KR101477425B1 - Back light unit - Google Patents

Abstract

The present invention relates to a backlight unit (BLU). More specifically, the present invention relates to an ultra-thin BLU of an edge light type, capable of local dimming. A BLU according to the present invention includes a light guide plate, at least one light source formed on a side of the light guide plate, a diffusion plate formed on the light guide plate, a prism sheet formed on the diffusion plate, and a liquid crystal film formed between the light guide plate and the diffusion plate or the diffusion plate and the prism sheet. The present invention implements local dimming to implement a high contrast range in an edge light type BLU and provides an ultra-thin BLU.

Description

Backlight unit {BACK LIGHT UNIT}

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a backlight unit (BLU), and more particularly, to an edge light type ultra slim backlight unit (BLU) capable of local dimming.

Recently, a liquid crystal display (LCD), which is widely used as a flat panel display, can not emit light by itself. The backlight unit is attached as a light source to the back of the liquid crystal display panel to display an image, Is affected by the structure of the backlight unit.

Therefore, the backlight unit is one of the important parts that must be indispensable for the liquid crystal display panel. The backlight unit generally has a direct light type and an edge light type. In the direct light type backlight unit, a plurality of light sources are positioned below the liquid crystal display panel and supply light to the liquid crystal display panel. In the edge light type backlight unit, a light source is disposed on a side surface of a liquid crystal display panel, and light is supplied to the liquid crystal display panel through a light guide plate. Here, the light guide plate guides the direction of the light, thereby improving the brightness of the panel and controlling the brightness uniformly. The edge light type backlight unit is always bright regardless of the brightness of the screen displayed on the liquid crystal display panel, so that light can be emitted even when unnecessary.

On the other hand, a backlight unit using a highly efficient LED (Light Emitting Diode) is widely used without using a fluorescent lamp such as CCFL (Cold Cathode Fluorescent Lamp) as a light source in an edge light type backlight unit. These LED backlights adopt environmentally friendly, low power consumption and long life LED as an alternative light source, and use a number of LEDs to make a linear light source like CCFL.

In the case of a backlight employing such an LED array, there is a difference in structure from the backlight using a conventional CCFL as follows. First, since the LED is a point light source, a plurality of LEDs are regularly or irregularly arranged on a PCB (Printed Circuit Board) in order to form a linear light source. However, even when a plurality of point light sources are arranged at regular intervals, the light efficiency is inferior to that of CCFL. The structure of the LED backlight uses double-tape or silicon with excellent thermal conductivity to fix the backside of the LED array to the cover bottom. LEDs generate a large amount of heat, so when there is no heat dissipation, there is a large change in optical characteristics.

After the LED array is attached to the cover bottom, the light guide plate is inserted, and the seat seat and the guide panel are tightened to constitute the backlight. In such a conventional LED backlight structure, the light emitted from the LED is incident on the light guide plate in the light incident portion (between the LED and the light guide plate), and a part of the light is not incident on the light guide plate through diffused reflection from the light entrance surface, Because it is reflected and lost to the bottom and LED arrays, the light efficiency drops, and more LEDs must be used to achieve the same brightness.

The liquid crystal display panel divides the backlight unit into a plurality of blocks, sets the dimming value for each block according to the image, controls the brightness of the backlight unit on a block basis, and compensates for the reduced brightness through the modulation of the pixel data, And the power consumption of the backlight unit is reduced. The driving method of such a backlight unit is referred to as local dimming. This local dimming method is used to prevent unnecessary consumption of light in a direct light type backlight unit, to achieve a darker color, and to improve color reproducibility.

A direct light type backlight unit is advantageous in terms of local dimming implementation, low cost, reliability and quality, and the edge light type backlight unit is advantageous for an ultra-thin configuration. On the other hand, the direct light type backlight unit is disadvantageous in that the cost is increased in the case of the ultra-thin structure, and the edge light type backlight unit is difficult to implement local dimming and is expensive. That is, although the edge light type backlight unit can be produced in an ultra-thin shape, it is difficult to achieve a high contrast ratio for a clear image because of difficult local dimming.

As a result, there has been a continuing need for a method for applying local dimming in an edge light type backlight unit.

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and it is an object of the present invention to provide an ultra-thin backlight unit that realizes local dimming for realizing a high contrast ratio in an edge light type backlight unit.

The problems of the present invention are not limited to the above-mentioned problems, and other problems not mentioned can be clearly understood by those skilled in the art from the following description.

According to an aspect of the present invention, there is provided a backlight unit including a light guide plate, at least one light source formed on one side of the light guide plate, a diffusion plate formed on the light guide plate, a prism sheet formed on the diffusion plate, And a liquid crystal film formed between the diffusion plate and the diffusion plate or between the diffusion plate and the prism sheet.

According to another aspect of the present invention, the refractive index of the liquid crystal film is smaller than the refractive index of the light guide plate.

According to still another aspect of the present invention, the liquid crystal film includes a control region capable of controlling the progress of light, and the control region is formed of a unit region.

According to another aspect of the present invention, there is provided a liquid crystal display device, further comprising a reflective sheet formed under the light guide plate, a protective sheet formed on the prism sheet, and a thin film transistor for controlling the liquid crystal film.

The details of other embodiments are included in the detailed description and drawings.

The present invention provides an edge light type backlight unit that realizes local dimming for realizing a high contrast ratio and provides an ultra-thin backlight unit.

The effects according to the present invention are not limited by the contents exemplified above, and more various effects are included in the specification.

1 is a perspective view of a backlight unit according to an embodiment of the present invention.
2 is a cross-sectional view of a backlight unit according to an embodiment of the present invention, taken along the XZ plane in FIG.
3 is a plan view showing a control region of a liquid crystal film divided into unit regions according to an embodiment of the present invention.
4 is a cross-sectional view of a backlight unit according to another embodiment of the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS The advantages and features of the present invention and the manner of achieving them will become apparent with reference to the embodiments described in detail below with reference to the accompanying drawings. The present invention may, however, be embodied in many different forms and should not be construed as being limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art. Is provided to fully convey the scope of the invention to those skilled in the art, and the invention is only defined by the scope of the claims.

It is to be understood that elements or layers are referred to as being " on " other elements or layers, including both intervening layers or other elements directly on or in between.

Although the first, second, etc. are used to describe various components, it goes without saying that these components are not limited by these terms. These terms are used only to distinguish one component from another. Therefore, it is needless to say that the first component mentioned below may be the second component within the technical spirit of the present invention.

Like reference numerals refer to like elements throughout the specification.

The sizes and thicknesses of the individual components shown in the figures are shown for convenience of explanation and the present invention is not necessarily limited to the size and thickness of the components shown.

It is to be understood that each of the features of the various embodiments of the present invention may be combined or combined with each other partially or entirely and technically various interlocking and driving is possible as will be appreciated by those skilled in the art, It may be possible to cooperate with each other in association.

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

1 is a perspective view of a backlight unit according to an embodiment of the present invention.

1, the backlight unit 100 includes a light guide plate 101, a light source 102, a liquid crystal film 103, a diffusion plate 105, and a prism sheet 107. As shown in FIG.

The light guide plate 101 guides the light incident from the light source 102 to the liquid crystal display panel. Although not shown in Fig. 1, the liquid crystal display panel is disposed on the optical sheet 110. Fig. The light guide plate 101 is formed in a plate shape and the light incident from the light source 102 to the light guide plate 101 is uniformly diffused over the entire light guide plate 101.

The light source 102 is formed on one side of the light guide plate 101. The light source 102 may be disposed separately from the light guide plate 101 with a predetermined gap therebetween. The light source 102 includes a configuration for generating light and a mounting section for reflecting the generated light source to the light guide plate 101. The light source 102 may be formed on two or more sides of the light guide plate 101 to improve the brightness of the backlight unit.

One surface of the light guide plate 101 may have a plane inclined to efficiently transmit the light incident through the light source 102 to the liquid crystal display panel.

The light source 102 may be composed of a plurality of CCFLs or LEDs.

The liquid crystal film 103 is a layer capable of changing the alignment state of the liquid crystal molecules therein according to whether an external voltage is applied or not. An alignment film is formed on at least one surface of the inside of the liquid crystal film 103 for the purpose of uniform alignment of the liquid crystal.

According to one embodiment of the present invention, the liquid crystal film 103 may include separate control elements capable of controlling alignment of liquid crystal molecules inside the liquid crystal film 103, and further, these separate control elements But may be additionally disposed outside or inside the liquid crystal film 103. The control element that can control the alignment of the liquid crystal molecules of the liquid crystal film 103 may be a direct addressing method, a passive matrix method, or an active matrix ) ≪ / RTI > mode. For example, the control element may be a thin film transistor.

When no voltage is applied to the liquid crystal film 103, the liquid crystal molecules in the liquid crystal film 103 are twisted or twisted in the alignment direction so that light emitted from the light source 102 does not pass through the liquid crystal film 103 I can not. On the other hand, when a voltage is applied to the liquid crystal film 103, the liquid crystal molecules in the liquid crystal film 103 are aligned in a certain direction according to the electromagnetic field, and light emitted from the light source 102 can pass through.

The optical sheet 110 may include a diffuser plate 105 and a prism sheet 107 as shown in FIG. 1, but may be defined as only one of the diffuser plate 105 and the prism sheet 107.

The diffusion plate 105 diffuses or concentrates the light that has passed through the light guide plate 101, thereby making the brightness uniform and widening the viewing angle. The upper portion of the diffuser plate 105 abuts the lower portion of the prism sheet 107 and can be engaged with the prism sheet 107.

The prism sheet 107 provides uniform brightness and a wide viewing angle to the liquid crystal display panel by refracting the light that has passed through the diffuser plate 105. [ The upper surface of the prism sheet 107 is composed of a plurality of prisms, as shown in Fig. 1, and the corners of each prism can be arranged in parallel.

Although not shown in FIG. 1, the light guide plate 101 may further include a reflective sheet under the light guide plate 101, and may further include a protective sheet on the prism sheet 107.

The reflective sheet reflects light leaking to the lower portion of the light guide plate 101 and re-enters the light guide plate 101, thereby improving the light efficiency of the backlight unit 100. [

The protective sheet protects the structures inside the backlight unit 100 from external pressure and impact from the top of the prism sheet 107. [

According to one embodiment of the present invention, the liquid crystal film 103 is disposed on the upper side of the light guide plate 101 and allows light diffused through the light guide plate 101 to pass therethrough according to whether a voltage is applied to the liquid crystal film 103, . The light having passed through the liquid crystal film 103 reaches the diffuser plate 105 on the liquid crystal film 103.

According to an embodiment of the present invention, the refractive index of the liquid crystal film 103 may be smaller than the refractive index of the light guide plate 101. When the refractive index of the liquid crystal film 103 is smaller than the refractive index of the light guide plate 101, the degree of diffusion of light passing through the liquid crystal film 103 can be reduced and the light passing through the liquid crystal film 103 The degree of condensation can be increased. Accordingly, the controlled light having passed through the liquid crystal film 103 can be more focused on the diffuser plate 105 and incident thereon. Therefore, the backlight unit 100 can realize a clearer image quality.

2 is a cross-sectional view of a backlight unit according to an embodiment of the present invention, taken along the XZ plane in FIG.

2, a backlight unit 100 according to an embodiment of the present invention includes a light source 102 formed on one side of a light guide plate 101, a light guide plate 101, and a light guide plate 101, A diffusion plate 105 disposed on the top of the liquid crystal film 103 and a prism sheet 107 disposed on the top of the diffusion plate 105. The liquid crystal film 103 is used to adjust the amount of light incident from the liquid crystal film 103. [

According to an embodiment of the present invention, as shown in FIG. 2, the arrangement of liquid crystals may be varied by control elements for predetermined regions of the liquid crystal film 103, respectively. Accordingly, local light can be realized because the light incident through the light guide plate 101 does not pass through or passes through the predetermined regions of the liquid crystal film 103. With such local dimming, efficient use of light, high contrast ratio, and color reproducibility can be achieved while using an edge light type backlight unit.

3 is a plan view showing a control region of a liquid crystal film divided into unit regions according to an embodiment of the present invention.

Referring to FIG. 3, the control region of the liquid crystal film 103 may be divided into unit regions L11 to Lnm of arbitrary size. The unit areas L11 to Lnm of the liquid crystal film 103 can be distinguished by control elements capable of controlling the alignment of liquid crystal molecules and each unit area L11 to Lnm has a uniform size Lt; / RTI > The liquid crystal film 103 controls the alignment direction of the liquid crystal molecules to adjust the amount of light diffused through the light guide plate 101. According to an embodiment of the present invention, a predetermined voltage is applied to an arbitrary region of the liquid crystal film 103, and thus the liquid crystal molecules inside the liquid crystal film 103 are aligned. Therefore, the alignment direction of the liquid crystal molecules in the liquid crystal film 103 can be controlled by adjusting the voltage applied to each of the unit areas L11 to Lnm of the liquid crystal film 103, The amount of light is controlled differently for each of the unit areas L11 to Lnm, thereby realizing a high contrast ratio of the liquid crystal display panel.

According to one embodiment of the present invention, the liquid crystal film 103 includes a control region, and the control region includes unit regions L11 to Lnm that are divided into arbitrary sizes. The control region of the liquid crystal film 103 may be formed on the surface through which the light is incident through the light guide plate 101. The unit areas L11 to Lnm may have a uniform size and may be arranged in the form of a matrix in the control area. More specifically, referring to FIG. 3, the unit areas L11 to Lnm may be rectangular areas and may be arranged in the form of a matrix of m X n. In addition, each of the unit areas L11 to Lnm may be defined in accordance with the control method of the liquid crystal molecules.

When the liquid crystal film 103 is driven in a manual arrangement mode, the liquid crystal molecules are aligned by applying a predetermined voltage to the upper or lower electrodes corresponding to the unit areas L11 to Lnm through which light is to be transmitted.

When the liquid crystal film 103 is driven in an active arrangement mode, liquid crystal molecules are aligned by driving the thin film transistors corresponding to the unit areas L11 to Lnm to which light is to be transmitted. In this case, the thin film transistor may be powered by external circuits connected to the gate line and the data line.

The liquid crystal molecules can be arranged by a manual arrangement method or an active arrangement method. More specifically, the arrangement of liquid crystal molecules can be controlled by TN (Twisted Nematic), VA (Vertical Alignment), IPS (In-Plane Switching) have.

As described above, the control region of the liquid crystal film 103 can be divided according to the arrangement of the control elements disposed on the inner or outer surface of the liquid crystal film 103. The control region of the liquid crystal film 103 can be divided into unit regions L11 to Lnm and the amount of light passing through each unit region L11 to Lnm can be varied by the control of the control elements. Accordingly, the amount of light transmitted to the liquid crystal display panel through the controllable liquid crystal film 103 is controlled, a high contrast ratio is realized, and a sharp image quality can be provided.

The backlight unit 100 includes a liquid crystal film 103 capable of adjusting the amount of light passing through each of the unit areas L11 to Lnm so that the edge light type backlight unit 100, It is possible to provide a high contrast ratio and a clear image quality by enabling local dimming.

4 is a cross-sectional view of a backlight unit according to another embodiment of the present invention.

4, the diffusion plate 105 is disposed on the upper surface of the light guide plate 101, and the liquid crystal film 103 is disposed on the upper surface of the diffusion plate 105, as shown in FIG. That is, the liquid crystal film 103 is disposed between the diffusion plate 105 and the prism sheet 107.

FIG. 4 is a view similar to FIG. 2 except that the position of the liquid crystal film 103 in the backlight unit is different from that of FIG. 2, and the other structures are substantially the same.

According to another embodiment of the present invention as shown in FIG. 4, the light having passed through the diffusion plate 105 is diffused or concentrated so that the brightness becomes uniform, and the light having uniform brightness passes through the liquid crystal film 103 The light passing through the prism sheet 107 and reaching the prism sheet 107 may have a uniform brightness and a small loss of light. When the light having passed through the liquid crystal film 103 passes through the prism sheet 107 again, light having more concentrated and uniform brightness is provided, so that an improved contrast ratio and color reproducibility can be realized.

While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it is to be understood that the present invention is not limited to the disclosed exemplary embodiments, but various changes and modifications may be made without departing from the spirit and scope of the invention. Therefore, the embodiments disclosed in the present invention are not intended to limit the scope of the present invention but to limit the scope of the technical idea of the present invention. The scope of protection of the present invention should be construed according to the following claims, and all technical ideas within the scope of equivalents should be construed as falling within the scope of the present invention.

100, 150 backlight unit
101 light guide plate
102 light source
103 liquid crystal film
105 diffuser plate
107 Prism sheet
110 optical sheet

Claims (4)

A light guide plate;
At least one light source formed on one side of the light guide plate;
A diffusion plate formed on the light guide plate;
A prism sheet formed on the diffusion plate; And
A liquid crystal film formed between the light guide plate and the diffusion plate;
A reflective sheet formed below the light guide plate;
A protective sheet formed on the prism sheet for protecting the light guide plate, the diffusion plate, the prism sheet, the liquid crystal film, and the reflective sheet from external pressure and impact from the upper portion of the prism sheet; And
And a thin film transistor for controlling the liquid crystal film,
Wherein the liquid crystal film includes a control region capable of controlling the progress of light diffused through the light guide plate for local dimming, and the control region is a unit region arranged in a matrix. Backlight unit. The method according to claim 1,
Wherein the refractive index of the liquid crystal film is smaller than the refractive index of the light guide plate. delete delete

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