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ATX Power Supplies

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PostPosted: Tue Nov 15, 2005 1:01 pm    Post subject: ATX Power Supplies Reply with quote

I am considering installing an ATX power supply in alternative equipment as they run fairly cool with a fan aswell as being cheap. The supplies required would be automatic switching 110/240 a.c input and outputs of +12V, -12V and +5V only are required (the -5V will not be used).
The question would be really How do these perform wouthout load and short circuit?
They would also reqire to be enabled at all times as the equipment would have external mains switched.
At the moment this is just an Idea and have not really looked into these supplies in any detail
All replies very much appreciated.
Many Thanks
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PostPosted: Wed Nov 30, 2005 4:34 am    Post subject: Reply with quote

Maybe this site is a good start:


there you will find a few pdf's with ATX power specifications.

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Joined: 12 Dec 2005
Posts: 4

PostPosted: Mon Dec 12, 2005 6:04 pm    Post subject: Reply with quote

somebody here: http://web2.murraystate.edu/andy.batts/ps/powersupply.htm
is using a pc supply as a desktop power supply, maybe you can gather some information from them..
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PostPosted: Thu Dec 15, 2005 4:14 am    Post subject: ATX Power Supplies Reply with quote

Many thanks for the information and is very useful.
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PostPosted: Sun Jan 01, 2006 4:21 am    Post subject: Re: ATX Power Supplies Reply with quote

I am pretty sure that all ATX switching power supplies require
a load to operate. Which voltage(s) require a load might
be different on different supplies. It depends on the design.

Switching power supplies are generally good for efficiency.
However a computer power supply is not in my opinion as
good a supply as you might find in other equipment.
Depending on what equipment we're talking about.

They have a certain point that they are most efficient.
I think typically that is at about the 70% of max load
point. Typically the efficiecy is bad at low loads. But
it does not matter particularly.

If the power supply is shorted then it's supposed to shut

Switching power supplies have it in their
design that they won't switch if their load is too high.
They depend on resonance to switch and a high load changes
the resonance to a point where it does not switch.
So the shut down with a short is self fullfilling.

You do need a minimum load to make the power supply work. Again
because of the design it needs some load to switch.
Usually it's the +5 that needs a load. Typically in my
experience of non-atx switching power supplies the various
voltages are interdependant typically through a commonly
wound switching transformer. A schematic would help you
see the interaction among the voltages just for fun.

Startup and holdup time - They are not as good for holdup time
as some supplies that I've worked with. Typically when the power
goes off the power is gone within 17ms. Some supplies hold up
for seconds or 200x longer. Just try your stereo at home. Turn
it off and see how long it operates.

Startup time is pretty good I think. No particular problems that I see.

One consideration since you mention cheap and cool is that
an ATX supply NEEDS the fan to operate or it will die. Some supplies
don't need a fan. Open frame supplies don't need fans. Some are
very cheap on the surplus market.

Power-One is one mfg who makes them. I have a bunch of them
with various multiple (2) voltages that I got for $10 ea. They are
linear instead of switching. Typically linear means better regulation.
And faster response to changing loads.

You didn't mention what the PS is for. We're all curious.

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