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Old 4th February 2005, 07:42 PM   #1
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Default DC/DC converter using parts from PC PSU

Hey guys, anyone got some diagrams for creating any sort of dc/dc converter using parts from a computer PSU? Ive got quite a bit of old ones lying around, ones that use TL494 etc.

Id like to use parts from them to create a converter that accepts 12v from like a car, and then converts it to around 80v

Thanks in advance
~Pentarino
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Old 4th February 2005, 09:11 PM   #2
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I seem to remember some people have reversed these. DigitalJunkie can probably tell you more...

Tim
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Old 10th February 2005, 01:40 PM   #3
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Default TL494-based DC-DC

Pentium-

Yes, you can. Look as any car amplifier with a DC-DC converter- they almost always use the '494. Some, like Alpine, might even have tech manuals available, complete with schematics in them.

If you really want to stay with the form-factor of the AT- or ATX-box, I seem to remember a website where the guy kept the secondary (output) section intact, but changed the input side from the hi-voltage half-bridge configuration to a low-voltage (probably 12V) center-tap push-pull topology. He kept the driver transformer, but with a little re-working of the circuit layout. The 400V bi-polars were swapped out for some 55-60V N-Channel MOSFETs of low Rds(on) rating. If I find it, I will post the web address on this thread.

His article accompanying the photos seemed to indicate good success with the project. So now, he can use his desk-top CPU on 12VDC instead of the regular 120VAC. Probably a good thing in the event of a power outage.

Since you're probably wanting to make a (+/-) supply, you will need to do something different. For usable parts on a typical AT or ATX PSU, assuming it is a half-bridge and not a flyback, you can use the transformer (though some rewinding will be necessary), the BIG output inductor, some of the little individual output inductors, the output rectifiers (they're the high-speed types), and, of course, the TL494 itself. But you're in for some new transistors, and a driver ckt, as the 494 will not directly drive MOSFETs. The electrolytic caps might be used, although you might want to use some better caps, like Panasonic, or others.

The electrolytics in the output section are rated for only 10- or 16VDC, and might not have high enough voltage rating for your application. In this case, you will definitely need some new caps, Low ESR, rated for high-frequency applications, and you might want to look at a really good brand, like Panasonic or Sprague, or some other high-quality brand.

Anyway, I am rambling, but if I come across that conversion project, I will post the link for it on this thread.


Steve
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Old 10th February 2005, 03:54 PM   #4
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Thanks Steve, I very much look forward to finishing this project!
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Old 10th February 2005, 04:13 PM   #5
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email me privately if you want the ATX article from QEX -- it even tells how to dissemble the transformer -- and some of the math which you would find necessary going from an off-line switcher to one operated from a car battery.
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Old 18th March 2005, 05:29 PM   #6
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Default DC-DC ATX PSU Pics

Pentium-

I finally figured out how to shrink the file size under the 102kB size limit. Here is the first DC-DC ATX PSU pic.......
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File Type: jpg rehashps small.jpg (50.7 KB, 527 views)
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Old 18th March 2005, 05:36 PM   #7
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Default DC-DC ATX PSU Pics

Here's the next one......
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Old 18th March 2005, 05:40 PM   #8
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Default DC-DC ATX PSU Pics

....and the next one....
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Old 18th March 2005, 05:44 PM   #9
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Default DC-DC ATX PSU Pics

....and the last one. tThe schematic os for a 200W unit, although it is adaptable for almost any ATX PSU. NOTE: These are NOT pics of my work- I pulled them off the web almost a year ago. Just wanted to post them here to answer your original question.

Hope these help, and I'm sorry it took soooooooooooo long!

Steve
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Old 18th March 2005, 05:50 PM   #10
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Default DC-DC ATX PSU Pics

Sorry for the duplicate pic post- here is the correct one- the schematic of the main power switch section.
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