| 摘要 |
PROBLEM TO BE SOLVED: To provide a switching power supply for reducing noise and improving a power factor. SOLUTION: A multiplier 9 multiplies an input voltage Vin by an error voltage Verr amplified by an amplifier 8. A first threshold signal Vth1 is generated, and has the same phase and similar figure as the input voltage Vin and an amplitude in proportion to the error voltage Verr. A second threshold signal Vth2 is generated from the first threshold signal Vth1 by a resistance dividing circuit 14R. Since a switching element 7 is controlled so as to be turned on/off through a drive circuit 13, an input current detected by a resistor 12 falls into a range between two thresholds. The power factor is improved by extending a duty ratio. The noise is reduced by extending a switching frequency. COPYRIGHT: (C)2007,JPO&INPIT
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