Thu February 16, 2012 By: Pratibha Roy

What is 'b' in the transistor as an amplifier?

Expert Reply
Fri February 17, 2012
To improve the full power efficiency of the previous Class A amplifier by reducing the wasted power in the form of heat, it is possible to design the power amplifier circuit with two transistors in its output stage producing what is commonly termed as a "push-pull" type amplifier configuration. Push-pull amplifiers use two "complementary" or matching transistors, one being an NPN-type and the other being a PNP-type with both power transistors receiving the same input signal together that is equal in magnitude, but in opposite phase to each other. This results in one transistor only amplifying one half or 180o of the input waveform cycle while the other transistor amplifies the other half or remaining 180o of the input waveform cycle with the resulting "two-halves" being put back together again at the output terminal. Then the conduction angle for this type of amplifier circuit is only 180o or 50% of the input signal. This pushing and pulling effect of the alternating half cycles by the transistors gives this type of circuit its amusing name, but these types of audio amplifier circuit are more generally known as the Class B Amplifier
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