Power amplifier
It is used as an output stage. The output stage must satisfy a number of spatial requirements. One of the most of them is to deliver a specified amount of signal power to a load with a low level af signal distortion. And minimizing the output impedance so the gain is unaffected by the level of load impedance. More complex output stage employ multiple output devices are also treated and comparisons are made of power output and efficiency. Because of excellent current handling capability, bipolar transistor is the preferred devices for use in output stage.
Consider now the power relation, when sinusoidal signal are present, the power dissipation in various elements varies with time. We are concerned with the instantaneous power dissipated with average power. Instantaneous power is important when considering the low frequency or dc signal. Average power is important because the power delivered to load is specified as average value.
To calculate the efficiency of the circuit the power drawn from the supply must calculated. The current drown from the supply is the collector current which is assumed to be sinusoidal with an average value. Since the supply voltage is constant the average power drown from it is constant. And the efficiency is defined as the ratio of the average power delivered to load to the average power drawn from the supply.
Since the devices is not ideal so a distortion will happened, due to the nonlinearity so an approximation of second harmonic and fourth harmonic will discuss for class A amp and class B push pull amp.