I've got this simple exercise about maximum power transfer.


simulate this circuit – Schematic created using CircuitLab

Where \$E_{th}=100\angle 0º \$ [V] and \$Z_{th}=100\angle 20º \$.

Then I completed this table with values I obtained after solving the equations on \$Mathematica\$.

enter image description here

I know that the theorem states that the maximum power transfer on the load will be when \$R_{L}=R_{eq}\$ and \$X_{L}=-X_{eq}\$ . This agrees with the values of \$P_L\$ .

The efficiency is bugging me. How is it the same efficiency with the first 2 values? and is it true that the efficiency isn't the best at the maximum power transfer load values?

Are my calculations wrong or is it something else?

Thank you!


Your results are correct.

MPT is always 50% efficiency for this circuit when (the load=) "conjugate Zl" is matched to source.

It is also 50% efficient when the Real part of Z ( load )is matched to source.

  • 1
    \$\begingroup\$ which Z? --- Zl ? \$\endgroup\$ – analogsystemsrf May 17 '19 at 3:04

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