Question 10.4: Amplifier Efficiency Find the input power, output power, sup...

The average signal power delivered to the amplifier is given by

P_i=\frac{V_i^2}{R_i}=10^{-11} \text{ W}=10 \text{ pW}

(\text{Recall that 1 pW = 1 picowatt = }10^{-12} W.) The output voltage is

V_o=A_{voc}V_i\frac{R_L}{R_L+R_o} =8 \text{ V rms}

Then, we find the average output power as

P_o=\frac{V_o^2}{R_L} =8 \text{ W}

The supply power is given by

P_s=V_{AA}I_A+V_{BB}I_B=15+7.5=22.5 \text{ W}

Notice that (as often happens) the power of the input signal is insignificant compared with the output and supply powers. The power dissipated as heat in the amplifier is

P_d=P_s+P_i-P_o=14.5 \text{ W}

and the efficiency of the amplifier is

\eta =\frac{P_o}{P_s}\times 100 \text{ percent} =35.6 \text{ percent}