PC power supply connectors

Motherboard power connector

Pin     Funtion         Wire color

1.      Power Good *    Orange
2.      +5Vdc           Red
3.      +12Vdc          Yellow
4.      -12Vdc          Blue
5.      Ground          Black
6.      Ground          Black

7.      Ground          Black
8.      Ground          Black
9.      -5Vdc           White
10.     +5Vdc           Red
11.     +5Vdc           Red
12.     +5Vdc           Red

NOTE: The colour information is just given as general reference. There is no strict standard for colouring so actual colouring used in your computer might be different !

* Power good pins gives +5V output when the voltage in the power supply outputs is according the specs. This power good pin is usually used for resetting purposes so that the motherboard reset signal is kept active until the power good signal is raised to +5V. This keeps the motherboard not trying to do anything before the operating voltages have stabilized. Some motherboards will only work if +5V is applied to the power good pins slightly after the power is turned on on other pins.

Floppy drive connector pinout

Normal floppy disk drives use normally +12V and +5V power supplies. They can load each power-line with current of less than 100 mA up to even more than 1 A. That depens on the model of the disk drive. Here is the power connector pinout when you look the connector on the drive back:

  /       \
 | 1 2 3 4 |

Pin Function

1   +5 V
2   Ground
3   Ground
4   +12 V

Using PC power supply for powering other circuits than PC

PC power supplies are specifically designed for PC electronics. Typically they work well in the current range a typical PC takes. If you take too low current form the ouputs, the power supply myght not work properly. If you load only one output, you might run into troubles of poor regulation. Typically PC power supplies regulate the output voltage of all outputs according the voltage in 5V output pin. If you don't put enough load to +5V output, you don't get stable +12V output from the power suppply.

Tomi Engdahl <[email protected]>