More on Fav Designs - switchmode power supplies

[Doug Forbes]

>> [Dave Halliday]  I think that the question is more one of using
>> computer surplus supplies and these have been designed without analog
>> considerations.  With PC Clone supplies selling for $20 new, it would
>> be tempting to be able to re-work one of them to give +/- 15 volts at
>> a couple of amps - maybe a good design project...
>
>Is this feasible at all?  I'm philosophically very
>much in favor of gleaning what ever we can from the mass
>manufacturing machine; let it work to *our* advantage once
>in a while.  Since they're cranking out enough of these
>things to make them dirt cheap, it'd be excellent if they
>could be adapted to our purposes; even if that adaptation
>is a little convoluted (I think I have a couple of blown
>PC PSs in my basement right now).  Or would one still
>spend more in the process than on a from-scratch approach.
>
>steve - the scavenger!

All you have to do is find the +- 5 volt supply windings on the
transformer. Usually it's only a couple of turns. Rewind it for whatever
voltage you want and change the filter caps' for ones with the new working
voltage. The new windings can be snaked through the ferrite core without
much trouble. The supply remains regulated because of the feedback winding
being independant of the +- 5 and +- 12 volt windings.

Hope this helps some.

Doug