Every electrical or electronic device needs power for work and the computer is not exception to it. Computers, too, have a particularly designed power supply component known as Switch Mode Power Supply (SMPS). SMPS converts raw input power to controlled voltage and current for the operation of various components of the computer. SMPS uses switches for high efficiency. The primary function of SMPS is to convert the alternating current (AC) power available in homes into direct current (DC) required for a computer system. In desktop computers, a metal box found in the corner of the CPU case supplies
power to various components in the CPU box. The power supply converts 115-230 volt AC into DC that is required for computer components to work.
The terms such as voltage, AC, DC, etc., are closely associated with the power supply or SMPS. Voltage is an electric potential difference between two points and is measured in volts. AC stands for alternating current. It is an electric
current whose magnitude and direction vary cyclically. DC stands for direct current. It is considered as the constant flow of electrons in a single direction from low to high potential. Computers use DC power. Because of the advantage of alternating current over direct current in transforming and transmission, electric power distribution today is nearly everywhere alternating current.
The SMPS or power supply of a computer comes in different form factor styles. The form factor refers to the physical dimensions of a component. The form factor of the power supply must match with the form factor of the computer case into which the SMPS is inserted. There are various industry standard form factors available. Some of the commonly used form factors with their characteristics are given below:
The LPX form factor style power supply has exactly the same motherboard and disk drive connectors as the previous standard power supply form factors. LPX form factor power supply differs in its reduced size that allows building much smaller and consumer oriented PCs. Due to their small size, they can be put into almost every type of computer cases.
The ATX form factor is developed by Intel in 1995. ATX is similar to LPX in physical dimensions. The difference between the two is that the power pass through-outlet for the monitor has been removed from ATX. Another difference is that in ATX, the cooling fan is mounted along the inner side of the power supply. With this kind of arrangement, the fan draws air in from the
back of the chassis and blows it inside across the motherboard.
The SFX form factor style power supply is 100 mm wide, 125 mm deep, and 63.5 mm in height. It includes a 60 mm power supply fan for cooling. The main SFX motherboard connector is in the same shape and size as the ATX connector. The one difference here is that the SFX power supply specification does not support the -5V compatibility voltage and, therefore, should not be used with motherboards that have ISA slots.