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From: mcarrick@gara.une.oz.au (Mick Carrick)
Newsgroups: sci.electronics
Subject: Re: Power supply help!
Message-ID: <6524@gara.une.oz.au>
Date: 23 May 91 08:33:42 GMT
Article-I.D.: gara.6524
References: <1991May22.060038.20285@booth.uucp>
Organization: University of New England, Armidale, Australia
Lines: 54

From article <1991May22.060038.20285@booth.uucp>, by jrn@booth.uucp (Jim Norton):
> 
> Hi everyone!
> 
> A friend and I are designing a Pulse Width Modulation Amplifier that will
> pump out 800 watts ( 200 watts / 4 channels) and have come up with some
> specifications for the whole circuit. (assuming 8 ohm speakers for load)
> 
> It seems obvious that we need a power supply that can put out 40 Volts at
> 20 Amps and be highly filtered.
> 
> Does anybody know how to build such a beast of a power supply?  Is it possible
> to buy one? If so how much?  Has anybody got any schematics?  Any know where
> is the best place to get these higher power handling diodes and capacitors?
> 
> We need any help that people can offer..... We have the rest of the amplifier
> designed.... Just need the power supply now....    :-()


In Audio Amateur 1/1980, James Boak published a low impedance
regulated power supply that I have successfully modified to 
allow 15 Amp @ 70 V output. Just use heavier pass transistors
and modify a couple of resistors and capacitors as suggested
by Boak. A followup note by Walt Jung contained suggested 
modifications which are well worth including.

The power supply is quite robust. In testing a power amp
using these supplies, I accidently used a 0.2 Ohm resistor
across the output instead of 200 Ohms, causing about a
70 Amp current to be drawn. The output track (1/4 inch wide)
on the board vaporized but the rest of the supply survived.
I was quite impressed.

If you can't find the articles mentioned, email me about it.
I am currently trying to find some reasonable PC board 
design software preferably on a Mac, to redesign the very
clutzy board I am now using, so can't offer a sensible board
design at present.

I think back issues of Audio Amateur can be ordered from 
PO Box 576, Peterborough, NH, 03458, USA.

Good luck with your beast

Mick Carrick



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