Lab: Thevenin Equivalent and Maximum Power Transfer
Introduction: In this experiment, you will find the Thevenin equivalent of a given network, and for both the original network and the Thevenin equivalent, experimentally determine the power dissipated in the load resistor when the load resistance is varied over a range of values. Additionally, you will determine whether the load resistance that produces maximum power transfer to the load is the same for both the original and Thevenin equivalent networks.
Pre-lab assignment:
1. Calculate the Thevenin equivalent for the network given in Figure A: determine VTH and RTH at the terminals marked A and B.
2. Determine the maximum power that can be transferred to the load resistance RL.
3. Perform a transfer function analysis in SPICE (.TF), and determine the values of VTH and RTH. Calculate VTH by hand using the voltage gain value (VOUT/VIN) given by SPICE.
4. Submit your hand calculations for the Thevenin equivalent network and maximum power transferred, and the output file from your SPICE analysis. On a copy of the circuit diagram in Figure A, label all nodes and components according to your netlist. Also, provide a printout of your netlist, if not already contained in the output file, and highlight the values of RTH and VOUT/VIN. Put your name in the first line of the netlist that is reserved for the program title.
Note: you will not receive credit for software simulations performed using schematic entry, such as OrCad Capture or CircuitLab.
Lab Assignment:
1. Build the network shown in Figure A on your breadboard. Use a resistive decade box for the load resistance.
2. Vary the load resistance from 2k? to 8k? in 250? increments. For each increment, record the voltage across the load resistor, and calculate the power dissipated in the load resistor. In addition, set the decade box to the value you calculated for RTH and calculate the power dissipated at that resistance. Determine the value of RL that maximizes the power dissipated in RL, and compare to the value of RTH.
3. Build the Thevenin equivalent network on your breadboard, set the voltage source to VTH, and use combinations of resistors from your kit or a decade box for RTH. Determine the power dissipated in RTH.
4. Compare the value of RL and the power dissipated in RL for both the original and Thevenin equivalent networks. Is the value of RL that produces maximum power transfer the same for both networks?
5. In your report, provide a table of your results for power dissipated in RL and voltage across RL for both networks. Use Excel or a similar graphing utility to graph the data points that you collected in step 2 (Hint: assign RL to the X-axis). Discuss the relationship that you see between the value of RL and the power dissipated in RL. Does the shape of the graph verify the theory that maximum power is transferred to the load when RL = RTH?
Signoff #1: Measurement of voltage across RL on original complex network, with RL = RTH, and hand calculation showing correct value of maximum power.
Signoff #2: Measurement of voltage across RL on Thevenin equivalent network, with RL = RTH, and hand calculation showing correct value of maximum power.