01.08.2010, 06:00 PM
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Zitat:Supply Pumping
One issue encountered in single-ended (SE) class-D amplifier designs is supply pumping. Power-supply pumping
is a rise in the local supply voltage due to energy being driven back to the supply by operation of the class-D
amplifier. This phenomenon is most evident at low audio frequencies and when both channels are operating at
the same frequency and phase. At low levels, power-supply pumping results in distortion in the audio output due
to fluctuations in supply voltage. At higher levels, pumping can cause the overvoltage protection to operate,
which temporarily shuts down the audio output.
Several things can be done to relieve power-supply pumping. The lowest impact is to operate the two inputs out
of phase 180° and reverse the speaker connections. Because most audio is highly correlated, this causes the
supply pumping to be out of phase and not as severe. If this is not enough, the amount of bulk capacitance on
the supply must be increased. Also, improvement is realized by hooking other supplies to this node, thereby,
sinking some of the excess current. Power-supply pumping should be tested by operating the amplifier at low
frequencies and high output levels