[sdiy] +/-12v from a single +12v psu - possible?

[WeAreAs1 at aol.com]

In a message dated 8/24/04 7:00:06 PM, julian at 22host24.com writes:

<< I dont know much about power supplies at all.  I have a +12v linear 
supply, 3.4A, with sense terminals (this meens its regulated, right?)


In short, is there a simple way to get a negative rail from this supply? >>

Julian,

Sense terminals?  Sounds like you have a nice supply.  Probably one of those 
Power One supplies, or something like it, right?  As Jim Patchell already 
said, it can be done -- but you should not do it.  Believe us, it will end up 
being cheaper and MUCH more elegant for you to simply get a real bipolar power 
supply.  For one thing, how much current will you need on your negative leg?  If 
you need more than one amp, you're asking for trouble.  How much noise can you 
afford to have your power supply create?  None, one would hope.  The methods 
one might use to derive the negative supply from the +12volt supply will 
surely create noise, or at least have the potential to create noise.  You'll also 
waste a bunch of current with your conversion circuitry.  And finally, you 
shouldn't try it because Jim Patchell told you not to -- his words carry a lot of 
weight around these parts!

BTW, you can't just simply connect a 7912 regulator to that supply to get a 
negative rail.  It will take much more than that.

Michael Bacich