Superposition and Thevenin’s Theorem ECE 2100 Circuit Analysis Laboratory updated 8 January 2008 Pre-Laboratory Assignment 1. Consider the circuit of Figure 1. Using a hand analysis, find node voltage 2 (with respect to ground of course) for three cases: a. V1=5V and V2=0V; b. V1=0V and V2=10V; c. V1=5V and V2=10V. Verify the superposition theorem using your results from parts a, b, and c. 2. Repeat pre-laboratory step 1 using your SPICE engine. Compare simulation results to your hand analysis results. Figure 1. Circuit with Two Sources 13. Consider the circuit of Figure 2. Note that RL is essentially an open circuit. Find the Thevenin equivalent circuit “looking into” nodes A and B; that is, find the Thevenin equivalent of the circuit “seen” by RL using hand analysis. 4. Find the Thevenin equivalent circuit using your SPICE engine as follows: a. Find VTH by using a .op simulation command; and b. Find RTH by using a .tf simulation command as shown. RTH is the value listed as the circuit “output impedance.” Compare your results of the results of pre-laboratory step 3. BRING AN ELECTRONIC COPY OF YOUR SPICE FILE TO LAB. Figure 2. Resistive Circuit Procedures Part One 1. Construct the circuit of Figure 1. Acquire experimental data for each of the three cases of pre-laboratory step 1. Compare the experimental, simulated, and hand analysis results using a table: 2case experimental V2simulated V2analysis V2% error (experimental vs. simulated) % error (experimental vs. analysis) a b c 2. Describe how the work of laboratory procedure step 1 provides an experimental example of the superposition theorem. Part Two 3. Construct the circuit of Figure 2 and measure VAB (node A is assumed positive with respect to node B) for three different values of RL. Then find VAB for each of the three RL values using a hand analysis and SPICE. Tabulate your results in a manner similar to that used in laboratory procedure step 1. 4. Now construct the Thevenin equivalent of the circuit of Figure 2 using a variable resistor to realize RTH. Find VAB for each of the three values of RL of laboratory procedure part 3 and compare results to the results of laboratory procedure step 3. 5. Explain how the results of laboratory procedure part 4 provide an experimental example of Thevenin’s theorem. Part Three 6. Experimentally determine the Thevenin output resistance of the lab station function generator. Analysis 1. For a fixed RTH maximum power is transferred from VTH when RL=RTH. Using your SPICE engine, demonstrate that the converse is not true for the circuit of Figure 2, i.e. maximum power is not delivered to a fixed RL by setting RTH=RL. Credits and Copyright Adapted from material developed by current and former ECE faculty, including Professor Joseph Kelemen. © 2008 Damon A. Miller and Frank L. Severance. All rights reserved.