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“Opened up a whole bunch of SMPS (around 12) from different manufacturers and carefully examined them. The worst power supply was a Chinese made brand which advertised a 250 watt rating together with 5 volts at 25 amps on the cover plate but on examination used 1N5404s in the 5 volt supply line (3 amps max.) and completely deleted all input and output RF filtering components. As the quality moved slowly upward from the this extraordinary low, each of the supplies had various serious shortcomings except for the Seven Team units. Most common was the serious under rating of the 5 volt rectifier diodes and/or the omission of the RF filtering components, and only one supply type (the ST221/230/300W series) had a rectifier diode rating exceeding 15 amps for the 5 volt rail, even though top plate ratings were given as 20 or 25 amps.
These supplies use a 30 amp diode which supplies both the 5 volt rail and the 12 volt rail. They also have more generously proportioned heat sinks for both the switch mode transistors and rectifier diodes, as well as a transformer nearly twice the size of any other similarly rated supply (much easier and safer to re-wind etc). Furthermore the quality of components used and assembly standards are impressive. In short this series of supplies are continuously rated units, unlike any of the other designs examined which are intermittently rated at best. They are AT supplies, but the same comments apply to their supplies of ATX form which can also be modified.
If you must use another supply other than the Seven Team unit, then make sure that the 5 volt rectifier diode pair is rated at 20 amps minimum. The supply should also use 2 switch mode transistors together with an LM339 quad comparator and a TL 494 or equivalent IC as the pulse width modulator driving IC for the switch mode transistors.
If you do discover another high quality, mass produced, conservatively rated switch mode supply, please let me know who made it and its part number.
Read More Source :
http://www.users.on.net/~endsodds/smps.htm
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