| 摘要 |
By an NMOS ( 22 ) being switched on or off, a direct-current voltage E<SUB>0 </SUB>is charged in a capacitor ( 24 ), and a DC/DC converting circuit ( 30 ) charges a direct-current output voltage V<SUB>0 </SUB>to be supplied to a load L in a capacitor ( 34 ). A load state detection circuit ( 40 ) determines whether the load L is in a lightly loaded state or in a non-lightly loaded state, and outputs a signal (S 40 ) as a determination signal. When the load state detection circuit ( 40 ) outputs a signal (S 41 ) of "L" as a signal representing that it is a lightly loaded state, a time period setting circuit ( 41 ) outputs a signal (S 41 ) of "L" after a preset time period elapses. A PFC on/off switching circuit ( 42 ) is supplied with the signal (S 41 ) of "L", and outputs a control signal (S 25 ) of "L" to a power factor improvement circuit ( 20 ). Accordingly, in the case where the load L enters a lightly loaded state, the operation of the power factor improvement circuit ( 20 ) is stopped when the preset time elapses.
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