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```									ELECTRIC CIRCUITS
ECSE-2010
Spring 2003
Class 4
ASSIGNMENTS DUE
•       Today (Tuesday/Wednesday):
•    HW #1 Due
•    Activities 4-1, 4-2, 4-3 (In Class)
•    4-2 in NOT in your Supplement
•       Thursday:
•    Activities 5-1, 5-2, 5-3 (In Class)
•       Next Monday:
•    HW #2 Due
•    Experiment #1 Report Due
•    Activities 6-1, 6-2, 6-3, 6-4 (In Class)
WEBSITE
• Main Website: http://www.ecse.rpi.edu
• Course Homepages
• Spring 2003 – ECSE 2010
• Backup Site :
http://128.113.60.136/ECSE-
2010/index.html
TA’S
• Section 1:
• Tong Zhang (zhant@rpi.edu)
• Section 2:
• Amit Kekare (kekara@rpi.edu)
•   Section 3:
• Sunil Rao (raos@rpi.edu)
• Shahab Uddin (uddins@rpi.edu)
• Activities:
• Amit Kekare – Sections 1&3
• Rahul Kalaskar – Section 2
• Experiments:
• Sunil Rao
• Homework:
• Shahab Uddin
• Computer Projects:
• Tong Zhang
REVIEW
• PSpice:
• Practice with Activities, Homework, etc.
• Get comfortable with “rules” for Circuit
Files and Learn to use Schematics
• We will slowly build our list of commands
MORE CIRCUIT ELEMENTS
• Potentiomenter:
• Variable Resistor with 3 terminals
• Resistance varies as shaft is turned
• Will Use Digital Pots in our Experiments
• Controlled or Dependent Sources:
• Source whose Voltage or Current Output Depends
on a Voltage or Current Somewhere Else in the
Circuit
POTENTIOMETER
CONTROLLED SOURCES
• 2 Types of Sources for Circuit Models:
• Independent Voltage and Current Sources
• Usually Model with Ideal Sources
• Controlled Voltage and Current Sources
• Also called Dependent Sources

• Controlled/Dependent Source:
• Voltage or current source whose value depends
on the v or i at some other point in the circuit
• Cannot buy a controlled source!
• Used to model the behavior of electronic devices
• Controlled Sources Make Ckt Analysis
Much, Much Harder!
CONTROLLED SOURCES
• Controlled Source cannot be the only
source of Energy in a complete circuit
• Need an Independent Source to create the
controlling current or voltage
• All circuit models for Transistors and
other Electronic Devices involve
Controlled Sources
• Whole field of analog electronics is based on
controlled sources
CONTROLLED SOURCES
CONTROLLED SOURCES

• See Example:
• Special Symbol for Controlled Sources
• Diamond
• 4 Types of Controlled Sources
•   Voltage Controlled Voltage Source (VCVS)
•   Voltage Controlled Current Source (VCCS)
•   Current Controlled Voltage Source (CCVS)
•   Current Controlled Current Source (CCCS)
• See Examples:
CONTROLLED SOURCES
CONTROLLED SOURCES
CONTROLLED SOURCES
CONTROLLED SOURCES
CONTROLLED SOURCES
USING SCHEMATICS
ACTIVITY 4-1
ACTIVITY 4-1
• KVL:
• v - i R + 6 i = 0 => v = i (R - 6)
• i = v / (R - 6)
• Note: Singularity at R = 6!; Current “blows up”
• Interesting things can happen with controlled
sources
• vc = 6 i = 6 v / (R - 6)
• Controlled source tries to put out infinite voltage
when R ~ 6 ohms
• What really happens is that circuit model fails
ACTIVITY 4-1
• Equivalent Resistance “Seen” by
Source:
• Req = v / i
• Req => 0 as R => 6 ohms
• Controlled sources allow much more
interesting things to happen, but make
circuit analysis much harder
ACTIVITY 4-1
• v = 20 Volts
APPLICATION OF
CONTROLLED SOURCES
• Controlled Sources are used to Model
the Behavior of Electronic Devices
• Single devices such as Transistors
• Complete circuits such as Amplifiers
• A good Example is given in Section
4.1 of your Text – Design Challenge
• Uses a Potentiometer and an Amplifier
• Models Audio Control on Stereo
• Let’s take a quick look at this – Activity 4-2
POTENTIOMETER
VOLTAGE AMPLIFIER
ACTIVITY 4-2
ACTIVITY 4-2
ACTIVITY 4-2
ACTIVITY 4-2
ACTIVITY 4-2
EQUIVALENT RESISTANCE
EQUIVALENT RESISTANCE
• Any Circuit with R’s and Controlled Sources
• No Independent Sources
• See Example:
• Define v, i using Passive Convention
• Req = v / i
• Can Replace Any Load Network with its Req
• Powerful Ckt Analysis Technique
• See Example
EQUIVALENT RESISTANCE
Req With Controlled Sources
• “Connect” Test Voltage, vt:
• Independent Source (Active Element)
• Define it using Active Convention
• Use Ckt Analysis to find it in terms of vt:
• Linear equation relating it to vt
• 1 Equation; 2 Unknowns
• Req = vt / it:
• See Example
Req with Controlled Sources
Req with Controlled Sources
Req with Controlled Sources
ACTIVITY 4-3
• Electronic devices allow for “amplification”
of a current or voltage:
• Make it bigger or smaller
• Will examine in more detail soon
• Model electronic devices with controlled sources
• Models will use controlled sources with
“Variable Gain”:
• Variable depends on characteristics of the
particular electronic device being used
• Usually want to solve general circuit - then put in
characteristics of particular device - from spec’s
ACTIVITY 4-3
ACTIVITY 4-3
• Part a): KVL

•

• Part b): “Supernode” around

•
ACTIVITY 4-3
ACTIVITY 4-3
• Part c):
ACTIVITY 4-3
• Part d):
• .2 A source in parallel with 10 ohms
• Model Amplifier with Rin
ACTIVITY 4-3
ACTIVITY 4-3

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