need a -5 volt supply

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MicroRem
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need a -5 volt supply

Post by MicroRem » Fri May 07, 2010 4:06 pm

Newer AT style computer power supplies omit the traditional -5volt function (white wire, I believe it was used to power the old ISA slots). Its getting difficult to find any of the older styles, many advertise the -5 in the specs but when I order one to test I find it's not there.
I need the -5 volt 500 ma supply to power another section of larger machine that uses the -5 supply in the control PC for another part of the machine it (the PC) controls. Is there a simple way to derive a -5 volt supply from one of the other sections?

Thanks all

Tom

Robert Reed
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Re: need a -5 volt supply

Post by Robert Reed » Fri May 07, 2010 4:16 pm

I think the easiest is to purchase a DC-DC converter. They are everywhere and in any flavor you desire. A little web searching should turn up the item you are looking for at a price you can afford.
But I am sure this has already occurred to you so maybe there are reasons I am not aware of.

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Lenp
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Re: need a -5 volt supply

Post by Lenp » Fri May 07, 2010 5:47 pm

Why not add a wallwart for the -5VDC? Cheap, Quick and available!
Len

“To invent, you need a good imagination and a big pile of junk.” (T. Edison)
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dyarker
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Re: need a -5 volt supply

Post by dyarker » Fri May 07, 2010 9:21 pm

... many advertise the -5 in the specs but when I order one to test I find it's not there.
The wire isn't there, or no -5V when measured?

Remember, PC supplies shut themselves down when there is no load. So when testing out of equipment and without enough dummy load; you won't see any voltage.

Cheers,
Dale Y

psycho
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Re: need a -5 volt supply

Post by psycho » Sat May 08, 2010 12:31 am

An LM7905 will give you -5v @ 1amp

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