In Class AB operation of an audio amplifier, how many degrees of the input signal wave allows current to flow through the active device?

In Class AB operation of an audio amplifier, current flows through the active device for more than 180 degrees but less than 360 degrees of the input signal wave. This characteristic allows Class AB amplifiers to combine the advantages of Class A and Class B operation, achieving higher efficiency than Class A while minimizing crossover distortion that occurs in Class B amplifiers.

During the conduction cycle in Class AB, the active devices (transistors) conduct for a portion of both the positive and negative halves of the input signal cycle. The range of conduction is set so that both devices can be biased to remain slightly ON, allowing them to efficiently handle transitions in the signal without significant distortion. This conduction range improves linearity while preventing the abrupt cutoff of current that is typical in Class B amplifiers where current only flows for exactly 180 degrees. Thus, the flexibility of allowing current flow for more than 180 degrees, but less than the full 360 degrees of the signal, is what defines the sound quality and performance of Class AB amplifiers effectively.