On Fri, 02 Dec 2005 12:27:10 +0800, Frank wrote:



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I don't know what you people are talking about.
Back to my question, how do I make a +-5V?


+ - 5volts is actually 2 supplies, each giving out 5 volts, but one supply
has it's negative output connected to the 0 volt (common), the other
supply has its positive output connected to the 0 volt (common).

The effect is if you measure from the 0 volt (common) to one supply rail,
you will measure positive 5 volts, measuring from the 0 volt to the other
5 volt supply rail will be negative 5 volts.

Your original assumption that if you measured from the +5 rail
to the -5 rail you would find 10 volts is correct, but don't forget that
BOTH of the 5 volt supplies need to reference to the 0 volt as the current
drawn in the -5 circuitry may not balance the current drawn by the +5 volt
circuits..... without a 0 volt reference, you could end up with +3 volts
and -7 being supplied (the ratio between the + and - would depend on the
current being drawn from each of the 2 supplies)


Now, as for the +3 volt and +3.3 volts you also mentioned in your original
post, these would also have their negative rail tied to the 0 volt (common).

This is the 'normal' way that these type of multi voltage computer power
supplies are hooked up.

So your supply would have 5 output connections....
1, 0 volts (common to all 4 of the supplies!)
2, +5 volts
3, -5 volts
4, +3 volts
5, +3.3 volts

Pip