• In class A amplifier the transistor is biased such that the output current flows i.e. the transistor is on for full cycle of the input ac signal.

• As class A operates in the linear region of the of the DC load line and the output device is always on at all times it is constantly carrying current, which represent the continuous loss of power in the amplifier.

• Due to this continuous loss of power class A amplifiers create tremendous amounts of heat adding to their very low efficiency of around 30 %.

• In a class B power amplifier transistor is biased almost at cutoff so that it remains forward bias for only one half cycle of the input signal hence its conduction angle is only 180 degree. due to this it has less power dissipation at the output side and have greater efficiency than class a which is more than 75%.