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Old 12-04-2012, 04:53 PM   #445
EVs Rule
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Join Date: Apr 2011
City & State: Leeds
My Country: UK
Line Voltage: 230Vac 50Hz
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Default Re: the gutless, bloated, and fried power supply hall of shame

Not with the fake 330F. If they are real, I put continuous power at 150W; but if they are fake 220F (from the size they look to be around that, and I've seen it before in cheapies) I'd say squeezing any more than 100W would be asking for trouble.

Problem is with those caps being so small, the transistors have to work in overdrive to put more current through the transformer to keep the output stable. They usually don't manage it so you see 600~1000mVp-p of ripple on the output in a 100Hz sawtooth wave. See this picture from a "430W" PSU with 350W load. It used 680F primaries, predicting 340W max output... and the ripple is already through the roof:

Notice how the ripple peaks every 10ms -- this is no coincidence. It is at 100Hz, so is due to lacklustre primary bulk caps.

And of course, the transistors don't last as long... probably one of the contributions to them going bang!
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