| 摘要 |
An AC-DC converter is provided which comprises a booster circuit 9 which has a MOS-FET 6 and a reactor 4 connected in series to MOS-FET 6 for generating a DC output voltage VOUT; a voltage generator 11 for providing a reference voltage VR; and a control circuit 10 for comparing reference voltage VR and DC output voltage VOUT and generating outputs to turn MOS-FET 6 ON and OFF in response to the difference between reference voltage VR and DC output voltage VOUT. The control circuit 10 comprises a voltage detector 18 for measuring an input voltage VIN applied on an input terminal of the reactor 4; and a voltage retainer 22 for keeping output voltage VOUT on a level elevated by a substantially constant voltage VP+VR or VZ above input voltage VIN measured by voltage detector 18 such that booster circuit 9 simply raises input voltage VIN, even if on a lower level, by a substantially constant voltage with a smaller step-up ratio VOUT/VIN than that of a case for voltage increase up to a constant high DC output voltage regardless of a level of input voltage VIN.
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