Power Amplifier Classes

[Zman]

anyone can give me a circuit design about each class of power amplifier? ( especially for class A, B, AB and C )

Regards

[Jerome Trent]

The Class A amplifier is one in which the amplifying device is on all the time.  It reproduces an inverted amplified replica of the input.  It also is the least efficient of all the amplifier classes because it is on all the time.

 

The Class B is said to be on half the time but in reality it is on slightly less than half the time.  Since it is only working half the time then the output is not a replica of the input, but only represents the positive half or the negative half.  For this reason many Class B amplifiers are used in a Push-Pull arrangement using two devices so that each device amplifies half the signal.  Since the Class B is on for slightly less than half the signal, we have a little crossover distortion at the point where both devices are off.

 

Since the Class B amplifier has some distortion, a modified version of it is the Class AB amplifier which has biasing diodes to eliminate the distortion.

The Class C amplifier is the most efficient of all these amps but has the most distortion since it is on for less than half the input.  These amplifiers are often used in conjunction with tuned resonant circuits to recapture the full input signal.