Switched Mode Power Supply

Switched-Mode Power Supply, SMPS is a type of power supply that uses a switching regulator to control and stabilize the output voltage by switching the load current on and off. These types of power supplies offer a greater power conversion and reduce the overall power loss.

A switched-mode power supply, switching-mode power supply or SMPS, is an electronic power supply unit (PSU) that incorporates a switching regulator. While a linear regulator uses a transistor biased in its active region to specify an output voltage, an SMPS actively switches a transistor between full saturation and full cutoff at a high rate. The resulting rectangular waveform is then passed through a low-pass filter (typically an inductor and capacitor) to achieve an approximated output voltage. Advantages of this method include smaller size, better power efficiency, and lower heat generation. Disadvantages include the fact that SMPSs are generally more complex than linear supplies, generate high-frequency electrical noise that may need to be carefully suppressed, and have a characteristic ripple voltage at the switching frequency.

SMPS can be classified into four types according to the input and output waveforms, as follows.

* AC in, DC out: rectifier, off-line converter
* DC in, DC out: voltage converter, or current converter, or DC to DC converter
* AC in, AC out: frequency changer, cycloconverter
* DC in, AC out: inverter
A switched-mode power supply, or SMPS or switching regulator, is an electronic power supply circuit that attempts to produce a smoothed, constant-voltage, output from a varying input voltage.

Switched-mode power supplies may be designed to convert from alternating current or direct current, or both. They generally output direct current, although an inverter is technically a switched-mode power supply.

Switched-mode power supplies operate by using an inverter to convert the input direct current supply to alternating current, usually at around 20 kHz. If the input is alternating current but at a lower frequency (such as 50 Hz or 60 Hz line power) then an inverter is still used to bump the frequency up.

This high frequency means that the output transformer of the inverter will operate more efficiently than if it were run at 50 Hz or 60 Hz, due to hysteresis in the transformer core, and the transformer will not need to be as large or heavy. This high-frequency output is then fed through a rectifier to produce the output direct current.

Regulation is achieved through feedback. The output voltage is compared to a reference voltage and the result used to alter the switching frequency or duty cycle of the inverter oscillator, which affects its output voltage.

Switched-mode PSUs in domestic products such as personal computers often have universal inputs, meaning that they can accept power from most mains supplies throughout the world, with frequencies from 50 Hz to 60 Hz and voltages from 100 V to 240 V.

Unlike most other appliances, switched mode power supplies tend to be constant power devices, drawing more current as the line voltage reduces. Also, in common with many static rectifiers, maximum current draw occurs at the peaks of the waveform cycle. This means that basic switched mode power supplies tend to produce more harmonics and have a worse power factor than other types of appliances. This may cause stability problems in some situations such as emergency generator systems. However, higher-quality switched-mode power supplies with power-factor correction (PFC) are available, which are designed to present close to a resistive load to the mains.

SMPS stand for Switched Mode Power Supply. It is the power supply section for any Computer.
It is the component to which you connect the power supply cable at the back of your computer. It converts the 110V AC (220 V AC if you are in UK) into multiple DC power lines which supply power to the motherboard, drives etc.
Unlike the old power supplies of the past, which used large, heavy transformers, SMPS’s use transistors switching DC power on and off at very high rates (typically 40 to 80 thousand times per second) into the primary of a much smaller, more efficient transformer. SMPS, in addition to being lighter and more efficient, afford better regulation of voltages. They’re a bit harder to work on, but the benefits far outweigh that little inconvenience. FYI, they can also be called DC-DC converters since in a conventional setup, the house current is converted to DC by a rectifier before it goes into the SMPS. Nearly all consumer electronics products are using SMPS nowadays.