Verification Thevenin’s Theorem and Maximum Power Transfer

Introduction:The purpose of this experiment is to study the principle of Thevenin’s Theorem. Thevenin’s Theorem will be explored by numerically analyzing a particular circuit in the preliminary part of this experiment. This same circuit will then be experimentally examined in the laboratory. Corresponding calculated and measured circuit response values will be compared. A secondary purpose of this experiment is to use the Thevenin equivalent circuit to study the principle of maximum power transfer.

We will demonstrate the validity of Thevenin’s Theorem in the laboratory by applying it to the circuit shown in Figure 1.

OBJECTIVES To verify the practical usage of Thevenin theorems. To verify maximum power transfer therem.

EXPERIMENTAL EXERCISE

Figure 2 Laboratory version of the circuit in Figure 1

1. With the DC supply turned off, construct the circuit shown in Figure 2 to the left of terminals A-B.

2. Energize the DC supply and set it at 10 Volts.

3. Measure the open circuit voltage between terminals A-B and record below. Compare this value with the open circuit voltage determined analytically in the preliminary exercise.

Vth = vOC = 5V Measured vth =5.01v

4. Now disconnect voltage source from the circuit and replace theme with short circuit for this state measure the net resistance across a and b note that this value is the thevenin resistance (Rth) across a and b

calculated Rth = 600 Ω Measured Rth = 600 Ω

measured calculatedVth 5.01 V 5 VRth 600 Ω 600 ΩIL 5.26mA 5.38 mA

5. For the last part of this experiment, we want to examine the power delivered from the supply to the load and determine what load resistor value will dissipate the most power. What value of Rt should result in maximum power dissipation in RL?

RL = Rth = 600 Ω

6. Calculate the maximum power dissipated in RL.

PL = V2

RL = 2.52

600 = 10.4 mw

Assemble the circuit of Figure 4. The values of vOC and Rt are the same as those used for the circuit of Figure 3. Use the decade resistance box for RL since RL will take on a range of values. For each value of RL given in the table below, measure iL and vL and record in the spaces provided. Calculate the corresponding value of power, PL, dissipated in RL, and record. Make a note of which value of RL gives rise to maximum power dissipation. Plot PL vs. RL .

RL (Ω) IL (mA) VL (VOLT) PL (mw) I2RL400 4.92 2 9.68256500 4.45 2.30 9.90125600 4.10 2.518 10.086700 3.79 2.716 10.05487800 3.50 2.891 9.8

conclusion

the power delivered to the load resistance is maximum when the load resistance is equal to the Thevenin resistance of the source.