KR100983280B1 - Back light unit - Google Patents

Abstract

The present invention relates to a backlight unit, and more particularly, to a backlight unit that allows a light source to be uniformly distributed. The present invention, the backlight unit, the circuit board on which the LED is mounted; A diffusion plate located above the circuit board; The light guide plate may be disposed between the circuit board and the diffuser plate, and includes a light guide plate having a top pattern and a bottom pattern formed on the top and bottom surfaces thereof to uniformly reach the light emitted from the LED.

Backlight, LCD, LED, diffuser, light guide plate.

Description

Back light unit

The present invention relates to a backlight unit, and more particularly, to a backlight unit that allows a light source to be uniformly distributed.

Light Emitting Diodes (LEDs) are well-known semiconductor light emitting devices that convert current into light.In 1962, red LEDs using GaAsP compound semiconductors were commercialized, along with GaP: N series green LEDs. It has been used as a light source for display images of electronic devices, including.

The wavelength of light emitted by such LEDs depends on the semiconductor material used to make the LEDs. This is because the wavelength of the emitted light depends on the band-gap of the semiconductor material, which represents the energy difference between the valence band electrons and the conduction band electrons.

Gallium nitride compound semiconductors (Gallium Nitride (GaN)) have high thermal stability and wide bandgap (0.8 to 6.2 eV), which has attracted much attention in the development of high-power electronic components including LEDs.

One reason for this is that GaN can be combined with other elements (indium (In), aluminum (Al), etc.) to produce semiconductor layers that emit green, blue and white light.

In this way, the emission wavelength can be adjusted to match the material's characteristics to specific device characteristics. For example, GaN can be used to create white LEDs that can replace incandescent and blue LEDs that are beneficial for optical recording.

Since white light can be emitted, it can be used for illumination, and one example thereof is used for a backlight unit of a liquid crystal display device.

Liquid crystal display (LCD), which is a kind of light-receiving flat panel display, does not have its own light emitting capability, and thus forms an image by selectively transmitting illumination light emitted from the outside. To this end, a light source unit for illuminating light is required on the back of the liquid crystal display, which is called a backlight unit (BLU).

The backlight unit of the liquid crystal display device arranges a plurality of white LEDs on a substrate, and uniformly diffuses the light emitted from the white LEDs.

An object of the present invention is to provide a backlight unit in which a light is uniformly distributed in a backlight unit having a thin thickness.

As a first aspect for achieving the above technical problem, the present invention provides a backlight unit comprising: a circuit board on which an LED is mounted; A diffusion plate located above the circuit board; The light guide plate may be disposed between the circuit board and the diffuser plate, and includes a light guide plate having a top pattern and a bottom pattern formed on the top and bottom surfaces thereof to uniformly reach the light emitted from the LED.

As a second aspect for achieving the above technical problem, the present invention provides a backlight unit comprising: a plurality of optical cells comprising a first plate and a second plate positioned on the first plate; A light source mounted on the first plate of the optical cell; And a light guide plate positioned in the optical cell and having at least two concentric or concentric polygonal patterns formed on the top and / or bottom of the light source.

The present invention can provide a uniform backlight light source at a thin thickness while maintaining high light efficiency in the direct type LED backlight unit using the LED. In addition, the use of expensive optical film can reduce the manufacturing cost of the backlight, improve the light efficiency under the same conditions, and reduce the number of LEDs used, thereby reducing thermal resistance and reducing material costs. There is.

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

While the invention allows for various modifications and variations, specific embodiments thereof are illustrated by way of example in the drawings and will be described in detail below. However, it is not intended to be exhaustive or to limit the invention to the precise forms disclosed, but rather the invention includes all modifications, equivalents, and alternatives consistent with the spirit of the invention as defined by the claims.

When an element such as a layer, region or substrate is referred to as being on another component "on", it will be understood that it may be directly on another element or there may be an intermediate element in between. . If a part of a component, such as a surface, is expressed as 'inner', it will be understood that this means that it is farther from the outside of the device than other parts of the element.

It will be understood that these terms are intended to include other directions of the device in addition to the direction depicted in the figures. Finally, the term 'directly' means that there is no element in between. As used herein, the term 'and / or' includes any and all combinations of one or more of the recorded related items.

Although the terms first, second, etc. may be used to describe various elements, components, regions, layers, and / or regions, such elements, components, regions, layers, and / or regions It will be understood that they should not be limited by these terms.

The backlight module is a lighting device located on the back of the LCD panel. On the large size screen, there is a product using a thin tube-type cold cathode tube (CCFL) as a light source, and a light emitting diode (LED) mainly for medium and small devices. There is a backlight product with the light source.

As the thickness of LCD TVs is getting thinner, the thickness of backlight modules is accelerating. To achieve this, the thickness of optical module components (film and instruments, etc.) must be accompanied by LC panels.

Backlight modules using white LEDs have a much wider color gamut than CCFLs, accounting for 85% of the NTSC color gamut specification and much longer in life. In addition, the LED is basically impulse-driven, it can help to improve the video quality by reproducing more dynamic flash scenes that can be seen on CRT TV, which is difficult to reproduce in conventional LCD TV.

Background Art [0002] The structure of a backlight using LEDs is known as a method of indirectly irradiating from the back of the liquid crystal panel (Edge-lit) and a direct type of directly disposing a plurality of light sources behind the liquid crystal panel and directly irradiating the back of the liquid crystal panel.

Among these, the direct type light emits light directly from the back of the liquid crystal panel without passing through the light guide plate, so that the utilization efficiency of the light is high and can be used for a high brightness liquid crystal display device. Therefore, the direct type method can be used as a backlight device of a large liquid crystal display device such as an LCD TV, a liquid crystal display of a personal computer (PC), which requires high brightness.

The present invention relates to a backlight for a thin LCD TV using a direct light guide plate technology. In the present invention, in the LED backlight structure for LCD TV using the conventional LED, the thickness of the existing LED backlight is designed to be less than 50mm in order to improve light diffusion and color mixing, but the light utilization efficiency is lowered.

However, such a backlight is preferably slimmed, and particularly, it is advantageous to provide a uniform backlight light source by effectively diffusing the LED light in the backlight within 15mm thickness.

As an example of the direct-type backlight structure, as shown in FIGS. 1 and 2, a circuit board 2 is positioned on a base reflector 1, and a plurality of LEDs 3 are arranged on the circuit board 2. do.

The transparent plate 4 is positioned on the LED 3 array, and the diffusion plate 5 and the optical films 6 and 7 are positioned at a predetermined distance from the transparent plate 4.

In manufacturing such a backlight, the more the number of the LEDs 3 is used, the more uniform the light source can be realized, but in mass production, it may be disadvantageous in terms of management, manufacturing process, and cost. In addition, since the price is 2 to 3 times higher than the current cold cathode tube (CCFL), as the number of LEDs 3 increases, the manufacturing cost of the backlight increases, thereby implementing a uniform light source using a smaller number of LEDs 3. It is advantageous.

At this time, BEF (bright enhancement film) 6 or prism sheet (prism sheet) and DBEF (dual bright enhancement film) 7 of the optical film is an expensive film, to develop an optical system that performs the same function or increases the light utilization efficiency This can reduce or eliminate the use of such films.

Hereinafter, a process of designing a light guide plate and a light guide plate for controlling the light path of the light emitted from the LED in order to implement a thin backlight module having the above-described characteristics will be described.

3 and 4 illustrate a focus point for designing a thin backlight, for example, if the distance from the surface where the LED is located to the diffuser is defined as the light guide path, a large area in the light guide path having a thickness of 10 mm is shown. The focus point for irradiating (4 inches or more) uniformly is shown.

That is, in FIG. 3, information on the outgoing light in the light guiding path having a thickness of 20 mm is shown. In order to uniformly irradiate a large area (4 inches or more) in the light guiding path having a thickness of 10 mm by changing the diffusion, light is output. It is necessary to change the luminance distribution on the plate to the state as shown in FIG.

To this end, first, the information about the LED output light is input to a light guide plate having a thickness of 20 mm, as shown in FIGS. An in-coupling surface is designed and applied to a backlight unit having a light guiding path having a height of 10 mm as shown in FIGS. 6A and 6B. Such a surface can take various shapes such as aspherical surface or spherical surface.

7A and 7B show light distribution in each region along the height of the light guide path having a thickness of 20 mm, and show a uniform light distribution. The goal is to have a uniform light distribution on the light-emitting surface of the light guide path having a thickness of 20 mm, even in the light guide path having a thickness of 10 mm as shown in FIGS. 8A and 8B.

In this way, in order to have a uniform light distribution on the light exit surface of the 20 mm thickness, the light guide plate 30 is configured to have a uniform light distribution on the light exit surface of the light guide path having a thickness of 10 mm. A structure design is required in which the area is calculated from Snell's law of refraction and totally reflected and re-reflected into the light guide plate 30 uniformly to the light guide plate 30 exit surface. An example of such a structure is illustrated in FIG. 9. As shown.

Here, the LED 20 may be a white LED or a combination of red, green, and blue LEDs. In addition, it is of course possible to use other light sources in addition to the LED.

As such, one example of the backlight unit presented by the structural design to have a uniform light distribution on the exit surface emitted from the LED 20 includes a circuit board 10 and a diffusion plate 40 on which the LEDs 20 are arranged. As an optical module for evenly distributing light between the light guides, the light guide plate 30 is positioned.

The light guide plate 30 may have a lower surface pattern 31 and a space part 32 positioned on the LED 20, and an upper surface pattern 33 on the upper surface of the light guide plate 30. Depending on the size or thickness of the backlight unit, any one of the lower surface pattern 31, the space part 32, and the upper surface pattern 33 may be omitted or may have a different shape. In this case, the space 32 on the LED 20 may have a negative lens shape.

For optimal design of the light guide plate 30 to evenly distribute the light distribution, first, as shown in FIGS. 10 and 11, the pattern of the bottom surface of the light guide plate 30 may be considered first.

For example, the lower surface pattern 31 may be a plurality of circular patterns forming a concentric circle around the portion where the LED 20 is located. The cross-section of the pattern may be a triangular intaglio shape, as shown. . In addition, another example of such a lower surface pattern 31 may take a Fresnel pattern such as a Fresnel lens.

In addition, the lower surface pattern 31 may have a plurality of concentric polygonal patterns, in some cases, not circular. That is, the pattern may be formed of a plurality of regular polygons such as a square, a regular hexagon, a regular octagon, and the like with respect to the position of the LED 20.

If the light guide plate 30 is designed as described above, since the light reflected from the lower surface pattern 31 is emitted vertically, it is possible to remove the expensive film BEF.

In this case, as shown in FIGS. 10 and 11, the respective light paths incident on the lower surface of the light guide plate 30 in order to redirect the light toward the lower surface by total reflection in the light guide plate 30 to the exit surface (vertical direction). By predicting the angle of the pattern 31 can be adjusted.

In Fig. 11, α is defined as in Equation 1, where θ _s corresponds to the incident angle of light at the emission surface. And if θ _i is θ _s / 2, it corresponds to α = θ _s / 2. That is, for example, when applied to the Fresnel pattern, the unit inclination angle α of the Fresnel pattern is advantageous in uniform light output when it corresponds to half of the incident angle of the LED light.

Therefore, the inclination angle of each unit pattern constituting the lower surface pattern 31 may be gradually changed depending on the position to satisfy the above-described conditions, and in some cases, all of the inclination angles may have the same inclination angle.

As such, the light guide plate 30 may be positioned as one block at one LED 20 location, and the unit block may be disposed at each LED 20 location. The light guide plate 30 may use a transparent resin, and a PMMA resin, an acrylic resin, an epoxy resin, or the like may be used. However, it is not limited to these resins, and any transparent resin can be used as a matter of course.

Light reaching the bottom surface by total reflection in the light guide plate 30 is vertically emitted to the top surface of the light guide plate by the bottom surface pattern 31. However, as shown in FIGS. 12 and 13, a shadow region in which light does not reach the distance difference d tan θ between the starting point of the region at which total reflection begins and the light rising vertically from the lower surface after being totally reflected for the first time is shown. This will occur.

In order to remove such a shade area, as shown in FIGS. 14 and 15, the distribution of the upper surface pattern 33 of the light guide plate 30 may be adjusted. That is, the upper surface pattern 33 may use a plurality of concentric circles, concentric polygonal patterns, or Fresnel patterns, as in the lower surface pattern 31 described above, and the distribution of the upper surface pattern 33 for preventing the shadow area from occurring It may be determined in the same process as in FIG. 15.

In Fig. 15, β is equal to Equation 2, and corresponds to β = π / 4-θ _r if θ _c is π / 4. Where _r is the exit angle at which light is emitted from the LED. That is, the unit inclination angle β of the Fresnel pattern of the upper surface pattern 33 is a value obtained by subtracting the emission angle θ _r of the LED from π / 4.

As described above, in the light pattern without the pattern as shown in FIG. 16A, when the light is redistributed in the shade region using the upper surface pattern 33, a uniform light distribution can be obtained as shown in FIG. 16B.

Hereinafter, the result of having simulated the light distribution when the upper surface pattern 33 and the lower surface pattern 31 is used when the light guide plate 30 is used is demonstrated.

17A to 17C show a state in which a pattern is not formed on the light guide plate. In this case, when the LED and the diffusion plate are combined without forming a pattern, the geometry is as shown in FIG. 17A, and the light emitting surface at this time is in a state as shown in FIGS. 17B and 17C. As shown, it can be seen that light is concentrated on the light source LED side.

In this case, as shown in FIG. 18A, when the lower surface pattern is formed on the light guide plate, the light pattern is distributed as shown in FIGS. 18B and 18C. That is, it can be seen that there are lights spread to the surroundings than in the case of FIGS. 17A to 17C.

As shown in FIG. 19A, it can be seen that the light pattern in the case of applying both the upper surface pattern and the lower surface pattern has a relatively very uniform light distribution as shown in FIGS. 19B and 19C.

An example of the backlight unit 100 using such a light guide plate is illustrated in FIG. 20A. 20A shows a part of the backlight unit 100, which is composed of a plurality of optical cells A. As shown in FIG.

As shown in FIG. 20B, the optical cell forms a specific space in which one light source 20 is located. As shown in FIG. 20C, one light guide plate 30 is blocked and positioned in one optical cell. In FIG. 20C, the top pattern 33 is formed on the light guide plate 30 on the light source 20. The upper surface pattern 33 may form a Fresnel pattern. In this case, the center 34 of the Fresnel pattern is positioned above the light source 20.

21 illustrates a specific example of such a backlight unit. That is, the circuit board 10 is positioned on the reflecting plate 50, and the diffusion plate 40 is positioned at a specific distance on the circuit board 10. The circuit board 10 and the diffusion plate 40 form an optical cell, and in some cases, the diffusion plate 40 may be replaced with a transparent plate.

In FIG. 21 two optical cells with two light sources 20 are shown. The light guide plate 30 described above is positioned in the optical cell, and the lower surface pattern 31 and the lens-shaped space 32 are positioned in the light guide plate 30.

Optical films 60 and 70 may be positioned on the diffusion plate 40, and the number of such optical films may be reduced or eliminated by the function of the light guide plate 30 described above. 21 illustrates that a backlight unit having a total thickness of 15 mm or less can be implemented.

22A and 22B show the light output surface and the graph when there is no light guide plate when one LED is used as the light source 20, respectively. FIGS. 23A and 23B show one LED as the light source 20, respectively. When used, the light output surface and the graph in the case of using the light guide plate are shown.

Hereinafter, the results of simulation and actual measurement of an example in which two backlight units (2 × 2) optical cells are formed in the backlight unit will be described.

24A-24C show images on a simulation. That is, the light output surface using the optical cell of 2 × 2 using the light guide plate as shown in FIG. 24a is in the same state as in FIG.

25A illustrates a backlight unit having an actual 2 × 2 optical cell using such a simulation. The light output surface of the backlight unit is shown in FIG. 25B, and the graph of the light output at this time is shown in FIG. 25C.

As shown, it can be seen that the simulation and the practically applied examples are roughly identical and present sufficiently available results.

The above embodiment is an example for explaining the technical idea of the present invention in detail, and the present invention is not limited to the above embodiment, various modifications are possible, and various embodiments of the technical idea are all of the present invention. Naturally, it belongs to the scope of protection.

1 and 2 are a perspective view and a cross-sectional view showing an example of the structure of the backlight unit of the direct type.

3 and 4 are schematic diagrams illustrating an interest point for designing a thin backlight unit.

5A to 8B are schematic diagrams illustrating a process for designing a thin thickness backlight unit.

9 is a cross-sectional view illustrating an embodiment of a backlight unit of the present invention.

10 to 15 are schematic views showing the light guide plate design of the backlight unit.

16A and 16B are schematic views showing the improvement of the light output surface.

17A to 19C are schematic diagrams showing various embodiments and light output using light guide plates.

20A to 20C are diagrams illustrating an example of a backlight unit to which a light guide plate is applied.

21 is a cross-sectional view showing another embodiment of the backlight unit of the present invention.

22A and 22B are diagrams showing the light output surface and the graph when there is no light guide plate when one LED is used as the light source, respectively.

23A and 23B are diagrams showing a light output surface and a graph when a light guide plate is used when one LED is used as a light source, respectively.

24A-C are images in a simulation using 2 × 2 optical cells.

25A to 25C are diagrams showing actual photographs and data using optical cells of 2x2.

Claims (12)

In the backlight unit, A circuit board on which an LED is mounted; A diffusion plate located above the circuit board; Located between the circuit board and the diffusion plate, a pattern for uniformly reaching the light emitted from the LED to the diffusion plate comprises a light guide plate formed on at least a lower surface, The pattern formed on the bottom surface is a Fresnel lens pattern centered on the LED position, the unit inclination angle of the Fresnel lens pattern is set to correspond to half of the angle of incidence of the LED light to the upper surface of the light guide plate. The backlight unit of claim 1, wherein the light guide plate is formed of a transparent resin. delete delete In the backlight unit, A circuit board on which an LED is mounted; A diffusion plate located above the circuit board; Located between the circuit board and the diffusion plate, a pattern for uniformly reaching the light emitted from the LED to the diffusion plate comprises a light guide plate formed on at least an upper surface, The pattern formed on the upper surface is a Fresnel lens pattern centered on the LED position, and the unit inclination angle of the Fresnel lens pattern is set to π / 4 minus the emission angle at which light is emitted from the LED. Backlight unit. delete The backlight unit of claim 1, wherein the light guide plate is positioned by blocking one light guide plate per LED position. The backlight unit of claim 1, wherein the light guide plate further includes a space portion at a position above the LED. The backlight unit of claim 8, wherein the space part has a lens shape. In the backlight unit, A plurality of optical cells comprising a first plate and a second plate positioned on the first plate; A light source mounted on the first plate of the optical cell; Located in the optical cell, and comprises a light guide plate on the upper and lower surfaces having a pattern centered on the position of the light source, The pattern of the light guide plate is a Fresnel lens pattern centered on the position of the light source, The unit inclination angle of the Fresnel lens pattern located on the upper surface is set to a value obtained by subtracting the emission angle at which light is emitted from the light source at π / 4, and the unit inclination angle of the Fresnel lens pattern located on the bottom surface is the light guide plate of the LED light. And at least one of conditions set to correspond to half of an incident angle to an upper surface. The backlight unit of claim 10, wherein the first plate is a circuit board. The backlight unit of claim 10, wherein the second plate is a diffusion plate or a transparent plate.

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