switching regulators.docâ€
A switched-mode power supply, switch mode power supply, or SMPS, is an electronic power supply unit (PSU) that incorporates a switching regulator — an internal control circuit that switches the load current rapidly on and off in order to stabilise the output voltage. Switching regulators are used as replacements for the linear regulators when higher efficiency, smaller size or lighter weight are required. They are, however, more complicated and more expensive, their switching currents can cause noise problems if not carefully suppressed, and simple designs may have a poor power factor.
SMPS can also 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
AC and DC are abbreviations for alternating current and direct current.
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 rated frequencies from 50 Hz to 60 Hz and voltages from 100 V to 240 V (although a manual voltage "range" switch may be required). In practice they will operate from a much wider frequency range and often from a DC supply as well.
In the case of TV sets, for example, one can test the excellent regulation of the power supply by using a variac. For example, in some models made by Philips, the power supply starts when the voltage reaches around 90 volts. From there, one can change the voltage with the variac, and go as low as 40 volts and as high as 260, and the image will show absolutely no alterations.
In electronics, a linear regulator is a voltage regulator based on an active device (such as a bipolar junction transistor, field effect transistor or vacuum tube) operating in its "linear region" (in contrast, a switching regulator is based on a transistor forced to act as an on/off switch) or passive devices like zener diodes operated in their breakdown region. The regulating device is made to act like a variable resistor.