PWM audio amplifiers

Although the concept of the pulse-width modulated or `Class-D` audio amplifier has been known since the late nineteen-forties, there has been little practical exploitation of the technique apart from a few short-lived designs by Sinclair and Mullard in the nineteen-sixties. However, recent advances in semiconductor technology, power FETs in particular, have made the class-D amplifier a more feasible proposition, and the PWM concept has been resurrected by some Japanese hi-fi firms. This article takes a look at the principles of class-D amplifiers and examines the circuit of a commercial design.