Class-D Amplifier

ELEKTOR ELECTRONICS APRIL 1989 CLASS-D AMPLIFIER by J. Bareford The terms digital amplifier, class-D amplifier, switched amplifier and PWM amplifier all refer to a type of amplifier that converts its input signal into a rectangular signal with variable duty factor. The high efficiency achieved by a class-D amplifier makes it of particular interest for mobile and public address applications, where low distortion is not a prime issue. The AF power amplifier described here works from a 6 V battery, and delivers up to 5 watts. A such, it is eminent for use in, for instance, a megaphone. A well-known prob- lem with mobile AF amplifiers is that their low efficiency makes it virtually impossible to generate high power levels from a low sup- ply voltage. The am- plifier described here has a total efficiency of almost 100% at a distortion level that is tolerable with mega- phones and similar P.A. equipment. The basic principle behind the design is Pulse-width modulation Figure 1 shows the ...