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Maximum DC Power Transfer

Load the file PSPICE file maxdcp.sch.

This circuit models a source (V_S, R_S) and a load R_L. The problem is that the source is given, and we want to determine the value of R_L for which the power absorbed by the load

$$P_L = \frac{V_L^2}{R_L}$$

is a maximum. Note that if R_L=0 (short circuit), then V_L=0 so no power will be absorbed, and if $R_L=\infty$ (open circuit), again no power will be absorbed - so there must be a value of R_L with maximum power. By calculating P_L, theory says that P_L will be maximized for

R_L = R_S ,

i.e. when the load resistance equals the source resistance.

Simulate and obtain a graph of P_L versus R_L, and determine the maximizing value of R_L and the maximum value of P_L.

The schematic has been set up for DC sweep, with R_L as a parameter.

When the PROBE screen appears,

Trace $\to$ Add...

Enter $V(VL)*V(VL)/RL\underline{\ } val$ in the Trace expression part of the window.

Repeat with different values of R_S.

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