Power supply

 

Power Supplies

Electricity from wall outlets is provided in alternating current (AC). However, all components inside a computer require direct current (DC) power. To obtain DC power, computers use a power supply, as shown here, to convert AC power into a lower voltage DC power.

The following describes the various computer desktop power supply form factors that have evolved over time:

• Advanced Technology (AT) – This is the original power supply for legacy computer systems now considered obsolete.

• AT Extended (ATX) – This is the updated version of the AT but still considered to be obsolete.

• ATX12V – This is the most common power supply on the market today. It includes a second motherboard connector to provide dedicated power to the CPU. There are several versions of ATX12V available.

• EPS12V – This was originally designed for network servers but is now commonly used in high-end desktop models.

Power Supply Voltage

The different connectors also provide different voltages. The most common voltages supplied are 3.3 volts, 5 volts, and 12 volts. The 3.3 volt and 5 volt supplies are typically used by digital circuits, while the 12 volt supply is used to run motors in disk drives and fans.

Power supplies can also be single rail, dual rail, or multi rail. A rail is the printed circuit board (PCB) inside the power supply to which the external cables are connected. A single rail has all of the connectors connected to the same PCB while a multi rail PCB has separate PCBs for each connector.

A computer can tolerate slight fluctuations in power, but a significant deviation can cause the power supply to fail.