When the industry began using voltage regulation modules (VRM) running off 12V2 to energize CPU and other motherboard components, the bulk of the wattage shifted to 12 volt buss. For more information on form factors see our computer PSU tutorial.

It was removed from ATX12V spec v2.0 in 2003 because extra wires were added to P1. That's why in early 2000's, some motherboards with 3.3V >18A and 5V >24A (mainly dual CPU AMD systems) used an auxiliary 6-pin power cable. This means with the old 20-pin style you can't get more than 18A from 3.3V and 24A from 5V. The rated current of the main Molex connector is 6A per contact. Some Apple models have this signal reversed.Īlso note that many brands such as Apple's Power Mac, Dell (during certain years), Compaq and HP used proprietary boards with entirely different pin designations- see this for info on some brand name power supplies.Īll voltages are referenced to the same common (if you need to measure any voltage, connect the return lead of your voltmeter to any of the COM contacts). Under normal operation, PS_ON# is activated when you press and release the computer power button while it is in standby mode. Otherwise, only 5V standby voltage will be present. If you want to do some testing of a stand alone unit, to start it up outside of a PC case you need to short PS_ON# line to the common. Well, under certain conditions a new PSU can still be used with an old PC and vise versa- see our guide on connecting 20-pin PSU to 24-pin motherboard.

People often want to know what to do if there is a mismatch. The old socket was 39-01-2200 and the mating header was 39-29-9202. Mating motherboard header is Molex 44206-0007. The colors are shown here just for reference (you won't see them from the front). The colors in this chart represent recommended wire colors in the PSU cables. Accordingly, different ATX-style PSU may use different number of power wires: see the pinout diagram to the right. To provide the additional wattage, the old part has been replaced by a new 24-pin P1. When PCI Express® bus was introduced, PCIe cards needed up to 75W extra. The original ATX systems had 20-pin main connector P1. Standard ATX power supplies typically have the main power connector P1, additional 12V connectors, as well as peripheral, floppy drive, serial ATA, and PCI Express® receptacles, which we will describe below.įor the operation basics of SMPS PSU see our power supply tutorial.

Download molex pinout