Maximum Average Power Transfer

MAXIMUM AVERAGE POWER TRANSFER

In maximizing the power directed by a power-supplying resistive network to a load RL. Representing the circuit by its Thevenin equivalent, we proved that the maximum power would be delivered to the load if the load resistance RL = RTH. An ac circuit is connected to a load ZL and is represented by its Thevenin equivalent. The load is usually represented by an impedance. 

In rectangular form the Thevenin Impedance ZTH, and the load impedance ZL are 

ZTH = RTH + jXTH

ZL = RL + jXL

The maximum average power can be transferred to the load if 

XL = - XTH

RL = RTH

It will give us a maximum average power as;

Pmax = (VTH)^2 / 8RTH

This means that for maximum average power transfer to a purely resistive load, the load impedance is equal to the magnitude of the Thevenin impedance.