A power amplifier circuit is the one with minimum output impedance, used to drive loads like a speaker, which require high power at low impedance. Here is designed a power amplifier circuit using push pull class AB configuration to derive a power of 150W to drive a load of 8 Ohms (speaker).
The basic principle behind this circuit is the different ways of biasing of a bipolar junction transistor. The electric signal output from a microphone is very low. This low voltage signal is amplified to a sustainable level using the CE configuration of a BJT, biased in class A mode. In this mode, the output is an inverted amplified signal. This signal is a low power signal. Two Darlington power transistors arranged in class AB configuration amplify the power level of this signal. A transistor configured in class A mode is used to drive this transistor.