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Reverse engineering a server CPU voltage regulator module




A recent ebay fishing expedition yielded an interesting little part for the very reasonable sum of about five pounds. It’s a voltage regulator module from a Dell PowerEdge 6650 Xeon server.Reverse engineering a server CPU voltage regulator module

I originally bought this because I had the idea of salvaging parts from it to use in another project. These are high quality modules that will have very good inductors and sometimes an array of high value ceramic capacitors that could be re-used (ceramics of at least 22µF at 16V and above are rather pricey at the moment). So the VRM arrived and I was rather impressed with the build quality and decided to have a go at reverse engineering it.

First impressions

The board is at least 2 layers and I’m betting that the topology is a switching buck converter. If I peek under that big heatsink I can see a large inductor, a smaller inductor, Fairchild FDP7030L and FDB7030L power MOSFETs, a bank of ceramic and a bank of tantalum capacitors. Basically all the components you need for the power section of a buck converter. The inductors are Coiltronics UP2B-R47 and UP4B-1R5, both with maximum current ratings in excess of 10A. There’s also a MIC4420BM MOSFET driver with a peak current rating of 6A which gives us a clue as to the output current limit of this board.

The FDP7030L power MOSFET is screwed to the heatsink so I thought it’d be easy to get the heatsink off by just removing that screw. Not so. There are a number of ‘posts’ that prop the heasink up into position and I just couldn’t get these to budge without risking damage to the part.

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