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ECE 4991 Electrical and Electronic
Circuits
Chapter 3
Where are we?
• Chapter 2 - The basic concepts and practice at
analyzing simple electric circuits with sources
and resistors
• Chapter 3 – More harder networks to analyze and
the notion of equivalent circuits
• Chapter 4 – Capacitors and inductors added to
the mix
• Chapter 5 – Analyzing transient situations in
complex passive networks
• Chapter 8 – New subject – the wonders of
operational amplifiers as system elements
• Chapter 9 – Introduction to semiconductors – the
basics and diodes – more network analysis
• Chapter 10 – Bipolar junction transistors and how
they work – now you can build your own op amp
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What’s Important in
Chapter 3
1.
2.
3.
4.
5.
Definitions
Nodal Analysis
Mesh Analysis
The Principle of Superposition
Thevenin and Norton Equivalent
Circuits
6. Condition for Maximum Power
Transfer
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1. Definitions
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Node voltages
Branch currents
“Ground”
KCL
Nodal Analysis
Mesh currents
KVL
Mesh Analysis
• Principle of
Superposition
• Equivalent circuit
• Thevenin theorem
• Norton theorem
• One-port networks
• Source loading
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2. Nodal Analysis
• Used to “analyze” circuits
• Solve for currents, voltages, power,
etc., throughout circuits
• Applies KCL to nodes
– Often used in concert with Ohm’s Law
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Node Method
• Find nodes – Identify ground node
• Label branch currents & node voltages
• Node voltages, if not defined by a voltage
source, are independent variables
• Write KCL for nodes
• Solve for unknowns
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Working with Nodal
Analysis
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Working with Nodal
Analysis
R4
R2
I
V
R1
R3
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Working with Nodal
Analysis
R3
R1
V
I
R4
R2
R5
R6
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Working with Nodal
Analysis
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For Next Time
1. Sign onto Blackboard, if still have
not
2. Practice Nodal Analysis
3. Learn about rest of chapter 3,
particularly about mesh analysis
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3. Mesh Analysis
• Also used to “analyze” circuits
• Solve for currents, voltages, power,
etc., throughout circuits
• Applies KVL to meshes
– Often used in concert with Ohm’s Law
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Node Method
• Identify meshes and mesh currents
• For n meshes and m current sources, there
are n-m independent variables
• Write KVL for all meshes with unknown
mesh currents
• Solve for unknowns
I
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Working with Mesh
Analysis
I
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Working with Mesh
Analysis
R4
R2
I
V
R1
R3
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Working with Mesh
Analysis
R6
R3
R1
I
R4
R2
R5
V
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Working with Mesh
Analysis
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For Next Time
1. Sign onto Blackboard, if still have
not
2. Keep practicing Nodal Analysis
3. Practice Mesh Analysis
4. Learn about rest of chapter 3,
particularly about equivalent
circuits
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4. The Principle of
Superposition
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When working with linear circuits, can
find the solution for each energy source
and combine the results
Procedure:
–
Remove all but one energy source
•
•
–
–
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V sources  wires
I sources  opens
Solve the circuit
Repeat for a different energy source
Add up the solutions
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5. Thévenin and Norton
Equivalent Circuits
I

RT
VT
• Thévenin Theorem
When viewed from the load, any network
composed of ideal voltage and current
sources and of linear resistors, may be
represented by an equivalent circuit
consisting of an ideal voltage source VT in
series with an equivalent resistance RT
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Thévenin and Norton
Equivalent Circuits
I

I
IN
RN
• Norton Theorem
When viewed from the load, any network
composed of ideal voltage and current
sources and of linear resistors, may be
represented by an equivalent circuit
consisting of an ideal current source IN in
parallel with an equivalent resistance RN
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Thévenin Equivalence
•
Equivalent Resistance
1. Remove load
2. Zero all current and voltage sources
•
•
V sources  wires
I sources  opens
3. Compute the resistance between the load
terminals
•
Equivalent Voltage
1. Remove the load
2. Define VOC as the open-circuit voltage across
the load terminals
3. Solve for VOC
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Thévenin Equivalent
Circuits
R1
V
R2
RT = ?
VT = ?
RL
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Thévenin Equivalent
Circuits
R1
RT
VT
V
R2
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Working with Thévenin
Equivalent Circuits
R2
I
V
R1
RT = ?
R3
VT = ?
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Working with Thévenin
Equivalent Circuits
RT
VT
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R2
Practice with Thévenin
Equivalent Circuits
I
R3
V
R1
R5
R4
RT = ?
VT = ?
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Practice with Thévenin
Equivalent Circuits
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Chapter 2 and 3 Practice
for Test
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Chapter 2 and 3 Practice
for Test
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Chapter 2 and 3 Practice
for Test
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Chapter 2 and 3 Practice
for Test
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Chapter 2 and 3 Practice
for Test
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Chapter 2 and 3 Practice
for Test
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