Classification of power amplifier

power amplifier are classified into following group

1. class 'A' power amplifier 
2. class 'B' power amplifier  
3. class 'AB' power amplifier 
4. class 'C' power amplifier   

 Class 'A' power amplifier  

let as consider the following amplifier circuit

Here we have n-p-n transistor operated in common emitter mode. Here bias battery VBB  is used in the input circuit to get forward bias in the input circuit during the passes of input signal, here bias battery is stronger then signal, on that case we get faithful amplification.

Here collector current is continuous during the passes  of signal OR collector current flows 0 to 360 degree of input signal.

 

 let us consider the following load line analysis with   waveform 

 For output circuit 

 VCC=VCE+ICRC

 VCE=VCC - ICRC

Note- for power transistor Rc is less therefore collector current Ic will be more this will result into current amplification 

Here the intersection point between AC load line and output characteristic is called operating point

 

Class A amplification 

 

From the above waveform it is clear that output voltage of power amplifier slightly reduce but output current of the amplifier is more thus we get current amplification .

collector efficiency varies from 25% to 50%.