Switching power supplies rectify the AC line voltage and filter it at about 320VDC (voltage doubler rectifier). This DC voltge supplies a pulse-width regulator that operates at 40 to 100kHz. The high frequency is passed thru a transformer and is rectified back into a DC voltage.
Why do all that? Transformers are much much smaller at high frequencies and the pulse-width "switcher" regulates the output voltage without generating heat the way a linear regulator does.
The result is a small and light power supply, often less than 10% the size of an "iron" power supply (xformer, rectifier, filter cap). If a linear voltage regulator is used with the "iron" supply then the heat generated can be enormous, a problem the "switcher" doesn't have.
Mariss |