Patent ID: 7375471

Claim:
A charging circuit that converts the output voltage of a DC power supply on a primary side of a transformer into an AC voltage by a switching operation and rectifies the AC voltage on a secondary side of the transformer to charge a capacitor for storing electric power comprising: a switching element arranged in a primary circuit of the transformer; a first switching circuit that monitors primary current flowing in the primary circuit and turns on the switching element from a OFF state when the value of the primary current has increased to a first reference value or larger; a second switching circuit that monitors voltage between the terminals of the primary coil or secondary coil of the transformer and turns on the switching element from the OFF state when the voltage between the terminals of the coil drops to a second reference value or lower; a third switching circuit that counts a first period from the time when the switching element was turned on and forcibly turns off the switching element from the ON state if the switching element has not turned off even after the first period has elapsed; and a fourth switching circuit that counts a second period from the time when the switching element was turned off and forcibly turns on the switching element from the OFF state if the switching element has not turned on even after the second period has elapsed.