Sorry but me braincell is in overload. I do not understand the logic behind
Mike Pearce's statement regarding currents. Power dissipation I would
understand as with AC it would be spread across 4 diodes instead of 2 with
DC.

My previous message regarding Inverters appears to have not been posted, I
appologise for this repeat of information if it has. We retail a 300 Watt
modified Sine Wave Inverter for #56. The "modified Sine Wave" bit of the
circuitry is done by chopping up the output of a 12 (or 24) to 350 volt DC
converter. If you want to start modifying products, eliminate the chopping
circuitry by cutting 2 track in the pcb (one if the 350 volts the other is
the 12 volts to the waveform generating logic) take the 350 volts dc to the
output. Then in the ATX PSU identify the outputs of the bridge
rectifier/voltage doubler and connect those points to the modified Inverter
output. This will eliminate unneccesary stages and improve efficiency a
little. Its not the most elegant solution but its quick, relatively cheap,
and it works.

Regards
Chris Carr

Oliver Broad wrote:

> Something spooky seems to have happened, I recognise my message but I
never
> saw it in the piclist, I have echo on, and my other messages came back.
I've
> seen some other strange effects on Piclist which I might raise in a
seperate
> message.
>
> Good point about the rectifier, Though I believe the devices are in
reality
> limited by their thermal characteristics, not by an absolute max current
> (whatever the datasheet says). Provided the PSU is only ever used for DC
> input a fused diode or two would probably improve it, I'm sure they almost
> always fail short.
>
> I'm thinking that if all else fails/is too expensive then a boost supply
> could be made using a largeish inductor and a Power Integrations topswitch
> switchmode chip, TO220 package three leads, switch ground and control. I
> haven't used one yet but they seem to be the lowest part-count SMPS parts
> I've seen yet.
>
> I think modifying the power supply could mean redesigning and rewinding
the
> transformer among other things, I know the turns ratio does not fix the
> output voltage but it does set a range over which the supply can work.
>
> Oliver.
>
> ----- Original Message -----
> From: Mike Pearce <MIKE@NEUTRONICS.CO.UK>
> To: <PICLIST@MITVMA.MIT.EDU>
> Sent: Monday, September 18, 2000 2:46 PM
> Subject: Re: [EE]: 125 VDC Input ATX Supply
>
>
> > 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!
> >
>
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