Patent ID: 7902797

Claim:
A control circuit of a capacitor charging apparatus, the capacitor charging apparatus including a transformer and an output capacitor charged with current flowing through a secondary coil of the transformer, which charges the output capacitor by performing a switching control of a switching transistor provided on a path leading to a primary coil of the transformer, the control circuit comprising: a switching control unit configured to repeat an operation (i) of turning on the switching transistor until current flowing through the primary coil of the transformer has reached a predetermined peak current and (ii) of then turning off the switching transistor during an off-time so as to control on and off of the switching transistor; and a voltage detector configured to monitor a voltage at a tap provided on the secondary coil of the transformer, wherein said switching control unit includes a charging completion detector configured to detect completion of charging by comparing the voltage at the tap with a predetermined threshold voltage; and when a completion of charging is detected, said switching control unit stops the on and off of the switching transistor.