP transistors have opposite polarity from
NPN transistors.

• In an NPN transistor, the major flow is made
up of electrons.
• In a PNP transistor, the major flow is made up
of holes.

IC = 99 mA

The current gain from
base to collector
is called b.
IB = 1 mA

b =

99
ICmA
1IBmA

= 99

IE = 100 mA

C
P

B

N

E

IC = 99 mA
Kirchhoff’s
current law:

IB = 1 mA

C
P

B

N

E

IE = I B + I C

= 1 mA + 99 mA
= 100 mA
IE = 100 mA

IC = 99 mA
In a PNP transistor,
holes flow from
emitter to collector.

IB = 1 mA
Notice the PNP
bias voltages.

C
B

E

IE = 100 mA

Transistor Currents Quiz
b is the ratio of collector current to
______ current.

base

The sum of the base and collector
currents is the __________ current.

emitter

In NPN transistors, the flow from emitter
to collector is composed of _______.

electrons

In PNP transistors, the flow from emitter
to collector is composed of _______.

holes

Both NPN and PNP transistors show
__________ gain.

current

Concept Review
• The base to collector gain is called b (beta).
• To find b, divide the collector current by the
base current.
• The emitter current is the largest since it is the
sum of the base and collector currents.
• PNP transistors have opposite polarity from
NPN transistors.
• In an NPN transistor, the major flow is made
up of electrons.
• In a PNP transistor, the major flow is made up
of holes.
Repeat Segment

Concept Preview
• The NPN schematic symbol shows the emitter
arrow as Not Pointing iN.
• The collector curves are a graph of collector
voltage versus collector current.
• Both dc beta (bdc) and ac beta (bac) can be
determined from the collector curves.
• The collector circuit of a transistor can be
modeled as a resistor, as a closed switch or as
an open switch.
• The amount of base current determines which
of the three models applies.

NPN Schematic Symbol
Collector

Base

C
B E

Emitter
Memory aid: NPN
means Not Pointing iN.

PNP Schematic Symbol
Collector

Base

C
B E

Emitter

IC

This circuit is used to
collect IC versus
VCE data for
several values of IB.
C

IB
B

E

VCE

When graphed, the data provide an
NPN collector family of curves.
100 mA

14
12
10
IC in mA 8
6
4
2

80 mA
60 mA
40 mA
20 mA

0 2 4 6

8 10 12 14 16 18

VCE in Volts

0 mA

100 mA

14
12
10
IC in mA 8
6
4
2

80 mA
60 mA

40 mA
20 mA

0 2 4 6

8 10 12 14 16 18

0 mA

VCE in Volts

b =

14
mA
6ICmA
40
IB mA
100
mA

150
== 140

This type of gain
is called bdc or hFE.

100 mA

14
12
10
IC in mA 8
6
4
2

80 mA
60 mA

40 mA
20 mA

0 2 4 6

bac =

2.5DImA
C
20DImA
B

8 10 12 14 16 18

0 mA

VCE in Volts
= 125

Another type of gain
is called bac or hfe.

100 mA

14
12
10
IC in mA 8
6
4
2

80 mA
60 mA

40 mA
20 mA

0 2 4 6
IB

C

8 10 12 14 16 18
VCE in Volts

0 mA

With these values of IB:
The C-E model is a resistor.
E

100 mA

14
12
10
IC in mA 8
6
4
2
0 2 4 6
IB

80 mA
60 mA

40 mA
20 mA
8 10 12 14 16 18
VCE in Volts

0 mA

When IB >> 100 mA
VCE @ 0
The model is a closed switch.

100 mA

14
12
10
IC in mA 8
6
4
2
0 2 4 6
IB

80 mA
60 mA

40 mA
20 mA
8 10 12 14 16 18
VCE in Volts

0 mA

When IB = 0
IC = 0
The model is an open switch.

Transistor Operating Conditions Quiz
When IB is large and VCE @ 0, the transistor
acts as a ___________ switch.
closed
When IB = 0 and IC = 0, the transistor
acts as an ___________ switch.

open

When IB > 0 and VCE > 0, the transistor
acts as a ___________.

resistor

Two current gain measures are bdc and
__________.

bac

The symbol hfe is the same as _________.

bac

Concept Review
• The NPN schematic symbol shows the emitter
arrow as Not Pointing iN.
• The collector curves are a graph of collector
voltage versus collector current.
• Both dc beta (bdc) and ac beta (bac) can be
determined from the collector curves.
• The collector circuit of a transistor can be
modeled as a resistor, as a closed switch or as
an open switch.
• The amount of base current determines which
of the three models applies.
Repeat Segment

Concept Preview
• It is possible to test transistors out-of-circuit
using an ohmmeter.
• The E-B and C-B junctions act as diodes
during ohmmeter testing.

• The C-E test shows a high resistance because
two junctions are involved; one of which is
reverse biased by the ohmmeter.
• Gain can be verified by using a resistor in
conjunction with the ohmmeter test.

NPN

V

mA

E
B
C

The E-B junction is forward biased by the ohmmeter.

NPN

V

mA

E
B
C

The C-E resistance is very high.

NPN

V

mA

E
B
C
100 kW

The meter reading is < 100 kW due to gain.

Concept Review
• It is possible to test transistors out-of-circuit
using an ohmmeter.
• The E-B and C-B junctions act as diodes
during ohmmeter testing.
• The C-E test shows a high resistance because
two junctions are involved; one of which is
reverse biased by the ohmmeter.
• Gain can be verified by using a resistor in
conjunction with the ohmmeter test.
Repeat Segment

Concept Preview
• Bipolar junction transistors (BJTs) are controlled by
base current.
• Junction field effect transistors (JFETs) are controlled
by gate voltage.

• JFETs operate in the depletion mode (as normally on
devices).
• Metal oxide semiconductor field effect transistors
(MOSFETs) usually operate in the enhancement mode
(as normally off devices).
• Insulated gate bipolar transistors (IGBTs) are modified
MOSFETs and have very low on-resistance.
• Unijunction transistors (UJTs) are not used as
amplifiers.

Current In

The BJT is
a current
amplifier.

Current
Amplifier

Current Out

Voltage In

The JFET is
a voltage
controlled
amplifier.

Voltage
Amplifier

Current Out

Source

Gate

Drain

P

N-channel
P-type substrate
Structure of an
N-channel JFET

The channel has carriers so it
conducts from source to drain.

Drain

Gate
Source

Source

Gate

Drain

P

N-channel
P-type substrate

A negative gate voltage
can push the carriers from
the channel and turn
the JFET off.

Drain

Gate
Source

0V
-1 V
-2 V

ID in mA

-3 V

VGS

-4 V

0

-5 V
VDS in Volts

This is known as a depletion-mode device.
N-channel JFET drain family of characteristic curves

It’s possible to make enhancement
type field effect transistors as well.
Metal
oxide
insulator

Drain

n

Gate

VGG

D

VDD

p

G

n

S
N-channel
MOSFET

Source

Gate bias enhances the channel and turns the device on.

5V
4V
3V

ID in mA

2V

VGS

1V

0

0V
Drain

VDS in Volts

Enhancement mode
MOSFET drain family of
characteristic curves

Gate
Source

The IGBT (insulated gate bipolar transistor)
Operation and structure
similar to a MOSFET
Voltage controlled
(like the MOSFET)
Has one more junction
than a MOSFET
Hole injection reduces
the collector resistance

Faster turn off than
BJTs but not as fast
as MOSFETS

RCE = 8.33 mW

Three major device technologies

hole injection
Extra
junction

Courtesy of Powerex, Inc.

Typical IGBT Driver Circuit
Typically +15 V for turn on
Typically - 5 to -15 V for turn off

Control signal

IGBT

Powerex IGBT Module Structure

Powerex high voltage IGBT package

Emitter voltage

The unijunction transistor fires
when its emitter voltage reaches VP.
VP

Then, the emitter voltage
drops due to its negative
resistance characteristic.
Base 2

Emitter current
Emitter

The UJT is not useful as an amplifier.
It is used in timing and control applications.

Base 1

Other Transistor Types Quiz
BJTs are _________-controlled
amplifiers.

current

FETs are __________-controlled
amplifiers.

voltage

JFETs operate in the __________ mode. depletion
MOSFETs operate in the __________
mode.

enhancement

IGBTs are __________-controlled
amplifiers.

voltage

UJTs are not useful as __________.

amplifiers

Concept Review
• Bipolar junction transistors (BJTs) are controlled by
base current.
• Junction field effect transistors (JFETs) are controlled
by gate voltage.
• JFETs operate in the depletion mode (as normally on
devices).
• Metal oxide semiconductor field effect transistors
(MOSFETs) usually operate in the enhancement mode
(as normally off devices).
• Insulated gate bipolar transistors (IGBTs) are modified
MOSFETs and have very low on-resistance.
• Unijunction transistors (UJTs) are not used as
amplifiers.
Repeat Segment

Concept Preview
• BJTs can be used as switches.
• No base current = switch is off.
• High base current = switch is on.
• The dissipation is always zero in an ideal
switch: off = no current flow and on = no
voltage drop.

• MOSFETs can also be used as switches: no
gate voltage = switch is off and high gate
voltage = switch is on.

How do transistor switches work?
Can be viewed as solid state relays:
they are either ON or they are OFF.
BJT switches are characterized by:
high base current (switch is on)
(or no base current … off)

low resistance from collector to emitter (on)
(or very high resistance … off)
low collector dissipation (on or off)
PC = VCE x IC
PC = 0 x IC = 0 W
(on)
(or PC = VCE x 0 = 0 W … off)

NPN SWITCH
LOAD

RCE @ 
W
0W
DRIVER

The
The
driver
driver
output
output
isiszero
positive,
volts,
IIBB>=I0
0and
andthe
theload
loadis
ison
off
The
driver
output
is
zero
volts,
B = 0 and ILOAD = 0

PNP SWITCH
DRIVER

LOAD

The
Z):
Thedriver
driveroutput
outputisgoes
isoff
off(high
(highthe
Z):the
theresistor
resistor
low:
voltage
drop
pulls
the
base
voltage
up
that
VV
pulls
thethe
base
voltage
upso
soV
that
across
resistor
makes
BE
BE==00
BE negative

PNP SWITCH WITH NPN DRIVER

LOAD

NPN SWITCH WITH PNP DRIVER
(NEGATIVE POWER SUPPLY)

VV
0VV
BE
BE@ @+0.7

VVBE
0 VV
BE@@-0.7

LOAD

STEPPER MOTOR

A

B

C

A

Enhancement mode
power MOSFETs
used as switches

B

C
D

D

Concept Review
• BJTs can be used as switches.
• No base current = switch is off.
• High base current = switch is on.
• The dissipation is always zero in an ideal
switch: off = no current flow and on = no
voltage drop.
• MOSFETs can also be used as switches: no
gate voltage = switch is off and high gate
voltage = switch is on.
Repeat Segment

REVIEW
• Amplification
• Transistors
• Characteristic Curves
• Transistor Testing
• Other Transistor Types
• Transistors as Switches


Slide 37

Electronics
Principles & Applications
Sixth Edition

Charles A. Schuler
Chapter 5

Transistors
(student version)
©2003

Glencoe/McGraw-Hill

INTRODUCTION
• Amplification
• Transistors
• Characteristic Curves
• Transistor Testing
• Other Transistor Types
• Transistors as Switches

Dear Student:
This presentation is arranged in segments.
Each segment is preceded by a Concept
Preview slide and is followed by a Concept
Review slide. When you reach a Concept
Review slide, you can return to the
beginning of that segment by clicking on the
Repeat Segment button. This will allow you
to view that segment again, if you want to.

Concept Preview
• Amplifiers provide gain (the output is larger
than the input).
• Transistors have gain.
• Transistors have a collector, a base, and an
emitter.
• The C-B junction is reverse biased.
• The B-E junction is forward biased.
• Most of the emitter carriers reach the collector.
• The base current is relatively small but controls
the larger currents.

In

Gain =

Amplifier

Out

In

Out

NPN Transistor Structure

The collector is lightly doped.

N

C

The base is thin and
is lightly doped.

P

B

The emitter is heavily doped.

N

E

NPN Transistor Bias
No current flows.
The C-B junction
is reverse biased.

N

C

P

B

N

E

NPN Transistor Bias

The B-E junction
is forward biased.

Current flows.

N

C

P

B

N

E

NPN Transistor Bias
IC
Current flows
everywhere.
Most of the emitter carriers
diffuse through the thin base
When
both
junctions
region since they are attracted
biased....
by are
the collector.

Note that IB is smaller
than IE or IC.

N

C

P

B

N

E

IB

IE

Note: when the
switch opens, all
currents go to zero.
Although IB is smaller
it controls IE and IC.

Gain is something small
controlling something large
(IB is small).

IC
N

C

P

B

N

E

IB

IE

Transistor Structure and Bias Quiz
The heaviest doping is found in
the ___________ region.

emitter

The thinnest of all three regions
is called the ____________.

base

The collector-base junction is
___________ biased.

reverse

The base-emitter junction is
____________ biased.

forward

The majority of the emitter
carriers flow to the ___________.

collector

Concept Review
• Amplifiers provide gain (the output is larger than
the input).
• Transistors have gain.

• Transistors have a collector, a base, and an emitter.
• The C-B junction is reverse biased.
• The B-E junction is forward biased.

• Most of the emitter carriers reach the collector.
• The base current is relatively small but controls the
larger currents.
Repeat Segment

Concept Preview
• The base to collector gain is called b (beta).
• To find b, divide the collector current by the
base current.
• The emitter current is the largest since it is the
sum of the base and collector currents.
• PNP transistors have opposite polarity from
NPN transistors.

• In an NPN transistor, the major flow is made
up of electrons.
• In a PNP transistor, the major flow is made up
of holes.

IC = 99 mA

The current gain from
base to collector
is called b.
IB = 1 mA

b =

99
ICmA
1IBmA

= 99

IE = 100 mA

C
P

B

N

E

IC = 99 mA
Kirchhoff’s
current law:

IB = 1 mA

C
P

B

N

E

IE = I B + I C

= 1 mA + 99 mA
= 100 mA
IE = 100 mA

IC = 99 mA
In a PNP transistor,
holes flow from
emitter to collector.

IB = 1 mA
Notice the PNP
bias voltages.

C
B

E

IE = 100 mA

Transistor Currents Quiz
b is the ratio of collector current to
______ current.

base

The sum of the base and collector
currents is the __________ current.

emitter

In NPN transistors, the flow from emitter
to collector is composed of _______.

electrons

In PNP transistors, the flow from emitter
to collector is composed of _______.

holes

Both NPN and PNP transistors show
__________ gain.

current

Concept Review
• The base to collector gain is called b (beta).
• To find b, divide the collector current by the
base current.
• The emitter current is the largest since it is the
sum of the base and collector currents.
• PNP transistors have opposite polarity from
NPN transistors.
• In an NPN transistor, the major flow is made
up of electrons.
• In a PNP transistor, the major flow is made up
of holes.
Repeat Segment

Concept Preview
• The NPN schematic symbol shows the emitter
arrow as Not Pointing iN.
• The collector curves are a graph of collector
voltage versus collector current.
• Both dc beta (bdc) and ac beta (bac) can be
determined from the collector curves.
• The collector circuit of a transistor can be
modeled as a resistor, as a closed switch or as
an open switch.
• The amount of base current determines which
of the three models applies.

NPN Schematic Symbol
Collector

Base

C
B E

Emitter
Memory aid: NPN
means Not Pointing iN.

PNP Schematic Symbol
Collector

Base

C
B E

Emitter

IC

This circuit is used to
collect IC versus
VCE data for
several values of IB.
C

IB
B

E

VCE

When graphed, the data provide an
NPN collector family of curves.
100 mA

14
12
10
IC in mA 8
6
4
2

80 mA
60 mA
40 mA
20 mA

0 2 4 6

8 10 12 14 16 18

VCE in Volts

0 mA

100 mA

14
12
10
IC in mA 8
6
4
2

80 mA
60 mA

40 mA
20 mA

0 2 4 6

8 10 12 14 16 18

0 mA

VCE in Volts

b =

14
mA
6ICmA
40
IB mA
100
mA

150
== 140

This type of gain
is called bdc or hFE.

100 mA

14
12
10
IC in mA 8
6
4
2

80 mA
60 mA

40 mA
20 mA

0 2 4 6

bac =

2.5DImA
C
20DImA
B

8 10 12 14 16 18

0 mA

VCE in Volts
= 125

Another type of gain
is called bac or hfe.

100 mA

14
12
10
IC in mA 8
6
4
2

80 mA
60 mA

40 mA
20 mA

0 2 4 6
IB

C

8 10 12 14 16 18
VCE in Volts

0 mA

With these values of IB:
The C-E model is a resistor.
E

100 mA

14
12
10
IC in mA 8
6
4
2
0 2 4 6
IB

80 mA
60 mA

40 mA
20 mA
8 10 12 14 16 18
VCE in Volts

0 mA

When IB >> 100 mA
VCE @ 0
The model is a closed switch.

100 mA

14
12
10
IC in mA 8
6
4
2
0 2 4 6
IB

80 mA
60 mA

40 mA
20 mA
8 10 12 14 16 18
VCE in Volts

0 mA

When IB = 0
IC = 0
The model is an open switch.

Transistor Operating Conditions Quiz
When IB is large and VCE @ 0, the transistor
acts as a ___________ switch.
closed
When IB = 0 and IC = 0, the transistor
acts as an ___________ switch.

open

When IB > 0 and VCE > 0, the transistor
acts as a ___________.

resistor

Two current gain measures are bdc and
__________.

bac

The symbol hfe is the same as _________.

bac

Concept Review
• The NPN schematic symbol shows the emitter
arrow as Not Pointing iN.
• The collector curves are a graph of collector
voltage versus collector current.
• Both dc beta (bdc) and ac beta (bac) can be
determined from the collector curves.
• The collector circuit of a transistor can be
modeled as a resistor, as a closed switch or as
an open switch.
• The amount of base current determines which
of the three models applies.
Repeat Segment

Concept Preview
• It is possible to test transistors out-of-circuit
using an ohmmeter.
• The E-B and C-B junctions act as diodes
during ohmmeter testing.

• The C-E test shows a high resistance because
two junctions are involved; one of which is
reverse biased by the ohmmeter.
• Gain can be verified by using a resistor in
conjunction with the ohmmeter test.

NPN

V

mA

E
B
C

The E-B junction is forward biased by the ohmmeter.

NPN

V

mA

E
B
C

The C-E resistance is very high.

NPN

V

mA

E
B
C
100 kW

The meter reading is < 100 kW due to gain.

Concept Review
• It is possible to test transistors out-of-circuit
using an ohmmeter.
• The E-B and C-B junctions act as diodes
during ohmmeter testing.
• The C-E test shows a high resistance because
two junctions are involved; one of which is
reverse biased by the ohmmeter.
• Gain can be verified by using a resistor in
conjunction with the ohmmeter test.
Repeat Segment

Concept Preview
• Bipolar junction transistors (BJTs) are controlled by
base current.
• Junction field effect transistors (JFETs) are controlled
by gate voltage.

• JFETs operate in the depletion mode (as normally on
devices).
• Metal oxide semiconductor field effect transistors
(MOSFETs) usually operate in the enhancement mode
(as normally off devices).
• Insulated gate bipolar transistors (IGBTs) are modified
MOSFETs and have very low on-resistance.
• Unijunction transistors (UJTs) are not used as
amplifiers.

Current In

The BJT is
a current
amplifier.

Current
Amplifier

Current Out

Voltage In

The JFET is
a voltage
controlled
amplifier.

Voltage
Amplifier

Current Out

Source

Gate

Drain

P

N-channel
P-type substrate
Structure of an
N-channel JFET

The channel has carriers so it
conducts from source to drain.

Drain

Gate
Source

Source

Gate

Drain

P

N-channel
P-type substrate

A negative gate voltage
can push the carriers from
the channel and turn
the JFET off.

Drain

Gate
Source

0V
-1 V
-2 V

ID in mA

-3 V

VGS

-4 V

0

-5 V
VDS in Volts

This is known as a depletion-mode device.
N-channel JFET drain family of characteristic curves

It’s possible to make enhancement
type field effect transistors as well.
Metal
oxide
insulator

Drain

n

Gate

VGG

D

VDD

p

G

n

S
N-channel
MOSFET

Source

Gate bias enhances the channel and turns the device on.

5V
4V
3V

ID in mA

2V

VGS

1V

0

0V
Drain

VDS in Volts

Enhancement mode
MOSFET drain family of
characteristic curves

Gate
Source

The IGBT (insulated gate bipolar transistor)
Operation and structure
similar to a MOSFET
Voltage controlled
(like the MOSFET)
Has one more junction
than a MOSFET
Hole injection reduces
the collector resistance

Faster turn off than
BJTs but not as fast
as MOSFETS

RCE = 8.33 mW

Three major device technologies

hole injection
Extra
junction

Courtesy of Powerex, Inc.

Typical IGBT Driver Circuit
Typically +15 V for turn on
Typically - 5 to -15 V for turn off

Control signal

IGBT

Powerex IGBT Module Structure

Powerex high voltage IGBT package

Emitter voltage

The unijunction transistor fires
when its emitter voltage reaches VP.
VP

Then, the emitter voltage
drops due to its negative
resistance characteristic.
Base 2

Emitter current
Emitter

The UJT is not useful as an amplifier.
It is used in timing and control applications.

Base 1

Other Transistor Types Quiz
BJTs are _________-controlled
amplifiers.

current

FETs are __________-controlled
amplifiers.

voltage

JFETs operate in the __________ mode. depletion
MOSFETs operate in the __________
mode.

enhancement

IGBTs are __________-controlled
amplifiers.

voltage

UJTs are not useful as __________.

amplifiers

Concept Review
• Bipolar junction transistors (BJTs) are controlled by
base current.
• Junction field effect transistors (JFETs) are controlled
by gate voltage.
• JFETs operate in the depletion mode (as normally on
devices).
• Metal oxide semiconductor field effect transistors
(MOSFETs) usually operate in the enhancement mode
(as normally off devices).
• Insulated gate bipolar transistors (IGBTs) are modified
MOSFETs and have very low on-resistance.
• Unijunction transistors (UJTs) are not used as
amplifiers.
Repeat Segment

Concept Preview
• BJTs can be used as switches.
• No base current = switch is off.
• High base current = switch is on.
• The dissipation is always zero in an ideal
switch: off = no current flow and on = no
voltage drop.

• MOSFETs can also be used as switches: no
gate voltage = switch is off and high gate
voltage = switch is on.

How do transistor switches work?
Can be viewed as solid state relays:
they are either ON or they are OFF.
BJT switches are characterized by:
high base current (switch is on)
(or no base current … off)

low resistance from collector to emitter (on)
(or very high resistance … off)
low collector dissipation (on or off)
PC = VCE x IC
PC = 0 x IC = 0 W
(on)
(or PC = VCE x 0 = 0 W … off)

NPN SWITCH
LOAD

RCE @ 
W
0W
DRIVER

The
The
driver
driver
output
output
isiszero
positive,
volts,
IIBB>=I0
0and
andthe
theload
loadis
ison
off
The
driver
output
is
zero
volts,
B = 0 and ILOAD = 0

PNP SWITCH
DRIVER

LOAD

The
Z):
Thedriver
driveroutput
outputisgoes
isoff
off(high
(highthe
Z):the
theresistor
resistor
low:
voltage
drop
pulls
the
base
voltage
up
that
VV
pulls
thethe
base
voltage
upso
soV
that
across
resistor
makes
BE
BE==00
BE negative

PNP SWITCH WITH NPN DRIVER

LOAD

NPN SWITCH WITH PNP DRIVER
(NEGATIVE POWER SUPPLY)

VV
0VV
BE
BE@ @+0.7

VVBE
0 VV
BE@@-0.7

LOAD

STEPPER MOTOR

A

B

C

A

Enhancement mode
power MOSFETs
used as switches

B

C
D

D

Concept Review
• BJTs can be used as switches.
• No base current = switch is off.
• High base current = switch is on.
• The dissipation is always zero in an ideal
switch: off = no current flow and on = no
voltage drop.
• MOSFETs can also be used as switches: no
gate voltage = switch is off and high gate
voltage = switch is on.
Repeat Segment

REVIEW
• Amplification
• Transistors
• Characteristic Curves
• Transistor Testing
• Other Transistor Types
• Transistors as Switches


Slide 38

Electronics
Principles & Applications
Sixth Edition

Charles A. Schuler
Chapter 5

Transistors
(student version)
©2003

Glencoe/McGraw-Hill

INTRODUCTION
• Amplification
• Transistors
• Characteristic Curves
• Transistor Testing
• Other Transistor Types
• Transistors as Switches

Dear Student:
This presentation is arranged in segments.
Each segment is preceded by a Concept
Preview slide and is followed by a Concept
Review slide. When you reach a Concept
Review slide, you can return to the
beginning of that segment by clicking on the
Repeat Segment button. This will allow you
to view that segment again, if you want to.

Concept Preview
• Amplifiers provide gain (the output is larger
than the input).
• Transistors have gain.
• Transistors have a collector, a base, and an
emitter.
• The C-B junction is reverse biased.
• The B-E junction is forward biased.
• Most of the emitter carriers reach the collector.
• The base current is relatively small but controls
the larger currents.

In

Gain =

Amplifier

Out

In

Out

NPN Transistor Structure

The collector is lightly doped.

N

C

The base is thin and
is lightly doped.

P

B

The emitter is heavily doped.

N

E

NPN Transistor Bias
No current flows.
The C-B junction
is reverse biased.

N

C

P

B

N

E

NPN Transistor Bias

The B-E junction
is forward biased.

Current flows.

N

C

P

B

N

E

NPN Transistor Bias
IC
Current flows
everywhere.
Most of the emitter carriers
diffuse through the thin base
When
both
junctions
region since they are attracted
biased....
by are
the collector.

Note that IB is smaller
than IE or IC.

N

C

P

B

N

E

IB

IE

Note: when the
switch opens, all
currents go to zero.
Although IB is smaller
it controls IE and IC.

Gain is something small
controlling something large
(IB is small).

IC
N

C

P

B

N

E

IB

IE

Transistor Structure and Bias Quiz
The heaviest doping is found in
the ___________ region.

emitter

The thinnest of all three regions
is called the ____________.

base

The collector-base junction is
___________ biased.

reverse

The base-emitter junction is
____________ biased.

forward

The majority of the emitter
carriers flow to the ___________.

collector

Concept Review
• Amplifiers provide gain (the output is larger than
the input).
• Transistors have gain.

• Transistors have a collector, a base, and an emitter.
• The C-B junction is reverse biased.
• The B-E junction is forward biased.

• Most of the emitter carriers reach the collector.
• The base current is relatively small but controls the
larger currents.
Repeat Segment

Concept Preview
• The base to collector gain is called b (beta).
• To find b, divide the collector current by the
base current.
• The emitter current is the largest since it is the
sum of the base and collector currents.
• PNP transistors have opposite polarity from
NPN transistors.

• In an NPN transistor, the major flow is made
up of electrons.
• In a PNP transistor, the major flow is made up
of holes.

IC = 99 mA

The current gain from
base to collector
is called b.
IB = 1 mA

b =

99
ICmA
1IBmA

= 99

IE = 100 mA

C
P

B

N

E

IC = 99 mA
Kirchhoff’s
current law:

IB = 1 mA

C
P

B

N

E

IE = I B + I C

= 1 mA + 99 mA
= 100 mA
IE = 100 mA

IC = 99 mA
In a PNP transistor,
holes flow from
emitter to collector.

IB = 1 mA
Notice the PNP
bias voltages.

C
B

E

IE = 100 mA

Transistor Currents Quiz
b is the ratio of collector current to
______ current.

base

The sum of the base and collector
currents is the __________ current.

emitter

In NPN transistors, the flow from emitter
to collector is composed of _______.

electrons

In PNP transistors, the flow from emitter
to collector is composed of _______.

holes

Both NPN and PNP transistors show
__________ gain.

current

Concept Review
• The base to collector gain is called b (beta).
• To find b, divide the collector current by the
base current.
• The emitter current is the largest since it is the
sum of the base and collector currents.
• PNP transistors have opposite polarity from
NPN transistors.
• In an NPN transistor, the major flow is made
up of electrons.
• In a PNP transistor, the major flow is made up
of holes.
Repeat Segment

Concept Preview
• The NPN schematic symbol shows the emitter
arrow as Not Pointing iN.
• The collector curves are a graph of collector
voltage versus collector current.
• Both dc beta (bdc) and ac beta (bac) can be
determined from the collector curves.
• The collector circuit of a transistor can be
modeled as a resistor, as a closed switch or as
an open switch.
• The amount of base current determines which
of the three models applies.

NPN Schematic Symbol
Collector

Base

C
B E

Emitter
Memory aid: NPN
means Not Pointing iN.

PNP Schematic Symbol
Collector

Base

C
B E

Emitter

IC

This circuit is used to
collect IC versus
VCE data for
several values of IB.
C

IB
B

E

VCE

When graphed, the data provide an
NPN collector family of curves.
100 mA

14
12
10
IC in mA 8
6
4
2

80 mA
60 mA
40 mA
20 mA

0 2 4 6

8 10 12 14 16 18

VCE in Volts

0 mA

100 mA

14
12
10
IC in mA 8
6
4
2

80 mA
60 mA

40 mA
20 mA

0 2 4 6

8 10 12 14 16 18

0 mA

VCE in Volts

b =

14
mA
6ICmA
40
IB mA
100
mA

150
== 140

This type of gain
is called bdc or hFE.

100 mA

14
12
10
IC in mA 8
6
4
2

80 mA
60 mA

40 mA
20 mA

0 2 4 6

bac =

2.5DImA
C
20DImA
B

8 10 12 14 16 18

0 mA

VCE in Volts
= 125

Another type of gain
is called bac or hfe.

100 mA

14
12
10
IC in mA 8
6
4
2

80 mA
60 mA

40 mA
20 mA

0 2 4 6
IB

C

8 10 12 14 16 18
VCE in Volts

0 mA

With these values of IB:
The C-E model is a resistor.
E

100 mA

14
12
10
IC in mA 8
6
4
2
0 2 4 6
IB

80 mA
60 mA

40 mA
20 mA
8 10 12 14 16 18
VCE in Volts

0 mA

When IB >> 100 mA
VCE @ 0
The model is a closed switch.

100 mA

14
12
10
IC in mA 8
6
4
2
0 2 4 6
IB

80 mA
60 mA

40 mA
20 mA
8 10 12 14 16 18
VCE in Volts

0 mA

When IB = 0
IC = 0
The model is an open switch.

Transistor Operating Conditions Quiz
When IB is large and VCE @ 0, the transistor
acts as a ___________ switch.
closed
When IB = 0 and IC = 0, the transistor
acts as an ___________ switch.

open

When IB > 0 and VCE > 0, the transistor
acts as a ___________.

resistor

Two current gain measures are bdc and
__________.

bac

The symbol hfe is the same as _________.

bac

Concept Review
• The NPN schematic symbol shows the emitter
arrow as Not Pointing iN.
• The collector curves are a graph of collector
voltage versus collector current.
• Both dc beta (bdc) and ac beta (bac) can be
determined from the collector curves.
• The collector circuit of a transistor can be
modeled as a resistor, as a closed switch or as
an open switch.
• The amount of base current determines which
of the three models applies.
Repeat Segment

Concept Preview
• It is possible to test transistors out-of-circuit
using an ohmmeter.
• The E-B and C-B junctions act as diodes
during ohmmeter testing.

• The C-E test shows a high resistance because
two junctions are involved; one of which is
reverse biased by the ohmmeter.
• Gain can be verified by using a resistor in
conjunction with the ohmmeter test.

NPN

V

mA

E
B
C

The E-B junction is forward biased by the ohmmeter.

NPN

V

mA

E
B
C

The C-E resistance is very high.

NPN

V

mA

E
B
C
100 kW

The meter reading is < 100 kW due to gain.

Concept Review
• It is possible to test transistors out-of-circuit
using an ohmmeter.
• The E-B and C-B junctions act as diodes
during ohmmeter testing.
• The C-E test shows a high resistance because
two junctions are involved; one of which is
reverse biased by the ohmmeter.
• Gain can be verified by using a resistor in
conjunction with the ohmmeter test.
Repeat Segment

Concept Preview
• Bipolar junction transistors (BJTs) are controlled by
base current.
• Junction field effect transistors (JFETs) are controlled
by gate voltage.

• JFETs operate in the depletion mode (as normally on
devices).
• Metal oxide semiconductor field effect transistors
(MOSFETs) usually operate in the enhancement mode
(as normally off devices).
• Insulated gate bipolar transistors (IGBTs) are modified
MOSFETs and have very low on-resistance.
• Unijunction transistors (UJTs) are not used as
amplifiers.

Current In

The BJT is
a current
amplifier.

Current
Amplifier

Current Out

Voltage In

The JFET is
a voltage
controlled
amplifier.

Voltage
Amplifier

Current Out

Source

Gate

Drain

P

N-channel
P-type substrate
Structure of an
N-channel JFET

The channel has carriers so it
conducts from source to drain.

Drain

Gate
Source

Source

Gate

Drain

P

N-channel
P-type substrate

A negative gate voltage
can push the carriers from
the channel and turn
the JFET off.

Drain

Gate
Source

0V
-1 V
-2 V

ID in mA

-3 V

VGS

-4 V

0

-5 V
VDS in Volts

This is known as a depletion-mode device.
N-channel JFET drain family of characteristic curves

It’s possible to make enhancement
type field effect transistors as well.
Metal
oxide
insulator

Drain

n

Gate

VGG

D

VDD

p

G

n

S
N-channel
MOSFET

Source

Gate bias enhances the channel and turns the device on.

5V
4V
3V

ID in mA

2V

VGS

1V

0

0V
Drain

VDS in Volts

Enhancement mode
MOSFET drain family of
characteristic curves

Gate
Source

The IGBT (insulated gate bipolar transistor)
Operation and structure
similar to a MOSFET
Voltage controlled
(like the MOSFET)
Has one more junction
than a MOSFET
Hole injection reduces
the collector resistance

Faster turn off than
BJTs but not as fast
as MOSFETS

RCE = 8.33 mW

Three major device technologies

hole injection
Extra
junction

Courtesy of Powerex, Inc.

Typical IGBT Driver Circuit
Typically +15 V for turn on
Typically - 5 to -15 V for turn off

Control signal

IGBT

Powerex IGBT Module Structure

Powerex high voltage IGBT package

Emitter voltage

The unijunction transistor fires
when its emitter voltage reaches VP.
VP

Then, the emitter voltage
drops due to its negative
resistance characteristic.
Base 2

Emitter current
Emitter

The UJT is not useful as an amplifier.
It is used in timing and control applications.

Base 1

Other Transistor Types Quiz
BJTs are _________-controlled
amplifiers.

current

FETs are __________-controlled
amplifiers.

voltage

JFETs operate in the __________ mode. depletion
MOSFETs operate in the __________
mode.

enhancement

IGBTs are __________-controlled
amplifiers.

voltage

UJTs are not useful as __________.

amplifiers

Concept Review
• Bipolar junction transistors (BJTs) are controlled by
base current.
• Junction field effect transistors (JFETs) are controlled
by gate voltage.
• JFETs operate in the depletion mode (as normally on
devices).
• Metal oxide semiconductor field effect transistors
(MOSFETs) usually operate in the enhancement mode
(as normally off devices).
• Insulated gate bipolar transistors (IGBTs) are modified
MOSFETs and have very low on-resistance.
• Unijunction transistors (UJTs) are not used as
amplifiers.
Repeat Segment

Concept Preview
• BJTs can be used as switches.
• No base current = switch is off.
• High base current = switch is on.
• The dissipation is always zero in an ideal
switch: off = no current flow and on = no
voltage drop.

• MOSFETs can also be used as switches: no
gate voltage = switch is off and high gate
voltage = switch is on.

How do transistor switches work?
Can be viewed as solid state relays:
they are either ON or they are OFF.
BJT switches are characterized by:
high base current (switch is on)
(or no base current … off)

low resistance from collector to emitter (on)
(or very high resistance … off)
low collector dissipation (on or off)
PC = VCE x IC
PC = 0 x IC = 0 W
(on)
(or PC = VCE x 0 = 0 W … off)

NPN SWITCH
LOAD

RCE @ 
W
0W
DRIVER

The
The
driver
driver
output
output
isiszero
positive,
volts,
IIBB>=I0
0and
andthe
theload
loadis
ison
off
The
driver
output
is
zero
volts,
B = 0 and ILOAD = 0

PNP SWITCH
DRIVER

LOAD

The
Z):
Thedriver
driveroutput
outputisgoes
isoff
off(high
(highthe
Z):the
theresistor
resistor
low:
voltage
drop
pulls
the
base
voltage
up
that
VV
pulls
thethe
base
voltage
upso
soV
that
across
resistor
makes
BE
BE==00
BE negative

PNP SWITCH WITH NPN DRIVER

LOAD

NPN SWITCH WITH PNP DRIVER
(NEGATIVE POWER SUPPLY)

VV
0VV
BE
BE@ @+0.7

VVBE
0 VV
BE@@-0.7

LOAD

STEPPER MOTOR

A

B

C

A

Enhancement mode
power MOSFETs
used as switches

B

C
D

D

Concept Review
• BJTs can be used as switches.
• No base current = switch is off.
• High base current = switch is on.
• The dissipation is always zero in an ideal
switch: off = no current flow and on = no
voltage drop.
• MOSFETs can also be used as switches: no
gate voltage = switch is off and high gate
voltage = switch is on.
Repeat Segment

REVIEW
• Amplification
• Transistors
• Characteristic Curves
• Transistor Testing
• Other Transistor Types
• Transistors as Switches


Slide 39

Electronics
Principles & Applications
Sixth Edition

Charles A. Schuler
Chapter 5

Transistors
(student version)
©2003

Glencoe/McGraw-Hill

INTRODUCTION
• Amplification
• Transistors
• Characteristic Curves
• Transistor Testing
• Other Transistor Types
• Transistors as Switches

Dear Student:
This presentation is arranged in segments.
Each segment is preceded by a Concept
Preview slide and is followed by a Concept
Review slide. When you reach a Concept
Review slide, you can return to the
beginning of that segment by clicking on the
Repeat Segment button. This will allow you
to view that segment again, if you want to.

Concept Preview
• Amplifiers provide gain (the output is larger
than the input).
• Transistors have gain.
• Transistors have a collector, a base, and an
emitter.
• The C-B junction is reverse biased.
• The B-E junction is forward biased.
• Most of the emitter carriers reach the collector.
• The base current is relatively small but controls
the larger currents.

In

Gain =

Amplifier

Out

In

Out

NPN Transistor Structure

The collector is lightly doped.

N

C

The base is thin and
is lightly doped.

P

B

The emitter is heavily doped.

N

E

NPN Transistor Bias
No current flows.
The C-B junction
is reverse biased.

N

C

P

B

N

E

NPN Transistor Bias

The B-E junction
is forward biased.

Current flows.

N

C

P

B

N

E

NPN Transistor Bias
IC
Current flows
everywhere.
Most of the emitter carriers
diffuse through the thin base
When
both
junctions
region since they are attracted
biased....
by are
the collector.

Note that IB is smaller
than IE or IC.

N

C

P

B

N

E

IB

IE

Note: when the
switch opens, all
currents go to zero.
Although IB is smaller
it controls IE and IC.

Gain is something small
controlling something large
(IB is small).

IC
N

C

P

B

N

E

IB

IE

Transistor Structure and Bias Quiz
The heaviest doping is found in
the ___________ region.

emitter

The thinnest of all three regions
is called the ____________.

base

The collector-base junction is
___________ biased.

reverse

The base-emitter junction is
____________ biased.

forward

The majority of the emitter
carriers flow to the ___________.

collector

Concept Review
• Amplifiers provide gain (the output is larger than
the input).
• Transistors have gain.

• Transistors have a collector, a base, and an emitter.
• The C-B junction is reverse biased.
• The B-E junction is forward biased.

• Most of the emitter carriers reach the collector.
• The base current is relatively small but controls the
larger currents.
Repeat Segment

Concept Preview
• The base to collector gain is called b (beta).
• To find b, divide the collector current by the
base current.
• The emitter current is the largest since it is the
sum of the base and collector currents.
• PNP transistors have opposite polarity from
NPN transistors.

• In an NPN transistor, the major flow is made
up of electrons.
• In a PNP transistor, the major flow is made up
of holes.

IC = 99 mA

The current gain from
base to collector
is called b.
IB = 1 mA

b =

99
ICmA
1IBmA

= 99

IE = 100 mA

C
P

B

N

E

IC = 99 mA
Kirchhoff’s
current law:

IB = 1 mA

C
P

B

N

E

IE = I B + I C

= 1 mA + 99 mA
= 100 mA
IE = 100 mA

IC = 99 mA
In a PNP transistor,
holes flow from
emitter to collector.

IB = 1 mA
Notice the PNP
bias voltages.

C
B

E

IE = 100 mA

Transistor Currents Quiz
b is the ratio of collector current to
______ current.

base

The sum of the base and collector
currents is the __________ current.

emitter

In NPN transistors, the flow from emitter
to collector is composed of _______.

electrons

In PNP transistors, the flow from emitter
to collector is composed of _______.

holes

Both NPN and PNP transistors show
__________ gain.

current

Concept Review
• The base to collector gain is called b (beta).
• To find b, divide the collector current by the
base current.
• The emitter current is the largest since it is the
sum of the base and collector currents.
• PNP transistors have opposite polarity from
NPN transistors.
• In an NPN transistor, the major flow is made
up of electrons.
• In a PNP transistor, the major flow is made up
of holes.
Repeat Segment

Concept Preview
• The NPN schematic symbol shows the emitter
arrow as Not Pointing iN.
• The collector curves are a graph of collector
voltage versus collector current.
• Both dc beta (bdc) and ac beta (bac) can be
determined from the collector curves.
• The collector circuit of a transistor can be
modeled as a resistor, as a closed switch or as
an open switch.
• The amount of base current determines which
of the three models applies.

NPN Schematic Symbol
Collector

Base

C
B E

Emitter
Memory aid: NPN
means Not Pointing iN.

PNP Schematic Symbol
Collector

Base

C
B E

Emitter

IC

This circuit is used to
collect IC versus
VCE data for
several values of IB.
C

IB
B

E

VCE

When graphed, the data provide an
NPN collector family of curves.
100 mA

14
12
10
IC in mA 8
6
4
2

80 mA
60 mA
40 mA
20 mA

0 2 4 6

8 10 12 14 16 18

VCE in Volts

0 mA

100 mA

14
12
10
IC in mA 8
6
4
2

80 mA
60 mA

40 mA
20 mA

0 2 4 6

8 10 12 14 16 18

0 mA

VCE in Volts

b =

14
mA
6ICmA
40
IB mA
100
mA

150
== 140

This type of gain
is called bdc or hFE.

100 mA

14
12
10
IC in mA 8
6
4
2

80 mA
60 mA

40 mA
20 mA

0 2 4 6

bac =

2.5DImA
C
20DImA
B

8 10 12 14 16 18

0 mA

VCE in Volts
= 125

Another type of gain
is called bac or hfe.

100 mA

14
12
10
IC in mA 8
6
4
2

80 mA
60 mA

40 mA
20 mA

0 2 4 6
IB

C

8 10 12 14 16 18
VCE in Volts

0 mA

With these values of IB:
The C-E model is a resistor.
E

100 mA

14
12
10
IC in mA 8
6
4
2
0 2 4 6
IB

80 mA
60 mA

40 mA
20 mA
8 10 12 14 16 18
VCE in Volts

0 mA

When IB >> 100 mA
VCE @ 0
The model is a closed switch.

100 mA

14
12
10
IC in mA 8
6
4
2
0 2 4 6
IB

80 mA
60 mA

40 mA
20 mA
8 10 12 14 16 18
VCE in Volts

0 mA

When IB = 0
IC = 0
The model is an open switch.

Transistor Operating Conditions Quiz
When IB is large and VCE @ 0, the transistor
acts as a ___________ switch.
closed
When IB = 0 and IC = 0, the transistor
acts as an ___________ switch.

open

When IB > 0 and VCE > 0, the transistor
acts as a ___________.

resistor

Two current gain measures are bdc and
__________.

bac

The symbol hfe is the same as _________.

bac

Concept Review
• The NPN schematic symbol shows the emitter
arrow as Not Pointing iN.
• The collector curves are a graph of collector
voltage versus collector current.
• Both dc beta (bdc) and ac beta (bac) can be
determined from the collector curves.
• The collector circuit of a transistor can be
modeled as a resistor, as a closed switch or as
an open switch.
• The amount of base current determines which
of the three models applies.
Repeat Segment

Concept Preview
• It is possible to test transistors out-of-circuit
using an ohmmeter.
• The E-B and C-B junctions act as diodes
during ohmmeter testing.

• The C-E test shows a high resistance because
two junctions are involved; one of which is
reverse biased by the ohmmeter.
• Gain can be verified by using a resistor in
conjunction with the ohmmeter test.

NPN

V

mA

E
B
C

The E-B junction is forward biased by the ohmmeter.

NPN

V

mA

E
B
C

The C-E resistance is very high.

NPN

V

mA

E
B
C
100 kW

The meter reading is < 100 kW due to gain.

Concept Review
• It is possible to test transistors out-of-circuit
using an ohmmeter.
• The E-B and C-B junctions act as diodes
during ohmmeter testing.
• The C-E test shows a high resistance because
two junctions are involved; one of which is
reverse biased by the ohmmeter.
• Gain can be verified by using a resistor in
conjunction with the ohmmeter test.
Repeat Segment

Concept Preview
• Bipolar junction transistors (BJTs) are controlled by
base current.
• Junction field effect transistors (JFETs) are controlled
by gate voltage.

• JFETs operate in the depletion mode (as normally on
devices).
• Metal oxide semiconductor field effect transistors
(MOSFETs) usually operate in the enhancement mode
(as normally off devices).
• Insulated gate bipolar transistors (IGBTs) are modified
MOSFETs and have very low on-resistance.
• Unijunction transistors (UJTs) are not used as
amplifiers.

Current In

The BJT is
a current
amplifier.

Current
Amplifier

Current Out

Voltage In

The JFET is
a voltage
controlled
amplifier.

Voltage
Amplifier

Current Out

Source

Gate

Drain

P

N-channel
P-type substrate
Structure of an
N-channel JFET

The channel has carriers so it
conducts from source to drain.

Drain

Gate
Source

Source

Gate

Drain

P

N-channel
P-type substrate

A negative gate voltage
can push the carriers from
the channel and turn
the JFET off.

Drain

Gate
Source

0V
-1 V
-2 V

ID in mA

-3 V

VGS

-4 V

0

-5 V
VDS in Volts

This is known as a depletion-mode device.
N-channel JFET drain family of characteristic curves

It’s possible to make enhancement
type field effect transistors as well.
Metal
oxide
insulator

Drain

n

Gate

VGG

D

VDD

p

G

n

S
N-channel
MOSFET

Source

Gate bias enhances the channel and turns the device on.

5V
4V
3V

ID in mA

2V

VGS

1V

0

0V
Drain

VDS in Volts

Enhancement mode
MOSFET drain family of
characteristic curves

Gate
Source

The IGBT (insulated gate bipolar transistor)
Operation and structure
similar to a MOSFET
Voltage controlled
(like the MOSFET)
Has one more junction
than a MOSFET
Hole injection reduces
the collector resistance

Faster turn off than
BJTs but not as fast
as MOSFETS

RCE = 8.33 mW

Three major device technologies

hole injection
Extra
junction

Courtesy of Powerex, Inc.

Typical IGBT Driver Circuit
Typically +15 V for turn on
Typically - 5 to -15 V for turn off

Control signal

IGBT

Powerex IGBT Module Structure

Powerex high voltage IGBT package

Emitter voltage

The unijunction transistor fires
when its emitter voltage reaches VP.
VP

Then, the emitter voltage
drops due to its negative
resistance characteristic.
Base 2

Emitter current
Emitter

The UJT is not useful as an amplifier.
It is used in timing and control applications.

Base 1

Other Transistor Types Quiz
BJTs are _________-controlled
amplifiers.

current

FETs are __________-controlled
amplifiers.

voltage

JFETs operate in the __________ mode. depletion
MOSFETs operate in the __________
mode.

enhancement

IGBTs are __________-controlled
amplifiers.

voltage

UJTs are not useful as __________.

amplifiers

Concept Review
• Bipolar junction transistors (BJTs) are controlled by
base current.
• Junction field effect transistors (JFETs) are controlled
by gate voltage.
• JFETs operate in the depletion mode (as normally on
devices).
• Metal oxide semiconductor field effect transistors
(MOSFETs) usually operate in the enhancement mode
(as normally off devices).
• Insulated gate bipolar transistors (IGBTs) are modified
MOSFETs and have very low on-resistance.
• Unijunction transistors (UJTs) are not used as
amplifiers.
Repeat Segment

Concept Preview
• BJTs can be used as switches.
• No base current = switch is off.
• High base current = switch is on.
• The dissipation is always zero in an ideal
switch: off = no current flow and on = no
voltage drop.

• MOSFETs can also be used as switches: no
gate voltage = switch is off and high gate
voltage = switch is on.

How do transistor switches work?
Can be viewed as solid state relays:
they are either ON or they are OFF.
BJT switches are characterized by:
high base current (switch is on)
(or no base current … off)

low resistance from collector to emitter (on)
(or very high resistance … off)
low collector dissipation (on or off)
PC = VCE x IC
PC = 0 x IC = 0 W
(on)
(or PC = VCE x 0 = 0 W … off)

NPN SWITCH
LOAD

RCE @ 
W
0W
DRIVER

The
The
driver
driver
output
output
isiszero
positive,
volts,
IIBB>=I0
0and
andthe
theload
loadis
ison
off
The
driver
output
is
zero
volts,
B = 0 and ILOAD = 0

PNP SWITCH
DRIVER

LOAD

The
Z):
Thedriver
driveroutput
outputisgoes
isoff
off(high
(highthe
Z):the
theresistor
resistor
low:
voltage
drop
pulls
the
base
voltage
up
that
VV
pulls
thethe
base
voltage
upso
soV
that
across
resistor
makes
BE
BE==00
BE negative

PNP SWITCH WITH NPN DRIVER

LOAD

NPN SWITCH WITH PNP DRIVER
(NEGATIVE POWER SUPPLY)

VV
0VV
BE
BE@ @+0.7

VVBE
0 VV
BE@@-0.7

LOAD

STEPPER MOTOR

A

B

C

A

Enhancement mode
power MOSFETs
used as switches

B

C
D

D

Concept Review
• BJTs can be used as switches.
• No base current = switch is off.
• High base current = switch is on.
• The dissipation is always zero in an ideal
switch: off = no current flow and on = no
voltage drop.
• MOSFETs can also be used as switches: no
gate voltage = switch is off and high gate
voltage = switch is on.
Repeat Segment

REVIEW
• Amplification
• Transistors
• Characteristic Curves
• Transistor Testing
• Other Transistor Types
• Transistors as Switches


Slide 40

Electronics
Principles & Applications
Sixth Edition

Charles A. Schuler
Chapter 5

Transistors
(student version)
©2003

Glencoe/McGraw-Hill

INTRODUCTION
• Amplification
• Transistors
• Characteristic Curves
• Transistor Testing
• Other Transistor Types
• Transistors as Switches

Dear Student:
This presentation is arranged in segments.
Each segment is preceded by a Concept
Preview slide and is followed by a Concept
Review slide. When you reach a Concept
Review slide, you can return to the
beginning of that segment by clicking on the
Repeat Segment button. This will allow you
to view that segment again, if you want to.

Concept Preview
• Amplifiers provide gain (the output is larger
than the input).
• Transistors have gain.
• Transistors have a collector, a base, and an
emitter.
• The C-B junction is reverse biased.
• The B-E junction is forward biased.
• Most of the emitter carriers reach the collector.
• The base current is relatively small but controls
the larger currents.

In

Gain =

Amplifier

Out

In

Out

NPN Transistor Structure

The collector is lightly doped.

N

C

The base is thin and
is lightly doped.

P

B

The emitter is heavily doped.

N

E

NPN Transistor Bias
No current flows.
The C-B junction
is reverse biased.

N

C

P

B

N

E

NPN Transistor Bias

The B-E junction
is forward biased.

Current flows.

N

C

P

B

N

E

NPN Transistor Bias
IC
Current flows
everywhere.
Most of the emitter carriers
diffuse through the thin base
When
both
junctions
region since they are attracted
biased....
by are
the collector.

Note that IB is smaller
than IE or IC.

N

C

P

B

N

E

IB

IE

Note: when the
switch opens, all
currents go to zero.
Although IB is smaller
it controls IE and IC.

Gain is something small
controlling something large
(IB is small).

IC
N

C

P

B

N

E

IB

IE

Transistor Structure and Bias Quiz
The heaviest doping is found in
the ___________ region.

emitter

The thinnest of all three regions
is called the ____________.

base

The collector-base junction is
___________ biased.

reverse

The base-emitter junction is
____________ biased.

forward

The majority of the emitter
carriers flow to the ___________.

collector

Concept Review
• Amplifiers provide gain (the output is larger than
the input).
• Transistors have gain.

• Transistors have a collector, a base, and an emitter.
• The C-B junction is reverse biased.
• The B-E junction is forward biased.

• Most of the emitter carriers reach the collector.
• The base current is relatively small but controls the
larger currents.
Repeat Segment

Concept Preview
• The base to collector gain is called b (beta).
• To find b, divide the collector current by the
base current.
• The emitter current is the largest since it is the
sum of the base and collector currents.
• PNP transistors have opposite polarity from
NPN transistors.

• In an NPN transistor, the major flow is made
up of electrons.
• In a PNP transistor, the major flow is made up
of holes.

IC = 99 mA

The current gain from
base to collector
is called b.
IB = 1 mA

b =

99
ICmA
1IBmA

= 99

IE = 100 mA

C
P

B

N

E

IC = 99 mA
Kirchhoff’s
current law:

IB = 1 mA

C
P

B

N

E

IE = I B + I C

= 1 mA + 99 mA
= 100 mA
IE = 100 mA

IC = 99 mA
In a PNP transistor,
holes flow from
emitter to collector.

IB = 1 mA
Notice the PNP
bias voltages.

C
B

E

IE = 100 mA

Transistor Currents Quiz
b is the ratio of collector current to
______ current.

base

The sum of the base and collector
currents is the __________ current.

emitter

In NPN transistors, the flow from emitter
to collector is composed of _______.

electrons

In PNP transistors, the flow from emitter
to collector is composed of _______.

holes

Both NPN and PNP transistors show
__________ gain.

current

Concept Review
• The base to collector gain is called b (beta).
• To find b, divide the collector current by the
base current.
• The emitter current is the largest since it is the
sum of the base and collector currents.
• PNP transistors have opposite polarity from
NPN transistors.
• In an NPN transistor, the major flow is made
up of electrons.
• In a PNP transistor, the major flow is made up
of holes.
Repeat Segment

Concept Preview
• The NPN schematic symbol shows the emitter
arrow as Not Pointing iN.
• The collector curves are a graph of collector
voltage versus collector current.
• Both dc beta (bdc) and ac beta (bac) can be
determined from the collector curves.
• The collector circuit of a transistor can be
modeled as a resistor, as a closed switch or as
an open switch.
• The amount of base current determines which
of the three models applies.

NPN Schematic Symbol
Collector

Base

C
B E

Emitter
Memory aid: NPN
means Not Pointing iN.

PNP Schematic Symbol
Collector

Base

C
B E

Emitter

IC

This circuit is used to
collect IC versus
VCE data for
several values of IB.
C

IB
B

E

VCE

When graphed, the data provide an
NPN collector family of curves.
100 mA

14
12
10
IC in mA 8
6
4
2

80 mA
60 mA
40 mA
20 mA

0 2 4 6

8 10 12 14 16 18

VCE in Volts

0 mA

100 mA

14
12
10
IC in mA 8
6
4
2

80 mA
60 mA

40 mA
20 mA

0 2 4 6

8 10 12 14 16 18

0 mA

VCE in Volts

b =

14
mA
6ICmA
40
IB mA
100
mA

150
== 140

This type of gain
is called bdc or hFE.

100 mA

14
12
10
IC in mA 8
6
4
2

80 mA
60 mA

40 mA
20 mA

0 2 4 6

bac =

2.5DImA
C
20DImA
B

8 10 12 14 16 18

0 mA

VCE in Volts
= 125

Another type of gain
is called bac or hfe.

100 mA

14
12
10
IC in mA 8
6
4
2

80 mA
60 mA

40 mA
20 mA

0 2 4 6
IB

C

8 10 12 14 16 18
VCE in Volts

0 mA

With these values of IB:
The C-E model is a resistor.
E

100 mA

14
12
10
IC in mA 8
6
4
2
0 2 4 6
IB

80 mA
60 mA

40 mA
20 mA
8 10 12 14 16 18
VCE in Volts

0 mA

When IB >> 100 mA
VCE @ 0
The model is a closed switch.

100 mA

14
12
10
IC in mA 8
6
4
2
0 2 4 6
IB

80 mA
60 mA

40 mA
20 mA
8 10 12 14 16 18
VCE in Volts

0 mA

When IB = 0
IC = 0
The model is an open switch.

Transistor Operating Conditions Quiz
When IB is large and VCE @ 0, the transistor
acts as a ___________ switch.
closed
When IB = 0 and IC = 0, the transistor
acts as an ___________ switch.

open

When IB > 0 and VCE > 0, the transistor
acts as a ___________.

resistor

Two current gain measures are bdc and
__________.

bac

The symbol hfe is the same as _________.

bac

Concept Review
• The NPN schematic symbol shows the emitter
arrow as Not Pointing iN.
• The collector curves are a graph of collector
voltage versus collector current.
• Both dc beta (bdc) and ac beta (bac) can be
determined from the collector curves.
• The collector circuit of a transistor can be
modeled as a resistor, as a closed switch or as
an open switch.
• The amount of base current determines which
of the three models applies.
Repeat Segment

Concept Preview
• It is possible to test transistors out-of-circuit
using an ohmmeter.
• The E-B and C-B junctions act as diodes
during ohmmeter testing.

• The C-E test shows a high resistance because
two junctions are involved; one of which is
reverse biased by the ohmmeter.
• Gain can be verified by using a resistor in
conjunction with the ohmmeter test.

NPN

V

mA

E
B
C

The E-B junction is forward biased by the ohmmeter.

NPN

V

mA

E
B
C

The C-E resistance is very high.

NPN

V

mA

E
B
C
100 kW

The meter reading is < 100 kW due to gain.

Concept Review
• It is possible to test transistors out-of-circuit
using an ohmmeter.
• The E-B and C-B junctions act as diodes
during ohmmeter testing.
• The C-E test shows a high resistance because
two junctions are involved; one of which is
reverse biased by the ohmmeter.
• Gain can be verified by using a resistor in
conjunction with the ohmmeter test.
Repeat Segment

Concept Preview
• Bipolar junction transistors (BJTs) are controlled by
base current.
• Junction field effect transistors (JFETs) are controlled
by gate voltage.

• JFETs operate in the depletion mode (as normally on
devices).
• Metal oxide semiconductor field effect transistors
(MOSFETs) usually operate in the enhancement mode
(as normally off devices).
• Insulated gate bipolar transistors (IGBTs) are modified
MOSFETs and have very low on-resistance.
• Unijunction transistors (UJTs) are not used as
amplifiers.

Current In

The BJT is
a current
amplifier.

Current
Amplifier

Current Out

Voltage In

The JFET is
a voltage
controlled
amplifier.

Voltage
Amplifier

Current Out

Source

Gate

Drain

P

N-channel
P-type substrate
Structure of an
N-channel JFET

The channel has carriers so it
conducts from source to drain.

Drain

Gate
Source

Source

Gate

Drain

P

N-channel
P-type substrate

A negative gate voltage
can push the carriers from
the channel and turn
the JFET off.

Drain

Gate
Source

0V
-1 V
-2 V

ID in mA

-3 V

VGS

-4 V

0

-5 V
VDS in Volts

This is known as a depletion-mode device.
N-channel JFET drain family of characteristic curves

It’s possible to make enhancement
type field effect transistors as well.
Metal
oxide
insulator

Drain

n

Gate

VGG

D

VDD

p

G

n

S
N-channel
MOSFET

Source

Gate bias enhances the channel and turns the device on.

5V
4V
3V

ID in mA

2V

VGS

1V

0

0V
Drain

VDS in Volts

Enhancement mode
MOSFET drain family of
characteristic curves

Gate
Source

The IGBT (insulated gate bipolar transistor)
Operation and structure
similar to a MOSFET
Voltage controlled
(like the MOSFET)
Has one more junction
than a MOSFET
Hole injection reduces
the collector resistance

Faster turn off than
BJTs but not as fast
as MOSFETS

RCE = 8.33 mW

Three major device technologies

hole injection
Extra
junction

Courtesy of Powerex, Inc.

Typical IGBT Driver Circuit
Typically +15 V for turn on
Typically - 5 to -15 V for turn off

Control signal

IGBT

Powerex IGBT Module Structure

Powerex high voltage IGBT package

Emitter voltage

The unijunction transistor fires
when its emitter voltage reaches VP.
VP

Then, the emitter voltage
drops due to its negative
resistance characteristic.
Base 2

Emitter current
Emitter

The UJT is not useful as an amplifier.
It is used in timing and control applications.

Base 1

Other Transistor Types Quiz
BJTs are _________-controlled
amplifiers.

current

FETs are __________-controlled
amplifiers.

voltage

JFETs operate in the __________ mode. depletion
MOSFETs operate in the __________
mode.

enhancement

IGBTs are __________-controlled
amplifiers.

voltage

UJTs are not useful as __________.

amplifiers

Concept Review
• Bipolar junction transistors (BJTs) are controlled by
base current.
• Junction field effect transistors (JFETs) are controlled
by gate voltage.
• JFETs operate in the depletion mode (as normally on
devices).
• Metal oxide semiconductor field effect transistors
(MOSFETs) usually operate in the enhancement mode
(as normally off devices).
• Insulated gate bipolar transistors (IGBTs) are modified
MOSFETs and have very low on-resistance.
• Unijunction transistors (UJTs) are not used as
amplifiers.
Repeat Segment

Concept Preview
• BJTs can be used as switches.
• No base current = switch is off.
• High base current = switch is on.
• The dissipation is always zero in an ideal
switch: off = no current flow and on = no
voltage drop.

• MOSFETs can also be used as switches: no
gate voltage = switch is off and high gate
voltage = switch is on.

How do transistor switches work?
Can be viewed as solid state relays:
they are either ON or they are OFF.
BJT switches are characterized by:
high base current (switch is on)
(or no base current … off)

low resistance from collector to emitter (on)
(or very high resistance … off)
low collector dissipation (on or off)
PC = VCE x IC
PC = 0 x IC = 0 W
(on)
(or PC = VCE x 0 = 0 W … off)

NPN SWITCH
LOAD

RCE @ 
W
0W
DRIVER

The
The
driver
driver
output
output
isiszero
positive,
volts,
IIBB>=I0
0and
andthe
theload
loadis
ison
off
The
driver
output
is
zero
volts,
B = 0 and ILOAD = 0

PNP SWITCH
DRIVER

LOAD

The
Z):
Thedriver
driveroutput
outputisgoes
isoff
off(high
(highthe
Z):the
theresistor
resistor
low:
voltage
drop
pulls
the
base
voltage
up
that
VV
pulls
thethe
base
voltage
upso
soV
that
across
resistor
makes
BE
BE==00
BE negative

PNP SWITCH WITH NPN DRIVER

LOAD

NPN SWITCH WITH PNP DRIVER
(NEGATIVE POWER SUPPLY)

VV
0VV
BE
BE@ @+0.7

VVBE
0 VV
BE@@-0.7

LOAD

STEPPER MOTOR

A

B

C

A

Enhancement mode
power MOSFETs
used as switches

B

C
D

D

Concept Review
• BJTs can be used as switches.
• No base current = switch is off.
• High base current = switch is on.
• The dissipation is always zero in an ideal
switch: off = no current flow and on = no
voltage drop.
• MOSFETs can also be used as switches: no
gate voltage = switch is off and high gate
voltage = switch is on.
Repeat Segment

REVIEW
• Amplification
• Transistors
• Characteristic Curves
• Transistor Testing
• Other Transistor Types
• Transistors as Switches


Slide 41

Electronics
Principles & Applications
Sixth Edition

Charles A. Schuler
Chapter 5

Transistors
(student version)
©2003

Glencoe/McGraw-Hill

INTRODUCTION
• Amplification
• Transistors
• Characteristic Curves
• Transistor Testing
• Other Transistor Types
• Transistors as Switches

Dear Student:
This presentation is arranged in segments.
Each segment is preceded by a Concept
Preview slide and is followed by a Concept
Review slide. When you reach a Concept
Review slide, you can return to the
beginning of that segment by clicking on the
Repeat Segment button. This will allow you
to view that segment again, if you want to.

Concept Preview
• Amplifiers provide gain (the output is larger
than the input).
• Transistors have gain.
• Transistors have a collector, a base, and an
emitter.
• The C-B junction is reverse biased.
• The B-E junction is forward biased.
• Most of the emitter carriers reach the collector.
• The base current is relatively small but controls
the larger currents.

In

Gain =

Amplifier

Out

In

Out

NPN Transistor Structure

The collector is lightly doped.

N

C

The base is thin and
is lightly doped.

P

B

The emitter is heavily doped.

N

E

NPN Transistor Bias
No current flows.
The C-B junction
is reverse biased.

N

C

P

B

N

E

NPN Transistor Bias

The B-E junction
is forward biased.

Current flows.

N

C

P

B

N

E

NPN Transistor Bias
IC
Current flows
everywhere.
Most of the emitter carriers
diffuse through the thin base
When
both
junctions
region since they are attracted
biased....
by are
the collector.

Note that IB is smaller
than IE or IC.

N

C

P

B

N

E

IB

IE

Note: when the
switch opens, all
currents go to zero.
Although IB is smaller
it controls IE and IC.

Gain is something small
controlling something large
(IB is small).

IC
N

C

P

B

N

E

IB

IE

Transistor Structure and Bias Quiz
The heaviest doping is found in
the ___________ region.

emitter

The thinnest of all three regions
is called the ____________.

base

The collector-base junction is
___________ biased.

reverse

The base-emitter junction is
____________ biased.

forward

The majority of the emitter
carriers flow to the ___________.

collector

Concept Review
• Amplifiers provide gain (the output is larger than
the input).
• Transistors have gain.

• Transistors have a collector, a base, and an emitter.
• The C-B junction is reverse biased.
• The B-E junction is forward biased.

• Most of the emitter carriers reach the collector.
• The base current is relatively small but controls the
larger currents.
Repeat Segment

Concept Preview
• The base to collector gain is called b (beta).
• To find b, divide the collector current by the
base current.
• The emitter current is the largest since it is the
sum of the base and collector currents.
• PNP transistors have opposite polarity from
NPN transistors.

• In an NPN transistor, the major flow is made
up of electrons.
• In a PNP transistor, the major flow is made up
of holes.

IC = 99 mA

The current gain from
base to collector
is called b.
IB = 1 mA

b =

99
ICmA
1IBmA

= 99

IE = 100 mA

C
P

B

N

E

IC = 99 mA
Kirchhoff’s
current law:

IB = 1 mA

C
P

B

N

E

IE = I B + I C

= 1 mA + 99 mA
= 100 mA
IE = 100 mA

IC = 99 mA
In a PNP transistor,
holes flow from
emitter to collector.

IB = 1 mA
Notice the PNP
bias voltages.

C
B

E

IE = 100 mA

Transistor Currents Quiz
b is the ratio of collector current to
______ current.

base

The sum of the base and collector
currents is the __________ current.

emitter

In NPN transistors, the flow from emitter
to collector is composed of _______.

electrons

In PNP transistors, the flow from emitter
to collector is composed of _______.

holes

Both NPN and PNP transistors show
__________ gain.

current

Concept Review
• The base to collector gain is called b (beta).
• To find b, divide the collector current by the
base current.
• The emitter current is the largest since it is the
sum of the base and collector currents.
• PNP transistors have opposite polarity from
NPN transistors.
• In an NPN transistor, the major flow is made
up of electrons.
• In a PNP transistor, the major flow is made up
of holes.
Repeat Segment

Concept Preview
• The NPN schematic symbol shows the emitter
arrow as Not Pointing iN.
• The collector curves are a graph of collector
voltage versus collector current.
• Both dc beta (bdc) and ac beta (bac) can be
determined from the collector curves.
• The collector circuit of a transistor can be
modeled as a resistor, as a closed switch or as
an open switch.
• The amount of base current determines which
of the three models applies.

NPN Schematic Symbol
Collector

Base

C
B E

Emitter
Memory aid: NPN
means Not Pointing iN.

PNP Schematic Symbol
Collector

Base

C
B E

Emitter

IC

This circuit is used to
collect IC versus
VCE data for
several values of IB.
C

IB
B

E

VCE

When graphed, the data provide an
NPN collector family of curves.
100 mA

14
12
10
IC in mA 8
6
4
2

80 mA
60 mA
40 mA
20 mA

0 2 4 6

8 10 12 14 16 18

VCE in Volts

0 mA

100 mA

14
12
10
IC in mA 8
6
4
2

80 mA
60 mA

40 mA
20 mA

0 2 4 6

8 10 12 14 16 18

0 mA

VCE in Volts

b =

14
mA
6ICmA
40
IB mA
100
mA

150
== 140

This type of gain
is called bdc or hFE.

100 mA

14
12
10
IC in mA 8
6
4
2

80 mA
60 mA

40 mA
20 mA

0 2 4 6

bac =

2.5DImA
C
20DImA
B

8 10 12 14 16 18

0 mA

VCE in Volts
= 125

Another type of gain
is called bac or hfe.

100 mA

14
12
10
IC in mA 8
6
4
2

80 mA
60 mA

40 mA
20 mA

0 2 4 6
IB

C

8 10 12 14 16 18
VCE in Volts

0 mA

With these values of IB:
The C-E model is a resistor.
E

100 mA

14
12
10
IC in mA 8
6
4
2
0 2 4 6
IB

80 mA
60 mA

40 mA
20 mA
8 10 12 14 16 18
VCE in Volts

0 mA

When IB >> 100 mA
VCE @ 0
The model is a closed switch.

100 mA

14
12
10
IC in mA 8
6
4
2
0 2 4 6
IB

80 mA
60 mA

40 mA
20 mA
8 10 12 14 16 18
VCE in Volts

0 mA

When IB = 0
IC = 0
The model is an open switch.

Transistor Operating Conditions Quiz
When IB is large and VCE @ 0, the transistor
acts as a ___________ switch.
closed
When IB = 0 and IC = 0, the transistor
acts as an ___________ switch.

open

When IB > 0 and VCE > 0, the transistor
acts as a ___________.

resistor

Two current gain measures are bdc and
__________.

bac

The symbol hfe is the same as _________.

bac

Concept Review
• The NPN schematic symbol shows the emitter
arrow as Not Pointing iN.
• The collector curves are a graph of collector
voltage versus collector current.
• Both dc beta (bdc) and ac beta (bac) can be
determined from the collector curves.
• The collector circuit of a transistor can be
modeled as a resistor, as a closed switch or as
an open switch.
• The amount of base current determines which
of the three models applies.
Repeat Segment

Concept Preview
• It is possible to test transistors out-of-circuit
using an ohmmeter.
• The E-B and C-B junctions act as diodes
during ohmmeter testing.

• The C-E test shows a high resistance because
two junctions are involved; one of which is
reverse biased by the ohmmeter.
• Gain can be verified by using a resistor in
conjunction with the ohmmeter test.

NPN

V

mA

E
B
C

The E-B junction is forward biased by the ohmmeter.

NPN

V

mA

E
B
C

The C-E resistance is very high.

NPN

V

mA

E
B
C
100 kW

The meter reading is < 100 kW due to gain.

Concept Review
• It is possible to test transistors out-of-circuit
using an ohmmeter.
• The E-B and C-B junctions act as diodes
during ohmmeter testing.
• The C-E test shows a high resistance because
two junctions are involved; one of which is
reverse biased by the ohmmeter.
• Gain can be verified by using a resistor in
conjunction with the ohmmeter test.
Repeat Segment

Concept Preview
• Bipolar junction transistors (BJTs) are controlled by
base current.
• Junction field effect transistors (JFETs) are controlled
by gate voltage.

• JFETs operate in the depletion mode (as normally on
devices).
• Metal oxide semiconductor field effect transistors
(MOSFETs) usually operate in the enhancement mode
(as normally off devices).
• Insulated gate bipolar transistors (IGBTs) are modified
MOSFETs and have very low on-resistance.
• Unijunction transistors (UJTs) are not used as
amplifiers.

Current In

The BJT is
a current
amplifier.

Current
Amplifier

Current Out

Voltage In

The JFET is
a voltage
controlled
amplifier.

Voltage
Amplifier

Current Out

Source

Gate

Drain

P

N-channel
P-type substrate
Structure of an
N-channel JFET

The channel has carriers so it
conducts from source to drain.

Drain

Gate
Source

Source

Gate

Drain

P

N-channel
P-type substrate

A negative gate voltage
can push the carriers from
the channel and turn
the JFET off.

Drain

Gate
Source

0V
-1 V
-2 V

ID in mA

-3 V

VGS

-4 V

0

-5 V
VDS in Volts

This is known as a depletion-mode device.
N-channel JFET drain family of characteristic curves

It’s possible to make enhancement
type field effect transistors as well.
Metal
oxide
insulator

Drain

n

Gate

VGG

D

VDD

p

G

n

S
N-channel
MOSFET

Source

Gate bias enhances the channel and turns the device on.

5V
4V
3V

ID in mA

2V

VGS

1V

0

0V
Drain

VDS in Volts

Enhancement mode
MOSFET drain family of
characteristic curves

Gate
Source

The IGBT (insulated gate bipolar transistor)
Operation and structure
similar to a MOSFET
Voltage controlled
(like the MOSFET)
Has one more junction
than a MOSFET
Hole injection reduces
the collector resistance

Faster turn off than
BJTs but not as fast
as MOSFETS

RCE = 8.33 mW

Three major device technologies

hole injection
Extra
junction

Courtesy of Powerex, Inc.

Typical IGBT Driver Circuit
Typically +15 V for turn on
Typically - 5 to -15 V for turn off

Control signal

IGBT

Powerex IGBT Module Structure

Powerex high voltage IGBT package

Emitter voltage

The unijunction transistor fires
when its emitter voltage reaches VP.
VP

Then, the emitter voltage
drops due to its negative
resistance characteristic.
Base 2

Emitter current
Emitter

The UJT is not useful as an amplifier.
It is used in timing and control applications.

Base 1

Other Transistor Types Quiz
BJTs are _________-controlled
amplifiers.

current

FETs are __________-controlled
amplifiers.

voltage

JFETs operate in the __________ mode. depletion
MOSFETs operate in the __________
mode.

enhancement

IGBTs are __________-controlled
amplifiers.

voltage

UJTs are not useful as __________.

amplifiers

Concept Review
• Bipolar junction transistors (BJTs) are controlled by
base current.
• Junction field effect transistors (JFETs) are controlled
by gate voltage.
• JFETs operate in the depletion mode (as normally on
devices).
• Metal oxide semiconductor field effect transistors
(MOSFETs) usually operate in the enhancement mode
(as normally off devices).
• Insulated gate bipolar transistors (IGBTs) are modified
MOSFETs and have very low on-resistance.
• Unijunction transistors (UJTs) are not used as
amplifiers.
Repeat Segment

Concept Preview
• BJTs can be used as switches.
• No base current = switch is off.
• High base current = switch is on.
• The dissipation is always zero in an ideal
switch: off = no current flow and on = no
voltage drop.

• MOSFETs can also be used as switches: no
gate voltage = switch is off and high gate
voltage = switch is on.

How do transistor switches work?
Can be viewed as solid state relays:
they are either ON or they are OFF.
BJT switches are characterized by:
high base current (switch is on)
(or no base current … off)

low resistance from collector to emitter (on)
(or very high resistance … off)
low collector dissipation (on or off)
PC = VCE x IC
PC = 0 x IC = 0 W
(on)
(or PC = VCE x 0 = 0 W … off)

NPN SWITCH
LOAD

RCE @ 
W
0W
DRIVER

The
The
driver
driver
output
output
isiszero
positive,
volts,
IIBB>=I0
0and
andthe
theload
loadis
ison
off
The
driver
output
is
zero
volts,
B = 0 and ILOAD = 0

PNP SWITCH
DRIVER

LOAD

The
Z):
Thedriver
driveroutput
outputisgoes
isoff
off(high
(highthe
Z):the
theresistor
resistor
low:
voltage
drop
pulls
the
base
voltage
up
that
VV
pulls
thethe
base
voltage
upso
soV
that
across
resistor
makes
BE
BE==00
BE negative

PNP SWITCH WITH NPN DRIVER

LOAD

NPN SWITCH WITH PNP DRIVER
(NEGATIVE POWER SUPPLY)

VV
0VV
BE
BE@ @+0.7

VVBE
0 VV
BE@@-0.7

LOAD

STEPPER MOTOR

A

B

C

A

Enhancement mode
power MOSFETs
used as switches

B

C
D

D

Concept Review
• BJTs can be used as switches.
• No base current = switch is off.
• High base current = switch is on.
• The dissipation is always zero in an ideal
switch: off = no current flow and on = no
voltage drop.
• MOSFETs can also be used as switches: no
gate voltage = switch is off and high gate
voltage = switch is on.
Repeat Segment

REVIEW
• Amplification
• Transistors
• Characteristic Curves
• Transistor Testing
• Other Transistor Types
• Transistors as Switches


Slide 42

Electronics
Principles & Applications
Sixth Edition

Charles A. Schuler
Chapter 5

Transistors
(student version)
©2003

Glencoe/McGraw-Hill

INTRODUCTION
• Amplification
• Transistors
• Characteristic Curves
• Transistor Testing
• Other Transistor Types
• Transistors as Switches

Dear Student:
This presentation is arranged in segments.
Each segment is preceded by a Concept
Preview slide and is followed by a Concept
Review slide. When you reach a Concept
Review slide, you can return to the
beginning of that segment by clicking on the
Repeat Segment button. This will allow you
to view that segment again, if you want to.

Concept Preview
• Amplifiers provide gain (the output is larger
than the input).
• Transistors have gain.
• Transistors have a collector, a base, and an
emitter.
• The C-B junction is reverse biased.
• The B-E junction is forward biased.
• Most of the emitter carriers reach the collector.
• The base current is relatively small but controls
the larger currents.

In

Gain =

Amplifier

Out

In

Out

NPN Transistor Structure

The collector is lightly doped.

N

C

The base is thin and
is lightly doped.

P

B

The emitter is heavily doped.

N

E

NPN Transistor Bias
No current flows.
The C-B junction
is reverse biased.

N

C

P

B

N

E

NPN Transistor Bias

The B-E junction
is forward biased.

Current flows.

N

C

P

B

N

E

NPN Transistor Bias
IC
Current flows
everywhere.
Most of the emitter carriers
diffuse through the thin base
When
both
junctions
region since they are attracted
biased....
by are
the collector.

Note that IB is smaller
than IE or IC.

N

C

P

B

N

E

IB

IE

Note: when the
switch opens, all
currents go to zero.
Although IB is smaller
it controls IE and IC.

Gain is something small
controlling something large
(IB is small).

IC
N

C

P

B

N

E

IB

IE

Transistor Structure and Bias Quiz
The heaviest doping is found in
the ___________ region.

emitter

The thinnest of all three regions
is called the ____________.

base

The collector-base junction is
___________ biased.

reverse

The base-emitter junction is
____________ biased.

forward

The majority of the emitter
carriers flow to the ___________.

collector

Concept Review
• Amplifiers provide gain (the output is larger than
the input).
• Transistors have gain.

• Transistors have a collector, a base, and an emitter.
• The C-B junction is reverse biased.
• The B-E junction is forward biased.

• Most of the emitter carriers reach the collector.
• The base current is relatively small but controls the
larger currents.
Repeat Segment

Concept Preview
• The base to collector gain is called b (beta).
• To find b, divide the collector current by the
base current.
• The emitter current is the largest since it is the
sum of the base and collector currents.
• PNP transistors have opposite polarity from
NPN transistors.

• In an NPN transistor, the major flow is made
up of electrons.
• In a PNP transistor, the major flow is made up
of holes.

IC = 99 mA

The current gain from
base to collector
is called b.
IB = 1 mA

b =

99
ICmA
1IBmA

= 99

IE = 100 mA

C
P

B

N

E

IC = 99 mA
Kirchhoff’s
current law:

IB = 1 mA

C
P

B

N

E

IE = I B + I C

= 1 mA + 99 mA
= 100 mA
IE = 100 mA

IC = 99 mA
In a PNP transistor,
holes flow from
emitter to collector.

IB = 1 mA
Notice the PNP
bias voltages.

C
B

E

IE = 100 mA

Transistor Currents Quiz
b is the ratio of collector current to
______ current.

base

The sum of the base and collector
currents is the __________ current.

emitter

In NPN transistors, the flow from emitter
to collector is composed of _______.

electrons

In PNP transistors, the flow from emitter
to collector is composed of _______.

holes

Both NPN and PNP transistors show
__________ gain.

current

Concept Review
• The base to collector gain is called b (beta).
• To find b, divide the collector current by the
base current.
• The emitter current is the largest since it is the
sum of the base and collector currents.
• PNP transistors have opposite polarity from
NPN transistors.
• In an NPN transistor, the major flow is made
up of electrons.
• In a PNP transistor, the major flow is made up
of holes.
Repeat Segment

Concept Preview
• The NPN schematic symbol shows the emitter
arrow as Not Pointing iN.
• The collector curves are a graph of collector
voltage versus collector current.
• Both dc beta (bdc) and ac beta (bac) can be
determined from the collector curves.
• The collector circuit of a transistor can be
modeled as a resistor, as a closed switch or as
an open switch.
• The amount of base current determines which
of the three models applies.

NPN Schematic Symbol
Collector

Base

C
B E

Emitter
Memory aid: NPN
means Not Pointing iN.

PNP Schematic Symbol
Collector

Base

C
B E

Emitter

IC

This circuit is used to
collect IC versus
VCE data for
several values of IB.
C

IB
B

E

VCE

When graphed, the data provide an
NPN collector family of curves.
100 mA

14
12
10
IC in mA 8
6
4
2

80 mA
60 mA
40 mA
20 mA

0 2 4 6

8 10 12 14 16 18

VCE in Volts

0 mA

100 mA

14
12
10
IC in mA 8
6
4
2

80 mA
60 mA

40 mA
20 mA

0 2 4 6

8 10 12 14 16 18

0 mA

VCE in Volts

b =

14
mA
6ICmA
40
IB mA
100
mA

150
== 140

This type of gain
is called bdc or hFE.

100 mA

14
12
10
IC in mA 8
6
4
2

80 mA
60 mA

40 mA
20 mA

0 2 4 6

bac =

2.5DImA
C
20DImA
B

8 10 12 14 16 18

0 mA

VCE in Volts
= 125

Another type of gain
is called bac or hfe.

100 mA

14
12
10
IC in mA 8
6
4
2

80 mA
60 mA

40 mA
20 mA

0 2 4 6
IB

C

8 10 12 14 16 18
VCE in Volts

0 mA

With these values of IB:
The C-E model is a resistor.
E

100 mA

14
12
10
IC in mA 8
6
4
2
0 2 4 6
IB

80 mA
60 mA

40 mA
20 mA
8 10 12 14 16 18
VCE in Volts

0 mA

When IB >> 100 mA
VCE @ 0
The model is a closed switch.

100 mA

14
12
10
IC in mA 8
6
4
2
0 2 4 6
IB

80 mA
60 mA

40 mA
20 mA
8 10 12 14 16 18
VCE in Volts

0 mA

When IB = 0
IC = 0
The model is an open switch.

Transistor Operating Conditions Quiz
When IB is large and VCE @ 0, the transistor
acts as a ___________ switch.
closed
When IB = 0 and IC = 0, the transistor
acts as an ___________ switch.

open

When IB > 0 and VCE > 0, the transistor
acts as a ___________.

resistor

Two current gain measures are bdc and
__________.

bac

The symbol hfe is the same as _________.

bac

Concept Review
• The NPN schematic symbol shows the emitter
arrow as Not Pointing iN.
• The collector curves are a graph of collector
voltage versus collector current.
• Both dc beta (bdc) and ac beta (bac) can be
determined from the collector curves.
• The collector circuit of a transistor can be
modeled as a resistor, as a closed switch or as
an open switch.
• The amount of base current determines which
of the three models applies.
Repeat Segment

Concept Preview
• It is possible to test transistors out-of-circuit
using an ohmmeter.
• The E-B and C-B junctions act as diodes
during ohmmeter testing.

• The C-E test shows a high resistance because
two junctions are involved; one of which is
reverse biased by the ohmmeter.
• Gain can be verified by using a resistor in
conjunction with the ohmmeter test.

NPN

V

mA

E
B
C

The E-B junction is forward biased by the ohmmeter.

NPN

V

mA

E
B
C

The C-E resistance is very high.

NPN

V

mA

E
B
C
100 kW

The meter reading is < 100 kW due to gain.

Concept Review
• It is possible to test transistors out-of-circuit
using an ohmmeter.
• The E-B and C-B junctions act as diodes
during ohmmeter testing.
• The C-E test shows a high resistance because
two junctions are involved; one of which is
reverse biased by the ohmmeter.
• Gain can be verified by using a resistor in
conjunction with the ohmmeter test.
Repeat Segment

Concept Preview
• Bipolar junction transistors (BJTs) are controlled by
base current.
• Junction field effect transistors (JFETs) are controlled
by gate voltage.

• JFETs operate in the depletion mode (as normally on
devices).
• Metal oxide semiconductor field effect transistors
(MOSFETs) usually operate in the enhancement mode
(as normally off devices).
• Insulated gate bipolar transistors (IGBTs) are modified
MOSFETs and have very low on-resistance.
• Unijunction transistors (UJTs) are not used as
amplifiers.

Current In

The BJT is
a current
amplifier.

Current
Amplifier

Current Out

Voltage In

The JFET is
a voltage
controlled
amplifier.

Voltage
Amplifier

Current Out

Source

Gate

Drain

P

N-channel
P-type substrate
Structure of an
N-channel JFET

The channel has carriers so it
conducts from source to drain.

Drain

Gate
Source

Source

Gate

Drain

P

N-channel
P-type substrate

A negative gate voltage
can push the carriers from
the channel and turn
the JFET off.

Drain

Gate
Source

0V
-1 V
-2 V

ID in mA

-3 V

VGS

-4 V

0

-5 V
VDS in Volts

This is known as a depletion-mode device.
N-channel JFET drain family of characteristic curves

It’s possible to make enhancement
type field effect transistors as well.
Metal
oxide
insulator

Drain

n

Gate

VGG

D

VDD

p

G

n

S
N-channel
MOSFET

Source

Gate bias enhances the channel and turns the device on.

5V
4V
3V

ID in mA

2V

VGS

1V

0

0V
Drain

VDS in Volts

Enhancement mode
MOSFET drain family of
characteristic curves

Gate
Source

The IGBT (insulated gate bipolar transistor)
Operation and structure
similar to a MOSFET
Voltage controlled
(like the MOSFET)
Has one more junction
than a MOSFET
Hole injection reduces
the collector resistance

Faster turn off than
BJTs but not as fast
as MOSFETS

RCE = 8.33 mW

Three major device technologies

hole injection
Extra
junction

Courtesy of Powerex, Inc.

Typical IGBT Driver Circuit
Typically +15 V for turn on
Typically - 5 to -15 V for turn off

Control signal

IGBT

Powerex IGBT Module Structure

Powerex high voltage IGBT package

Emitter voltage

The unijunction transistor fires
when its emitter voltage reaches VP.
VP

Then, the emitter voltage
drops due to its negative
resistance characteristic.
Base 2

Emitter current
Emitter

The UJT is not useful as an amplifier.
It is used in timing and control applications.

Base 1

Other Transistor Types Quiz
BJTs are _________-controlled
amplifiers.

current

FETs are __________-controlled
amplifiers.

voltage

JFETs operate in the __________ mode. depletion
MOSFETs operate in the __________
mode.

enhancement

IGBTs are __________-controlled
amplifiers.

voltage

UJTs are not useful as __________.

amplifiers

Concept Review
• Bipolar junction transistors (BJTs) are controlled by
base current.
• Junction field effect transistors (JFETs) are controlled
by gate voltage.
• JFETs operate in the depletion mode (as normally on
devices).
• Metal oxide semiconductor field effect transistors
(MOSFETs) usually operate in the enhancement mode
(as normally off devices).
• Insulated gate bipolar transistors (IGBTs) are modified
MOSFETs and have very low on-resistance.
• Unijunction transistors (UJTs) are not used as
amplifiers.
Repeat Segment

Concept Preview
• BJTs can be used as switches.
• No base current = switch is off.
• High base current = switch is on.
• The dissipation is always zero in an ideal
switch: off = no current flow and on = no
voltage drop.

• MOSFETs can also be used as switches: no
gate voltage = switch is off and high gate
voltage = switch is on.

How do transistor switches work?
Can be viewed as solid state relays:
they are either ON or they are OFF.
BJT switches are characterized by:
high base current (switch is on)
(or no base current … off)

low resistance from collector to emitter (on)
(or very high resistance … off)
low collector dissipation (on or off)
PC = VCE x IC
PC = 0 x IC = 0 W
(on)
(or PC = VCE x 0 = 0 W … off)

NPN SWITCH
LOAD

RCE @ 
W
0W
DRIVER

The
The
driver
driver
output
output
isiszero
positive,
volts,
IIBB>=I0
0and
andthe
theload
loadis
ison
off
The
driver
output
is
zero
volts,
B = 0 and ILOAD = 0

PNP SWITCH
DRIVER

LOAD

The
Z):
Thedriver
driveroutput
outputisgoes
isoff
off(high
(highthe
Z):the
theresistor
resistor
low:
voltage
drop
pulls
the
base
voltage
up
that
VV
pulls
thethe
base
voltage
upso
soV
that
across
resistor
makes
BE
BE==00
BE negative

PNP SWITCH WITH NPN DRIVER

LOAD

NPN SWITCH WITH PNP DRIVER
(NEGATIVE POWER SUPPLY)

VV
0VV
BE
BE@ @+0.7

VVBE
0 VV
BE@@-0.7

LOAD

STEPPER MOTOR

A

B

C

A

Enhancement mode
power MOSFETs
used as switches

B

C
D

D

Concept Review
• BJTs can be used as switches.
• No base current = switch is off.
• High base current = switch is on.
• The dissipation is always zero in an ideal
switch: off = no current flow and on = no
voltage drop.
• MOSFETs can also be used as switches: no
gate voltage = switch is off and high gate
voltage = switch is on.
Repeat Segment

REVIEW
• Amplification
• Transistors
• Characteristic Curves
• Transistor Testing
• Other Transistor Types
• Transistors as Switches


Slide 43

Electronics
Principles & Applications
Sixth Edition

Charles A. Schuler
Chapter 5

Transistors
(student version)
©2003

Glencoe/McGraw-Hill

INTRODUCTION
• Amplification
• Transistors
• Characteristic Curves
• Transistor Testing
• Other Transistor Types
• Transistors as Switches

Dear Student:
This presentation is arranged in segments.
Each segment is preceded by a Concept
Preview slide and is followed by a Concept
Review slide. When you reach a Concept
Review slide, you can return to the
beginning of that segment by clicking on the
Repeat Segment button. This will allow you
to view that segment again, if you want to.

Concept Preview
• Amplifiers provide gain (the output is larger
than the input).
• Transistors have gain.
• Transistors have a collector, a base, and an
emitter.
• The C-B junction is reverse biased.
• The B-E junction is forward biased.
• Most of the emitter carriers reach the collector.
• The base current is relatively small but controls
the larger currents.

In

Gain =

Amplifier

Out

In

Out

NPN Transistor Structure

The collector is lightly doped.

N

C

The base is thin and
is lightly doped.

P

B

The emitter is heavily doped.

N

E

NPN Transistor Bias
No current flows.
The C-B junction
is reverse biased.

N

C

P

B

N

E

NPN Transistor Bias

The B-E junction
is forward biased.

Current flows.

N

C

P

B

N

E

NPN Transistor Bias
IC
Current flows
everywhere.
Most of the emitter carriers
diffuse through the thin base
When
both
junctions
region since they are attracted
biased....
by are
the collector.

Note that IB is smaller
than IE or IC.

N

C

P

B

N

E

IB

IE

Note: when the
switch opens, all
currents go to zero.
Although IB is smaller
it controls IE and IC.

Gain is something small
controlling something large
(IB is small).

IC
N

C

P

B

N

E

IB

IE

Transistor Structure and Bias Quiz
The heaviest doping is found in
the ___________ region.

emitter

The thinnest of all three regions
is called the ____________.

base

The collector-base junction is
___________ biased.

reverse

The base-emitter junction is
____________ biased.

forward

The majority of the emitter
carriers flow to the ___________.

collector

Concept Review
• Amplifiers provide gain (the output is larger than
the input).
• Transistors have gain.

• Transistors have a collector, a base, and an emitter.
• The C-B junction is reverse biased.
• The B-E junction is forward biased.

• Most of the emitter carriers reach the collector.
• The base current is relatively small but controls the
larger currents.
Repeat Segment

Concept Preview
• The base to collector gain is called b (beta).
• To find b, divide the collector current by the
base current.
• The emitter current is the largest since it is the
sum of the base and collector currents.
• PNP transistors have opposite polarity from
NPN transistors.

• In an NPN transistor, the major flow is made
up of electrons.
• In a PNP transistor, the major flow is made up
of holes.

IC = 99 mA

The current gain from
base to collector
is called b.
IB = 1 mA

b =

99
ICmA
1IBmA

= 99

IE = 100 mA

C
P

B

N

E

IC = 99 mA
Kirchhoff’s
current law:

IB = 1 mA

C
P

B

N

E

IE = I B + I C

= 1 mA + 99 mA
= 100 mA
IE = 100 mA

IC = 99 mA
In a PNP transistor,
holes flow from
emitter to collector.

IB = 1 mA
Notice the PNP
bias voltages.

C
B

E

IE = 100 mA

Transistor Currents Quiz
b is the ratio of collector current to
______ current.

base

The sum of the base and collector
currents is the __________ current.

emitter

In NPN transistors, the flow from emitter
to collector is composed of _______.

electrons

In PNP transistors, the flow from emitter
to collector is composed of _______.

holes

Both NPN and PNP transistors show
__________ gain.

current

Concept Review
• The base to collector gain is called b (beta).
• To find b, divide the collector current by the
base current.
• The emitter current is the largest since it is the
sum of the base and collector currents.
• PNP transistors have opposite polarity from
NPN transistors.
• In an NPN transistor, the major flow is made
up of electrons.
• In a PNP transistor, the major flow is made up
of holes.
Repeat Segment

Concept Preview
• The NPN schematic symbol shows the emitter
arrow as Not Pointing iN.
• The collector curves are a graph of collector
voltage versus collector current.
• Both dc beta (bdc) and ac beta (bac) can be
determined from the collector curves.
• The collector circuit of a transistor can be
modeled as a resistor, as a closed switch or as
an open switch.
• The amount of base current determines which
of the three models applies.

NPN Schematic Symbol
Collector

Base

C
B E

Emitter
Memory aid: NPN
means Not Pointing iN.

PNP Schematic Symbol
Collector

Base

C
B E

Emitter

IC

This circuit is used to
collect IC versus
VCE data for
several values of IB.
C

IB
B

E

VCE

When graphed, the data provide an
NPN collector family of curves.
100 mA

14
12
10
IC in mA 8
6
4
2

80 mA
60 mA
40 mA
20 mA

0 2 4 6

8 10 12 14 16 18

VCE in Volts

0 mA

100 mA

14
12
10
IC in mA 8
6
4
2

80 mA
60 mA

40 mA
20 mA

0 2 4 6

8 10 12 14 16 18

0 mA

VCE in Volts

b =

14
mA
6ICmA
40
IB mA
100
mA

150
== 140

This type of gain
is called bdc or hFE.

100 mA

14
12
10
IC in mA 8
6
4
2

80 mA
60 mA

40 mA
20 mA

0 2 4 6

bac =

2.5DImA
C
20DImA
B

8 10 12 14 16 18

0 mA

VCE in Volts
= 125

Another type of gain
is called bac or hfe.

100 mA

14
12
10
IC in mA 8
6
4
2

80 mA
60 mA

40 mA
20 mA

0 2 4 6
IB

C

8 10 12 14 16 18
VCE in Volts

0 mA

With these values of IB:
The C-E model is a resistor.
E

100 mA

14
12
10
IC in mA 8
6
4
2
0 2 4 6
IB

80 mA
60 mA

40 mA
20 mA
8 10 12 14 16 18
VCE in Volts

0 mA

When IB >> 100 mA
VCE @ 0
The model is a closed switch.

100 mA

14
12
10
IC in mA 8
6
4
2
0 2 4 6
IB

80 mA
60 mA

40 mA
20 mA
8 10 12 14 16 18
VCE in Volts

0 mA

When IB = 0
IC = 0
The model is an open switch.

Transistor Operating Conditions Quiz
When IB is large and VCE @ 0, the transistor
acts as a ___________ switch.
closed
When IB = 0 and IC = 0, the transistor
acts as an ___________ switch.

open

When IB > 0 and VCE > 0, the transistor
acts as a ___________.

resistor

Two current gain measures are bdc and
__________.

bac

The symbol hfe is the same as _________.

bac

Concept Review
• The NPN schematic symbol shows the emitter
arrow as Not Pointing iN.
• The collector curves are a graph of collector
voltage versus collector current.
• Both dc beta (bdc) and ac beta (bac) can be
determined from the collector curves.
• The collector circuit of a transistor can be
modeled as a resistor, as a closed switch or as
an open switch.
• The amount of base current determines which
of the three models applies.
Repeat Segment

Concept Preview
• It is possible to test transistors out-of-circuit
using an ohmmeter.
• The E-B and C-B junctions act as diodes
during ohmmeter testing.

• The C-E test shows a high resistance because
two junctions are involved; one of which is
reverse biased by the ohmmeter.
• Gain can be verified by using a resistor in
conjunction with the ohmmeter test.

NPN

V

mA

E
B
C

The E-B junction is forward biased by the ohmmeter.

NPN

V

mA

E
B
C

The C-E resistance is very high.

NPN

V

mA

E
B
C
100 kW

The meter reading is < 100 kW due to gain.

Concept Review
• It is possible to test transistors out-of-circuit
using an ohmmeter.
• The E-B and C-B junctions act as diodes
during ohmmeter testing.
• The C-E test shows a high resistance because
two junctions are involved; one of which is
reverse biased by the ohmmeter.
• Gain can be verified by using a resistor in
conjunction with the ohmmeter test.
Repeat Segment

Concept Preview
• Bipolar junction transistors (BJTs) are controlled by
base current.
• Junction field effect transistors (JFETs) are controlled
by gate voltage.

• JFETs operate in the depletion mode (as normally on
devices).
• Metal oxide semiconductor field effect transistors
(MOSFETs) usually operate in the enhancement mode
(as normally off devices).
• Insulated gate bipolar transistors (IGBTs) are modified
MOSFETs and have very low on-resistance.
• Unijunction transistors (UJTs) are not used as
amplifiers.

Current In

The BJT is
a current
amplifier.

Current
Amplifier

Current Out

Voltage In

The JFET is
a voltage
controlled
amplifier.

Voltage
Amplifier

Current Out

Source

Gate

Drain

P

N-channel
P-type substrate
Structure of an
N-channel JFET

The channel has carriers so it
conducts from source to drain.

Drain

Gate
Source

Source

Gate

Drain

P

N-channel
P-type substrate

A negative gate voltage
can push the carriers from
the channel and turn
the JFET off.

Drain

Gate
Source

0V
-1 V
-2 V

ID in mA

-3 V

VGS

-4 V

0

-5 V
VDS in Volts

This is known as a depletion-mode device.
N-channel JFET drain family of characteristic curves

It’s possible to make enhancement
type field effect transistors as well.
Metal
oxide
insulator

Drain

n

Gate

VGG

D

VDD

p

G

n

S
N-channel
MOSFET

Source

Gate bias enhances the channel and turns the device on.

5V
4V
3V

ID in mA

2V

VGS

1V

0

0V
Drain

VDS in Volts

Enhancement mode
MOSFET drain family of
characteristic curves

Gate
Source

The IGBT (insulated gate bipolar transistor)
Operation and structure
similar to a MOSFET
Voltage controlled
(like the MOSFET)
Has one more junction
than a MOSFET
Hole injection reduces
the collector resistance

Faster turn off than
BJTs but not as fast
as MOSFETS

RCE = 8.33 mW

Three major device technologies

hole injection
Extra
junction

Courtesy of Powerex, Inc.

Typical IGBT Driver Circuit
Typically +15 V for turn on
Typically - 5 to -15 V for turn off

Control signal

IGBT

Powerex IGBT Module Structure

Powerex high voltage IGBT package

Emitter voltage

The unijunction transistor fires
when its emitter voltage reaches VP.
VP

Then, the emitter voltage
drops due to its negative
resistance characteristic.
Base 2

Emitter current
Emitter

The UJT is not useful as an amplifier.
It is used in timing and control applications.

Base 1

Other Transistor Types Quiz
BJTs are _________-controlled
amplifiers.

current

FETs are __________-controlled
amplifiers.

voltage

JFETs operate in the __________ mode. depletion
MOSFETs operate in the __________
mode.

enhancement

IGBTs are __________-controlled
amplifiers.

voltage

UJTs are not useful as __________.

amplifiers

Concept Review
• Bipolar junction transistors (BJTs) are controlled by
base current.
• Junction field effect transistors (JFETs) are controlled
by gate voltage.
• JFETs operate in the depletion mode (as normally on
devices).
• Metal oxide semiconductor field effect transistors
(MOSFETs) usually operate in the enhancement mode
(as normally off devices).
• Insulated gate bipolar transistors (IGBTs) are modified
MOSFETs and have very low on-resistance.
• Unijunction transistors (UJTs) are not used as
amplifiers.
Repeat Segment

Concept Preview
• BJTs can be used as switches.
• No base current = switch is off.
• High base current = switch is on.
• The dissipation is always zero in an ideal
switch: off = no current flow and on = no
voltage drop.

• MOSFETs can also be used as switches: no
gate voltage = switch is off and high gate
voltage = switch is on.

How do transistor switches work?
Can be viewed as solid state relays:
they are either ON or they are OFF.
BJT switches are characterized by:
high base current (switch is on)
(or no base current … off)

low resistance from collector to emitter (on)
(or very high resistance … off)
low collector dissipation (on or off)
PC = VCE x IC
PC = 0 x IC = 0 W
(on)
(or PC = VCE x 0 = 0 W … off)

NPN SWITCH
LOAD

RCE @ 
W
0W
DRIVER

The
The
driver
driver
output
output
isiszero
positive,
volts,
IIBB>=I0
0and
andthe
theload
loadis
ison
off
The
driver
output
is
zero
volts,
B = 0 and ILOAD = 0

PNP SWITCH
DRIVER

LOAD

The
Z):
Thedriver
driveroutput
outputisgoes
isoff
off(high
(highthe
Z):the
theresistor
resistor
low:
voltage
drop
pulls
the
base
voltage
up
that
VV
pulls
thethe
base
voltage
upso
soV
that
across
resistor
makes
BE
BE==00
BE negative

PNP SWITCH WITH NPN DRIVER

LOAD

NPN SWITCH WITH PNP DRIVER
(NEGATIVE POWER SUPPLY)

VV
0VV
BE
BE@ @+0.7

VVBE
0 VV
BE@@-0.7

LOAD

STEPPER MOTOR

A

B

C

A

Enhancement mode
power MOSFETs
used as switches

B

C
D

D

Concept Review
• BJTs can be used as switches.
• No base current = switch is off.
• High base current = switch is on.
• The dissipation is always zero in an ideal
switch: off = no current flow and on = no
voltage drop.
• MOSFETs can also be used as switches: no
gate voltage = switch is off and high gate
voltage = switch is on.
Repeat Segment

REVIEW
• Amplification
• Transistors
• Characteristic Curves
• Transistor Testing
• Other Transistor Types
• Transistors as Switches


Slide 44

Electronics
Principles & Applications
Sixth Edition

Charles A. Schuler
Chapter 5

Transistors
(student version)
©2003

Glencoe/McGraw-Hill

INTRODUCTION
• Amplification
• Transistors
• Characteristic Curves
• Transistor Testing
• Other Transistor Types
• Transistors as Switches

Dear Student:
This presentation is arranged in segments.
Each segment is preceded by a Concept
Preview slide and is followed by a Concept
Review slide. When you reach a Concept
Review slide, you can return to the
beginning of that segment by clicking on the
Repeat Segment button. This will allow you
to view that segment again, if you want to.

Concept Preview
• Amplifiers provide gain (the output is larger
than the input).
• Transistors have gain.
• Transistors have a collector, a base, and an
emitter.
• The C-B junction is reverse biased.
• The B-E junction is forward biased.
• Most of the emitter carriers reach the collector.
• The base current is relatively small but controls
the larger currents.

In

Gain =

Amplifier

Out

In

Out

NPN Transistor Structure

The collector is lightly doped.

N

C

The base is thin and
is lightly doped.

P

B

The emitter is heavily doped.

N

E

NPN Transistor Bias
No current flows.
The C-B junction
is reverse biased.

N

C

P

B

N

E

NPN Transistor Bias

The B-E junction
is forward biased.

Current flows.

N

C

P

B

N

E

NPN Transistor Bias
IC
Current flows
everywhere.
Most of the emitter carriers
diffuse through the thin base
When
both
junctions
region since they are attracted
biased....
by are
the collector.

Note that IB is smaller
than IE or IC.

N

C

P

B

N

E

IB

IE

Note: when the
switch opens, all
currents go to zero.
Although IB is smaller
it controls IE and IC.

Gain is something small
controlling something large
(IB is small).

IC
N

C

P

B

N

E

IB

IE

Transistor Structure and Bias Quiz
The heaviest doping is found in
the ___________ region.

emitter

The thinnest of all three regions
is called the ____________.

base

The collector-base junction is
___________ biased.

reverse

The base-emitter junction is
____________ biased.

forward

The majority of the emitter
carriers flow to the ___________.

collector

Concept Review
• Amplifiers provide gain (the output is larger than
the input).
• Transistors have gain.

• Transistors have a collector, a base, and an emitter.
• The C-B junction is reverse biased.
• The B-E junction is forward biased.

• Most of the emitter carriers reach the collector.
• The base current is relatively small but controls the
larger currents.
Repeat Segment

Concept Preview
• The base to collector gain is called b (beta).
• To find b, divide the collector current by the
base current.
• The emitter current is the largest since it is the
sum of the base and collector currents.
• PNP transistors have opposite polarity from
NPN transistors.

• In an NPN transistor, the major flow is made
up of electrons.
• In a PNP transistor, the major flow is made up
of holes.

IC = 99 mA

The current gain from
base to collector
is called b.
IB = 1 mA

b =

99
ICmA
1IBmA

= 99

IE = 100 mA

C
P

B

N

E

IC = 99 mA
Kirchhoff’s
current law:

IB = 1 mA

C
P

B

N

E

IE = I B + I C

= 1 mA + 99 mA
= 100 mA
IE = 100 mA

IC = 99 mA
In a PNP transistor,
holes flow from
emitter to collector.

IB = 1 mA
Notice the PNP
bias voltages.

C
B

E

IE = 100 mA

Transistor Currents Quiz
b is the ratio of collector current to
______ current.

base

The sum of the base and collector
currents is the __________ current.

emitter

In NPN transistors, the flow from emitter
to collector is composed of _______.

electrons

In PNP transistors, the flow from emitter
to collector is composed of _______.

holes

Both NPN and PNP transistors show
__________ gain.

current

Concept Review
• The base to collector gain is called b (beta).
• To find b, divide the collector current by the
base current.
• The emitter current is the largest since it is the
sum of the base and collector currents.
• PNP transistors have opposite polarity from
NPN transistors.
• In an NPN transistor, the major flow is made
up of electrons.
• In a PNP transistor, the major flow is made up
of holes.
Repeat Segment

Concept Preview
• The NPN schematic symbol shows the emitter
arrow as Not Pointing iN.
• The collector curves are a graph of collector
voltage versus collector current.
• Both dc beta (bdc) and ac beta (bac) can be
determined from the collector curves.
• The collector circuit of a transistor can be
modeled as a resistor, as a closed switch or as
an open switch.
• The amount of base current determines which
of the three models applies.

NPN Schematic Symbol
Collector

Base

C
B E

Emitter
Memory aid: NPN
means Not Pointing iN.

PNP Schematic Symbol
Collector

Base

C
B E

Emitter

IC

This circuit is used to
collect IC versus
VCE data for
several values of IB.
C

IB
B

E

VCE

When graphed, the data provide an
NPN collector family of curves.
100 mA

14
12
10
IC in mA 8
6
4
2

80 mA
60 mA
40 mA
20 mA

0 2 4 6

8 10 12 14 16 18

VCE in Volts

0 mA

100 mA

14
12
10
IC in mA 8
6
4
2

80 mA
60 mA

40 mA
20 mA

0 2 4 6

8 10 12 14 16 18

0 mA

VCE in Volts

b =

14
mA
6ICmA
40
IB mA
100
mA

150
== 140

This type of gain
is called bdc or hFE.

100 mA

14
12
10
IC in mA 8
6
4
2

80 mA
60 mA

40 mA
20 mA

0 2 4 6

bac =

2.5DImA
C
20DImA
B

8 10 12 14 16 18

0 mA

VCE in Volts
= 125

Another type of gain
is called bac or hfe.

100 mA

14
12
10
IC in mA 8
6
4
2

80 mA
60 mA

40 mA
20 mA

0 2 4 6
IB

C

8 10 12 14 16 18
VCE in Volts

0 mA

With these values of IB:
The C-E model is a resistor.
E

100 mA

14
12
10
IC in mA 8
6
4
2
0 2 4 6
IB

80 mA
60 mA

40 mA
20 mA
8 10 12 14 16 18
VCE in Volts

0 mA

When IB >> 100 mA
VCE @ 0
The model is a closed switch.

100 mA

14
12
10
IC in mA 8
6
4
2
0 2 4 6
IB

80 mA
60 mA

40 mA
20 mA
8 10 12 14 16 18
VCE in Volts

0 mA

When IB = 0
IC = 0
The model is an open switch.

Transistor Operating Conditions Quiz
When IB is large and VCE @ 0, the transistor
acts as a ___________ switch.
closed
When IB = 0 and IC = 0, the transistor
acts as an ___________ switch.

open

When IB > 0 and VCE > 0, the transistor
acts as a ___________.

resistor

Two current gain measures are bdc and
__________.

bac

The symbol hfe is the same as _________.

bac

Concept Review
• The NPN schematic symbol shows the emitter
arrow as Not Pointing iN.
• The collector curves are a graph of collector
voltage versus collector current.
• Both dc beta (bdc) and ac beta (bac) can be
determined from the collector curves.
• The collector circuit of a transistor can be
modeled as a resistor, as a closed switch or as
an open switch.
• The amount of base current determines which
of the three models applies.
Repeat Segment

Concept Preview
• It is possible to test transistors out-of-circuit
using an ohmmeter.
• The E-B and C-B junctions act as diodes
during ohmmeter testing.

• The C-E test shows a high resistance because
two junctions are involved; one of which is
reverse biased by the ohmmeter.
• Gain can be verified by using a resistor in
conjunction with the ohmmeter test.

NPN

V

mA

E
B
C

The E-B junction is forward biased by the ohmmeter.

NPN

V

mA

E
B
C

The C-E resistance is very high.

NPN

V

mA

E
B
C
100 kW

The meter reading is < 100 kW due to gain.

Concept Review
• It is possible to test transistors out-of-circuit
using an ohmmeter.
• The E-B and C-B junctions act as diodes
during ohmmeter testing.
• The C-E test shows a high resistance because
two junctions are involved; one of which is
reverse biased by the ohmmeter.
• Gain can be verified by using a resistor in
conjunction with the ohmmeter test.
Repeat Segment

Concept Preview
• Bipolar junction transistors (BJTs) are controlled by
base current.
• Junction field effect transistors (JFETs) are controlled
by gate voltage.

• JFETs operate in the depletion mode (as normally on
devices).
• Metal oxide semiconductor field effect transistors
(MOSFETs) usually operate in the enhancement mode
(as normally off devices).
• Insulated gate bipolar transistors (IGBTs) are modified
MOSFETs and have very low on-resistance.
• Unijunction transistors (UJTs) are not used as
amplifiers.

Current In

The BJT is
a current
amplifier.

Current
Amplifier

Current Out

Voltage In

The JFET is
a voltage
controlled
amplifier.

Voltage
Amplifier

Current Out

Source

Gate

Drain

P

N-channel
P-type substrate
Structure of an
N-channel JFET

The channel has carriers so it
conducts from source to drain.

Drain

Gate
Source

Source

Gate

Drain

P

N-channel
P-type substrate

A negative gate voltage
can push the carriers from
the channel and turn
the JFET off.

Drain

Gate
Source

0V
-1 V
-2 V

ID in mA

-3 V

VGS

-4 V

0

-5 V
VDS in Volts

This is known as a depletion-mode device.
N-channel JFET drain family of characteristic curves

It’s possible to make enhancement
type field effect transistors as well.
Metal
oxide
insulator

Drain

n

Gate

VGG

D

VDD

p

G

n

S
N-channel
MOSFET

Source

Gate bias enhances the channel and turns the device on.

5V
4V
3V

ID in mA

2V

VGS

1V

0

0V
Drain

VDS in Volts

Enhancement mode
MOSFET drain family of
characteristic curves

Gate
Source

The IGBT (insulated gate bipolar transistor)
Operation and structure
similar to a MOSFET
Voltage controlled
(like the MOSFET)
Has one more junction
than a MOSFET
Hole injection reduces
the collector resistance

Faster turn off than
BJTs but not as fast
as MOSFETS

RCE = 8.33 mW

Three major device technologies

hole injection
Extra
junction

Courtesy of Powerex, Inc.

Typical IGBT Driver Circuit
Typically +15 V for turn on
Typically - 5 to -15 V for turn off

Control signal

IGBT

Powerex IGBT Module Structure

Powerex high voltage IGBT package

Emitter voltage

The unijunction transistor fires
when its emitter voltage reaches VP.
VP

Then, the emitter voltage
drops due to its negative
resistance characteristic.
Base 2

Emitter current
Emitter

The UJT is not useful as an amplifier.
It is used in timing and control applications.

Base 1

Other Transistor Types Quiz
BJTs are _________-controlled
amplifiers.

current

FETs are __________-controlled
amplifiers.

voltage

JFETs operate in the __________ mode. depletion
MOSFETs operate in the __________
mode.

enhancement

IGBTs are __________-controlled
amplifiers.

voltage

UJTs are not useful as __________.

amplifiers

Concept Review
• Bipolar junction transistors (BJTs) are controlled by
base current.
• Junction field effect transistors (JFETs) are controlled
by gate voltage.
• JFETs operate in the depletion mode (as normally on
devices).
• Metal oxide semiconductor field effect transistors
(MOSFETs) usually operate in the enhancement mode
(as normally off devices).
• Insulated gate bipolar transistors (IGBTs) are modified
MOSFETs and have very low on-resistance.
• Unijunction transistors (UJTs) are not used as
amplifiers.
Repeat Segment

Concept Preview
• BJTs can be used as switches.
• No base current = switch is off.
• High base current = switch is on.
• The dissipation is always zero in an ideal
switch: off = no current flow and on = no
voltage drop.

• MOSFETs can also be used as switches: no
gate voltage = switch is off and high gate
voltage = switch is on.

How do transistor switches work?
Can be viewed as solid state relays:
they are either ON or they are OFF.
BJT switches are characterized by:
high base current (switch is on)
(or no base current … off)

low resistance from collector to emitter (on)
(or very high resistance … off)
low collector dissipation (on or off)
PC = VCE x IC
PC = 0 x IC = 0 W
(on)
(or PC = VCE x 0 = 0 W … off)

NPN SWITCH
LOAD

RCE @ 
W
0W
DRIVER

The
The
driver
driver
output
output
isiszero
positive,
volts,
IIBB>=I0
0and
andthe
theload
loadis
ison
off
The
driver
output
is
zero
volts,
B = 0 and ILOAD = 0

PNP SWITCH
DRIVER

LOAD

The
Z):
Thedriver
driveroutput
outputisgoes
isoff
off(high
(highthe
Z):the
theresistor
resistor
low:
voltage
drop
pulls
the
base
voltage
up
that
VV
pulls
thethe
base
voltage
upso
soV
that
across
resistor
makes
BE
BE==00
BE negative

PNP SWITCH WITH NPN DRIVER

LOAD

NPN SWITCH WITH PNP DRIVER
(NEGATIVE POWER SUPPLY)

VV
0VV
BE
BE@ @+0.7

VVBE
0 VV
BE@@-0.7

LOAD

STEPPER MOTOR

A

B

C

A

Enhancement mode
power MOSFETs
used as switches

B

C
D

D

Concept Review
• BJTs can be used as switches.
• No base current = switch is off.
• High base current = switch is on.
• The dissipation is always zero in an ideal
switch: off = no current flow and on = no
voltage drop.
• MOSFETs can also be used as switches: no
gate voltage = switch is off and high gate
voltage = switch is on.
Repeat Segment

REVIEW
• Amplification
• Transistors
• Characteristic Curves
• Transistor Testing
• Other Transistor Types
• Transistors as Switches


Slide 45

Electronics
Principles & Applications
Sixth Edition

Charles A. Schuler
Chapter 5

Transistors
(student version)
©2003

Glencoe/McGraw-Hill

INTRODUCTION
• Amplification
• Transistors
• Characteristic Curves
• Transistor Testing
• Other Transistor Types
• Transistors as Switches

Dear Student:
This presentation is arranged in segments.
Each segment is preceded by a Concept
Preview slide and is followed by a Concept
Review slide. When you reach a Concept
Review slide, you can return to the
beginning of that segment by clicking on the
Repeat Segment button. This will allow you
to view that segment again, if you want to.

Concept Preview
• Amplifiers provide gain (the output is larger
than the input).
• Transistors have gain.
• Transistors have a collector, a base, and an
emitter.
• The C-B junction is reverse biased.
• The B-E junction is forward biased.
• Most of the emitter carriers reach the collector.
• The base current is relatively small but controls
the larger currents.

In

Gain =

Amplifier

Out

In

Out

NPN Transistor Structure

The collector is lightly doped.

N

C

The base is thin and
is lightly doped.

P

B

The emitter is heavily doped.

N

E

NPN Transistor Bias
No current flows.
The C-B junction
is reverse biased.

N

C

P

B

N

E

NPN Transistor Bias

The B-E junction
is forward biased.

Current flows.

N

C

P

B

N

E

NPN Transistor Bias
IC
Current flows
everywhere.
Most of the emitter carriers
diffuse through the thin base
When
both
junctions
region since they are attracted
biased....
by are
the collector.

Note that IB is smaller
than IE or IC.

N

C

P

B

N

E

IB

IE

Note: when the
switch opens, all
currents go to zero.
Although IB is smaller
it controls IE and IC.

Gain is something small
controlling something large
(IB is small).

IC
N

C

P

B

N

E

IB

IE

Transistor Structure and Bias Quiz
The heaviest doping is found in
the ___________ region.

emitter

The thinnest of all three regions
is called the ____________.

base

The collector-base junction is
___________ biased.

reverse

The base-emitter junction is
____________ biased.

forward

The majority of the emitter
carriers flow to the ___________.

collector

Concept Review
• Amplifiers provide gain (the output is larger than
the input).
• Transistors have gain.

• Transistors have a collector, a base, and an emitter.
• The C-B junction is reverse biased.
• The B-E junction is forward biased.

• Most of the emitter carriers reach the collector.
• The base current is relatively small but controls the
larger currents.
Repeat Segment

Concept Preview
• The base to collector gain is called b (beta).
• To find b, divide the collector current by the
base current.
• The emitter current is the largest since it is the
sum of the base and collector currents.
• PNP transistors have opposite polarity from
NPN transistors.

• In an NPN transistor, the major flow is made
up of electrons.
• In a PNP transistor, the major flow is made up
of holes.

IC = 99 mA

The current gain from
base to collector
is called b.
IB = 1 mA

b =

99
ICmA
1IBmA

= 99

IE = 100 mA

C
P

B

N

E

IC = 99 mA
Kirchhoff’s
current law:

IB = 1 mA

C
P

B

N

E

IE = I B + I C

= 1 mA + 99 mA
= 100 mA
IE = 100 mA

IC = 99 mA
In a PNP transistor,
holes flow from
emitter to collector.

IB = 1 mA
Notice the PNP
bias voltages.

C
B

E

IE = 100 mA

Transistor Currents Quiz
b is the ratio of collector current to
______ current.

base

The sum of the base and collector
currents is the __________ current.

emitter

In NPN transistors, the flow from emitter
to collector is composed of _______.

electrons

In PNP transistors, the flow from emitter
to collector is composed of _______.

holes

Both NPN and PNP transistors show
__________ gain.

current

Concept Review
• The base to collector gain is called b (beta).
• To find b, divide the collector current by the
base current.
• The emitter current is the largest since it is the
sum of the base and collector currents.
• PNP transistors have opposite polarity from
NPN transistors.
• In an NPN transistor, the major flow is made
up of electrons.
• In a PNP transistor, the major flow is made up
of holes.
Repeat Segment

Concept Preview
• The NPN schematic symbol shows the emitter
arrow as Not Pointing iN.
• The collector curves are a graph of collector
voltage versus collector current.
• Both dc beta (bdc) and ac beta (bac) can be
determined from the collector curves.
• The collector circuit of a transistor can be
modeled as a resistor, as a closed switch or as
an open switch.
• The amount of base current determines which
of the three models applies.

NPN Schematic Symbol
Collector

Base

C
B E

Emitter
Memory aid: NPN
means Not Pointing iN.

PNP Schematic Symbol
Collector

Base

C
B E

Emitter

IC

This circuit is used to
collect IC versus
VCE data for
several values of IB.
C

IB
B

E

VCE

When graphed, the data provide an
NPN collector family of curves.
100 mA

14
12
10
IC in mA 8
6
4
2

80 mA
60 mA
40 mA
20 mA

0 2 4 6

8 10 12 14 16 18

VCE in Volts

0 mA

100 mA

14
12
10
IC in mA 8
6
4
2

80 mA
60 mA

40 mA
20 mA

0 2 4 6

8 10 12 14 16 18

0 mA

VCE in Volts

b =

14
mA
6ICmA
40
IB mA
100
mA

150
== 140

This type of gain
is called bdc or hFE.

100 mA

14
12
10
IC in mA 8
6
4
2

80 mA
60 mA

40 mA
20 mA

0 2 4 6

bac =

2.5DImA
C
20DImA
B

8 10 12 14 16 18

0 mA

VCE in Volts
= 125

Another type of gain
is called bac or hfe.

100 mA

14
12
10
IC in mA 8
6
4
2

80 mA
60 mA

40 mA
20 mA

0 2 4 6
IB

C

8 10 12 14 16 18
VCE in Volts

0 mA

With these values of IB:
The C-E model is a resistor.
E

100 mA

14
12
10
IC in mA 8
6
4
2
0 2 4 6
IB

80 mA
60 mA

40 mA
20 mA
8 10 12 14 16 18
VCE in Volts

0 mA

When IB >> 100 mA
VCE @ 0
The model is a closed switch.

100 mA

14
12
10
IC in mA 8
6
4
2
0 2 4 6
IB

80 mA
60 mA

40 mA
20 mA
8 10 12 14 16 18
VCE in Volts

0 mA

When IB = 0
IC = 0
The model is an open switch.

Transistor Operating Conditions Quiz
When IB is large and VCE @ 0, the transistor
acts as a ___________ switch.
closed
When IB = 0 and IC = 0, the transistor
acts as an ___________ switch.

open

When IB > 0 and VCE > 0, the transistor
acts as a ___________.

resistor

Two current gain measures are bdc and
__________.

bac

The symbol hfe is the same as _________.

bac

Concept Review
• The NPN schematic symbol shows the emitter
arrow as Not Pointing iN.
• The collector curves are a graph of collector
voltage versus collector current.
• Both dc beta (bdc) and ac beta (bac) can be
determined from the collector curves.
• The collector circuit of a transistor can be
modeled as a resistor, as a closed switch or as
an open switch.
• The amount of base current determines which
of the three models applies.
Repeat Segment

Concept Preview
• It is possible to test transistors out-of-circuit
using an ohmmeter.
• The E-B and C-B junctions act as diodes
during ohmmeter testing.

• The C-E test shows a high resistance because
two junctions are involved; one of which is
reverse biased by the ohmmeter.
• Gain can be verified by using a resistor in
conjunction with the ohmmeter test.

NPN

V

mA

E
B
C

The E-B junction is forward biased by the ohmmeter.

NPN

V

mA

E
B
C

The C-E resistance is very high.

NPN

V

mA

E
B
C
100 kW

The meter reading is < 100 kW due to gain.

Concept Review
• It is possible to test transistors out-of-circuit
using an ohmmeter.
• The E-B and C-B junctions act as diodes
during ohmmeter testing.
• The C-E test shows a high resistance because
two junctions are involved; one of which is
reverse biased by the ohmmeter.
• Gain can be verified by using a resistor in
conjunction with the ohmmeter test.
Repeat Segment

Concept Preview
• Bipolar junction transistors (BJTs) are controlled by
base current.
• Junction field effect transistors (JFETs) are controlled
by gate voltage.

• JFETs operate in the depletion mode (as normally on
devices).
• Metal oxide semiconductor field effect transistors
(MOSFETs) usually operate in the enhancement mode
(as normally off devices).
• Insulated gate bipolar transistors (IGBTs) are modified
MOSFETs and have very low on-resistance.
• Unijunction transistors (UJTs) are not used as
amplifiers.

Current In

The BJT is
a current
amplifier.

Current
Amplifier

Current Out

Voltage In

The JFET is
a voltage
controlled
amplifier.

Voltage
Amplifier

Current Out

Source

Gate

Drain

P

N-channel
P-type substrate
Structure of an
N-channel JFET

The channel has carriers so it
conducts from source to drain.

Drain

Gate
Source

Source

Gate

Drain

P

N-channel
P-type substrate

A negative gate voltage
can push the carriers from
the channel and turn
the JFET off.

Drain

Gate
Source

0V
-1 V
-2 V

ID in mA

-3 V

VGS

-4 V

0

-5 V
VDS in Volts

This is known as a depletion-mode device.
N-channel JFET drain family of characteristic curves

It’s possible to make enhancement
type field effect transistors as well.
Metal
oxide
insulator

Drain

n

Gate

VGG

D

VDD

p

G

n

S
N-channel
MOSFET

Source

Gate bias enhances the channel and turns the device on.

5V
4V
3V

ID in mA

2V

VGS

1V

0

0V
Drain

VDS in Volts

Enhancement mode
MOSFET drain family of
characteristic curves

Gate
Source

The IGBT (insulated gate bipolar transistor)
Operation and structure
similar to a MOSFET
Voltage controlled
(like the MOSFET)
Has one more junction
than a MOSFET
Hole injection reduces
the collector resistance

Faster turn off than
BJTs but not as fast
as MOSFETS

RCE = 8.33 mW

Three major device technologies

hole injection
Extra
junction

Courtesy of Powerex, Inc.

Typical IGBT Driver Circuit
Typically +15 V for turn on
Typically - 5 to -15 V for turn off

Control signal

IGBT

Powerex IGBT Module Structure

Powerex high voltage IGBT package

Emitter voltage

The unijunction transistor fires
when its emitter voltage reaches VP.
VP

Then, the emitter voltage
drops due to its negative
resistance characteristic.
Base 2

Emitter current
Emitter

The UJT is not useful as an amplifier.
It is used in timing and control applications.

Base 1

Other Transistor Types Quiz
BJTs are _________-controlled
amplifiers.

current

FETs are __________-controlled
amplifiers.

voltage

JFETs operate in the __________ mode. depletion
MOSFETs operate in the __________
mode.

enhancement

IGBTs are __________-controlled
amplifiers.

voltage

UJTs are not useful as __________.

amplifiers

Concept Review
• Bipolar junction transistors (BJTs) are controlled by
base current.
• Junction field effect transistors (JFETs) are controlled
by gate voltage.
• JFETs operate in the depletion mode (as normally on
devices).
• Metal oxide semiconductor field effect transistors
(MOSFETs) usually operate in the enhancement mode
(as normally off devices).
• Insulated gate bipolar transistors (IGBTs) are modified
MOSFETs and have very low on-resistance.
• Unijunction transistors (UJTs) are not used as
amplifiers.
Repeat Segment

Concept Preview
• BJTs can be used as switches.
• No base current = switch is off.
• High base current = switch is on.
• The dissipation is always zero in an ideal
switch: off = no current flow and on = no
voltage drop.

• MOSFETs can also be used as switches: no
gate voltage = switch is off and high gate
voltage = switch is on.

How do transistor switches work?
Can be viewed as solid state relays:
they are either ON or they are OFF.
BJT switches are characterized by:
high base current (switch is on)
(or no base current … off)

low resistance from collector to emitter (on)
(or very high resistance … off)
low collector dissipation (on or off)
PC = VCE x IC
PC = 0 x IC = 0 W
(on)
(or PC = VCE x 0 = 0 W … off)

NPN SWITCH
LOAD

RCE @ 
W
0W
DRIVER

The
The
driver
driver
output
output
isiszero
positive,
volts,
IIBB>=I0
0and
andthe
theload
loadis
ison
off
The
driver
output
is
zero
volts,
B = 0 and ILOAD = 0

PNP SWITCH
DRIVER

LOAD

The
Z):
Thedriver
driveroutput
outputisgoes
isoff
off(high
(highthe
Z):the
theresistor
resistor
low:
voltage
drop
pulls
the
base
voltage
up
that
VV
pulls
thethe
base
voltage
upso
soV
that
across
resistor
makes
BE
BE==00
BE negative

PNP SWITCH WITH NPN DRIVER

LOAD

NPN SWITCH WITH PNP DRIVER
(NEGATIVE POWER SUPPLY)

VV
0VV
BE
BE@ @+0.7

VVBE
0 VV
BE@@-0.7

LOAD

STEPPER MOTOR

A

B

C

A

Enhancement mode
power MOSFETs
used as switches

B

C
D

D

Concept Review
• BJTs can be used as switches.
• No base current = switch is off.
• High base current = switch is on.
• The dissipation is always zero in an ideal
switch: off = no current flow and on = no
voltage drop.
• MOSFETs can also be used as switches: no
gate voltage = switch is off and high gate
voltage = switch is on.
Repeat Segment

REVIEW
• Amplification
• Transistors
• Characteristic Curves
• Transistor Testing
• Other Transistor Types
• Transistors as Switches


Slide 46

Electronics
Principles & Applications
Sixth Edition

Charles A. Schuler
Chapter 5

Transistors
(student version)
©2003

Glencoe/McGraw-Hill

INTRODUCTION
• Amplification
• Transistors
• Characteristic Curves
• Transistor Testing
• Other Transistor Types
• Transistors as Switches

Dear Student:
This presentation is arranged in segments.
Each segment is preceded by a Concept
Preview slide and is followed by a Concept
Review slide. When you reach a Concept
Review slide, you can return to the
beginning of that segment by clicking on the
Repeat Segment button. This will allow you
to view that segment again, if you want to.

Concept Preview
• Amplifiers provide gain (the output is larger
than the input).
• Transistors have gain.
• Transistors have a collector, a base, and an
emitter.
• The C-B junction is reverse biased.
• The B-E junction is forward biased.
• Most of the emitter carriers reach the collector.
• The base current is relatively small but controls
the larger currents.

In

Gain =

Amplifier

Out

In

Out

NPN Transistor Structure

The collector is lightly doped.

N

C

The base is thin and
is lightly doped.

P

B

The emitter is heavily doped.

N

E

NPN Transistor Bias
No current flows.
The C-B junction
is reverse biased.

N

C

P

B

N

E

NPN Transistor Bias

The B-E junction
is forward biased.

Current flows.

N

C

P

B

N

E

NPN Transistor Bias
IC
Current flows
everywhere.
Most of the emitter carriers
diffuse through the thin base
When
both
junctions
region since they are attracted
biased....
by are
the collector.

Note that IB is smaller
than IE or IC.

N

C

P

B

N

E

IB

IE

Note: when the
switch opens, all
currents go to zero.
Although IB is smaller
it controls IE and IC.

Gain is something small
controlling something large
(IB is small).

IC
N

C

P

B

N

E

IB

IE

Transistor Structure and Bias Quiz
The heaviest doping is found in
the ___________ region.

emitter

The thinnest of all three regions
is called the ____________.

base

The collector-base junction is
___________ biased.

reverse

The base-emitter junction is
____________ biased.

forward

The majority of the emitter
carriers flow to the ___________.

collector

Concept Review
• Amplifiers provide gain (the output is larger than
the input).
• Transistors have gain.

• Transistors have a collector, a base, and an emitter.
• The C-B junction is reverse biased.
• The B-E junction is forward biased.

• Most of the emitter carriers reach the collector.
• The base current is relatively small but controls the
larger currents.
Repeat Segment

Concept Preview
• The base to collector gain is called b (beta).
• To find b, divide the collector current by the
base current.
• The emitter current is the largest since it is the
sum of the base and collector currents.
• PNP transistors have opposite polarity from
NPN transistors.

• In an NPN transistor, the major flow is made
up of electrons.
• In a PNP transistor, the major flow is made up
of holes.

IC = 99 mA

The current gain from
base to collector
is called b.
IB = 1 mA

b =

99
ICmA
1IBmA

= 99

IE = 100 mA

C
P

B

N

E

IC = 99 mA
Kirchhoff’s
current law:

IB = 1 mA

C
P

B

N

E

IE = I B + I C

= 1 mA + 99 mA
= 100 mA
IE = 100 mA

IC = 99 mA
In a PNP transistor,
holes flow from
emitter to collector.

IB = 1 mA
Notice the PNP
bias voltages.

C
B

E

IE = 100 mA

Transistor Currents Quiz
b is the ratio of collector current to
______ current.

base

The sum of the base and collector
currents is the __________ current.

emitter

In NPN transistors, the flow from emitter
to collector is composed of _______.

electrons

In PNP transistors, the flow from emitter
to collector is composed of _______.

holes

Both NPN and PNP transistors show
__________ gain.

current

Concept Review
• The base to collector gain is called b (beta).
• To find b, divide the collector current by the
base current.
• The emitter current is the largest since it is the
sum of the base and collector currents.
• PNP transistors have opposite polarity from
NPN transistors.
• In an NPN transistor, the major flow is made
up of electrons.
• In a PNP transistor, the major flow is made up
of holes.
Repeat Segment

Concept Preview
• The NPN schematic symbol shows the emitter
arrow as Not Pointing iN.
• The collector curves are a graph of collector
voltage versus collector current.
• Both dc beta (bdc) and ac beta (bac) can be
determined from the collector curves.
• The collector circuit of a transistor can be
modeled as a resistor, as a closed switch or as
an open switch.
• The amount of base current determines which
of the three models applies.

NPN Schematic Symbol
Collector

Base

C
B E

Emitter
Memory aid: NPN
means Not Pointing iN.

PNP Schematic Symbol
Collector

Base

C
B E

Emitter

IC

This circuit is used to
collect IC versus
VCE data for
several values of IB.
C

IB
B

E

VCE

When graphed, the data provide an
NPN collector family of curves.
100 mA

14
12
10
IC in mA 8
6
4
2

80 mA
60 mA
40 mA
20 mA

0 2 4 6

8 10 12 14 16 18

VCE in Volts

0 mA

100 mA

14
12
10
IC in mA 8
6
4
2

80 mA
60 mA

40 mA
20 mA

0 2 4 6

8 10 12 14 16 18

0 mA

VCE in Volts

b =

14
mA
6ICmA
40
IB mA
100
mA

150
== 140

This type of gain
is called bdc or hFE.

100 mA

14
12
10
IC in mA 8
6
4
2

80 mA
60 mA

40 mA
20 mA

0 2 4 6

bac =

2.5DImA
C
20DImA
B

8 10 12 14 16 18

0 mA

VCE in Volts
= 125

Another type of gain
is called bac or hfe.

100 mA

14
12
10
IC in mA 8
6
4
2

80 mA
60 mA

40 mA
20 mA

0 2 4 6
IB

C

8 10 12 14 16 18
VCE in Volts

0 mA

With these values of IB:
The C-E model is a resistor.
E

100 mA

14
12
10
IC in mA 8
6
4
2
0 2 4 6
IB

80 mA
60 mA

40 mA
20 mA
8 10 12 14 16 18
VCE in Volts

0 mA

When IB >> 100 mA
VCE @ 0
The model is a closed switch.

100 mA

14
12
10
IC in mA 8
6
4
2
0 2 4 6
IB

80 mA
60 mA

40 mA
20 mA
8 10 12 14 16 18
VCE in Volts

0 mA

When IB = 0
IC = 0
The model is an open switch.

Transistor Operating Conditions Quiz
When IB is large and VCE @ 0, the transistor
acts as a ___________ switch.
closed
When IB = 0 and IC = 0, the transistor
acts as an ___________ switch.

open

When IB > 0 and VCE > 0, the transistor
acts as a ___________.

resistor

Two current gain measures are bdc and
__________.

bac

The symbol hfe is the same as _________.

bac

Concept Review
• The NPN schematic symbol shows the emitter
arrow as Not Pointing iN.
• The collector curves are a graph of collector
voltage versus collector current.
• Both dc beta (bdc) and ac beta (bac) can be
determined from the collector curves.
• The collector circuit of a transistor can be
modeled as a resistor, as a closed switch or as
an open switch.
• The amount of base current determines which
of the three models applies.
Repeat Segment

Concept Preview
• It is possible to test transistors out-of-circuit
using an ohmmeter.
• The E-B and C-B junctions act as diodes
during ohmmeter testing.

• The C-E test shows a high resistance because
two junctions are involved; one of which is
reverse biased by the ohmmeter.
• Gain can be verified by using a resistor in
conjunction with the ohmmeter test.

NPN

V

mA

E
B
C

The E-B junction is forward biased by the ohmmeter.

NPN

V

mA

E
B
C

The C-E resistance is very high.

NPN

V

mA

E
B
C
100 kW

The meter reading is < 100 kW due to gain.

Concept Review
• It is possible to test transistors out-of-circuit
using an ohmmeter.
• The E-B and C-B junctions act as diodes
during ohmmeter testing.
• The C-E test shows a high resistance because
two junctions are involved; one of which is
reverse biased by the ohmmeter.
• Gain can be verified by using a resistor in
conjunction with the ohmmeter test.
Repeat Segment

Concept Preview
• Bipolar junction transistors (BJTs) are controlled by
base current.
• Junction field effect transistors (JFETs) are controlled
by gate voltage.

• JFETs operate in the depletion mode (as normally on
devices).
• Metal oxide semiconductor field effect transistors
(MOSFETs) usually operate in the enhancement mode
(as normally off devices).
• Insulated gate bipolar transistors (IGBTs) are modified
MOSFETs and have very low on-resistance.
• Unijunction transistors (UJTs) are not used as
amplifiers.

Current In

The BJT is
a current
amplifier.

Current
Amplifier

Current Out

Voltage In

The JFET is
a voltage
controlled
amplifier.

Voltage
Amplifier

Current Out

Source

Gate

Drain

P

N-channel
P-type substrate
Structure of an
N-channel JFET

The channel has carriers so it
conducts from source to drain.

Drain

Gate
Source

Source

Gate

Drain

P

N-channel
P-type substrate

A negative gate voltage
can push the carriers from
the channel and turn
the JFET off.

Drain

Gate
Source

0V
-1 V
-2 V

ID in mA

-3 V

VGS

-4 V

0

-5 V
VDS in Volts

This is known as a depletion-mode device.
N-channel JFET drain family of characteristic curves

It’s possible to make enhancement
type field effect transistors as well.
Metal
oxide
insulator

Drain

n

Gate

VGG

D

VDD

p

G

n

S
N-channel
MOSFET

Source

Gate bias enhances the channel and turns the device on.

5V
4V
3V

ID in mA

2V

VGS

1V

0

0V
Drain

VDS in Volts

Enhancement mode
MOSFET drain family of
characteristic curves

Gate
Source

The IGBT (insulated gate bipolar transistor)
Operation and structure
similar to a MOSFET
Voltage controlled
(like the MOSFET)
Has one more junction
than a MOSFET
Hole injection reduces
the collector resistance

Faster turn off than
BJTs but not as fast
as MOSFETS

RCE = 8.33 mW

Three major device technologies

hole injection
Extra
junction

Courtesy of Powerex, Inc.

Typical IGBT Driver Circuit
Typically +15 V for turn on
Typically - 5 to -15 V for turn off

Control signal

IGBT

Powerex IGBT Module Structure

Powerex high voltage IGBT package

Emitter voltage

The unijunction transistor fires
when its emitter voltage reaches VP.
VP

Then, the emitter voltage
drops due to its negative
resistance characteristic.
Base 2

Emitter current
Emitter

The UJT is not useful as an amplifier.
It is used in timing and control applications.

Base 1

Other Transistor Types Quiz
BJTs are _________-controlled
amplifiers.

current

FETs are __________-controlled
amplifiers.

voltage

JFETs operate in the __________ mode. depletion
MOSFETs operate in the __________
mode.

enhancement

IGBTs are __________-controlled
amplifiers.

voltage

UJTs are not useful as __________.

amplifiers

Concept Review
• Bipolar junction transistors (BJTs) are controlled by
base current.
• Junction field effect transistors (JFETs) are controlled
by gate voltage.
• JFETs operate in the depletion mode (as normally on
devices).
• Metal oxide semiconductor field effect transistors
(MOSFETs) usually operate in the enhancement mode
(as normally off devices).
• Insulated gate bipolar transistors (IGBTs) are modified
MOSFETs and have very low on-resistance.
• Unijunction transistors (UJTs) are not used as
amplifiers.
Repeat Segment

Concept Preview
• BJTs can be used as switches.
• No base current = switch is off.
• High base current = switch is on.
• The dissipation is always zero in an ideal
switch: off = no current flow and on = no
voltage drop.

• MOSFETs can also be used as switches: no
gate voltage = switch is off and high gate
voltage = switch is on.

How do transistor switches work?
Can be viewed as solid state relays:
they are either ON or they are OFF.
BJT switches are characterized by:
high base current (switch is on)
(or no base current … off)

low resistance from collector to emitter (on)
(or very high resistance … off)
low collector dissipation (on or off)
PC = VCE x IC
PC = 0 x IC = 0 W
(on)
(or PC = VCE x 0 = 0 W … off)

NPN SWITCH
LOAD

RCE @ 
W
0W
DRIVER

The
The
driver
driver
output
output
isiszero
positive,
volts,
IIBB>=I0
0and
andthe
theload
loadis
ison
off
The
driver
output
is
zero
volts,
B = 0 and ILOAD = 0

PNP SWITCH
DRIVER

LOAD

The
Z):
Thedriver
driveroutput
outputisgoes
isoff
off(high
(highthe
Z):the
theresistor
resistor
low:
voltage
drop
pulls
the
base
voltage
up
that
VV
pulls
thethe
base
voltage
upso
soV
that
across
resistor
makes
BE
BE==00
BE negative

PNP SWITCH WITH NPN DRIVER

LOAD

NPN SWITCH WITH PNP DRIVER
(NEGATIVE POWER SUPPLY)

VV
0VV
BE
BE@ @+0.7

VVBE
0 VV
BE@@-0.7

LOAD

STEPPER MOTOR

A

B

C

A

Enhancement mode
power MOSFETs
used as switches

B

C
D

D

Concept Review
• BJTs can be used as switches.
• No base current = switch is off.
• High base current = switch is on.
• The dissipation is always zero in an ideal
switch: off = no current flow and on = no
voltage drop.
• MOSFETs can also be used as switches: no
gate voltage = switch is off and high gate
voltage = switch is on.
Repeat Segment

REVIEW
• Amplification
• Transistors
• Characteristic Curves
• Transistor Testing
• Other Transistor Types
• Transistors as Switches


Slide 47

Electronics
Principles & Applications
Sixth Edition

Charles A. Schuler
Chapter 5

Transistors
(student version)
©2003

Glencoe/McGraw-Hill

INTRODUCTION
• Amplification
• Transistors
• Characteristic Curves
• Transistor Testing
• Other Transistor Types
• Transistors as Switches

Dear Student:
This presentation is arranged in segments.
Each segment is preceded by a Concept
Preview slide and is followed by a Concept
Review slide. When you reach a Concept
Review slide, you can return to the
beginning of that segment by clicking on the
Repeat Segment button. This will allow you
to view that segment again, if you want to.

Concept Preview
• Amplifiers provide gain (the output is larger
than the input).
• Transistors have gain.
• Transistors have a collector, a base, and an
emitter.
• The C-B junction is reverse biased.
• The B-E junction is forward biased.
• Most of the emitter carriers reach the collector.
• The base current is relatively small but controls
the larger currents.

In

Gain =

Amplifier

Out

In

Out

NPN Transistor Structure

The collector is lightly doped.

N

C

The base is thin and
is lightly doped.

P

B

The emitter is heavily doped.

N

E

NPN Transistor Bias
No current flows.
The C-B junction
is reverse biased.

N

C

P

B

N

E

NPN Transistor Bias

The B-E junction
is forward biased.

Current flows.

N

C

P

B

N

E

NPN Transistor Bias
IC
Current flows
everywhere.
Most of the emitter carriers
diffuse through the thin base
When
both
junctions
region since they are attracted
biased....
by are
the collector.

Note that IB is smaller
than IE or IC.

N

C

P

B

N

E

IB

IE

Note: when the
switch opens, all
currents go to zero.
Although IB is smaller
it controls IE and IC.

Gain is something small
controlling something large
(IB is small).

IC
N

C

P

B

N

E

IB

IE

Transistor Structure and Bias Quiz
The heaviest doping is found in
the ___________ region.

emitter

The thinnest of all three regions
is called the ____________.

base

The collector-base junction is
___________ biased.

reverse

The base-emitter junction is
____________ biased.

forward

The majority of the emitter
carriers flow to the ___________.

collector

Concept Review
• Amplifiers provide gain (the output is larger than
the input).
• Transistors have gain.

• Transistors have a collector, a base, and an emitter.
• The C-B junction is reverse biased.
• The B-E junction is forward biased.

• Most of the emitter carriers reach the collector.
• The base current is relatively small but controls the
larger currents.
Repeat Segment

Concept Preview
• The base to collector gain is called b (beta).
• To find b, divide the collector current by the
base current.
• The emitter current is the largest since it is the
sum of the base and collector currents.
• PNP transistors have opposite polarity from
NPN transistors.

• In an NPN transistor, the major flow is made
up of electrons.
• In a PNP transistor, the major flow is made up
of holes.

IC = 99 mA

The current gain from
base to collector
is called b.
IB = 1 mA

b =

99
ICmA
1IBmA

= 99

IE = 100 mA

C
P

B

N

E

IC = 99 mA
Kirchhoff’s
current law:

IB = 1 mA

C
P

B

N

E

IE = I B + I C

= 1 mA + 99 mA
= 100 mA
IE = 100 mA

IC = 99 mA
In a PNP transistor,
holes flow from
emitter to collector.

IB = 1 mA
Notice the PNP
bias voltages.

C
B

E

IE = 100 mA

Transistor Currents Quiz
b is the ratio of collector current to
______ current.

base

The sum of the base and collector
currents is the __________ current.

emitter

In NPN transistors, the flow from emitter
to collector is composed of _______.

electrons

In PNP transistors, the flow from emitter
to collector is composed of _______.

holes

Both NPN and PNP transistors show
__________ gain.

current

Concept Review
• The base to collector gain is called b (beta).
• To find b, divide the collector current by the
base current.
• The emitter current is the largest since it is the
sum of the base and collector currents.
• PNP transistors have opposite polarity from
NPN transistors.
• In an NPN transistor, the major flow is made
up of electrons.
• In a PNP transistor, the major flow is made up
of holes.
Repeat Segment

Concept Preview
• The NPN schematic symbol shows the emitter
arrow as Not Pointing iN.
• The collector curves are a graph of collector
voltage versus collector current.
• Both dc beta (bdc) and ac beta (bac) can be
determined from the collector curves.
• The collector circuit of a transistor can be
modeled as a resistor, as a closed switch or as
an open switch.
• The amount of base current determines which
of the three models applies.

NPN Schematic Symbol
Collector

Base

C
B E

Emitter
Memory aid: NPN
means Not Pointing iN.

PNP Schematic Symbol
Collector

Base

C
B E

Emitter

IC

This circuit is used to
collect IC versus
VCE data for
several values of IB.
C

IB
B

E

VCE

When graphed, the data provide an
NPN collector family of curves.
100 mA

14
12
10
IC in mA 8
6
4
2

80 mA
60 mA
40 mA
20 mA

0 2 4 6

8 10 12 14 16 18

VCE in Volts

0 mA

100 mA

14
12
10
IC in mA 8
6
4
2

80 mA
60 mA

40 mA
20 mA

0 2 4 6

8 10 12 14 16 18

0 mA

VCE in Volts

b =

14
mA
6ICmA
40
IB mA
100
mA

150
== 140

This type of gain
is called bdc or hFE.

100 mA

14
12
10
IC in mA 8
6
4
2

80 mA
60 mA

40 mA
20 mA

0 2 4 6

bac =

2.5DImA
C
20DImA
B

8 10 12 14 16 18

0 mA

VCE in Volts
= 125

Another type of gain
is called bac or hfe.

100 mA

14
12
10
IC in mA 8
6
4
2

80 mA
60 mA

40 mA
20 mA

0 2 4 6
IB

C

8 10 12 14 16 18
VCE in Volts

0 mA

With these values of IB:
The C-E model is a resistor.
E

100 mA

14
12
10
IC in mA 8
6
4
2
0 2 4 6
IB

80 mA
60 mA

40 mA
20 mA
8 10 12 14 16 18
VCE in Volts

0 mA

When IB >> 100 mA
VCE @ 0
The model is a closed switch.

100 mA

14
12
10
IC in mA 8
6
4
2
0 2 4 6
IB

80 mA
60 mA

40 mA
20 mA
8 10 12 14 16 18
VCE in Volts

0 mA

When IB = 0
IC = 0
The model is an open switch.

Transistor Operating Conditions Quiz
When IB is large and VCE @ 0, the transistor
acts as a ___________ switch.
closed
When IB = 0 and IC = 0, the transistor
acts as an ___________ switch.

open

When IB > 0 and VCE > 0, the transistor
acts as a ___________.

resistor

Two current gain measures are bdc and
__________.

bac

The symbol hfe is the same as _________.

bac

Concept Review
• The NPN schematic symbol shows the emitter
arrow as Not Pointing iN.
• The collector curves are a graph of collector
voltage versus collector current.
• Both dc beta (bdc) and ac beta (bac) can be
determined from the collector curves.
• The collector circuit of a transistor can be
modeled as a resistor, as a closed switch or as
an open switch.
• The amount of base current determines which
of the three models applies.
Repeat Segment

Concept Preview
• It is possible to test transistors out-of-circuit
using an ohmmeter.
• The E-B and C-B junctions act as diodes
during ohmmeter testing.

• The C-E test shows a high resistance because
two junctions are involved; one of which is
reverse biased by the ohmmeter.
• Gain can be verified by using a resistor in
conjunction with the ohmmeter test.

NPN

V

mA

E
B
C

The E-B junction is forward biased by the ohmmeter.

NPN

V

mA

E
B
C

The C-E resistance is very high.

NPN

V

mA

E
B
C
100 kW

The meter reading is < 100 kW due to gain.

Concept Review
• It is possible to test transistors out-of-circuit
using an ohmmeter.
• The E-B and C-B junctions act as diodes
during ohmmeter testing.
• The C-E test shows a high resistance because
two junctions are involved; one of which is
reverse biased by the ohmmeter.
• Gain can be verified by using a resistor in
conjunction with the ohmmeter test.
Repeat Segment

Concept Preview
• Bipolar junction transistors (BJTs) are controlled by
base current.
• Junction field effect transistors (JFETs) are controlled
by gate voltage.

• JFETs operate in the depletion mode (as normally on
devices).
• Metal oxide semiconductor field effect transistors
(MOSFETs) usually operate in the enhancement mode
(as normally off devices).
• Insulated gate bipolar transistors (IGBTs) are modified
MOSFETs and have very low on-resistance.
• Unijunction transistors (UJTs) are not used as
amplifiers.

Current In

The BJT is
a current
amplifier.

Current
Amplifier

Current Out

Voltage In

The JFET is
a voltage
controlled
amplifier.

Voltage
Amplifier

Current Out

Source

Gate

Drain

P

N-channel
P-type substrate
Structure of an
N-channel JFET

The channel has carriers so it
conducts from source to drain.

Drain

Gate
Source

Source

Gate

Drain

P

N-channel
P-type substrate

A negative gate voltage
can push the carriers from
the channel and turn
the JFET off.

Drain

Gate
Source

0V
-1 V
-2 V

ID in mA

-3 V

VGS

-4 V

0

-5 V
VDS in Volts

This is known as a depletion-mode device.
N-channel JFET drain family of characteristic curves

It’s possible to make enhancement
type field effect transistors as well.
Metal
oxide
insulator

Drain

n

Gate

VGG

D

VDD

p

G

n

S
N-channel
MOSFET

Source

Gate bias enhances the channel and turns the device on.

5V
4V
3V

ID in mA

2V

VGS

1V

0

0V
Drain

VDS in Volts

Enhancement mode
MOSFET drain family of
characteristic curves

Gate
Source

The IGBT (insulated gate bipolar transistor)
Operation and structure
similar to a MOSFET
Voltage controlled
(like the MOSFET)
Has one more junction
than a MOSFET
Hole injection reduces
the collector resistance

Faster turn off than
BJTs but not as fast
as MOSFETS

RCE = 8.33 mW

Three major device technologies

hole injection
Extra
junction

Courtesy of Powerex, Inc.

Typical IGBT Driver Circuit
Typically +15 V for turn on
Typically - 5 to -15 V for turn off

Control signal

IGBT

Powerex IGBT Module Structure

Powerex high voltage IGBT package

Emitter voltage

The unijunction transistor fires
when its emitter voltage reaches VP.
VP

Then, the emitter voltage
drops due to its negative
resistance characteristic.
Base 2

Emitter current
Emitter

The UJT is not useful as an amplifier.
It is used in timing and control applications.

Base 1

Other Transistor Types Quiz
BJTs are _________-controlled
amplifiers.

current

FETs are __________-controlled
amplifiers.

voltage

JFETs operate in the __________ mode. depletion
MOSFETs operate in the __________
mode.

enhancement

IGBTs are __________-controlled
amplifiers.

voltage

UJTs are not useful as __________.

amplifiers

Concept Review
• Bipolar junction transistors (BJTs) are controlled by
base current.
• Junction field effect transistors (JFETs) are controlled
by gate voltage.
• JFETs operate in the depletion mode (as normally on
devices).
• Metal oxide semiconductor field effect transistors
(MOSFETs) usually operate in the enhancement mode
(as normally off devices).
• Insulated gate bipolar transistors (IGBTs) are modified
MOSFETs and have very low on-resistance.
• Unijunction transistors (UJTs) are not used as
amplifiers.
Repeat Segment

Concept Preview
• BJTs can be used as switches.
• No base current = switch is off.
• High base current = switch is on.
• The dissipation is always zero in an ideal
switch: off = no current flow and on = no
voltage drop.

• MOSFETs can also be used as switches: no
gate voltage = switch is off and high gate
voltage = switch is on.

How do transistor switches work?
Can be viewed as solid state relays:
they are either ON or they are OFF.
BJT switches are characterized by:
high base current (switch is on)
(or no base current … off)

low resistance from collector to emitter (on)
(or very high resistance … off)
low collector dissipation (on or off)
PC = VCE x IC
PC = 0 x IC = 0 W
(on)
(or PC = VCE x 0 = 0 W … off)

NPN SWITCH
LOAD

RCE @ 
W
0W
DRIVER

The
The
driver
driver
output
output
isiszero
positive,
volts,
IIBB>=I0
0and
andthe
theload
loadis
ison
off
The
driver
output
is
zero
volts,
B = 0 and ILOAD = 0

PNP SWITCH
DRIVER

LOAD

The
Z):
Thedriver
driveroutput
outputisgoes
isoff
off(high
(highthe
Z):the
theresistor
resistor
low:
voltage
drop
pulls
the
base
voltage
up
that
VV
pulls
thethe
base
voltage
upso
soV
that
across
resistor
makes
BE
BE==00
BE negative

PNP SWITCH WITH NPN DRIVER

LOAD

NPN SWITCH WITH PNP DRIVER
(NEGATIVE POWER SUPPLY)

VV
0VV
BE
BE@ @+0.7

VVBE
0 VV
BE@@-0.7

LOAD

STEPPER MOTOR

A

B

C

A

Enhancement mode
power MOSFETs
used as switches

B

C
D

D

Concept Review
• BJTs can be used as switches.
• No base current = switch is off.
• High base current = switch is on.
• The dissipation is always zero in an ideal
switch: off = no current flow and on = no
voltage drop.
• MOSFETs can also be used as switches: no
gate voltage = switch is off and high gate
voltage = switch is on.
Repeat Segment

REVIEW
• Amplification
• Transistors
• Characteristic Curves
• Transistor Testing
• Other Transistor Types
• Transistors as Switches


Slide 48

Electronics
Principles & Applications
Sixth Edition

Charles A. Schuler
Chapter 5

Transistors
(student version)
©2003

Glencoe/McGraw-Hill

INTRODUCTION
• Amplification
• Transistors
• Characteristic Curves
• Transistor Testing
• Other Transistor Types
• Transistors as Switches

Dear Student:
This presentation is arranged in segments.
Each segment is preceded by a Concept
Preview slide and is followed by a Concept
Review slide. When you reach a Concept
Review slide, you can return to the
beginning of that segment by clicking on the
Repeat Segment button. This will allow you
to view that segment again, if you want to.

Concept Preview
• Amplifiers provide gain (the output is larger
than the input).
• Transistors have gain.
• Transistors have a collector, a base, and an
emitter.
• The C-B junction is reverse biased.
• The B-E junction is forward biased.
• Most of the emitter carriers reach the collector.
• The base current is relatively small but controls
the larger currents.

In

Gain =

Amplifier

Out

In

Out

NPN Transistor Structure

The collector is lightly doped.

N

C

The base is thin and
is lightly doped.

P

B

The emitter is heavily doped.

N

E

NPN Transistor Bias
No current flows.
The C-B junction
is reverse biased.

N

C

P

B

N

E

NPN Transistor Bias

The B-E junction
is forward biased.

Current flows.

N

C

P

B

N

E

NPN Transistor Bias
IC
Current flows
everywhere.
Most of the emitter carriers
diffuse through the thin base
When
both
junctions
region since they are attracted
biased....
by are
the collector.

Note that IB is smaller
than IE or IC.

N

C

P

B

N

E

IB

IE

Note: when the
switch opens, all
currents go to zero.
Although IB is smaller
it controls IE and IC.

Gain is something small
controlling something large
(IB is small).

IC
N

C

P

B

N

E

IB

IE

Transistor Structure and Bias Quiz
The heaviest doping is found in
the ___________ region.

emitter

The thinnest of all three regions
is called the ____________.

base

The collector-base junction is
___________ biased.

reverse

The base-emitter junction is
____________ biased.

forward

The majority of the emitter
carriers flow to the ___________.

collector

Concept Review
• Amplifiers provide gain (the output is larger than
the input).
• Transistors have gain.

• Transistors have a collector, a base, and an emitter.
• The C-B junction is reverse biased.
• The B-E junction is forward biased.

• Most of the emitter carriers reach the collector.
• The base current is relatively small but controls the
larger currents.
Repeat Segment

Concept Preview
• The base to collector gain is called b (beta).
• To find b, divide the collector current by the
base current.
• The emitter current is the largest since it is the
sum of the base and collector currents.
• PNP transistors have opposite polarity from
NPN transistors.

• In an NPN transistor, the major flow is made
up of electrons.
• In a PNP transistor, the major flow is made up
of holes.

IC = 99 mA

The current gain from
base to collector
is called b.
IB = 1 mA

b =

99
ICmA
1IBmA

= 99

IE = 100 mA

C
P

B

N

E

IC = 99 mA
Kirchhoff’s
current law:

IB = 1 mA

C
P

B

N

E

IE = I B + I C

= 1 mA + 99 mA
= 100 mA
IE = 100 mA

IC = 99 mA
In a PNP transistor,
holes flow from
emitter to collector.

IB = 1 mA
Notice the PNP
bias voltages.

C
B

E

IE = 100 mA

Transistor Currents Quiz
b is the ratio of collector current to
______ current.

base

The sum of the base and collector
currents is the __________ current.

emitter

In NPN transistors, the flow from emitter
to collector is composed of _______.

electrons

In PNP transistors, the flow from emitter
to collector is composed of _______.

holes

Both NPN and PNP transistors show
__________ gain.

current

Concept Review
• The base to collector gain is called b (beta).
• To find b, divide the collector current by the
base current.
• The emitter current is the largest since it is the
sum of the base and collector currents.
• PNP transistors have opposite polarity from
NPN transistors.
• In an NPN transistor, the major flow is made
up of electrons.
• In a PNP transistor, the major flow is made up
of holes.
Repeat Segment

Concept Preview
• The NPN schematic symbol shows the emitter
arrow as Not Pointing iN.
• The collector curves are a graph of collector
voltage versus collector current.
• Both dc beta (bdc) and ac beta (bac) can be
determined from the collector curves.
• The collector circuit of a transistor can be
modeled as a resistor, as a closed switch or as
an open switch.
• The amount of base current determines which
of the three models applies.

NPN Schematic Symbol
Collector

Base

C
B E

Emitter
Memory aid: NPN
means Not Pointing iN.

PNP Schematic Symbol
Collector

Base

C
B E

Emitter

IC

This circuit is used to
collect IC versus
VCE data for
several values of IB.
C

IB
B

E

VCE

When graphed, the data provide an
NPN collector family of curves.
100 mA

14
12
10
IC in mA 8
6
4
2

80 mA
60 mA
40 mA
20 mA

0 2 4 6

8 10 12 14 16 18

VCE in Volts

0 mA

100 mA

14
12
10
IC in mA 8
6
4
2

80 mA
60 mA

40 mA
20 mA

0 2 4 6

8 10 12 14 16 18

0 mA

VCE in Volts

b =

14
mA
6ICmA
40
IB mA
100
mA

150
== 140

This type of gain
is called bdc or hFE.

100 mA

14
12
10
IC in mA 8
6
4
2

80 mA
60 mA

40 mA
20 mA

0 2 4 6

bac =

2.5DImA
C
20DImA
B

8 10 12 14 16 18

0 mA

VCE in Volts
= 125

Another type of gain
is called bac or hfe.

100 mA

14
12
10
IC in mA 8
6
4
2

80 mA
60 mA

40 mA
20 mA

0 2 4 6
IB

C

8 10 12 14 16 18
VCE in Volts

0 mA

With these values of IB:
The C-E model is a resistor.
E

100 mA

14
12
10
IC in mA 8
6
4
2
0 2 4 6
IB

80 mA
60 mA

40 mA
20 mA
8 10 12 14 16 18
VCE in Volts

0 mA

When IB >> 100 mA
VCE @ 0
The model is a closed switch.

100 mA

14
12
10
IC in mA 8
6
4
2
0 2 4 6
IB

80 mA
60 mA

40 mA
20 mA
8 10 12 14 16 18
VCE in Volts

0 mA

When IB = 0
IC = 0
The model is an open switch.

Transistor Operating Conditions Quiz
When IB is large and VCE @ 0, the transistor
acts as a ___________ switch.
closed
When IB = 0 and IC = 0, the transistor
acts as an ___________ switch.

open

When IB > 0 and VCE > 0, the transistor
acts as a ___________.

resistor

Two current gain measures are bdc and
__________.

bac

The symbol hfe is the same as _________.

bac

Concept Review
• The NPN schematic symbol shows the emitter
arrow as Not Pointing iN.
• The collector curves are a graph of collector
voltage versus collector current.
• Both dc beta (bdc) and ac beta (bac) can be
determined from the collector curves.
• The collector circuit of a transistor can be
modeled as a resistor, as a closed switch or as
an open switch.
• The amount of base current determines which
of the three models applies.
Repeat Segment

Concept Preview
• It is possible to test transistors out-of-circuit
using an ohmmeter.
• The E-B and C-B junctions act as diodes
during ohmmeter testing.

• The C-E test shows a high resistance because
two junctions are involved; one of which is
reverse biased by the ohmmeter.
• Gain can be verified by using a resistor in
conjunction with the ohmmeter test.

NPN

V

mA

E
B
C

The E-B junction is forward biased by the ohmmeter.

NPN

V

mA

E
B
C

The C-E resistance is very high.

NPN

V

mA

E
B
C
100 kW

The meter reading is < 100 kW due to gain.

Concept Review
• It is possible to test transistors out-of-circuit
using an ohmmeter.
• The E-B and C-B junctions act as diodes
during ohmmeter testing.
• The C-E test shows a high resistance because
two junctions are involved; one of which is
reverse biased by the ohmmeter.
• Gain can be verified by using a resistor in
conjunction with the ohmmeter test.
Repeat Segment

Concept Preview
• Bipolar junction transistors (BJTs) are controlled by
base current.
• Junction field effect transistors (JFETs) are controlled
by gate voltage.

• JFETs operate in the depletion mode (as normally on
devices).
• Metal oxide semiconductor field effect transistors
(MOSFETs) usually operate in the enhancement mode
(as normally off devices).
• Insulated gate bipolar transistors (IGBTs) are modified
MOSFETs and have very low on-resistance.
• Unijunction transistors (UJTs) are not used as
amplifiers.

Current In

The BJT is
a current
amplifier.

Current
Amplifier

Current Out

Voltage In

The JFET is
a voltage
controlled
amplifier.

Voltage
Amplifier

Current Out

Source

Gate

Drain

P

N-channel
P-type substrate
Structure of an
N-channel JFET

The channel has carriers so it
conducts from source to drain.

Drain

Gate
Source

Source

Gate

Drain

P

N-channel
P-type substrate

A negative gate voltage
can push the carriers from
the channel and turn
the JFET off.

Drain

Gate
Source

0V
-1 V
-2 V

ID in mA

-3 V

VGS

-4 V

0

-5 V
VDS in Volts

This is known as a depletion-mode device.
N-channel JFET drain family of characteristic curves

It’s possible to make enhancement
type field effect transistors as well.
Metal
oxide
insulator

Drain

n

Gate

VGG

D

VDD

p

G

n

S
N-channel
MOSFET

Source

Gate bias enhances the channel and turns the device on.

5V
4V
3V

ID in mA

2V

VGS

1V

0

0V
Drain

VDS in Volts

Enhancement mode
MOSFET drain family of
characteristic curves

Gate
Source

The IGBT (insulated gate bipolar transistor)
Operation and structure
similar to a MOSFET
Voltage controlled
(like the MOSFET)
Has one more junction
than a MOSFET
Hole injection reduces
the collector resistance

Faster turn off than
BJTs but not as fast
as MOSFETS

RCE = 8.33 mW

Three major device technologies

hole injection
Extra
junction

Courtesy of Powerex, Inc.

Typical IGBT Driver Circuit
Typically +15 V for turn on
Typically - 5 to -15 V for turn off

Control signal

IGBT

Powerex IGBT Module Structure

Powerex high voltage IGBT package

Emitter voltage

The unijunction transistor fires
when its emitter voltage reaches VP.
VP

Then, the emitter voltage
drops due to its negative
resistance characteristic.
Base 2

Emitter current
Emitter

The UJT is not useful as an amplifier.
It is used in timing and control applications.

Base 1

Other Transistor Types Quiz
BJTs are _________-controlled
amplifiers.

current

FETs are __________-controlled
amplifiers.

voltage

JFETs operate in the __________ mode. depletion
MOSFETs operate in the __________
mode.

enhancement

IGBTs are __________-controlled
amplifiers.

voltage

UJTs are not useful as __________.

amplifiers

Concept Review
• Bipolar junction transistors (BJTs) are controlled by
base current.
• Junction field effect transistors (JFETs) are controlled
by gate voltage.
• JFETs operate in the depletion mode (as normally on
devices).
• Metal oxide semiconductor field effect transistors
(MOSFETs) usually operate in the enhancement mode
(as normally off devices).
• Insulated gate bipolar transistors (IGBTs) are modified
MOSFETs and have very low on-resistance.
• Unijunction transistors (UJTs) are not used as
amplifiers.
Repeat Segment

Concept Preview
• BJTs can be used as switches.
• No base current = switch is off.
• High base current = switch is on.
• The dissipation is always zero in an ideal
switch: off = no current flow and on = no
voltage drop.

• MOSFETs can also be used as switches: no
gate voltage = switch is off and high gate
voltage = switch is on.

How do transistor switches work?
Can be viewed as solid state relays:
they are either ON or they are OFF.
BJT switches are characterized by:
high base current (switch is on)
(or no base current … off)

low resistance from collector to emitter (on)
(or very high resistance … off)
low collector dissipation (on or off)
PC = VCE x IC
PC = 0 x IC = 0 W
(on)
(or PC = VCE x 0 = 0 W … off)

NPN SWITCH
LOAD

RCE @ 
W
0W
DRIVER

The
The
driver
driver
output
output
isiszero
positive,
volts,
IIBB>=I0
0and
andthe
theload
loadis
ison
off
The
driver
output
is
zero
volts,
B = 0 and ILOAD = 0

PNP SWITCH
DRIVER

LOAD

The
Z):
Thedriver
driveroutput
outputisgoes
isoff
off(high
(highthe
Z):the
theresistor
resistor
low:
voltage
drop
pulls
the
base
voltage
up
that
VV
pulls
thethe
base
voltage
upso
soV
that
across
resistor
makes
BE
BE==00
BE negative

PNP SWITCH WITH NPN DRIVER

LOAD

NPN SWITCH WITH PNP DRIVER
(NEGATIVE POWER SUPPLY)

VV
0VV
BE
BE@ @+0.7

VVBE
0 VV
BE@@-0.7

LOAD

STEPPER MOTOR

A

B

C

A

Enhancement mode
power MOSFETs
used as switches

B

C
D

D

Concept Review
• BJTs can be used as switches.
• No base current = switch is off.
• High base current = switch is on.
• The dissipation is always zero in an ideal
switch: off = no current flow and on = no
voltage drop.
• MOSFETs can also be used as switches: no
gate voltage = switch is off and high gate
voltage = switch is on.
Repeat Segment

REVIEW
• Amplification
• Transistors
• Characteristic Curves
• Transistor Testing
• Other Transistor Types
• Transistors as Switches


Slide 49

Electronics
Principles & Applications
Sixth Edition

Charles A. Schuler
Chapter 5

Transistors
(student version)
©2003

Glencoe/McGraw-Hill

INTRODUCTION
• Amplification
• Transistors
• Characteristic Curves
• Transistor Testing
• Other Transistor Types
• Transistors as Switches

Dear Student:
This presentation is arranged in segments.
Each segment is preceded by a Concept
Preview slide and is followed by a Concept
Review slide. When you reach a Concept
Review slide, you can return to the
beginning of that segment by clicking on the
Repeat Segment button. This will allow you
to view that segment again, if you want to.

Concept Preview
• Amplifiers provide gain (the output is larger
than the input).
• Transistors have gain.
• Transistors have a collector, a base, and an
emitter.
• The C-B junction is reverse biased.
• The B-E junction is forward biased.
• Most of the emitter carriers reach the collector.
• The base current is relatively small but controls
the larger currents.

In

Gain =

Amplifier

Out

In

Out

NPN Transistor Structure

The collector is lightly doped.

N

C

The base is thin and
is lightly doped.

P

B

The emitter is heavily doped.

N

E

NPN Transistor Bias
No current flows.
The C-B junction
is reverse biased.

N

C

P

B

N

E

NPN Transistor Bias

The B-E junction
is forward biased.

Current flows.

N

C

P

B

N

E

NPN Transistor Bias
IC
Current flows
everywhere.
Most of the emitter carriers
diffuse through the thin base
When
both
junctions
region since they are attracted
biased....
by are
the collector.

Note that IB is smaller
than IE or IC.

N

C

P

B

N

E

IB

IE

Note: when the
switch opens, all
currents go to zero.
Although IB is smaller
it controls IE and IC.

Gain is something small
controlling something large
(IB is small).

IC
N

C

P

B

N

E

IB

IE

Transistor Structure and Bias Quiz
The heaviest doping is found in
the ___________ region.

emitter

The thinnest of all three regions
is called the ____________.

base

The collector-base junction is
___________ biased.

reverse

The base-emitter junction is
____________ biased.

forward

The majority of the emitter
carriers flow to the ___________.

collector

Concept Review
• Amplifiers provide gain (the output is larger than
the input).
• Transistors have gain.

• Transistors have a collector, a base, and an emitter.
• The C-B junction is reverse biased.
• The B-E junction is forward biased.

• Most of the emitter carriers reach the collector.
• The base current is relatively small but controls the
larger currents.
Repeat Segment

Concept Preview
• The base to collector gain is called b (beta).
• To find b, divide the collector current by the
base current.
• The emitter current is the largest since it is the
sum of the base and collector currents.
• PNP transistors have opposite polarity from
NPN transistors.

• In an NPN transistor, the major flow is made
up of electrons.
• In a PNP transistor, the major flow is made up
of holes.

IC = 99 mA

The current gain from
base to collector
is called b.
IB = 1 mA

b =

99
ICmA
1IBmA

= 99

IE = 100 mA

C
P

B

N

E

IC = 99 mA
Kirchhoff’s
current law:

IB = 1 mA

C
P

B

N

E

IE = I B + I C

= 1 mA + 99 mA
= 100 mA
IE = 100 mA

IC = 99 mA
In a PNP transistor,
holes flow from
emitter to collector.

IB = 1 mA
Notice the PNP
bias voltages.

C
B

E

IE = 100 mA

Transistor Currents Quiz
b is the ratio of collector current to
______ current.

base

The sum of the base and collector
currents is the __________ current.

emitter

In NPN transistors, the flow from emitter
to collector is composed of _______.

electrons

In PNP transistors, the flow from emitter
to collector is composed of _______.

holes

Both NPN and PNP transistors show
__________ gain.

current

Concept Review
• The base to collector gain is called b (beta).
• To find b, divide the collector current by the
base current.
• The emitter current is the largest since it is the
sum of the base and collector currents.
• PNP transistors have opposite polarity from
NPN transistors.
• In an NPN transistor, the major flow is made
up of electrons.
• In a PNP transistor, the major flow is made up
of holes.
Repeat Segment

Concept Preview
• The NPN schematic symbol shows the emitter
arrow as Not Pointing iN.
• The collector curves are a graph of collector
voltage versus collector current.
• Both dc beta (bdc) and ac beta (bac) can be
determined from the collector curves.
• The collector circuit of a transistor can be
modeled as a resistor, as a closed switch or as
an open switch.
• The amount of base current determines which
of the three models applies.

NPN Schematic Symbol
Collector

Base

C
B E

Emitter
Memory aid: NPN
means Not Pointing iN.

PNP Schematic Symbol
Collector

Base

C
B E

Emitter

IC

This circuit is used to
collect IC versus
VCE data for
several values of IB.
C

IB
B

E

VCE

When graphed, the data provide an
NPN collector family of curves.
100 mA

14
12
10
IC in mA 8
6
4
2

80 mA
60 mA
40 mA
20 mA

0 2 4 6

8 10 12 14 16 18

VCE in Volts

0 mA

100 mA

14
12
10
IC in mA 8
6
4
2

80 mA
60 mA

40 mA
20 mA

0 2 4 6

8 10 12 14 16 18

0 mA

VCE in Volts

b =

14
mA
6ICmA
40
IB mA
100
mA

150
== 140

This type of gain
is called bdc or hFE.

100 mA

14
12
10
IC in mA 8
6
4
2

80 mA
60 mA

40 mA
20 mA

0 2 4 6

bac =

2.5DImA
C
20DImA
B

8 10 12 14 16 18

0 mA

VCE in Volts
= 125

Another type of gain
is called bac or hfe.

100 mA

14
12
10
IC in mA 8
6
4
2

80 mA
60 mA

40 mA
20 mA

0 2 4 6
IB

C

8 10 12 14 16 18
VCE in Volts

0 mA

With these values of IB:
The C-E model is a resistor.
E

100 mA

14
12
10
IC in mA 8
6
4
2
0 2 4 6
IB

80 mA
60 mA

40 mA
20 mA
8 10 12 14 16 18
VCE in Volts

0 mA

When IB >> 100 mA
VCE @ 0
The model is a closed switch.

100 mA

14
12
10
IC in mA 8
6
4
2
0 2 4 6
IB

80 mA
60 mA

40 mA
20 mA
8 10 12 14 16 18
VCE in Volts

0 mA

When IB = 0
IC = 0
The model is an open switch.

Transistor Operating Conditions Quiz
When IB is large and VCE @ 0, the transistor
acts as a ___________ switch.
closed
When IB = 0 and IC = 0, the transistor
acts as an ___________ switch.

open

When IB > 0 and VCE > 0, the transistor
acts as a ___________.

resistor

Two current gain measures are bdc and
__________.

bac

The symbol hfe is the same as _________.

bac

Concept Review
• The NPN schematic symbol shows the emitter
arrow as Not Pointing iN.
• The collector curves are a graph of collector
voltage versus collector current.
• Both dc beta (bdc) and ac beta (bac) can be
determined from the collector curves.
• The collector circuit of a transistor can be
modeled as a resistor, as a closed switch or as
an open switch.
• The amount of base current determines which
of the three models applies.
Repeat Segment

Concept Preview
• It is possible to test transistors out-of-circuit
using an ohmmeter.
• The E-B and C-B junctions act as diodes
during ohmmeter testing.

• The C-E test shows a high resistance because
two junctions are involved; one of which is
reverse biased by the ohmmeter.
• Gain can be verified by using a resistor in
conjunction with the ohmmeter test.

NPN

V

mA

E
B
C

The E-B junction is forward biased by the ohmmeter.

NPN

V

mA

E
B
C

The C-E resistance is very high.

NPN

V

mA

E
B
C
100 kW

The meter reading is < 100 kW due to gain.

Concept Review
• It is possible to test transistors out-of-circuit
using an ohmmeter.
• The E-B and C-B junctions act as diodes
during ohmmeter testing.
• The C-E test shows a high resistance because
two junctions are involved; one of which is
reverse biased by the ohmmeter.
• Gain can be verified by using a resistor in
conjunction with the ohmmeter test.
Repeat Segment

Concept Preview
• Bipolar junction transistors (BJTs) are controlled by
base current.
• Junction field effect transistors (JFETs) are controlled
by gate voltage.

• JFETs operate in the depletion mode (as normally on
devices).
• Metal oxide semiconductor field effect transistors
(MOSFETs) usually operate in the enhancement mode
(as normally off devices).
• Insulated gate bipolar transistors (IGBTs) are modified
MOSFETs and have very low on-resistance.
• Unijunction transistors (UJTs) are not used as
amplifiers.

Current In

The BJT is
a current
amplifier.

Current
Amplifier

Current Out

Voltage In

The JFET is
a voltage
controlled
amplifier.

Voltage
Amplifier

Current Out

Source

Gate

Drain

P

N-channel
P-type substrate
Structure of an
N-channel JFET

The channel has carriers so it
conducts from source to drain.

Drain

Gate
Source

Source

Gate

Drain

P

N-channel
P-type substrate

A negative gate voltage
can push the carriers from
the channel and turn
the JFET off.

Drain

Gate
Source

0V
-1 V
-2 V

ID in mA

-3 V

VGS

-4 V

0

-5 V
VDS in Volts

This is known as a depletion-mode device.
N-channel JFET drain family of characteristic curves

It’s possible to make enhancement
type field effect transistors as well.
Metal
oxide
insulator

Drain

n

Gate

VGG

D

VDD

p

G

n

S
N-channel
MOSFET

Source

Gate bias enhances the channel and turns the device on.

5V
4V
3V

ID in mA

2V

VGS

1V

0

0V
Drain

VDS in Volts

Enhancement mode
MOSFET drain family of
characteristic curves

Gate
Source

The IGBT (insulated gate bipolar transistor)
Operation and structure
similar to a MOSFET
Voltage controlled
(like the MOSFET)
Has one more junction
than a MOSFET
Hole injection reduces
the collector resistance

Faster turn off than
BJTs but not as fast
as MOSFETS

RCE = 8.33 mW

Three major device technologies

hole injection
Extra
junction

Courtesy of Powerex, Inc.

Typical IGBT Driver Circuit
Typically +15 V for turn on
Typically - 5 to -15 V for turn off

Control signal

IGBT

Powerex IGBT Module Structure

Powerex high voltage IGBT package

Emitter voltage

The unijunction transistor fires
when its emitter voltage reaches VP.
VP

Then, the emitter voltage
drops due to its negative
resistance characteristic.
Base 2

Emitter current
Emitter

The UJT is not useful as an amplifier.
It is used in timing and control applications.

Base 1

Other Transistor Types Quiz
BJTs are _________-controlled
amplifiers.

current

FETs are __________-controlled
amplifiers.

voltage

JFETs operate in the __________ mode. depletion
MOSFETs operate in the __________
mode.

enhancement

IGBTs are __________-controlled
amplifiers.

voltage

UJTs are not useful as __________.

amplifiers

Concept Review
• Bipolar junction transistors (BJTs) are controlled by
base current.
• Junction field effect transistors (JFETs) are controlled
by gate voltage.
• JFETs operate in the depletion mode (as normally on
devices).
• Metal oxide semiconductor field effect transistors
(MOSFETs) usually operate in the enhancement mode
(as normally off devices).
• Insulated gate bipolar transistors (IGBTs) are modified
MOSFETs and have very low on-resistance.
• Unijunction transistors (UJTs) are not used as
amplifiers.
Repeat Segment

Concept Preview
• BJTs can be used as switches.
• No base current = switch is off.
• High base current = switch is on.
• The dissipation is always zero in an ideal
switch: off = no current flow and on = no
voltage drop.

• MOSFETs can also be used as switches: no
gate voltage = switch is off and high gate
voltage = switch is on.

How do transistor switches work?
Can be viewed as solid state relays:
they are either ON or they are OFF.
BJT switches are characterized by:
high base current (switch is on)
(or no base current … off)

low resistance from collector to emitter (on)
(or very high resistance … off)
low collector dissipation (on or off)
PC = VCE x IC
PC = 0 x IC = 0 W
(on)
(or PC = VCE x 0 = 0 W … off)

NPN SWITCH
LOAD

RCE @ 
W
0W
DRIVER

The
The
driver
driver
output
output
isiszero
positive,
volts,
IIBB>=I0
0and
andthe
theload
loadis
ison
off
The
driver
output
is
zero
volts,
B = 0 and ILOAD = 0

PNP SWITCH
DRIVER

LOAD

The
Z):
Thedriver
driveroutput
outputisgoes
isoff
off(high
(highthe
Z):the
theresistor
resistor
low:
voltage
drop
pulls
the
base
voltage
up
that
VV
pulls
thethe
base
voltage
upso
soV
that
across
resistor
makes
BE
BE==00
BE negative

PNP SWITCH WITH NPN DRIVER

LOAD

NPN SWITCH WITH PNP DRIVER
(NEGATIVE POWER SUPPLY)

VV
0VV
BE
BE@ @+0.7

VVBE
0 VV
BE@@-0.7

LOAD

STEPPER MOTOR

A

B

C

A

Enhancement mode
power MOSFETs
used as switches

B

C
D

D

Concept Review
• BJTs can be used as switches.
• No base current = switch is off.
• High base current = switch is on.
• The dissipation is always zero in an ideal
switch: off = no current flow and on = no
voltage drop.
• MOSFETs can also be used as switches: no
gate voltage = switch is off and high gate
voltage = switch is on.
Repeat Segment

REVIEW
• Amplification
• Transistors
• Characteristic Curves
• Transistor Testing
• Other Transistor Types
• Transistors as Switches


Slide 50

Electronics
Principles & Applications
Sixth Edition

Charles A. Schuler
Chapter 5

Transistors
(student version)
©2003

Glencoe/McGraw-Hill

INTRODUCTION
• Amplification
• Transistors
• Characteristic Curves
• Transistor Testing
• Other Transistor Types
• Transistors as Switches

Dear Student:
This presentation is arranged in segments.
Each segment is preceded by a Concept
Preview slide and is followed by a Concept
Review slide. When you reach a Concept
Review slide, you can return to the
beginning of that segment by clicking on the
Repeat Segment button. This will allow you
to view that segment again, if you want to.

Concept Preview
• Amplifiers provide gain (the output is larger
than the input).
• Transistors have gain.
• Transistors have a collector, a base, and an
emitter.
• The C-B junction is reverse biased.
• The B-E junction is forward biased.
• Most of the emitter carriers reach the collector.
• The base current is relatively small but controls
the larger currents.

In

Gain =

Amplifier

Out

In

Out

NPN Transistor Structure

The collector is lightly doped.

N

C

The base is thin and
is lightly doped.

P

B

The emitter is heavily doped.

N

E

NPN Transistor Bias
No current flows.
The C-B junction
is reverse biased.

N

C

P

B

N

E

NPN Transistor Bias

The B-E junction
is forward biased.

Current flows.

N

C

P

B

N

E

NPN Transistor Bias
IC
Current flows
everywhere.
Most of the emitter carriers
diffuse through the thin base
When
both
junctions
region since they are attracted
biased....
by are
the collector.

Note that IB is smaller
than IE or IC.

N

C

P

B

N

E

IB

IE

Note: when the
switch opens, all
currents go to zero.
Although IB is smaller
it controls IE and IC.

Gain is something small
controlling something large
(IB is small).

IC
N

C

P

B

N

E

IB

IE

Transistor Structure and Bias Quiz
The heaviest doping is found in
the ___________ region.

emitter

The thinnest of all three regions
is called the ____________.

base

The collector-base junction is
___________ biased.

reverse

The base-emitter junction is
____________ biased.

forward

The majority of the emitter
carriers flow to the ___________.

collector

Concept Review
• Amplifiers provide gain (the output is larger than
the input).
• Transistors have gain.

• Transistors have a collector, a base, and an emitter.
• The C-B junction is reverse biased.
• The B-E junction is forward biased.

• Most of the emitter carriers reach the collector.
• The base current is relatively small but controls the
larger currents.
Repeat Segment

Concept Preview
• The base to collector gain is called b (beta).
• To find b, divide the collector current by the
base current.
• The emitter current is the largest since it is the
sum of the base and collector currents.
• PNP transistors have opposite polarity from
NPN transistors.

• In an NPN transistor, the major flow is made
up of electrons.
• In a PNP transistor, the major flow is made up
of holes.

IC = 99 mA

The current gain from
base to collector
is called b.
IB = 1 mA

b =

99
ICmA
1IBmA

= 99

IE = 100 mA

C
P

B

N

E

IC = 99 mA
Kirchhoff’s
current law:

IB = 1 mA

C
P

B

N

E

IE = I B + I C

= 1 mA + 99 mA
= 100 mA
IE = 100 mA

IC = 99 mA
In a PNP transistor,
holes flow from
emitter to collector.

IB = 1 mA
Notice the PNP
bias voltages.

C
B

E

IE = 100 mA

Transistor Currents Quiz
b is the ratio of collector current to
______ current.

base

The sum of the base and collector
currents is the __________ current.

emitter

In NPN transistors, the flow from emitter
to collector is composed of _______.

electrons

In PNP transistors, the flow from emitter
to collector is composed of _______.

holes

Both NPN and PNP transistors show
__________ gain.

current

Concept Review
• The base to collector gain is called b (beta).
• To find b, divide the collector current by the
base current.
• The emitter current is the largest since it is the
sum of the base and collector currents.
• PNP transistors have opposite polarity from
NPN transistors.
• In an NPN transistor, the major flow is made
up of electrons.
• In a PNP transistor, the major flow is made up
of holes.
Repeat Segment

Concept Preview
• The NPN schematic symbol shows the emitter
arrow as Not Pointing iN.
• The collector curves are a graph of collector
voltage versus collector current.
• Both dc beta (bdc) and ac beta (bac) can be
determined from the collector curves.
• The collector circuit of a transistor can be
modeled as a resistor, as a closed switch or as
an open switch.
• The amount of base current determines which
of the three models applies.

NPN Schematic Symbol
Collector

Base

C
B E

Emitter
Memory aid: NPN
means Not Pointing iN.

PNP Schematic Symbol
Collector

Base

C
B E

Emitter

IC

This circuit is used to
collect IC versus
VCE data for
several values of IB.
C

IB
B

E

VCE

When graphed, the data provide an
NPN collector family of curves.
100 mA

14
12
10
IC in mA 8
6
4
2

80 mA
60 mA
40 mA
20 mA

0 2 4 6

8 10 12 14 16 18

VCE in Volts

0 mA

100 mA

14
12
10
IC in mA 8
6
4
2

80 mA
60 mA

40 mA
20 mA

0 2 4 6

8 10 12 14 16 18

0 mA

VCE in Volts

b =

14
mA
6ICmA
40
IB mA
100
mA

150
== 140

This type of gain
is called bdc or hFE.

100 mA

14
12
10
IC in mA 8
6
4
2

80 mA
60 mA

40 mA
20 mA

0 2 4 6

bac =

2.5DImA
C
20DImA
B

8 10 12 14 16 18

0 mA

VCE in Volts
= 125

Another type of gain
is called bac or hfe.

100 mA

14
12
10
IC in mA 8
6
4
2

80 mA
60 mA

40 mA
20 mA

0 2 4 6
IB

C

8 10 12 14 16 18
VCE in Volts

0 mA

With these values of IB:
The C-E model is a resistor.
E

100 mA

14
12
10
IC in mA 8
6
4
2
0 2 4 6
IB

80 mA
60 mA

40 mA
20 mA
8 10 12 14 16 18
VCE in Volts

0 mA

When IB >> 100 mA
VCE @ 0
The model is a closed switch.

100 mA

14
12
10
IC in mA 8
6
4
2
0 2 4 6
IB

80 mA
60 mA

40 mA
20 mA
8 10 12 14 16 18
VCE in Volts

0 mA

When IB = 0
IC = 0
The model is an open switch.

Transistor Operating Conditions Quiz
When IB is large and VCE @ 0, the transistor
acts as a ___________ switch.
closed
When IB = 0 and IC = 0, the transistor
acts as an ___________ switch.

open

When IB > 0 and VCE > 0, the transistor
acts as a ___________.

resistor

Two current gain measures are bdc and
__________.

bac

The symbol hfe is the same as _________.

bac

Concept Review
• The NPN schematic symbol shows the emitter
arrow as Not Pointing iN.
• The collector curves are a graph of collector
voltage versus collector current.
• Both dc beta (bdc) and ac beta (bac) can be
determined from the collector curves.
• The collector circuit of a transistor can be
modeled as a resistor, as a closed switch or as
an open switch.
• The amount of base current determines which
of the three models applies.
Repeat Segment

Concept Preview
• It is possible to test transistors out-of-circuit
using an ohmmeter.
• The E-B and C-B junctions act as diodes
during ohmmeter testing.

• The C-E test shows a high resistance because
two junctions are involved; one of which is
reverse biased by the ohmmeter.
• Gain can be verified by using a resistor in
conjunction with the ohmmeter test.

NPN

V

mA

E
B
C

The E-B junction is forward biased by the ohmmeter.

NPN

V

mA

E
B
C

The C-E resistance is very high.

NPN

V

mA

E
B
C
100 kW

The meter reading is < 100 kW due to gain.

Concept Review
• It is possible to test transistors out-of-circuit
using an ohmmeter.
• The E-B and C-B junctions act as diodes
during ohmmeter testing.
• The C-E test shows a high resistance because
two junctions are involved; one of which is
reverse biased by the ohmmeter.
• Gain can be verified by using a resistor in
conjunction with the ohmmeter test.
Repeat Segment

Concept Preview
• Bipolar junction transistors (BJTs) are controlled by
base current.
• Junction field effect transistors (JFETs) are controlled
by gate voltage.

• JFETs operate in the depletion mode (as normally on
devices).
• Metal oxide semiconductor field effect transistors
(MOSFETs) usually operate in the enhancement mode
(as normally off devices).
• Insulated gate bipolar transistors (IGBTs) are modified
MOSFETs and have very low on-resistance.
• Unijunction transistors (UJTs) are not used as
amplifiers.

Current In

The BJT is
a current
amplifier.

Current
Amplifier

Current Out

Voltage In

The JFET is
a voltage
controlled
amplifier.

Voltage
Amplifier

Current Out

Source

Gate

Drain

P

N-channel
P-type substrate
Structure of an
N-channel JFET

The channel has carriers so it
conducts from source to drain.

Drain

Gate
Source

Source

Gate

Drain

P

N-channel
P-type substrate

A negative gate voltage
can push the carriers from
the channel and turn
the JFET off.

Drain

Gate
Source

0V
-1 V
-2 V

ID in mA

-3 V

VGS

-4 V

0

-5 V
VDS in Volts

This is known as a depletion-mode device.
N-channel JFET drain family of characteristic curves

It’s possible to make enhancement
type field effect transistors as well.
Metal
oxide
insulator

Drain

n

Gate

VGG

D

VDD

p

G

n

S
N-channel
MOSFET

Source

Gate bias enhances the channel and turns the device on.

5V
4V
3V

ID in mA

2V

VGS

1V

0

0V
Drain

VDS in Volts

Enhancement mode
MOSFET drain family of
characteristic curves

Gate
Source

The IGBT (insulated gate bipolar transistor)
Operation and structure
similar to a MOSFET
Voltage controlled
(like the MOSFET)
Has one more junction
than a MOSFET
Hole injection reduces
the collector resistance

Faster turn off than
BJTs but not as fast
as MOSFETS

RCE = 8.33 mW

Three major device technologies

hole injection
Extra
junction

Courtesy of Powerex, Inc.

Typical IGBT Driver Circuit
Typically +15 V for turn on
Typically - 5 to -15 V for turn off

Control signal

IGBT

Powerex IGBT Module Structure

Powerex high voltage IGBT package

Emitter voltage

The unijunction transistor fires
when its emitter voltage reaches VP.
VP

Then, the emitter voltage
drops due to its negative
resistance characteristic.
Base 2

Emitter current
Emitter

The UJT is not useful as an amplifier.
It is used in timing and control applications.

Base 1

Other Transistor Types Quiz
BJTs are _________-controlled
amplifiers.

current

FETs are __________-controlled
amplifiers.

voltage

JFETs operate in the __________ mode. depletion
MOSFETs operate in the __________
mode.

enhancement

IGBTs are __________-controlled
amplifiers.

voltage

UJTs are not useful as __________.

amplifiers

Concept Review
• Bipolar junction transistors (BJTs) are controlled by
base current.
• Junction field effect transistors (JFETs) are controlled
by gate voltage.
• JFETs operate in the depletion mode (as normally on
devices).
• Metal oxide semiconductor field effect transistors
(MOSFETs) usually operate in the enhancement mode
(as normally off devices).
• Insulated gate bipolar transistors (IGBTs) are modified
MOSFETs and have very low on-resistance.
• Unijunction transistors (UJTs) are not used as
amplifiers.
Repeat Segment

Concept Preview
• BJTs can be used as switches.
• No base current = switch is off.
• High base current = switch is on.
• The dissipation is always zero in an ideal
switch: off = no current flow and on = no
voltage drop.

• MOSFETs can also be used as switches: no
gate voltage = switch is off and high gate
voltage = switch is on.

How do transistor switches work?
Can be viewed as solid state relays:
they are either ON or they are OFF.
BJT switches are characterized by:
high base current (switch is on)
(or no base current … off)

low resistance from collector to emitter (on)
(or very high resistance … off)
low collector dissipation (on or off)
PC = VCE x IC
PC = 0 x IC = 0 W
(on)
(or PC = VCE x 0 = 0 W … off)

NPN SWITCH
LOAD

RCE @ 
W
0W
DRIVER

The
The
driver
driver
output
output
isiszero
positive,
volts,
IIBB>=I0
0and
andthe
theload
loadis
ison
off
The
driver
output
is
zero
volts,
B = 0 and ILOAD = 0

PNP SWITCH
DRIVER

LOAD

The
Z):
Thedriver
driveroutput
outputisgoes
isoff
off(high
(highthe
Z):the
theresistor
resistor
low:
voltage
drop
pulls
the
base
voltage
up
that
VV
pulls
thethe
base
voltage
upso
soV
that
across
resistor
makes
BE
BE==00
BE negative

PNP SWITCH WITH NPN DRIVER

LOAD

NPN SWITCH WITH PNP DRIVER
(NEGATIVE POWER SUPPLY)

VV
0VV
BE
BE@ @+0.7

VVBE
0 VV
BE@@-0.7

LOAD

STEPPER MOTOR

A

B

C

A

Enhancement mode
power MOSFETs
used as switches

B

C
D

D

Concept Review
• BJTs can be used as switches.
• No base current = switch is off.
• High base current = switch is on.
• The dissipation is always zero in an ideal
switch: off = no current flow and on = no
voltage drop.
• MOSFETs can also be used as switches: no
gate voltage = switch is off and high gate
voltage = switch is on.
Repeat Segment

REVIEW
• Amplification
• Transistors
• Characteristic Curves
• Transistor Testing
• Other Transistor Types
• Transistors as Switches


Slide 51

Electronics
Principles & Applications
Sixth Edition

Charles A. Schuler
Chapter 5

Transistors
(student version)
©2003

Glencoe/McGraw-Hill

INTRODUCTION
• Amplification
• Transistors
• Characteristic Curves
• Transistor Testing
• Other Transistor Types
• Transistors as Switches

Dear Student:
This presentation is arranged in segments.
Each segment is preceded by a Concept
Preview slide and is followed by a Concept
Review slide. When you reach a Concept
Review slide, you can return to the
beginning of that segment by clicking on the
Repeat Segment button. This will allow you
to view that segment again, if you want to.

Concept Preview
• Amplifiers provide gain (the output is larger
than the input).
• Transistors have gain.
• Transistors have a collector, a base, and an
emitter.
• The C-B junction is reverse biased.
• The B-E junction is forward biased.
• Most of the emitter carriers reach the collector.
• The base current is relatively small but controls
the larger currents.

In

Gain =

Amplifier

Out

In

Out

NPN Transistor Structure

The collector is lightly doped.

N

C

The base is thin and
is lightly doped.

P

B

The emitter is heavily doped.

N

E

NPN Transistor Bias
No current flows.
The C-B junction
is reverse biased.

N

C

P

B

N

E

NPN Transistor Bias

The B-E junction
is forward biased.

Current flows.

N

C

P

B

N

E

NPN Transistor Bias
IC
Current flows
everywhere.
Most of the emitter carriers
diffuse through the thin base
When
both
junctions
region since they are attracted
biased....
by are
the collector.

Note that IB is smaller
than IE or IC.

N

C

P

B

N

E

IB

IE

Note: when the
switch opens, all
currents go to zero.
Although IB is smaller
it controls IE and IC.

Gain is something small
controlling something large
(IB is small).

IC
N

C

P

B

N

E

IB

IE

Transistor Structure and Bias Quiz
The heaviest doping is found in
the ___________ region.

emitter

The thinnest of all three regions
is called the ____________.

base

The collector-base junction is
___________ biased.

reverse

The base-emitter junction is
____________ biased.

forward

The majority of the emitter
carriers flow to the ___________.

collector

Concept Review
• Amplifiers provide gain (the output is larger than
the input).
• Transistors have gain.

• Transistors have a collector, a base, and an emitter.
• The C-B junction is reverse biased.
• The B-E junction is forward biased.

• Most of the emitter carriers reach the collector.
• The base current is relatively small but controls the
larger currents.
Repeat Segment

Concept Preview
• The base to collector gain is called b (beta).
• To find b, divide the collector current by the
base current.
• The emitter current is the largest since it is the
sum of the base and collector currents.
• PNP transistors have opposite polarity from
NPN transistors.

• In an NPN transistor, the major flow is made
up of electrons.
• In a PNP transistor, the major flow is made up
of holes.

IC = 99 mA

The current gain from
base to collector
is called b.
IB = 1 mA

b =

99
ICmA
1IBmA

= 99

IE = 100 mA

C
P

B

N

E

IC = 99 mA
Kirchhoff’s
current law:

IB = 1 mA

C
P

B

N

E

IE = I B + I C

= 1 mA + 99 mA
= 100 mA
IE = 100 mA

IC = 99 mA
In a PNP transistor,
holes flow from
emitter to collector.

IB = 1 mA
Notice the PNP
bias voltages.

C
B

E

IE = 100 mA

Transistor Currents Quiz
b is the ratio of collector current to
______ current.

base

The sum of the base and collector
currents is the __________ current.

emitter

In NPN transistors, the flow from emitter
to collector is composed of _______.

electrons

In PNP transistors, the flow from emitter
to collector is composed of _______.

holes

Both NPN and PNP transistors show
__________ gain.

current

Concept Review
• The base to collector gain is called b (beta).
• To find b, divide the collector current by the
base current.
• The emitter current is the largest since it is the
sum of the base and collector currents.
• PNP transistors have opposite polarity from
NPN transistors.
• In an NPN transistor, the major flow is made
up of electrons.
• In a PNP transistor, the major flow is made up
of holes.
Repeat Segment

Concept Preview
• The NPN schematic symbol shows the emitter
arrow as Not Pointing iN.
• The collector curves are a graph of collector
voltage versus collector current.
• Both dc beta (bdc) and ac beta (bac) can be
determined from the collector curves.
• The collector circuit of a transistor can be
modeled as a resistor, as a closed switch or as
an open switch.
• The amount of base current determines which
of the three models applies.

NPN Schematic Symbol
Collector

Base

C
B E

Emitter
Memory aid: NPN
means Not Pointing iN.

PNP Schematic Symbol
Collector

Base

C
B E

Emitter

IC

This circuit is used to
collect IC versus
VCE data for
several values of IB.
C

IB
B

E

VCE

When graphed, the data provide an
NPN collector family of curves.
100 mA

14
12
10
IC in mA 8
6
4
2

80 mA
60 mA
40 mA
20 mA

0 2 4 6

8 10 12 14 16 18

VCE in Volts

0 mA

100 mA

14
12
10
IC in mA 8
6
4
2

80 mA
60 mA

40 mA
20 mA

0 2 4 6

8 10 12 14 16 18

0 mA

VCE in Volts

b =

14
mA
6ICmA
40
IB mA
100
mA

150
== 140

This type of gain
is called bdc or hFE.

100 mA

14
12
10
IC in mA 8
6
4
2

80 mA
60 mA

40 mA
20 mA

0 2 4 6

bac =

2.5DImA
C
20DImA
B

8 10 12 14 16 18

0 mA

VCE in Volts
= 125

Another type of gain
is called bac or hfe.

100 mA

14
12
10
IC in mA 8
6
4
2

80 mA
60 mA

40 mA
20 mA

0 2 4 6
IB

C

8 10 12 14 16 18
VCE in Volts

0 mA

With these values of IB:
The C-E model is a resistor.
E

100 mA

14
12
10
IC in mA 8
6
4
2
0 2 4 6
IB

80 mA
60 mA

40 mA
20 mA
8 10 12 14 16 18
VCE in Volts

0 mA

When IB >> 100 mA
VCE @ 0
The model is a closed switch.

100 mA

14
12
10
IC in mA 8
6
4
2
0 2 4 6
IB

80 mA
60 mA

40 mA
20 mA
8 10 12 14 16 18
VCE in Volts

0 mA

When IB = 0
IC = 0
The model is an open switch.

Transistor Operating Conditions Quiz
When IB is large and VCE @ 0, the transistor
acts as a ___________ switch.
closed
When IB = 0 and IC = 0, the transistor
acts as an ___________ switch.

open

When IB > 0 and VCE > 0, the transistor
acts as a ___________.

resistor

Two current gain measures are bdc and
__________.

bac

The symbol hfe is the same as _________.

bac

Concept Review
• The NPN schematic symbol shows the emitter
arrow as Not Pointing iN.
• The collector curves are a graph of collector
voltage versus collector current.
• Both dc beta (bdc) and ac beta (bac) can be
determined from the collector curves.
• The collector circuit of a transistor can be
modeled as a resistor, as a closed switch or as
an open switch.
• The amount of base current determines which
of the three models applies.
Repeat Segment

Concept Preview
• It is possible to test transistors out-of-circuit
using an ohmmeter.
• The E-B and C-B junctions act as diodes
during ohmmeter testing.

• The C-E test shows a high resistance because
two junctions are involved; one of which is
reverse biased by the ohmmeter.
• Gain can be verified by using a resistor in
conjunction with the ohmmeter test.

NPN

V

mA

E
B
C

The E-B junction is forward biased by the ohmmeter.

NPN

V

mA

E
B
C

The C-E resistance is very high.

NPN

V

mA

E
B
C
100 kW

The meter reading is < 100 kW due to gain.

Concept Review
• It is possible to test transistors out-of-circuit
using an ohmmeter.
• The E-B and C-B junctions act as diodes
during ohmmeter testing.
• The C-E test shows a high resistance because
two junctions are involved; one of which is
reverse biased by the ohmmeter.
• Gain can be verified by using a resistor in
conjunction with the ohmmeter test.
Repeat Segment

Concept Preview
• Bipolar junction transistors (BJTs) are controlled by
base current.
• Junction field effect transistors (JFETs) are controlled
by gate voltage.

• JFETs operate in the depletion mode (as normally on
devices).
• Metal oxide semiconductor field effect transistors
(MOSFETs) usually operate in the enhancement mode
(as normally off devices).
• Insulated gate bipolar transistors (IGBTs) are modified
MOSFETs and have very low on-resistance.
• Unijunction transistors (UJTs) are not used as
amplifiers.

Current In

The BJT is
a current
amplifier.

Current
Amplifier

Current Out

Voltage In

The JFET is
a voltage
controlled
amplifier.

Voltage
Amplifier

Current Out

Source

Gate

Drain

P

N-channel
P-type substrate
Structure of an
N-channel JFET

The channel has carriers so it
conducts from source to drain.

Drain

Gate
Source

Source

Gate

Drain

P

N-channel
P-type substrate

A negative gate voltage
can push the carriers from
the channel and turn
the JFET off.

Drain

Gate
Source

0V
-1 V
-2 V

ID in mA

-3 V

VGS

-4 V

0

-5 V
VDS in Volts

This is known as a depletion-mode device.
N-channel JFET drain family of characteristic curves

It’s possible to make enhancement
type field effect transistors as well.
Metal
oxide
insulator

Drain

n

Gate

VGG

D

VDD

p

G

n

S
N-channel
MOSFET

Source

Gate bias enhances the channel and turns the device on.

5V
4V
3V

ID in mA

2V

VGS

1V

0

0V
Drain

VDS in Volts

Enhancement mode
MOSFET drain family of
characteristic curves

Gate
Source

The IGBT (insulated gate bipolar transistor)
Operation and structure
similar to a MOSFET
Voltage controlled
(like the MOSFET)
Has one more junction
than a MOSFET
Hole injection reduces
the collector resistance

Faster turn off than
BJTs but not as fast
as MOSFETS

RCE = 8.33 mW

Three major device technologies

hole injection
Extra
junction

Courtesy of Powerex, Inc.

Typical IGBT Driver Circuit
Typically +15 V for turn on
Typically - 5 to -15 V for turn off

Control signal

IGBT

Powerex IGBT Module Structure

Powerex high voltage IGBT package

Emitter voltage

The unijunction transistor fires
when its emitter voltage reaches VP.
VP

Then, the emitter voltage
drops due to its negative
resistance characteristic.
Base 2

Emitter current
Emitter

The UJT is not useful as an amplifier.
It is used in timing and control applications.

Base 1

Other Transistor Types Quiz
BJTs are _________-controlled
amplifiers.

current

FETs are __________-controlled
amplifiers.

voltage

JFETs operate in the __________ mode. depletion
MOSFETs operate in the __________
mode.

enhancement

IGBTs are __________-controlled
amplifiers.

voltage

UJTs are not useful as __________.

amplifiers

Concept Review
• Bipolar junction transistors (BJTs) are controlled by
base current.
• Junction field effect transistors (JFETs) are controlled
by gate voltage.
• JFETs operate in the depletion mode (as normally on
devices).
• Metal oxide semiconductor field effect transistors
(MOSFETs) usually operate in the enhancement mode
(as normally off devices).
• Insulated gate bipolar transistors (IGBTs) are modified
MOSFETs and have very low on-resistance.
• Unijunction transistors (UJTs) are not used as
amplifiers.
Repeat Segment

Concept Preview
• BJTs can be used as switches.
• No base current = switch is off.
• High base current = switch is on.
• The dissipation is always zero in an ideal
switch: off = no current flow and on = no
voltage drop.

• MOSFETs can also be used as switches: no
gate voltage = switch is off and high gate
voltage = switch is on.

How do transistor switches work?
Can be viewed as solid state relays:
they are either ON or they are OFF.
BJT switches are characterized by:
high base current (switch is on)
(or no base current … off)

low resistance from collector to emitter (on)
(or very high resistance … off)
low collector dissipation (on or off)
PC = VCE x IC
PC = 0 x IC = 0 W
(on)
(or PC = VCE x 0 = 0 W … off)

NPN SWITCH
LOAD

RCE @ 
W
0W
DRIVER

The
The
driver
driver
output
output
isiszero
positive,
volts,
IIBB>=I0
0and
andthe
theload
loadis
ison
off
The
driver
output
is
zero
volts,
B = 0 and ILOAD = 0

PNP SWITCH
DRIVER

LOAD

The
Z):
Thedriver
driveroutput
outputisgoes
isoff
off(high
(highthe
Z):the
theresistor
resistor
low:
voltage
drop
pulls
the
base
voltage
up
that
VV
pulls
thethe
base
voltage
upso
soV
that
across
resistor
makes
BE
BE==00
BE negative

PNP SWITCH WITH NPN DRIVER

LOAD

NPN SWITCH WITH PNP DRIVER
(NEGATIVE POWER SUPPLY)

VV
0VV
BE
BE@ @+0.7

VVBE
0 VV
BE@@-0.7

LOAD

STEPPER MOTOR

A

B

C

A

Enhancement mode
power MOSFETs
used as switches

B

C
D

D

Concept Review
• BJTs can be used as switches.
• No base current = switch is off.
• High base current = switch is on.
• The dissipation is always zero in an ideal
switch: off = no current flow and on = no
voltage drop.
• MOSFETs can also be used as switches: no
gate voltage = switch is off and high gate
voltage = switch is on.
Repeat Segment

REVIEW
• Amplification
• Transistors
• Characteristic Curves
• Transistor Testing
• Other Transistor Types
• Transistors as Switches


Slide 52

Electronics
Principles & Applications
Sixth Edition

Charles A. Schuler
Chapter 5

Transistors
(student version)
©2003

Glencoe/McGraw-Hill

INTRODUCTION
• Amplification
• Transistors
• Characteristic Curves
• Transistor Testing
• Other Transistor Types
• Transistors as Switches

Dear Student:
This presentation is arranged in segments.
Each segment is preceded by a Concept
Preview slide and is followed by a Concept
Review slide. When you reach a Concept
Review slide, you can return to the
beginning of that segment by clicking on the
Repeat Segment button. This will allow you
to view that segment again, if you want to.

Concept Preview
• Amplifiers provide gain (the output is larger
than the input).
• Transistors have gain.
• Transistors have a collector, a base, and an
emitter.
• The C-B junction is reverse biased.
• The B-E junction is forward biased.
• Most of the emitter carriers reach the collector.
• The base current is relatively small but controls
the larger currents.

In

Gain =

Amplifier

Out

In

Out

NPN Transistor Structure

The collector is lightly doped.

N

C

The base is thin and
is lightly doped.

P

B

The emitter is heavily doped.

N

E

NPN Transistor Bias
No current flows.
The C-B junction
is reverse biased.

N

C

P

B

N

E

NPN Transistor Bias

The B-E junction
is forward biased.

Current flows.

N

C

P

B

N

E

NPN Transistor Bias
IC
Current flows
everywhere.
Most of the emitter carriers
diffuse through the thin base
When
both
junctions
region since they are attracted
biased....
by are
the collector.

Note that IB is smaller
than IE or IC.

N

C

P

B

N

E

IB

IE

Note: when the
switch opens, all
currents go to zero.
Although IB is smaller
it controls IE and IC.

Gain is something small
controlling something large
(IB is small).

IC
N

C

P

B

N

E

IB

IE

Transistor Structure and Bias Quiz
The heaviest doping is found in
the ___________ region.

emitter

The thinnest of all three regions
is called the ____________.

base

The collector-base junction is
___________ biased.

reverse

The base-emitter junction is
____________ biased.

forward

The majority of the emitter
carriers flow to the ___________.

collector

Concept Review
• Amplifiers provide gain (the output is larger than
the input).
• Transistors have gain.

• Transistors have a collector, a base, and an emitter.
• The C-B junction is reverse biased.
• The B-E junction is forward biased.

• Most of the emitter carriers reach the collector.
• The base current is relatively small but controls the
larger currents.
Repeat Segment

Concept Preview
• The base to collector gain is called b (beta).
• To find b, divide the collector current by the
base current.
• The emitter current is the largest since it is the
sum of the base and collector currents.
• PNP transistors have opposite polarity from
NPN transistors.

• In an NPN transistor, the major flow is made
up of electrons.
• In a PNP transistor, the major flow is made up
of holes.

IC = 99 mA

The current gain from
base to collector
is called b.
IB = 1 mA

b =

99
ICmA
1IBmA

= 99

IE = 100 mA

C
P

B

N

E

IC = 99 mA
Kirchhoff’s
current law:

IB = 1 mA

C
P

B

N

E

IE = I B + I C

= 1 mA + 99 mA
= 100 mA
IE = 100 mA

IC = 99 mA
In a PNP transistor,
holes flow from
emitter to collector.

IB = 1 mA
Notice the PNP
bias voltages.

C
B

E

IE = 100 mA

Transistor Currents Quiz
b is the ratio of collector current to
______ current.

base

The sum of the base and collector
currents is the __________ current.

emitter

In NPN transistors, the flow from emitter
to collector is composed of _______.

electrons

In PNP transistors, the flow from emitter
to collector is composed of _______.

holes

Both NPN and PNP transistors show
__________ gain.

current

Concept Review
• The base to collector gain is called b (beta).
• To find b, divide the collector current by the
base current.
• The emitter current is the largest since it is the
sum of the base and collector currents.
• PNP transistors have opposite polarity from
NPN transistors.
• In an NPN transistor, the major flow is made
up of electrons.
• In a PNP transistor, the major flow is made up
of holes.
Repeat Segment

Concept Preview
• The NPN schematic symbol shows the emitter
arrow as Not Pointing iN.
• The collector curves are a graph of collector
voltage versus collector current.
• Both dc beta (bdc) and ac beta (bac) can be
determined from the collector curves.
• The collector circuit of a transistor can be
modeled as a resistor, as a closed switch or as
an open switch.
• The amount of base current determines which
of the three models applies.

NPN Schematic Symbol
Collector

Base

C
B E

Emitter
Memory aid: NPN
means Not Pointing iN.

PNP Schematic Symbol
Collector

Base

C
B E

Emitter

IC

This circuit is used to
collect IC versus
VCE data for
several values of IB.
C

IB
B

E

VCE

When graphed, the data provide an
NPN collector family of curves.
100 mA

14
12
10
IC in mA 8
6
4
2

80 mA
60 mA
40 mA
20 mA

0 2 4 6

8 10 12 14 16 18

VCE in Volts

0 mA

100 mA

14
12
10
IC in mA 8
6
4
2

80 mA
60 mA

40 mA
20 mA

0 2 4 6

8 10 12 14 16 18

0 mA

VCE in Volts

b =

14
mA
6ICmA
40
IB mA
100
mA

150
== 140

This type of gain
is called bdc or hFE.

100 mA

14
12
10
IC in mA 8
6
4
2

80 mA
60 mA

40 mA
20 mA

0 2 4 6

bac =

2.5DImA
C
20DImA
B

8 10 12 14 16 18

0 mA

VCE in Volts
= 125

Another type of gain
is called bac or hfe.

100 mA

14
12
10
IC in mA 8
6
4
2

80 mA
60 mA

40 mA
20 mA

0 2 4 6
IB

C

8 10 12 14 16 18
VCE in Volts

0 mA

With these values of IB:
The C-E model is a resistor.
E

100 mA

14
12
10
IC in mA 8
6
4
2
0 2 4 6
IB

80 mA
60 mA

40 mA
20 mA
8 10 12 14 16 18
VCE in Volts

0 mA

When IB >> 100 mA
VCE @ 0
The model is a closed switch.

100 mA

14
12
10
IC in mA 8
6
4
2
0 2 4 6
IB

80 mA
60 mA

40 mA
20 mA
8 10 12 14 16 18
VCE in Volts

0 mA

When IB = 0
IC = 0
The model is an open switch.

Transistor Operating Conditions Quiz
When IB is large and VCE @ 0, the transistor
acts as a ___________ switch.
closed
When IB = 0 and IC = 0, the transistor
acts as an ___________ switch.

open

When IB > 0 and VCE > 0, the transistor
acts as a ___________.

resistor

Two current gain measures are bdc and
__________.

bac

The symbol hfe is the same as _________.

bac

Concept Review
• The NPN schematic symbol shows the emitter
arrow as Not Pointing iN.
• The collector curves are a graph of collector
voltage versus collector current.
• Both dc beta (bdc) and ac beta (bac) can be
determined from the collector curves.
• The collector circuit of a transistor can be
modeled as a resistor, as a closed switch or as
an open switch.
• The amount of base current determines which
of the three models applies.
Repeat Segment

Concept Preview
• It is possible to test transistors out-of-circuit
using an ohmmeter.
• The E-B and C-B junctions act as diodes
during ohmmeter testing.

• The C-E test shows a high resistance because
two junctions are involved; one of which is
reverse biased by the ohmmeter.
• Gain can be verified by using a resistor in
conjunction with the ohmmeter test.

NPN

V

mA

E
B
C

The E-B junction is forward biased by the ohmmeter.

NPN

V

mA

E
B
C

The C-E resistance is very high.

NPN

V

mA

E
B
C
100 kW

The meter reading is < 100 kW due to gain.

Concept Review
• It is possible to test transistors out-of-circuit
using an ohmmeter.
• The E-B and C-B junctions act as diodes
during ohmmeter testing.
• The C-E test shows a high resistance because
two junctions are involved; one of which is
reverse biased by the ohmmeter.
• Gain can be verified by using a resistor in
conjunction with the ohmmeter test.
Repeat Segment

Concept Preview
• Bipolar junction transistors (BJTs) are controlled by
base current.
• Junction field effect transistors (JFETs) are controlled
by gate voltage.

• JFETs operate in the depletion mode (as normally on
devices).
• Metal oxide semiconductor field effect transistors
(MOSFETs) usually operate in the enhancement mode
(as normally off devices).
• Insulated gate bipolar transistors (IGBTs) are modified
MOSFETs and have very low on-resistance.
• Unijunction transistors (UJTs) are not used as
amplifiers.

Current In

The BJT is
a current
amplifier.

Current
Amplifier

Current Out

Voltage In

The JFET is
a voltage
controlled
amplifier.

Voltage
Amplifier

Current Out

Source

Gate

Drain

P

N-channel
P-type substrate
Structure of an
N-channel JFET

The channel has carriers so it
conducts from source to drain.

Drain

Gate
Source

Source

Gate

Drain

P

N-channel
P-type substrate

A negative gate voltage
can push the carriers from
the channel and turn
the JFET off.

Drain

Gate
Source

0V
-1 V
-2 V

ID in mA

-3 V

VGS

-4 V

0

-5 V
VDS in Volts

This is known as a depletion-mode device.
N-channel JFET drain family of characteristic curves

It’s possible to make enhancement
type field effect transistors as well.
Metal
oxide
insulator

Drain

n

Gate

VGG

D

VDD

p

G

n

S
N-channel
MOSFET

Source

Gate bias enhances the channel and turns the device on.

5V
4V
3V

ID in mA

2V

VGS

1V

0

0V
Drain

VDS in Volts

Enhancement mode
MOSFET drain family of
characteristic curves

Gate
Source

The IGBT (insulated gate bipolar transistor)
Operation and structure
similar to a MOSFET
Voltage controlled
(like the MOSFET)
Has one more junction
than a MOSFET
Hole injection reduces
the collector resistance

Faster turn off than
BJTs but not as fast
as MOSFETS

RCE = 8.33 mW

Three major device technologies

hole injection
Extra
junction

Courtesy of Powerex, Inc.

Typical IGBT Driver Circuit
Typically +15 V for turn on
Typically - 5 to -15 V for turn off

Control signal

IGBT

Powerex IGBT Module Structure

Powerex high voltage IGBT package

Emitter voltage

The unijunction transistor fires
when its emitter voltage reaches VP.
VP

Then, the emitter voltage
drops due to its negative
resistance characteristic.
Base 2

Emitter current
Emitter

The UJT is not useful as an amplifier.
It is used in timing and control applications.

Base 1

Other Transistor Types Quiz
BJTs are _________-controlled
amplifiers.

current

FETs are __________-controlled
amplifiers.

voltage

JFETs operate in the __________ mode. depletion
MOSFETs operate in the __________
mode.

enhancement

IGBTs are __________-controlled
amplifiers.

voltage

UJTs are not useful as __________.

amplifiers

Concept Review
• Bipolar junction transistors (BJTs) are controlled by
base current.
• Junction field effect transistors (JFETs) are controlled
by gate voltage.
• JFETs operate in the depletion mode (as normally on
devices).
• Metal oxide semiconductor field effect transistors
(MOSFETs) usually operate in the enhancement mode
(as normally off devices).
• Insulated gate bipolar transistors (IGBTs) are modified
MOSFETs and have very low on-resistance.
• Unijunction transistors (UJTs) are not used as
amplifiers.
Repeat Segment

Concept Preview
• BJTs can be used as switches.
• No base current = switch is off.
• High base current = switch is on.
• The dissipation is always zero in an ideal
switch: off = no current flow and on = no
voltage drop.

• MOSFETs can also be used as switches: no
gate voltage = switch is off and high gate
voltage = switch is on.

How do transistor switches work?
Can be viewed as solid state relays:
they are either ON or they are OFF.
BJT switches are characterized by:
high base current (switch is on)
(or no base current … off)

low resistance from collector to emitter (on)
(or very high resistance … off)
low collector dissipation (on or off)
PC = VCE x IC
PC = 0 x IC = 0 W
(on)
(or PC = VCE x 0 = 0 W … off)

NPN SWITCH
LOAD

RCE @ 
W
0W
DRIVER

The
The
driver
driver
output
output
isiszero
positive,
volts,
IIBB>=I0
0and
andthe
theload
loadis
ison
off
The
driver
output
is
zero
volts,
B = 0 and ILOAD = 0

PNP SWITCH
DRIVER

LOAD

The
Z):
Thedriver
driveroutput
outputisgoes
isoff
off(high
(highthe
Z):the
theresistor
resistor
low:
voltage
drop
pulls
the
base
voltage
up
that
VV
pulls
thethe
base
voltage
upso
soV
that
across
resistor
makes
BE
BE==00
BE negative

PNP SWITCH WITH NPN DRIVER

LOAD

NPN SWITCH WITH PNP DRIVER
(NEGATIVE POWER SUPPLY)

VV
0VV
BE
BE@ @+0.7

VVBE
0 VV
BE@@-0.7

LOAD

STEPPER MOTOR

A

B

C

A

Enhancement mode
power MOSFETs
used as switches

B

C
D

D

Concept Review
• BJTs can be used as switches.
• No base current = switch is off.
• High base current = switch is on.
• The dissipation is always zero in an ideal
switch: off = no current flow and on = no
voltage drop.
• MOSFETs can also be used as switches: no
gate voltage = switch is off and high gate
voltage = switch is on.
Repeat Segment

REVIEW
• Amplification
• Transistors
• Characteristic Curves
• Transistor Testing
• Other Transistor Types
• Transistors as Switches


Slide 53

Electronics
Principles & Applications
Sixth Edition

Charles A. Schuler
Chapter 5

Transistors
(student version)
©2003

Glencoe/McGraw-Hill

INTRODUCTION
• Amplification
• Transistors
• Characteristic Curves
• Transistor Testing
• Other Transistor Types
• Transistors as Switches

Dear Student:
This presentation is arranged in segments.
Each segment is preceded by a Concept
Preview slide and is followed by a Concept
Review slide. When you reach a Concept
Review slide, you can return to the
beginning of that segment by clicking on the
Repeat Segment button. This will allow you
to view that segment again, if you want to.

Concept Preview
• Amplifiers provide gain (the output is larger
than the input).
• Transistors have gain.
• Transistors have a collector, a base, and an
emitter.
• The C-B junction is reverse biased.
• The B-E junction is forward biased.
• Most of the emitter carriers reach the collector.
• The base current is relatively small but controls
the larger currents.

In

Gain =

Amplifier

Out

In

Out

NPN Transistor Structure

The collector is lightly doped.

N

C

The base is thin and
is lightly doped.

P

B

The emitter is heavily doped.

N

E

NPN Transistor Bias
No current flows.
The C-B junction
is reverse biased.

N

C

P

B

N

E

NPN Transistor Bias

The B-E junction
is forward biased.

Current flows.

N

C

P

B

N

E

NPN Transistor Bias
IC
Current flows
everywhere.
Most of the emitter carriers
diffuse through the thin base
When
both
junctions
region since they are attracted
biased....
by are
the collector.

Note that IB is smaller
than IE or IC.

N

C

P

B

N

E

IB

IE

Note: when the
switch opens, all
currents go to zero.
Although IB is smaller
it controls IE and IC.

Gain is something small
controlling something large
(IB is small).

IC
N

C

P

B

N

E

IB

IE

Transistor Structure and Bias Quiz
The heaviest doping is found in
the ___________ region.

emitter

The thinnest of all three regions
is called the ____________.

base

The collector-base junction is
___________ biased.

reverse

The base-emitter junction is
____________ biased.

forward

The majority of the emitter
carriers flow to the ___________.

collector

Concept Review
• Amplifiers provide gain (the output is larger than
the input).
• Transistors have gain.

• Transistors have a collector, a base, and an emitter.
• The C-B junction is reverse biased.
• The B-E junction is forward biased.

• Most of the emitter carriers reach the collector.
• The base current is relatively small but controls the
larger currents.
Repeat Segment

Concept Preview
• The base to collector gain is called b (beta).
• To find b, divide the collector current by the
base current.
• The emitter current is the largest since it is the
sum of the base and collector currents.
• PNP transistors have opposite polarity from
NPN transistors.

• In an NPN transistor, the major flow is made
up of electrons.
• In a PNP transistor, the major flow is made up
of holes.

IC = 99 mA

The current gain from
base to collector
is called b.
IB = 1 mA

b =

99
ICmA
1IBmA

= 99

IE = 100 mA

C
P

B

N

E

IC = 99 mA
Kirchhoff’s
current law:

IB = 1 mA

C
P

B

N

E

IE = I B + I C

= 1 mA + 99 mA
= 100 mA
IE = 100 mA

IC = 99 mA
In a PNP transistor,
holes flow from
emitter to collector.

IB = 1 mA
Notice the PNP
bias voltages.

C
B

E

IE = 100 mA

Transistor Currents Quiz
b is the ratio of collector current to
______ current.

base

The sum of the base and collector
currents is the __________ current.

emitter

In NPN transistors, the flow from emitter
to collector is composed of _______.

electrons

In PNP transistors, the flow from emitter
to collector is composed of _______.

holes

Both NPN and PNP transistors show
__________ gain.

current

Concept Review
• The base to collector gain is called b (beta).
• To find b, divide the collector current by the
base current.
• The emitter current is the largest since it is the
sum of the base and collector currents.
• PNP transistors have opposite polarity from
NPN transistors.
• In an NPN transistor, the major flow is made
up of electrons.
• In a PNP transistor, the major flow is made up
of holes.
Repeat Segment

Concept Preview
• The NPN schematic symbol shows the emitter
arrow as Not Pointing iN.
• The collector curves are a graph of collector
voltage versus collector current.
• Both dc beta (bdc) and ac beta (bac) can be
determined from the collector curves.
• The collector circuit of a transistor can be
modeled as a resistor, as a closed switch or as
an open switch.
• The amount of base current determines which
of the three models applies.

NPN Schematic Symbol
Collector

Base

C
B E

Emitter
Memory aid: NPN
means Not Pointing iN.

PNP Schematic Symbol
Collector

Base

C
B E

Emitter

IC

This circuit is used to
collect IC versus
VCE data for
several values of IB.
C

IB
B

E

VCE

When graphed, the data provide an
NPN collector family of curves.
100 mA

14
12
10
IC in mA 8
6
4
2

80 mA
60 mA
40 mA
20 mA

0 2 4 6

8 10 12 14 16 18

VCE in Volts

0 mA

100 mA

14
12
10
IC in mA 8
6
4
2

80 mA
60 mA

40 mA
20 mA

0 2 4 6

8 10 12 14 16 18

0 mA

VCE in Volts

b =

14
mA
6ICmA
40
IB mA
100
mA

150
== 140

This type of gain
is called bdc or hFE.

100 mA

14
12
10
IC in mA 8
6
4
2

80 mA
60 mA

40 mA
20 mA

0 2 4 6

bac =

2.5DImA
C
20DImA
B

8 10 12 14 16 18

0 mA

VCE in Volts
= 125

Another type of gain
is called bac or hfe.

100 mA

14
12
10
IC in mA 8
6
4
2

80 mA
60 mA

40 mA
20 mA

0 2 4 6
IB

C

8 10 12 14 16 18
VCE in Volts

0 mA

With these values of IB:
The C-E model is a resistor.
E

100 mA

14
12
10
IC in mA 8
6
4
2
0 2 4 6
IB

80 mA
60 mA

40 mA
20 mA
8 10 12 14 16 18
VCE in Volts

0 mA

When IB >> 100 mA
VCE @ 0
The model is a closed switch.

100 mA

14
12
10
IC in mA 8
6
4
2
0 2 4 6
IB

80 mA
60 mA

40 mA
20 mA
8 10 12 14 16 18
VCE in Volts

0 mA

When IB = 0
IC = 0
The model is an open switch.

Transistor Operating Conditions Quiz
When IB is large and VCE @ 0, the transistor
acts as a ___________ switch.
closed
When IB = 0 and IC = 0, the transistor
acts as an ___________ switch.

open

When IB > 0 and VCE > 0, the transistor
acts as a ___________.

resistor

Two current gain measures are bdc and
__________.

bac

The symbol hfe is the same as _________.

bac

Concept Review
• The NPN schematic symbol shows the emitter
arrow as Not Pointing iN.
• The collector curves are a graph of collector
voltage versus collector current.
• Both dc beta (bdc) and ac beta (bac) can be
determined from the collector curves.
• The collector circuit of a transistor can be
modeled as a resistor, as a closed switch or as
an open switch.
• The amount of base current determines which
of the three models applies.
Repeat Segment

Concept Preview
• It is possible to test transistors out-of-circuit
using an ohmmeter.
• The E-B and C-B junctions act as diodes
during ohmmeter testing.

• The C-E test shows a high resistance because
two junctions are involved; one of which is
reverse biased by the ohmmeter.
• Gain can be verified by using a resistor in
conjunction with the ohmmeter test.

NPN

V

mA

E
B
C

The E-B junction is forward biased by the ohmmeter.

NPN

V

mA

E
B
C

The C-E resistance is very high.

NPN

V

mA

E
B
C
100 kW

The meter reading is < 100 kW due to gain.

Concept Review
• It is possible to test transistors out-of-circuit
using an ohmmeter.
• The E-B and C-B junctions act as diodes
during ohmmeter testing.
• The C-E test shows a high resistance because
two junctions are involved; one of which is
reverse biased by the ohmmeter.
• Gain can be verified by using a resistor in
conjunction with the ohmmeter test.
Repeat Segment

Concept Preview
• Bipolar junction transistors (BJTs) are controlled by
base current.
• Junction field effect transistors (JFETs) are controlled
by gate voltage.

• JFETs operate in the depletion mode (as normally on
devices).
• Metal oxide semiconductor field effect transistors
(MOSFETs) usually operate in the enhancement mode
(as normally off devices).
• Insulated gate bipolar transistors (IGBTs) are modified
MOSFETs and have very low on-resistance.
• Unijunction transistors (UJTs) are not used as
amplifiers.

Current In

The BJT is
a current
amplifier.

Current
Amplifier

Current Out

Voltage In

The JFET is
a voltage
controlled
amplifier.

Voltage
Amplifier

Current Out

Source

Gate

Drain

P

N-channel
P-type substrate
Structure of an
N-channel JFET

The channel has carriers so it
conducts from source to drain.

Drain

Gate
Source

Source

Gate

Drain

P

N-channel
P-type substrate

A negative gate voltage
can push the carriers from
the channel and turn
the JFET off.

Drain

Gate
Source

0V
-1 V
-2 V

ID in mA

-3 V

VGS

-4 V

0

-5 V
VDS in Volts

This is known as a depletion-mode device.
N-channel JFET drain family of characteristic curves

It’s possible to make enhancement
type field effect transistors as well.
Metal
oxide
insulator

Drain

n

Gate

VGG

D

VDD

p

G

n

S
N-channel
MOSFET

Source

Gate bias enhances the channel and turns the device on.

5V
4V
3V

ID in mA

2V

VGS

1V

0

0V
Drain

VDS in Volts

Enhancement mode
MOSFET drain family of
characteristic curves

Gate
Source

The IGBT (insulated gate bipolar transistor)
Operation and structure
similar to a MOSFET
Voltage controlled
(like the MOSFET)
Has one more junction
than a MOSFET
Hole injection reduces
the collector resistance

Faster turn off than
BJTs but not as fast
as MOSFETS

RCE = 8.33 mW

Three major device technologies

hole injection
Extra
junction

Courtesy of Powerex, Inc.

Typical IGBT Driver Circuit
Typically +15 V for turn on
Typically - 5 to -15 V for turn off

Control signal

IGBT

Powerex IGBT Module Structure

Powerex high voltage IGBT package

Emitter voltage

The unijunction transistor fires
when its emitter voltage reaches VP.
VP

Then, the emitter voltage
drops due to its negative
resistance characteristic.
Base 2

Emitter current
Emitter

The UJT is not useful as an amplifier.
It is used in timing and control applications.

Base 1

Other Transistor Types Quiz
BJTs are _________-controlled
amplifiers.

current

FETs are __________-controlled
amplifiers.

voltage

JFETs operate in the __________ mode. depletion
MOSFETs operate in the __________
mode.

enhancement

IGBTs are __________-controlled
amplifiers.

voltage

UJTs are not useful as __________.

amplifiers

Concept Review
• Bipolar junction transistors (BJTs) are controlled by
base current.
• Junction field effect transistors (JFETs) are controlled
by gate voltage.
• JFETs operate in the depletion mode (as normally on
devices).
• Metal oxide semiconductor field effect transistors
(MOSFETs) usually operate in the enhancement mode
(as normally off devices).
• Insulated gate bipolar transistors (IGBTs) are modified
MOSFETs and have very low on-resistance.
• Unijunction transistors (UJTs) are not used as
amplifiers.
Repeat Segment

Concept Preview
• BJTs can be used as switches.
• No base current = switch is off.
• High base current = switch is on.
• The dissipation is always zero in an ideal
switch: off = no current flow and on = no
voltage drop.

• MOSFETs can also be used as switches: no
gate voltage = switch is off and high gate
voltage = switch is on.

How do transistor switches work?
Can be viewed as solid state relays:
they are either ON or they are OFF.
BJT switches are characterized by:
high base current (switch is on)
(or no base current … off)

low resistance from collector to emitter (on)
(or very high resistance … off)
low collector dissipation (on or off)
PC = VCE x IC
PC = 0 x IC = 0 W
(on)
(or PC = VCE x 0 = 0 W … off)

NPN SWITCH
LOAD

RCE @ 
W
0W
DRIVER

The
The
driver
driver
output
output
isiszero
positive,
volts,
IIBB>=I0
0and
andthe
theload
loadis
ison
off
The
driver
output
is
zero
volts,
B = 0 and ILOAD = 0

PNP SWITCH
DRIVER

LOAD

The
Z):
Thedriver
driveroutput
outputisgoes
isoff
off(high
(highthe
Z):the
theresistor
resistor
low:
voltage
drop
pulls
the
base
voltage
up
that
VV
pulls
thethe
base
voltage
upso
soV
that
across
resistor
makes
BE
BE==00
BE negative

PNP SWITCH WITH NPN DRIVER

LOAD

NPN SWITCH WITH PNP DRIVER
(NEGATIVE POWER SUPPLY)

VV
0VV
BE
BE@ @+0.7

VVBE
0 VV
BE@@-0.7

LOAD

STEPPER MOTOR

A

B

C

A

Enhancement mode
power MOSFETs
used as switches

B

C
D

D

Concept Review
• BJTs can be used as switches.
• No base current = switch is off.
• High base current = switch is on.
• The dissipation is always zero in an ideal
switch: off = no current flow and on = no
voltage drop.
• MOSFETs can also be used as switches: no
gate voltage = switch is off and high gate
voltage = switch is on.
Repeat Segment

REVIEW
• Amplification
• Transistors
• Characteristic Curves
• Transistor Testing
• Other Transistor Types
• Transistors as Switches


Slide 54

Electronics
Principles & Applications
Sixth Edition

Charles A. Schuler
Chapter 5

Transistors
(student version)
©2003

Glencoe/McGraw-Hill

INTRODUCTION
• Amplification
• Transistors
• Characteristic Curves
• Transistor Testing
• Other Transistor Types
• Transistors as Switches

Dear Student:
This presentation is arranged in segments.
Each segment is preceded by a Concept
Preview slide and is followed by a Concept
Review slide. When you reach a Concept
Review slide, you can return to the
beginning of that segment by clicking on the
Repeat Segment button. This will allow you
to view that segment again, if you want to.

Concept Preview
• Amplifiers provide gain (the output is larger
than the input).
• Transistors have gain.
• Transistors have a collector, a base, and an
emitter.
• The C-B junction is reverse biased.
• The B-E junction is forward biased.
• Most of the emitter carriers reach the collector.
• The base current is relatively small but controls
the larger currents.

In

Gain =

Amplifier

Out

In

Out

NPN Transistor Structure

The collector is lightly doped.

N

C

The base is thin and
is lightly doped.

P

B

The emitter is heavily doped.

N

E

NPN Transistor Bias
No current flows.
The C-B junction
is reverse biased.

N

C

P

B

N

E

NPN Transistor Bias

The B-E junction
is forward biased.

Current flows.

N

C

P

B

N

E

NPN Transistor Bias
IC
Current flows
everywhere.
Most of the emitter carriers
diffuse through the thin base
When
both
junctions
region since they are attracted
biased....
by are
the collector.

Note that IB is smaller
than IE or IC.

N

C

P

B

N

E

IB

IE

Note: when the
switch opens, all
currents go to zero.
Although IB is smaller
it controls IE and IC.

Gain is something small
controlling something large
(IB is small).

IC
N

C

P

B

N

E

IB

IE

Transistor Structure and Bias Quiz
The heaviest doping is found in
the ___________ region.

emitter

The thinnest of all three regions
is called the ____________.

base

The collector-base junction is
___________ biased.

reverse

The base-emitter junction is
____________ biased.

forward

The majority of the emitter
carriers flow to the ___________.

collector

Concept Review
• Amplifiers provide gain (the output is larger than
the input).
• Transistors have gain.

• Transistors have a collector, a base, and an emitter.
• The C-B junction is reverse biased.
• The B-E junction is forward biased.

• Most of the emitter carriers reach the collector.
• The base current is relatively small but controls the
larger currents.
Repeat Segment

Concept Preview
• The base to collector gain is called b (beta).
• To find b, divide the collector current by the
base current.
• The emitter current is the largest since it is the
sum of the base and collector currents.
• PNP transistors have opposite polarity from
NPN transistors.

• In an NPN transistor, the major flow is made
up of electrons.
• In a PNP transistor, the major flow is made up
of holes.

IC = 99 mA

The current gain from
base to collector
is called b.
IB = 1 mA

b =

99
ICmA
1IBmA

= 99

IE = 100 mA

C
P

B

N

E

IC = 99 mA
Kirchhoff’s
current law:

IB = 1 mA

C
P

B

N

E

IE = I B + I C

= 1 mA + 99 mA
= 100 mA
IE = 100 mA

IC = 99 mA
In a PNP transistor,
holes flow from
emitter to collector.

IB = 1 mA
Notice the PNP
bias voltages.

C
B

E

IE = 100 mA

Transistor Currents Quiz
b is the ratio of collector current to
______ current.

base

The sum of the base and collector
currents is the __________ current.

emitter

In NPN transistors, the flow from emitter
to collector is composed of _______.

electrons

In PNP transistors, the flow from emitter
to collector is composed of _______.

holes

Both NPN and PNP transistors show
__________ gain.

current

Concept Review
• The base to collector gain is called b (beta).
• To find b, divide the collector current by the
base current.
• The emitter current is the largest since it is the
sum of the base and collector currents.
• PNP transistors have opposite polarity from
NPN transistors.
• In an NPN transistor, the major flow is made
up of electrons.
• In a PNP transistor, the major flow is made up
of holes.
Repeat Segment

Concept Preview
• The NPN schematic symbol shows the emitter
arrow as Not Pointing iN.
• The collector curves are a graph of collector
voltage versus collector current.
• Both dc beta (bdc) and ac beta (bac) can be
determined from the collector curves.
• The collector circuit of a transistor can be
modeled as a resistor, as a closed switch or as
an open switch.
• The amount of base current determines which
of the three models applies.

NPN Schematic Symbol
Collector

Base

C
B E

Emitter
Memory aid: NPN
means Not Pointing iN.

PNP Schematic Symbol
Collector

Base

C
B E

Emitter

IC

This circuit is used to
collect IC versus
VCE data for
several values of IB.
C

IB
B

E

VCE

When graphed, the data provide an
NPN collector family of curves.
100 mA

14
12
10
IC in mA 8
6
4
2

80 mA
60 mA
40 mA
20 mA

0 2 4 6

8 10 12 14 16 18

VCE in Volts

0 mA

100 mA

14
12
10
IC in mA 8
6
4
2

80 mA
60 mA

40 mA
20 mA

0 2 4 6

8 10 12 14 16 18

0 mA

VCE in Volts

b =

14
mA
6ICmA
40
IB mA
100
mA

150
== 140

This type of gain
is called bdc or hFE.

100 mA

14
12
10
IC in mA 8
6
4
2

80 mA
60 mA

40 mA
20 mA

0 2 4 6

bac =

2.5DImA
C
20DImA
B

8 10 12 14 16 18

0 mA

VCE in Volts
= 125

Another type of gain
is called bac or hfe.

100 mA

14
12
10
IC in mA 8
6
4
2

80 mA
60 mA

40 mA
20 mA

0 2 4 6
IB

C

8 10 12 14 16 18
VCE in Volts

0 mA

With these values of IB:
The C-E model is a resistor.
E

100 mA

14
12
10
IC in mA 8
6
4
2
0 2 4 6
IB

80 mA
60 mA

40 mA
20 mA
8 10 12 14 16 18
VCE in Volts

0 mA

When IB >> 100 mA
VCE @ 0
The model is a closed switch.

100 mA

14
12
10
IC in mA 8
6
4
2
0 2 4 6
IB

80 mA
60 mA

40 mA
20 mA
8 10 12 14 16 18
VCE in Volts

0 mA

When IB = 0
IC = 0
The model is an open switch.

Transistor Operating Conditions Quiz
When IB is large and VCE @ 0, the transistor
acts as a ___________ switch.
closed
When IB = 0 and IC = 0, the transistor
acts as an ___________ switch.

open

When IB > 0 and VCE > 0, the transistor
acts as a ___________.

resistor

Two current gain measures are bdc and
__________.

bac

The symbol hfe is the same as _________.

bac

Concept Review
• The NPN schematic symbol shows the emitter
arrow as Not Pointing iN.
• The collector curves are a graph of collector
voltage versus collector current.
• Both dc beta (bdc) and ac beta (bac) can be
determined from the collector curves.
• The collector circuit of a transistor can be
modeled as a resistor, as a closed switch or as
an open switch.
• The amount of base current determines which
of the three models applies.
Repeat Segment

Concept Preview
• It is possible to test transistors out-of-circuit
using an ohmmeter.
• The E-B and C-B junctions act as diodes
during ohmmeter testing.

• The C-E test shows a high resistance because
two junctions are involved; one of which is
reverse biased by the ohmmeter.
• Gain can be verified by using a resistor in
conjunction with the ohmmeter test.

NPN

V

mA

E
B
C

The E-B junction is forward biased by the ohmmeter.

NPN

V

mA

E
B
C

The C-E resistance is very high.

NPN

V

mA

E
B
C
100 kW

The meter reading is < 100 kW due to gain.

Concept Review
• It is possible to test transistors out-of-circuit
using an ohmmeter.
• The E-B and C-B junctions act as diodes
during ohmmeter testing.
• The C-E test shows a high resistance because
two junctions are involved; one of which is
reverse biased by the ohmmeter.
• Gain can be verified by using a resistor in
conjunction with the ohmmeter test.
Repeat Segment

Concept Preview
• Bipolar junction transistors (BJTs) are controlled by
base current.
• Junction field effect transistors (JFETs) are controlled
by gate voltage.

• JFETs operate in the depletion mode (as normally on
devices).
• Metal oxide semiconductor field effect transistors
(MOSFETs) usually operate in the enhancement mode
(as normally off devices).
• Insulated gate bipolar transistors (IGBTs) are modified
MOSFETs and have very low on-resistance.
• Unijunction transistors (UJTs) are not used as
amplifiers.

Current In

The BJT is
a current
amplifier.

Current
Amplifier

Current Out

Voltage In

The JFET is
a voltage
controlled
amplifier.

Voltage
Amplifier

Current Out

Source

Gate

Drain

P

N-channel
P-type substrate
Structure of an
N-channel JFET

The channel has carriers so it
conducts from source to drain.

Drain

Gate
Source

Source

Gate

Drain

P

N-channel
P-type substrate

A negative gate voltage
can push the carriers from
the channel and turn
the JFET off.

Drain

Gate
Source

0V
-1 V
-2 V

ID in mA

-3 V

VGS

-4 V

0

-5 V
VDS in Volts

This is known as a depletion-mode device.
N-channel JFET drain family of characteristic curves

It’s possible to make enhancement
type field effect transistors as well.
Metal
oxide
insulator

Drain

n

Gate

VGG

D

VDD

p

G

n

S
N-channel
MOSFET

Source

Gate bias enhances the channel and turns the device on.

5V
4V
3V

ID in mA

2V

VGS

1V

0

0V
Drain

VDS in Volts

Enhancement mode
MOSFET drain family of
characteristic curves

Gate
Source

The IGBT (insulated gate bipolar transistor)
Operation and structure
similar to a MOSFET
Voltage controlled
(like the MOSFET)
Has one more junction
than a MOSFET
Hole injection reduces
the collector resistance

Faster turn off than
BJTs but not as fast
as MOSFETS

RCE = 8.33 mW

Three major device technologies

hole injection
Extra
junction

Courtesy of Powerex, Inc.

Typical IGBT Driver Circuit
Typically +15 V for turn on
Typically - 5 to -15 V for turn off

Control signal

IGBT

Powerex IGBT Module Structure

Powerex high voltage IGBT package

Emitter voltage

The unijunction transistor fires
when its emitter voltage reaches VP.
VP

Then, the emitter voltage
drops due to its negative
resistance characteristic.
Base 2

Emitter current
Emitter

The UJT is not useful as an amplifier.
It is used in timing and control applications.

Base 1

Other Transistor Types Quiz
BJTs are _________-controlled
amplifiers.

current

FETs are __________-controlled
amplifiers.

voltage

JFETs operate in the __________ mode. depletion
MOSFETs operate in the __________
mode.

enhancement

IGBTs are __________-controlled
amplifiers.

voltage

UJTs are not useful as __________.

amplifiers

Concept Review
• Bipolar junction transistors (BJTs) are controlled by
base current.
• Junction field effect transistors (JFETs) are controlled
by gate voltage.
• JFETs operate in the depletion mode (as normally on
devices).
• Metal oxide semiconductor field effect transistors
(MOSFETs) usually operate in the enhancement mode
(as normally off devices).
• Insulated gate bipolar transistors (IGBTs) are modified
MOSFETs and have very low on-resistance.
• Unijunction transistors (UJTs) are not used as
amplifiers.
Repeat Segment

Concept Preview
• BJTs can be used as switches.
• No base current = switch is off.
• High base current = switch is on.
• The dissipation is always zero in an ideal
switch: off = no current flow and on = no
voltage drop.

• MOSFETs can also be used as switches: no
gate voltage = switch is off and high gate
voltage = switch is on.

How do transistor switches work?
Can be viewed as solid state relays:
they are either ON or they are OFF.
BJT switches are characterized by:
high base current (switch is on)
(or no base current … off)

low resistance from collector to emitter (on)
(or very high resistance … off)
low collector dissipation (on or off)
PC = VCE x IC
PC = 0 x IC = 0 W
(on)
(or PC = VCE x 0 = 0 W … off)

NPN SWITCH
LOAD

RCE @ 
W
0W
DRIVER

The
The
driver
driver
output
output
isiszero
positive,
volts,
IIBB>=I0
0and
andthe
theload
loadis
ison
off
The
driver
output
is
zero
volts,
B = 0 and ILOAD = 0

PNP SWITCH
DRIVER

LOAD

The
Z):
Thedriver
driveroutput
outputisgoes
isoff
off(high
(highthe
Z):the
theresistor
resistor
low:
voltage
drop
pulls
the
base
voltage
up
that
VV
pulls
thethe
base
voltage
upso
soV
that
across
resistor
makes
BE
BE==00
BE negative

PNP SWITCH WITH NPN DRIVER

LOAD

NPN SWITCH WITH PNP DRIVER
(NEGATIVE POWER SUPPLY)

VV
0VV
BE
BE@ @+0.7

VVBE
0 VV
BE@@-0.7

LOAD

STEPPER MOTOR

A

B

C

A

Enhancement mode
power MOSFETs
used as switches

B

C
D

D

Concept Review
• BJTs can be used as switches.
• No base current = switch is off.
• High base current = switch is on.
• The dissipation is always zero in an ideal
switch: off = no current flow and on = no
voltage drop.
• MOSFETs can also be used as switches: no
gate voltage = switch is off and high gate
voltage = switch is on.
Repeat Segment

REVIEW
• Amplification
• Transistors
• Characteristic Curves
• Transistor Testing
• Other Transistor Types
• Transistors as Switches


Slide 55

Electronics
Principles & Applications
Sixth Edition

Charles A. Schuler
Chapter 5

Transistors
(student version)
©2003

Glencoe/McGraw-Hill

INTRODUCTION
• Amplification
• Transistors
• Characteristic Curves
• Transistor Testing
• Other Transistor Types
• Transistors as Switches

Dear Student:
This presentation is arranged in segments.
Each segment is preceded by a Concept
Preview slide and is followed by a Concept
Review slide. When you reach a Concept
Review slide, you can return to the
beginning of that segment by clicking on the
Repeat Segment button. This will allow you
to view that segment again, if you want to.

Concept Preview
• Amplifiers provide gain (the output is larger
than the input).
• Transistors have gain.
• Transistors have a collector, a base, and an
emitter.
• The C-B junction is reverse biased.
• The B-E junction is forward biased.
• Most of the emitter carriers reach the collector.
• The base current is relatively small but controls
the larger currents.

In

Gain =

Amplifier

Out

In

Out

NPN Transistor Structure

The collector is lightly doped.

N

C

The base is thin and
is lightly doped.

P

B

The emitter is heavily doped.

N

E

NPN Transistor Bias
No current flows.
The C-B junction
is reverse biased.

N

C

P

B

N

E

NPN Transistor Bias

The B-E junction
is forward biased.

Current flows.

N

C

P

B

N

E

NPN Transistor Bias
IC
Current flows
everywhere.
Most of the emitter carriers
diffuse through the thin base
When
both
junctions
region since they are attracted
biased....
by are
the collector.

Note that IB is smaller
than IE or IC.

N

C

P

B

N

E

IB

IE

Note: when the
switch opens, all
currents go to zero.
Although IB is smaller
it controls IE and IC.

Gain is something small
controlling something large
(IB is small).

IC
N

C

P

B

N

E

IB

IE

Transistor Structure and Bias Quiz
The heaviest doping is found in
the ___________ region.

emitter

The thinnest of all three regions
is called the ____________.

base

The collector-base junction is
___________ biased.

reverse

The base-emitter junction is
____________ biased.

forward

The majority of the emitter
carriers flow to the ___________.

collector

Concept Review
• Amplifiers provide gain (the output is larger than
the input).
• Transistors have gain.

• Transistors have a collector, a base, and an emitter.
• The C-B junction is reverse biased.
• The B-E junction is forward biased.

• Most of the emitter carriers reach the collector.
• The base current is relatively small but controls the
larger currents.
Repeat Segment

Concept Preview
• The base to collector gain is called b (beta).
• To find b, divide the collector current by the
base current.
• The emitter current is the largest since it is the
sum of the base and collector currents.
• PNP transistors have opposite polarity from
NPN transistors.

• In an NPN transistor, the major flow is made
up of electrons.
• In a PNP transistor, the major flow is made up
of holes.

IC = 99 mA

The current gain from
base to collector
is called b.
IB = 1 mA

b =

99
ICmA
1IBmA

= 99

IE = 100 mA

C
P

B

N

E

IC = 99 mA
Kirchhoff’s
current law:

IB = 1 mA

C
P

B

N

E

IE = I B + I C

= 1 mA + 99 mA
= 100 mA
IE = 100 mA

IC = 99 mA
In a PNP transistor,
holes flow from
emitter to collector.

IB = 1 mA
Notice the PNP
bias voltages.

C
B

E

IE = 100 mA

Transistor Currents Quiz
b is the ratio of collector current to
______ current.

base

The sum of the base and collector
currents is the __________ current.

emitter

In NPN transistors, the flow from emitter
to collector is composed of _______.

electrons

In PNP transistors, the flow from emitter
to collector is composed of _______.

holes

Both NPN and PNP transistors show
__________ gain.

current

Concept Review
• The base to collector gain is called b (beta).
• To find b, divide the collector current by the
base current.
• The emitter current is the largest since it is the
sum of the base and collector currents.
• PNP transistors have opposite polarity from
NPN transistors.
• In an NPN transistor, the major flow is made
up of electrons.
• In a PNP transistor, the major flow is made up
of holes.
Repeat Segment

Concept Preview
• The NPN schematic symbol shows the emitter
arrow as Not Pointing iN.
• The collector curves are a graph of collector
voltage versus collector current.
• Both dc beta (bdc) and ac beta (bac) can be
determined from the collector curves.
• The collector circuit of a transistor can be
modeled as a resistor, as a closed switch or as
an open switch.
• The amount of base current determines which
of the three models applies.

NPN Schematic Symbol
Collector

Base

C
B E

Emitter
Memory aid: NPN
means Not Pointing iN.

PNP Schematic Symbol
Collector

Base

C
B E

Emitter

IC

This circuit is used to
collect IC versus
VCE data for
several values of IB.
C

IB
B

E

VCE

When graphed, the data provide an
NPN collector family of curves.
100 mA

14
12
10
IC in mA 8
6
4
2

80 mA
60 mA
40 mA
20 mA

0 2 4 6

8 10 12 14 16 18

VCE in Volts

0 mA

100 mA

14
12
10
IC in mA 8
6
4
2

80 mA
60 mA

40 mA
20 mA

0 2 4 6

8 10 12 14 16 18

0 mA

VCE in Volts

b =

14
mA
6ICmA
40
IB mA
100
mA

150
== 140

This type of gain
is called bdc or hFE.

100 mA

14
12
10
IC in mA 8
6
4
2

80 mA
60 mA

40 mA
20 mA

0 2 4 6

bac =

2.5DImA
C
20DImA
B

8 10 12 14 16 18

0 mA

VCE in Volts
= 125

Another type of gain
is called bac or hfe.

100 mA

14
12
10
IC in mA 8
6
4
2

80 mA
60 mA

40 mA
20 mA

0 2 4 6
IB

C

8 10 12 14 16 18
VCE in Volts

0 mA

With these values of IB:
The C-E model is a resistor.
E

100 mA

14
12
10
IC in mA 8
6
4
2
0 2 4 6
IB

80 mA
60 mA

40 mA
20 mA
8 10 12 14 16 18
VCE in Volts

0 mA

When IB >> 100 mA
VCE @ 0
The model is a closed switch.

100 mA

14
12
10
IC in mA 8
6
4
2
0 2 4 6
IB

80 mA
60 mA

40 mA
20 mA
8 10 12 14 16 18
VCE in Volts

0 mA

When IB = 0
IC = 0
The model is an open switch.

Transistor Operating Conditions Quiz
When IB is large and VCE @ 0, the transistor
acts as a ___________ switch.
closed
When IB = 0 and IC = 0, the transistor
acts as an ___________ switch.

open

When IB > 0 and VCE > 0, the transistor
acts as a ___________.

resistor

Two current gain measures are bdc and
__________.

bac

The symbol hfe is the same as _________.

bac

Concept Review
• The NPN schematic symbol shows the emitter
arrow as Not Pointing iN.
• The collector curves are a graph of collector
voltage versus collector current.
• Both dc beta (bdc) and ac beta (bac) can be
determined from the collector curves.
• The collector circuit of a transistor can be
modeled as a resistor, as a closed switch or as
an open switch.
• The amount of base current determines which
of the three models applies.
Repeat Segment

Concept Preview
• It is possible to test transistors out-of-circuit
using an ohmmeter.
• The E-B and C-B junctions act as diodes
during ohmmeter testing.

• The C-E test shows a high resistance because
two junctions are involved; one of which is
reverse biased by the ohmmeter.
• Gain can be verified by using a resistor in
conjunction with the ohmmeter test.

NPN

V

mA

E
B
C

The E-B junction is forward biased by the ohmmeter.

NPN

V

mA

E
B
C

The C-E resistance is very high.

NPN

V

mA

E
B
C
100 kW

The meter reading is < 100 kW due to gain.

Concept Review
• It is possible to test transistors out-of-circuit
using an ohmmeter.
• The E-B and C-B junctions act as diodes
during ohmmeter testing.
• The C-E test shows a high resistance because
two junctions are involved; one of which is
reverse biased by the ohmmeter.
• Gain can be verified by using a resistor in
conjunction with the ohmmeter test.
Repeat Segment

Concept Preview
• Bipolar junction transistors (BJTs) are controlled by
base current.
• Junction field effect transistors (JFETs) are controlled
by gate voltage.

• JFETs operate in the depletion mode (as normally on
devices).
• Metal oxide semiconductor field effect transistors
(MOSFETs) usually operate in the enhancement mode
(as normally off devices).
• Insulated gate bipolar transistors (IGBTs) are modified
MOSFETs and have very low on-resistance.
• Unijunction transistors (UJTs) are not used as
amplifiers.

Current In

The BJT is
a current
amplifier.

Current
Amplifier

Current Out

Voltage In

The JFET is
a voltage
controlled
amplifier.

Voltage
Amplifier

Current Out

Source

Gate

Drain

P

N-channel
P-type substrate
Structure of an
N-channel JFET

The channel has carriers so it
conducts from source to drain.

Drain

Gate
Source

Source

Gate

Drain

P

N-channel
P-type substrate

A negative gate voltage
can push the carriers from
the channel and turn
the JFET off.

Drain

Gate
Source

0V
-1 V
-2 V

ID in mA

-3 V

VGS

-4 V

0

-5 V
VDS in Volts

This is known as a depletion-mode device.
N-channel JFET drain family of characteristic curves

It’s possible to make enhancement
type field effect transistors as well.
Metal
oxide
insulator

Drain

n

Gate

VGG

D

VDD

p

G

n

S
N-channel
MOSFET

Source

Gate bias enhances the channel and turns the device on.

5V
4V
3V

ID in mA

2V

VGS

1V

0

0V
Drain

VDS in Volts

Enhancement mode
MOSFET drain family of
characteristic curves

Gate
Source

The IGBT (insulated gate bipolar transistor)
Operation and structure
similar to a MOSFET
Voltage controlled
(like the MOSFET)
Has one more junction
than a MOSFET
Hole injection reduces
the collector resistance

Faster turn off than
BJTs but not as fast
as MOSFETS

RCE = 8.33 mW

Three major device technologies

hole injection
Extra
junction

Courtesy of Powerex, Inc.

Typical IGBT Driver Circuit
Typically +15 V for turn on
Typically - 5 to -15 V for turn off

Control signal

IGBT

Powerex IGBT Module Structure

Powerex high voltage IGBT package

Emitter voltage

The unijunction transistor fires
when its emitter voltage reaches VP.
VP

Then, the emitter voltage
drops due to its negative
resistance characteristic.
Base 2

Emitter current
Emitter

The UJT is not useful as an amplifier.
It is used in timing and control applications.

Base 1

Other Transistor Types Quiz
BJTs are _________-controlled
amplifiers.

current

FETs are __________-controlled
amplifiers.

voltage

JFETs operate in the __________ mode. depletion
MOSFETs operate in the __________
mode.

enhancement

IGBTs are __________-controlled
amplifiers.

voltage

UJTs are not useful as __________.

amplifiers

Concept Review
• Bipolar junction transistors (BJTs) are controlled by
base current.
• Junction field effect transistors (JFETs) are controlled
by gate voltage.
• JFETs operate in the depletion mode (as normally on
devices).
• Metal oxide semiconductor field effect transistors
(MOSFETs) usually operate in the enhancement mode
(as normally off devices).
• Insulated gate bipolar transistors (IGBTs) are modified
MOSFETs and have very low on-resistance.
• Unijunction transistors (UJTs) are not used as
amplifiers.
Repeat Segment

Concept Preview
• BJTs can be used as switches.
• No base current = switch is off.
• High base current = switch is on.
• The dissipation is always zero in an ideal
switch: off = no current flow and on = no
voltage drop.

• MOSFETs can also be used as switches: no
gate voltage = switch is off and high gate
voltage = switch is on.

How do transistor switches work?
Can be viewed as solid state relays:
they are either ON or they are OFF.
BJT switches are characterized by:
high base current (switch is on)
(or no base current … off)

low resistance from collector to emitter (on)
(or very high resistance … off)
low collector dissipation (on or off)
PC = VCE x IC
PC = 0 x IC = 0 W
(on)
(or PC = VCE x 0 = 0 W … off)

NPN SWITCH
LOAD

RCE @ 
W
0W
DRIVER

The
The
driver
driver
output
output
isiszero
positive,
volts,
IIBB>=I0
0and
andthe
theload
loadis
ison
off
The
driver
output
is
zero
volts,
B = 0 and ILOAD = 0

PNP SWITCH
DRIVER

LOAD

The
Z):
Thedriver
driveroutput
outputisgoes
isoff
off(high
(highthe
Z):the
theresistor
resistor
low:
voltage
drop
pulls
the
base
voltage
up
that
VV
pulls
thethe
base
voltage
upso
soV
that
across
resistor
makes
BE
BE==00
BE negative

PNP SWITCH WITH NPN DRIVER

LOAD

NPN SWITCH WITH PNP DRIVER
(NEGATIVE POWER SUPPLY)

VV
0VV
BE
BE@ @+0.7

VVBE
0 VV
BE@@-0.7

LOAD

STEPPER MOTOR

A

B

C

A

Enhancement mode
power MOSFETs
used as switches

B

C
D

D

Concept Review
• BJTs can be used as switches.
• No base current = switch is off.
• High base current = switch is on.
• The dissipation is always zero in an ideal
switch: off = no current flow and on = no
voltage drop.
• MOSFETs can also be used as switches: no
gate voltage = switch is off and high gate
voltage = switch is on.
Repeat Segment

REVIEW
• Amplification
• Transistors
• Characteristic Curves
• Transistor Testing
• Other Transistor Types
• Transistors as Switches


Slide 56

Electronics
Principles & Applications
Sixth Edition

Charles A. Schuler
Chapter 5

Transistors
(student version)
©2003

Glencoe/McGraw-Hill

INTRODUCTION
• Amplification
• Transistors
• Characteristic Curves
• Transistor Testing
• Other Transistor Types
• Transistors as Switches

Dear Student:
This presentation is arranged in segments.
Each segment is preceded by a Concept
Preview slide and is followed by a Concept
Review slide. When you reach a Concept
Review slide, you can return to the
beginning of that segment by clicking on the
Repeat Segment button. This will allow you
to view that segment again, if you want to.

Concept Preview
• Amplifiers provide gain (the output is larger
than the input).
• Transistors have gain.
• Transistors have a collector, a base, and an
emitter.
• The C-B junction is reverse biased.
• The B-E junction is forward biased.
• Most of the emitter carriers reach the collector.
• The base current is relatively small but controls
the larger currents.

In

Gain =

Amplifier

Out

In

Out

NPN Transistor Structure

The collector is lightly doped.

N

C

The base is thin and
is lightly doped.

P

B

The emitter is heavily doped.

N

E

NPN Transistor Bias
No current flows.
The C-B junction
is reverse biased.

N

C

P

B

N

E

NPN Transistor Bias

The B-E junction
is forward biased.

Current flows.

N

C

P

B

N

E

NPN Transistor Bias
IC
Current flows
everywhere.
Most of the emitter carriers
diffuse through the thin base
When
both
junctions
region since they are attracted
biased....
by are
the collector.

Note that IB is smaller
than IE or IC.

N

C

P

B

N

E

IB

IE

Note: when the
switch opens, all
currents go to zero.
Although IB is smaller
it controls IE and IC.

Gain is something small
controlling something large
(IB is small).

IC
N

C

P

B

N

E

IB

IE

Transistor Structure and Bias Quiz
The heaviest doping is found in
the ___________ region.

emitter

The thinnest of all three regions
is called the ____________.

base

The collector-base junction is
___________ biased.

reverse

The base-emitter junction is
____________ biased.

forward

The majority of the emitter
carriers flow to the ___________.

collector

Concept Review
• Amplifiers provide gain (the output is larger than
the input).
• Transistors have gain.

• Transistors have a collector, a base, and an emitter.
• The C-B junction is reverse biased.
• The B-E junction is forward biased.

• Most of the emitter carriers reach the collector.
• The base current is relatively small but controls the
larger currents.
Repeat Segment

Concept Preview
• The base to collector gain is called b (beta).
• To find b, divide the collector current by the
base current.
• The emitter current is the largest since it is the
sum of the base and collector currents.
• PNP transistors have opposite polarity from
NPN transistors.

• In an NPN transistor, the major flow is made
up of electrons.
• In a PNP transistor, the major flow is made up
of holes.

IC = 99 mA

The current gain from
base to collector
is called b.
IB = 1 mA

b =

99
ICmA
1IBmA

= 99

IE = 100 mA

C
P

B

N

E

IC = 99 mA
Kirchhoff’s
current law:

IB = 1 mA

C
P

B

N

E

IE = I B + I C

= 1 mA + 99 mA
= 100 mA
IE = 100 mA

IC = 99 mA
In a PNP transistor,
holes flow from
emitter to collector.

IB = 1 mA
Notice the PNP
bias voltages.

C
B

E

IE = 100 mA

Transistor Currents Quiz
b is the ratio of collector current to
______ current.

base

The sum of the base and collector
currents is the __________ current.

emitter

In NPN transistors, the flow from emitter
to collector is composed of _______.

electrons

In PNP transistors, the flow from emitter
to collector is composed of _______.

holes

Both NPN and PNP transistors show
__________ gain.

current

Concept Review
• The base to collector gain is called b (beta).
• To find b, divide the collector current by the
base current.
• The emitter current is the largest since it is the
sum of the base and collector currents.
• PNP transistors have opposite polarity from
NPN transistors.
• In an NPN transistor, the major flow is made
up of electrons.
• In a PNP transistor, the major flow is made up
of holes.
Repeat Segment

Concept Preview
• The NPN schematic symbol shows the emitter
arrow as Not Pointing iN.
• The collector curves are a graph of collector
voltage versus collector current.
• Both dc beta (bdc) and ac beta (bac) can be
determined from the collector curves.
• The collector circuit of a transistor can be
modeled as a resistor, as a closed switch or as
an open switch.
• The amount of base current determines which
of the three models applies.

NPN Schematic Symbol
Collector

Base

C
B E

Emitter
Memory aid: NPN
means Not Pointing iN.

PNP Schematic Symbol
Collector

Base

C
B E

Emitter

IC

This circuit is used to
collect IC versus
VCE data for
several values of IB.
C

IB
B

E

VCE

When graphed, the data provide an
NPN collector family of curves.
100 mA

14
12
10
IC in mA 8
6
4
2

80 mA
60 mA
40 mA
20 mA

0 2 4 6

8 10 12 14 16 18

VCE in Volts

0 mA

100 mA

14
12
10
IC in mA 8
6
4
2

80 mA
60 mA

40 mA
20 mA

0 2 4 6

8 10 12 14 16 18

0 mA

VCE in Volts

b =

14
mA
6ICmA
40
IB mA
100
mA

150
== 140

This type of gain
is called bdc or hFE.

100 mA

14
12
10
IC in mA 8
6
4
2

80 mA
60 mA

40 mA
20 mA

0 2 4 6

bac =

2.5DImA
C
20DImA
B

8 10 12 14 16 18

0 mA

VCE in Volts
= 125

Another type of gain
is called bac or hfe.

100 mA

14
12
10
IC in mA 8
6
4
2

80 mA
60 mA

40 mA
20 mA

0 2 4 6
IB

C

8 10 12 14 16 18
VCE in Volts

0 mA

With these values of IB:
The C-E model is a resistor.
E

100 mA

14
12
10
IC in mA 8
6
4
2
0 2 4 6
IB

80 mA
60 mA

40 mA
20 mA
8 10 12 14 16 18
VCE in Volts

0 mA

When IB >> 100 mA
VCE @ 0
The model is a closed switch.

100 mA

14
12
10
IC in mA 8
6
4
2
0 2 4 6
IB

80 mA
60 mA

40 mA
20 mA
8 10 12 14 16 18
VCE in Volts

0 mA

When IB = 0
IC = 0
The model is an open switch.

Transistor Operating Conditions Quiz
When IB is large and VCE @ 0, the transistor
acts as a ___________ switch.
closed
When IB = 0 and IC = 0, the transistor
acts as an ___________ switch.

open

When IB > 0 and VCE > 0, the transistor
acts as a ___________.

resistor

Two current gain measures are bdc and
__________.

bac

The symbol hfe is the same as _________.

bac

Concept Review
• The NPN schematic symbol shows the emitter
arrow as Not Pointing iN.
• The collector curves are a graph of collector
voltage versus collector current.
• Both dc beta (bdc) and ac beta (bac) can be
determined from the collector curves.
• The collector circuit of a transistor can be
modeled as a resistor, as a closed switch or as
an open switch.
• The amount of base current determines which
of the three models applies.
Repeat Segment

Concept Preview
• It is possible to test transistors out-of-circuit
using an ohmmeter.
• The E-B and C-B junctions act as diodes
during ohmmeter testing.

• The C-E test shows a high resistance because
two junctions are involved; one of which is
reverse biased by the ohmmeter.
• Gain can be verified by using a resistor in
conjunction with the ohmmeter test.

NPN

V

mA

E
B
C

The E-B junction is forward biased by the ohmmeter.

NPN

V

mA

E
B
C

The C-E resistance is very high.

NPN

V

mA

E
B
C
100 kW

The meter reading is < 100 kW due to gain.

Concept Review
• It is possible to test transistors out-of-circuit
using an ohmmeter.
• The E-B and C-B junctions act as diodes
during ohmmeter testing.
• The C-E test shows a high resistance because
two junctions are involved; one of which is
reverse biased by the ohmmeter.
• Gain can be verified by using a resistor in
conjunction with the ohmmeter test.
Repeat Segment

Concept Preview
• Bipolar junction transistors (BJTs) are controlled by
base current.
• Junction field effect transistors (JFETs) are controlled
by gate voltage.

• JFETs operate in the depletion mode (as normally on
devices).
• Metal oxide semiconductor field effect transistors
(MOSFETs) usually operate in the enhancement mode
(as normally off devices).
• Insulated gate bipolar transistors (IGBTs) are modified
MOSFETs and have very low on-resistance.
• Unijunction transistors (UJTs) are not used as
amplifiers.

Current In

The BJT is
a current
amplifier.

Current
Amplifier

Current Out

Voltage In

The JFET is
a voltage
controlled
amplifier.

Voltage
Amplifier

Current Out

Source

Gate

Drain

P

N-channel
P-type substrate
Structure of an
N-channel JFET

The channel has carriers so it
conducts from source to drain.

Drain

Gate
Source

Source

Gate

Drain

P

N-channel
P-type substrate

A negative gate voltage
can push the carriers from
the channel and turn
the JFET off.

Drain

Gate
Source

0V
-1 V
-2 V

ID in mA

-3 V

VGS

-4 V

0

-5 V
VDS in Volts

This is known as a depletion-mode device.
N-channel JFET drain family of characteristic curves

It’s possible to make enhancement
type field effect transistors as well.
Metal
oxide
insulator

Drain

n

Gate

VGG

D

VDD

p

G

n

S
N-channel
MOSFET

Source

Gate bias enhances the channel and turns the device on.

5V
4V
3V

ID in mA

2V

VGS

1V

0

0V
Drain

VDS in Volts

Enhancement mode
MOSFET drain family of
characteristic curves

Gate
Source

The IGBT (insulated gate bipolar transistor)
Operation and structure
similar to a MOSFET
Voltage controlled
(like the MOSFET)
Has one more junction
than a MOSFET
Hole injection reduces
the collector resistance

Faster turn off than
BJTs but not as fast
as MOSFETS

RCE = 8.33 mW

Three major device technologies

hole injection
Extra
junction

Courtesy of Powerex, Inc.

Typical IGBT Driver Circuit
Typically +15 V for turn on
Typically - 5 to -15 V for turn off

Control signal

IGBT

Powerex IGBT Module Structure

Powerex high voltage IGBT package

Emitter voltage

The unijunction transistor fires
when its emitter voltage reaches VP.
VP

Then, the emitter voltage
drops due to its negative
resistance characteristic.
Base 2

Emitter current
Emitter

The UJT is not useful as an amplifier.
It is used in timing and control applications.

Base 1

Other Transistor Types Quiz
BJTs are _________-controlled
amplifiers.

current

FETs are __________-controlled
amplifiers.

voltage

JFETs operate in the __________ mode. depletion
MOSFETs operate in the __________
mode.

enhancement

IGBTs are __________-controlled
amplifiers.

voltage

UJTs are not useful as __________.

amplifiers

Concept Review
• Bipolar junction transistors (BJTs) are controlled by
base current.
• Junction field effect transistors (JFETs) are controlled
by gate voltage.
• JFETs operate in the depletion mode (as normally on
devices).
• Metal oxide semiconductor field effect transistors
(MOSFETs) usually operate in the enhancement mode
(as normally off devices).
• Insulated gate bipolar transistors (IGBTs) are modified
MOSFETs and have very low on-resistance.
• Unijunction transistors (UJTs) are not used as
amplifiers.
Repeat Segment

Concept Preview
• BJTs can be used as switches.
• No base current = switch is off.
• High base current = switch is on.
• The dissipation is always zero in an ideal
switch: off = no current flow and on = no
voltage drop.

• MOSFETs can also be used as switches: no
gate voltage = switch is off and high gate
voltage = switch is on.

How do transistor switches work?
Can be viewed as solid state relays:
they are either ON or they are OFF.
BJT switches are characterized by:
high base current (switch is on)
(or no base current … off)

low resistance from collector to emitter (on)
(or very high resistance … off)
low collector dissipation (on or off)
PC = VCE x IC
PC = 0 x IC = 0 W
(on)
(or PC = VCE x 0 = 0 W … off)

NPN SWITCH
LOAD

RCE @ 
W
0W
DRIVER

The
The
driver
driver
output
output
isiszero
positive,
volts,
IIBB>=I0
0and
andthe
theload
loadis
ison
off
The
driver
output
is
zero
volts,
B = 0 and ILOAD = 0

PNP SWITCH
DRIVER

LOAD

The
Z):
Thedriver
driveroutput
outputisgoes
isoff
off(high
(highthe
Z):the
theresistor
resistor
low:
voltage
drop
pulls
the
base
voltage
up
that
VV
pulls
thethe
base
voltage
upso
soV
that
across
resistor
makes
BE
BE==00
BE negative

PNP SWITCH WITH NPN DRIVER

LOAD

NPN SWITCH WITH PNP DRIVER
(NEGATIVE POWER SUPPLY)

VV
0VV
BE
BE@ @+0.7

VVBE
0 VV
BE@@-0.7

LOAD

STEPPER MOTOR

A

B

C

A

Enhancement mode
power MOSFETs
used as switches

B

C
D

D

Concept Review
• BJTs can be used as switches.
• No base current = switch is off.
• High base current = switch is on.
• The dissipation is always zero in an ideal
switch: off = no current flow and on = no
voltage drop.
• MOSFETs can also be used as switches: no
gate voltage = switch is off and high gate
voltage = switch is on.
Repeat Segment

REVIEW
• Amplification
• Transistors
• Characteristic Curves
• Transistor Testing
• Other Transistor Types
• Transistors as Switches


Slide 57

Electronics
Principles & Applications
Sixth Edition

Charles A. Schuler
Chapter 5

Transistors
(student version)
©2003

Glencoe/McGraw-Hill

INTRODUCTION
• Amplification
• Transistors
• Characteristic Curves
• Transistor Testing
• Other Transistor Types
• Transistors as Switches

Dear Student:
This presentation is arranged in segments.
Each segment is preceded by a Concept
Preview slide and is followed by a Concept
Review slide. When you reach a Concept
Review slide, you can return to the
beginning of that segment by clicking on the
Repeat Segment button. This will allow you
to view that segment again, if you want to.

Concept Preview
• Amplifiers provide gain (the output is larger
than the input).
• Transistors have gain.
• Transistors have a collector, a base, and an
emitter.
• The C-B junction is reverse biased.
• The B-E junction is forward biased.
• Most of the emitter carriers reach the collector.
• The base current is relatively small but controls
the larger currents.

In

Gain =

Amplifier

Out

In

Out

NPN Transistor Structure

The collector is lightly doped.

N

C

The base is thin and
is lightly doped.

P

B

The emitter is heavily doped.

N

E

NPN Transistor Bias
No current flows.
The C-B junction
is reverse biased.

N

C

P

B

N

E

NPN Transistor Bias

The B-E junction
is forward biased.

Current flows.

N

C

P

B

N

E

NPN Transistor Bias
IC
Current flows
everywhere.
Most of the emitter carriers
diffuse through the thin base
When
both
junctions
region since they are attracted
biased....
by are
the collector.

Note that IB is smaller
than IE or IC.

N

C

P

B

N

E

IB

IE

Note: when the
switch opens, all
currents go to zero.
Although IB is smaller
it controls IE and IC.

Gain is something small
controlling something large
(IB is small).

IC
N

C

P

B

N

E

IB

IE

Transistor Structure and Bias Quiz
The heaviest doping is found in
the ___________ region.

emitter

The thinnest of all three regions
is called the ____________.

base

The collector-base junction is
___________ biased.

reverse

The base-emitter junction is
____________ biased.

forward

The majority of the emitter
carriers flow to the ___________.

collector

Concept Review
• Amplifiers provide gain (the output is larger than
the input).
• Transistors have gain.

• Transistors have a collector, a base, and an emitter.
• The C-B junction is reverse biased.
• The B-E junction is forward biased.

• Most of the emitter carriers reach the collector.
• The base current is relatively small but controls the
larger currents.
Repeat Segment

Concept Preview
• The base to collector gain is called b (beta).
• To find b, divide the collector current by the
base current.
• The emitter current is the largest since it is the
sum of the base and collector currents.
• PNP transistors have opposite polarity from
NPN transistors.

• In an NPN transistor, the major flow is made
up of electrons.
• In a PNP transistor, the major flow is made up
of holes.

IC = 99 mA

The current gain from
base to collector
is called b.
IB = 1 mA

b =

99
ICmA
1IBmA

= 99

IE = 100 mA

C
P

B

N

E

IC = 99 mA
Kirchhoff’s
current law:

IB = 1 mA

C
P

B

N

E

IE = I B + I C

= 1 mA + 99 mA
= 100 mA
IE = 100 mA

IC = 99 mA
In a PNP transistor,
holes flow from
emitter to collector.

IB = 1 mA
Notice the PNP
bias voltages.

C
B

E

IE = 100 mA

Transistor Currents Quiz
b is the ratio of collector current to
______ current.

base

The sum of the base and collector
currents is the __________ current.

emitter

In NPN transistors, the flow from emitter
to collector is composed of _______.

electrons

In PNP transistors, the flow from emitter
to collector is composed of _______.

holes

Both NPN and PNP transistors show
__________ gain.

current

Concept Review
• The base to collector gain is called b (beta).
• To find b, divide the collector current by the
base current.
• The emitter current is the largest since it is the
sum of the base and collector currents.
• PNP transistors have opposite polarity from
NPN transistors.
• In an NPN transistor, the major flow is made
up of electrons.
• In a PNP transistor, the major flow is made up
of holes.
Repeat Segment

Concept Preview
• The NPN schematic symbol shows the emitter
arrow as Not Pointing iN.
• The collector curves are a graph of collector
voltage versus collector current.
• Both dc beta (bdc) and ac beta (bac) can be
determined from the collector curves.
• The collector circuit of a transistor can be
modeled as a resistor, as a closed switch or as
an open switch.
• The amount of base current determines which
of the three models applies.

NPN Schematic Symbol
Collector

Base

C
B E

Emitter
Memory aid: NPN
means Not Pointing iN.

PNP Schematic Symbol
Collector

Base

C
B E

Emitter

IC

This circuit is used to
collect IC versus
VCE data for
several values of IB.
C

IB
B

E

VCE

When graphed, the data provide an
NPN collector family of curves.
100 mA

14
12
10
IC in mA 8
6
4
2

80 mA
60 mA
40 mA
20 mA

0 2 4 6

8 10 12 14 16 18

VCE in Volts

0 mA

100 mA

14
12
10
IC in mA 8
6
4
2

80 mA
60 mA

40 mA
20 mA

0 2 4 6

8 10 12 14 16 18

0 mA

VCE in Volts

b =

14
mA
6ICmA
40
IB mA
100
mA

150
== 140

This type of gain
is called bdc or hFE.

100 mA

14
12
10
IC in mA 8
6
4
2

80 mA
60 mA

40 mA
20 mA

0 2 4 6

bac =

2.5DImA
C
20DImA
B

8 10 12 14 16 18

0 mA

VCE in Volts
= 125

Another type of gain
is called bac or hfe.

100 mA

14
12
10
IC in mA 8
6
4
2

80 mA
60 mA

40 mA
20 mA

0 2 4 6
IB

C

8 10 12 14 16 18
VCE in Volts

0 mA

With these values of IB:
The C-E model is a resistor.
E

100 mA

14
12
10
IC in mA 8
6
4
2
0 2 4 6
IB

80 mA
60 mA

40 mA
20 mA
8 10 12 14 16 18
VCE in Volts

0 mA

When IB >> 100 mA
VCE @ 0
The model is a closed switch.

100 mA

14
12
10
IC in mA 8
6
4
2
0 2 4 6
IB

80 mA
60 mA

40 mA
20 mA
8 10 12 14 16 18
VCE in Volts

0 mA

When IB = 0
IC = 0
The model is an open switch.

Transistor Operating Conditions Quiz
When IB is large and VCE @ 0, the transistor
acts as a ___________ switch.
closed
When IB = 0 and IC = 0, the transistor
acts as an ___________ switch.

open

When IB > 0 and VCE > 0, the transistor
acts as a ___________.

resistor

Two current gain measures are bdc and
__________.

bac

The symbol hfe is the same as _________.

bac

Concept Review
• The NPN schematic symbol shows the emitter
arrow as Not Pointing iN.
• The collector curves are a graph of collector
voltage versus collector current.
• Both dc beta (bdc) and ac beta (bac) can be
determined from the collector curves.
• The collector circuit of a transistor can be
modeled as a resistor, as a closed switch or as
an open switch.
• The amount of base current determines which
of the three models applies.
Repeat Segment

Concept Preview
• It is possible to test transistors out-of-circuit
using an ohmmeter.
• The E-B and C-B junctions act as diodes
during ohmmeter testing.

• The C-E test shows a high resistance because
two junctions are involved; one of which is
reverse biased by the ohmmeter.
• Gain can be verified by using a resistor in
conjunction with the ohmmeter test.

NPN

V

mA

E
B
C

The E-B junction is forward biased by the ohmmeter.

NPN

V

mA

E
B
C

The C-E resistance is very high.

NPN

V

mA

E
B
C
100 kW

The meter reading is < 100 kW due to gain.

Concept Review
• It is possible to test transistors out-of-circuit
using an ohmmeter.
• The E-B and C-B junctions act as diodes
during ohmmeter testing.
• The C-E test shows a high resistance because
two junctions are involved; one of which is
reverse biased by the ohmmeter.
• Gain can be verified by using a resistor in
conjunction with the ohmmeter test.
Repeat Segment

Concept Preview
• Bipolar junction transistors (BJTs) are controlled by
base current.
• Junction field effect transistors (JFETs) are controlled
by gate voltage.

• JFETs operate in the depletion mode (as normally on
devices).
• Metal oxide semiconductor field effect transistors
(MOSFETs) usually operate in the enhancement mode
(as normally off devices).
• Insulated gate bipolar transistors (IGBTs) are modified
MOSFETs and have very low on-resistance.
• Unijunction transistors (UJTs) are not used as
amplifiers.

Current In

The BJT is
a current
amplifier.

Current
Amplifier

Current Out

Voltage In

The JFET is
a voltage
controlled
amplifier.

Voltage
Amplifier

Current Out

Source

Gate

Drain

P

N-channel
P-type substrate
Structure of an
N-channel JFET

The channel has carriers so it
conducts from source to drain.

Drain

Gate
Source

Source

Gate

Drain

P

N-channel
P-type substrate

A negative gate voltage
can push the carriers from
the channel and turn
the JFET off.

Drain

Gate
Source

0V
-1 V
-2 V

ID in mA

-3 V

VGS

-4 V

0

-5 V
VDS in Volts

This is known as a depletion-mode device.
N-channel JFET drain family of characteristic curves

It’s possible to make enhancement
type field effect transistors as well.
Metal
oxide
insulator

Drain

n

Gate

VGG

D

VDD

p

G

n

S
N-channel
MOSFET

Source

Gate bias enhances the channel and turns the device on.

5V
4V
3V

ID in mA

2V

VGS

1V

0

0V
Drain

VDS in Volts

Enhancement mode
MOSFET drain family of
characteristic curves

Gate
Source

The IGBT (insulated gate bipolar transistor)
Operation and structure
similar to a MOSFET
Voltage controlled
(like the MOSFET)
Has one more junction
than a MOSFET
Hole injection reduces
the collector resistance

Faster turn off than
BJTs but not as fast
as MOSFETS

RCE = 8.33 mW

Three major device technologies

hole injection
Extra
junction

Courtesy of Powerex, Inc.

Typical IGBT Driver Circuit
Typically +15 V for turn on
Typically - 5 to -15 V for turn off

Control signal

IGBT

Powerex IGBT Module Structure

Powerex high voltage IGBT package

Emitter voltage

The unijunction transistor fires
when its emitter voltage reaches VP.
VP

Then, the emitter voltage
drops due to its negative
resistance characteristic.
Base 2

Emitter current
Emitter

The UJT is not useful as an amplifier.
It is used in timing and control applications.

Base 1

Other Transistor Types Quiz
BJTs are _________-controlled
amplifiers.

current

FETs are __________-controlled
amplifiers.

voltage

JFETs operate in the __________ mode. depletion
MOSFETs operate in the __________
mode.

enhancement

IGBTs are __________-controlled
amplifiers.

voltage

UJTs are not useful as __________.

amplifiers

Concept Review
• Bipolar junction transistors (BJTs) are controlled by
base current.
• Junction field effect transistors (JFETs) are controlled
by gate voltage.
• JFETs operate in the depletion mode (as normally on
devices).
• Metal oxide semiconductor field effect transistors
(MOSFETs) usually operate in the enhancement mode
(as normally off devices).
• Insulated gate bipolar transistors (IGBTs) are modified
MOSFETs and have very low on-resistance.
• Unijunction transistors (UJTs) are not used as
amplifiers.
Repeat Segment

Concept Preview
• BJTs can be used as switches.
• No base current = switch is off.
• High base current = switch is on.
• The dissipation is always zero in an ideal
switch: off = no current flow and on = no
voltage drop.

• MOSFETs can also be used as switches: no
gate voltage = switch is off and high gate
voltage = switch is on.

How do transistor switches work?
Can be viewed as solid state relays:
they are either ON or they are OFF.
BJT switches are characterized by:
high base current (switch is on)
(or no base current … off)

low resistance from collector to emitter (on)
(or very high resistance … off)
low collector dissipation (on or off)
PC = VCE x IC
PC = 0 x IC = 0 W
(on)
(or PC = VCE x 0 = 0 W … off)

NPN SWITCH
LOAD

RCE @ 
W
0W
DRIVER

The
The
driver
driver
output
output
isiszero
positive,
volts,
IIBB>=I0
0and
andthe
theload
loadis
ison
off
The
driver
output
is
zero
volts,
B = 0 and ILOAD = 0

PNP SWITCH
DRIVER

LOAD

The
Z):
Thedriver
driveroutput
outputisgoes
isoff
off(high
(highthe
Z):the
theresistor
resistor
low:
voltage
drop
pulls
the
base
voltage
up
that
VV
pulls
thethe
base
voltage
upso
soV
that
across
resistor
makes
BE
BE==00
BE negative

PNP SWITCH WITH NPN DRIVER

LOAD

NPN SWITCH WITH PNP DRIVER
(NEGATIVE POWER SUPPLY)

VV
0VV
BE
BE@ @+0.7

VVBE
0 VV
BE@@-0.7

LOAD

STEPPER MOTOR

A

B

C

A

Enhancement mode
power MOSFETs
used as switches

B

C
D

D

Concept Review
• BJTs can be used as switches.
• No base current = switch is off.
• High base current = switch is on.
• The dissipation is always zero in an ideal
switch: off = no current flow and on = no
voltage drop.
• MOSFETs can also be used as switches: no
gate voltage = switch is off and high gate
voltage = switch is on.
Repeat Segment

REVIEW
• Amplification
• Transistors
• Characteristic Curves
• Transistor Testing
• Other Transistor Types
• Transistors as Switches


Slide 58

Electronics
Principles & Applications
Sixth Edition

Charles A. Schuler
Chapter 5

Transistors
(student version)
©2003

Glencoe/McGraw-Hill

INTRODUCTION
• Amplification
• Transistors
• Characteristic Curves
• Transistor Testing
• Other Transistor Types
• Transistors as Switches

Dear Student:
This presentation is arranged in segments.
Each segment is preceded by a Concept
Preview slide and is followed by a Concept
Review slide. When you reach a Concept
Review slide, you can return to the
beginning of that segment by clicking on the
Repeat Segment button. This will allow you
to view that segment again, if you want to.

Concept Preview
• Amplifiers provide gain (the output is larger
than the input).
• Transistors have gain.
• Transistors have a collector, a base, and an
emitter.
• The C-B junction is reverse biased.
• The B-E junction is forward biased.
• Most of the emitter carriers reach the collector.
• The base current is relatively small but controls
the larger currents.

In

Gain =

Amplifier

Out

In

Out

NPN Transistor Structure

The collector is lightly doped.

N

C

The base is thin and
is lightly doped.

P

B

The emitter is heavily doped.

N

E

NPN Transistor Bias
No current flows.
The C-B junction
is reverse biased.

N

C

P

B

N

E

NPN Transistor Bias

The B-E junction
is forward biased.

Current flows.

N

C

P

B

N

E

NPN Transistor Bias
IC
Current flows
everywhere.
Most of the emitter carriers
diffuse through the thin base
When
both
junctions
region since they are attracted
biased....
by are
the collector.

Note that IB is smaller
than IE or IC.

N

C

P

B

N

E

IB

IE

Note: when the
switch opens, all
currents go to zero.
Although IB is smaller
it controls IE and IC.

Gain is something small
controlling something large
(IB is small).

IC
N

C

P

B

N

E

IB

IE

Transistor Structure and Bias Quiz
The heaviest doping is found in
the ___________ region.

emitter

The thinnest of all three regions
is called the ____________.

base

The collector-base junction is
___________ biased.

reverse

The base-emitter junction is
____________ biased.

forward

The majority of the emitter
carriers flow to the ___________.

collector

Concept Review
• Amplifiers provide gain (the output is larger than
the input).
• Transistors have gain.

• Transistors have a collector, a base, and an emitter.
• The C-B junction is reverse biased.
• The B-E junction is forward biased.

• Most of the emitter carriers reach the collector.
• The base current is relatively small but controls the
larger currents.
Repeat Segment

Concept Preview
• The base to collector gain is called b (beta).
• To find b, divide the collector current by the
base current.
• The emitter current is the largest since it is the
sum of the base and collector currents.
• PNP transistors have opposite polarity from
NPN transistors.

• In an NPN transistor, the major flow is made
up of electrons.
• In a PNP transistor, the major flow is made up
of holes.

IC = 99 mA

The current gain from
base to collector
is called b.
IB = 1 mA

b =

99
ICmA
1IBmA

= 99

IE = 100 mA

C
P

B

N

E

IC = 99 mA
Kirchhoff’s
current law:

IB = 1 mA

C
P

B

N

E

IE = I B + I C

= 1 mA + 99 mA
= 100 mA
IE = 100 mA

IC = 99 mA
In a PNP transistor,
holes flow from
emitter to collector.

IB = 1 mA
Notice the PNP
bias voltages.

C
B

E

IE = 100 mA

Transistor Currents Quiz
b is the ratio of collector current to
______ current.

base

The sum of the base and collector
currents is the __________ current.

emitter

In NPN transistors, the flow from emitter
to collector is composed of _______.

electrons

In PNP transistors, the flow from emitter
to collector is composed of _______.

holes

Both NPN and PNP transistors show
__________ gain.

current

Concept Review
• The base to collector gain is called b (beta).
• To find b, divide the collector current by the
base current.
• The emitter current is the largest since it is the
sum of the base and collector currents.
• PNP transistors have opposite polarity from
NPN transistors.
• In an NPN transistor, the major flow is made
up of electrons.
• In a PNP transistor, the major flow is made up
of holes.
Repeat Segment

Concept Preview
• The NPN schematic symbol shows the emitter
arrow as Not Pointing iN.
• The collector curves are a graph of collector
voltage versus collector current.
• Both dc beta (bdc) and ac beta (bac) can be
determined from the collector curves.
• The collector circuit of a transistor can be
modeled as a resistor, as a closed switch or as
an open switch.
• The amount of base current determines which
of the three models applies.

NPN Schematic Symbol
Collector

Base

C
B E

Emitter
Memory aid: NPN
means Not Pointing iN.

PNP Schematic Symbol
Collector

Base

C
B E

Emitter

IC

This circuit is used to
collect IC versus
VCE data for
several values of IB.
C

IB
B

E

VCE

When graphed, the data provide an
NPN collector family of curves.
100 mA

14
12
10
IC in mA 8
6
4
2

80 mA
60 mA
40 mA
20 mA

0 2 4 6

8 10 12 14 16 18

VCE in Volts

0 mA

100 mA

14
12
10
IC in mA 8
6
4
2

80 mA
60 mA

40 mA
20 mA

0 2 4 6

8 10 12 14 16 18

0 mA

VCE in Volts

b =

14
mA
6ICmA
40
IB mA
100
mA

150
== 140

This type of gain
is called bdc or hFE.

100 mA

14
12
10
IC in mA 8
6
4
2

80 mA
60 mA

40 mA
20 mA

0 2 4 6

bac =

2.5DImA
C
20DImA
B

8 10 12 14 16 18

0 mA

VCE in Volts
= 125

Another type of gain
is called bac or hfe.

100 mA

14
12
10
IC in mA 8
6
4
2

80 mA
60 mA

40 mA
20 mA

0 2 4 6
IB

C

8 10 12 14 16 18
VCE in Volts

0 mA

With these values of IB:
The C-E model is a resistor.
E

100 mA

14
12
10
IC in mA 8
6
4
2
0 2 4 6
IB

80 mA
60 mA

40 mA
20 mA
8 10 12 14 16 18
VCE in Volts

0 mA

When IB >> 100 mA
VCE @ 0
The model is a closed switch.

100 mA

14
12
10
IC in mA 8
6
4
2
0 2 4 6
IB

80 mA
60 mA

40 mA
20 mA
8 10 12 14 16 18
VCE in Volts

0 mA

When IB = 0
IC = 0
The model is an open switch.

Transistor Operating Conditions Quiz
When IB is large and VCE @ 0, the transistor
acts as a ___________ switch.
closed
When IB = 0 and IC = 0, the transistor
acts as an ___________ switch.

open

When IB > 0 and VCE > 0, the transistor
acts as a ___________.

resistor

Two current gain measures are bdc and
__________.

bac

The symbol hfe is the same as _________.

bac

Concept Review
• The NPN schematic symbol shows the emitter
arrow as Not Pointing iN.
• The collector curves are a graph of collector
voltage versus collector current.
• Both dc beta (bdc) and ac beta (bac) can be
determined from the collector curves.
• The collector circuit of a transistor can be
modeled as a resistor, as a closed switch or as
an open switch.
• The amount of base current determines which
of the three models applies.
Repeat Segment

Concept Preview
• It is possible to test transistors out-of-circuit
using an ohmmeter.
• The E-B and C-B junctions act as diodes
during ohmmeter testing.

• The C-E test shows a high resistance because
two junctions are involved; one of which is
reverse biased by the ohmmeter.
• Gain can be verified by using a resistor in
conjunction with the ohmmeter test.

NPN

V

mA

E
B
C

The E-B junction is forward biased by the ohmmeter.

NPN

V

mA

E
B
C

The C-E resistance is very high.

NPN

V

mA

E
B
C
100 kW

The meter reading is < 100 kW due to gain.

Concept Review
• It is possible to test transistors out-of-circuit
using an ohmmeter.
• The E-B and C-B junctions act as diodes
during ohmmeter testing.
• The C-E test shows a high resistance because
two junctions are involved; one of which is
reverse biased by the ohmmeter.
• Gain can be verified by using a resistor in
conjunction with the ohmmeter test.
Repeat Segment

Concept Preview
• Bipolar junction transistors (BJTs) are controlled by
base current.
• Junction field effect transistors (JFETs) are controlled
by gate voltage.

• JFETs operate in the depletion mode (as normally on
devices).
• Metal oxide semiconductor field effect transistors
(MOSFETs) usually operate in the enhancement mode
(as normally off devices).
• Insulated gate bipolar transistors (IGBTs) are modified
MOSFETs and have very low on-resistance.
• Unijunction transistors (UJTs) are not used as
amplifiers.

Current In

The BJT is
a current
amplifier.

Current
Amplifier

Current Out

Voltage In

The JFET is
a voltage
controlled
amplifier.

Voltage
Amplifier

Current Out

Source

Gate

Drain

P

N-channel
P-type substrate
Structure of an
N-channel JFET

The channel has carriers so it
conducts from source to drain.

Drain

Gate
Source

Source

Gate

Drain

P

N-channel
P-type substrate

A negative gate voltage
can push the carriers from
the channel and turn
the JFET off.

Drain

Gate
Source

0V
-1 V
-2 V

ID in mA

-3 V

VGS

-4 V

0

-5 V
VDS in Volts

This is known as a depletion-mode device.
N-channel JFET drain family of characteristic curves

It’s possible to make enhancement
type field effect transistors as well.
Metal
oxide
insulator

Drain

n

Gate

VGG

D

VDD

p

G

n

S
N-channel
MOSFET

Source

Gate bias enhances the channel and turns the device on.

5V
4V
3V

ID in mA

2V

VGS

1V

0

0V
Drain

VDS in Volts

Enhancement mode
MOSFET drain family of
characteristic curves

Gate
Source

The IGBT (insulated gate bipolar transistor)
Operation and structure
similar to a MOSFET
Voltage controlled
(like the MOSFET)
Has one more junction
than a MOSFET
Hole injection reduces
the collector resistance

Faster turn off than
BJTs but not as fast
as MOSFETS

RCE = 8.33 mW

Three major device technologies

hole injection
Extra
junction

Courtesy of Powerex, Inc.

Typical IGBT Driver Circuit
Typically +15 V for turn on
Typically - 5 to -15 V for turn off

Control signal

IGBT

Powerex IGBT Module Structure

Powerex high voltage IGBT package

Emitter voltage

The unijunction transistor fires
when its emitter voltage reaches VP.
VP

Then, the emitter voltage
drops due to its negative
resistance characteristic.
Base 2

Emitter current
Emitter

The UJT is not useful as an amplifier.
It is used in timing and control applications.

Base 1

Other Transistor Types Quiz
BJTs are _________-controlled
amplifiers.

current

FETs are __________-controlled
amplifiers.

voltage

JFETs operate in the __________ mode. depletion
MOSFETs operate in the __________
mode.

enhancement

IGBTs are __________-controlled
amplifiers.

voltage

UJTs are not useful as __________.

amplifiers

Concept Review
• Bipolar junction transistors (BJTs) are controlled by
base current.
• Junction field effect transistors (JFETs) are controlled
by gate voltage.
• JFETs operate in the depletion mode (as normally on
devices).
• Metal oxide semiconductor field effect transistors
(MOSFETs) usually operate in the enhancement mode
(as normally off devices).
• Insulated gate bipolar transistors (IGBTs) are modified
MOSFETs and have very low on-resistance.
• Unijunction transistors (UJTs) are not used as
amplifiers.
Repeat Segment

Concept Preview
• BJTs can be used as switches.
• No base current = switch is off.
• High base current = switch is on.
• The dissipation is always zero in an ideal
switch: off = no current flow and on = no
voltage drop.

• MOSFETs can also be used as switches: no
gate voltage = switch is off and high gate
voltage = switch is on.

How do transistor switches work?
Can be viewed as solid state relays:
they are either ON or they are OFF.
BJT switches are characterized by:
high base current (switch is on)
(or no base current … off)

low resistance from collector to emitter (on)
(or very high resistance … off)
low collector dissipation (on or off)
PC = VCE x IC
PC = 0 x IC = 0 W
(on)
(or PC = VCE x 0 = 0 W … off)

NPN SWITCH
LOAD

RCE @ 
W
0W
DRIVER

The
The
driver
driver
output
output
isiszero
positive,
volts,
IIBB>=I0
0and
andthe
theload
loadis
ison
off
The
driver
output
is
zero
volts,
B = 0 and ILOAD = 0

PNP SWITCH
DRIVER

LOAD

The
Z):
Thedriver
driveroutput
outputisgoes
isoff
off(high
(highthe
Z):the
theresistor
resistor
low:
voltage
drop
pulls
the
base
voltage
up
that
VV
pulls
thethe
base
voltage
upso
soV
that
across
resistor
makes
BE
BE==00
BE negative

PNP SWITCH WITH NPN DRIVER

LOAD

NPN SWITCH WITH PNP DRIVER
(NEGATIVE POWER SUPPLY)

VV
0VV
BE
BE@ @+0.7

VVBE
0 VV
BE@@-0.7

LOAD

STEPPER MOTOR

A

B

C

A

Enhancement mode
power MOSFETs
used as switches

B

C
D

D

Concept Review
• BJTs can be used as switches.
• No base current = switch is off.
• High base current = switch is on.
• The dissipation is always zero in an ideal
switch: off = no current flow and on = no
voltage drop.
• MOSFETs can also be used as switches: no
gate voltage = switch is off and high gate
voltage = switch is on.
Repeat Segment

REVIEW
• Amplification
• Transistors
• Characteristic Curves
• Transistor Testing
• Other Transistor Types
• Transistors as Switches


Slide 59

Electronics
Principles & Applications
Sixth Edition

Charles A. Schuler
Chapter 5

Transistors
(student version)
©2003

Glencoe/McGraw-Hill

INTRODUCTION
• Amplification
• Transistors
• Characteristic Curves
• Transistor Testing
• Other Transistor Types
• Transistors as Switches

Dear Student:
This presentation is arranged in segments.
Each segment is preceded by a Concept
Preview slide and is followed by a Concept
Review slide. When you reach a Concept
Review slide, you can return to the
beginning of that segment by clicking on the
Repeat Segment button. This will allow you
to view that segment again, if you want to.

Concept Preview
• Amplifiers provide gain (the output is larger
than the input).
• Transistors have gain.
• Transistors have a collector, a base, and an
emitter.
• The C-B junction is reverse biased.
• The B-E junction is forward biased.
• Most of the emitter carriers reach the collector.
• The base current is relatively small but controls
the larger currents.

In

Gain =

Amplifier

Out

In

Out

NPN Transistor Structure

The collector is lightly doped.

N

C

The base is thin and
is lightly doped.

P

B

The emitter is heavily doped.

N

E

NPN Transistor Bias
No current flows.
The C-B junction
is reverse biased.

N

C

P

B

N

E

NPN Transistor Bias

The B-E junction
is forward biased.

Current flows.

N

C

P

B

N

E

NPN Transistor Bias
IC
Current flows
everywhere.
Most of the emitter carriers
diffuse through the thin base
When
both
junctions
region since they are attracted
biased....
by are
the collector.

Note that IB is smaller
than IE or IC.

N

C

P

B

N

E

IB

IE

Note: when the
switch opens, all
currents go to zero.
Although IB is smaller
it controls IE and IC.

Gain is something small
controlling something large
(IB is small).

IC
N

C

P

B

N

E

IB

IE

Transistor Structure and Bias Quiz
The heaviest doping is found in
the ___________ region.

emitter

The thinnest of all three regions
is called the ____________.

base

The collector-base junction is
___________ biased.

reverse

The base-emitter junction is
____________ biased.

forward

The majority of the emitter
carriers flow to the ___________.

collector

Concept Review
• Amplifiers provide gain (the output is larger than
the input).
• Transistors have gain.

• Transistors have a collector, a base, and an emitter.
• The C-B junction is reverse biased.
• The B-E junction is forward biased.

• Most of the emitter carriers reach the collector.
• The base current is relatively small but controls the
larger currents.
Repeat Segment

Concept Preview
• The base to collector gain is called b (beta).
• To find b, divide the collector current by the
base current.
• The emitter current is the largest since it is the
sum of the base and collector currents.
• PNP transistors have opposite polarity from
NPN transistors.

• In an NPN transistor, the major flow is made
up of electrons.
• In a PNP transistor, the major flow is made up
of holes.

IC = 99 mA

The current gain from
base to collector
is called b.
IB = 1 mA

b =

99
ICmA
1IBmA

= 99

IE = 100 mA

C
P

B

N

E

IC = 99 mA
Kirchhoff’s
current law:

IB = 1 mA

C
P

B

N

E

IE = I B + I C

= 1 mA + 99 mA
= 100 mA
IE = 100 mA

IC = 99 mA
In a PNP transistor,
holes flow from
emitter to collector.

IB = 1 mA
Notice the PNP
bias voltages.

C
B

E

IE = 100 mA

Transistor Currents Quiz
b is the ratio of collector current to
______ current.

base

The sum of the base and collector
currents is the __________ current.

emitter

In NPN transistors, the flow from emitter
to collector is composed of _______.

electrons

In PNP transistors, the flow from emitter
to collector is composed of _______.

holes

Both NPN and PNP transistors show
__________ gain.

current

Concept Review
• The base to collector gain is called b (beta).
• To find b, divide the collector current by the
base current.
• The emitter current is the largest since it is the
sum of the base and collector currents.
• PNP transistors have opposite polarity from
NPN transistors.
• In an NPN transistor, the major flow is made
up of electrons.
• In a PNP transistor, the major flow is made up
of holes.
Repeat Segment

Concept Preview
• The NPN schematic symbol shows the emitter
arrow as Not Pointing iN.
• The collector curves are a graph of collector
voltage versus collector current.
• Both dc beta (bdc) and ac beta (bac) can be
determined from the collector curves.
• The collector circuit of a transistor can be
modeled as a resistor, as a closed switch or as
an open switch.
• The amount of base current determines which
of the three models applies.

NPN Schematic Symbol
Collector

Base

C
B E

Emitter
Memory aid: NPN
means Not Pointing iN.

PNP Schematic Symbol
Collector

Base

C
B E

Emitter

IC

This circuit is used to
collect IC versus
VCE data for
several values of IB.
C

IB
B

E

VCE

When graphed, the data provide an
NPN collector family of curves.
100 mA

14
12
10
IC in mA 8
6
4
2

80 mA
60 mA
40 mA
20 mA

0 2 4 6

8 10 12 14 16 18

VCE in Volts

0 mA

100 mA

14
12
10
IC in mA 8
6
4
2

80 mA
60 mA

40 mA
20 mA

0 2 4 6

8 10 12 14 16 18

0 mA

VCE in Volts

b =

14
mA
6ICmA
40
IB mA
100
mA

150
== 140

This type of gain
is called bdc or hFE.

100 mA

14
12
10
IC in mA 8
6
4
2

80 mA
60 mA

40 mA
20 mA

0 2 4 6

bac =

2.5DImA
C
20DImA
B

8 10 12 14 16 18

0 mA

VCE in Volts
= 125

Another type of gain
is called bac or hfe.

100 mA

14
12
10
IC in mA 8
6
4
2

80 mA
60 mA

40 mA
20 mA

0 2 4 6
IB

C

8 10 12 14 16 18
VCE in Volts

0 mA

With these values of IB:
The C-E model is a resistor.
E

100 mA

14
12
10
IC in mA 8
6
4
2
0 2 4 6
IB

80 mA
60 mA

40 mA
20 mA
8 10 12 14 16 18
VCE in Volts

0 mA

When IB >> 100 mA
VCE @ 0
The model is a closed switch.

100 mA

14
12
10
IC in mA 8
6
4
2
0 2 4 6
IB

80 mA
60 mA

40 mA
20 mA
8 10 12 14 16 18
VCE in Volts

0 mA

When IB = 0
IC = 0
The model is an open switch.

Transistor Operating Conditions Quiz
When IB is large and VCE @ 0, the transistor
acts as a ___________ switch.
closed
When IB = 0 and IC = 0, the transistor
acts as an ___________ switch.

open

When IB > 0 and VCE > 0, the transistor
acts as a ___________.

resistor

Two current gain measures are bdc and
__________.

bac

The symbol hfe is the same as _________.

bac

Concept Review
• The NPN schematic symbol shows the emitter
arrow as Not Pointing iN.
• The collector curves are a graph of collector
voltage versus collector current.
• Both dc beta (bdc) and ac beta (bac) can be
determined from the collector curves.
• The collector circuit of a transistor can be
modeled as a resistor, as a closed switch or as
an open switch.
• The amount of base current determines which
of the three models applies.
Repeat Segment

Concept Preview
• It is possible to test transistors out-of-circuit
using an ohmmeter.
• The E-B and C-B junctions act as diodes
during ohmmeter testing.

• The C-E test shows a high resistance because
two junctions are involved; one of which is
reverse biased by the ohmmeter.
• Gain can be verified by using a resistor in
conjunction with the ohmmeter test.

NPN

V

mA

E
B
C

The E-B junction is forward biased by the ohmmeter.

NPN

V

mA

E
B
C

The C-E resistance is very high.

NPN

V

mA

E
B
C
100 kW

The meter reading is < 100 kW due to gain.

Concept Review
• It is possible to test transistors out-of-circuit
using an ohmmeter.
• The E-B and C-B junctions act as diodes
during ohmmeter testing.
• The C-E test shows a high resistance because
two junctions are involved; one of which is
reverse biased by the ohmmeter.
• Gain can be verified by using a resistor in
conjunction with the ohmmeter test.
Repeat Segment

Concept Preview
• Bipolar junction transistors (BJTs) are controlled by
base current.
• Junction field effect transistors (JFETs) are controlled
by gate voltage.

• JFETs operate in the depletion mode (as normally on
devices).
• Metal oxide semiconductor field effect transistors
(MOSFETs) usually operate in the enhancement mode
(as normally off devices).
• Insulated gate bipolar transistors (IGBTs) are modified
MOSFETs and have very low on-resistance.
• Unijunction transistors (UJTs) are not used as
amplifiers.

Current In

The BJT is
a current
amplifier.

Current
Amplifier

Current Out

Voltage In

The JFET is
a voltage
controlled
amplifier.

Voltage
Amplifier

Current Out

Source

Gate

Drain

P

N-channel
P-type substrate
Structure of an
N-channel JFET

The channel has carriers so it
conducts from source to drain.

Drain

Gate
Source

Source

Gate

Drain

P

N-channel
P-type substrate

A negative gate voltage
can push the carriers from
the channel and turn
the JFET off.

Drain

Gate
Source

0V
-1 V
-2 V

ID in mA

-3 V

VGS

-4 V

0

-5 V
VDS in Volts

This is known as a depletion-mode device.
N-channel JFET drain family of characteristic curves

It’s possible to make enhancement
type field effect transistors as well.
Metal
oxide
insulator

Drain

n

Gate

VGG

D

VDD

p

G

n

S
N-channel
MOSFET

Source

Gate bias enhances the channel and turns the device on.

5V
4V
3V

ID in mA

2V

VGS

1V

0

0V
Drain

VDS in Volts

Enhancement mode
MOSFET drain family of
characteristic curves

Gate
Source

The IGBT (insulated gate bipolar transistor)
Operation and structure
similar to a MOSFET
Voltage controlled
(like the MOSFET)
Has one more junction
than a MOSFET
Hole injection reduces
the collector resistance

Faster turn off than
BJTs but not as fast
as MOSFETS

RCE = 8.33 mW

Three major device technologies

hole injection
Extra
junction

Courtesy of Powerex, Inc.

Typical IGBT Driver Circuit
Typically +15 V for turn on
Typically - 5 to -15 V for turn off

Control signal

IGBT

Powerex IGBT Module Structure

Powerex high voltage IGBT package

Emitter voltage

The unijunction transistor fires
when its emitter voltage reaches VP.
VP

Then, the emitter voltage
drops due to its negative
resistance characteristic.
Base 2

Emitter current
Emitter

The UJT is not useful as an amplifier.
It is used in timing and control applications.

Base 1

Other Transistor Types Quiz
BJTs are _________-controlled
amplifiers.

current

FETs are __________-controlled
amplifiers.

voltage

JFETs operate in the __________ mode. depletion
MOSFETs operate in the __________
mode.

enhancement

IGBTs are __________-controlled
amplifiers.

voltage

UJTs are not useful as __________.

amplifiers

Concept Review
• Bipolar junction transistors (BJTs) are controlled by
base current.
• Junction field effect transistors (JFETs) are controlled
by gate voltage.
• JFETs operate in the depletion mode (as normally on
devices).
• Metal oxide semiconductor field effect transistors
(MOSFETs) usually operate in the enhancement mode
(as normally off devices).
• Insulated gate bipolar transistors (IGBTs) are modified
MOSFETs and have very low on-resistance.
• Unijunction transistors (UJTs) are not used as
amplifiers.
Repeat Segment

Concept Preview
• BJTs can be used as switches.
• No base current = switch is off.
• High base current = switch is on.
• The dissipation is always zero in an ideal
switch: off = no current flow and on = no
voltage drop.

• MOSFETs can also be used as switches: no
gate voltage = switch is off and high gate
voltage = switch is on.

How do transistor switches work?
Can be viewed as solid state relays:
they are either ON or they are OFF.
BJT switches are characterized by:
high base current (switch is on)
(or no base current … off)

low resistance from collector to emitter (on)
(or very high resistance … off)
low collector dissipation (on or off)
PC = VCE x IC
PC = 0 x IC = 0 W
(on)
(or PC = VCE x 0 = 0 W … off)

NPN SWITCH
LOAD

RCE @ 
W
0W
DRIVER

The
The
driver
driver
output
output
isiszero
positive,
volts,
IIBB>=I0
0and
andthe
theload
loadis
ison
off
The
driver
output
is
zero
volts,
B = 0 and ILOAD = 0

PNP SWITCH
DRIVER

LOAD

The
Z):
Thedriver
driveroutput
outputisgoes
isoff
off(high
(highthe
Z):the
theresistor
resistor
low:
voltage
drop
pulls
the
base
voltage
up
that
VV
pulls
thethe
base
voltage
upso
soV
that
across
resistor
makes
BE
BE==00
BE negative

PNP SWITCH WITH NPN DRIVER

LOAD

NPN SWITCH WITH PNP DRIVER
(NEGATIVE POWER SUPPLY)

VV
0VV
BE
BE@ @+0.7

VVBE
0 VV
BE@@-0.7

LOAD

STEPPER MOTOR

A

B

C

A

Enhancement mode
power MOSFETs
used as switches

B

C
D

D

Concept Review
• BJTs can be used as switches.
• No base current = switch is off.
• High base current = switch is on.
• The dissipation is always zero in an ideal
switch: off = no current flow and on = no
voltage drop.
• MOSFETs can also be used as switches: no
gate voltage = switch is off and high gate
voltage = switch is on.
Repeat Segment

REVIEW
• Amplification
• Transistors
• Characteristic Curves
• Transistor Testing
• Other Transistor Types
• Transistors as Switches