摘要 |
PROBLEM TO BE SOLVED: To provide a switching power supply reducing noises and improving power factor. SOLUTION: An error voltage Verr amplified by an amplifier 8, and an input voltage Vin, are multiplied together by a multiplier 9 to generate a first threshold value signal Vth1, which is in-phase with and similar in waveform to the input voltage Vin, and proportional in amplitude to the error voltage Verr. A second threshold value signal Vth2 is generated from the first threshold value signal Vth1 by a series circuit of a diode 14G and a resistor 14B. The power factor is increased by on/off-control of a switching element 7 via a drive circuit 13, so that a current detection signal, which is detected by a resistor 12 and corresponds to an input current, falls between the two threshold value signals Vth1 and Vth2. Since the off time is not fixed, the noise spectrum is spread and increase of the switching frequency is suppressed. Noise reduction is thus achieved. COPYRIGHT: (C)2009,JPO&INPIT
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