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

[James Patchell]

Sorry, the bad news is yes, it can be done...but....you would be a whole 
lot better off just buying a new +/- 12 volt power supply.

Just running the voltage through a 7912 will not do the trick...

You will need to use a variation on a switching regulator to get -12 
volts...and trust me...it would be easier just to buy the power supply you 
need...

At 02:55 AM 8/25/2004 +0100, Julian wrote:
>Hello,
>
>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?)
>
>I want a +/- 12v supply, which can happily be some ammount under the 3.4A.
>
>Now someones informed me that i can just run it through somthing like a 
>7912 regulator / invertor, but i thought these needed some
>ammount of headroom?  The data sheet for the 7912 certainly lists the min 
>voltage at somthing arround +15v.
>
>In short, is there a simple way to get a negative rail from this supply?
>
>I know i could take it all appart and just use the transformer, etc. but 
>theres a lot of circitary on there allready, which, i
>assume (like i said - i dont know a lot about psus) is giving it a good 
>stable output, and it seems somewhat of a shame to junk all
>that.
>
>The psu is an advance-power unit, for which the manual is online here: 
>http://www.farnell.com/datasheets/21071.pdf
>
>(not that its very informative at all, in fact, so i wouldnt actually 
>bother looking ; )
>
>Any suggestions?
>
>Or just give up and build / buy a differnt psu?
>
>Cheers, Julian

         -Jim
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