Back-light control circuit of multi-lamps liquid crystal display
a backlight control circuit and liquid crystal display technology, applied in process and machine control, electric variable regulation, instruments, etc., can solve problems such as several problems of bridge phase shift converters in lcd screens, and achieve the effect of reducing frequency retardation interference and reducing phase retardation interferen
Inactive Publication Date: 2011-03-01
BEYOND INNOVATION TECH
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Benefits of technology
[0006]It is a second object of the invention to provide a CCFL control circuit that incorporates a step-up voltage transformer so that the number of high-voltage resistant elements can be reduced within the control circuit.
[0007]Furthermore, it is third object of the invention to provide a CCFL control circuit that incorporates PMOSFET as power switches so that additional step-up circuits are not needed to directly drive the switches.
[0008]Still, it is a fourth object of the invention to provide a CCFL control circuit in which the cycle of ground switches is fixed so as to change the cycle of the power switches, thereby the voltage conversion is more efficient.
[0009]Furthermore, it is a fifth object of the invention to provide a CCFL control circuit in which the cycle of ground switches is fixed so as to change the cycle of the power switches, thereby most of the circuit current flows through the ground switches. Loss increase due to higher resistivity of PMOS-FET power switches is therefore favorably reduced.
[0011]Yet, it is a seventh object of the invention to provide a CCFL control circuit in which constant frequency and frequency synchronization are implemented to reduce frequency retardation interference within the multi-lamp circuit, caused by the use of different driving circuits.
[0012]Furthermore, it is an eighth object of the invention to provide a CCFL control circuit in which constant frequency and phase synchronization are implemented to reduce phase retardation interference within the multi-lamp circuit, caused by the use of different driving circuits.
Problems solved by technology
However, the present use of traditional fixed frequency operation full bridge phase shift converter in LCD screens presents several problems.
Method used
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[0026]Wherever possible in the following description, like reference numerals will refer to like elements and parts unless otherwise illustrated.
[0027]FIG. 3, FIG. 4, and FIG. 5 are schematic views respectively illustrating a cold cathode fluorescent lamp (CCFL) control circuit, a resonance network circuit, and a multi-lamps applying circuit according to an embodiment of the invention. The multi-lamp LCD back-light control circuit of the invention uses a constant operating frequency and PWM (pulse width modulation) feedback to control the CCFL current.
[0028]As shown in FIG. 3, the multi-lamp LCD back-light control circuit comprises full bridge switches 317, 318, 319, 320. The resonance network circuit 321, comprised of a step-up transformer 324, inductor 322, and capacitors 323, 326, converts a direct current (DC) from a power source 335 to an alternating current (AC) needed by the CCFL circuit 325. The inductor 322 and capacitors 323, 326 of the resonance network circuit 321 can be...
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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%.
Description
FIELD OF THE INVENTION[0001]The invention relates to a multi-lamps LCD back-light control circuit. More particularly, the invention provides a control circuit that can simplify the circuitry of dimensionally larger LCD devices.BACKGROUND OF THE INVENTION[0002]Compared to traditional white thermal lamps, cold cathode fluorescent lamps (CCFL) have many advantages such as higher efficiency and longer service life. Therefore, an important number of liquid crystal display (LCD) presently uses CCFL as light source. To achieve a stable operation of the CCFL, the power frequency needed is about 30 KHz through 80 KHz without the stringed wave from the DC current part while the operating voltage is approximately constant. The illumination of the lamp is determined according to the tube current there through. The voltage needed to turn on the lamp is higher than the normal stable operating voltage 2 to 2.5 times. The turn on voltage and operating voltage of the CCFL are determined from the siz...
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IPC IPC(8): G09G3/36G09G3/34H05B41/282H05B41/392
CPCH05B41/2828H05B41/3927Y02B20/00
InventorYU, CHUNG-CHE
OwnerBEYOND INNOVATION TECH