WAYNE CHIRNSIDE wrote in a message to ROY J. TELLASON:



 WC>  You might need to adjust the torroid core parameters

 RJT> I wouldn't even begin to know where to start with that one.

 WC> Actually thinking it through again I cannot see this being a
 WC> problem at all.  Why would a core care if the amps were on one 
 WC> side, the other or both?  As it stand those cores carry a LOT of 
 WC> amperes on the secondary.

Yep,  and lots of amps means heavier wire -- where are you gonna put it? 
I'd bet that there isn't room for it in existing cores,  so you're talking
about rebuilding the transformer into something a bit bigger than what you
started with.  Not something I'd care to tackle,  but then I never did get
along all that well with inductors...

 WC> and change the drive oscillators capacitor if as I suspect the
 WC> driver is setup push pull at a frequency determined by the
 WC> inductance and capacitance.

 RJT> I think that the oscillator is likely to be in the chip that runs
 RJT> things in there.

 WC>  Could very well be a duty cycle device and suspect you're quite 
 WC> correct in this.

I actually did stumble across one site (Russian?) where they provided a
schematic of an ATX power supply and an explanation of how it worked.  I
can email it to you if you like.  Unfortunately it doesn't match what I
have on hand here to try and figure out...  :-)

 WC> I merely was referencing a project I did when I very successfull 
 WC> employed a color T.V. flyback transformer where I applied an 
 WC> external winding, powered it from a stiff 12 volt supply with 
 WC> spectacularly successful results.

Yeah,  but on those you have a lot more core to work with -- and those
cores have a gap built into them so they won't saturate,  I don't know if
that's the case with switching power supply inductors or not.



 RJT> What wattage were the units you saw?

 WC> I believe around 85 watts which is way to light.

 RJT> Yep.

Smallest PS I have here is one I took out of an old P-B that was getting
tossed,  it's marked at 100W max output.

 WC> Seems manufacturers can make such supplies for those huge wattage
 WC> car stereo amplifiers and they are pretty darn cheap.

 RJT> Sure,  but those are only designed to put out _one_ voltage,  and
 RJT> there's no telling what the other specs are,  in terms of how tight the
 RJT> regulation needs to be,  etc. -- probably not very.  While there's
 RJT> *some* comparison I don't think they're exactly what you could call
 RJT> parallel.

 WC> That's where the duty cycle switching control chip enters the
 WC> picture. IIRC it's regulated to the 5 volt output with the other
 WC> rails regulation being tied to that. I STILL say it should be 
 WC> quite simple.

Ok.

 WC> Have not done it but have done similar as above.

Well,  if you go ahead and build one I'll sure be interested in hearing
about how well it works.  :-)

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