Be careful of assuming that the bride rectifier can handle the full load
current through only one half of its diode matrix, as this will be twice the
original design current!.
regards

Mike Pearce
Neutronics

I see the problem of the voltage doubler has been mentioned. A PSU intended
for the US market might have a straight bridge rectifier front end, which
would accept DC probably up to 190v?, though you are still a bit low. Dual
range supplies would be useless although they would accept around 350v DC.
I'm uncertain but I've seen bus voltages of 385v DC described, though maybe
this is the absolute max.

There is a power factor correction and universal input circuit shown in
databooks which converts almost anything to 380v, which I believe is fitted
to some of the larger industrial PSUs. An ATX psu with this type of true
universal input might be available at a premium. A module might be available
to put in front of the bog standard PSU but expect to pay 5 or 10 times the
cost of the PSU. If I remember there was one from either Astec or Vicor.

I've an idea how you could make a simple voltage booster but it would be a
last resort!

----- Original Message -----
From: Mark Peterson <markp@CANNONTECH.COM>
To: <PICLIST@MITVMA.MIT.EDU>
Sent: Wednesday, September 20, 2000 4:45 PM
Subject: [EE]: 125 VDC Input ATX Supply


> I need to power a PC from a nominal 125 VDC source.  The voltage may vary
> from 110 to 140 VDC.  I want a 300 W ATX supply that will be a direct swap
> with the existing 120 VAC unit in the PC.  I'm finding that this type of
> supply is very rare.  A couple vendors in China responded to my email
> inquiry stating that they would consider modifying their standard units.
> They lost interest when I told them I only need three or four of them.
>
> I've considered modifying a standard supply, which are abundant and cheap.
> I searched for schematics but found that they are nearly impossible to
get.
> It appears that the first thing a standard ATX supply does is rectify the
> AC input, filter it a bit, and then present it to the switching part of
the
> supply.  I'm wondering if I can simply connect the 125 VDC source just
> ahead of this switching section.  I'm going to do some experimenting but I
> wanted to check if anybody knows of a source of such a supply or if they
> have ever tried what I'm planning to attempt.
>
> Thanks.
>
> Mark P
>
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