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EWorkshop1708 20th April 2008 03:07 PM

My New 12V SMPS w/Computer PSU Transformer
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I finished building a simple 12V SMPS to test with and run amplifiers with. I've worked with SMPS before, but this is my 1st one I built. Although simple, I used big components to help reliability.

I used a computer PSU transformer from a dead 550W TTGI ATX Supply. I didn't have a decent toroid to use, so I used this instead to see how it would work, and it turned out well. I drive the 12V secondary coils in it with 12V and get my output from the mains side of it.

It uses TL594 @ 45khz in a socket driving hefty high-gain MJE15034/35 NPN/PNP Totem Pole Outputs to drive the MOSFETS. MOSFETS are NTY100N10 (123A) and output rectifiers are MUR3020 x 4 to make a bridge. (30A, 200V)

Rails depending on input voltage I've given it 11.5-15V gives me +/-35-50V rails. I haven't used it on a car battery at full power yet, but I've gotten over 150W with ease and no heat on a 14.4V NiCd battery. The MOSFETS stayed cool with NO heatsink with up to 100W, but work cool with the heatsinks at over 150W so far, and plan to test up to 300-400W.

Man, the post pic size is small. :( I have better larger pics too.

EWorkshop1708 20th April 2008 03:09 PM

more pics of smps
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more pics

EWorkshop1708 20th April 2008 03:11 PM

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Underside uses short pieces of thick 12AWG house wiring for 12V high current paths. The red is 15awg coil wire for the caps leads.

EWorkshop1708 20th April 2008 03:16 PM

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High speed diodes 30A 200V.

I used plastic marking tape (no adhesive) as insulators and greased both sides and put tight to heatsink to squeeze out excess heatsink grease. Same with MOSFETS but used blue tape.

I get that sticky HS grease all over my fingers that's why the heatsink looks covered, it really is a bunch of finger marks and extra grease for the most part.

EWorkshop1708 20th April 2008 03:28 PM

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schematic, sorry it's blurry, i need to scan it instead

areza 22nd April 2008 07:11 PM

really liked it , care to share how u construct the transformer, how many turns, core size , shape, bmax , etc, thank you

TheMG 22nd April 2008 11:17 PM

You should invest in some mica insulators, they're like $5 for 50, no joke. :)

EWorkshop1708 23rd April 2008 01:47 AM


Originally posted by areza
really liked it , care to share how u construct the transformer, how many turns, core size , shape, bmax , etc, thank you
Sure, Gladly :)
The transformer is stock. I did not modify it in any way. :D

The Transformer has 2 CT secondary outputs, one center tapped for +/- 5V and one same way for +/- 12V, other side for 120V mains voltage in, and had a clipped off lead for a center tap, I just soldered a #12 wire to the clipped lead to make it useable. Just use the transformer backwards and "drive" the 12V side, and get high voltage from the 120V side.

BTW, if you drive the 5v side instead with 12V you get real high voltage. :bigeyes: I got +/-90V (180V) by doing this, so there's more uses still for this transformer (power inverter maybe)

It's a high-wattage computer PSU SMPS transformer (It's just slightly bigger than the transformers on 250-500W computer supplies of other kinds I've opened)
I'm still wondering how much this transformer is capable of. It does not get hot, it does have paralleled turns of wire, but not super thick.

I'm wondering if my semiconductors will hold up, how far I can really try to push it. My guess is the transformer will easily handle 300W but I'm hoping to try much more.

To get somewhat of an idea of what the transformer may handle, here's the ratings of the PSU it came from:

Original 550W TTGI Computer PSU ratings:

Input: 120/240VAC
10/5 Amps

5V 55A
3.3V 28A (comes from the 5V section of PSU)
12V 22A

Any of you have any ideas? I'm about to get a bunch of dead computer PSU to strip down and make easy SMPS with. :D

EWorkshop1708 23rd April 2008 02:18 AM


Originally posted by TheMG
You should invest in some mica insulators, they're like $5 for 50, no joke. :)
Really...........where to get mica?

What I have also used with good performance is clear wide box (packing) tape, I stick the sticky side to the heatsink, and grease the semiconductor and put it tight against the non-stick side.

TheMG 23rd April 2008 05:27 PM

The problem with using tape, aside from the thermal performance, is if something ever goes wrong with the circuit that causes the mosfets or whatever other part to suddenly output a lot of heat, it might melt through the tape and short to the heatsink, likely resulting in (more) damage.

You can get the insulators off eBay, but most electronics suppliers will also have them. They are cheap, have good thermal conductivity, very low electrical conductivity (only a tiny bit of capacitance) and are resistant to high temperatures.

eBay item (example, there's more): 160200773161

Or from your favorite electronics part supplier, just search for "transistor insulator" or something similar.

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