In electronics, an amplifier circuit is most commonly used in audio devices to strengthen the input signal. There are different types of amplifiers available which are classified based on different considerations like a number of stages, input signals, output, biasing conditions, frequency range, transistor configuration, and coupling methods. Amplifiers are classified based on operation modes like class A amplifier, class B amplifier, class C amplifier, class D, and class AB. Here, classes are letter symbols that are applied to different power amplifiers to indicate the performance and characteristics. This article discusses an overview of a class b amplifier and its working.

Class B Amplifier

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 a Class B Amplifier also known as a push-pull 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 180^o of the input waveform cycle while the other transistor amplifies the other half or remaining 180^o 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 180^o 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 “push-pull” name but is more generally known as the Class B Amplifier as shown below.

Applications

The applications of class B amplifiers include the following.

• These are mainly used in the low-cost design.
• These amplifiers are very significant as compared to the class-A amplifiers.
• This type of amplifier suffers mainly from distortion if the level of signal is low.
• These are mainly used in two complementary transistors like bipolar and FET.