Transcript No Slide Title

Diodes
1. Basic diode concept.
2. Load-line analysis of diode circuit.
3. Zener-diode voltage regulator circuit.
4. Ideal-diode model.
5. Applications of diodes.
BASIC DIODE CONCEPTS
A pn junction
Drift and diffusion currents in a pn junction
Forward- and reverse-biased pn junctions
Figure
9.7
Semiconductor diode i-v
characteristic
Figure 9.8,
9.9
Semiconductor diode circuit symbol
The i-v characteristic of the semiconductor diode
Figure
9.10
Shockley Equation
  vD
iD  I s exp
  nVT
 
  1
 
kT
VT 
q
k = 1.38 × 10–23 J/K is Boltzmann’s constant and q = 1.60
× 10–19 C is the magnitude of the electrical charge of an
electron. At a
temperature of 300 K, we haveV  26 mV
T
Exercise 10.1
At a temperature of 300K, a certain junction
diode has iD = 0.1mA for vD = 0.6V. Assume
that n is unity and use VT = 0.026V. find the
value of the saturation current Is.
  vD
iD  I s exp
  nVT
 
  1
 
iD
Is 
exp( vD / nVT )  1
104

exp( 0.6 / 0.026)  1
 9.502  1015 A
LOAD-LINE ANASYSIS OF
DIODE CIRCUITS
LOAD-LINE ANALYSIS OF
DIODE CIRCUITS
By applying KVL, we get
VSS  RiD  vD
But two unknowns, we need one more equation
relating iD and vD to solve the problem.
Example 10.1
If the circuit of Figure 10.5 has Vss = 2V,
R = 1kW, and a diode with the characteristic
shown in Figure 10.7, find the diode voltage
and current at the operating point.
Example 10.2
Repeat Example 10.1 if Vss = 10V, R = 10kW
Vss = i R + VD
Vss = 2, R = 1k
Vss=10, R=10k
ZENER-DIODE VOLTAGEREGULATOR CIRCUITS
What is a Zener diode?
Zener Diodes
Diodes that are intended to operate in
the breakdown region are called Zener
diodes.
Breakdown
region
ZENER-DIODE VOLTAGEREGULATOR CIRCUITS
A voltage regulator circuit provides a nearly
constant voltage to a load from a variable
source.
VSS  RiD  vD  0
Example 10.3
The voltage-regulator circuit of Figure 10.9
has R = 1kW and use a Zener diode having the
characteristic shown in Figure 10.10. Find the
output voltage for Vss = 15V. Repeat for Vss =
20V.
R = 1k
Vss + i R +VD = 0
i = 0, VD = -Vss
VD = 0, i = Vss/R
IDEAL-DIODE MODEL
IDEAL-DIODE MODEL
The ideal diode acts as a short
circuit for forward currents
and as an open circuit with
reverse voltage applied.
Large-signal on/off diode model
Figure 9.11
Circuit containing ideal diode
Circuit of Figure 9.12, assuming that the
ideal diode conducts
Figure 9.13
Figure
9.12,
9.13,
9.14
Circuit of Figure 9.12, assuming that the
ideal diode does not conduct
Figure 9.14
Figure 9.16
Figure 9.15, 9.16, 9.17
Figure 9.17
Summary of Guidelines to
analysis ideal-diode circuits
APPLICATION OF DIODES
DC power supply
Figure 9.45
RECTIFIER CIRCUITS
Half-Wave Rectifier Circuits
Ideal diode rectifier input and output voltages
Figure
9.20,
9.21
As Vs reaches VB, then diode starts to conduct
Vr/ 2
I LT
C
Vr
Vr
VL  Vm 
2
Full-Wave Rectifier Circuits
Full-wave rectifier
Operation of bridge rectifier
Figure
9.42
(a) A Zener diode voltage regulator;
(b) (b) simplified circuit for Zener regulator
Figure 9.49