KR20060076994A - Back-light unit of liquid crystal display device - Google Patents

Abstract

The present invention relates to a backlight unit of a liquid crystal display device, comprising: a lamp in which luminance of light emitted according to a supplied current is controlled; A power conversion unit converting the DC power into AC power, transforming the converted AC power, and supplying the converted AC power; A control unit controlling the power conversion unit to adjust a current supplied to a lamp; It is connected to both ends of the lamp, including a current stabilizer element for reducing the deviation of the input current and output current of the lamp by interaction to maintain a constant supply current of each lamp constituting the backlight unit, and By keeping the supply current of the lamp the same, it is possible to stably supply light to the display panel.

Lamp, Luminance, Current, Coupling, Parallel Drive

Description

BACK-LIGHT UNIT OF LIQUID CRYSTAL DISPLAY DEVICE}

1 is a view showing a backlight unit of a liquid crystal display device according to the present invention;

2 is a view showing a backlight unit according to the present invention by applying parallel driving of a lamp;

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

110: inverter 112: control unit

114: switching unit 116: transformer

122: coupled inductor 123: capacitor

126: lamp VIN: external power

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a back-light unit of a liquid crystal display device. In particular, the present invention can stably supply light to a liquid crystal panel by maintaining a constant current supplied to a lamp. A backlight unit of a liquid crystal display device.                         

Recently, in response to the development of information technology, development of a display device for visual realization of information has been actively made. Cathode ray tubes (CRTs), which are widely used in the related art, are being replaced by liquid crystal displays having advantages of small size, light weight, and low power consumption. Liquid crystal display devices are widely applied to televisions, measuring devices, information terminal devices and the like.

The principle of the liquid crystal display device is to use the optical anisotropy and polarization properties of the liquid crystal. That is, by artificially adjusting the alignment direction of liquid crystal molecules having directionality using polarization, light can be transmitted and blocked by optical anisotropy according to the alignment direction of the liquid crystal. This application is used as a display device. Currently, active matrix liquid crystal display devices in which thin film transistors and pixel electrodes connected thereto are arranged in a matrix manner are used most often because they provide excellent image quality.

The liquid crystal display as described above does not emit light by itself and displays an image by adjusting light transmittance, so that a separate light source for supplying light is required. The liquid crystal display device includes a liquid crystal panel provided with liquid crystal between two substrates to display an image, a driving unit for driving the liquid crystal panel, and a backlight unit provided on a rear surface of the liquid crystal panel to supply light to the liquid crystal panel. .

The backlight unit is composed of an inverter and a lamp. The inverter converts a DC power applied from the outside into an AC power, and then converts the DC power into a high voltage suitable for driving a lamp and supplies the lamp to the lamp. The lamp emits light by the power applied from the inverter to the liquid crystal panel. It is a device to supply.                         

Since the LCD displays an image by adjusting the transmittance of light supplied from the backlight unit, stable driving of the lamp directly affects the image quality of the LCD. In order to drive the lamp stably, the inverter requires high quality and reliable power supply. In particular, in order to reduce manufacturing costs and lighten the liquid crystal display device, a parallel drive for driving a plurality of lamps connected to a single inverter has been studied in recent years. The same driving power is supplied to each lamp having different characteristics when driving in parallel. Research on how to do this is constantly being done. That is, even lamps made in the same manufacturing environment have slightly different material properties, so the internal impedance is different, and the current input to each lamp is also different. In addition, since the lamps are electrically connected to each other, the supply current of adjacent lamps is changed as the current supplied to one lamp changes.

As described above, when a stable current is not supplied to the lamp, it is impossible to stably supply light having a desired brightness to the liquid crystal panel, thereby degrading image quality.

The present invention was devised to solve the conventional problems as described above, and an object of the present invention is to adjust the current balance of both ends of the lamp, so that the current output from the inverter is stably supplied to each lamp The present invention provides a backlight unit of a liquid crystal display device.

The backlight unit for achieving the object of the present invention as described above includes a lamp in which the brightness of light emitted according to the current supplied is adjusted; A power conversion unit converting the DC power into AC power, transforming the converted AC power, and supplying the converted AC power; A control unit controlling the power conversion unit to adjust a current supplied to a lamp; It is connected to both ends of the lamp, and comprises a current stabilizer element for reducing the deviation of the input current and output current of the lamp by interaction.

A feature of the present invention is to maintain a constant brightness of light emitted from a lamp by connecting a current stabilizing element in series at both ends of the lamp and maintaining a constant current supplied to the lamp by a coupling action between the current stabilizing elements. .

Such features of the present invention will be described in detail with reference to the accompanying drawings.

1 is a view showing a backlight unit of a liquid crystal display according to the present invention.

Referring to FIG. 1, the backlight unit receives a lamp 25 for emitting light, a power converter 15 for supplying high voltage AC to the lamp, and an external power supply VIN. And a control unit 12 controlling the power conversion unit 15 to adjust the current supplied to the lamp 25.

The inverter 10 including the control unit 12 and the power conversion unit 15 receives an external power source (VIN), which is a DC power source, converts the AC power, and converts the converted AC power into a high voltage suitable for driving the lamp 25. Step up.

The lamp 25 is electrically connected to the power converter 15, and a coupled inductor 22 serving as a current stabilizer is connected to the input terminal and the output terminal of the lamp 25 in series. do. The coupled inductor 22 is a kind of transformer. Typically, the transformer is used for decompression or boosting through a 1: N turns ratio. It is used to keep the output equal to the input in the circuit by using the characteristic that the same voltage is induced in the coil and the secondary coil.

As the coupled inductor 22 is connected in series to the input terminal and the output terminal of the lamp, respectively, the two coupled inductors 22 interact with each other, that is, the coupling 25. The voltage across both ends is kept constant. For example, when a change occurs in the voltage applied to the input terminal of the lamp 25, the voltage applied to the output terminal is coupled and varies, so that the voltage difference across the lamp 25 is kept constant. That is, a constant current is input to the lamp 25.

In addition, the current flowing across the lamp 25 is maintained by the interaction of the coupled inductor 22. That is, when 6.5 mA of current flows through the input terminal of the lamp 25, 10 mA also flows through the output terminal, thereby reducing the current deviation across the lamp 25. In addition, the distortion of the current waveform is prevented to keep the waveform of the current input to the lamp 25 and the output current the same.

As shown in the figure, the inverter 10 may be driven by connecting only a single lamp 25, but may be driven by connecting a plurality of lamps 25 in parallel. Recently, in accordance with the trend toward larger area and lighter weight of liquid crystal display devices, a single inverter is used to drive a plurality of lamps to realize high luminance and to lightly manufacture a liquid crystal display device.

2 is a view showing a backlight unit according to the present invention by applying parallel driving of a lamp.

Referring to FIG. 2, the backlight unit converts a DC power source into an AC power source, converts the voltage into a high voltage, and delivers the inverter 110, and a plurality of lamps that emit light according to the AC power supplied from the inverter 110. 126).

The inverter 110 receives and transmits the external power VIN, which is a DC power source, and converts the DC power from the controller 112 into an AC power source. It is composed of a switching unit 114 for controlling the amount of current and outputting, and a transformer 116 to convert the AC power supplied from the switching unit 114 according to the winding ratio of the primary side and secondary side to supply to the lamp 126 do.

Although not shown in the drawing, in order to adjust the brightness of the light emitted from the lamp 126, the control unit 110 receives a control signal according to the brightness characteristics of the image information and the switching unit 114 according to the control signal The control adjusts the amount of current supplied to the lamp 126. Therefore, the brightness of the light emitted from the lamp 126 varies according to the current controlled by the switching unit 114.

In addition, the switching unit 114 converts the DC power applied from the control unit 112 into an AC power capable of driving the lamp 126. As described above, the converted AC power is applied to both ends of the primary coil of the transformer 116, and the AC current transformed according to the winding ratio of 1: N is output through the secondary coil and supplied to the lamp 126. .                     

Both ends of the secondary coil of the transformer 116 are respectively connected to both ends of the lamp 126, all lamps 126 are connected in parallel to the secondary coil.

The coupled inductor 122 is provided at both ends of all lamps 126. Thus, as in the single lamp of Fig. 1, a pair of coupled inductors 122 connected to both ends of each lamp 126 are supplied by keeping the voltage difference across the corresponding lamp 126 constant by a coupling action. Keep the current constant.

In addition, since one side of the plurality of lamps 126 are commonly connected, when a voltage change occurs in one lamp 126, the voltage change is equally performed by the coupling action of the coupled inductor 122 in the other lamp 126. This happens. As such, if all the lamps 126 have the same voltage fluctuation in one side of the electrically connected side by using the coupling action between the coupled inductors 122, the voltage across both lamps 126 will be the same. Therefore, since the currents supplied from all the lamps 126 connected in parallel can be kept the same, the phenomenon in which the currents supplied to the lamps 126 vary due to the impedance and the wiring resistance of each lamp 126 can be prevented. Can be. On the other hand, as in the case of driving a single lamp of FIG. 1, even when driving the plurality of lamps 126 in parallel, there is an effect of reducing the deviation of the current flowing through both ends of each lamp 126, the current input to each lamp 126 The waveform can be maintained while being output as it is.

As described above, the coupled inductor 122 provided at both ends of the lamp 126 keeps the supply current of the lamp 126 constant, and the current supplied to all the lamps 126 connected in parallel. Make the values the same. That is, light emitted from the lamp 126 will maintain the same brightness, and each lamp 126 will emit the same brightness. As such, when light is stably supplied to the liquid crystal panel through the backlight unit, it is possible to display a high quality image with high reliability.

A cold cathode fluorescent lamp (CCFL) or an external electrode fluorescent lamp (EEFL) may be used as the lamp 126 connected in parallel to the inverter 110. Conventionally, due to the non-linear characteristics between the current and the voltage, the cold cathode fluorescent lamp is not applied to the parallel driving, but as shown, the capacitor 123 is connected in series across the lamp 126 to correct the phase difference by correcting the phase difference. By making it linear, it is possible to drive a plurality of cold cathode fluorescent lamps in parallel. If the external electrode fluorescent lamp is used for parallel driving, the capacitor 123 may be removed from both ends of the lamp 126 and the coupled inductor 122 may be configured.

As described above, the backlight unit of the liquid crystal display according to the present invention maintains the current supplied to the lamps individually, and maintains the current supplied to each lamp as a whole so that light is stably emitted from the lamps. The image quality of the liquid crystal display device can be improved.

Claims (10)

A lamp in which brightness of light emitted according to a supplied current is controlled; A power conversion unit converting a DC power into an AC power, transforming the converted AC power, and supplying the converted AC power; A controller which controls the power converter to adjust a current supplied to a lamp; And And a current stabilizing element connected to both ends of the lamp, the current stabilizing element reducing the current deviation across the lamp by interaction. The backlight unit of claim 1, wherein the current stabilizer is a transformer having a turns ratio of 1: 1. The backlight unit of claim 1, wherein the lamp is a cold cathode fluorescent lamp (CCFL). The backlight unit of claim 1, wherein the lamp is an external electrode fluorescent lamp (EEFL). The backlight unit of claim 1, wherein one lamp is connected to the power converter in series. The backlight unit of claim 1, wherein a plurality of lamps are connected to the power converter in parallel. 7. The backlight unit of claim 6, wherein the current stabilizing elements provided at both ends of each lamp maintain the same voltage difference across all lamps according to their interaction. 7. The backlight unit of claim 6, wherein when the lamp is a cold cathode fluorescent lamp, a capacitor is connected in series at both ends of each lamp. The method of claim 1, wherein the voltage conversion unit A switching unit converting direct current into alternating current and controlling the amount of current controlled by the controller; And And a transformer for transforming the AC power applied from the switching unit according to a winding ratio of 1: N to supply the lamp to the lamp. An inverter that receives an external DC power source and converts the same into an AC power source, and converts and outputs the AC power source; A light source emitting light according to a current supplied from the inverter; And And a current stabilizing element provided at both ends of the lamp and configured to maintain a constant current input to the lamp by interaction.

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