KR101451573B1 - Back light unit and liquid crystal display device using the same and driving method thereof - Google Patents

Abstract

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a backlight unit for preventing image distortion of an AC driving signal for driving a plurality of light sources to improve image display efficiency, a liquid crystal display using the same, and a driving method thereof, An inverter control unit for generating a pulse width modulation signal by compensating a constant current and a feedback current input from the outside to the dimming control signal; An inverter for generating and supplying the feedback current to the inverter control unit and generating an AC drive signal in response to the pulse width modulation signal; And a backlight which has a plurality of light sources and generates light in accordance with the AC drive signal.

Backlight unit, inverter, inverter control unit, feedback current

Description

BACKLIGHT UNIT AND LIQUID CRYSTAL DISPLAY DEVICE USING THE SAME AND DRIVING METHOD THEREOF BACKGROUND OF THE INVENTION [0001]

1A and 1B are waveform diagrams showing an AC drive signal according to a conventional PWM signal.

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a backlight unit and a liquid crystal display using the same.

Fig. 3 is a configuration diagram showing the backlight unit shown in Fig. 2 more specifically. Fig.

4 is a waveform diagram showing a PWM signal and an AC drive signal according to an embodiment of the present invention;

BRIEF DESCRIPTION OF THE DRAWINGS FIG.

2: liquid crystal panel 4: data driver

6: Gate driver 8: Timing controller

10: Backlight unit 12: Backlight

14: inverter control unit 16: inverter

22: Transformer 24: Feedback circuit

26: constant current generator PWM signal: pulse width modulated signal

ImI: Constant current ADS: AC drive signal

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a backlight unit for preventing an AC driving signal for driving a plurality of light sources from being distorted and improving the display efficiency of an image, and a liquid crystal display using the same, and a driving method thereof.

BACKGROUND ART Demands for video display devices have been increasing in various forms as an information society has developed. In recent years, a liquid crystal display, a field emission display, a plasma display panel, Various flat panel display devices such as a light emitting display are utilized.

In the liquid crystal display, liquid crystal panels including a plurality of liquid crystal cells arranged in a matrix form controls the amount of light transmitted from a backlight unit to display a desired image on the screen. Specifically, a liquid crystal display device obtains a desired image by forming an electric field in a liquid crystal layer according to a data signal to adjust transmittance of light passing through the liquid crystal layer.

The backlight unit includes a plurality of light sources for generating light, an inverter for driving each light source, and an inverter control unit for controlling the inverter.

Here, the inverter control unit generates a pulse width modulation (PWM) signal in response to a dimming control signal (dimming control signal) inputted from the outside, and supplies it to the inverter. The inverter drives the plurality of light sources by generating the AC drive signal in response to the PWM signal. In addition, the inverter feeds back the currents flowing through the respective light sources to the inverter control unit in order to control the currents flowing through the respective light sources constantly. Accordingly, the inverter control unit compensates the feedback current for the dimming control signal inputted from the outside, generates the PWM signal, and supplies it to the inverter.

However, in the conventional backlight unit, an overcurrent IO is generated in the process of generating the AC driving signal ADS according to the PWM signal, as shown in FIG. 1A, and the AC driving signal ADS is distorted. In order to solve this problem, the feedback current is supplied to the inverter control unit through the capacitor, thereby preventing the occurrence of the overcurrent (IO). However, in this case, as shown in FIG. 1B, the AC drive signal ADS is delayed, causing problems such as being out of synchronization with the PWM signal.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems, and it is an object of the present invention to provide a backlight unit for preventing distortion of an AC driving signal for driving a plurality of light sources to improve image display efficiency, The purpose of the method is to provide.

According to another aspect of the present invention, there is provided a backlight unit including: an inverter controller for generating a pulse width modulated signal by compensating a constant current and a feedback current input from an externally inputted dimming control signal; An inverter for generating the feedback current and supplying the feedback current to the inverter control unit and generating an AC drive signal in response to the pulse width modulation signal; And a backlight which has a plurality of light sources and generates light in accordance with the AC drive signal.

Wherein the inverter control unit generates a pulse width modulation signal such that the duty ratio is variable according to the dimming control signal and converts the amplitude or pulse width of the generated pulse width modulation signal to correspond to the magnitude of the constant current and the feedback current, And the like.

The inverter includes a transformer for generating the AC drive signal in response to the pulse width modulation signal supplied from the inverter controller, a feedback circuit for sensing the current or voltage flowing from the backlight to the transformer, And a constant current generator for generating the constant current and supplying the constant current to the inverter control unit.

The inverter control unit includes an inverter control IC such as BD9766FV or BD9897FV, and the feedback current from the feedback circuit unit is supplied to the current control terminal of the inverter control IC, and the constant current and the charge / As shown in FIG.

According to another aspect of the present invention, there is provided a liquid crystal display device including: a liquid crystal panel including a plurality of pixels; A driver for driving the plurality of pixels; And a backlight unit having the above-described characteristics for irradiating light to the liquid crystal panel. The backlight unit may include a backlight unit.

According to an aspect of the present invention, there is provided a method of driving a backlight unit for generating light by providing a plurality of light sources, Generating a pulse width modulated signal by compensating a constant current and a feedback current input from the constant current circuit; Generating the feedback current and generating an AC drive signal in response to the pulse width modulation signal; And generating light according to the AC drive signal.

According to another aspect of the present invention, there is provided a method of driving a liquid crystal display device including a liquid crystal panel having a plurality of pixels and a liquid crystal display device having a backlight unit for irradiating the liquid crystal panel with light, The method comprising: displaying an image by adjusting a transmittance of light; And a driving method of the backlight unit having the above-described characteristic for irradiating the liquid crystal panel with light.

Hereinafter, a backlight unit according to an exemplary embodiment of the present invention, a liquid crystal display using the same, and a driving method thereof will be described in detail with reference to the accompanying drawings.

2 is a configuration diagram illustrating a backlight unit and a liquid crystal display device using the same according to an embodiment of the present invention. 3 is a configuration diagram showing the backlight unit shown in Fig. 2 in more detail.

The backlight unit 10 shown in Figs. 2 and 3 controls the dimming value control signal input from the outside, that is, the constant current ImI and the feedback current FI input from the outside to the dimming control signal Dim, An inverter control unit 14 for generating a pulse width modulation (PWM) signal by compensating the PWM signal to generate an AC drive signal ADS in response to a PWM signal from the inverter control unit 14, And a backlight 12 having a plurality of lamps and generating light in accordance with the AC drive signal ADS. The configuration and operation method of the backlight unit 10 will be described later in detail with reference to FIGS. 3 and 4. FIG.

2 includes a liquid crystal panel 2 formed with a plurality of pixels, a data driver 4 for driving a plurality of data lines DL1 to DLm, a plurality of gate lines GL1 to GLn, A timing controller 8 for supplying image data RGB inputted from the outside to the data driver 4 and controlling the data driver 4 and the gate driver 6, The backlight unit 10 according to the embodiment of the present invention as described above is provided.

The liquid crystal panel 2 includes a thin film transistor (TFT) formed in each pixel region defined by a plurality of gate lines GL1 to GLn and a plurality of data lines DL1 to DLm, And a capacitor Clc. The liquid crystal capacitor Clc is composed of a pixel electrode connected to the TFT and a common electrode facing the pixel electrode with the liquid crystal therebetween. The TFT supplies data signals from the respective data lines DL1 to DLm to the pixel electrodes in response to scan pulses from the respective gate lines GL1 to GLn. The liquid crystal capacitor Clc charges the difference voltage between the data signal supplied to the pixel electrode and the common voltage supplied to the common electrode, adjusts the arrangement of the liquid crystal molecules according to the difference voltage, and adjusts the light transmittance to implement the gradation. The storage capacitor Cst is connected in parallel to the liquid crystal capacitor Clc so that the voltage charged in the liquid crystal capacitor Clc is maintained until the next data signal is supplied. The storage capacitor Cst is formed by overlapping the pixel electrode with the previous gate line sandwiched by the insulating film. Alternatively, the storage capacitor Cst may be formed by overlapping the pixel electrode with the storage line and the insulating film interposed therebetween.

The data driver 4 converts the digital video data Data into an analog video signal in accordance with the data control signal DCS from the timing controller 8 and supplies the video signals to the respective horizontal lines GL1 to GLn, And supplies analog video signals for one horizontal line to each of the data lines DL1 to DLm for each period. That is, the data driver 4 selects a gamma voltage having a predetermined level according to the gradation value of the analog video signal and supplies the selected gamma voltage to each of the data lines DL1 to DLm.

The gate driver 6 sequentially generates a scan pulse, for example, a gate high pulse in response to the gate control signal GCS from the timing controller 8, and sequentially supplies the gate pulse to each of the gate lines GL1 to GLn.

The timing controller 8 arranges image data (RGB) from the outside so as to be suitable for driving the liquid crystal panel 2 and supplies it to the data driver 4. [ The data driver 4 and the gate driver 6 are controlled by generating a gate control signal GCS and a data control signal DCS using synchronous signals DCLK, DE, Hsync and Vsync from the outside . The timing controller 8 generates a dimming control signal Dim using external synchronizing signals DCLK, DE, Hsync and Vsync and image data RGB and outputs the dimming control signal Dim to the backlight unit 10 Supply.

The backlight 12 includes a plurality of light sources (not shown) that generate light. Here, the light source may be an external electrode fluorescent lamp (EEFL), a light emitting diode (LED), a cold cathode fluorescent lamp (CCFL), a hot cathode fluorescent lamp (HCFL) ) And the like are mainly used. The lamp is driven by a high-voltage AC voltage from the inverter 16, that is, the AC drive signal ADS to generate light.

The inverter control unit 14 compensates the constant current ImI and the feedback current FI input from the inverter 16 to the dimming control signal Dim supplied from the external system or the timing controller 8 to generate a PWM signal, And supplies it to the inverter 16 again. For example, the inverter control unit 14 generates the PWM signal so that the duty ratio, that is, the high signal ratio in one period is varied according to the dimming control signal Dim. The PWM signal is generated by compensating the constant current ImI and the feedback current FI by converting the amplitude or pulse width of the PWM signal according to the constant current ImI and the feedback current FI. In other words, the PWM signal is generated in response to the dimming control signal (Dim), and the amplitude or pulse width is converted and output so as to correspond to the magnitude of the feedback current (FI) input. The constant current ImI is also supplied to the inverter control unit 14 during the period in which the feedback current FI is charged in the capacitor Cap, that is, during the period during which the feedback current FI is not output. Accordingly, the PWM signal can be output in synchronization with the dimming control signal Dim without being delayed. Here, the high period of the PWM signal is the lamp driving time, that is, the lamp ON time.

Meanwhile, the inverter control unit 14 may generate the PWM signal by compensating the constant current ImI and the feedback current FI to the dimming control signal Dim through a switching circuit (not shown). Specifically, the switching circuit of the inverter control unit 14 outputs the feedback current FI and the constant current ImI in response to the dimming control signal Dim, and may generate the PWM signal so as to correspond to the magnitude of the output current . Since the constant current ImI is also supplied to the inverter control unit 14 during the period in which the feedback current FI is charged in the capacitor Cap, the PWM signal can be output so as to be synchronized with the dimming control signal Dim without being delayed .

Although the inverter control unit 14 of the present invention has been described with reference to FIG. 3 as a separate structure from the inverter 16 for convenience of explanation, the inverter control unit 14 may be configured inside the inverter 16. FIG. In other words, since the inverter control unit 14 uses an inverter control IC such as BD9766FV or BD9897FV, the inverter control unit 14 can be formed inside or outside the inverter 16, respectively. At this time, the feedback current (FI) and the constant current (ImI) are inputted to the current control terminal and feedback control terminal of the inverter control IC, respectively.

3 and 4, the inverter 16 of the present invention includes a transformer 22 for generating an AC drive signal ADS in response to a PWM signal from the inverter control unit 14, A feedback circuit portion 24 for sensing a current or voltage flowing through the capacitor 22 and generating a feedback current FI corresponding thereto, a capacitor Cap for charging / discharging a feedback current FI to prevent overcurrent generation, And a constant current generating unit 26 for generating a constant current ImI and supplying it to the inverter control unit 14. [

The thus configured inverter 16 is driven in a burst mode in which the lamp on / off time of the backlight 12 is varied in response to the PWM signal, as shown in FIG. At this time, the inverter 16 adjusts the brightness of the lamp by changing the ON / OFF time of the lamp or varying the voltage level of the AC driving signal ADS.

The transformer 22 is composed of first and second windings or the like, and generates a high-voltage AC drive signal ADS according to the turns ratio of the first and second windings. 4, the AC voltage from the outside is amplified by the high-voltage AC drive signal ADS so as to correspond to the ON / OFF time and the amplitude of the PWM signal and supplied to the backlight 12. Here, the lamp driving signal ADS is supplied at a different frequency level depending on the frequency for driving the liquid crystal display device and the number of lamps used. For example, when driving a liquid crystal display device composed of eight lamp groups at 60 Hz, one frame is 1/60 second (16.7 ms). Therefore, in order to drive eight lamp groups for one frame, one cycle is 2.08 ms And may be supplied with a pulse width according to the set frequency. Also, the voltage level of the lamp driving signal ADS may be set differently according to the size of the liquid crystal display device and the number of the lamps, but may be set to have a level of 100V to 220V in the case of a general large-screen liquid crystal display device.

The feedback circuit portion 24 senses a current or voltage flowing from the backlight 12 to the transformer 22 and generates a feedback current FI corresponding thereto. To this end, the feed back circuit portion 24 includes a diode Di and a first resistor R1 connected in series in a grounding direction at a contact point between the transformer 22 and the backlight 12, a diode Di and a first resistor R1 and a second resistor R2 connected between the contact point of the inverter control unit 14 and the current control terminal of the inverter control unit 14. [

The feedback circuit unit 24 may include a capacitor Cap between the second resistor R2 and the feedback control terminal of the inverter control unit 14 to prevent an overcurrent from being generated. That is, a capacitor Cap that stabilizes the AC drive signal ADS by preventing the occurrence of an overcurrent by charging / discharging the feedback current FI may be provided inside the feedback circuit portion 24. [

The constant current generating section 26 generates a constant current ImI or a constant voltage and supplies it to the inverter control section 14. [ Here, if the constant current ImI supplied to the feedback control terminal is excessively applied, an overcurrent may be generated when the AC drive signal ADS is generated, and the AC drive signal ADS may be delayed if it is too small. Therefore, the intensity of the constant current ImI supplied to the feedback control terminal is preferably adjusted according to the size of the backlight unit 10 and the intensity of the AC drive signal ADS. Here, the constant current generating unit 26 is provided as a single device, and is usually manufactured as a reference voltage terminal as a power input terminal, a cathode terminal as a constant current / voltage output terminal, and a 3-pin device having an anode terminal. As described above, in the present invention, the constant current generating unit 26 composed of a single element is constructed inside the inverter 16. However, the constant current ImI necessary for the embodiment of the present invention is not limited to the power source of the liquid crystal display device System and so on.

As described above, the backlight unit 10 according to the embodiment of the present invention, the liquid crystal display using the same, and the driving method thereof are provided with a feedback current control unit FI) and a constant current (ImI). Thus, the AC drive signal ADS is generated in synchronization with the PWM signal without being delayed, because the constant current ImI is also supplied during the period in which the feedback current FI is charged in the capacitor Cap. That is, the backlight unit 10 according to the present invention can prevent the occurrence of an overcurrent and minimize the distortion of the AC drive signal ADS, such as preventing the AC drive signal ADS from being delayed, The efficiency can be improved.

It will be apparent to those skilled in the art that various modifications and variations can be made in the present invention without departing from the spirit or scope of the invention. Will be clear to those who have knowledge of.

As described above, the backlight unit according to the embodiment of the present invention, the liquid crystal display using the same, and the driving method thereof have the following effects.

First, the backlight unit of the present invention can prevent the occurrence of an overcurrent and also prevent an AC drive signal distortion such as a delay of an AC drive signal for driving a light source.

Second, the liquid crystal display device using the backlight unit of the present invention can prevent the AC drive signal for driving the light source from being distorted, thereby improving the display efficiency of the displayed image.

Claims (10)

An inverter control unit for generating a pulse width modulation signal in accordance with a dimming control signal input from the outside and converting the pulse width modulation signal so as to correspond to a magnitude of at least one of a constant current and a feedback current; An inverter for generating and supplying the feedback current to the inverter control unit and generating an AC drive signal in response to the converted pulse width modulation signal; And And a backlight which has a plurality of light sources and generates light in accordance with the AC drive signal, The inverter control unit Generating a pulse width modulation signal such that the duty ratio varies according to the dimming control signal, and converting at least one of the amplitude or the pulse width of the generated pulse width modulation signal to correspond to the magnitude of the constant current and the feedback current And supplies it to the inverter, The inverter A feedback circuit unit for sensing a current or voltage flowing from the backlight to the transformer and generating the feedback current corresponding to the current or voltage flowing in the transformer, A capacitor for charging / discharging the feedback current to prevent the generation of the feedback current, and a constant current generating unit for generating the constant current and supplying the constant current to the inverter control unit. delete delete The method according to claim 1, The inverter control unit BD9766FV or BD9897FV, and the feedback current from the feedback circuit portion is supplied to the current control terminal of the inverter control IC, and the constant current and the charge / discharge feedback current are supplied to the feedback control terminal And a backlight unit. A liquid crystal panel formed with a plurality of pixels; A driver for driving the plurality of pixels; And supplies the image data input from the outside to the driving unit, The liquid crystal display device according to any one of claims 1 to 4, further comprising a backlight unit for emitting light to the liquid crystal panel. A driving method of a backlight unit for generating light by providing a plurality of light sources, Generating a pulse width modulation signal in accordance with a dimming control signal input from the outside and converting and outputting the pulse width modulation signal so as to correspond to a magnitude of at least one of a constant current and a feedback current; Generating the feedback current and generating an AC drive signal in response to the converted pulse width modulated signal; And And generating light in accordance with the AC drive signal, The step of generating and converting the pulse width modulation signal and outputting Generating a pulse width modulation signal such that the duty ratio is variable according to the dimming control signal and converting the amplitude or pulse width of the generated pulse width modulation signal to correspond to the magnitude of the constant current and the feedback current, Including, The step of generating the AC drive signal Generating the AC drive signal in response to the pulse width modulated signal, Detecting the current or voltage from the plurality of light sources and generating the corresponding feedback current, charging / discharging the feedback current to prevent the occurrence of an overcurrent, and generating the constant current And a driving method of the backlight unit. delete delete The method according to claim 6, The step of generating and converting the pulse width modulation signal and outputting Supplying the feedback current to an inverter control IC current control terminal of the backlight unit, and And supplying the constant current and the charged / discharged feedback current to a feedback control terminal of the inverter control IC. A method of driving a liquid crystal display device including a liquid crystal panel having a plurality of pixels and a backlight unit for emitting light to the liquid crystal panel, Adjusting an optical transmittance to display an image; And The method of driving a liquid crystal display device according to claim 6 or 9, further comprising the step of driving the liquid crystal panel.

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