Patent ID: 7511974

Claim:
A high voltage charging circuit, for charging a high voltage capacitor, comprising: a DC source for outputting a large current at a low voltage level; a transformer for receiving the large current at the low voltage level and then performing an energy conversion to output a small current at a high voltage level; a diode receiving the small current at the high voltage level, the diode then outputting the small current to the high voltage capacitor to charge the high voltage capacitor; a power transistor, when the power transistor is turned on, enabling the transformer to receive the large current at the low voltage level and then perform an energy conversion without outputting the small current at the high voltage level, and when the power transistor is turned off, disabling the transformer to receive the large current at the low voltage level and then perform the energy conversion and output the small current at high voltage level; a turn-on control circuit for controlling a turn-on time of the power transistor; a turn-off control circuit for controlling a turn-off time of the power transistor, wherein the power transistor is turned off by the turn-off control circuit when the energy of the transformer is released to a threshold; and a standby detection circuit for stopping switching the power transistor when the voltage of the high voltage capacitor is greater than a predetermined voltage, wherein the standby detection circuit further comprises: a breakdown device coupled to the high voltage capacitor; a first comparator for detecting a terminal voltage of the breakdown device, wherein the power transistor is stopped from switching when the terminal voltage of the breakdown device is greater than a first predetermined value; and a second comparator for detecting the terminal voltage of the breakdown device, wherein the power transistor is restored to switching when the terminal voltage of the breakdown device is less than a second predetermined value.