Hello,
Can the output voltage of computer power supplies be varied. I would like to get about 7 volts from the 5v output. Would putting a potentiometer on the brown sense wire fool the supply into putting out more voltage. There are two pot's on the board of a number of supplies that I have. What are they for. They vary the voltage a small amount when twisted.
Andy
That is not going to work. The potmeters are probably for fine adjustment. You'll need to modify the feedback loop. This means that all output voltages will go up (or down)!
-- Reply to nico@nctdevpuntnl (punt=.) Bedrijven en winkels vindt U op www.adresboekje.nl
Usually, a sense wire internally connects to the power wire via a diode. If a sense wire is broken, then it will never see more than
0.7 volts difference from the power wire; power supply will not increase voltage into runaway.Better is to learn the supply's controller circuit, find resistors that regulate voltage, and replace / shunt those resistors. But another problem exists. Properly constructed power supplies must have other circuits so that voltage cannot exceed maximums. Better is to lower 12 volts to 7. Increasing 5 volts to 7 will trigger overvoltage protection circuits that all minimally acceptable supplies must contain.
Reminds me of the time I contacted Phihong and asked how I can get 3 more voltages out of one of their switching supplies. I actually got practical info and got the supply working with 3 more volts.
D from BC
You will be better off tracing the schematic first.
As another poster explained, you will have to change the feedback circuit AND also modify the over-voltage cut-off circuit that would normally trigger before 7V to shut down the power supply to protect the motherboard etc.
The circuit may not be very happy running at 7V - that's 40% above normal. Check the voltage rating of the electrolytic capacitors on that rail, amongst other things. If you won't be loading it heavily and you don't require very high reliability then you might get away with it. Otherwise you could possibly reduce all of the supply voltages until the "12V" rail measures 7V instead. Make sure the fan goes fast enough with the voltage reduced - you might have to make some changes to fix that, e.g. put the fan between the +7V rail and one of the -ve rails.
If you only require a small current then you could use the power supply un-modified, and add a linear regulator to reduce the 12V rail down to the voltage that you require.
Good luck, and be careful of the high voltage and things that might go bang
- safety glasses and an isolation transformer would be a good idea, and don't put your hands near it when the power is on or the capacitors are still charged up.
Chris
ElectronDepot website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.