Class B push pull Amplifier
The advantage of class A power amp. is the large power dissipation occur even for no ac input. In many applications, the circuit may spend long periods of time in standby condition with no input signal. Power dissipation in the standby period is important for
1- In battery Operated equipment, supply power must be conserved to extend the battery life.
2- Any power wasted in the circuit is dissipated by the active devices, which increasing the temperature and the chance of failure are increased too.
A class B solves this problem by having zero power dissipation with zero input signal. To active devices are used to deliver the power to the load, and each device conducts for alternative half cycle. This is called push pull. Also its efficiency is very higher than class A.
The push pull design will eliminate all even harmonic and maintain the third harmonic factor as a source of the distortion, which making the distortion very small as compare with class A for example. These advantages of class B explain the widespread use of it. Its temperature is increased when nonzero signal is applied.