University of California, Santa Cruz
Department of Electrical Engineering
EE 101L - Introduction to Electronic Circuits Laboratory
Winter 2016
EXPERIMENT 2: Thévenin and Norton Equivalents; Maximum Power Transfer
Introduction: Building on what you have learned in experiment 1, this experiment deals with resistive circuits as
well. This time, the emphasis is on how circuits, which may potentially be large and complicated, can be
described by simple equivalent circuit models. You will investigate how a real voltage source such as a battery
deviates from its ideal circuit model. In addition, you will use the load line method to analyze a linear circuit.
In the design part, you will see that you don’t need to know the internal structure of a circuit in order to draw
the maximum power from it. Theévenin’s and Norton’s theorems will allow you to determine the right load
with two quick measurements. At the end of this lab, you should be able to:
1. understand real voltage sources.
2. replace an unkown circuit with a simple equivalent circuit.
3. match the output load resistor to an unknown circuit for maximum power transfer.
4. use graphical methods for analyzing linear circuits.
Topics from the lecture you need to be familiar with:
1. Thévenin’s Equivalent
2. Norton’s Equivalent
3. Power Transfer Function
Pre-Lab Questions: Please see prelab handout on webpage.
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EE 101L W2016
Experiment 2
EXPERIMENTAL PROCEDURE
Part 1: Basics of Equivalent Circuits
Consider the following circuit shown below.
1. Let V1 = 5V, R1 = R2 = 1kΩ, and R3 = 2kΩ. Verify the value of V0 by measuring it and comparing it
to the value in your prelab.
2. Connect the ammeter to the output terminals, in parallel with R3 , and measure the short circuit current
Is at the output. Using this short circuit current and the output voltage V0 , determine the Thévenin
resistance of the circuit.
3. Draw the circuits for the Thévenin equivalent and the Norton equivalent to this circuit, with respect to
the output terminals.
4. Connect a 10kΩ potentiometer and set it to 1kΩ. Connect the potentiometer in parallel with R3 . Calculate
the power Pload dissipated in Rload .
5. Vary Rload = 100, 200, . . . , 1k, 2k, . . . , 10k. Determine the power dissipated for each value (use Excel for
quick computation). Plot Pload vs. Rload . Finally, tune Rload to maximize Pload (record all measurements
taken to achieve this).
6. Compare and verify your experimental result against the theoretical maximizing Rload value. How large
is the discrepency (absolute in mW and relative in percent) and what could be the reasons for the
discrepency?
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EE 101L W2016
Experiment 2
Part 2: Realistic Voltage Source
Obtain a 9V battery from the instructor and determine its Thévenin equivalent and Norton equivalent.
1. Find the Thévenin voltage by measuring the open circuit voltage across the battery.
2. To find the internal resistance and the Norton current, one cannot find it by measuring the short circuit
current, as the battery may malfunction. Instead, connect a load resistor to the output of the battery.
By using the principle of voltage division, compute Rth and then IN . The circuit will look as follows:
IN
IN
Rth
Rth
⇐
RL
=⇒
Part 3: Matching the Load to an Unknown Circuit
1. Obtain one of the "black" boxes from the TA. Record its number in your report.
2. Find Vth , IN , and Rth of the box. Make sure the circuit switch power is "on," when taking measurements.
When finished, you must make sure the power is set to off.
3. Determine the maching load resistor for maximum power transfer.
4. Connect the matching load across the output terminals and measure the actual dissipated power of the
load. Compare with your expectations.
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