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Building my own power supply?

Last response: in Components
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March 7, 2004 6:31:31 PM

Ok the title is a bit missleading, I dont want to build a power supply from scratch, rather I would like to upgrade (for want of a better word) one of my old PSU's just 4 a laugh. Was wondering if anyone new any sites that show you what each part of the PSU does? and how it works. Anyone ever tried anything similar?

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March 7, 2004 9:20:19 PM

I bought a generic 400W unit a long time ago and when the fan failed I replaced it. I noticed it was well engineered with lots of capacitors and filter coils, but used cheap capacitors. So as the capacitors failed, I replaced them all with the best quality units. Then the housing failed (yes, the housing, all the screws pulled through and everything), so I replaced it with a heavy duty Sparkle enclosure from a 235W unit.

Since then I've taken apart several other cheap supplies to repair them. Most had no filter coils whatsoever. Not worth upgrading IMO.

As a former audio enthusiast I know what filter (inductive) coils do, they block high frequency line noise. And capacitors across a DC circuit absorb spikes and fill surges, like a tiny reservoir.

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March 7, 2004 10:57:21 PM

Ok, you dont happen to know of any sites that show basic diagrams of all the standard PSU components and what they do, do u? I opened up this PSU to change the fan, then I thought I would be interesting to find out how a PSU works and maybe tweak it a bit.

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March 7, 2004 11:47:40 PM

I know most of how a CPU works, it's not that interesting. Most have 2 transformers with different taps at different numbers of turns to provide different voltages. They have diods to turn AC into DC (rectification). They have filters (Capacitors, which act as a buffer, and sometimes inductive coils, which block high frequency line noise). The rest is a bit more complicated. For example they have these transistors that controll voltage level (fine tune what comes out of the transformers), I believe they're called MOSFET's, those are attached to the sinks. Some have thermal protection, smart fan control chips, and overload protection, those are chips I'm not familiar with.

The most likely part of a power supply to fail is the capacitors.

Hmm, I actually had a manual on ATX12v power supply design specification, I might have downloaded it from formfactors.org...I deleted it yesterday.

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March 8, 2004 6:11:13 AM

Ok cool, I will take mine apart in a few days to see if I can identify those parts. I will also check out fromfactors.org. Thanx for ur help crash.

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March 8, 2004 8:59:26 PM

A special IC drives the mosfets and activly regulates the voltage they put out. My understanding is the mosfets switch on and off a few khz per second, this switching on and off is then filtered out by capacitors and inductors (as crashman pointed out). The only things that you could do without starting from scratch would be to use bigger capacitors and higher rated inductors other than that you really cannot do much. Another major factor that influences the psus output quality is the switching frequency of the driver/mosfet, the higher the better because after "smoothed" by inductors and capacitors a higher frequency mosfet/driver como will have less a distance between the peaks and vallys of each cycle.

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