Push Pull Amplifier Design

A push-pull class B amplifier design is a complementary symmetrical type because it has NPN and PNP transistors that are emitter followers conducting for opposite halves of the input cycle. The NPN transistor conducts for the positive half of the cycle whilst the PNP transistor conducts for the negative half of the cycle. One advantage of this type of amplifier over class A is that it has much higher efficiency, defined as the ratio of ac output power to dc input power.

Class B amplifier bias design is such that it operates within the cut-off region for only 180° of the input cycle. This means that the Q point would have to be within the cut-off region. Crossover distortion occurs when the input signal voltage is between ±VBE, during which time the output signal flat-lines along the zero line. In order to eliminate this crossover distortion, it is customary to bias each transistor to operate slightly above the cut-off region.

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