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In Reply to: RE: Power supply design for low power PC posted by John Swenson on January 03, 2009 at 16:46:07
john, i jumped the gun and ordered the parts for the power supply from digikey, and scored the choke from mouser (they still had a few in stock).
i was going to build one up as a straight 12v for the sim phono preamp, which draws very low current, and figured the other one could be devoted to the sound card (and give me a good excuse to buy one, as soon as someone has them in stock!).
what sort of changes are required, other than the trafo, to accomodate either higher or lower current delivery? also, i have a custom wound electraprint trafo, with electrostatic shield, which is rated at, iirc, 12v and 1 amp. would that work as a drop-in replacement for the triad, in the straight 12v design?
thanks for hadling lots of questions,
mark
Follow Ups:
Hi Mark,
whether that 12V 1A is going to work depends on the current draw. At 1A, no way. At much lower current it might, let me know what current you need and I'll see if it will work or not.
Lower currents will work fine with the design as is, its just that the peak currents through the diodes can be made a little lower with a design optimized for the low current. It would be something like (these are off the top of my head not real numbers) at 1A you have 1.5A peak. At 0.5A you have 1A peak but you could get 0.7A peak with an optimized design.
Higher currents are a different story. Much above 2A is going to stress the chokes badly, they will get hot and probably will start buzzing. For higher currents it will definately take a different choke (the one that is one slot down in the 159 series. Its like 4mH I think) It will also take different cap values as well.
John S.
the word on the sound card (which i ordered today) is that it draws a max of about 20 watts on the 12 and 5v lines combines, but "typically much less". this from a 3rd party source who is reviewing the card, and probably got the info from a legit source.
i bought the big 12v tranny that you mentioned 36-2200, and what i think are some bigger heatsinks than you speced (to use for the 5 v line. i may try it as is, and see how it sounds just connected to the molex from the antec psu that came with my fusion case, so in case it sounds horrid, i won't waste the effort on the psu.
most of the parts are pretty cheap, and look like worthwwhile parts-bin inventory anyway, so if you;re game to do some tweeking, so am i. the card may be here in time for the weekend, so we shall see what happens.
sounds like i may be able to get away with building the supply pretty much as-designed, but using two chokes and maybe even two of everything except the tranny for the two different voltages. we shall see......
Unfortunately that might mean 3A on the 5V and .5A on the 12, 2A on the 5 and 1 on the 12 would be fine.
Send me an email with the specifics of what parts you have and I'll see what I can come up with.
John S.
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