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PC Power Supplies

PC power supplies deliver required DC power to the computer electronic sub-systems including Motherboard, Hard drive, CDROM drive, Keyboard, Mouse, and others. Usually, regular CRT monitors derive power separately from the mains. PC power supplies work by converting the AC mains power supply to required DC power supplies.

There are mainly two types of power supplies used in computers:

ATX Power Supply
ATX12V Power Supply

ATX12V power supplies are intended to be downward compatible with ATX power supplies.

As the PC components take more and more power, to enable the delivery of more +12 VDC current to the motherboard, additional 4-pins are provided for taking care of +12 V power supply. Thus, ATX12V will have a +12 V power connector, and a simple ATX power supply with not have the +12V power connector.

An ATX power supply, typically found in all Pentium class computers is shown below:

The voltages produced by ATX/ATX12V power supplies are:

+3.3 Volts DC
+5 Volts DC
-5 Volts DC
+5 Volts DC Standby
+12 Volts DC
-12 Volts DC

ATX and ATX12V power supply connectors pin configuration is shown below:


ATX12V Connector (it has 24 pins)	ATX Connector (it has 20 pins)

In addition to the Motherboard power connector, a power supply may have a CPU power connector, and an Auxiliary power connector.

Following are the most commonly used power supply connectors:

4 Pin Berg Connector: Used to connect the PSU to small form factor devices, such as 3.5" floppy drives. Available in: ATX & ATX12V
4 Pin Molex Connector 4 Pin Molex Connector: This is used to power various components, including hard drives and optical drives. Available in: ATX and ATX12V
20 Pin Molex ATX Power Connector: This is used to power the motherboard in ATX systems.available in: ATX (ATX12V have 24 pins)
4 Pin Molex P4 12V Power Connector: Used specifically for Pentium 4 Processor Motherboards. available in: ATX (integrated into the power connector in ATX12V)
6 Pin AUX Connector 6 Pin AUX Connector: Provides +5V DC, and two connections of +3.3V.available in: ATX/ATX12V

To power up an ATX or ATX12V PSU for testing, short pin 14 (PS_ON) with any of the ground pins.

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