Ability to obtain and analyze the Thevenin equivalent circuit: Electronic Assignment, MMU, Malaysia

Objective:

To characterize multiple resistive networks by its Thévenin’s equivalent circuit.

 Learning Outcome:

Ability to obtain and analyze the Thevenin equivalent circuit.

Theory:

 Thévenin’s Theorem: It is a process by which a complex circuit is reduced to an equivalent series circuit consisting of a single voltage source (V_TH), a series resistance (R_TH), and a load resistance (R_L). After creating the Thévenin Equivalent Circuit, the load voltage V_L or the load current I_L may be easily determined.

One of the main uses of Thévenin’s theorem is the replacement of a large part of a circuit, often a complicated and uninteresting part, with a very simple equivalent. The new simpler circuit enables us to make rapid calculations of the voltage, current, and power that the original circuit is able to deliver to a load. It also helps us to choose the best value of this load resistance for maximum power transfer.

                         Figure 7.1

                                                               Figure 7.2

Maximum Power Transfer Theorem states that an independent voltage source in series with a resistance R_S or an independent current source in parallel with a resistance R_S delivers maximum power to that load resistance R_L for which R_L = R_S.

In terms of a Thévenin Equivalent Circuit, maximum power is delivered to the load resistance R_L when R_L is equal to the Thévenin equivalent resistance R_TH of the circuit.

                                                                                            Figure 7.3

Task 1: Verifying Thévenin’s theorem 

• Construct the circuit of Figure 7.1 using the following component values:

R1 = 300 W

R2 = 560 W

R3 = 560 W

R4 = 300 W

R5 = 820 W

RL = 1.2 kW

VS = 10 V

• Measure the voltage VL across the load resistance, RL.

• Find VTH: Remove the load resistance RL and measure the open-circuit voltage, Voc across the terminals. This is equal to VTH.

• Find RTH: Remove the source voltage VS and replace it with a short circuit. Measure the resistance by looking into the opening where R_L was with an ohmmeter. This gives RTH.

• Obtaining VTH and RTH, construct the circuit of Figure 6.2. Set the value of RTH using a variable resistor. For simulation using Proteus just use the ordinary resistor and change the value to the RTH value. Measure the VL for this circuit and compare it to the VL obtained from the circuit of Figure 7.1. State your observation.

• Construct the circuit as in Figure 7.3 using the following values:

VS = 10 V

R1 = R2 = 560 W

R3 = 820 W

RL = Variable Resistor (0-2kW)

Connect the Voltmeter across RL for measuring the load voltage (VL) and Ammeter through RL for measuring load current (IL). Vary the resistance between 600 W to 1.6 kW and note down VL and IL for each case.

Answer

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