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I have a damaged ATX 230WCE power supply unit and wondered if I could find 12V, 5V, and 3.3V Voltage regulators inside. I tried looking in another unknown model psu and only found transistors and diodes which looked like voltage regulators. If I can find voltage regulators, what might the part numbers be? Keep in mind, this is a very old PSU. If I won't be able to find regulator inside them, then how does it have 12v, 5v, -5v, -12v, and 3.3v outputs?

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jonnyguru.com/… I'd check out reviews on jonnyguru for a basic disassembly/component overview of different computer PSUs. They are all built (as far as I've ever seen) quite similarly to this specific model; all PSUs I've ever seen are switch-mode supplies. –  Shamtam Jun 24 '12 at 15:52
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2 Answers 2

up vote 3 down vote accepted

As AndrejaKo mentioned, you may be able to find a LM7805 (or similar) linear regulator in the 5V standby section of the PSU. Look for it near the end of the purple wire.

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Computer supplies don't usually have integrated voltage regulators inside. But they have all the necessary elements of a voltage regulator inside. In a sense, the whole supply is a regulator.

There will be a voltage reference inside. The output voltage (possibly scaled by a resistor divider) is compared to the voltage reference, and the supply is turned "up" or "down" to make it match the voltage reference. The reference might be a TL431 or a 5.1V zener diode.

Computer supplies often regulate a main voltage (the 5V or 3.3V output) and arrange the other outputs to be ratios of the main one, by turns ratio on the transformer for example. This is not really precise but works well enough for powering computers.

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Actually it's not uncommon to today find 3.3 V linear regulators inside cheaper computer PSUs connected to the 5 V rail since there's usually low demand for 3.3 V lines now. Also in some units 5 V stand-by may come from a linear regulator. –  AndrejaKo Jun 23 '12 at 19:38
    
Why don't power supplies just use linear voltage regulators instead of having a bazillion components inside? And are the TL431s just programmable voltage regulators? That's what I understood from the datasheet. –  Seif Shawkat Jun 23 '12 at 19:56
    
Also, what could I extract that could regulate a 12v input to a 5v output from this PSU? –  Seif Shawkat Jun 23 '12 at 20:02
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@Seif Shawkat Linear regulators aren't used because of the need to have a huge transformer and the fact that linear regulators turn all extra voltage into heat. Look up switch-mode regulator on Wikipedia for a good explanation on that (or use search on this site, there are many questions about switch-mode regulators). As for salvaging, there's a good chance that nothing will be useful or easy to use. You can only hope that the powe supply has a linear regulator somewhere inside and hope that you can find it if it's there. –  AndrejaKo Jun 23 '12 at 20:16
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