Backlight unit and liquid crystal display device having the same

A backlight unit includes an optical sheet, a receiving member configured to receive the optical sheet, the receiving member having a support surface supporting the optical sheet, an extension configured to protrude from a side surface of the optical sheet, an inner surface position defining portion configured to define a location of the optical sheet, the inner surface position defining portion being substantially perpendicular to the support surface of the receiving member and facing an inner surface of the extension, and an outer surface position defining portion substantially perpendicular to the supporting surface of the receiving member and facing an outer surface of the extension, wherein a first distance between the inner surface position defining portion and the inner surface of the extension is less than a second distance between the outer surface position defining portion and the outer surface of the extension.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority to and the benefit of Korean Patent Application No. 10-2007-0010548 filed on Feb. 1, 2007, the entire contents of which are incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Technical Field

The present invention relates to a backlight unit and a liquid crystal display having the same, and more particularly, to a backlight unit and a liquid crystal display device having the same capable of precisely defining a location of an optical sheet and preventing deformation of the sheet.

2. Discussion of the Related Art

A backlight unit is an element of a liquid crystal display (“LCD”) device that irradiates light at a rear surface of an LCD panel mounted in an LCD monitor, a personal computer, a navigation system for a vehicle, and the like. The LCD device displays various images and information. The LCD device uses a backlight unit for supplying light to the LCD panel because the LCD device is a passive display that does not emit light by itself.

The backlight unit includes a receiving member, a light source, a light guide plate, and a plurality of optical sheets. The receiving member receives the light guide plate and the optical sheets that include, for example, a reflection sheet, a diffusion sheet, a prism sheet, and a protection sheet.

The optical sheets deliver uniform light to the LCD panel. Therefore, a location where the optical sheets are initially mounted within the backlight unit preferably remains unchanged. An optical property is affected by the distance between the optical sheets and light guide plate.

Heat is generated from the light source during an operation of the backlight unit, thereby increasing the temperature of the backlight unit. Thin optical sheets experience changes in length by heat expansion. If the frame is not capable of accommodating for such changes in length, the optical sheets deform within the backlight unit. Such deformation may result in a change in distance between the optical sheet and light guide plate, thereby causing a display failure of the LCD device.

Tightly securing the optical sheets within the backlight unit to prevent the movement of the optical sheets can compromise the ability to maintain a sufficient distance between the optical sheets and the frame to sufficiently accept heat expansion of the optical sheets. As a result a way of preventing movement of the optical sheets while also maintaining sufficient distance between the optical sheets and the frame is required.

SUMMARY OF THE INVENTION

Embodiments of the present invention provide a backlight unit and an LCD device having the same, capable of obtaining a sufficient distance to bear deformation of the optical sheet by its expansion and tightly securing the optical sheet by tightly contacting an inner side of the optical sheet.

An exemplary embodiment of the present invention provides a backlight unit including an optical sheet, a receiving member configured to receive the optical sheet, the receiving member having a supporting surface supporting the optical sheet, an extension protruding from a side surface of the optical sheet, an inner surface position defining portion configured to define a location of the optical sheet, the inner surface position defining portions being substantially perpendicular to the supporting surface of the receiving member and facing an inner surface of the extension, and an outer surface position defining portion substantially perpendicular to the supporting surface of the receiving member and facing an outer surface of the extension, wherein a first distance between the inner surface position defining portion and the inner surface of the extension is less than a second distance between the outer surface position defining portion and the outer surface of the extension.

A ratio of the first distance between the inner surface of the extension and the inner surface position defining portion to the second distance between the outer surface of the extension and the outer surface position defining portion ranges from 1:3 to 1:6, and can be 1:5.

At least one other extension may be formed to protrude from another side surface of the optical sheet.

The extensions can be formed at opposing sides of the optical sheet, respectively.

The inner surface position defining portion is a fastening protrusion portion configured to protrude upwardly from an edge area of a side of the receiving member and to fasten the extension. An outer surface of the fastening protrusion portion comes in tight contact with the inner surface of the extension.

The optical sheet comprises at least one of a diffusion sheet, a prism sheet, a protection sheet, and a reflection sheet.

The receiving member comprises at least one of a mold frame and a bottom chassis.

An exemplary embodiment of the present invention provides an LCD device including an LCD panel configured to display an image, and a backlight unit configured to supply light to the LCD panel, wherein the backlight unit comprises an optical sheet, a receiving member configured to receive the optical sheet, the receiving member having a supporting surface supporting a bottom surface of the optical sheet and a sidewall bordering a side surface of the optical sheet, a first extension protruding from an edge area of the optical sheet in a first direction, a second extension protruding from an edge area of the optical sheet in a second direction different from the first direction, first and second inner surface position defining portions substantially perpendicular to the supporting surface of the receiving member and facing an inner surface of the first and second extensions, respectively, and first and second outer surface position defining portions substantially perpendicular to the supporting surface of the receiving member and facing an outer surface of the first and second extensions, respectively.

DETAILED DESCRIPTION OF EMBODIMENTS

Exemplary embodiments of the present invention will now be described with reference to the attached drawings. This invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein.

FIG. 1is an exploded perspective view of an LCD device in accordance with an embodiment of the present invention.

As shown inFIG. 1, an LCD device according to an embodiment of the present invention includes an LCD panel100, which receives an image signal and displays an image, a backlight unit200, which supplies light to the LCD panel100, and a driving portion300having a circuit for driving the LCD panel100.

The LCD panel100comprises a thin film transistor (TFT) substrate110and a color filter substrate120. The TFT substrate110and the color filter substrate120are arranged to be opposite to each other and spaced apart by a constant distance. Liquid crystals are injected between the TFT substrate110and the color filter substrate120.

The color filter substrate120has a black matrix, a color filter, a common electrode, and an alignment layer formed on a transparent insulating substrate made of, for example, glass or plastic.

The black matrix defines sub-pixels and prevents light leakage between sub-pixels. The color filter that displays a color is provided for each sub-pixel. Alternatively, the color filter may be formed on the TFT substrate. Such an LCD panel is called a COA (Color filter On Array) panel.

Further, the common electrode induces an electric field along with a pixel electrode formed on the TFT substrate, and the liquid crystal is driven by the electric field. Alternatively, the common electrode may be patterned on the color filter substrate to have, for example, a constant shape, depending upon a liquid crystal mode.

An overcoat layer formed of an organic material is further formed between the color filter and the common electrode. An alignment layer can be formed on the color filter substrate to align the liquid crystal in a constant direction. The alignment layer may be aligned in a horizontal direction or in a vertical direction, and alternatively, may be omitted.

A polarization plate may be adhered to a top surface of the color filter substrate. The polarization plate polarizes light in a specific direction. A phase difference film may be further adhered to the polarization plate.

The TFT substrate110includes gate lines, data lines, TFTs, pixel electrodes, and an alignment layer formed on a transparent insulating substrate made of glass or plastic.

The gate lines and the data lines intersect each other on the insulating substrate. A red sub-pixel, a green sub-pixel, and a blue sub-pixel are arranged in a row and constitute a pixel.

A gate line delivers a scan signal to a gate electrode of a TFT, and a data line delivers a data signal to a source electrode of the TFT. Further, the TFT is formed at the intersection of the gate line and the data line and functions as a switching element. The TFT comprises a gate electrode, a semiconductor layer, and source and drain electrodes.

The pixel electrode is connected to the drain electrode and induces an electric field along with the common electrode of the color filter substrate. The pixel electrode is a transparent electrode, which transmits light, and may be patterned in a constant shape. The alignment layer is formed on an upper portion, for example, the uppermost portion, of the TFT substrate and aligns the liquid crystal in a constant direction.

A polarization plate may be adhered to the bottom surface of the TFT substrate. The polarization plate may be positioned on the TFT substrate to be perpendicular to a polarization axis thereof. Alternatively, the polarization plate may be positioned parallel to a polarization axis thereof.

Liquid crystals are injected between the TFT substrate and the color filter substrate. Various modes of the liquid crystal may be used, such as a TN (Twisted Nematic) mode, a VA (Vertical Alignment) mode, and the like, which has an optical and electromagnetic anisotropic property.

The driving portion300is connected to a side of the TFT substrate110and supplies a driving signal to the gate line and the data line. Accordingly, the driving portion300comprises a gate driving IC (Integrated Circuit) (not shown), a data driving IC310, a power supply (not shown), and a timing controller320.

The gate driving IC is mounted in a gate tape carrier package (TCP) with a film shape and electrically connected with the LCD panel by a TCP bonding process. Alternatively, the gate driving IC may be directly integrated on the TFT substrate110. The data driving IC310is mounted in a data TCP340with a film shape and electrically connected to the LCD panel100by a TCP bonding process.

The timing controller320, which is mounted on a printed circuit board330, processes externally supplied signals, generates a timing signal, and supplies the timing signal to the gate driving IC and the data driving IC310. Accordingly, the gate driving IC supplies the timing signal from the timing controller320and a power source signal from the power source portion to the gate line. Further, the data driving IC310supplies the timing signal from the timing controller320, an image signal, and a power source signal through a signal line formed in the data TCP340to the data line.

The power supply supplies the power source signal to the gate driving IC and the data driving IC310.

As shown inFIGS. 1 and 2, the backlight unit200according to an embodiment of the present invention includes a light source210, a light guide plate220, optical sheets230, and a mold frame240.

The light source210that emits light may use, for example, a cold cathode fluorescent lamp (CCFL), an external electrode fluorescent lamp (EEFL), or a light emitting diode (LED). Although a side emitting type of the light source210, which is mounted at a side of the backlight unit, is illustrated inFIG. 1, a direct emitting type of the light source may also be employed for large-area LCD devices, which is uniformly arranged throughout the entire surface of the backlight unit to directly irradiate light toward the LCD panel. A diffusion plate that uniformly diffuses light emitted from the light source may be provided instead of the light guide plate.

When the light source210is a lamp such as a CCFL or an EEFL, it is mounted at a side of the mold frame240. In this exemplary embodiment, one or two lamps may be mounted if necessary. When two lamps are mounted, lamps may be arranged at left and right sides or top and bottom sides of the light guide plate220to face each other.

A light source cover212is further provided at the outer surface of the light source210, which reflects light from the light source210to the light guide plate220and covers the light source210. Referring toFIGS. 1 and 2, one side of the light source cover212is opened towards the light guide plate220to cover the outer surface of the light source210except for the outer surface of the light source210positioned facing the light guide plate220. The light source cover212is spaced apart from the light source210by a constant distance, and a reflection film (not shown) is formed on an inner surface of the light source cover212.

The reflection film may be formed by coating a reflection material or adding a sheet with a reflective property on the inner surface of the light source cover212. Further, a reflection sheet250may be used as the reflection film by bending an end portion of the reflection sheet250in the shape of the light source cover212.

The light guide plate220is positioned adjacent to the light source210. The light guide plate220guides light from the light source210to the LCD panel100. Referring toFIG. 1, when the light source210is positioned at a side of the backlight unit200, the light guide plate220guides light from the light source to the LCD panel100. However, the light guide plate220may be omitted when a direct-type backlight unit is used. Accordingly, a diffusion plate may be used without a light guide plate.

The reflection sheet250may be positioned at a lower portion of the light guide plate220. The reflection sheet250reflects light from the lower portion of the light guide plate220toward the LCD panel100. Therefore, unused light may be recycled, thereby improving the usage efficiency of light.

Referring toFIG. 1, the optical sheets230include a plurality of sheets including a diffusion sheet232, a prism sheet234, and a protection sheet236. Any appropriate combination of one, two or three of the sheets may be used.

The diffusion sheet232disperses and uniformly diffuses light from the light guide plate220. The diffusion sheet232may be configured such that a diffusion member is dispersed inside a transparent sheet or a diffusion pattern is formed on the surface of a transparent sheet in order to diffuse light.

The prism sheet234collects light diffused by the diffusion sheet232to improve brightness. The prism sheet234may have a light-collection pattern formed on the surface of a transparent sheet.

The protection sheet236positioned above the diffusion and prism sheets232,234prevents contamination and damage to the prism sheet234or the diffusion sheet232from dust or scratches, and prevents movement of other sheets.

Each of the optical sheets230further includes an extension260. In this exemplary embodiment, the diffusion sheet232, the prism sheet234, the protection sheet236, and the reflection sheet250may include the extension260. The diffusion sheet232is described below as including the extension260by way of example.

Referring toFIG. 2, the extensions260protrude at the edge of the diffusion sheet232to define the location of the diffusion sheet232within the backlight unit200. The extensions260may be formed on either of transverse and longitudinal sides as shown inFIG. 2, or formed on both transverse and longitudinal sides as shown inFIGS. 4 and 5.

Two or more extensions260may extend from an edge of the diffusion sheet232. In this embodiment, the inner surfaces262of two extensions260that are provided at the same edge come in tight contact with the receiving member (e.g., mold frame240), so that the location of the receiving member is defined.

The extension260is positioned at or adjacent a corner of the diffusion sheet232extends from the edge of the diffusion sheet232.

According to an exemplary embodiment of the present invention, the inner surface262of the extension260intersects the edge of the diffusion sheet232. The inner surface262of the extension260defines the location of the diffusion sheet232by contacting the receiving member, and therefore, the inner surface262of the extension260is shaped to fit with the inner surface of the receiving member.

The height of the extension260should be the same as or smaller than the thickness/height of the sidewall242of the receiving member. When the height of the extension260is larger than the thickness/height of the sidewall242of the mold frame240, the size of the backlight unit200increases.

As shown inFIG. 1, the light source210, the light guide plate220, the reflection sheet250, and the optical sheets230are received in the receiving member such as the mold frame240or a bottom chassis. The mold frame240is described below as an example of the receiving member.

The mold frame240receives the light source210, the light guide plate220, the reflection sheet250, the optical sheets230, and the LCD panel100. A printed circuit board330mounted on the LCD panel100is bent to contact the rear surface of the mold frame240. The mold frame240includes a supporting surface241, a sidewall242, a printed circuit board insertion hole243, and a data driving circuit insertion groove244so as to receive all the elements described above.

The backlight unit200may include either the mold frame240or a bottom chassis, or both the mold frame240and the bottom chassis. Although the receiving member using the mold frame240is illustrated inFIG. 1, the receiving member may be a bottom chassis or a combination of mold the frame and the bottom chassis.

The mold frame240according to this embodiment comprises the supporting surface241supporting the bottom surface of the diffusion sheet232and the sidewall242supporting a side surface of the diffusion sheet232. Accordingly, the sidewall242is substantially perpendicular to the supporting surface241and has the height sufficient to receive the light guide plate220, the optical sheets230, and the LCD panel100.

Returning toFIG. 1, the mold frame240further includes an inner surface position defining portion, which is formed at a sidewall242thereof, faces the inner surface262of the extension260, and secures the extension260. Since the inner surface position defining portion corresponds to the extension260of the diffusion sheet232, the number of inner surface position defining portions is the same as that of the extensions260.

In this embodiment, the inner surface position defining portion may be implemented in two ways.

Referring toFIGS. 2 and 3, the inner surface position defining portion may include a fastening protrusion portion245that upwardly protrudes from the sidewall242of the mold frame240and faces the inner surface262of the extension260. The fastening protrusion portion245upwardly protrudes higher than the sidewall of the mold frame240, and the side surface of the fastening protrusion portion245is substantially perpendicular to a top surface of the sidewall242of the mold frame240and tightly contacts the inner surface262of the extension260.

Since the fastening protrusion portion245defines the location of the diffusion sheet232by contacting the extension260, the fastening protrusion portion245should be positioned to tightly contact the inner surface262of the extension260. In other words, as shown inFIG. 2, the distance d2between the fastening protrusion portion245and the inner surface262should be zero or almost zero. The diffusion sheet232may move within the backlight unit200by the distance d2. Accordingly, as the distance d2decreases, a moving range of the diffusion sheet232within the backlight unit200also decreases.

The distance d2should be determined with reference to properties of an optical sheet230when the backlight unit200maintains a sufficiently low temperature. An optical sheet230expands or shrinks depending upon a temperature variation. Accordingly, the distance d2should be determined based on a sufficiently low temperature considering all temperature environments under which the LCD device operates so that the fastening protrusion portion245and the inner surface262of the extension260may come in tight contact with each other. When the distance between the fastening protrusion portions245and the extensions260is too large, the optical sheet230may be deformed within the backlight unit200because there was not sufficient allowance for a shrinkage amount of the optical sheet230due to a temperature drop.

Referring toFIGS. 2 and 3, an outer surface position defining portion246may be further provided at a corner portion of the mold frame240. The outer surface position defining portion246faces the fastening protrusion portion245. In this embodiment, the distance between the outer surface position defining portion246and the extension260(d1) is longer than that between the inner surface position defining portion and the extension260(d2). The outer surface position defining portion246prevents the movement of the optical sheet230after an expansion of the optical sheet230, and therefore, the distance d1is larger than the distance d2. The inner surface position defining portion defines the location of the optical sheet230while engaged with the extension260of the optical sheet230, and therefore, the distance d2is smaller than the distance d1. The outer surface position defining portion246may be omitted as shown inFIG. 6.

The outer surface position defining portion246should be sufficiently spaced apart from the outer surface264of the extension260. Referring toFIG. 8, the distance d1between the outer surface position defining portion246and the outer surface264of the extension260is set up for an allowance by which the optical sheet230may expand depending upon a temperature variation of the diffusion sheet232. In this exemplary embodiment of the present invention, a ratio of the distance d1between the outer surface of the extension260and the outer surface position defining portion to the distance d2between the inner surface of the extension260and the inner surface position defining portion ranges from 3:1 to 6:1, and is preferably 5:1.

The height/thickness of the fastening protrusion portion245and the outer surface position defining portion246is the same as or larger than the height/thickness of the diffusion sheet232. Since the extension260having the same thickness as that of the diffusion sheet232defines the location of the diffusion sheet232by being secured by the fastening protrusion portion245, the fastening protrusion portion245protrudes beyond the thickness of the extension260, so that the extension260is secured by bordering the fastening protrusion portion245. As the thickness of an LCD device is reduced, the height of the fastening protrusion portion245may also be reduced. Accordingly, the height of the fastening protrusion portion245may be reduced to be substantially the same as that of the extension260so as to obtain a height to sufficiently secure the extension260as well as minimize the thickness of the mold frame240.

Referring toFIG. 7, the upper edge of the fastening protrusion portion245may have a curved shape (R). In mounting the diffusion sheet232to the mold frame240, the extension260is inserted adjacent the fastening protrusion portion245while the diffusion sheet232descends from an upper side to a lower side of the mold frame240. Therefore, when the upper edge of the fastening protrusion portion245has a curved shape, the mounting process may be facilitated. In addition the upper edge of the outer surface position defining portion246can also be curved to facilitate mounting of an optical sheet.

In this embodiment, the location of the diffusion sheet232is defined by closely contacting the inner surface262of the extension260with the fastening protrusion portion245, and the distance between the outer surface264of the extension260and the outer surface position defining portion246is large enough to accommodate for deformation caused by an expansion of the diffusion sheet232. Therefore, it is possible to sufficiently allow for deformation of the diffusion sheet232due to heat as well as tightly secure the diffusion sheet232within the backlight unit200.

Referring toFIG. 9, the inner surface position defining portion may be formed as a fastening groove247for receiving and securing the extension260therein. As shown inFIG. 9, the fastening groove247is a recessed portion of the sidewall242of the mold frame240, so that its inner surface247acomes in tight contact with the inner surface262of the location defining portion. The height of the fastening groove247is lower than the rest of the sidewall242of the mold frame242in order to receive the extension260.

The inner surface247aof the fastening groove247may directly contact or be spaced from the inner surface262of the location defining portion by a minimum distance d3. The location of the diffusion sheet232within the backlight unit200is defined by the distance d3between the inner surface247aof the fastening groove247and the inner surface262of the extension260. The inner surface262of the extension260and the inner surface247aof the fastening groove247come in tight contact with each other so as to prevent the movement of the diffusion sheet232.

The outer surface247bof the fastening groove247should be sufficiently spaced apart from the outer surface264of the extension260. The distance d4between the outer surface247bof the fastening groove247and the outer surface264of the extension260is an allowance for accepting deformation of the diffusion sheet232due to heat, and therefore, the distance d4should be determined in order to prevent the diffusion sheet232from wrinkling by the expansion of the diffusion sheet232.

The backlight unit200and the LCD panel100are received in the mold frame240, and then the top chassis400is mounted thereon to tightly secure outer surfaces of the LCD panel100and the mold frame240.

A bottom chassis (not shown) may further be adhered to the rear surface of the mold frame240, and more specifically, to the rear surface of a portion of the mold frame240where the light source210is positioned. The bottom chassis protects the light source210, the light guide plate220, and the like.

According to embodiments of the present invention, the location of the optical sheet may be precisely defined within the backlight unit and the deformation of the optical sheet due to heat may be sufficiently allowed for by varying the distances between inner and outer surfaces of an extension portion of an optical sheet and defining portions formed on the receiving member. In other words, the location of the optical sheet may be defined by tightly contacting the receiving member with the inner surface of the extension, and the deformation of the optical sheet caused by heat may be prevented by making the outer surface of the extension spaced sufficiently from the receiving member.

Although exemplary embodiments of the present invention have been described above, it is understood that the present invention should not be limited to these exemplary embodiments and that various changes and modifications can be made by one of ordinary skill in the art within the sprit and scope of the present invention as hereinafter claimed.