Found that these run at about 10khz. this depends on the timing resistor and
cap. .01uf and 12kohm give 10k per the data sheet. not sure what the
formula is from there but the freq seems to vary linearly with changes in R
and C

"Kasper" wrote in message
. ..

"Jimmy" wrote in message
. com...
I am attempting to build an ATX power supply to work from 12VDC input.
The
device willl use the switching transformer from a COTS unit. My question
is
what frequency do this normally operate. At present I do not have a way
to
measure this from an operating power supply and would greatly appreciate
this info so I can continue my design work until I have acess to my test
equipment again.

Hey
I think your project will be cheaper to buy a finished 12V atx supply for
arround £200 or build a 160-200 VDC stepup converter and remove the
rectifier in a normal atx supply


Actually you would need about 300VDC to do this.

Probably what I will do is build a 12 dc to 120 vac inverter operating at
10khz. This should be considerable more efficent than one working at 60hz .
I have some old UPSs here that I may be able to modify.They converted 24
volts to 300vdc then the 300 vdc to 120 ac @60hz

What I wanted to do was rewind the switcher transformer in the ATX for 12
volts on the primary instead of 300. This would let me do all my conversions
in one box