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: Academics Course Homepages Spring 2003 – ECSE 2010 Backup Site : /index.htmlhttp:// /ECSE- 2010/index.html

TA’S Section 1: Tong Zhang Section 2: Amit Kekare Rahul Kalaskar Section 3: Sunil Rao Shahab Uddin

GRADING ASSIGNMENTS Activities: Amit Kekare – Sections 1&3 Rahul Kalaskar – Section 2 Experiments: Sunil Rao Homework: Shahab Uddin Computer Projects: Tong Zhang

REVIEW PSpice: Download a copy and start practicing loads/PSpicestudent/default.asp 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

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 USING SCHEMATICS

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 v c = 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: R eq = v / i R eq => 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

EQUIVALENT RESISTANCE

LOAD Network: Any Circuit with R’s and Controlled Sources No Independent Sources See Example: Define v, i using Passive Convention R eq = v / i Can Replace Any Load Network with its R eq Powerful Ckt Analysis Technique See Example

EQUIVALENT RESISTANCE

Req With Controlled Sources “ Connect” Test Voltage, v t : Independent Source (Active Element) Define i t using Active Convention Use Ckt Analysis to find i t in terms of v t : Linear equation relating i t to v t 1 Equation; 2 Unknowns R eq = v t / i t : See Example

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

Part a): KVL Part b): “Supernode” around

ACTIVITY 4-3

Part c):

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

ACTIVITY 4-3