Patent ID: 7176657

Claim:
A capacitor charging circuit for controlling a transformer such that a voltage source coupled to a primary winding of the transformer charges a capacitive load coupled to a secondary winding of the transformer, comprising: a power switch coupled to the primary winding such that a primary winding current is allowed to flow during an ON-time of the power switch but is terminated during an OFF-time of the power switch; a switch controller for controlling the ON-time and the OFF-time; a soft-start circuit for modulating the ON-time to gradually increase during an initial period of a charging process; a first current detector for detecting the primary winding current to generate a primary current detection signal; a reference voltage generator controlled by the soft-start circuit to generate a soft-start reference voltage; and a first voltage comparator for comparing the primary current detection signal with the soft-start reference voltage so as to output an ON-time ending signal to the switch controller.