Transcript Lecture 5 - Sonoma State University

Lecture 5
Source Transformation
Thevenin Equivalent Circuit
Norton Equivalent Circuit
Circuit Techinques
•
•
•
•
•
•
•
•
•
•
Ohm’s Law
P=VI
KCL, KVL
Voltage/current divider
Series/parallel resistance
Mesh/Nodal Analysis
Source Transformation
Thevenin/Norton Equivalent Circuit
Superposition Principle
Maximum Power Transfer
Source Transformation
Show that
iS=vS/R for any
RL
Thevenin Equivalent Circuit
Determine the Thevenin Voltage
(VTh)
• If RL=∞ (load across a-b is removed), then Vab=VTH
– RTH does not play a role!
3 Bit Digital to Analog Converter
741 Op-Amp
Chapter 5
Sample DAC Waveform
DAC
Output
Digital Input
Applications
• Most modern audio signals are stored
in digital form (e.g. MP3 and CDs) and
in order to be heard through speakers
they must be converted into an
analog signal
Thevenin Equivalent Circuit
Determine VTH
Methods of Finding RTH
• RTH=VTH/iSC
– If RL=0, the short circuit current from a to b (i.e. iab)
should equal to isc=VTh/RTH.
– So RTH=VTh/isc
• If the network contains only independent
sources:
– Deactivate a voltage source by replacing it
with a short
– Deactivate a current source by replacing it
with an open
• If the network contains dependent sources
– Apply a test source
Calculate the Thevenin
Resistance
RTH
If the network contains only
independent sources
RTH?
RTH
Methods of Finding RTH
• RTH=VTH/iSC
– If RL=0, the short circuit current from a to b (i.e. iab)
should equal to isc=VTh/RTH.
– So RTH=VTh/isc
• If the network contains only independent
sources:
– Deactivate a voltage source by replacing it
with a short
– Deactivate a current source by replacing it
with an open
• If the network contains dependent sources
– Apply a test source
Degenerated Common Emitter
Amplifier (from last lecture)
What if we drive the base with a
small signal?
Vin, m=1 mV
Vout, m=46 mV
Mesh Analysis (Last Lecture)
ne=2 essential nodes
be=3 essential branches
3-(2-1)=2 equations
Mesh Analysis (Last Lecture)
1
2
Loop 1: clockwise
Loop 2: counter-clockwise
Clockwise around loop 1:
+Vin-i1rπ-(i1+i2)RE=0
Counter-clockwise around loop 2:
i2=gmi1rπ
Vout =-i2RC
Mesh Analysis (Details)
Determine RTH when a
Dependent Source is Present
IT
Methods of Finding RTH
• RTH=VTH/iSC
– If RL=0, the short circuit current from a to b (i.e. iab)
should equal to isc=VTh/RTH.
– So RTH=VTh/isc
• If the network contains only independent
sources:
– Deactivate a voltage source by replacing it
with a short
– Deactivate a current source by replacing it
with an open
• If the network contains dependent sources
– Apply a test source
Another Way to Find RTH
isc
RTH Calculation
• iSC=10V/100 KOhms=0.1 mA
• VTH=10V/2=5V
• RTH=VTH/iSC=5V/0.1 mA=50 KOhms
Norton Equivalent Circuit
• A Norton Equivalent circuit consists of
– Short-Circuit Current
– Norton Equivalent Resistance, which
is equal to Thevenin Equivalent
Resistance
Getting A Norton Equivalent
Circuit from Thevenin Equivalent
Circuit
RTH
Thevenin Equivalent Circuit
VTH
Norton Equivalent Circuit
IN=VTH/RTH
RTH
Derivation of Norton Equivalent
Circuit
RTH
VTH
IN=VTH/RTH
RTH
Extra Credit Assignment
Derive 4.1-4.3
More about the Extra Credit
Assignment
Extra Slides on Thevenin
Determine vab
Show that
V =v
Determine iSC and RTH
Example 4.10
Determine the Thevenin Equivalent Voltage
Example 4.10
1. Determine the short circuit current
2. Determine RTH
Slides on Source Transformation
RTH
Application
Determine whether the 6V source is
absorbing or delivering the power.
Step-by-step simplification
Redundant Resistor (1)
Prove that the left circuit and the right circuit ar
equivalent for any load resistor.
Redundant Resistor (2)
Prove that the left circuit and
the right circuit are equivalent
for any load resistor.
Example 4.9
Simplified Circuit