A push pull amplifier is an amplifier
which has an output stage that can drive a current in either direction
through through the load. The output stage of a typical push pull
amplifier consists of of two identical BJTs or MOSFETs one sourcing
current through the load while the other one sinking the current from
the load. Push pull amplifiers are superior over single ended amplifiers
(using a single transistor at the output for driving the load) in terms
of distortion and performance. A single ended amplifier, how well it
may be designed will surely introduce some distortion due to the non
linearity of its dynamic transfer characteristics. Push pull amplifiers
are commonly used in situations where low distortion, high efficiency
and high output power are required. The basic operation of a push pull
amplifier is as follows: The signal to be amplified is first split into
two identical signals 180° out of phase. Generally this splitting is
done using an input coupling transformer. The input coupling transformer
is so arranged that one signal in applied to the input of one
transistor and the other signal is applied to the input of the other
transistor. Advantages of push pull amplifier are low distortion,
absence of magnetic saturation in the coupling transformer core, and
cancellation of power supply ripples which results in the absence of hum
while the disadvantages are the need of two identical transistors and
the requirement of bulky and costly coupling transformers.
Class A push pull amplifier.
