need a -5 volt supply

[MicroRem]

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]

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.

[Lenp]

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

[dyarker]

... 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,

[psycho]

An LM7905 will give you -5v @ 1amp