Switching power supplies have become the norm in almost all electronic systems. The switchers' excellent line and load regulation, high conversion efficiency, and compactness all contribute to-their popularity. Low-loss power MOSFETs and IGBTs (insulated-gate bipolar transistors), coupled with low-drop rectifiers, are at the heart of these switching supplies. A potential problem with some of these supplies is power factor, a measure of the effect the supply and the load have on the ac line. Some of you might remember from engineering school that the term "power factor" applied to the out-of-phase line current accruing from reactive loads. But the term also applies to harmonics injected back into the line. Stringent norms, especially in Europe, govern how much a system and its power supply are allowed to mess up the ac line with harmonics and out-of-phase signals. A variety of preregulator ICs and other products helps keep the line clean by providing power-factor correction.
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