AT. vs ATX

A typical installation of an ATX form factor Computer Power Supply.

There are two basic differences between old AT and newer ATX power supplies:

• The PC main connectors (see above description of connectors).
• The soft switch. On older AT power supplies, the Power-on switch wire from the front of the computer connected directly to the power supply. On newer ATX power supplies, the switch goes to the motherboard, allowing it to control the turning off of the system via a message from the operating system.

Wiring Diagrams

24 pins power supply connector.

20 pins power supply connector cut off 11,12,23,24

Connector

Various connectors from a computer PSU.

Typically, power supplies have the following connectors:

• PC Main power connector (usually called P1):

  

  Is the connector that goes to the motherboard to provide it with power. The connector has 20 or 24 pins. One of the pins belongs to the PS-ON wire mentioned above (it is usually green). This connector is the largest of all the connectors. In older AT power supplies, this connector was split in two: P8 and P9. If you have a power supply with 24-pin connector, you can plug it into a motherboard with a 20-pin connector. In cases where the motherboard has a 24-pin connector, some power supplies come with two connectors (one with 20-pin and other wi th 4-pin) which can be used together to form the 24-pin connector.
• 4-Pin Peripheral power connectors (usually called Molex for its manufacturer):

  

  These are the other, smaller connectors that go to the various disk drives of the computer. Most of them have four wires: two black, one red, and one yellow. Unlike the standard mains electrical wire color-coding, each black wire is a ground, the orange wire is +3.3 V, the red wire is +5 V, and the yellow wire is +12 V.
• 4-Pin Floppy drive power connectors (usually called Mini-connector): This is one of the smallest connectors that supplies the floppy drive with power. In some cases, it can be used as an auxiliary connector for AGP video cards. Its cable configuration is similar to the Peripheral connector.

• Auxiliary power connectors:

  

  There are several types of auxiliary connectors designed to provide additional power if it is needed.

• Serial ATA power connectors:

  

  a 15-pin connector for components which use SATA power plugs. This connector supplies power at three different voltages: +3.3, +5, and +12 volts.
• Most modern computer power supplies include 6-pin connectors which are generally used for PCI Express graphics cards, but a newly introduced 8-pin connector should be seen on the latest model power supplies. Each PCI Express 6-pin connector can output a maximum of 75 W.

Power Suppy Nuded

Internal

Inside the computer power supply is a complex arrangement of electrical components, including diodes, capacitors and transformers. Also, most computer power supplies have metal heat sinks and fans to dissipate the heat produced. The speed of the fan is often dependent on the temperature, or less often the power load. It may be dangerous to open a power supply even if it is not connected to anelectrical outlet , as high voltages may still be present in charged capacitors. However, for most PSU's this can be fixed by unplugging the PSU and then pressing the power-on button, which will drain the capacitors. Still, care should be taken as some PSU's require a load on the output in order to discharge the capacitors fully. Even when thePC is turned off, a PSU will draw some power from the wall, most of it going to power the 5Vsb (standby) rail.

Power Suppy Unit

A power supply (sometimes known as a power supply unit or PSU) is a device or system that supplies electrical or other types of energy to an output load or group of loads. The term is most commonly applied to electrical energy supplies, less often to mechanical ones, and rarely to others.

Computer power supply
From Wikipedia, the free encyclopedia

The top cover has been removed to show the internals of a computer Power supply Unit.
This article is about the common off-line switching power supplies used in desktop IBM PC compatible computers. There are many other kinds of computers with differing power supplies.
A computer power supply unit (Computer PSU), or Modular Power Supply Unit (MPS) is the component that supplies power to a computer. More specifically, a power supply is typically designed to convert 100-120 V (North America and Japan) or 220-240 V (Europe, Asia and Australia) AC power from the mains to usable low-voltage DC power for the internal components of the computer. Some power supplies have a switch to change between 230V and 115V. Other models have automatic sensors that switch input voltage automatically, or are able to accept any voltage between those limits.

The most common computer power supplies are built to conform with the ATX form factor. The most recent specification of the ATX standard is version 2.2, released in 2004. This enables different power supplies to be interchangeable with different components inside the computer. ATX power supplies also are designed to turn on and off using a signal from the motherboard (PS-ON wire), and provide support for modern functions such as the standby mode available in many computers.