KR20040046795A - Back light unit - Google Patents

Abstract

PURPOSE: A backlight unit is provided to reduce problems generated by non-uniformity of luminance, color coordinate, and a tube voltage although a light emitting lamp is positioned asymmetrically. CONSTITUTION: Plural outside electrode light emitting lamps are arranged at a lower portion of an LCD(Liquid Crystal Display) panel with a constant interval, as a direct type. In the outside electrode light emitting lamp, the first and second outside electrodes(52a,52b) are formed at the outsides of both ends of a tube(51). Fluorescent material is coated on the inside of the tube(51). Mercury is injected into the inside of the tube(51). The first and second electrodes(52a,52b) are alternately arranged. Electrodes arranged at the left are commonly connected to an end of an inverter(53) and electrodes arranged at the right are commonly connected to the other end of the inverter(53).

Description

Back light unit {BACK LIGHT UNIT}

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a backlight unit, and more particularly, to a backlight unit suitable for reducing occurrence of problems due to luminance unevenness, color coordinate unevenness, and tube voltage unevenness even when the external electrode light emitting lamp is asymmetrical.

CRT (Cathode Ray Tube), one of the commonly used display devices, is mainly used for monitors such as TVs, measuring devices, and information terminal devices.However, due to the weight and size of the CRT itself, Could not respond actively to demands.

Therefore, in the trend of miniaturization and light weight of various electronic products, CRT has a certain limit in weight and size, and is expected to replace the liquid crystal display (LCD) and gas discharge using electro-optic effects. Plasma Display Panels (PDPs) and Electro Luminescence Displays (ELDs) using electroluminescent effects are used. Among them, research on liquid crystal displays is being actively conducted.

In order to replace the CRT, liquid crystal display devices having advantages such as small size, light weight, and low power consumption have been actively developed. Recently, the liquid crystal display device has been developed enough to perform a role as a flat panel display device. As it is used for a monitor of a desktop computer and a large information display device, the demand for a liquid crystal display device is continuously increasing.

Since most of the liquid crystal display devices are light-receiving devices that display images by controlling the amount of light coming from the outside, a separate light source, that is, a back light, for irradiating light to the LCD panel is necessary.

In general, the backlight unit of the liquid crystal display device is a method of arranging a cylindrical light emitting lamp, and is divided into an edge method and a direct method.

In the double-edge method, the lamp unit is installed on the side of the light guide plate for guiding the light, and the lamp unit covers a lamp emitting light, a lamp holder inserted at both ends of the lamp to protect the lamp, and an outer circumferential surface of the lamp, and one side It is provided with a lamp reflector plate fitted to the side of the light guide plate to reflect the light emitted from the lamp toward the light guide plate.

The edge method in which the lamp unit is installed on the side of the light guide plate is applied to a relatively small liquid crystal display device such as a monitor of a laptop computer and a desktop computer, and has good uniformity of light and a long service life. It is advantageous to thin the liquid crystal display device.

On the other hand, the direct type method has been developed mainly as the size of the liquid crystal display device has increased to 20 inches or more, and a plurality of lamps are arranged in a row on the lower surface of the diffuser plate to direct light directly to the front of the LCD panel. will be.

The direct method is mainly used for a large screen liquid crystal display device requiring high luminance because the light utilization efficiency is higher than that of the edge method.

However, the liquid crystal display device adopting the direct method is used as a large monitor or a television, so it takes longer to use than a laptop computer and the number of lamps is larger, so the liquid crystal of the direct method is lower than the edge type liquid crystal display device. It is more likely that a lamp that will not turn on will appear due to the failure and life of the lamp in the display.

In addition, in the edge method in which the lamp units are installed on both side surfaces of the light guide plate, due to the life and failure of the lamp, for example, when only one lamp is not turned on, only the brightness on the screen is lowered. However, in the direct method, since a plurality of lamps are installed at the bottom of the screen, for example, due to the life and failure of the lamp, if one lamp does not light up, the part where the lamp is not lit becomes significantly darker than the other part. The part that does not appear immediately on the screen.

For this reason, since the lamp is frequently replaced in the direct type liquid crystal display device, the direct type liquid crystal display device should have an easy structure for disassembling and assembling the lamp unit.

Hereinafter, a general direct type backlight unit will be described with reference to the accompanying drawings.

1 is a perspective view of a direct type backlight unit having an internal electrode light emitting lamp, and FIG. 2 is a view illustrating a power lead wire connected to the light emitting lamp and the connector of FIG. 1.

As shown in FIG. 1, a backlight unit for a liquid crystal display device having an internal electrode light emitting lamp includes a plurality of light emitting lamps 1, an outer case 3 for fixing and supporting the light emitting lamps 1, and Light scattering means 5a, 5b, 5c disposed between the light emitting lamps 1 and the liquid crystal panel (not shown).

The light scattering means (5a, 5b, 5c) is to prevent the shape of the light emitting lamp from appearing on the display surface of the liquid crystal panel and to provide a light source having an overall uniform brightness distribution, in order to enhance the light scattering effect A plurality of diffusion sheets, diffusion plates, and the like are disposed between the cells.

The inner surface of the outer case 3 is disposed with a reflector 7 so that the light emitted from the light emitting lamp 1 can be concentrated to the display unit of the liquid crystal panel, which is to maximize the utilization efficiency of the light.

The light emitting lamp 1 is a Cold Cathode Fluorescent Lamp (CCFL), as shown in FIG. 2, and electrodes 2 and 2a are disposed at both ends of a tube to supply power to the electrode. When light is emitted, both ends of the light emitting lamp 1 are fitted into grooves formed on both sides of the outer case 3 as shown in FIG. 1.

Power lead wires 9 and 9a for transmitting power for driving the lamp are connected to both electrodes of the light emitting lamp, and the power lead wires 9 and 9a are connected to a separate connector 11 and connected to the driving circuit. Therefore, a separate connector 11 is required for each light emitting lamp 1.

That is, a power lead wire 9 connected to one electrode 2 of the light emitting lamp and a power lead wire 9a connected to the other electrode 2a are connected to one connector 11, and among the power lead wires 9 and 9a. One is bent to the bottom of the outer case (3) is connected to the connector (11).

However, in such a backlight unit for a liquid crystal display device, since the connector is connected to the power supply lead of the light emitting lamp and connected to the driving circuit, a connector is required for each light emitting lamp, which leads to complicated wiring and reduces the thickness of the backlight. The purpose is to not only reduce work efficiency because the power lead wire is bent and connected to the connector for the purpose, but also a separate work is required for this purpose, which increases process time and decreases productivity.

In addition, in order to connect the electrode and the connector, a hole penetrating the outer case must be drilled and both electrodes of the light emitting lamp must be inserted into the hole so that both electrodes of the light emitting lamp are exposed to the outside of the outer case. Falling and maintenance of the luminous lamp is difficult.

On the other hand, the light emitting lamp may be configured by using an EEFL (External Electrode Fluorescent Lamp) having electrodes on both ends of the tube instead of the Cold Cathode Fluorescent Lamp (CCFL).

Hereinafter, an external electrode light emitting lamp (EEFL) and a backlight unit for a liquid crystal display device according to the related art having the same will be described with reference to the accompanying drawings.

3A is a view showing an external electrode light emitting lamp used for a backlight, and FIG. 3B is an equivalent circuit diagram of the light emitting lamp of FIG. 3A.

4 is a layout plan view of an external electrode light emitting lamp of a conventional direct backlight.

In the external electrode light emitting lamp EEFL, first and second external electrodes 32a and 32b are formed at both ends of the tube 31, as shown in FIG. 3A. The fluorescent material is coated, and mercury is injected into the tube 31.

The external electrode light emitting lamp is driven using wall charges formed on the first and second external electrodes 32a and 32b formed at both ends, and both ends serve as capacitors C1 and C2. This equivalent circuit is shown in Figure 3b.

The external electrode light emitting lamp is a state in which one end of the tube 31 is open, mercury is introduced into the open end, and a fluorescent material is injected to coat the open one end with a transparent glass. Is produced.

Since mercury is injected (hereinafter, referred to as a 'mercury injection hole') to be opened and blocked, the shapes of the ends of the light emitting lamps are easily asymmetric with each other. In this case, the mercury inlet is a part of the second external electrode 32b in FIG. 3A.

As a result, a difference occurs in the capacitances C1 and C2 of the first external electrode 32a and the second external electrode 32b, and the tube voltage also varies depending on the direction in which the light emitting lamp is arranged even when the inverter is driven.

Therefore, when the light emitting lamp is turned on for a long time, problems such as pink lighting may occur due to residual DC components and asymmetric tube voltage.

The pink lighting is a phenomenon in which the whole or part of the light emitting lamp is lit in red color due to the decrease or uneven distribution of mercury in the light emitting lamp.

In addition, the fluorescent material may be unevenly applied to the inner wall of the tube 31 during the manufacturing process of the light emitting lamp.

As a result, there arises a problem of luminance unevenness and color coordinate unevenness with respect to the length of the light emitting lamp.

In the conventional direct type backlight unit configured by arranging a plurality of external electrode light emitting lamps asymmetrically at both ends, as shown in FIG. 4, the first external electrodes of the first external electrode part 42a are arranged in the same direction. The second external electrodes of the second external electrode part 42b are also arranged in the same direction.

The first external electrodes of the first external electrode part 42a are connected in parallel to one end of the inverter, and the second external electrodes of the second external electrode part 42b are connected in parallel to the other end of the inverter.

In the backlight unit having the above configuration, since the first and second external electrodes of the light emitting lamps which are asymmetrical to each other are arranged in the same direction, problems of luminance unevenness, color coordinate unevenness, and tube voltage unevenness caused by asymmetry are more prominent.

The present invention has been made to solve the above problems, and in particular, even if the light emitting lamp is asymmetrical, to provide a backlight unit suitable for reducing the occurrence of problems caused by luminance unevenness, color coordinate unevenness and tube voltage unevenness There is this.

1 is a perspective view of a conventional direct type backlight unit having an internal electrode fluorescent lamp;

2 is a view showing a connector connected to the light emitting lamp of FIG.

3A is a view illustrating an external electrode light emitting lamp used in a backlight unit;

3B is an equivalent circuit diagram of the light emitting lamp of FIG. 3A.

4 is a layout plan view of a direct type backlight unit having a conventional external electrode light emitting lamp;

5 is a layout plan view of a direct type backlight unit having an external electrode light emitting lamp according to an embodiment of the present invention;

Explanation of symbols on the main parts of the drawings

51 tube 52a first external electrode

52b: second external electrode 53: inverter

The backlight unit of the present invention for achieving the above object comprises a plurality of light emitting lamps in which the first and second external electrodes formed at both ends are arranged in the left and right; And an inverter connecting the electrodes at the left and right ends of the light emitting lamps in common.

An end of the light emitting lamp having the second external electrode formed therein is sealed after injecting a fluorescent material and mercury into the light emitting lamp.

The backlight unit may include a direct type in which the light emitting lamps are disposed under the liquid crystal panel.

The backlight unit may further include an edge method in which the light emitting lamp is disposed on one side or both sides of the light guide plate.

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

5 is a layout plan view of a direct type backlight unit having an external electrode light emitting lamp according to an embodiment of the present invention.

In the backlight unit of the present invention, as shown in FIG. 5, a plurality of external electrode light emitting lamps are arranged under the liquid crystal panel (not shown) at a predetermined interval, and the external electrode light emitting lamp is a tube (tube) ( 51) The first and second external electrodes 52a and 52b are formed at both ends of the both ends, the inner wall of the tube 51 is coated with a fluorescent substance, and mercury is injected into the tube 51.

The second external electrode 52b is an injection hole into which a fluorescent material and mercury are injected. The second external electrode 52b may be asymmetrically formed with the first external electrode 52a in the sealing process after the mercury injection.

As described above, when the first and second external electrodes 52a and 52b are asymmetrically configured, tube voltage asymmetry, luminance nonuniformity, and color coordinate nonuniformity occur. In the present invention, when the plurality of light emitting lamps are arranged in order to solve the problem, The second external electrodes 52a and 52b are alternately arranged.

That is, if the first light emitting lamp has the first external electrode 52a on the left side and the second external electrode 52b on the right side, the second light emitting lamp adjacent to the second light emitting lamp on the left side and the first external electrode on the right side The external electrode 52b is arranged, and the third light emitting lamp is arranged such that the first external electrode 52a is disposed on the left side and the second external electrode 52b is disposed on the right side.

The electrodes arranged on the left side are commonly connected to one end of the inverter 53, and the electrodes arranged on the right side are commonly connected to the other end of the inverter 53.

If the first and second external electrodes 52a and 52b of the asymmetric light emitting lamps are arranged in cross and then connected in parallel, the impedances of both light emitting lamps become almost equal, so that the tube voltages applied to both ends of the inverter 53 are also equal. The difference is reduced.

As a result, the possibility of a problem occurring when the light emitting lamp is turned on for a long time is reduced, and problems of luminance unevenness and color coordinate unevenness of the backlight generated in the lamp length direction can be solved.

Although not shown, a light scattering means is provided between the light emitting lamps and the liquid crystal panel (not shown).

The light scattering means is to prevent the shape of the light emitting lamp from appearing on the display surface of the liquid crystal panel and to provide a light source having an overall uniform brightness distribution. It is configured by arranging a sheet (Diffusion sheet) and a diffusion plate (Diffusion plate).

In addition to the direct backlight unit as described above, the light emitting lamp can be arranged in the same manner as above in the edge backlight unit.

That is, when two or more light emitting lamps are arranged on one side or both side portions of the light guide plate, the injection holes for injecting the fluorescent material and mercury may be arranged to face different directions as described above.

The backlight unit of the present invention as described above has the following effects.

When arranging a plurality of light emitting lamps of which both ends are asymmetrical, by arranging both ends of the light emitting lamps crosswise, it is possible to solve the problems of tube voltage asymmetry, luminance unevenness and color coordinate unevenness as a whole.

Claims (4)

A plurality of light emitting lamps in which first and second external electrodes formed at both ends are alternately arranged at left and right sides; And an inverter for common connection between the electrodes of the left and right ends of the light emitting lamps. The method of claim 1, And an end portion of the light emitting lamp having the second external electrode formed therein is sealed after injecting a fluorescent material and mercury into the light emitting lamp. The method of claim 1, The backlight unit may include a direct type in which the light emitting lamps are disposed under the liquid crystal panel. The method of claim 1, The backlight unit may further include an edge method in which the light emitting lamp is disposed on one side or both sides of the light guide plate.