# Power Supply Pumping

A similar question has been asked, but I wanted to get to a more fundamental understanding of when, in general, power supply pumping occurs in a class D amplifier.

In general terms "power supply pumping" is the return of energy from a load to a power supply via output switches so that the power supply is forced to accept energy via an unintended path.

This quote was from an answer that was given before. How is the energy being supplied back? Is it mainly due to the inductive voltage spikes from the abrupt current switches? If I was driving something that was not a speaker, and say, purely resistive, would this still happen, or is it irrespective of the load type?

I was told that using a full bridge output (4 driving FETs) would help alleviate this problem versus using just a half bridge topology, but I do not see how. Any links to outside reading would be useful.

EDIT: I don’t have a specific schematic issue, I just wanted to know more about this specific issue that occurs.

• Could you include a schematic illustrating the problem? Oct 11, 2018 at 7:24
• It does depend what the amp is driving. Some loads (like electric motors) also act as generators. Oct 11, 2018 at 7:27
• For the load to be able to deliver power back into the amplifier it cannot be purely resistive. So for a purely resistive load: supply pumping cannot occur. I think the main source of energy coming back is mechanical/acoustic energy from the loudspeaker. A loudspeaker can also act as a generator when the diaphragm is moved (or it moves back after being moved by the amplifier) and that creates EMF in the loudspeaker coil. Oct 11, 2018 at 7:32
• There's a decent explanation of supply pumping in the datasheet of the MAX9742: datasheets.maximintegrated.com/en/ds/MAX9742.pdf page 25. Unfortunately it does not explain why this less of an issue in bridged configurations. My guess: in a bridged config. the grounded side of the speaker can be connected to the supply so that the pumping current cannot charge the supply anymore. Oct 11, 2018 at 8:09