COMPUTER POWER SUPPLY:
PINOUTS, CABLES, CONNECTORS
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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 see our Computer Power Supply Guide and Schematics. For SMPS PSU operation basics see Power Supply tutorial.
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.
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 see our Computer Power Supply Guide and Schematics. For SMPS PSU operation basics see Power Supply tutorial.
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 power
connector has been replaced by a 24-pin connector. See the
diagram for pinouts of the old and new power connectors. The
colors represent recommended colors of the wires in the PSU power
cables. The diagrams show the front
(pin-side) view. The colors are shown just for reference,
but you need to look from the back of the
connector to see them. 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. Also see our guide on connecting 20-pin PSU to 24-pin motherboard. To power up a stand alone PSU for testing purposes, you need to short PS_ON pin with 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. All voltages are referenced to the same common (if you need to measure a voltage, connect the return lead of your voltmeter to any of the COM pins). |
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| Note that
between 1996 and 2000 Dell used
proprietary (non-standard) power supplies and motherboards with
entirely different pinouts. The current rating of the main Molex power connector is 6A/pin. 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 power 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 standard 4-pin connector is Molex 39-01-2040 or equivalent. |
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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. 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 connector 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. |
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Power supplies over 450W intended 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. |
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| © 2008 Lazar Rozenblat | |