Multiple-ccfl parallel driving circuit and the associated current balancing control method for liquid crystal display
AssigneesHsiu-Ying Li, Kai-Jun Pai
InventorChang-Hua Lin
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Abstract
A multiple-CCFL parallel driving circuit and the associated current balancing control method for LCD are presented, wherein the circuit comprises a plurality of CCFLs for providing the backlight for a LCD; a boosting transformer with a plurality of outputs for providing the driving voltage and current for driving the plurality CCFLs; a plurality of ballast capacitors, the ballast capacitors connect between the boosting transformer and the CCFLs; and a multiple CCFL current balancing circuit. This invention uses a low cost current mirror circuit to equalize the driving current of a plurality of CCFLs and thus significantly improve the uniformity of the displayed image on a large-size LCD.
Claims18
A multiple-CCFL parallel driving circuit for a LCD, comprising:
- a plurality of sets of CCFLs, providing a backlight for a LCD;
- a boosting transformer with a plurality of sets of outputs, providing the driving voltage and current for driving the plurality of sets of CCFLs;
- a plurality of ballast capacitors, the ballast capacitors are connected between the boosting transformer and the CCFLs;
- and
- a multiple-CCFL current balancing circuit, the multiple-CCFL current balancing circuit is a current mirror circuit comprised of a plurality of bipolar junction transistors and equalizes driving current of the plurality of sets of CCFLs, the reference of the current mirror circuit is connected to output of the first CCFL of the plurality sets of CCFLs in order to equalize the driving current of the second CCFL, the third CCFL and the fourth CCFL.
A multiple-CCFL parallel driving circuit for a LCD, comprising:
- a plurality of sets of CCFLs, providing a backlight for a LCD;
- a main controller, providing a high frequency switching pulse;
- a plurality of inverters, converting the inputted dc power into a plurality of high frequency sine waves;
- a plurality of transformers, boosting the high frequency sine waves outputted from inverters to drive the CCFLs;
- and
- a multiple-CCFL current balancing circuit, the multiple-CCFL current balancing circuit is a current mirror circuit comprised of a plurality of bipolar junction transistors and equalizes driving current of the plurality sets of CCFLs, the reference of the current mirror circuit is connected to an output of the first CCFL of the plurality of sets of CCFLs in order to equalize the driving current of the second CCFL, the third CCFL and the fourth CCFL.
A current balancing control method for a multiple-CCFL parallel driving circuit of LCD, comprises steps of:
- inputting dc power, the dc power provides a dc voltage to a switching circuit;
- transferring the dc power to a switching circuit, the switching circuit is turned on and off by a timing signal, so as to convert the dc power to high frequency pulse power;
- passing the high frequency pulse power to a resonant circuit, the resonant circuit transfers the high frequency pulse power produced by the switching circuit to a sine wave voltage;
- coupling the power to drive loads, it couples and boosts the sine wave power outputted from the resonant circuit and drive loads;
- and
- equalizing the driving current of the loads by a multiple CCFL current balancing circuit.
Dependencies are inferred from the claim text.