Patent ID: 7619394
Filing Date: 2009-11-17
Classification: H02M,H05B

Abstract:
1. A capacitor charger connected with an input voltage, comprising: a transformer having a primary winding connected with the input voltage and a secondary winding for transforming a primary current flowing through the primary winding to a secondary current flowing through the secondary winding; a current control circuit for maintaining a magnitude of the primary current wherein the current control circuit comprises: a switch connected to the primary winding for switching the primary current; a voltage generator for providing a first voltage varying with the monitoring voltage; a current source for providing a reference current according to the first voltage; a current mirror for mirroring the reference current to generate a mirror current; a charge/discharge circuit for generating a second voltage according to the mirror current; and a comparator for comparing the second voltage with a threshold to generate a comparison signal to adjust an on-time period of the switch; and a current set circuit connected to the current control circuit for changing the magnitude of the primary current from a first value to a second lower value responsive to a change in a monitoring voltage corresponding to a decrease in the input voltage below a certain value.