On 26 Oct 2005 12:03:41 GMT, Jim Yanik wrote:

default wrote in :

On Wed, 26 Oct 2005 06:23:45 -0400, Darmok
wrote:

Hi,

I've got an ATX computer PS pulled from an old computer.

I know that 2 of the 20 pins on the ATX power plug have to be jumpered
in order for the thing to power up .. not sure which ones .. was it
13-14? ... Also, after those are jumped, what turns on the supply?
Normally, there's a push button on the computer which goes to a 2 pin
header on the MB, which I assume sends some sort of "power up" signal
to the ATX supply ... how do I fake that out?

Thanks,

Bill

See http://www.pavouk.comp.cz/hw/en_atxps.html

For a schematic of an ATX supply. We owe Pavel Ruzicka for taking
the time to reverse engineer it. The info you're looking for is in
the theory of operation on the site.

The start up line 5V start bus is a separate tiny supply that is
running whenever the computer is plugged in (and turned on) It shares
the input rectifier and filters with the main supply but is otherwise
totally independent. A little three terminal regulator handles the
output.

He probably needs a minimum load on the PS output,too,most likely the +5V
line.

Possibly. The ATX diagram is representative of the type. In this
particular one both the +5 and +12 / -12 are referenced back to the
PWM via a voltage divider, which would suggest one or some
combination of supplies might need some minimum load to regulate
properly.

Hopefully he understands how dangerous the input circuits can be . . .
never mind the outputs.

The schematic does show some (minimal) load resistors on the outputs.

A good basic info on switching supplies:

http://repairfaq.ece.drexel.edu/sam/smpsfaq.htm

A better text on switching supplies with instructions on starting an
ATX and using a dummy load on the +5 supply:

http://www.wies-hs.eu.dodea.edu/Cour...oc/TrbPSGD.pdf
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