The specifications of different types of power amplifiers are tabulated below-

Class-A Power Amplifier

(i) Output current flows during the entire cycle of the A.C. input signal.

(ii) The operation of the amplifier is restricted to smaller central region of the load line,so that it can operate in the linear region of the load line.

(iii) The circuit efficiency of the amplifier circuit is defined as the ratio of A.C. power delivered to the load to the total power supplied by the D.C. source.

Class-B Power Amplifier

(i) Output current flows only for one-half of the cycle of the input signal.

(ii) The transistor dissipates no power with zero input signal.However,it increase with the increase in the amplitude of the input signal.

(iii) The overall efficiency of the circuit is higher than that of case-A amplifier. Its maximum value has been obtained to be equal to 78.5%.

Class-C Power Amplifier

(i) Output current flows only during a part of the positive or negative half-cycle of the input signal.

(ii) The output signal does not resemble the input signal because it consist of narrow pulses.

(iii) The class-C amplifier is the most efficient power amplifier and its overall efficiency under certain conditions may approach even hundred percent