POWER SUPPLY

Power supply unit(sometimes abbreviated power supply 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. plugs into an ordinary outlet, but contains a transformer to lower and regulate the voltage level of the electricity provided to the computer

The power supply is a small box inside the computer; it is an important part of a computer because it provides power in a form that is suitable for every other component inside or attached to the computer in order for it to work. If only a small voltage is needed the main supply of power needs to be transformed to a suitable level in order for the component to work in other words it converts the alternating current (AC) line from your home to the direct current (DC) needed by the personal computer

The regulated power supply technology can really be divided into two distinct forms; firstly, the linear or series regulator and, secondly, the switched-mode conversion technique. Switched-mode technology is multi-facetted with a wide variety of topologies achieving the end result of providing a regulated DC voltage. The main differences between the linear and switched-mode regulator are in the size, weight and efficiency. The linear regulator utilises simple techniques of controlled energy dissipation to achieve a regulated output voltage independent of line and load variation. It is, therefore, inherently inefficient, especially when a wide input voltage range has to be catered for.

Power supplies, often referred to as "switching power supplies", use switcher technology to convert the AC input to lower DC voltages. The typical voltages supplied are:

The 12-volt is used to run motors in disk drives and fans, while the 5-volts and 3.3-volts are typically used by digital circuits. The main specification of a power supply is in watts

POWER in watt =VOLTAGE in volts X CURRENT in amperes or amps.

The operating system can send a signal to the power supply to tell it to turn off. The push button sends a 5-volt signal to the power supply to tell it when to turn on. The power supply also has a circuit that supplies 5 volts, called VSB for "standby voltage" even when it is officially "off", so that the button will work.

Power Supply Standardization
Over time, there have been at least six different standard power supplies for personal computers. Recently, the industry has settled on using ATX-based power supplies. ATX is an industry specification that means the power supply has the physical characteristics to fit a standard ATX case and the electrical characteristics to work with an ATX motherboard.
PC power-supply cables use standardized, keyed connectors that make it difficult to connect the wrong ones. Also, fan manufacturers often use the same connectors as the power cables for disk drives, allowing a fan to easily obtain the 12 volts it needs. Color-coded wires and industry standard connectors make it possible for the consumer to have many choices for a replacement power supply.

Power Supply Wattage
A large supply may be needed if you use every available slot on the motherboard or every available drive bay in the personal computer case. It is not a good idea to have a 250-watt supply if you have 250 watts total in devices, since the supply should not be loaded to 100 percent of its capacity. To be in safe side a 400-watt switching power supply will necessarily use more power than a 250-watt supply
According to PC Power & Cooling, Inc., some power consumption values (in watts) for common items in a personal computer are:

Note:Power supplies of the same form factor ("form factor" refers to the actual shape of the motherboard) are typically differentiated by the wattage they supply and the length of the warranty.

Power Supply Problems
The PC power supply is probably the most failure-prone item in a personal computer. It heats and cools each time it is used and receives the first in-rush of AC current when the PC is switched on. Typically, a stalled cooling fan is a predictor of a power supply failure due to subsequent overheated components. All devices in a PC receive their DC power via the power supply.

Sometimes a power supply is a buffer circuit that provides power with the characteristics required by the load from a primary power source with characteristics incompatible with the load. It makes the load compatible with its power source. A power supply is sometimes called a power converter and the process is called power conversion. It is also sometimes called a power conditioner and the process is called power conditioning.

A typical failure of a PC power supply is often noticed as a burning smell just before the computer shuts down. Another problem could be the failure of the vital cooling fan, which allows components in the power supply to overheat. Failure symptoms include random rebooting or failure in Windows for no apparent reason.

For any problems you suspect to be the fault of the power supply, use the documentation that came with your computer. If you have ever removed the case from your personal computer to add an adapter card or memory, you can change a power supply. Make sure you remove the power cord first, since voltages are present even though your computer is off.

To avoide you suspection for power supply you need UPS