KR20070041042A - Liquid crystal display device and method for driving the same - Google Patents

Abstract

The present invention relates to a liquid crystal display device and a driving method thereof, which are designed to implement scanning driving of a lamp even in a backlight unit to which an external electrode fluorescent lamp is applied. A plurality of light sources for supplying a light source, an inverter for supplying current to the plurality of light sources, a switching unit connected to the light source to apply current supplied from the inverter to the light sources, and a control corresponding to each switching unit. And a timing controller for sequentially driving the light source by applying a signal.

Scanning drive, lamp, external fluorescent lamp, scanning duty, timing controller

Description

Liquid crystal display and its driving method {LIQUID CRYSTAL DISPLAY DEVICE AND METHOD FOR DRIVING THE SAME}

1 is an exemplary view showing a driving state of a lamp to which a general scanning driving method is applied.

2 is a view illustrating a backlight unit to which an external electrode fluorescent lamp is applied.

3 is a view showing a liquid crystal display device according to the present invention;

4 is a view showing an internal configuration of the switching unit of FIG.

FIG. 5 is a timing diagram showing waveforms of a control signal output from the timing controller of FIG. 3; FIG.

*** Description of the symbols for the main parts of the drawings ***

110: lamp 120: inverter

125: common electrode 140: timing control unit

150: switching unit CS1 to CSn: control signal

T10: transistor R10: resistor

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid crystal display device and a driving method thereof. In particular, a liquid crystal display device and a driving method thereof capable of scanning driving a lamp to which an external electrode fluorescent lamp (EEFL) is applied. It is about.

BACKGROUND ART Liquid crystal display devices that represent data as visual information have recently been widely adopted in various devices such as mobile devices, notebooks, and televisions.

A liquid crystal display device is a device using optical anisotropy and polarization properties of liquid crystals. By applying a constant electric field to the liquid crystal, light transmittance is adjusted to realize images of various gradations.

Since the liquid crystal provided in the liquid crystal display is not a light emitting material itself but a material which transmits light supplied from the outside to display an image, the liquid crystal display includes a backlight unit for supplying light to the liquid crystal.

The liquid crystal display device includes a liquid crystal panel in which a thin film transistor array substrate and a color filter substrate are bonded to each other, a liquid crystal panel into which liquid crystal is injected, a driving unit controlling the liquid crystal panel, and a backlight unit for supplying light to the liquid crystal panel. .

The backlight unit includes a plurality of lamps and an inverter for supplying electric power to the lamps to control the lighting and turning off of the lamps.

The backlight unit may be divided into an edge type lamp in which a lamp is disposed on a side surface of the liquid crystal panel and a direct type method in which a lamp is disposed on a rear surface of the liquid crystal panel.

The direct type backlight unit has an advantage of providing high luminance to the liquid crystal panel because a plurality of lamps are disposed on the rear surface of the liquid crystal panel. Therefore, in recent years, many direct type backlight units are used.

In the liquid crystal panel, a plurality of data lines are arranged in a vertical direction, and a plurality of gate lines are arranged in a horizontal direction, and the plurality of pixels partitioned by the data line and the gate line are arranged along the gate lines. The images are sequentially displayed along the gate lines to which scan signals are applied.

Due to the inherent viscosity and elasticity, the liquid crystal takes a certain time to rearrange even after an electric field is applied. In other words, several hours of reaction time are required to reach the desired arrangement. If light is supplied in a state in which the liquid crystal does not completely respond, an image different from a desired gray scale may be displayed.

Therefore, a scanning driving method has been proposed in which a lamp corresponding to the pixel is turned off while the pixel is responding, and the lamp is turned on after the response is completed.

1 is an exemplary view illustrating a driving state of a backlight to which a general scanning driving method is applied.

FIG. 1 illustrates a case in which a lamp is controlled by dividing one frame (16.7 ms) into eight subframes (2.09 ms). Here, the white lamp indicates a lighting state, and the black lamp shows a lighting state.

In the first subframe, five lamps are turned on in the liquid crystal panel, but the first lamp is turned off. During this light-off state, a response of the liquid crystal occurs in the pixel corresponding to this lamp.

In the second subframe, five lamps are turned on as in the first liquid crystal panel. However, this time the lamp goes out until the second lamp. As described above, since the response speed of the liquid crystal takes several orders of magnitude, the pixels corresponding to the first lamp are still responding to the liquid crystal.

Five lamps are turned on in the third subframe, and the third lamp is turned off. That is, in the scanning driving method, the lamps are sequentially turned on and off, but a certain number is always lit. This is to maintain the same brightness in each subframe.

In the fourth subframe, the first lamp is turned on and the fourth lamp is turned off. The extinguishing positions of the lamps were shifted one by one.

As a result, each lamp is turned on only for a certain time in one frame and turned off for the remaining time. As such, the time that is turned on in one frame is called a scanning duty. In Fig. 1, the scanning duty is set to 62%.

In order to apply the scanning driving method, lamps must be individually controlled. Cold cathode fluorescent lamps (CCFLs), which are commonly used as lamps in the related art, have an inverter in each one, so that individual control through the inverter is easy. However, as the number of cold cathode fluorescent lamps provided increases, the number of inverters must be increased to drive the cold cathode fluorescent lamps, making it difficult to reduce the thickness of the liquid crystal display and increase the manufacturing cost.

In particular, luminance deviation may occur according to characteristic deviations of the respective cold cathode fluorescent lamps and the inverter 30, which may result in deterioration of image quality.

In order to solve this problem, the use of an external electrode fluorescent lamp controlled by one inverter has been increasing recently.

Unlike the cold cathode fluorescent lamp, the external electrode fluorescent lamp can easily manufacture a surface light source by installing an electrode outside the discharge tube, and greatly reduce the amount of heat generated by the liquid crystal display device and prevent lamp damage due to electrode damage. It is a next generation lighting lamp having five times more energy efficiency than a cold cathode fluorescent lamp.

2 illustrates a backlight unit to which an external electrode fluorescent lamp is applied.

Referring to FIG. 2, the backlight unit includes a plurality of lamps 10 arranged at regular intervals, a common electrode 25 commonly connected to the external electrodes 12 of the lamp 10, and the common electrode 25. It consists of an interversus 20 for supplying power to all lamps 10 through.

The lamp 10 is an external electrode fluorescent lamp, which is connected to the inverter 20 in parallel. Therefore, all the lamps 10 are simultaneously turned on or off by the control of the inverter 20 at the same time. As described above, since the lamp 10 using the external electrode fluorescent lamp can use the inverter 20 in common, the volume of the liquid crystal display device can be significantly reduced compared to the case of using the cold cathode fluorescent lamp. In addition, since all the lamps 10 are controlled by one inverter 20, the control of the lamp 10 is easy.

As described above, the external electrode fluorescent lamp has an advantage of being able to be driven in parallel compared to the cold cathode fluorescent lamp, but the scanning drive of the lamp 10 is applied because all the lamps 10 are simultaneously controlled by one inverter 20. You can't. Accordingly, deterioration of image quality due to the slow response speed of the liquid crystal cannot be prevented.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems, and an object of the present invention is to provide a liquid crystal display device and a driving method thereof capable of scanning driving while driving a plurality of lamps in parallel with a single inverter. have.

As described above, the liquid crystal display device for achieving the object of the present invention is connected to the liquid crystal panel, a plurality of light sources for supplying light to the liquid crystal panel, an inverter for supplying current to the plurality of light sources, respectively And a switching unit for applying a current supplied from the inverter to the light sources, and a timing control unit for sequentially driving the light sources by applying a control signal corresponding to each switching unit.

3 is a view showing a liquid crystal display device according to the present invention.

Referring to FIG. 3, a liquid crystal display device includes a liquid crystal panel (not shown), a plurality of lamps 110 arranged at regular intervals to supply light to the liquid crystal panel, and switching provided separately on the lamp 110. Timing for controlling the flashing of the lamp 110 by individually controlling the unit 150, the inverter 120 connected to the lamp 110 through the switching unit 150, and the switching unit 150. It is configured to include a controller 140.

An external electrode fluorescent lamp is used for the lamp 110. Both ends of the lamp 110 are provided with two external electrodes 112 exposed to the outside, and the lamp 110 receives current through the external electrode 112 and emits light. As shown, the external electrode 112 of the lamp 110 is commonly connected by the common electrode 125. However, one side of the lamp 110 is commonly connected through the switching unit 150.

The inverter 120 converts power supplied from the outside into high voltage alternating current and supplies the lamp 110 to the lamp 110. The inverter 120 supplies a current to the lamp 110 through the switching unit 150.

The switching unit 150 provided in each lamp 110 is connected between the lamp 110 and the inverter 120 to cut off the current output from the inverter 120 so that the current is not supplied to the lamp 110. Or to be conducted to the lamp 110.

As described above, the liquid crystal display according to the present invention includes a switching unit 150 for each of the lamps 110. The switching unit 150 is connected between the inverter 120 and the lamp 110 to provide the inverter. The lamp 110 is turned on or off by controlling the current output from the 120. Since the switching unit 150 is provided for each lamp 110, the lamp 110 may be individually controlled by the control of the switching unit 150.

The timing controller 140 actually controls the switching unit 150. The switching unit 150 is turned on or cut off according to the control signals CS1 to CSn applied from the timing controller 140.

The timing controller 140 applies control signals CS1 to CSn to each of the switching units 150 individually. Some of the control signals CS1 to CSn are applied to the lamp 110 at low potential voltage, and others are applied to the lamp 110 at high potential voltage.

The timing controller 140 alternately applies a low potential voltage and a high potential voltage to the lamp 110 to scan and drive the lamp 110. That is, the timing controller 140 alternately applies the low potential voltage and the high potential voltage to the switching unit 150 so that the switching unit 150 is turned on for a predetermined time in every frame, and the remaining time is cut off. .

As described above, the timing controller 140 adjusts the voltage of the control signals CS1 to CSn applied to the respective switching units 150 so that each lamp 110 is turned on for a predetermined time, i.e., the scanning duty in each frame. Keep your status. Accordingly, the lamp 110 is driven to scan.

In the liquid crystal display according to the present invention, the switching unit 150 is connected to each lamp to control the lamps 110 that are simultaneously turned on by the current supplied from the inverter 120. Accordingly, since the lamp 110 cannot receive current unless the corresponding switching unit 150 is turned on, lighting or turning off of the lamp 110 is entirely controlled by the switching unit 150. The switching unit 150 is controlled by the timing controller 140.

The timing controller 140 controls the lamps 110 to be sequentially supplied with current by sequentially conducting the switching units 150, and adjusts the conduction time of the switching unit 150 to control the lamps ( 110 controls the length of time it remains lit. That is, the timing controller 140 may control the respective switching units 150 to drive the lamp 110 in scanning.

In FIG. 3, the scanning driving method in which one lamp 110 is turned on or off is explained. However, it may be sufficient to connect two or more lamps 110 in one group to perform the scanning driving in group units.

Hereinafter, the switching unit 150 will be described in more detail with reference to the accompanying drawings.

4 is a diagram illustrating an internal configuration of the switching unit of FIG. 3.

Referring to FIG. 4, the switching unit includes a transistor T10 and a resistor R10 connected in parallel.

The control signal CSm output from the timing controller is applied to the gate electrode of the transistor T10. That is, the transistor T10 is turned on or turned off in accordance with the control signal CSm.

When the transistor T10 is turned off, the only passage electrically connected from the inverter to the backlight is the resistor R10, but since the resistor R10 is set to a high resistance of several kilowatts or more, the current actually flows into the backlight. It can hardly flow. Thus, the backlight is turned off.

On the other hand, when the transistor T10 is turned on, the current output from the inverter is easily introduced into the lamp through the transistor T10, so that the lamp is turned on.

As described above, the switching unit provided in each lamp is turned on or off according to the control signal CSm applied from the timing controller so that the current output from the inverter is transmitted to the lamp or blocked. Since the control signal is output differently for each lamp, the timing controller may individually control the flashing of all lamps by the control signal.

FIG. 5 is a timing diagram illustrating waveforms of a control signal output from the timing controller of FIG. 3.

Referring to FIG. 5, the plurality of control signals CS1 to CSn output from the timing controller maintain a low potential voltage for a predetermined time and a high potential voltage for a predetermined time. However, the timing at which the control signals CS1 to CSn transition to the high potential voltage is different from each other. That is, as shown in the figure, the control signals CS1 to CSn applied to the respective switching units sequentially transition to high potential voltages. Similarly, after maintaining the high potential voltage state for a predetermined time, the transition to the low potential voltage is sequentially performed again.

As a result, the timings at which all the control signals CS1 to CSn transition to the high potential voltage or the low potential voltage for one frame are different, but maintain the high potential voltage state for the same time. That is, since the timing controller conducts each switching unit by the control signal for the same time, all the lamps have the same scanning duty. However, the time period during which each lamp maintains the lighting state is controlled to be different.

As described above, the liquid crystal display according to the present invention controls the flashing of each lamp sequentially by controlling the switching unit connected to each lamp while emitting all the lamps connected in parallel with one inverter, thereby reducing the external electrode fluorescent lamp. The scanning driving method can also be used in the applied backlight unit.

As described above, the liquid crystal display device according to the present invention can control the blinking of each lamp individually even when driving a plurality of lamps with a single inverter, it is possible to implement the scanning drive of the lamp, the response speed of the liquid crystal It is possible to prevent the deterioration of the image quality caused by.

Claims (13)

A liquid crystal panel; A plurality of light sources for supplying light to the liquid crystal panel; An inverter for supplying current to the plurality of light sources; A switching unit connected to each of the light sources to apply a current supplied from the inverter to the light sources; And And a timing controller for sequentially driving the light source by applying a control signal corresponding to each switching unit. The liquid crystal display of claim 1, wherein the light sources are connected in parallel to each other. The liquid crystal display of claim 1, wherein at least one of the control signals is output at a low potential voltage. The liquid crystal display of claim 1, wherein at least one of the control signals is output at a high potential voltage. The liquid crystal display of claim 1, wherein the light source is an external electrode fluorescent lamp (EEFL). The liquid crystal display of claim 1, wherein the switching unit is turned on every frame for a time set according to the control signal. The liquid crystal display of claim 1, wherein the switching units are sequentially turned on or off in response to the control signal in every frame. 2. The liquid crystal display device according to claim 1, wherein the number of switching parts conducted in accordance with the control signal is kept constant. The method of claim 1, wherein the switching unit Resistance to block current from being transmitted to the light source; And And a transistor which is turned on by the control signal and transfers current to a light source. In a liquid crystal display device having a backlight unit for supplying current to a plurality of light sources with an inverter, Coupling a switching unit to each lamp to control a current supplied from the light source; Sequentially lighting the lamps by sequentially communicating the switching units; Maintaining a lighting state of each lamp for a set time; And sequentially turning off the lamps by sequentially blocking the switching unit. The method of claim 10, wherein the set time is smaller than one frame. The method of claim 10, wherein the number of lamps lit among the plurality of lamps is constant. The driving method of claim 10, wherein the first lamp among the lamps in the lit state is sequentially turned off.

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