View Full Version : PSU output 18v 3A DC for inside PC

17-11-2003, 12:09 AM
is there any way i can use my normal 400w PSU to convert it to this output?
it is because i have a mini PC that i want to run inside my PC
it normally runs on an adaptor
i don't mind having to make a circuit
my PSU says this
DC output
+3.3V @ 14A
+5V @ 40A
+12V @ 14A
-5V @ 0.5A
-12V @ 0.8A
+5VSB @ 2A
i understood it until it came to the VSB
if i can, i spose i will have to crack out the 5th form electronics book

17-11-2003, 09:15 AM
SB = StandyBy It is a 5 Volt supply that provides power to motherboard circuitry, when PC is off. This is so you can use a non-locking push button to start your computer, and such things as wake-on-ring etc...
BTW, only used on ATX machines.
You won't be able to produce the 18Volts from your power supply as all negative's are commoned, so making the ability to use a 12V and 5V in series a non-starter.

17-11-2003, 09:16 AM
You would need to redesign the power supply to produce an 18v rail.
All present outputs share a common 0v rail, so you can't series the 5 and 12 volts to get 17v.

In particular you would need to rewind the switchmode transformer and replace the filtering stages. It would be much easier to put a normal laptop switchmode power supply inside the case, as 18v at 3 amps is typical for these.

You really do need a switchmode though, I made a transformer based 18v/4 amp regulated supply using conventional means, and it requires a lot of heatsinking, plus its quite expensive as well.

Not sure what you mean by "understood it until it came to the VSB"?
+5V Stand By (+5VSB) is the 5 volt rail thats alive in the standby mode as far as I know, its nothing special.

Graham L
17-11-2003, 03:59 PM
A recent issue of Silicon Chip magazine tells how to convert a PC supply for 13.8V (a standard value) but 18V is just a few more turns on the rewound transformer.

However, you will probably find it a lot easier to buy one. :D I think Jaycar sell a supply for laptops, with adjustable output, which will do what you need.