Class B power amplifier

The class B amplifier is biased at cutoff. No current will flow until an input signal provides the bias to turn on the amplifier.

Fig. 10-2: Q point of a class B amplifier

Only one half of the input signal is amplified. Two transistors can be operate in class B together in one circuit, one transistor for the positive portion of the signal and one transistor for the negative portion of the signal (Push Pull):

Fig. 10-3: Push Pull amplifier

Fig. 10-4: Signal swing of a. push pull amplifier, Class B operation

Problem: Crossover distortion, the emitter diode takes 0,7V to turn on.

Fig. 10-5: Crossover distortion

Efficiency: 78.5%

Distortion: High

Application: High power stages, not used in audio applications.