| 摘要 |
PROBLEM TO BE SOLVED: To improve power factor by enlarging the conduction angle of an input current over a wide input voltage range while avoiding increase in size and cost, and to reduce switching loss by removing harmonic components of the input current. SOLUTION: The switching power supply comprises a rectifier circuit 5, a series circuit of a fourth winding 7d, a diode 21 and a smoothing capacitor 6, a series circuit of a diode 22, a first winding 7a and a first switching element 24, a series circuit of a diode 23, a third winding 7c and a second switching element 25, a second winding 7b, an error amplifier 20 outputting an error amplification signal, and a control circuit 30 performing PWM control of the switching element 24 by a first modulation wave generated based on the inverted amplification waveform of the product of the error amplification signal and the full-wave rectification waveform of an AC input voltage, and performing PWM control of the switching element 25 by a second modulation wave generated based on the error amplification signal and the full-wave rectification waveform of the AC input voltage thus turning both switching elements on/off alternately. COPYRIGHT: (C)2004,JPO&NCIPI
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