Book Analog Interfacing to Embedded Microprocessors
tance, not at the power supply, but at the board with the PWM circuit.
Audio Applications
PWM techniques were originally developed to improve efficiency and reduce heating
in control applications. However, PWM has been applied to audio amplifiers as well.
A block diagram of an audio PWM amplifier is shown in Figure B.5. An audio ampli-
fier using PWM is referred to as a class D amplifier. The Philips TDA8920 is a typical
class D power amplifier IC, with two 50W audio amplifiers operating at up to 90% effi-
252 Appendix B
Figure B.5
PWM audio amplifier.
ciency. Class D audio amplifiers typically switch at hundreds of kHz to avoid influenc-
ing the audio output with the PWM frequency. The advantages of PWM for audio appli-
cations are the same as for any other application: better driver efficiency, smaller power
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