Modifying ATX PSU from AC-DC to DC_DC

Not without a lot of work. The ATX supplies, in general want something over 300VDC into the primary of their transformer (some 115V supplies only want about 150v, but most use a switchable input topology, with a voltage doubler connected when

115v is selected), so conversion, would require complete redesign of the main transformer. Not a small task. If you are not worried about efficiency, then you could make a DC to AC inverter, and leave the ATX supply as it is. There are plenty of circuits for these on the web, but be prepared for how large the transformer will need to be for a unit able to run a ATX supply. Given that you should not need the isolation offered by the ATX supply, a DC-DC buck inverter, would be simpler and cheaper to make, and could feed the main PC rails. There are off the shelf IC's, which control an external FET to give this sort of supply, which in combination with a suitable inductor, and a couple of discretes, would give one of the rails, for only a very few dollars. Some rails you can probably ignore (The -5v rail has been dropped from the latest ATX specs, and many boards do not require -12v, except for serial ports). Unless you have a very big DC source, you might be much better off, assuming this is to run a PC, looking at a board and processor specifically designed for this sort of operation. A typical modern PC, will draw about 10A at 12v, continuously, and may peak at over 30A. Conversely, a proper 'low power' system, based on something like the Mini-itx board, with 2.5" disk drives, and basic video card, will have only perhaps 1/4 the performance, but typically draw less than a couple of amps...

Best Wishes

This quite an involved task. Many parts would have to be replaced. I'd forget it.

Graham

If you really want to do this, my suggestion would be to build an inverter from 12VDC to 170VDC, and connect that to the input of the ATX supply. I would try to use the transformer from a second PC power supply along with a couple of power MOSFETs and a switched-mode power supply controller IC. This would be quite challenging but probably educational. Provided you construct everything within well earthed metal enclosures, make sure all capacitors are discharged before opening the enclosures, and provided you test it with a dummy load rather than your new mobo, I think it could be a good project for someone with plenty of time.

Chris

There are plenty of 12V dc (car battery) to 120V ac converters out there, the technology is not real hard. Build or buy?

This should have been posted to news:alt.binaries.schematics.electronic instead of text newsgroups that may or may not propogate your images.