文档介绍：外文文献
Switched-mode power supply
A switched-mode power supply (also switching-mode power supply, SMPS, or simply switcher) is an electronic power supply unit (PSU) that incorporates a switching regulator. While a linear regulator maintains the desired output voltage by dissipating excess power in a pass power transistor, the switched-mode power supply switches a power transistor between saturation (full on) and cutoff (completely off) with a variable duty cycle whose average is the desired output voltage. It switches at a much-higher frequency (tens to hundreds of kHz) than that of the AC line (mains), which means that the transformer that it feeds can be much smaller than one connected directly to the line/mains. Switching creates a rectangular waveform that typically goes to the primary of the transformer; typically several secondaries feed rectifiers, series inductors, and filter capacitors to provide various DC outputs with low ripple.
The main advantage of this method is greater efficiency because the switching transistor dissipates little power in the saturated state and the off pared to the semiconducting state (active region). Other advantages include smaller size and lighter weight (from the elimination of low frequency transformers which have a high weight) and lower heat generation due to higher efficiency. Disadvantages include plexity, the generation of high amplitude, high frequency energy that the low-pass filter must block to avoid ic interference (EMI), and a ripple voltage at the switching frequency and the harmonic frequencies thereof.
A note about terminology
Although the term "power supply" has been in use since radios were first powered from the line/mains, that does not mean that it is a source of power, in the sense that a battery provides power. It is simply a device that (usually) mercial AC power and provides one or more DC outputs. It would be more correctly referred to as a power converter, but long usage has established the term.
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