| 摘要 |
A switching power supply unit, which rectifies and smoothes an AC current and an AC voltage from the on-off switching operation of a main switching element to output a DC current and a DC voltage, has an output current detection circuit including a current detection resistor disposed in an intermittent-current flowing path through which a current intermittently flows in sync with the on-off switching operation of the main switching element, a synchronous rectifying a switching element for rectifying a current flowing through the current detection resistor, and a capacitor for charging the current rectified by the synchronous rectifying element, wherein the current flowing through the current detection resistor is charged in the capacitor by a rectifying operation of the synchronous rectifying element, and the charging voltage of the capacitor is outputted as a voltage corresponding to the output current of the switching power supply unit.
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