| 摘要 |
PROBLEM TO BE SOLVED: To reduce the power loss of a switching element of an AC-DC con verter when a supplied voltage from an AC power source is low and to improve the conversion efficiency. SOLUTION: This AC-DC converter controls on/off of a MOSFET (6) according to a control signal VG of a control circuit (10) in response to a detected voltage VP of a peak voltage detector (18) for detecting a peak voltage VP of an AC input voltage VIN of an AC power source (1), and holds a DC output voltage VOUT of a booster circuit (9) at a level of a reference voltage VR from the peak voltage VP of the AC input voltage VIN of the power source (1) at a high voltage. Thus, when the voltage VIN of the power source (1) is low, the output voltage VOUT of the circuit (9) is controlled to low, and a boosting ratio VOUT/VIN is suppressed to a small value. Accordingly, when the voltage VIN supplied from the power source (1) is low, a current IDS flowing to the MOSFET (6) is reduced. Therefore, a power loss generated in the MOSFET (6) is decreased, and the conversion efficiency of the converter can be improved.
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