AN628设计催功率因数转换预调节，L4981连续模式

AN628设计催功率因数转换预调节，L4981连续模式

AN628
APPLICATION NOTE
DESIGNING A HIGH POWER FACTOR SWITCHING
PREREGULATOR WITH THE L4981 CONTINUOUS MODE
by Ugo Moriconi




INTRODUCTION
Conventional AC-DC converters usually employ a full wave rectifier bridge with a simple capacitor filter to draw
power from the AC line. This "bulk" capacitor must be big enough to supply the total power during most of each
half-cycle, while instantaneous line voltage is below the DC rectified voltage. Consequentely, the line current
waveform is a narrow pulse, and the power factor is poor (