Patent ID: RE42182

Claim:
A multi-lamps liquid crystal display (LCD) panel back-light control circuit, comprising a control unit, an full bridge switch, a resonance network circuit, a voltage transformer, a lamp, and a feedback network, wherein a constant operating frequency and a pulse width modulation (PWM) feedback are used to control a current of cold cathode fluorescent lamps (CCFL) (CCFLs) , the back-light control circuit being characterized in that a power switch of the full bridge switch outputs a duty cycle that is controlled and changed via a PWM controller of the control unit, while a ground switch of the full bridge switch outputs a constant duty cycle controllable above 50%; wherein a phase relationship between a signal that controls the ground switch and a signal that controls the power switch is constant, the ground switch being formed from at least a an NMOSFET and the power switch being formed at least from a PMOSFET; wherein with a common drain connection of the ground switch and the power switch, the power switch is turned off when the ground switch is turned on, and without a common drain connection, the power switch is turned on only after a preset delay from a turn on of the ground switch.