Power Supply Pumping with full bridge

edogd · 3rd February 2005, 07:23 PM

On a class-d using a full bridge there is the potential to send current back to the battery (or supply) during the second half cycle.

Isn't send current back to a battery, especially if its not a rechargeable one, a bad thing?

I have only seen one reference on the topic:

http://www.irf.com/product-info/audi...sdtutorial.pdf page 13.

Do you know of any other references?

ingrast · 3rd February 2005, 08:02 PM

Power supply pumping is an essential part of class D efficiency.

Think of it this way, what you have at the switches output is a square wave. Desirably you pass it through a purely reactive filter to get ride of switching carrier and harmonics and recover the original audio signal.

Now, where does that not negligible energy goes? Back to the power supply via the freewheeling diodes across each switch.

It is not a bad thing at all if some care is taken with design, in this case ample bypass low ESR capacitance across each power supply output. Non rechargable batteries will no suffer as long as most of the returned energy is stored in the capacitors, meaning the PSU does not rise but a few percent during the return current pulse.

Rodolfo

3rd February 2005, 07:23 PM	#1
edogd diyAudio Member Join Date: Feb 2005 Location: CA	Power Supply Pumping with full bridge On a class-d using a full bridge there is the potential to send current back to the battery (or supply) during the second half cycle. Isn't send current back to a battery, especially if its not a rechargeable one, a bad thing? I have only seen one reference on the topic: http://www.irf.com/product-info/audi...sdtutorial.pdf page 13. Do you know of any other references?

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3rd February 2005, 08:02 PM	#2
ingrast diyAudio Member Join Date: Sep 2004 Location: Montevideo	Power supply pumping is an essential part of class D efficiency. Think of it this way, what you have at the switches output is a square wave. Desirably you pass it through a purely reactive filter to get ride of switching carrier and harmonics and recover the original audio signal. Now, where does that not negligible energy goes? Back to the power supply via the freewheeling diodes across each switch. It is not a bad thing at all if some care is taken with design, in this case ample bypass low ESR capacitance across each power supply output. Non rechargable batteries will no suffer as long as most of the returned energy is stored in the capacitors, meaning the PSU does not rise but a few percent during the return current pulse. Rodolfo