KR20060108226A - Apparatus and method for driving backlight - Google Patents

Abstract

An apparatus and a driving method for driving a backlight for providing light to a liquid crystal display are provided. A driving device, comprising: a sensing sensor for sensing a temperature or a brightness, and an initial brightness stabilizing unit for supplying an overcurrent greater than a preset steady state current according to a sensing signal transmitted from the sensing sensor at an initial stage of backlight driving; And a mid-term luminance stabilizer that gradually reduces current from an overcurrent supplied at the beginning of driving to a steady state current, and a late luminance stabilizer that compensates for a change or instability of luminance during steady state backlight driving. According to the present invention, the luminance is quickly stabilized in each step of driving the backlight, thereby further improving the display quality of the liquid crystal display.

Backlight, stabilization, sensor, temperature, brightness

Description

Backlight driving device and driving method {APPARATUS AND METHOD FOR DRIVING BACKLIGHT}

1 is a perspective view showing an example of a flat panel backlight.

2 is a schematic diagram schematically showing a configuration of a backlight driving apparatus according to the present invention.

3 is a flowchart illustrating a backlight driving method according to the present invention.

4 is a graph showing initial luminance stabilization of a backlight according to the present invention.

5 is a graph showing the medium-term luminance stabilization of the backlight according to the present invention.

6 is a schematic view showing an LCD device including the backlight drive device of the present invention.

*** Explanation of symbols for the main parts of the drawing ***

200: drive unit 210: drive unit

220: switching unit 230: feedback circuit

240: detection sensor 250: control unit

260: backlight

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a backlight driving apparatus and a driving method for a liquid crystal display (LCD), and more particularly, to a backlight driving apparatus and a driving method with improved driving stability.

The liquid crystal display displays an image by using electrical and optical characteristics of the liquid crystal. Liquid crystal displays have the advantages of being very small in volume and light in weight compared to cathode ray tubes (CRTs). As a result, they are widely used in portable computers, communication devices, liquid crystal television receivers, and aerospace industries. .

The liquid crystal display device includes a liquid crystal controller for controlling liquid crystal and a backlight for supplying light to the liquid crystal. The liquid crystal controller includes a pixel electrode disposed on the first substrate, a common electrode disposed on the second substrate, and a liquid crystal interposed between the pixel electrode and the common electrode. The pixel electrode is formed in plural in correspondence with the resolution, and the common electrode is made of one and facing the pixel electrode. A thin film transistor (TFT) is connected to each pixel electrode to apply a pixel voltage having a different level, and a reference voltage of the same level is applied to the common electrode. The pixel electrode and the common electrode are made of a transparent material having conductivity.

Light supplied from the backlight sequentially passes through the pixel electrode, the liquid crystal, and the common electrode. In this case, the display quality of the image passing through the liquid crystal largely depends on the brightness and uniformity of the backlight. In general, the higher the luminance and the uniformity of the luminance, the better the display quality.

Conventionally, a cold cathode fluorescent lamp (CCFL) having a rod shape or a light emitting diode (LED) having a dot shape is mainly used as a backlight of a liquid crystal display. Cold cathode fluorescent lamps have the advantage of high brightness and long life, and very low heat generation compared to incandescent lamps. On the other hand, the light emitting diode has the advantage of low power consumption and high brightness. However, cold cathode fluorescent lamps or light emitting diodes have poor brightness uniformity. Accordingly, a backlight having a cold cathode fluorescent lamp or a light emitting diode as a light source may have an optical member such as a light guide panel (LGP), a diffusion member, a prism sheet, or the like to increase luminance uniformity. member). As a result, a liquid crystal display using a cold cathode fluorescent lamp or a light emitting diode has a problem in that the volume and weight of the optical member are greatly increased.

As a backlight for a liquid crystal display device, a flat fluorescent lamp (FFL) has been proposed. Referring to FIG. 1, the flat fluorescent lamp includes a light source body 10 and electrodes 20 provided on outer surfaces of both edges of the light source body 10. The light source body 10 includes first and second substrates (not shown) disposed to face each other at predetermined intervals. A plurality of partitions 30 are disposed between the first and second substrates to partition the space between the first and second substrates into a plurality of discharge spaces 50. A sealing member 40 is disposed between the edges of the first and second substrates to isolate the discharge spaces 50 from the outside. Discharge gas is injected into the isolated discharge space 50.

In order to discharge-drive the planar fluorescent lamp, an electrode 20 may be formed on the first substrate, the second substrate, or one of the two substrates in the form of a strip of strips or in the form of an island electrode. The electrode was applied to have. Therefore, when the flat fluorescent lamp is driven using an inverter, all the front channels are discharged in the same manner.

Since the brightness of the mercury lamp is closely correlated with the operating temperature and the ambient temperature in the driving device for the surface light source backlight, there is a problem that it takes a long time to obtain a stable normal luminance because the brightness increase slowly during the initial driving of the backlight. . For this reason, the overall luminance of the liquid crystal panel which receives light from the backlight is dark at the time of initial driving, and it takes a considerable time to obtain the normal luminance. This problem is exacerbated when a flat fluorescent lamp is used as a backlight rather than a cold cathode fluorescent lamp. For example, in the case of a cold cathode fluorescent lamp, the time to reach the initial luminance stabilization luminance is approximately one minute, whereas in the case of a flat fluorescent lamp, it takes one minute or more. The initial luminance stabilization delay problem is a serious obstacle especially when implementing a large screen LCD TV.

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and an object of the present invention is to provide an apparatus and method for driving a backlight which can quickly stabilize the brightness of the backlight.

In addition, another object of the present invention is to provide a backlight that can be driven stably so that a sudden change in brightness is not recognized in the stabilization of the backlight.

In addition, another object of the present invention is to implement continuous stabilization in response to temperature or luminance changes generated during the driving of the backlight.

In order to achieve the above object, the present invention provides a driving device for driving a backlight for providing light to a liquid crystal display, the sensor comprising a sensing sensor for sensing a temperature or brightness, according to the detection signal transmitted from the sensing sensor An initial luminance stabilizer for supplying an overcurrent greater than a set steady state current at the initial stage of backlight driving; A medium-term luminance stabilizer that gradually reduces current from an overcurrent supplied at the beginning of driving to a current in a steady state; And a late luminance stabilizer for compensating for a change or instability of luminance during driving of the backlight in a steady state.

The initial brightness stabilization unit driving unit for providing a signal for driving the backlight according to a control signal; A sensor for sensing the backlight or ambient temperature or luminance, or the liquid crystal display or ambient temperature or luminance and outputting the detected signal; And a first control unit outputting a control signal to the driving unit to output a driving signal of a predetermined current level or more until the temperature or luminance indicated by the sensed signal reaches a preset value.

The medium-term luminance stabilizer includes a second controller that outputs a control signal to the driver to output a drive signal that gradually reduces the current for a predetermined range of time from an overcurrent to a current in a steady state. The second control unit may be integrated with the first control unit to configure one control unit.

The late luminance stabilizer includes a feedback circuit that provides a feedback signal to the driver so that a constant current is stably applied to the backlight after the temperature or luminance of the backlight reaches a preset value. The late luminance stabilization may be controlled by the first controller or the second controller.

The present invention also provides a backlight driving method for providing light to a liquid crystal display device, comprising the steps of: sensing temperature or brightness from a sensing sensor; An initial luminance stabilizing step of supplying an overcurrent greater than a preset steady state current to the backlight according to a sensing signal transmitted from the sensing sensor; A medium-term luminance stabilization step of gradually reducing the current from the supplied overcurrent to a steady state current; And a late luminance stabilizing step of compensating for luminance when there is a change or instability of luminance during driving of the backlight in a steady state.

The backlight driving apparatus according to the present invention is a backlight driving inverter or the inverter designed to compare and supply the overcurrent or the normal current according to a sensing signal and a predetermined temperature or luminance value detected by the sensing sensor It may include a microcomputer programmed to control the inverter. The inverter or the microcomputer includes a current control circuit to supply a constant steady current when the detection signal outputs a signal related to a preset value after overcurrent supply, and gradually supplies current for a predetermined time when the steady current is supplied. It may include a current control circuit for reducing. In addition, the inverter or the microcomputer may include a current control circuit that supplies an overcurrent again when a detection signal that is out of a predetermined value is transferred from the sensing sensor after a constant steady current supply.

On the other hand, the inverter or the microcomputer may be designed to supply more than the minimum current required for low-temperature lighting without exceeding the limit current that can generate a pinhole in the flat fluorescent lamp when the overcurrent supply compared to the normal current.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings. 2 illustrates a backlight 260 for supplying light to the liquid crystal panel and a driving device 200 for driving the backlight 260. The driving device 200 includes a driving unit 210, a switching unit 220, a feedback circuit 230, a detection sensor 240, and a control unit 250.

The control unit 250 may be a separate control unit to be able to independently control each step stabilization according to the present invention, one control unit may be integrated control of step stabilization. The driver 210 outputs a pulse width modulation (PWM) signal having a duty ratio according to feedback control for applying a constant current to the backlight. The switching unit 220 boosts the pulse width modulation signal input from the driving unit 210 to a voltage level high enough to drive the backlight 260 through on / off switching and resonance. Output to the backlight.

The feedback circuit 230 provides a feedback signal to the driver 210 so that a constant current is stably applied to the backlight 260. Since the current applied to the backlight 260 changes when the load of the backlight 260 changes due to an operating temperature or the like, the luminance of the backlight 260 also changes. To correct this, the feedback circuit 230 provides a feedback signal to the driver 210 to stabilize the current applied to the backlight 260, and the current applied to the backlight is stabilized by such feedback control. do. That is, the backlight 260 has its brightness stabilized by this feedback control to obtain a uniform normal brightness.

In the driving method of the backlight 260, an initial luminance stabilization driving step for rapidly increasing the luminance of the backlight 260, and a medium-term luminance for stabilizing the luminance of the backlight 260 to normal luminance after the initial driving process A stabilization step and a means for compensating for luminance due to a temperature change during driving of the backlight are classified into a later luminance stabilization step, and the details of the steps will be described below.

I. Initial luminance stabilization driving process

The driving unit 210 outputs a driving signal which is a pulse width modulation signal having a duty ratio according to a control signal of the control unit 250 during initial driving. That is, the driving unit 210 outputs a driving signal having a current level indicated by the control signal during initial driving.

The switching unit 220 boosts and outputs a driving signal input from the driving unit 210 to a level high enough to drive the backlight 260 through on / off switching and resonance. .

The sensor 240 detects a temperature or luminance of a lamp, a lamp, or an LCD TV around the backlight 260, and outputs a detection signal indicating this. As the sensor 240, a general temperature sensor or an optical sensor such as a photodiode may be used. In the initial driving, the brightness of the backlight is in proportion to the operating temperature.

The control unit 250 outputs a control signal according to the detection signal to the driving unit 210, and continuously generates a constant transient current higher than the normal current until the temperature or luminance indicated by the detection signal reaches a preset value. The driving unit 210 is controlled to output. At this time, even when the temperature of the lamp, the lamp surroundings or the LDC TV, or the brightness of the lamp or LCD reaches a set value, it is in an unstable (or variable) state, and then, through the stabilization process, the backlight 260 is stable and normal brightness. You get That is, the controller 250 recognizes that the backlight 260 is initially driven when the temperature of the lamp, the lamp, or the LCD TV indicated by the detection signal, or the brightness of the lamp or the LCD TV is lower than the set value. A control signal instructing to output a transient current higher than the normal current is output to the driver 210. Accordingly, the driver 210 continuously outputs a current of a predetermined level or more until the temperature of the lamp or the lamp of the backlight 260, the brightness of the lamp, or the temperature or the brightness of the LCD TV reaches a set value. . As a result, a transient current is applied to the backlight 260, thereby rapidly increasing the luminance of the backlight 260.

In the present invention, the preset temperature or brightness or the control signal for each stage is variable according to the size of the backlight. As a specific example, when the size of the backlight 260 is 32 inches, the (preset) normal current is 120 mA, the transient current is 160 ~ 200 mA, the set temperature around the lamp or LCD TV is 35 ℃, the normal brightness Is 450 cd / m ² , and the duty ratio of the driving signal is 50% or more.

The overcurrent supplied initially is set according to the characteristics of the flat fluorescent lamp. Flat fluorescent lamps using external electrodes do not exceed the limit current that can cause pinholes, and supply overcurrent during low-temperature lighting. In this case, it can be selected beyond the minimum current without problem of low-temperature lighting.

II. Medium-term luminance stabilization process

When the temperature of the lamp of the backlight 260, the lamp periphery, or the temperature of the LCD TV reaches a preset normal value, the driver 210 controls the feedback signal of the feedback circuit 230 under the control of the controller 250. Outputs a drive signal having a current level determined by

The feedback circuit 230 provides a feedback signal to the driver 210 so that a constant current is stably applied to the backlight 260. The feedback circuit 230 provides a feedback signal to the driver 210 to stabilize the current applied to the backlight 260, and the current applied to the backlight 260 is stabilized by such feedback control. When the temperature or brightness of the lamp or lamp, or the temperature or brightness of the LCD TV reaches a preset value, the LCD is driven with normal current in the initial overcurrent state in the process of providing the backlight with a driving signal of a constant current level. The lowering of the brightness of the panel can be visually recognized. To prevent this, it is possible to prevent the sudden change in brightness by sequentially lowering the current from the overcurrent to the normal current level within the range of about 10 seconds to 10 minutes.

III. Late luminance stabilization process

If the temperature of the lamp, the temperature around the lamp, or the temperature of the LCD TV drops again from the preset temperature while the backlight is driven at the normal current, the overcurrent may be supplied to the lamp again. That is, according to the present invention, by continuously detecting the temperature or brightness instability that may occur during the driving of the backlight to control the feedback to maintain a predetermined normal value.

In the above-described example, the output current of the driving unit 210 is changed by adjusting the duty ratio during initial driving, but the output current may be changed by adjusting the applied voltage of the switching unit 220 as necessary. . In addition, the function of the switching unit 220 may be integrated into the driving unit 210, and the switching unit 220 may be removed.

3 is a flowchart illustrating a luminance stabilization process of a backlight according to the present invention described above.

First, when the backlight is driven in an on state, as a first stabilization step (I), the sensing sensor senses the temperature or brightness of the backlight, the ambient temperature or brightness of the backlight, and the temperature or brightness of the LCD panel. The detected signal is compared with a preset value to determine whether to apply overcurrent or normal current.

If the ambient temperature or brightness of the backlight, LCD panel temperature or brightness does not reach the preset value, the overcurrent is continuously supplied to the backlight until the set value is reached. Is applied to the backlight.

As the second stabilization step (II), when the normal current is applied to the backlight from the overcurrent, the current may be sequentially lowered for 10 seconds to 10 minutes to prevent the luminance from changing rapidly.

Next, as a third stabilization step (III), if a variable or unstable temperature or brightness occurs in the driving process of the backlight after the initial stabilization, the detection sensor detects this and continuously stabilizes the brightness of the backlight to reach a set value.

4 is a graph showing comparison of initial luminance stabilization time between cold cathode fluorescent lamps and flat fluorescent lamps. Cold cathode fluorescent lamps initially require T1 to reach the target brightness (see A), while flat fluorescent lamps typically require a long time of T3 (see B). However, when the initial stabilization drive according to the present invention is applied, the initial luminance stabilization time of the flat fluorescent lamp is shortened by T2 (see C), so that the initial luminance stabilization time similar to the cold cathode lamp requiring T1 may be reached. Can be.

5 is a graph showing the results of sequentially decreasing the current to drive to the normal current after the initial overcurrent.

Lowering the current directly from the overcurrent to the normal current can visually decrease the brightness. Therefore, to prevent this, the brightness can be prevented from changing rapidly by sequentially lowering the current from the overcurrent to the normal current. As shown, a steady current is gradually applied by applying a steady current from a time point t2 close to the target brightness after a gradual decrease period td from a time point t1 after initially supplying an overcurrent to reach initial stabilization. Change.

Sequential current reduction can be reduced by 1 to 3 mA per second, for example from 180 mA of overcurrent to 120 mA of steady current. The sequential decrement time may vary depending on the difference between overcurrent and steady current, but a range of 10 seconds to 10 minutes is appropriate.

6 is a cross-sectional view schematically showing an LCD device including a driving device for backlight of the present invention. As shown, the liquid crystal panel 370 and the backlight 360 are mounted in the housing 380, and the driving device 300 is shown outside the housing for understanding.

The housing 380 has a box shape having an open top surface, and includes a base portion 382 having a rectangular flat plate shape, a sidewall 384 extending vertically from an edge of the base portion 382, and the sidewall 384. And a protrusion 386 formed transversely from an upper end of the base 382, the side wall 384 and the protrusion 386 are integrally formed. The liquid crystal panel 370 is mounted on the upper side of the housing 380, and the backlight 360 is mounted on the lower side of the housing 380. The liquid crystal panel 370 includes first and second substrates 372 and 376 disposed in parallel with the liquid crystal 374 and the liquid crystal 374 interposed therebetween. The first substrate 372 includes a plurality of pixel electrodes according to the resolution of the liquid crystal panel 370, wherein each pixel electrode is a thin film transistor (TFT) for voltage application. ) Can be connected. The second substrate 376 includes a common electrode to which a reference voltage is applied. The pixel electrodes and the common electrode are made of a transparent material having conductivity.

The backlight 360 includes first and second substrates 362 and 364 having opposite surfaces attached to each other. The second substrate 364 has a shape of a square plate, the first substrate 362 has a shape of a square plate as a whole, and the discharge spaces 366 are formed to communicate with each other. For example, by disposing the partitions alternately so that the discharge spaces have a serpentine, or by independently forming the discharge spaces and forming through-holes in the partitions, the discharge gas is discharged between the discharge spaces. It is also possible to provide a passage for movement. Discharge gas is filled in the discharge space 366 between the first and second substrates 362 and 364, and a phosphor is coated on an inner wall of the discharge space 366. When discharge is initiated in the discharge space 366, the phosphor emits light.

The discharge space 366 of the backlight 360 may form the first substrate 362 so as to protrude convexly along a predetermined pattern from a bottom surface thereof, as in the present exemplary embodiment, or the first substrate 362 may be formed. Instead of molding, the barrier ribs of various materials may be erected on the upper surface of the second substrate, or the first or second substrate having a flat plate shape may be etched to form a plurality of barrier ribs.

A sensor 340 that senses temperature or brightness adjacent to the backlight 360 is installed around the backlight or around the LCD panel. For example, the sensor 340 may be attached to the side wall 384 or the base 382 of the housing 380. The sensor 340 detects a backlight lamp, a lamp periphery, a temperature of the LCD panel, or a brightness of the lamp or the LCD panel, and outputs the detected signal to the controller 350. As an example of the temperature sensor, a negative temperature coefficient thermistor (NTC thermistor), a thermocouple, or the like may be used.

The backlight driving apparatus 300 includes a driving unit 310, a switching unit 320, a feedback circuit 330, a sensing sensor 340, and a control unit 350. Although the driving device is schematically illustrated for the sake of understanding, in practice, the driving device may be implemented in a circuit of at least one printed circuit board or the like, and may be mounted inside or outside the housing 380.

The driving unit 310 outputs a driving signal having a current level according to a control signal in an initial driving process, and outputs a driving signal having a current level according to a feedback signal in a middle or late stabilization process. The switching unit 320 boosts and outputs a driving signal input from the driving unit 310 to a current level high enough to drive the backlight 360 through on / off switching and resonance. The control unit 350 outputs a control signal according to the detection signal to the driver 310, and outputs a transient current having a current level higher than the normal current until the temperature or luminance indicated by the detection signal reaches a set value. The driving unit 310 is controlled to be.

The feedback circuit 330 maintains a constant current in the backlight 360 during the mid-term brightness stabilization process after the temperature or brightness of the backlight 360, the ambient temperature of the backlight, or the temperature or brightness of the LCD panel reaches a normal value. The feedback signal is provided to the driver 310 to be stably applied. In addition, the feedback circuit 330 continuously provides a feedback signal to the driver 310 to cope with a change in temperature or brightness during the driving of the backlight 360, and a current applied to the backlight 360. Can continue to be stabilized by this feedback control.

In the above, the present invention has been described through the preferred embodiments, but those skilled in the art or those skilled in the art to which the present invention pertains the present invention without departing from the technical spirit described in the claims to be described later. Various modifications and improvements will be made.

According to the present invention, the backlight can be optimally stabilized step by step, thereby contributing to the improvement of the image quality of the LCD TV.

In particular, by applying a transient current to the backlight for a short time during the initial driving, there is an advantage that the brightness of the backlight can be stabilized faster than before. In addition, when driving to the normal current after stabilization, it is possible to prevent the sudden change of the brightness visually by visually reducing the current from the overcurrent to the normal current.

The backlight driving device and driving method of the present invention are particularly suitable for the stable driving of a large screen LCD TV.

Claims (13)

A driving apparatus for driving a backlight for providing light to a liquid crystal display, the driving apparatus comprising a sensing sensor sensing a temperature or a brightness, and overcurrent greater than a predetermined steady state according to a sensing signal transmitted from the sensing sensor. An initial luminance stabilizer configured to supply the initial backlight driving; A medium-term luminance stabilizer that gradually reduces current from an overcurrent supplied at the beginning of driving to a current in a steady state; And a late luminance stabilizer for compensating for a change or instability of luminance during driving of the backlight in a steady state. The display apparatus of claim 1, wherein the initial luminance stabilizer comprises: a driver configured to provide a signal for driving the backlight according to a control signal; A sensor for sensing the backlight or ambient temperature or luminance, or the liquid crystal display or ambient temperature or luminance and outputting the detected signal; And a first control unit outputting a control signal to the driving unit to output a driving signal of a predetermined current level or more until a temperature or luminance indicated by the sensed signal reaches a preset value. The backlight driving apparatus of claim 2, further comprising a switching unit configured to boost the driving signal input from the driving unit and output the boosted driving signal to the backlight. The backlight unit of claim 1, wherein the medium-term luminance stabilization unit includes a second control unit which outputs a control signal to the driving unit to output a driving signal that gradually reduces the current for a predetermined range of time from an overcurrent to a steady state current. drive. The feedback circuit of claim 1, wherein the late luminance stabilizer is configured to provide a feedback signal to the driver so that a constant current can be stably applied to the backlight after the temperature or luminance of the backlight reaches a preset value. Backlight driving device comprising a. The backlight driving inverter or the inverter designed to compare and supply an overcurrent or a normal current according to a sensing signal and a preset temperature or luminance detected by the sensing sensor. Driving device of a backlight comprising a microcomputer programmed to control. The apparatus of claim 6, wherein the inverter or the microcomputer includes a current control circuit to supply a constant steady current when the sensing signal outputs a signal related to a preset value after the overcurrent is supplied. 8. The backlight driving apparatus according to claim 7, comprising a current control circuit which gradually reduces the current at a range of 10 seconds to 10 minutes when supplying a constant steady current. The apparatus of claim 7, wherein the inverter or the microcomputer includes a current control circuit to supply overcurrent again when a detection signal deviating from a predetermined value is transmitted from the sensing sensor after a constant steady current supply. The inverter of claim 1, further comprising an inverter designed to supply the minimum current required for the low-temperature lighting without exceeding a limit current at which pinholes can be generated in the flat fluorescent lamp when the overcurrent is supplied to the normal current, and a microcomputer programmed to control the inverter. The driving device of the backlight. In the backlight driving method for providing light to the liquid crystal display device, Sensing temperature or brightness from the sensing sensor; An initial luminance stabilizing step of supplying an overcurrent greater than a preset steady state current to the backlight according to a sensing signal transmitted from the sensing sensor; A medium-term luminance stabilization step of gradually reducing the current from the supplied overcurrent to a steady state current; And And a late luminance stabilizing step of compensating for the luminance when there is a change or instability of the luminance during driving of the backlight in a steady state. Backlight driving method. The method of claim 11, wherein the sensing sensor detects a backlight or ambient temperature or brightness, or a liquid crystal display or ambient temperature or brightness. 12. The method of claim 11, wherein the medium-term stabilization step is reduced by 1 to 3 mA per second in a range of 10 seconds to 10 minutes.

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