ENGR 2255 - Lab #14

Title: 

AC Thevenin and Norton Equivalent Circuits

Objectives: 

• Gain experience with AC Thevenin and Norton equivalent circuits
• Gain experience using PSpice for AC sweep analysis

Preparation: 

1. Find both the Thevenin and Norton equivalent circuits for the above circuit if Vac is 1 V peak amplitude at 500 Hz.
2. Use PSpice to determine the Thevenin equivalent circuit for Vac = 1 V at 500 Hz by finding V_oc and I_sc.
3. Use PSpice AC sweep analysis to determine the frequency at which the Thevenin impedence is purely resistive. Use a value for RL of 1.0 x 10¹⁰ Ω (about the resistance of air) to examine the open circuit voltage. Use a value for RL of 1.0 x 10^-10 Ω to examine the short circuit current. This determination can be easily done in one schematic with two circuits having different loads. Do a decade sweep analysis from 100 Hz to 10 kHz and plot the magnitude and phase of V_oc and I_sc using probe.

Equipment and Parts: 

• Signal Generator
• Oscilloscope
• Resistors:  1000 Ω (3) & 51 Ω
• Capacitor:  1 μF
• Inductor:  100 mH

Procedure: 

1. Using the oscilloscope, set the signal generator to a 1 V peak amplitude 500 Hz sinusoidal signal.
2. Connect a 51 Ω load resistor to the signal generator and measure the voltage across the resistor.
3. Determine the impedance of the signal generator by assuming a simple voltage divider between the source impedance and the load resistor.
4. Measure the internal resistance of the inductor. Pick a resistor so that the total series resistance (R1) with the source is 1000 Ω. This includes the source resistance, the resistor, and the inductor resistance.
5. Create the circuit from the preparation on a proto board.
6. Measure both the magnitude and phase of V_oc.
7. Measure both the magnitude and phase of I_sc. This can be done by measuring the voltage across R3.
8. Calculate Z_TH.
9. Change the frequency of Vac to the frequency determined in the preparation for which the Thevenin impedance is purely resistive.
10. Repeat steps 6 through 8.

Conclusions: 

• Compare the theoretical, predicted (simulated), and measured results. Explain any significant differences.
• Discuss how well the objectives were met.