Patent ID: 8436540

Claim:
A multi-lamp driving system, to drive a plurality of lamps, comprising a filter circuit, a switch circuit, a pulse width modulation (PWM) controller to control output of the switch circuit, and a plurality of transformers each with primary windings connected to the output of the switch circuit in parallel, wherein high voltage ends of secondary windings of the transformers are connected to lamps respectively, and the multi-lamp driving system further comprises: a current difference detection circuit, connected to low voltage ends of the secondary windings of the plurality of transformers, to detect difference among current flowing through the plurality of lamps to determine if the current flowing through the plurality of lamps fluctuates; a lighting detection circuit, connected to the current difference detection circuit, to determine if the plurality of lamps are lit according to the current flowing through the plurality of lamps and to generate a lighting indication signal after the plurality of lamps are lit; a frequency regulating circuit, connected to the lighting detection circuit, to regulate frequency of PWM signals generated by the PWM controller according to the lighting indication signal; a frequency scanning detection circuit, connected to the lighting detection circuit, to determine if the multi-lamp driving system is in a frequency scanning process according to the lighting indication signal and to generate a frequency scanning indication signal if the multi-lamp driving system is in the frequency scanning process; and a duty cycle regulating circuit, connected to the current difference detection circuit, the lighting detection circuit, and the frequency scanning detection circuit, to regulate duty cycles of the PWM signals generated by the PWM controller upon the condition that the current flowing through the plurality of lamps fluctuates and the multi-lamp driving system is in the frequency scanning process.