COMPUTER POWER SUPPLY:
PINOUT, CABLES, CONNECTORS


Home Reference Power Units Magnetic Units Power Supply
Color Codes Metric Conversion Engineering Jobs Calculators ATX pinout

Computer power supply units (PSU) deliver the power to the PC hardware via a number of cables with connectors. The generic specifications for various PSU form factors intended for use with desktop systems are defined in Intel's design guides, which are periodically revised. The latest standard is Design Guide rev.1.1 released on March 2007, which combines the requirements for CFX12V, LFX12V, ATX12V, SFX12V, TFX12V and FLEX ATX. For more information on form factors and the operation basics see our computer PSU guide and schematics.



Standard ATX-style power supplies for desktop PCs typically have the main power connector and additional 12V connectors, as well as peripheral, floppy drive, serial ATA, and PCI Express® connectors.
To support 75W PCI Express® requirements, in the new ATX systems the old 20-pin main connector has been replaced by a 24-pin connector. Accordingly, different ATX-style SMPS may use different number of power supply wires: see the diagram for pinouts of the old and new power connectors. The colors in this chart represent recommended colors of the wires in the PSU cables. The diagrams reflect the front (pin-side) view. The colors are shown here just for reference (you won't see them from the front). You need to look from the back of the connector to see the colored wires. Main connector uses Molex Housing Mini-Fit Jr. P/N# 39-01-2240 or equivalent (old part number 5557-24R), contacts: Molex 44476-1112 or equivalent, mating motherboard connector is Molex 44206-0007. The old 20-pin ATX connector was Molex 39-01-2200 or equivalent, mating motherboard part was Molex 39-29-9202. Under certain conditions new PSU can still be used in an old PC and vise versa- see our guide on connecting 20-pin PSU to 24-pin motherboard.

To start up a stand alone PSU for testing purposes, you need to short PS_ON pin to one of the common pins. Normally, PS_ON is activated when you press and release the computer power button while it is in standby mode.

ATX power connector pinout 24 and 20 pin
All 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 pins).

Note that between 1996 and 2000 Dell used proprietary (non-standard) units and motherboards with entirely different pinouts.

The rated current of the main Molex connector is 6A per pin. Which means with the old 20-pin style you can't get more than 18A from 3.3V and 24A from 5V. 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. It was removed from ATX12V spec v2.0 in 2003 because extra pins were added to the main connector.

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 bus. Most of today's motherboards supply their CPU with a separate 12 volt cable, which has 4 pins for ATX style (sometimes called P4) or 8 or more pins for EPS and non-standard high-power systems. Some PSUs may have three or four 12 volt 4-pin connectors. The part number for standard 4-pin connector is Molex 39-01-2040 or equivalent.



ATX connectots pinout- 12V, floppy, peripheral, aux

4-pin peripheral power connector go to disk drives, fans, and other smaller devices. The floppy drive connector as the name implies powers the floppy drive.

Note that pin numbers and wire numbers in Serial Power ATA (SATA) connector are not 1:1. There are three pins for each voltage. One pin from each voltage is used for pre-charge in the backplane. Mating serial plug of ATA devices contains both signal and power segments.

Some units may also have an optional 2x3 connector that can be used for ancillary functions, such as fan monitoring and control, IEEE-1394 power source, and a remote sense of 3.3 V.

Serial ATA (SATA) connector pinout


PSU over 450W designed for high-end discrete graphics cards normally have additional 2x3 or 2x4 connectors to supply extra power to graphics that require more than 75 watts total.
The 6-pin PCI Express® power connector is Molex part number 0455590002.
 Pinout of PCI Express power connector







Follow me on Twitter FIND POWER SUPPLY BY SPEC

Disclaimer and TOS | Privacy | Contact

© 2008, 2011 Lazar Rozenblat