Back-light control circuit of multi-lamps liquid crystal display
First Claim
1. A multi-lamps liquid crystal display 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), 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 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.
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Accused Products
Abstract
A multi-lamps LCD back-light control circuit comprises a control unit, an full bridge switch, a resonance network circuit, a voltage transformer, a lamp, and a feedback network. A constant operating frequency and a pulse width modulation (PWM) feedback are used to control the CCFL current. The back-light control circuit is such 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%.
22 Citations
11 Claims
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1. A multi-lamps liquid crystal display 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), 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 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.- View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11)
Specification