Patent ID: 7310246

Claim:
A capacitor charging circuit comprising: a flyback transformer having a primary coil, a secondary coil and a tertiary coil; a switching element arranged to turn a current that flows in the primary coil on and off; a capacitor arranged to be charged by a current produced in the secondary coil by the on-off action of the switching element; a charge control circuit that controls the on-off action of the switching element; a resistor connected to the switching element and to ground potential and arranged to measure a current in the primary coil of the flyback transformer; and a rectifier diode connected to the capacitor and arranged to transmit the current in the secondary coil that is produced by the on-off action of the switching element to the capacitor, a diode arranged to measure the current in the secondary coil, and another resistor arranged to bias a cathode of the diode to ground potential; wherein the charge control circuit is arranged to cause the on-off action of the switching element to stop for a period of time when the switching element is off and a voltage produced at a first end of the tertiary coil is greater than a reference voltage corresponding to a predetermined voltage of a charge voltage of the capacitor.