Lab-7 Maximum Power Transfer:

Name:

Date:

Objectives:

To analyze a network and determine the maximum power transfer.

Equipment:

1 – 56Ω fixed resistor, 1 – Decade box, Breadboard, Agilent DMM, 4 – Long leads, Bag of Wires.

Introduction:

The internal resistance of the bench power supply is very small and therefore it is difficult to obtain accurate results if we try to determine maximum power transfer to a practical load. Consequently, we will simulate a practical source by connecting a 56 Ω resistor in series with the bench power supply. The bench power supply will be considered an ideal source since its internal resistance is negligible when compared to the 56 Ω resistor.

Procedure:

Part I:

  1. Set up the circuit shown in Figure 7.1.

  2. With RL disconnected from the circuit, set the open-circuit voltage to 10 volts (\(V_{oc}\) = 10.0 V) using the digital multimeter.

  3. Set the resistance of the decade box to 150 Ω and connect it into the circuit. Record \(V_L\) and \(I_L\).

\(V_L\) = _______________________

\(I_L\) = _______________________

  1. Calculate the internal resistance using

\(R_i\) = \(\frac{V_{oc}-V_L}{R_L}\)

\(R_i\) = _______________________

  1. Now turn off the bench power supply, remove the 56 Ω resistor and measure its value.

\(R_S\) = ___________________________

  1. The Rs value measured in step 5 should equal \(R_i\). If not repeat steps 2 through 4 and if still does not explain the reason(s).

Part II:

Maximum power into the load occurs when the resistance of the load is equal to the internal resistance of the power source.

  1. Reconnect the 56 Ω resistor as in Part I.

  2. Vary \(R_L\) using the dial settings on the decade box for the values given in the following table and record the corresponding values of \(V_L\) and \(I_L\). Enter the data into an Excel spreadsheet.

\(R_L\) 1568 784 392 196 112 64 56 49 28 16 8 4 2 0
\(V_L\)
\(I_L\)
\(P_L\)
  1. Calculate the value of \(P_L\) for each set of readings and plot \(P_L\) against \(R_L\).

Question:

If \(R_L\) were fixed at 10 Ω and \(R_i\) could be varied (for example by using various power supplies from different manufactures), what value of \(R_i\) would you choose so that the 10 Ω load resistor would dissipate maximum power for a given voltage setting of the ideal power supply voltage (\(V_{oc}\))?