Patent ID: 7443141

Claim:
A capacitor charging circuit comprising: a transformer adapted to store and discharge energy; a main capacitor adapted to charge energy discharged from the transformer; a switch circuit adapted to regulate a flow of an electric current in a primary winding of the transformer; a detection control circuit adapted to control the switch circuit according to a result of a comparison between a detection voltage, which is used for detecting an electric current flowing through the primary winding of the transformer, and a reference voltage; and a reference voltage control circuit adapted to set, after the detection control circuit causes the switch circuit to turn off an electric current flowing through the primary winding, the reference voltage to be lower than the detection voltage, wherein the reference voltage control circuit comprises a first reference voltage control circuit adapted to control the reference voltage according to an output signal outputted from the detection control circuit so as to control the switch circuit, and a second reference voltage control circuit adapted to control, after the switch circuit is caused to turn off an electric current flowing through the primary winding, the reference voltage according to a secondary current flowing through a secondary winding of the transformer, wherein the detection control circuit has a comparator, wherein the comparator has a first input terminal to which the reference voltage is inputted, a second input terminal to which the detection voltage is inputted, and an output terminal for outputting the output signal to the switch circuit according to a result of a comparison between the reference voltage and the detection voltage, wherein the first reference voltage control circuit has a resistor and a capacitor, wherein one terminal of the capacitor of the first reference voltage control circuit is connected to the output terminal of the comparator, wherein a second terminal of the capacitor of the first reference voltage control circuit is connected to one terminal of the resistor, and wherein a second terminal of the resistor is connected to the first input terminal of the comparator.