Working of Push Pull Amplifier

Push Pull Amplifier

In single ended amplifiers, appreciable distortion may result due to non-linearity of transfer characteristics. This distortion may be reduced considerably by push pull operation of transistors. A push pull amplifier uses two active devices that excited by the same input signal but with a phase difference of 180^o. The input signal is applied to the input of the two transistors through a centre tapped transformer T₁.
The voltages at the bases of the transistors Q₁ and Q₂ are in push pull, i.e. in phase opposition. When the base of T₁ is positive due to the input signal, the base of Q₂ will be negative.

Push-Pull Amplifier

Working:

The circuit of push pull amplifier is shown in the above fig. the resistors R₁ and R₂ provide the necessary biasing required for the transistors Q₁ and Q₂. The input signal is applied to the amplifier through a centre tapped transformer T₁. Thus the inputs supplied to the bases of two transistors Q₁ and Q₂ are accurately out of phase. Thus the two transistors conduct on alternate half cycles of the input signal. Hence the collector current flow in opposite direction. So the net d.c. in the primary of output transformer T₂ is zero. However the secondary of the output transformer will have induced voltage. Therefore, the output of the amplifier will be twice that of the output offered by the single transistor. The type of operation chose for the push pull amplifiers be either in class AB or class B.

It is to be noted that, all the even harmonics are cancelled in the output of the push-pull amplifier. Hence the distortion is reduced very well.