Class AB operation of an audio amplifier means that current flows through the active device for how many degrees of the input signal wave?

Class AB operation of an audio amplifier is characterized by the way the active devices, typically transistors, conduct current in relation to the input signal wave. In Class AB operation, the active devices are designed to conduct for more than half of the input signal cycle, which is more than 180 degrees but less than the full 360 degrees of the cycle. This operation allows the amplifier to combine the efficiency of Class B with the linearity of Class A.

When the signal is small, one of the transistors is turned on just enough to conduct, while the other remains off, meaning that current flows through the active device for a portion of the waveform. As the signal level increases, both devices may become active, covering even more of the waveform's cycle, but the key aspect is that they never fully turn on for the entire 360 degrees. Instead, they operate in a way that reduces distortion for typical input signals, thus improving the sound quality of the audio output while maintaining reasonable efficiency.

This behavior is what distinguishes Class AB amplifiers from those operating in Class A, where current flows continuously for the entire 360 degrees of the cycle, and Class B, where current flows for exactly 180 degrees.