6-Channel Class-D Amplifier Board - Philips MX6000i Service Manual

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6-Channel Class-D Amplifier
Basic operation of a class-D amplifier
Basically, the output stage of a class-D amplifier outputs a continuous square wave swinging between positive and negative
power supplies with a fixed frequency ("clock" frequency) far beyond the audible range. The duty cycle of this square wave is
modulated with the audio signal. The output is followed by a low-pass filter which eliminates the clock frequency and allows
only the audio signal going to the speaker. See simplified drawing below:
Compared to a conventional power amplifier the benefits of the Class-D amplifier are:
6-Channel Class-D • Higher effiency
• Lower power dissipation
• Smaller heatsink required
• Smaller mains transformer required
Amplifier Board
The main disadvantage of this concept is:
• The amplifier is operating with a high-frequency square wave at high amplitude and currents. This requires special
precautions to prevent excessive electromagnetic ratiation (EMC).