Thevenin equivalent circuit lab report

ENGR2105 Lab2 Thevenin Theorem

Student Name __________________________________

Objectives:

To determine the Thevenin equivalent circuit by computing V_TH and R_TH. To learn the use

of a computer to solve electrical circuits and compare calculated results with simulated results.

Materials:

Computer Browser to access Multisim Live: https://multisim.com

Calculator

Background Information:

Thevenin’s Theorem states that a network with two open terminals can be replaced by a single

resistor R_TH in series with a single voltage source V_TH. The process of “Thevenizing” a

circuit involves finding R_TH and V_TH.

The process of “Thevenizing” a network at terminals A and B is described below:

Step1: Remove the Load Resistance

Step2: Short the Power Supplies

Step3: Compute the voltage “looking in” at terminals

A and B. This is V_TH.

Step4: Short the power supplies and Compute the Resistance "looking in” at terminals A

and B. This is R_TH.

Step5: Replace the original network with the Thevenin equivalent.

Step6: Add the load resistor to complete the series circuit and calculate the load current.

You are tasked with finding the equivalent Thevenin Voltage and Resistance for circuits at

specific points, where the load resistance would be connected. You are expected to show all the

formulas and calculations needed to find the answers and include these in your report. The Lab

Report should be typed and should include screenshots of the instruments in your MultiSim Live

simulation. There should be nothing handwritten or hand-drawn in your lab reports.

2

ENGR2105 Lab2 Thevenin Theorem Worksheet Thevenize Circuit 1:

Fig. 1. Circuit1

Procedure:

• Build the circuit in Fig1 in MultiSim Live. (You do not need to include the labels “A”

and “B”). RL is the load resistor.

• Measure the voltage across the load Resistor.

Measured V_L = ________________

• Thevenizing the circuit in Fig 1.

Step1: Remove the Load Resistance

Step2: Short the Power Supply

Fig2. Circuit1 with the load removed and power supply shorted

Step3: Compute the Resistance between terminals A and B. Be careful. Trace the

possible pathways from A to B and come up with an equivalent resistance. This is

R_TH.

3

Computed R_TH = ________________

We do not have a way to measure Resistance in Multisim Live, so no measurements are

Required for this step.

Step4: Reconnect the Power Supply and compute the voltage between points

A and B. (Hint: The right side of R2 is not connected to anything, so no current is

flowing through R2. If there is no current through R2, Ohm’s Law tells us there

is no voltage drop across R2. The voltage between A and B is not affected by the

presence of R2.) This is V_TH. Calculate V_TH, then build the circuit in Fig 3 in

MultiSim Live and measure the voltage at terminals A and B. The two values

should match!

Fig 3. Circuit1 with load removed and power supply reconnected

Computed V_TH = ________________ Measured V_TH=________________

Step5: Replace the original network with the Thevenin equivalent, using your values of

R_TH and V_TH. Design the circuit in Fig 4 in MultiSim.

Fig 4. Loaded Thevenin equivalent circuit.

Step6: Compute and measure the voltage across the Load Resistor.

4

Computed V_L = ________________ Measured V_L =________________

• Replace the load resistor with a 20 Ohm resistor. Compute and measure the voltage

across the Load Resistor.

Computed V_L = ________________ Measured V_L =________________

5

ENGR2105 Lab2 Thevenin Theorem