KR100912696B1 - A Back Light - Google Patents

Abstract

The present invention relates to a backlight which can increase reliability, and the backlight of the present invention collects a plurality of fluorescent lamps connected to respective electrodes from a high voltage side and a low voltage side of an inverter, and condenses white light emitted from the fluorescent lamps in one direction. It is formed in a 'c' shape to surround the fluorescent lamps to correspond to the high-voltage electrode of the top and bottom of the fluorescent lamp so that the corresponding area is equal from one electrode of the plurality of fluorescent lamps connected to the high-voltage side of the inverter By using a light collecting cover having a plurality of holes having a predetermined shape in a portion thereof, variations in leakage current can be reduced, thereby increasing reliability of backlight power consumption.

Fluorescent lamps, inverters, holes, condensing covers, light guide plates

Description

Backlight {A Back Light}

1 is a schematic perspective view of a liquid crystal display of a general transmissive TN mode.

2 is a cross-sectional view schematically illustrating a backlight of a general light guide plate type.

3 is a perspective view illustrating a light source unit of a backlight according to the related art.

4 is a general inverter circuit diagram.

5 is a perspective view showing a backlight of the present invention.

6 is a circuit diagram schematically showing an inverter of a backlight according to the present invention.

7 is a view schematically showing a backlight according to the present invention.

8 is a waveform diagram illustrating an applied voltage and a leakage current of a backlight according to the present invention.

* Description of the main parts of the drawings *

101: fluorescent lamp 101a: high voltage side electrode

101b: low voltage side electrode 102: inverter

103: light collecting cover 104: hole

105: DC / AC converter 107a: high voltage side

107b: low pressure side

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a backlight used in a liquid crystal display device. Specifically, a light collecting lamp for reflecting light emitted from a plurality of fluorescent lamps in one direction is a portion adjacent to the high voltage side electrodes of the top and bottom fluorescent lamps of the fluorescent lamp. The present invention relates to a backlight capable of increasing the reliability of backlight power consumption by forming a plurality of holes in the leakage current and reducing variations in leakage current.

Recently, due to the rapid development of the information and communication field, the importance of the display industry for displaying desired information is increasing day by day, and until now, CRT (cathode ray tube) among the information display devices can display various colors, and the brightness of the screen is increased. It has also enjoyed steady popularity so far because of its superiority.

However, there is an urgent need for the development of flat panel displays instead of CRTs that are bulky and bulky due to the desire for large, portable and high resolution displays. These flat panel displays have a wide range of applications from computer monitors to displays used in aircraft and spacecraft.

Currently produced or developed flat panel displays include liquid crystal display (LCD), electro luminescent display (ELD), field emission display (FED), plasma display panel (PDP), etc. In order to achieve an ideal flat panel display, light weight, high brightness, high efficiency, high resolution, high speed response characteristics, low driving voltage, low power consumption, low cost, and color display characteristics are required.

Among such flat panel displays, the liquid crystal display device is in the spotlight because of its durability as well as its desire.

A liquid crystal display device is an image display device using optical anisotropy characteristics of liquid crystals. When light is irradiated onto a liquid crystal having polarization characteristics according to a voltage application state, the liquid crystal display device determines the amount of light that passes according to the alignment state of the liquid crystals according to the voltage application. It is a device that can control and express an image.

As described above, in order to configure the liquid crystal display device, a liquid crystal panel including a liquid crystal formed between two substrates and a driving circuit provided around the liquid crystal panel to apply a signal to the liquid crystal panel and control such a signal are required. Do.

In this case, since the liquid crystal panel does not emit light by itself, the reflective liquid crystal display device is restricted from being used in a dark space when it is reflected from the liquid crystal panel using external light such as sunlight.

Accordingly, the transmissive liquid crystal display device may solve a problem of space limitation by providing a separate backlight under the liquid crystal panel and irradiating parallel rays.

Hereinafter, a liquid crystal display of a general transmissive TN mode will be described with reference to the drawings.

1 is a schematic perspective view of a liquid crystal display of a general transmissive TN mode.

As shown in FIG. 1, the LCD includes an upper substrate 11 for expressing color, a lower substrate 12 for applying a signal to each pixel, and a liquid crystal layer 13 formed between the two substrates. The liquid crystal panel 10 and the first and second polarizing plates 14 and 15 are disposed to be perpendicular to each other above and below the liquid crystal panel 10.

Although not shown, a lower portion of the liquid crystal panel 10 includes a light guide plate, a reflecting plate, a diffusion plate, and a prism for transmitting light emitted from a light source such as a fluorescent lamp.

Here, the lower substrate 12 is also called an array substrate, and a thin film transistor (not shown), which is a switching element, and a pixel electrode (not shown) for displaying an image are formed in a matrix type.

The upper substrate 11 is also referred to as a color filter substrate, and has a black matrix for preventing light leakage to the outside of the pixel region, and colors of R (red), G (green), and B (blue) corresponding to the pixel electrodes. And a common electrode (not shown) on the black matrix and the color filter.

Pixel electrodes (not shown) and common electrodes (not shown) respectively formed on the lower substrate 12 and the upper substrate 11 are indium-tin oxides for transmitting light emitted from the backlight. -oxide: It is composed of transparent conductive metal such as ITO). In this case, in the IPS mode liquid crystal display, the common electrode is formed on the lower substrate.

The liquid crystal molecules 18 of the liquid crystal layer 13 formed between the upper substrate 11 and the lower substrate 12 are formed by the alignment layer (not shown) formed on the surfaces of the two substrates facing each other. The azimuth angles from 12) to the upper substrate 11 are twisted by 90 degrees.

In addition, the first and second polarizing plates 14 and 15 have a characteristic in which the polarization direction is vertical.

That is, white light irradiated from the backlight is polarized in one direction by the first polarizing plate 14, and the light polarized by the first polarizing plate 14 is refracted by the lower substrate 12 and the liquid crystal layer 13. do.

At this time, as shown, the light incident on the liquid crystal layer 13 is refracted to be orthogonal to the direction polarized by the first polarizing plate 14 by rotating the azimuth angle by 90 degrees by the twisting of the liquid crystal molecules 18. . As such, the intensity of transmitted light may be adjusted by adjusting the azimuth or polar angle of the liquid crystal molecules 18 in the liquid crystal layer 13.

In addition, the white light refracted by the liquid crystal layer 13 passes through the upper substrate 11 on which a color filter (not shown) capable of expressing an RGB color is formed, and the upper substrate 11 has a color. Light passes through the second polarizing plate 15 and is represented as an image.

Therefore, a general liquid crystal display device may implement an image by making light emitted from a backlight into parallel light, polarizing and refracting the parallel light, adjusting the intensity of transmitted light, and expressing color.

On the other hand, the backlight for supplying parallel light in such a liquid crystal display device is a method of disposing a cylindrical fluorescent lamp, it is divided into a direct type method and a light guide plate method.

First, the direct type disposes the fluorescent lamp on the plane. Since the shape of the fluorescent lamp appears on the liquid crystal panel, the distance between the lamp and the liquid crystal panel must be maintained, and the light scattering means must be arranged for the uniform distribution of light quantity. Therefore, there is a limit to thinning. In addition, as the panel becomes larger, the area of the light exit surface of the backlight also increases. When the direct backlight is enlarged, the light exit surface is not flat unless the light scattering means secures sufficient thickness. Therefore, the thickness of the light scattering means must be sufficiently secured.

On the other hand, the light guide plate method is to install a fluorescent lamp on the outside and to distribute the light to the entire surface by using the light guide plate, the fluorescent lamp is installed on the side, the light has to pass through the light guide plate has a problem of low brightness. In addition, high optical design and processing technology for the light guide plate is required for uniform distribution of light intensity.

Since the direct type and the light guide plate have their disadvantages, the direct type backlight is mainly used in the liquid crystal display device where brightness is more important than the screen thickness. In the liquid crystal display device of importance, a light guide plate type backlight is mainly used.

Currently, research and development of a light guide plate type backlight for realizing a high brightness backlight with low power consumption continue.

FIG. 2 is a cross-sectional view schematically illustrating a backlight of a general light guide plate type. The general backlight includes a light source unit including a fluorescent lamp 20 and a light collecting cover 21 that emit white light, and the light emitted from the fluorescent lamp 20. A light guide plate 22 for supplying light to the front of the liquid crystal panel 27, a reflector 23 for reflecting light leaking to the back of the light guide plate 22, and for diffusing the light supplied from the light guide plate 22 It comprises a diffusion plate 24, a plurality of prism sheet 25 for increasing the brightness by collecting the light passing through the diffusion plate 24 and a protective sheet 26 for protecting the prism sheet 25 do.

Here, the light guide plate 22 has a structure that becomes thinner as it moves away from the light source part in order to solve the problem that the white light of the fluorescent lamp 20, which is a light source, is inferior in linearity and to distribute the white light evenly from the light source part to a distance.

In addition, the diffusion plate 24 and the prism sheet 25 are diffused and concentrated in order to make the light dispersed on the two-dimensional plane from the light guide plate 22 into a uniform light and parallel white light to the liquid crystal panel 27. To supply.

The fluorescent lamp 20 receives power from the outside to emit white light, and the condensing cover 21 collects the light emitted from the fluorescent lamp in one direction and supplies the light to the light guide plate 22.

On the other hand, in accordance with the trend toward larger size of the liquid crystal display device, a plurality of fluorescent lamps 20 may be positioned parallel to one side of the light guide plate 22 to supply white light having high luminance to the liquid crystal panel 27.

3 is a perspective view illustrating a light source unit of a backlight according to the prior art, in which a plurality of fluorescent lamps 20 are arranged in parallel at regular intervals in order to increase luminance, and the plurality of fluorescent lamps ( Condensing cover 21 is formed in a 'c' shape in order to focus the white light irradiated from 20 in one direction.

Although not shown, the fluorescent lamp 20 is sealed by a glass tube to protect a mixed gas such as an inert gas (not shown), and a fluorescent material is coated on an inner wall of the glass tube.

Here, the fluorescent lamp 20 is divided into a cold cathode fluorescent lamp (Cold Cathode Fluorescent Lamp) and an external electrode fluorescent lamp (External Electrode Fluorescent Lamp) according to the position of the electrode in the glass tube, generally the external electrode fluorescent lamp Cold cathode fluorescent lamp is mainly used because cold cathode fluorescent lamp has low power consumption at low voltage.

In addition, the light collecting cover 21 surrounds the plurality of parallel fluorescent lamps 20 and opens one side thereof to reflect white light emitted by the fluorescent lamps 20 in one direction.

In this case, the fluorescent lamp 20 is connected to the inverter circuit as shown in Fig. 4 a plurality of electrodes spaced apart from each other in the glass tube.

4 is a general inverter circuit diagram, the inverter converts the inverter driving DC voltage into a fluorescent lamp driving AC voltage using various switching elements (Q1, Q2) and transformer (T1) of the DC / AC converter 31 The fluorescent lamp 20 is output to the high pressure side 32a and the low pressure side 32b.

At this time, the high voltage side electrode 20a of the fluorescent lamp 20 has a high frequency based on a voltage flowing through the low voltage side electrode 20b by the switching elements Q1 and Q2 and a transformer, and a high voltage of about 1000 V or more is applied. Is approved.

Therefore, discharge occurs in the fluorescent lamp 20 due to the high voltage, and white light is emitted by the discharge.

As described above, the backlight of the prior art may provide a plurality of fluorescent lamps 20 driven by an inverter to one side of the light guide plate 22 to supply white light having high luminance to the liquid crystal panel 27.

However, the backlight of the prior art has the following problems.

In the backlight of the prior art, a current is induced in a condensing cover adjacent to a high voltage side of a fluorescent lamp to which a high voltage is applied from an inverter to generate a leakage current, and an area of the condensing cover adjacent to each of a plurality of fluorescent lamps is changed to determine the leakage current. Since the deviation occurs, the light efficiency may decrease due to the luminance difference between the plurality of fluorescent lamps.

In addition, in order to prevent the luminance difference between the plurality of fluorescent lamps in consideration of the leakage current, the inverter has to be complicatedly designed.

The present invention has been made to solve the above problems, a plurality of areas in a large area corresponding to the high-pressure side electrodes of the fluorescent lamp so that the area of the condensing cover adjacent to the high-pressure side electrodes of the plurality of fluorescent lamps. It is an object of the present invention to provide a backlight that can reduce the variation of leakage current by forming holes.

The backlight of the present invention for achieving the above object is generated in the inverter connected to the respective electrodes from the high voltage side and the low voltage side of the inverter and the high voltage side and the low voltage side of the inverter to convert the DC voltage into AC voltage A plurality of fluorescent lamps arranged in parallel in order to emit white light by receiving an alternating current voltage, and formed in a '-' shape so as to surround the fluorescent lamps to condense the white light emitted from the fluorescent lamps in one direction; And a plurality of holes having a certain shape in a portion adjacent to the high voltage side electrodes of the uppermost and the lowest fluorescent lamps so that corresponding areas are equal from one electrode of the plurality of fluorescent lamps connected to the high voltage side of the inverter. And a cover.

The light guide plate may further include a light guide plate formed on an open portion of the 'c'-shaped light collecting cover to receive white light emitted from the fluorescent lamp and focused in one direction by the light collecting cover to provide straightness and evenly distributed to a long distance. This is preferred.

The hole is preferably formed in the light collecting cover in the opposite direction in which the light guide plate is formed.

Preferably, the hole has a triangular, square, rhombus or ellipse shape.

The light collecting cover is preferably made of a material having excellent reflectivity made of aluminum.

When the condensing cover has three fluorescent lamps, the holes may be formed in the condensing cover of a portion adjacent to the high voltage side electrodes of the upper and lower fluorescent lamps.

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Hereinafter, the backlight of the present invention will be described in detail with reference to the accompanying drawings.

5 is a perspective view showing a backlight of the present invention.

As shown in FIG. 5, the backlight of the present invention is connected to an inverter (not shown) having a high voltage side and a low voltage side to convert a DC voltage into an AC voltage, and connected to the high voltage side and the low voltage side of the inverter, respectively. A plurality of fluorescent lamps 101 arranged vertically and parallel to emit white light by receiving an AC voltage generated from an inverter, and the fluorescent lamps for condensing white light emitted from the fluorescent lamps 101 in one direction; It is formed in a 'c' shape so as to surround the 101 horizontally, the uppermost and the lowermost fluorescent lamp 101 so that the contact area from one electrode of the plurality of fluorescent lamps 101 connected to the high voltage side of the inverter is equal And a condensing cover 103 having a plurality of holes 104 having a predetermined area in a portion corresponding to the high-pressure side electrode.

Although not shown, the 'C' shaped condensing cover 103 is provided to receive white light that is emitted from the fluorescent lamp 101 and condensed in one direction by the condensing cover 103 to impart straightness and evenly to a long distance. And a light guide plate formed at an open portion of the light guide plate, a reflecting plate reflecting white light leaking to the rear surface of the light guide plate, and a diffusion plate and a prism sheet for diffusing and concentrating white light supplied from the reflecting plate and the light guide plate.

In this case, the light collecting cover 103 uses a material having excellent reflectance, that is, a metallic material such as aluminum to concentrate the white light emitted from the plurality of fluorescent lamps 101 arranged side by side at a predetermined interval to the light guide plate.

In addition, the hole 104 may be formed in the light collecting cover 103 in the opposite direction in which the light guide plate is formed, and the shape of the hole 104 may have a triangular shape, a rectangular shape, a rhombus, an ellipse, and a circular shape.

The inverter includes a switching element and a transformer and outputs the AC voltage to two electrodes of the fluorescent lamp 101 through two terminals of the high voltage side and the low voltage side.

FIG. 6 is a circuit diagram schematically illustrating an inverter of a backlight according to the present invention, wherein the inverter 102 includes a DC / AC converter 105 for converting an inverter driving voltage Vcc1 into an AC high voltage for driving a lamp and outputting the same. A high voltage side 107a and a low voltage side 107b are connected in series to an output of the DC / AC converter 105 to apply an AC voltage to both electrodes of the fluorescent lamp 101.

The DC / AC converter 105 switches the switching elements Q1 and Q2 for alternately switching and outputting the inverter driving voltage Vcc1 and the voltage induced by the switching of the switching elements Q1 and Q2. and a transformer (T1) for inducing high pressure to the secondary side (n2) by n1: n2.

Reference numeral L1 denotes a line filter, R1-R3 denotes a resistor, C1-C3 denotes a capacitor, and D1 denotes a diode.                     

At this time, a high voltage of about ± 1000 V or less is applied to the high voltage side electrode 101a of the fluorescent lamp 101 connected to the high voltage side 107a of the inverter 102, and the low voltage side 107b of the inverter 102 is applied. A low voltage of about ± 5V or less is applied to the low voltage side electrode 101b of the fluorescent lamp 101 connected to.

Therefore, the fluorescent lamp 101 emits light by an alternating voltage applied to the high voltage side electrode 101a and the low voltage side electrode 101b of the fluorescent lamp 101.

7 is a schematic view of a backlight according to the present invention, and the high voltage side electrode 101a of the plurality of fluorescent lamps 101 parallel to one direction from the high voltage side 107a and the low voltage side 107b of the inverter 102. ) And the low voltage side electrode 101b.

At this time, the fluorescent lamp 101 is a cold cathode fluorescent lamp (Cold Cathode Fluorescent Lamp) located in the glass tube of the high-pressure side electrode (101a) and the low-pressure side electrode (101b), the mixture such as inert gas and mercury molecules in the glass tube In order to protect the gas (not shown), it is sealed and protected, and a fluorescent substance is coated on the inner wall of the glass tube.

 That is, the mixed gas between the high voltage side electrode 101a and the low voltage side electrode 101b of the fluorescent lamp 101 may be viewed as a resistor, and a high voltage is applied from the inverter 102 so that a high voltage is applied between the two electrodes. Is caught, the electrons collide with the mercury molecules in the process of moving the electrons applied from one of the two electrodes to the other electrode at high speed, and the secondary electrons are released in the process, and the mercury molecules are unstable. It is excited by state.                     

In addition, ultraviolet rays are generated in the process of reducing the excited mercury molecules to a stable state, and the ultraviolet rays are absorbed by the fluorescent material to excite the fluorescent material and stabilize to emit visible light.

However, as shown, when a high voltage is applied to the high voltage side electrode 101a of the fluorescent lamp 101, not only the potential difference with the low voltage side electrode 101b, but also the potential difference with the light collecting cover 103 outside the glass tube. Will have

At this time, a capacitance is generated due to the potential difference between the high voltage side electrode 101a of the fluorescent lamp 101 and the light collecting cover 103 to generate a leakage current in the light collecting cover 103.

8 is a waveform diagram showing an applied voltage and a leakage current of a backlight according to the present invention, wherein the leakage current is a constant phase according to an alternating current high voltage applied from the inverter 102 to the high voltage side electrode 101a of the fluorescent lamp 101. It is generated by the light collecting cover 103 with a difference.

This leakage current is generated more as the capacitance increases, so the capacitance must be reduced.

Accordingly, the capacitance is inversely proportional to the distance between the high voltage side electrode 101a of the fluorescent lamp 101 and the light collecting cover 103, and the high voltage side electrode 101a and the light collecting cover 103 of the fluorescent lamp 101 are inversely proportional to each other. Is proportional to the dielectric constant of the material (mixed gas, glass tube and air) present between the < RTI ID = 0.0 > and < / RTI >

At this time, since the distance between the high voltage side electrode 101a and the light collecting cover 103 of the fluorescent lamp 101 and the material existing between the two are not easy to change, the high pressure side of the fluorescent lamp 101 is not easy to change. The opposing area of the electrode 101a and the light collection curve can be changed.

Accordingly, the backlight of the present invention has a hole 104 having a predetermined shape in the light collecting cover 103 in the opposite direction in which the light guide plate is formed in order to reduce the opposing area of the light collecting curve in which the high voltage electrode 101a of the fluorescent lamp 101 is formed. The leakage current may be reduced by forming a voltage and reducing the capacitance by using the hole 104.

On the other hand, as shown, when the plurality of fluorescent lamps 101 are arranged side by side in parallel to surround the 'C' shaped condensing cover 103, the top and bottom of the fluorescent lamp 101 is the condensing cover The area in contact with 103 is widened.

The current supplied to the plurality of fluorescent lamps 101 is not the same as in Table 1 in the one-side tri-lamp backlight having the structure as described above, and the leakage current is generated in the upper and lower fluorescent lamps 101 so that the central fluorescent lamp 101 is generated. ) A lot of current flows.

Table 1

division    Current (mA) Top fluorescent lamp 5.7 Central fluorescent lamp 11.8 Bottom fluorescent lamp 5.5

At this time, the total current supplied from the inverter 102 to the plurality of fluorescent lamps is about 26.7 mA.

For example, the difference between the leakage current generated by the high voltage side electrodes 101a of the upper and center fluorescent lamps and the difference of the leakage current generated by the high voltage side electrodes 101a of the lower and center fluorescent lamps. If the deviation is 1 mA or more, the hole 104 is made larger in the condensing cover 103 of the portion adjacent to the high voltage side electrode 101a of the upper or lower fluorescent lamp with the higher leakage current. The deviation of the current can be prevented to make the luminance of the backlight uniform.

Therefore, the backlight of the present invention has a high-pressure electrode of each of the uppermost and the lowermost fluorescent lamps 101 so that the area of the light collecting cover 103 in contact with each of the high-pressure side electrodes 101a of the plurality of fluorescent lamps 101 is the same. A hole 104 having a predetermined shape may be formed in the light collecting cover 103 adjacent to 101a to make the currents flowing through the fluorescent lamps 101 the same, and the variation of the leakage current may be reduced.

In addition, when the hole 104 is formed on the high-pressure side of the fluorescent lamp 101 located at the center of the plurality of fluorescent lamps 101, the white light reflected from the part and incident on the light guide plate may be reduced, thereby decreasing luminance. The hole 104 is not formed in the light collecting cover 103 corresponding to the high pressure side of the fluorescent lamp 101 located at the center.

As a result, the backlight of the present invention uses the high voltage side electrodes of the top and bottom fluorescent lamps 101 so as to have the same area of the light collecting cover 103 in contact with each of the high voltage side electrodes 101a of the plurality of fluorescent lamps 101. Since the holes 104 having a predetermined shape are formed in the condensing cover 103 adjacent to 101a, the current flowing through the fluorescent lamps 101 can be equalized, and the variation in leakage current can be reduced. Can increase the reliability.

As described above, the backlight of the present invention has the following effects.                     

In the backlight of the present invention, when the fluorescent lamps of the plurality of fluorescent lamps are used, a plurality of holes are formed to make the area of the condensing cover adjacent to the corresponding electrode of the fluorescent lamp connected to the high voltage side of the inverter equal to the variation of the leakage current. Reliability can be increased because it can be reduced.

Claims (7)

An inverter having a high voltage side and a low voltage side for converting a DC voltage into an AC voltage, A plurality of fluorescent lamps connected to the respective electrodes from the high voltage side and the low voltage side of the inverter and vertically arranged in parallel to emit white light by receiving an AC voltage generated from the inverter; In order to condense the white light emitted from the fluorescent lamps in one direction, the fluorescent lamps are formed in a '-' shape so as to surround the fluorescent lamps, and the corresponding areas from one electrodes of the plurality of fluorescent lamps connected to the high voltage side of the inverter are the same. And a light collecting cover having a plurality of holes having a predetermined shape in a portion adjacent to the high voltage side electrodes of the fluorescent lamps at the uppermost and the lowermost stages. The method of claim 1, And a light guide plate formed at an open portion of the 'c' shaped condensing cover to receive white light emitted from the fluorescent lamp and condensed in one direction by the condensing cover to provide straightness and evenly distributed to a long distance. Backlight. In claim 2, The hole is formed in the light collecting cover in the opposite direction in which the light guide plate is formed. The method of claim 1, And the hole has a triangular, square, rhombus or ellipse shape. The method of claim 1, The light collecting cover is made of a material having excellent reflectivity made of aluminum. In claim 1, And the condensing cover is configured to form the hole in the condensing cover of a portion adjacent to the high voltage side electrodes of the upper and lower fluorescent lamps when the fluorescent lamps are three. delete

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