Electrical – Decreasing an ATX PSU voltage using the sense wire

atxpower supplyvoltage

I am trying to decrease the voltage of an ATX PSU to about 11.9 volts or so (it's 12.2v, a bit higher than what I would like for my project).

I did read some stuff about using the voltage sense wire with some resistors, but that only works to increase the voltage, not decreasing it. So I had this idea, of actually connecting the 3.3v sense wire to the +5v wire through a high resistor. Do you think this would work? And if so, what kind of pot range would you recommend?

Best Answer

I cannot see why connecting the 3.3V sense wire will have any affect on the 12V output. All it will do is try to pull the 3.3V output as low as possible, because the sense wire is feeding back 5V which tells the controller that the 3.3V output is over-voltage. It may even shut down the 3.3v output.

You could use a schottky diode in series with the 12V output. A good schottky will drop about 0.4V to give you 11.8V. What current do you need to draw from the power supply? You need to chose a schottky diode that is suitable for the current.