Switched Mode Power Supply (SMPS)

 Switch-Mode Power Supply

A switched-mode power supply or switch-mode power supply or SMPS, is an electronic power supply unit that incorporates a switching regulator that switches power transistors rapidly on and off (typically 40 to 80 thousand times per second) into the primary of a much smaller, more efficient transformer in order to stabilize the output voltage or current. By varying duty cycle, frequency or a relative phase of these transitions average value of output voltage or current is controlled.

SMPS converts the input AC voltage to the DC voltages needed by the personal computer. In older computers, AT SMPS were used. Currently ATX 12V SMPS are dominant.

SMPS supplies power to all components of a PC located in the CPU viz. motherboard, hard disk, floppy drive, CD ROM, fans etc. Most computer SMPS's have the appearance of a square metal box. They have a fan installed at one end and a large bundle of wires emerge out from the other end having:
One PC Main connector (20 or 24 pins) for power supply to the mother board.
4 pin Peripheral connectors for power supply to Hard Disk Drive, CD/DVD Drive etc.
One 4 pin floppy connector for power supply to floppy drive.
One Serial ATA connector for power supply to SATA devices.

Modern desktop SMPS's produce DC voltages of +/-5V, +3.3V and +/-12V outputs. The DC-DC converters on the motherboard step down SMPS voltage to the CPU core voltage and other low voltages needed for other motherboard components.

The electric energy is not normally used in the form in which it was produced or distributed. Practically all electronic systems require some form of energy conversion.

A device that transfers electric energy from a given source to a given load using electronic circuits is referred to as Power Supply.

A typical application of a DC power supply unit is to convert utility AC voltage into regulated DC voltages required for electronic equipment.

What is SMPS? 

Nowadays in most PSU the energy flow is controlled with semiconductors that are continuously switching on and off with high frequency. Such devices are referred to as switch mode power supplies or SMPS.

They offer greater efficiency compared with linear supplies because a switch can control energy flow with low losses: when a switch is on, it has low voltage drop and will pass any current imposed on it; when a switch is off, it blocks the flow of current.

In general, SMPS can be classified into four types according to the form of input and output voltages:

1. AC to DC,

2. DC to DC,

3. AC to AC, and

4. DC to AC