In this article I attempted to reverse engineer a voltage regulator module originally designed to fit into a Dell server. The theory was that these would be high quality, stable and robust designs that could prove useful if I could figure out how they worked. They’re certainly worth far more than the few pounds that you can get them for on ebay today.
I was able to determine the function of the key pins on the module myself by experimentation and then with some help from eagle-eyed readers out there on the internet we were able to identify the module as an Artesyn NXA66 and subsequently a summary datasheet was located that provided the full pinout. To summarise, the main features of the module are:
- Selectable voltages of 3.3V and a ‘secondary’ level selectable by the VSP pin.
- 12V input level.
- 20A (66W) continuous current delivery at the 3.3V level.
- Output enable pin.
- ‘Power Good’ output signal.
- Differential remote sense.
- Ability to chain the modules to share current delivery.
It’s worth expanding a little on that ‘secondary’ voltage capability. I now have a few of these modules and some of them have a secondary level of 5V and others have 2.5V. All of these levels are useful but I suspect that if you’re planning to follow the design outlined here then you’ll want the 3.3V/5V module.
I don’t know of a foolproof method of differentiating the two modules from their ebay listings. What I can say is that the model with the black heatsink reviewed in the original article is a 5V module and all those that I received with a silver heatsink are the 2.5V module.
Designing a power supply controller
I decided that the best way to exploit the results of the reverse engineering effort was to design a controller board that would host the NXA66 and expose its functionality via a front panel. I’d throw in a few simple extras myself such as current monitoring and data logging and finally I’d implement it as a through-hole design so that it could be implemented by people of all skill and equipment levels.
The end result will be a bench-power supply that’s cheap to build and has a current supply level greater than that of most supplies priced at hobbyist levels.
Schematic
Click on the thumbnail for a PDF schematic
It’s a relatively simple and modular schematic. Let’s take a look at each of the modules in turn and describe the functionality in more detail.
