Explain with circuit diagram and waveform the operation of class AB push pull power amplifier.

Explain with circuit diagram and waveform the operation of class AB push pull power amplifier.
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1 Answer

Answer :

Class AB Push Pull Power Amplifier: 

Circuit Diagram: 

image

Circuit Decription: The circuit consists of two centre-tapped transformers T1 and T2, two identical transistors Q1 and Q2 , Resistor R and diode D. The DC voltage developed across the diode D is connected to the bases of both the transistors through the secondary winding of the input transformer. This voltage acts as DC bias for the transistors because it is equal to cut-in voltage and they will conduct for complete half cycleperiod of the input to eliminate the cross-over distortion.


WORKING:

* When there is no a.c. input signal is applied both the transistors Q1& Q2 are cut off.

Hence no current is drawn from VCC.

* DURING POSITIVE HALF CYCLE:

# The base of the transistor Q1 is positive and that of Q2 is negative.

# As a result of this Q1 conducts, while the transistor Q2 is OFF.

* DURING NEGATIVE HALF CYCLE:

# The base of the transistor Q2 is positive and that of Q1 is negative.

# As a result of this Q2 conducts, while the transistor Q1 is OFF.

* Thus at any instant any one transistor in the circuit is conducting.

* Then the output transformer joins these two halves & produces a full sine wave in the load resistor.


Waveform :

image

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