What is a Switched-Mode Power Supply (SMPS)? What are the different components of SMPS ?

SMPS stands for Switching Mode Power Supply. It is a hardware component that supplies power to all other components of Motherboard. The power supply converts a volt AC (Alternating Current) into a steady low-voltage DC (Direct Current) usable by the computer and rated by the number of watts it generates. 

It is designed to convert 110 V or 230 V AC power from the mains to usable low-voltage DC power for the internal components of the computer. 

How SMPS Works ?

Interior View of an ATX Switched Mode Power Supply 

Input rectifier

The AC input from mains is first rectified in the SMPS using a rectifier to convert it into DC. The rectifier consisting of a full wave diode bridge or module that produces an unregulated DC voltage to the Smoothing capacitor. The input AC passing into the rectifier has AC voltage pulses that may reduce the power factor. So control techniques are used to force the average input current to follow the sine wave.

Inverter Chopper

This stage converts the rectified DC into AC using a power oscillator. The power oscillator has a small output transformer with a few windings at the frequency 20-100 kHz. Switching is controlled by a MOSFET amplifier. The output AC voltage is usually isolated optically from the input AC by using an Optocoupler IC for safety reasons.

Output Transformer

The output stage always monitors the output voltage by comparing with a reference voltage using a feedback system. For safety reasons, the output stage is isolated by an optoisolator as seen in the SMPS of computers. In some SMPS, Open loop regulation is used without feedback circuit and constant voltage is fed to the transformer input.

Output Rectifier

The output stage always monitors the output voltage by comparing with a reference voltage using a feedback system. For safety reasons, the output stage is isolated by an optoisolator as seen in the SMPS of computers. In some SMPS, Open loop regulation is used without feedback circuit and constant voltage is fed to the transformer input.

SMPS parts and Connectors

Power-IN:  A power cable is inserted here, the other end of which is connected to mains supply. The input supply gets converted to DC supply.

Power-OUT: It supplies the same AC supply that is fed to power-IN socket. The power-OUT connector is used to give supply to monitors or any display unit.

ATX Connector (20/24 Pin)

ATX connector. It is used to supply DC supply to the motherboards. Various color-coded wires connect to this connector and each colored wire supplies distinct DC voltage. 

4-PIN connectors

There are multiple 4-pin connectors that draw out from the SPMS unit. These connectors are used to supply DC power to various peripherals of computer like hard disk drive and CD-DVD-writers.

SATA-output connector

To feed the power to latest SATA hard drives and CD-DVD Writers, these connectors are used.

How to test computer SMPS

To check the supply, whether it is working properly or not, you can test it before fitting it in the cabinet. There is a simple way to test the SMPS, you just have to short the green wired connector to any black colored (ground) connector. If the SMPS is working perfectly, the fan of the supply will start to spinning.