Liquid crystal display device and television receiver

A liquid crystal display device includes: a liquid crystal panel; a reflection sheet arranged on a rear surface side of the liquid crystal panel, the reflection sheet being curved so that a surface facing the liquid crystal panel is recessed; and a light emitting diode substrate including: a light emitting diode array in which a plurality of light emitting diodes are arranged along a longitudinal direction; and electrodes connected to the plurality of light emitting diodes. In a circle which is centered at one light emitting diode and whose diameter is a distance from the one light emitting diode to another light emitting diode adjacent to the one light emitting diode, an area of the electrode connected to a high temperature side electrode of the one light emitting diode is larger than an area of the electrode connected to a low temperature side electrode of the one light emitting diode.

TECHNICAL FIELD

The present application relates to a liquid crystal display device including a backlight unit that uses LEDs as light sources, and a television receiver including the liquid crystal display device. In particular, the present application relates to a technology for improving heat dissipation performance for LEDs.

BACKGROUND

Japanese Patent Application Laid-open No. 2007-286627 discloses a liquid crystal display device including a direct type backlight unit. In the liquid crystal display device, a plurality of light emitting diodes are used as light sources of the backlight unit. The light emitting diodes are arranged in matrix across an entire region of the backlight unit.

Further, Japanese Patent Application Laid-open No. 2007-305341 also uses a direct type backlight unit in which a plurality of LEDs are arranged in matrix as light sources.

In the liquid crystal display device described in Japanese Patent Application Laid-open No. 2007-286627, the light emitting diodes are arranged across the entire region of the backlight unit, and hence the size of a substrate on which a large number of light emitting diodes are arranged needs to be large enough to cover the entire region of the backlight unit. This increases cost for preparing a large number of light emitting diodes as well as a material cost of the substrate on which the light emitting diodes are to be arranged.

Also in the structure in which the plurality of LEDs are arranged in matrix as exemplified by the backlight unit described in Japanese Patent Application Laid-open No. 2007-305341, the necessary number of LEDs is large to have the same problem.

To address the problem, studies have been made on the structure in which the light emitting diodes are arranged at a part of the backlight unit along a particular direction, that is, the LEDs are arranged only at a vertical or horizontal center portion of the backlight unit, and a reflection sheet is used to expand light of the LEDs in the vertical or horizontal direction. For example, it is conceivable to arrange the light emitting diodes in the vicinity of the lateral center of the backlight unit in a concentrated manner along the long-side direction of the backlight unit, and to reflect or diffuse light beams of the light emitting diodes with use of an appropriate reflection sheet so that the light beams may irradiate an entire image formation region. This structure, however, needs to increase the arrangement density of the LEDs, and hence temperature of the LEDs is liable to be high.

FIG. 9is a partial enlarged plan view illustrating how a plurality of light emitting diodes13are arranged linearly on a light emitting diode substrate7. Note that, a lens14for diffusing a light beam is arranged on a light emitting surface side of each light emitting diode13. InFIG. 9, parts located behind the lens14are illustrated by broken lines. As illustrated inFIG. 9, the light emitting diodes13are arranged in series in the longitudinal direction of the liquid crystal display device, that is, in the horizontal direction ofFIG. 9.

In this case, an electrode21connected to an anode and a cathode of each light emitting diode13is spread in plan to have a so-called solid pattern as illustrated inFIG. 9. This is for the purpose of diffusing and dissipating heat from the light emitting diode13owing to the electrode21having high heat conductivity. Upper limits of the maximum output and the arrangement density of the light emitting diodes13are determined based on such heat dissipation ability of the electrode21. In other words, as the electrode21has higher heat dissipation performance, the light emitting diode13with a higher output can be used for the light emitting diode substrate7of the same area, or the light emitting diodes13can be arranged at higher density. Alternatively, when the output of the light emitting diode13is the same, the size of the light emitting diode substrate7can be reduced more as the electrode21has higher heat dissipation performance.

By the way, heat generated from the light emitting diode13is transferred to the electrode21via the anode and the cathode, but in a light emitting diode13commonly used at present, the transfer amount of heat is not equal between the anode and the cathode. In the example illustrated inFIG. 9, no consideration is made on such circumstances and the electrode21has the same pattern on the side connected to the anode and on the side connected to the cathode. One of the anode and the cathode having a larger amount of heat generation with higher temperature is referred to as “high temperature side electrode”, and another having a smaller amount of heat generation with relatively lower temperature is referred to as “low temperature side electrode”. In this case, the maximum output and the arrangement density of the light emitting diodes13are determined based on heat dissipation performance for the high temperature side electrode subjected to severe thermal conditions. In such a case, heat dissipation performance for the low temperature side electrode has room to improve, and hence the heat dissipation performance has room to further improve. Note that, in most light emitting diodes used at present, the amount of heat generation at the cathode is larger than the amount of heat generation at the anode. In other words, the amount of heat transferred to the electrode21is larger on the cathode side and its temperature becomes higher as well.

Alternatively, depending on the size of the liquid crystal display device, it is sometimes necessary to arrange the light emitting diodes in two or more rows, because a sufficient amount of light for illuminating the entire image formation region cannot be obtained by simply arranging the light emitting diodes linearly in one row.

FIG. 18is a partial enlarged plan view illustrating how the plurality of light emitting diodes13are arranged linearly in two rows on the light emitting diode substrate7. Note that, the lens14for diffusing a light beam is arranged on the light emitting surface side of each light emitting diode13. InFIG. 18, parts located behind the lens14are illustrated by broken lines. As illustrated inFIG. 18, the light emitting diodes13are arranged in two rows in series in the longitudinal direction of the liquid crystal display device, that is, in the horizontal direction ofFIG. 18, and in parallel in the lateral direction of the liquid crystal display device, that is, in the vertical direction ofFIG. 18. The light emitting diodes13are arranged in the respective rows at staggered positions. This is for the purpose of obtaining as uniform illumination as possible in the longitudinal direction. In such a case, the arrangement density of the light emitting diodes13becomes higher, and the temperature of the light emitting diode13is liable to be higher.

Further, in the case where the plurality of LEDs are arranged in three or four rows at the vertical or horizontal center portion, the temperature of the LEDs arranged in the middle row(s) sandwiched by the two rows on both sides is liable to be high.

The present application has been made in view of the above-mentioned circumstances, and it is an object thereof to efficiently dissipate heat generated from a light emitting diode in a liquid crystal display device including a backlight unit for irradiating an entire image formation region with light of light emitting diodes arranged in a concentrated manner.

It is another object of the present application to provide a liquid crystal display device capable of improving heat dissipation performance for LEDs and a television receiver including the liquid crystal display device.

SUMMARY

Representative embodiments disclosed in the present application are briefly described as follows.

In one general aspect, the instant application describes a liquid crystal display device includes a liquid crystal panel; a reflection sheet arranged on a rear surface side of the liquid crystal panel, the reflection sheet being curved so that a surface facing the liquid crystal panel is recessed; and a light emitting diode substrate includes a light emitting diode array in which a plurality of light emitting diodes are arranged along a longitudinal direction of the light emitting diode substrate; and electrodes connected to the plurality of light emitting diodes. In a circle whose center is at one of the plurality of light emitting diodes and whose diameter is a distance from the one of the plurality of light emitting diodes to another of the plurality of light emitting diodes adjacent to the one of the plurality of light emitting diodes, an area of the electrode connected to a high temperature side electrode of the one of the plurality of light emitting diodes is larger than an area of the electrode connected to a low temperature side electrode of the one of the plurality of light emitting diodes. The plurality of light emitting diodes are arranged so that the low temperature side electrodes and the high temperature side electrodes are adjacent to one another in the longitudinal direction, and each of the plurality of light emitting diodes has a lens arranged in front thereof.

The above general aspect may include one or more of the following features. The low temperature side electrode may include an anode of each of the plurality of light emitting diodes, and the high temperature side electrode may include a cathode of the each of the plurality of light emitting diodes.

The electrode connected to the low temperature side electrode of the one of the plurality of light emitting diodes and the electrode connected to the high temperature side electrode of the one of the plurality of light emitting diodes may partially overlap with each other in a lateral direction of the light emitting diode substrate.

At least a part of a boundary to separate the electrode connected to the low temperature side electrode of the one of the plurality of light emitting diodes and the electrode connected to the high temperature side electrode of the one of the plurality of light emitting diodes may be non-parallel to a lateral direction, and may be inclined toward the electrode connected to the low temperature side electrode, starting from the one of the plurality of light emitting diodes.

In another general aspect, the liquid crystal display device of the present application includes a liquid crystal panel; a reflection sheet arranged on a rear surface side of the liquid crystal panel, the reflection sheet being curved so that a surface facing the liquid crystal panel is recessed; and a light emitting diode substrate includes a plurality of light emitting diode arrays, in each of which a plurality of light emitting diodes are arranged along a longitudinal direction of the light emitting diode substrate; and electrodes connected to the plurality of light emitting diodes. The electrode belonging to one of the plurality of light emitting diode arrays and the electrode belonging to another of the plurality of light emitting diode arrays are shaped to overlap with each other in the longitudinal direction. In a circle whose center is at one of the plurality of light emitting diodes and whose diameter is a distance from the one of the plurality of light emitting diodes to another of the plurality of light emitting diodes closest to the one of the plurality of light emitting diodes, an area of the electrode connected to a high temperature side electrode of the one of the plurality of light emitting diodes is larger than an area of the electrode connected to a low temperature side electrode of the one of the plurality of light emitting diodes.

The above another general aspect may include one or more of the following features. In a circle whose center is at one of the plurality of light emitting diodes and whose diameter is a distance from the one of the plurality of light emitting diodes to another of the plurality of light emitting diodes closest to the one of the plurality of light emitting diodes, an area of the electrode connected to a high temperature side electrode of the one of the plurality of light emitting diodes may be larger than an area of the electrode connected to a low temperature side electrode of the one of the plurality of light emitting diodes.

The low temperature side electrode may include an anode of each of the plurality of light emitting diodes, and the high temperature side electrode may include a cathode of the each of the plurality of light emitting diodes.

A length of a portion of the electrode connected to the high temperature side electrode in a lateral direction of the light emitting diode substrate may be larger than a length of a portion of the electrode connected to the low temperature side electrode in the lateral direction.

A radius of a semicircle whose center is at the one of the plurality of light emitting diodes and which is inscribed in the electrode on the high temperature side electrode side may be larger than a radius of a semicircle whose center is at the one of the plurality of light emitting diodes and which is inscribed in the electrode on the low temperature side electrode side.

In another general aspect, the liquid crystal display device of the present application includes a liquid crystal display panel; and a backlight unit, the backlight unit includes a circuit board having a plurality of light emitting diodes (LEDs) serving as light sources mounted thereon, the circuit board being arranged to be opposed to the liquid crystal display panel and being smaller than the liquid crystal display panel in width in a first direction that is one of a vertical direction and a horizontal direction of the liquid crystal display panel; and two regions devoid of the light sources, the two regions being located on opposite sides across the circuit board in the first direction and each having a width larger than the width of the circuit board in the first direction. The LEDs are arranged in at least three rows in a second direction orthogonal to the first direction. The circuit board includes a plurality of connection plates arranged thereon, the plurality of connection plates being located between two of the plurality of LEDs adjacent in the second direction so as to electrically connect the two of the plurality of LEDs to each other. The connection plates arranged in a row between two rows on both sides among the at least three rows are larger than the plurality of connection plates arranged in the two rows on both sides.

The above another general aspect may include one or more of the following features. The connection plates arranged in the row between the two rows on both sides may be larger than the plurality of connection plates arranged in the two rows on both sides in width in the first direction.

The connection plates arranged in the row between the two rows on both sides may be equal to the plurality of connection plates arranged in the two rows on both sides in width in the second direction.

Positions of the plurality of LEDs in one of two adjacent rows may be offset with respect to positions of the plurality of LEDs in another of the two adjacent rows in the second direction.

The liquid crystal display device may further include a reflection sheet for reflecting light of the plurality of LEDs toward the liquid crystal display panel. The reflection sheet may have a concave shape that is open toward the liquid crystal display panel, and the circuit board may be located at a bottom of the reflection sheet.

The circuit board may have at least five rows, each of which may include the plurality of LEDs and the plurality of connection plates. The connection plates arranged in the at least five rows may be larger in accordance with a distance from the two rows on both sides to the row in which the plurality of connection plates are arranged.

The connection plates may be rectangular.

The connection plates may include an edge portion connected to each of the plurality of LEDs. The connection plate may include a protrusion portion on the edge portion side to protrude in the first direction.

A television receive may include the liquid crystal display device, the television receiver being configured to receive a television broadcast wave to display a video and output sound.

According to the implementations described above, in the liquid crystal display device including the backlight unit for irradiating the entire image formation region with light of the light emitting diodes arranged in a concentrated manner, the heat generated from the light emitting diode can be efficiently dissipated.

Further, according to the implementations described above, heat of the LED can be released from the connection plates. The connection plate arranged in the row between the two rows on both sides is larger than the connection plate arranged in the two rows on both sides. Consequently, the heat of the LEDs arranged in the row between the two rows on both sides can be efficiently released.

Further, according to the implementations described above, there is no need to decrease arrangement density of the LEDs arranged in the middle row as compared to arrangement density of the LEDs arranged in the two rows on both sides. As a result, brightness of the backlight unit can be enhanced easily.

Further, according to the implementations described above, the arrangement density of the LEDs becomes uniform among the respective rows.

Further, according to the implementations described above, the heat from the LEDs is easily dispersed.

Further, according to the implementations described above, the light of the LEDs is easily expanded to the entire liquid crystal display panel.

Further, according to the implementations described above, also in the structure having a large number of rows, the heat of the LEDs arranged in the middle rows can be efficiently released.

Further, according to the implementations described above, the area of the connection plate is easily ensured.

In the circuit board, temperature becomes particularly higher in the vicinity of a terminal of the LED, and heat spreads in a concentric manner. According to the implementations described above, it is possible to increase the radius of a circle that can be drawn on the connection plate and is centered at the terminal of the LED. Consequently, the heat of the LED can be further efficiently released.

DETAILED DESCRIPTION

Now, a first embodiment of the present application is described below with reference to the accompanying drawings.

FIG. 1is an exploded perspective view of a liquid crystal display device101according to this embodiment. As illustrated inFIG. 1, the liquid crystal display device101is assembled by arranging, in order from the front side, an upper frame102, a liquid crystal panel103, an intermediate frame104, an optical sheet group105, a reflection sheet106, a light emitting diode substrate107, a radiator plate108, and a lower frame109. Note that, the optical sheet group105, the reflection sheet106, the light emitting diode substrate107, and the radiator plate108together construct a backlight unit110that functions as a planar light source for illuminating the liquid crystal panel103from the rear surface side thereof.FIG. 1illustrates only structural components of the liquid crystal display device101and omits other components, such as a control board and a speaker.

FIG. 2is a schematic cross-sectional view of the liquid crystal display device101taken along the line II-II ofFIG. 1.FIG. 2illustrates a schematic cross-section of the assembled liquid crystal display device101. As illustrated inFIG. 2, the liquid crystal display device101is structured to store the liquid crystal panel103and the backlight unit110in an outer frame formed of the upper frame102and the lower frame109. The intermediate frame104is provided between the liquid crystal panel103and the backlight unit110so that the liquid crystal panel103and the backlight unit110are retained independently. The left side inFIG. 2is the side where a user observes an image, which is hereinafter referred to as “front side”, and the surface facing the front side is referred to as “front surface”. The opposite side of the front side is referred to as “rear surface side”, and the surface facing the rear surface side is referred to as “rear surface”.

Note that, the liquid crystal display device101exemplified in this embodiment is a television receiver. Therefore, the liquid crystal display device101includes components for functioning as a television receiver, such as a speaker111illustrated inFIG. 2. Further, a control board112illustrated inFIG. 2includes a power supply, a control circuit for the liquid crystal panel103, and a control circuit for the backlight unit110, as well as a circuit such as a tuner for receiving television broadcast. Note that, the liquid crystal display device101is not necessarily a television receiver, and may be a computer monitor, for example. In this case, the liquid crystal display device101may omit the components for functioning as a television receiver.

The upper frame102and the lower frame109construct a housing for storing the liquid crystal panel103and the backlight unit110, and it is preferred that the upper frame102and the lower frame109be formed of a lightweight material having high rigidity. Examples of the material that may be used for the upper frame102and the lower frame109are metals, such as a steel plate, an aluminum alloy, and a magnesium alloy, FRP, and various kinds of synthetic resins. It is particularly preferred that the lower frame109be formed of a material having high heat conductivity in order to dissipate the heat generated due to light emission of the light emitting diodes efficiently, which is conducted from the light emitting diode substrate107via the radiator plate108. In this embodiment, a steel plate is used. The material of the upper frame102may be the same as that of the lower frame109or may be different, and can be determined as appropriate considering the size, intended use, appearance, weight, and other factors of the liquid crystal display device101. A buffer102ais provided on the surface of the upper frame102facing the liquid crystal panel103, so as to mitigate the shock occurring when the liquid crystal panel103swings due to vibration or the like and comes in contact with the upper frame102. As the buffer102a, an appropriate rubber, resin, sponge, or the like is used. It is to be understood that the support and buffer structure of the liquid crystal panel103described herein is an example.

The intermediate frame104is a member that retains the liquid crystal panel103and the backlight unit110independently in a separate manner. On the front surface of the intermediate frame104, a buffer104ais provided so as to mitigate the shock occurring when the liquid crystal panel103swings and comes in contact with the intermediate frame104. As the buffer104a, an appropriate rubber, resin, sponge, or the like is used. Note that, the structure of the intermediate frame104described herein is an example. The intermediate frame104may employ any structure that appropriately supports the liquid crystal panel103and the backlight unit110, and may be omitted as occasion demands.

Also the material of the intermediate frame104is not particularly limited, but it is preferred to use a synthetic resin in terms of moldability and cost. In this embodiment, polycarbonate is used in terms of strength, but the material is not always limited thereto. As in fiber reinforced plastics (FRP), a reinforcing material may be mixed into a synthetic resin. It is also preferred that the intermediate frame104have light blocking properties and therefore be in black or dark color. The coloring of the intermediate frame104may be attained by a black or dark color material itself or by coating the surface of the intermediate frame104. In this embodiment, the intermediate frame104is obtained by molding polycarbonate that is colored in black or dark color.

The backlight unit110includes the optical sheet group105, the reflection sheet106, the light emitting diode substrate107, and the radiator plate108. The light emitting diode substrate107of this embodiment is an elongated substrate on which a plurality of light emitting diodes113are linearly mounted, and is provided so that a longitudinal direction of the light emitting diode substrate107is aligned with a longitudinal direction of the liquid crystal display device101. The light emitting diode substrate107is fixed to the radiator plate108. In this case, the light emitting diode113in this embodiment is a so-called light emitting diode package in which a light emitting diode chip is sealed with a sealing resin, and is mounted onto the light emitting diode substrate107. However, this is not a limitation, and as another example, a light emitting diode chip may be formed directly on the light emitting diode substrate107. A lens114is an optical component for diffusing a light beam emitted from the light emitting diode113so as to obtain illumination with uniform brightness over an entire image formation region of the liquid crystal panel103.

Note that, the light emitting diode substrate107in this embodiment is sized so that the length in the longitudinal direction is slightly smaller than the length of the liquid crystal panel103in a corresponding direction, about 70% to 80% in this embodiment. The length of the light emitting diode substrate107in the lateral direction (direction orthogonal to the longitudinal direction in the plane of the light emitting diode substrate107) is smaller than the length of the liquid crystal panel103in the lateral direction, preferably half or less, and in this embodiment, roughly about 10% to 20%. Any insulating material can be used for the light emitting diode substrate107without any particular limitation, and the light emitting diode substrate107may be formed of an insulating material such as glass epoxy, paper phenol, and paper epoxy, or a metal with insulating coating. In the following, the longitudinal direction as used herein refers to the longitudinal direction of the light emitting diode substrate, that is, a direction in which the light emitting diodes113are arrayed. Note that, in this embodiment, the longitudinal direction of the light emitting diode substrate107is the direction parallel to the long side of the liquid crystal panel, but instead, the direction parallel to the short side of the liquid crystal display device101may be defined as the longitudinal direction. Further, the above-mentioned specific dimensions of the light emitting diode substrate107are an example, and may be arbitrarily changed depending on the design of the liquid crystal display device101.

The reflection sheet106is a member for reflecting light from the light emitting diodes113to irradiate the rear surface of the liquid crystal panel103with light uniformly. The reflection sheet106has a curved cross-section as illustrated inFIG. 2. A light beam from the light emitting diode113is diffused in the vertical direction by the lens114provided on the front surface of the light emitting diode113. As indicated by arrows115ofFIG. 2, the light beam enters directly the optical sheet group105, or is reflected on the reflection sheet106to enter the optical sheet group105. The reflection sheet106and the optical sheet group105have the sizes corresponding to the liquid crystal panel103, and hence the liquid crystal panel103is illuminated uniformly from the rear surface side thereof.

The reflection sheet106has the size corresponding to the liquid crystal panel103as described above, and has a curved shape to be recessed as viewed from the front surface side. The reflection sheet106is provided with holes at positions at which the light emitting diodes113are arranged, so as to expose the light emitting diodes113to the front surface side of the reflection sheet106. The material of the reflection sheet106is not particularly limited, and a white reflection sheet using a polyethylene terephthalate (PET) resin or the like or a mirrored reflection sheet may be used. In this embodiment, a white reflection sheet is used. The optical sheet group105is a plurality of optical films including a diffusion sheet for diffusing light entering from the light emitting diodes113, a prism sheet for refracting light beams toward the front surface side, and the like.

The radiator plate108is a metal plate to which the light emitting diode substrate107is mounted and which retains the reflection sheet106. The radiator plate108itself is fixed to the lower frame109. It is preferred that the material of the radiator plate108be high in heat conductivity, and various kinds of metal and alloy may be suitable for use. In this embodiment, aluminum is used. A molding method for the radiator plate108is not particularly limited, and any method such as pressing and cutting may be used. In this embodiment, the radiator plate108is obtained by an extrusion molding method.

FIG. 3is a configuration diagram illustrating a configuration of the liquid crystal display device101. Referring toFIG. 3, functions of respective members of the liquid crystal display device101are described below.

The liquid crystal panel103is rectangular, the lengths of which in the horizontal direction and the vertical direction are determined depending on the intended use of the liquid crystal display device101. The liquid crystal panel103may have a horizontally-elongated shape (the length in the horizontal direction is larger than the length in the vertical direction) or a vertically-elongated shape (the length in the horizontal direction is smaller than the length in the vertical direction). Alternatively, the lengths in the horizontal direction and the vertical direction may be equal to each other. In this embodiment, the liquid crystal display device101is assumed to be used for a television receiver, and hence the liquid crystal panel103has a horizontally-elongated shape.

The liquid crystal panel103includes a pair of transparent substrates. On a TFT substrate as one of the transparent substrates, a plurality of video signal lines Y and a plurality of scanning signal lines X are formed. The video signal lines Y and the scanning signal lines X are orthogonal to each other to form a grid pattern. A region surrounded by adjacent two video signal lines Y and adjacent two scanning signal lines X corresponds to one pixel.

FIG. 4illustrates a circuit diagram of one pixel formed in the liquid crystal panel103. InFIG. 4, a region surrounded by video signal lines Yn and Yn+1 and scanning signal lines Xn and Xn+1 corresponds to one pixel. The pixel focused here is driven by the video signal line Yn and the scanning signal line Xn. On the TFT substrate side of each of the pixels, a thin film transistor (TFT)103ais provided. The TFT103ais turned on by a scanning signal input from the scanning signal line Xn. The video signal line Yn applies a voltage (signal representing a grayscale value for each pixel) to a pixel electrode103bof the pixel via the on-state TFT103a.

On the other hand, a color filter is formed on a color filter substrate as the other of the transparent substrates and a liquid crystal103cis sealed between the TFT substrate and the color filter substrate. Then, a common electrode103dis formed so as to form a capacitance with the pixel electrode103bvia the liquid crystal103c. The common electrode103dis electrically connected to a common potential. Accordingly, depending on the voltage applied to the pixel electrode103b, an electric field between the pixel electrode103band the common electrode103dchanges, thereby changing the orientation state of the liquid crystal103cto control the polarization state of light beams passing through the liquid crystal panel103. Polarization filters are respectively adhered to a display surface of the liquid crystal panel103and a rear surface thereof, which is the opposite surface of the display surface. With this, each pixel formed in the liquid crystal panel103functions as an element that controls light transmittance. Then, the light transmittance of each pixel is controlled in accordance with input image data, to thereby form an image. Therefore, in the liquid crystal panel103, a region in which the pixels are formed is an image formation region.

Note that, the common electrode103dmay be provided in any of the TFT substrate and the color filter substrate. How to arrange the common electrode103ddepends on the liquid crystal driving mode. For example, in an in-plane switching (IPS) mode, the common electrode103dis provided on the TFT substrate. In a vertical alignment (VA) mode or a twisted nematic (TN) mode, the common electrode is provided on the color filter substrate. This embodiment uses the IPS mode, where the common electrode103dis provided on the TFT substrate. Further, the transparent substrates in this embodiment are formed of glass, but other materials such as a resin may be used.

Returning toFIG. 3, a control device116inputs video data received by a tuner or an antenna (both not shown) or video data generated in another device such as a video reproducing device. The control device116may be a microcomputer including a central processing unit (CPU) and a memory such as a read only memory (ROM) and a random access memory (RAM). The control device116performs various types of image processing, such as color adjustment, with respect to the input video data, and generates a video signal representing a grayscale value for each of the pixels. The control device116outputs the generated video signal to a video line drive circuit117b. Further, the control device116generates, based on the input video data, a timing signal for synchronizing the video line drive circuit117b, a scanning line drive circuit117a, and a backlight drive circuit118, and outputs the generated timing signal toward the respective drive circuits. Note that, this embodiment is not intended to limit the form of the control device116particularly. For example, the control device116may be including a plurality of large scale integrations (LSIs) or a single LSI. Further, the control device116may not be configured to synchronize between the backlight drive circuit118and the other circuits.

The backlight drive circuit118is a circuit for supplying a current necessary for the plurality of light emitting diodes113serving as light sources of the backlight unit110. In this embodiment, the control device116generates a signal for controlling brightness of the light emitting diode113based on input video data, and outputs the generated signal toward the backlight drive circuit118. Then, in accordance with the generated signal, the backlight drive circuit118controls the amount of current flowing through the light emitting diode113to adjust the brightness of the light emitting diode113. The brightness of the light emitting diodes113may be adjusted for each of the light emitting diodes113, or the plurality of light emitting diodes113may be divided into some groups and the brightness may be adjusted for each of the groups. Note that, as a method of controlling the brightness of the light emitting diode113, a pulse width modulation (PWM) method may be employed, in which the brightness is controlled based on a light emission period with a constant current amount. As an alternative method, the current amount may be set constant so as to obtain light with constant light intensity, without controlling the brightness of the light emitting diode113.

The scanning line drive circuit117ais connected to the scanning signal lines X formed on the TFT substrate. The scanning line drive circuit117aselects one of the scanning signal lines X in order in response to the timing signal input from the control device116, and applies a voltage to the selected scanning signal line X. When the voltage is applied to the scanning signal line X, the TFTs connected to the scanning signal line X are turned on.

The video line drive circuit117bis connected to the video signal lines Y formed on the TFT substrate. In synchronization with the selection of the scanning signal line X by the scanning line drive circuit117a, the video line drive circuit117bapplies, to each of the TFTs provided to the selected scanning signal line X, a voltage corresponding to the video signal representing the grayscale value for each of the pixels.

Note that, in this embodiment, the control device116and the backlight drive circuit118illustrated inFIG. 3are both formed on the control board112ofFIG. 2. Further, a liquid crystal panel drive circuit117including the scanning line drive circuit117aand the video line drive circuit117bis formed on flexible printed circuits (FPCs) electrically connected to the liquid crystal panel103(FIG. 3), or formed on a substrate constructing the liquid crystal panel103(so-called system-on-glass (SOG)). Note that, the arrangement described above is an example, and the respective circuits are provided at any portions.

FIG. 5is a view illustrating the reflection sheet106, the light emitting diode substrate107, and the radiator plate108of the liquid crystal display device as viewed from the front surface side. Note that, inFIG. 5, portions of the light emitting diode substrate107and the radiator plate108which are hidden behind the reflection sheet106are illustrated by broken lines.

On the periphery of the reflection sheet106, an appropriate number of fixing portions106aprotruding in a tongue shape are provided at appropriate intervals. The fixing portions106aare used for fixing a peripheral portion of the reflection sheet106, and in this embodiment, the fixing portions106aare each provided with a hole for hooking therein a protrusion (not shown) provided to the intermediate frame104for fixation. However, the structure of fixing the peripheral portion of the reflection sheet106may be of any type.

Further, in a region of the center portion of the reflection sheet106in the lateral direction, holes106bfor exposing the lenses114to the front surface side of the reflection sheet106are provided correspondingly to the array of the lenses114, that is, the light emitting diodes. Further, the array density of the light emitting diodes is high in the vicinity of the center portion in the longitudinal direction and low in the vicinity of both end portions. In other words, the interval between adjacent light emitting diodes is larger at the peripheral portion of the image formation region than at the center portion of the image formation region. The positions of the lenses114and the holes106billustrated inFIG. 5correspond to the positions of the above-mentioned light emitting diodes. Note that, inFIG. 5, only one lens114and only one hole106bare denoted by reference symbols as representatives.

FIG. 6is a partial enlarged cross-sectional view taken along the line VI-VI ofFIG. 5. InFIG. 6, the lower frame109is also illustrated. The left side inFIG. 6is the front surface side, and the right side inFIG. 6is the rear surface side.FIG. 6illustrates how the light emitting diode113mounted onto the light emitting diode substrate107and the lens114arranged on the front surface of the light emitting diode113pass through the hole106bprovided in the reflection sheet106and are exposed to the front surface side of the reflection sheet106. The reflection sheet106is further provided with a fixing hole106c. With a fixture119passing through the fixing hole106c, the reflection sheet106is fixed to the radiator plate108in a region on the outer side of the light emitting diode substrate107in the width direction. The size of the fixing hole106cis slightly larger than the cross section of a passing portion of the fixture119, in order to allow for a relative change in dimensions of the respective members caused by different linear expansion coefficients when the light emitting diode113generates heat to undergo thermal expansion. Further, the front surface of the light emitting diode substrate107and the front surface of the radiator plate108are substantially flush with each other, and hence, on the front surface side thereof, the reflection sheet106is retained flat without waving. The fixture119may be of any type and is not particularly limited. In this embodiment, a fixing pin having a snap-in mechanism is used as illustrated inFIG. 6, which facilitates the fixation of the reflection sheet106. It is preferred that the material of the fixture119be the same as that of the reflection sheet106or be a similar white synthetic resin. This minimizes brightness unevenness at the position where the fixture119is arranged.

FIG. 7is a partial enlarged view of the light emitting diode substrate107.FIG. 7illustrates the vicinity of the center of the light emitting diode substrate107illustrated inFIG. 5. Illustration of the lenses is omitted for simple description. As illustrated inFIG. 7, the light emitting diodes113are arrayed in the longitudinal direction to form alight emitting diode array. An electrode121with a solid pattern is formed between an anode and a cathode of adjacent light emitting diodes113to connect the light emitting diodes113in series. InFIG. 7, in particular, the light emitting diode113illustrated at the center is denoted by reference numeral, and the electrode121connected to a low temperature side electrode of this light emitting diode113is illustrated as “electrode121L” while the electrode121connected to a high temperature side electrode of this light emitting diode113is illustrated as “electrode121H”. A boundary122where no electrode121is formed is provided between the electrode121L and the electrode121H, and both electrodes121L and121H are separated from each other to prevent a short circuit. Note that, in this example, the anode is the low temperature side electrode and the cathode is the high temperature side electrode.

In this embodiment, the boundary122is non-parallel to the lateral direction (vertical direction ofFIG. 7) orthogonal to the longitudinal direction in the plane of the light emitting diode substrate107, and is inclined toward the electrode121L connected to the low temperature side electrode, starting from the light emitting diode113.

The reason why the boundary122is oriented in such a way is now described. Heat generated by the light emitting diode113propagates to the electrodes121L and121H via the low temperature side electrode and the high temperature side electrode and is then dissipated through heat exchange with the outside air. In this case, the heat transferred to the electrodes121L and121H via the low temperature side electrode and the high temperature side electrode propagates through the planes of the electrodes121L and121H radially to be diffused. Thus, the electrodes121L and121H have such concentric temperature distributions that the temperature decreases with distance from the low temperature side electrode and the high temperature side electrode with the low temperature side electrode and the high temperature side electrode as the centers. On the other hand, as well known, the magnitude of the heat flux density caused by the heat transfer to the outside air from the electrodes121L and121H is proportional to a temperature difference between the electrodes121L and121H and the outside air. Thus, when the outside air temperature is regarded as substantially constant due to convection, as the areas of high temperature portions of the electrodes121L and121H become larger, the heat transfer to the outside air from the electrodes121L and121H becomes larger to improve heat dissipation efficiency. In other words, it is desired that the electrodes121L and121H have such a shape that the areas of the high temperature portions close to the light emitting diode113serving as a heat source are made as large as possible. As already described above, the amount of heat generation at the high temperature side electrode of the light emitting diode113is larger than the amount of heat generation at the low temperature side electrode thereof. Thus, in the vicinity of a certain focused light emitting diode113, the electrode121H has a higher temperature. Accordingly, the shape of the electrode121is changed between the side connected to the low temperature side electrode and the side connected to the high temperature side electrode, thereby obtaining such a shape that the area of the high temperature portion connected to the high temperature side electrode is made as large as possible. In this manner, heat dissipation efficiency is improved as compared to a case of a shape different from the above-mentioned shape, that is, the shape in which the boundary122is parallel to the lateral direction as illustrated inFIG. 9. The shape of the boundary122illustrated inFIG. 7is an example of the shape of the electrode121for improving the heat dissipation efficiency in this way. In this shape, an optimal inclination angle of the boundary122may be selected depending on the difference between the amounts of heat generation from the low temperature side electrode and the high temperature side electrode of the light emitting diode113.

The feature of the shape of the electrode121for improving the heat dissipation efficiency can be described by various expressions. One example is the above-mentioned expression that the boundary122is non-parallel to the lateral direction and is inclined toward the electrode121L connected to the low temperature side electrode starting from the light emitting diode113. Alternatively, the following expressions are conceivable.

Specifically, the feature can be described by the expression that, in a circle which is centered at one light emitting diode and whose diameter is the distance from the one light emitting diode to another light emitting diode adjacent to the one light emitting diode, the area of an electrode connected to the high temperature side electrode of the one light emitting diode is larger than the area of an electrode connected to the low temperature side electrode of the one light emitting diode. This is described with reference toFIG. 7. When considering a circle123(illustrated by broken line inFIG. 7) which is centered at the light emitting diode113and whose diameter is the distance to an adjacent light emitting diode, the area of a portion124H (illustrated by hatching inFIG. 7) of the electrode121H included in the circle123and connected to the high temperature side electrode of the light emitting diode113is larger than the area of a portion124L (illustrated by hatching inFIG. 7) of the electrode121L included in the circle123and connected to the low temperature side electrode of the light emitting diode113.

Alternatively, the feature can be described by the expression that the electrode121L and the electrode121H are shaped to partially overlap with each other in the lateral direction. This is described with reference toFIG. 7. When considering a particular straight line extending in the lateral direction, specifically, a straight line125(illustrated by dashed line inFIG. 7) on the side of the low temperature side electrode of the light emitting diode113in the illustrated example, the straight line125intersects with both the electrode121L and the electrode121H.

Note that, the example ofFIG. 7illustrated as this embodiment satisfies all the above-mentioned features simultaneously, but all the features are not always required to be satisfied. It is only necessary that any one of the features be satisfied.

The light emitting diodes113in the above description are linearly arranged in one row in the longitudinal direction, but the arrangement is not always limited thereto. The light emitting diodes113may be arranged in a plurality of rows in the longitudinal direction.

FIG. 8illustrates such an example, which is a partial enlarged view of the light emitting diode substrate107according to a modified example where the light emitting diodes113are arranged in two rows in the longitudinal direction. Also in this case, similarly to the above-mentioned example, at least a part of the boundary122is non-parallel to the lateral direction, and is inclined toward the electrode121L connected to the low temperature side electrode, starting from the light emitting diode113. In the circle123which is centered at the light emitting diode113and whose diameter is the distance to an adjacent light emitting diode, the area of the portion124H of the electrode121H connected to the high temperature side electrode of the light emitting diode113is larger than the area of the portion124L of the electrode121L connected to the low temperature side electrode of the light emitting diode113. Further, the electrode121L and the electrode121H partially overlap with each other in the lateral direction, and the straight line125extending in the lateral direction intersects with both the electrode121L and the electrode121H.

Subsequently, a second embodiment of the present application is described with reference to the accompanying drawings.

FIG. 10is an exploded perspective view of a liquid crystal display device201according to this embodiment. As illustrated inFIG. 10, the liquid crystal display device201is assembled by arranging, in order from the front side, an upper frame202, a liquid crystal panel203, an intermediate frame204, an optical sheet group205, a reflection sheet206, a light emitting diode substrate207, a radiator plate208, and a lower frame209. Note that, the optical sheet group205, the reflection sheet206, the light emitting diode substrate207, and the radiator plate208together construct a backlight unit210that functions as a planar light source for illuminating the liquid crystal panel203from the rear surface side thereof.FIG. 10illustrates only structural components of the liquid crystal display device201and omits other components, such as a control board and a speaker.

FIG. 11is a schematic cross-sectional view of the liquid crystal display device201taken along the line XI-XI ofFIG. 10.FIG. 11illustrates a schematic cross-section of the assembled liquid crystal display device201. As illustrated inFIG. 11, the liquid crystal display device201is structured to store the liquid crystal panel203and the backlight unit210in an outer frame formed of the upper frame202and the lower frame209. The intermediate frame204is provided between the liquid crystal panel203and the backlight unit210so that the liquid crystal panel203and the backlight unit210are retained independently. The left side inFIG. 11is the front side, and the right side, which is the opposite side of the front side, is the rear surface side.

Note that, the liquid crystal display device201exemplified in this embodiment is a television receiver. Therefore, the liquid crystal display device201includes components for functioning as a television receiver, such as a speaker211illustrated inFIG. 11. Further, a control board212illustrated inFIG. 11includes a power supply, a control circuit for the liquid crystal panel203, and a control circuit for the backlight unit210, as well as a circuit such as a tuner for receiving television broadcast. Note that, the liquid crystal display device201is not necessarily a television receiver, and may be a computer monitor, for example. In this case, the liquid crystal display device201may omit the components for functioning as a television receiver.

The upper frame202and the lower frame209construct a housing for storing the liquid crystal panel203and the backlight unit210, and it is preferred that the upper frame202and the lower frame209be formed of a lightweight material having high rigidity. Examples of the material that may be used for the upper frame202and the lower frame209are metals, such as a steel plate, an aluminum alloy, and a magnesium alloy, FRP, and various kinds of synthetic resins. It is particularly preferred that the lower frame209be formed of a material having high heat conductivity in order to dissipate the heat generated due to light emission of the light emitting diodes efficiently, which is conducted from the light emitting diode substrate207via the radiator plate208. In this embodiment, a steel plate is used. The material of the upper frame202may be the same as that of the lower frame209or may be different, and can be determined as appropriate considering the size, intended use, appearance, weight, and other factors of the liquid crystal display device201. A buffer202ais provided on the surface of the upper frame202facing the liquid crystal panel203, so as to mitigate the shock occurring when the liquid crystal panel203swings due to vibration or the like and comes in contact with the upper frame202. As the buffer202a, an appropriate rubber, resin, sponge, or the like is used. It is to be understood that the support and buffer structure of the liquid crystal panel203described herein is an example.

The intermediate frame204is a member that retains the liquid crystal panel203and the backlight unit210independently in a separate manner. On the front surface of the intermediate frame204, a buffer204ais provided so as to mitigate the shock occurring when the liquid crystal panel203swings and comes in contact with the intermediate frame204. As the buffer204a, an appropriate rubber, resin, sponge, or the like is used. Note that, the structure of the intermediate frame204described herein is an example. The intermediate frame204may employ any structure that appropriately supports the liquid crystal panel203and the backlight unit210, and may be omitted as occasion demands.

Also the material of the intermediate frame204is not particularly limited, but it is preferred to use a synthetic resin in terms of moldability and cost. In this embodiment, polycarbonate is used in terms of strength, but the material is not always limited thereto. As in FRP, a reinforcing material may be mixed into a synthetic resin. It is also preferred that the intermediate frame204have light blocking properties and therefore be in black or dark color. The coloring of the intermediate frame204may be attained by a black or dark color material itself or by coating the surface of the intermediate frame204. In this embodiment, the intermediate frame204is obtained by molding polycarbonate that is colored in black or dark color.

The backlight unit210includes the optical sheet group205, the reflection sheet206, the light emitting diode substrate207, and the radiator plate208. The light emitting diode substrate207in this embodiment is an elongated substrate on which a plurality of light emitting diodes213are linearly mounted, and is provided so that a longitudinal direction of the light emitting diode substrate207is aligned with a longitudinal direction of the liquid crystal display device201. The light emitting diode substrate207is fixed to the radiator plate208. In this case, the light emitting diode213in this embodiment is a so-called light emitting diode package in which a light emitting diode chip is sealed with a sealing resin, and is mounted onto the light emitting diode substrate207. However, this is not a limitation, and as another example, a light emitting diode chip may be formed directly on the light emitting diode substrate207. A lens214is an optical component for diffusing a light beam emitted from the light emitting diode213so as to obtain illumination with uniform brightness over an entire image formation region of the liquid crystal panel203.

Note that, the light emitting diode substrate207in this embodiment is sized so that the length in the longitudinal direction is slightly smaller than the length of the liquid crystal panel203in a corresponding direction, about 70% to 80% in this embodiment. The length of the light emitting diode substrate207in the lateral direction is smaller than the length of the liquid crystal panel203in the lateral direction, preferably half or less, and in this embodiment, roughly about 10% to 20%. Any insulating material can be used for the light emitting diode substrate207without any particular limitation, and the light emitting diode substrate207may be formed of an insulating material such as glass epoxy, paper phenol, and paper epoxy, or a metal with insulating coating. Note that, in this embodiment, the longitudinal direction of the light emitting diode substrate207is the direction parallel to the long side of the liquid crystal panel, but instead, the direction parallel to the short side of the liquid crystal display device201may be defined as the longitudinal direction. Further, the above-mentioned specific dimensions of the light emitting diode substrate207are an example, and may be arbitrarily changed depending on the design of the liquid crystal display device201.

The reflection sheet206is a member for reflecting light from the light emitting diodes213to irradiate the rear surface of the liquid crystal panel203with light uniformly. The reflection sheet206has a curved cross-section as illustrated inFIG. 11. A light beam from the light emitting diode213is diffused in the vertical direction by the lens214provided on the front surface of the light emitting diode213. As indicated by arrows215ofFIG. 11, the light beam enters directly the optical sheet group205, or is reflected on the reflection sheet206to enter the optical sheet group205. The reflection sheet206and the optical sheet group205have the sizes corresponding to the liquid crystal panel203, and hence the liquid crystal panel203is illuminated uniformly from the rear surface side thereof.

The reflection sheet206has the size corresponding to the liquid crystal panel203as described above, and has a curved shape to be recessed as viewed from the front surface side. The reflection sheet206is provided with holes at positions at which the light emitting diodes213are arranged, so as to expose the light emitting diodes213to the front surface side of the reflection sheet206. The material of the reflection sheet206is not particularly limited, and a white reflection sheet using a PET resin or the like or a mirrored reflection sheet may be used. In this embodiment, a white reflection sheet is used. The optical sheet group205is a plurality of optical films including a diffusion sheet for diffusing light entering from the light emitting diodes213, a prism sheet for refracting light beams toward the front surface side, and the like.

The radiator plate208is a metal plate to which the light emitting diode substrate207is mounted and which retains the reflection sheet206. The radiator plate208itself is fixed to the lower frame209. It is preferred that the material of the radiator plate208be high in heat conductivity, and various kinds of metal and alloy may be suitable for use. In this embodiment, aluminum is used. A molding method for the radiator plate208is not particularly limited, and any method such as pressing and cutting may be used. In this embodiment, the radiator plate208is obtained by an extrusion molding method.

FIG. 12is a configuration diagram illustrating a configuration of the liquid crystal display device201. Referring toFIG. 12, functions of respective members of the liquid crystal display device201are described below.

The liquid crystal panel203is rectangular, the lengths of which in the horizontal direction and the vertical direction are determined depending on the intended use of the liquid crystal display device201. The liquid crystal panel203may have a horizontally-elongated shape or a vertically-elongated shape. Alternatively, the lengths in the horizontal direction and the vertical direction may be equal to each other. In this embodiment, the liquid crystal display device201is assumed to be used for a television receiver, and hence the liquid crystal panel203has a horizontally-elongated shape.

The liquid crystal panel203includes a pair of transparent substrates. On a TFT substrate as one of the transparent substrates, a plurality of video signal lines Y and a plurality of scanning signal lines X are formed. The video signal lines Y and the scanning signal lines X are orthogonal to each other to form a grid pattern. A region surrounded by adjacent two video signal lines Y and adjacent two scanning signal lines X corresponds to one pixel.

Note that, the circuit diagram of the pixel formed in the liquid crystal panel203in this embodiment is the same as that illustrated inFIG. 4, and the function thereof is also the same.

Returning toFIG. 12, a control device216inputs video data received by a tuner or an antenna (both not shown) or video data generated in another device such as a video reproducing device. The control device216may be a microcomputer including a CPU and a memory such as a ROM and a RAM. The control device216performs various types of image processing, such as color adjustment, with respect to the input video data, and generates a video signal representing a grayscale value for each of the pixels. The control device216outputs the generated video signal to a video line drive circuit217b. Further, the control device216generates, based on the input video data, a timing signal for synchronizing the video line drive circuit217b, a scanning line drive circuit217a, and a backlight drive circuit218, and outputs the generated timing signal toward the respective drive circuits. Note that, this embodiment is not intended to limit the form of the control device216particularly. For example, the control device216may be including a plurality of LSIs or a single LSI. Further, the control device216may not be configured to synchronize between the backlight drive circuit218and the other circuits.

The backlight drive circuit218is a circuit for supplying a current necessary for the plurality of light emitting diodes213serving as light sources of the backlight unit210. In this embodiment, the control device216generates a signal for controlling brightness of the light emitting diode213based on input video data, and outputs the generated signal toward the backlight drive circuit218. Then, in accordance with the generated signal, the backlight drive circuit218controls an amount of current flowing through the light emitting diode213to adjust the brightness of the light emitting diode213. The brightness of the light emitting diodes213may be adjusted for each of the light emitting diodes213, or the plurality of light emitting diodes213may be divided into some groups and the brightness may be adjusted for each of the groups. Note that, as a method of controlling the brightness of the light emitting diode213, a PWM method may be employed, in which the brightness is controlled based on a light emission period with a constant current amount. As an alternative method, the current amount may be set constant so as to obtain light with constant light intensity, without controlling the brightness of the light emitting diode213.

The scanning line drive circuit217ais connected to the scanning signal lines X formed on the TFT substrate. The scanning line drive circuit217aselects one of the scanning signal lines X in order in response to the timing signal input from the control device216, and applies a voltage to the selected scanning signal line X. When the voltage is applied to the scanning signal line X, the TFTs connected to the scanning signal line X are turned on.

The video line drive circuit217bis connected to the video signal lines Y formed on the TFT substrate. In synchronization with the selection of the scanning signal line X by the scanning line drive circuit217a, the video line drive circuit217bapplies, to each of the TFTs provided to the selected scanning signal line X, a voltage corresponding to the video signal representing the grayscale for each of the pixels.

Note that, in this embodiment, the control device216and the backlight drive circuit218illustrated inFIG. 12are both formed on the control board212ofFIG. 11. Further, a liquid crystal panel drive circuit217including the scanning line drive circuit217aand the video line drive circuit217bis formed on FPCs electrically connected to the liquid crystal panel203(FIG. 12), or formed on a substrate constructing the liquid crystal panel203(so-called SOG). Note that, the arrangement described above is an example, and the respective circuits are provided at any portions.

FIG. 13is a view illustrating the reflection sheet206, the light emitting diode substrate207, and the radiator plate208of the liquid crystal display device as viewed from the front surface side. Note that, inFIG. 13, portions of the light emitting diode substrate207and the radiator plate208which are hidden behind the reflection sheet206are illustrated by broken lines.

On the periphery of the reflection sheet206, an appropriate number of fixing portions206aprotruding in a tongue shape are provided at appropriate intervals. The fixing portions206aare used for fixing a peripheral portion of the reflection sheet206, and in this embodiment, the fixing portions206aare each provided with a hole for hooking therein a protrusion (not shown) provided to the intermediate frame204for fixation. However, the structure of fixing the peripheral portion of the reflection sheet206may be of any type.

Further, in a region of the center portion of the reflection sheet206in the lateral direction, holes206bfor exposing the lenses214to the front surface side of the reflection sheet206are provided correspondingly to the array of the lenses214, that is, the light emitting diodes. The light emitting diodes are arrayed linearly along the longitudinal direction to form a plurality of light emitting diode arrays. In this embodiment, two light emitting diode arrays are provided in parallel to the lateral direction. Note that, the number of light emitting diode arrays only needs to be more than one, and may be three or more. The light emitting diodes belonging to one light emitting diode array are arrayed in a staggered manner with respect to the light emitting diodes belonging to an adjacent light emitting diode array. Further, the array density of the light emitting diodes is high in the vicinity of the center portion in the longitudinal direction and low in the vicinity of both end portions. In other words, the interval between adjacent light emitting diodes is larger at the peripheral portion of the image formation region than at the center portion of the image formation region. The positions of the lenses214and the holes206billustrated inFIG. 13correspond to the positions of the above-mentioned light emitting diodes. Note that, inFIG. 13, only one lens214and only one hole206bare denoted by reference symbols as representatives.

FIG. 14is a partial enlarged cross-sectional view taken along the line XIV-XIV ofFIG. 13. InFIG. 14, the lower frame209is also illustrated. The left side inFIG. 14is the front surface side, and the right side inFIG. 14is the rear surface side.FIG. 14illustrates how the light emitting diode213mounted on the light emitting diode substrate207and the lens214arranged on the front surface of the light emitting diode213pass through the hole206bprovided in the reflection sheet206and are exposed to the front surface side of the reflection sheet206. The reflection sheet206is further provided with a fixing hole206c. With a fixture219passing through the fixing hole206c, the reflection sheet206is fixed onto the radiator plate208in a region on the outer side of the light emitting diode substrate207in the width direction. The size of the fixing hole206cis slightly larger than the cross section of a passing portion of the fixture219, in order to allow for a relative change in dimensions of the respective members caused by different linear expansion coefficients when the light emitting diode213generates heat to undergo thermal expansion. Further, the front surface of the light emitting diode substrate207and the front surface of the radiator plate208are substantially flush with each other, and hence, on the front surface side thereof, the reflection sheet206is retained flat without waving. The fixture219may be of any type and is not particularly limited. In this embodiment, a fixing pin having a snap-in mechanism is used as illustrated inFIG. 14, which facilitates the fixation of the reflection sheet206. It is preferred that the material of the fixture219be the same as that of the reflection sheet206or be a similar white synthetic resin. This minimizes brightness unevenness at the position where the fixture219is arranged.

FIG. 15is a partial enlarged view of the light emitting diode substrate207.FIG. 15illustrates the vicinity of the center of the light emitting diode substrate207illustrated inFIG. 13. Illustration of the lenses is omitted for simple description. As illustrated inFIG. 15, light emitting diodes213A and light emitting diodes213B are arrayed in the longitudinal direction to form a light emitting diode array220A and a light emitting diode array220B, respectively. Note that, alphabets A and B assigned to reference numeral213representing the light emitting diodes indicate that the light emitting diode belongs to the light emitting diode array220A and the light emitting diode array.220B, respectively. Further, an electrode221A with a solid pattern is formed between an anode and a cathode of adjacent light emitting diodes213A, and an electrode221B with a solid pattern is formed between an anode and a cathode of adjacent light emitting diodes213B.

In this case, as illustrated inFIG. 15, a boundary222between the electrode221A belonging to the light emitting diode array220A and the electrode221B belonging to the light emitting diode array220B is not a straight line extending in the longitudinal direction but has a zigzag shape alternately entering the light emitting diode array220A side and the light emitting diode array220B side. Accordingly, the electrode221A and the electrode221B are shaped to partially overlap with each other in the longitudinal direction. In other words, when considering a particular straight line extending in the longitudinal direction, for example, a straight line223(illustrated by broken line inFIG. 15) located in the middle between the light emitting diode array220A and the light emitting diode array220B, the straight line223intersects with both the electrode221A and the electrode221B. The boundary222is shaped so that, in regard to a given light emitting diode array, the electrodes enter an adjacent light emitting diode array in the lateral direction at the positions in the longitudinal direction where the light emitting diodes are provided. For example, in regard to the light emitting diode array220A, the electrodes221A enter the light emitting diode array220B side at the positions in the longitudinal direction where the light emitting diodes213A are provided.

The reason why the electrodes221A and221B have such a shape is now described. Heat generated by the light emitting diode213A or213B propagates to the electrode221A or221B via the anode and cathode and is then diffused through heat exchange with the outside air. In this case, the heat transferred to the electrode221A or221B via the anode and the cathode propagates through the plane of the electrode221A or221B radially to be diffused. Thus, the electrode221A or221B has such a concentric temperature distribution that the temperature decreases with distance from the anode and the cathode with the anode and the cathode as the center. On the other hand, as well known, the heat flux density caused by the heat transfer to the outside air from the electrode221A or221B is proportional to a temperature difference between the electrode221A or221B and the outside air. Thus, when the outside air temperature is regarded as substantially constant due to convection, as the area of a high temperature portion of the electrode221A or221B becomes larger, the heat transfer to the outside air from the electrode221A or221B becomes larger to improve heat dissipation efficiency. In other words, it is desired that the electrodes221A and221B have such a shape that the areas of the high temperature portions close to the light emitting diodes213A and213B serving as heat sources are made as large as possible. In view of the foregoing, in this embodiment, the boundary222is formed into a zigzag shape rather than a simple straight line shape. Note that, if it is assumed that the amounts of heat generation from the light emitting diodes213A and213B are equal to each other and that there is no difference between the amounts of heat generation from the anode and the cathode, the heat dissipation efficiency is improved most when the boundary222has a shape along the perpendicular bisector of a segment connecting adjacent light emitting diodes213A and213B.FIG. 15is a view illustrating this case.

By the way, the above description assumes that the amounts of heat generation from the light emitting diode are equal at the anode and at the cathode. In an actual light emitting diode, however, the amounts of heat generation from the anode and the cathode are often different from each other. One of the anode and the cathode having a larger amount of heat generation with higher temperature is referred to as “high temperature side electrode”, and another having a smaller amount of heat generation with relatively lower temperature is referred to as “low temperature side electrode”. In this case, it is preferred that the shape of the electrode be varied between the side connected to the high temperature side electrode and the side connected to the low temperature side electrode, thereby obtaining such a shape that the area of the high temperature portion connected to the high temperature side electrode is made as large as possible. Note that, inmost light emitting diodes used at present, the amount of heat generation at the cathode is larger than the amount of heat generation at the anode.

FIG. 16is a partial enlarged view of the light emitting diode substrate207in an example where the amount of heat generation differs between the anode and the cathode of each of the light emitting diodes213A and213B. In each of the light emitting diodes213A and213B illustrated inFIG. 16, the left side is a low temperature side electrode and the right side is a high temperature side electrode. Thus, the amount of heat generation on the right side of the light emitting diode213A or213B corresponding to the high temperature side electrode side is larger than that on the opposite side. Note that, in this example, the anode is the low temperature side electrode and the cathode is the high temperature side electrode.

In this cases, the shape of a boundary222between the electrodes221A and221B has a saw-tooth shape in which the electrodes221A and221B are engaged with each other as illustrated inFIG. 16, and in each of the electrodes221A and221B, the area of a portion connected to the high temperature side electrode and located in the vicinity thereof is larger than the area of a portion connected to the low temperature side electrode and located in the vicinity thereof. Also in this shape, similarly to the shape illustrated inFIG. 15, the electrode221A and the electrode221B are shaped to partially overlap with each other in the longitudinal direction.

What is important in the electrode shape as represented by the shape illustrated inFIG. 16for improving heat dissipation efficiency of heat from the light emitting diodes213A and213B whose amounts of heat generation are different at the anode and at the cathode is to increase the areas of the high temperature portions of the electrodes221A and221B as much as possible. Now, the features of the electrodes221A and221B having such a shape are described below with reference toFIG. 16.

The first feature is that, in a circle which is centered at one light emitting diode and whose diameter is the distance from the one light emitting diode to another light emitting diode closest to the one light emitting diode, the area of an electrode connected to a high temperature side electrode of the one light emitting diode is larger than the area of an electrode connected to a low temperature side electrode of the one light emitting diode.

This is described with reference toFIG. 16. When considering a circle224(illustrated by broken line inFIG. 16), which is centered at an arbitrary light emitting diode, for example, a light emitting diode denoted by reference symbol213A, and whose diameter is a distance to an adjacent light emitting diode, that is, a light emitting diode213B located on the lower left or right side of the light emitting diode213A inFIG. 16, the area of a portion225c(illustrated by hatching inFIG. 16) of the electrode221A included in the circle224and connected to the high temperature side electrode of the light emitting diode213A is larger than the area of a portion225a(illustrated by hatching inFIG. 16) of the electrode221A included in the circle224and connected to the low temperature side electrode of the light emitting diode213A.

The second feature is that, in regard to one light emitting diode, the length of a portion of the electrode connected to the high temperature side electrode in the lateral direction is larger than the length of a portion of the electrode connected to the low temperature side electrode in the lateral direction.

This is described with reference toFIG. 16. When considering an arbitrary light emitting diode, for example, a light emitting diode denoted by reference symbol213B, a length Lc in the lateral direction of the electrode221B connected to the high temperature side electrode side of the light emitting diode213B (this electrode221B is located on the right side of the light emitting diode213B inFIG. 16) at a portion connected to the high temperature side electrode is larger than a length La in the lateral direction of the electrode221B connected to the low temperature side electrode side of the light emitting diode213B (this electrode221B is located on the left side of the light emitting diode213B inFIG. 16) at a portion connected to the low temperature side electrode.

The third feature is that the radius of a semicircle which is centered at one light emitting diode and which is inscribed in the electrode on the high temperature side electrode side is larger than the radius of a semicircle which is centered at one light emitting diode and which is inscribed in the electrode on the low temperature side electrode side.

This is described with reference toFIG. 16. When considering an arbitrary light emitting diode, for example, the second light emitting diode213A from the left inFIG. 16, in a case where a semicircle which is centered at the light emitting diode213A and which is inscribed in the electrode221A is drawn, the radius of a semicircle226c(illustrated by two-dot chain line inFIG. 16) on the high temperature side electrode side is larger than the radius of a semicircle226a(illustrated by dashed line inFIG. 16) on the low temperature side electrode side.

All the features described above are not always required to be satisfied simultaneously, and it is only necessary that any one of the features be satisfied. It is to be understood that various other shapes than the shape illustrated inFIG. 16can be appropriately selected as the shape satisfying those features.

Note that, inFIG. 16, the boundary between the electrodes221A or221B adjacent across the light emitting diode213A or213B is parallel to the lateral direction, but the present invention is not limited thereto. For example, as illustrated inFIG. 17, the boundary between the electrodes221A or221B adjacent across the light emitting diode213A or213B may be non-parallel to the lateral direction so that the adjacent electrodes221A or221B belonging to one light emitting diode array220A or220B may be shaped to overlap with each other in the lateral direction. In this case, the terminal having a larger amount of heat generation, specifically, the electrodes221A and221B on the high temperature side electrode side in this example are shaped so as to enter the electrodes221A and221B on the low temperature side electrode side. In this manner, the areas of the portions on the cathode side where the temperature of the electrodes221A and221B becomes higher are increased, and hence heat dissipation efficiency is improved.

Further, a third embodiment of the present application is described with reference to the accompanying drawings.FIG. 19is a schematic cross-sectional view of a liquid crystal display device301according to this embodiment.FIG. 20is a plan view of a backlight unit310included in the liquid crystal display device301.

In the following description, y illustrated inFIG. 20is the first direction, and x is the second direction orthogonal to the first direction. In the example described herein, the first direction y is the vertical direction of a liquid crystal display panel320to be described below, and the second direction x is the horizontal direction of the liquid crystal display panel320. Note that, the first direction may be defined as the horizontal direction of the liquid crystal display panel320, and the second direction may be defined as the vertical direction of the liquid crystal display panel320.

As illustrated inFIG. 19, the liquid crystal display device301includes the liquid crystal display panel320. The liquid crystal display panel320has two glass substrates, and liquid crystal is encapsulated therebetween. A TFT, a source signal line, and a gate signal line are formed on one substrate (TFT substrate). A color filter is formed on the other substrate. The gate signal line and the source signal line are pulled to the outside of the liquid crystal display panel320and connected to a driver IC. Polarizing plates (not shown) are adhered onto the respective surfaces of the glass substrates. A backlight unit310for irradiating the liquid crystal display panel320with light is arranged on the rear surface side of the liquid crystal display panel320. The plurality of optical sheets321, such as a diffusion sheet and a prism sheet, are arranged between the liquid crystal display panel320and the backlight unit310.

The backlight unit310includes a circuit board311having a plurality of LEDs312serving as light sources mounted thereon. As illustrated inFIG. 20, the circuit board311in this example is a substrate elongated in the second direction x, and is arranged at a center part of the backlight unit310in the first direction y. The width of the circuit board311in the first direction y is smaller than the width of the liquid crystal display panel320in the first direction y. The backlight unit310has regions A and B in which no light source is provided. The regions A and B are regions on both sides of the circuit board311and are located on opposite sides across the circuit board311in the first direction y. In this example, the region A is an upper region of the circuit board311, and the region B is a lower region of the circuit board311. The widths of the regions A and B in the first direction y are larger than that of the circuit board311.

As illustrated inFIG. 19, the backlight unit310includes a reflection sheet313for reflecting light of the LEDs312toward the liquid crystal display panel320. The reflection sheet313is formed so as to avoid the positions of the plurality of LEDs312, and is arranged above the circuit board311. In this example, as illustrated inFIG. 20, the reflection sheet313has holes formed therein at the positions of the LEDs312, and the LEDs312are arranged inside the respective holes. Note that, holes elongated in the second direction x may be formed in the reflection sheet313, and the plurality of LEDs312may be arranged inside the respective holes.

As illustrated inFIG. 19, the reflection sheet313has a concave shape that opens toward the liquid crystal display panel320. The circuit board311is located at the bottom of the reflection sheet313. With such a shape of the reflection sheet313, the entire surface of the liquid crystal display panel320can be irradiated with light of the plurality of LEDs312. The reflection sheet313has a flat surface (hereinafter referred to as “bottom surface”)313eat the bottom thereof (seeFIG. 20). The circuit board311is arranged on the rear surface side of the bottom surface313e. Holes for arranging the plurality of LEDs312therein are formed in the bottom surface313e.

In the reflective sheet313, an upper portion313a(portion belonging to the above-mentioned region A) and a lower portion313b(portion belonging to the above-mentioned region B) each approach the liquid crystal display panel320while being spread in the first direction y from the bottom surface313e. In the example illustrated inFIG. 19, the upper portion313aand the lower portion313bare curved to approach the liquid crystal display panel320. In this example, as illustrated inFIG. 20, a right portion313cand a left portion313dof the reflective sheet313also each approach the liquid crystal display panel320while being spread from the bottom surface313e. In this example, the right portion313cand the left portion313dare flat oblique surfaces. Note that, the shape of the reflective sheet313is not limited thereto. For example, the upper portion313aand the lower portion313bmay be oblique surfaces that are not curved.

As illustrated inFIG. 19, in this example, the lens315is arranged on each LED312. The pair of the LED312and the lens315constructs one point light source S. The lens315is formed of an acrylic resin, for example. The lens315has a function of expanding light of the LED312in the first direction y. In other words, the irradiation angle of the light is expanded by the lens315in the vertical direction. Thus, a part of the light of the LED312is directed to the upper portion313aand the lower portion313bof the reflective sheet313, and is reflected on those portions313aand313btoward the liquid crystal display panel320. As a result, a wide area of the liquid crystal display panel320is irradiated with light. As described above, the right portion313cand the left portion313dof the reflective sheet313are inclined toward the liquid crystal display panel320. Light of the LED312directed to the right portion313cand the left portion313dis reflected on those portions313cand313dtoward the liquid crystal display panel320.

As illustrated inFIG. 19, the liquid crystal display device301includes a back cabinet331for storing the reflective sheet313and the circuit board311. The circuit board311is fixed onto the back cabinet331. In this example, a radiator plate332having the size corresponding to the circuit board311is arranged on the rear surface of the circuit board311, and the circuit board311is fixed onto the back cabinet331via the radiator plate332. In other words, the circuit board311is fixed onto the radiator plate332, and the radiator plate332is fixed onto the back cabinet331. Heat of the circuit board311is released through connection plates314A and314B to be described later and the radiator plate332.

As described above, the circuit board311in this example is a board elongated in the second direction x.FIG. 21is a plan view illustrating an example of the circuit board311. InFIG. 21, the above-mentioned lenses315are omitted. The plurality of LEDs312are arranged on the circuit board311in three rows in the second direction x. In this example, the plurality of LEDs312are arranged at equal intervals in the second direction x. Note that, the arrangement density of the LEDs312may vary in the second direction x. For example, the interval between two adjacent LEDs312may be gradually enlarged more at the side in the right or left direction.

The plurality of connection plates314A and314B are arranged on the circuit board311. Each of the connection plates314A and314B is arranged between two LEDs312adjacent in the second direction x, and electrically connects the two LEDs to each other. In other words, each LED312is arranged over two connection plates314A or314B adjacent in the second direction x. One edge of each of the connection plates314A and314B is connected to a cathode of one LED312of the two LEDs312, and the other edge is connected to an anode of the other LED312of the two LEDs312. With this structure, the plurality of LEDs312are connected to one another via the connection plates314A and314B. The LEDs312and the connection plates314A and314B are all arranged on a front surface311aof the circuit board311that faces the liquid crystal display panel320.

The connection plates314A and314B are formed of a metal foil such as copper. The connection plates314A and314B are formed to have the function of emitting heat of the LEDs312. In general, the temperature of the LED is higher on the cathode side than on the anode side. Accordingly, the connection plates314A and314B are used for decreasing the temperature on the cathode side, in particular. In this example, as illustrated inFIG. 21, the connection plates314A and314B are rectangles larger than the LEDs312in plan view.

Each of the connection plates314A and314B is formed by, for example, the same step as the step of forming a wiring pattern on the circuit board. Specifically, the connection plates314A and314B are formed on the circuit board311by plating with a metal foil and thereafter partially removing the metal foil by etching. Note that, a metal foil formed as a separate member from the circuit board311may be adhered onto the circuit board311as the connection plates314A and314B.

As described above, the circuit board311in the example illustrated inFIG. 21includes the plurality of LEDs312arranged in three rows. The circuit board311has three parallel rows L1, L2, and L3as rows composed of the LEDs312and the connection plate314A or314B. The three rows L1, L2, and L3are arranged in the first direction y. The rows L1and L3are two rows on both sides, that is, two rows on edge sides. The row L2is a row between the rows L1and L3(hereinafter referred to as “middle row”).

When the circuit board311has three or more rows, the temperature of the LEDs312arranged in the middle row L2tends to be higher. To deal with this, in this embodiment, the plurality of connection plates314B arranged in the row L2are larger than the connection plates314A arranged in the two rows L1and L3on both sides in plan view of the circuit board311. Specifically, the area of the connection plate314B is larger than the area of the connection plate314A. In this example, a width Wy2of the connection plate314B in the first direction y is larger than widths Wy1and Wy3of the connection plates314A in the first direction y. On the other hand, a width Wx2of the connection plate314B in the second direction x is equal to widths Wx1and Wix3of the connection plates314A in the second direction x. In other words, the connection plate314B has a shape obtained by extending the connection plate314A in the first direction y. Thus, the intervals between two LEDs adjacent in the second direction x are equal among the row L1, the row L2, and the row L3.

Note that, in the example illustrated inFIG. 21, the width Wy1of the connection plate314A in the row L1and the width Wy3of the connection plate314A in the row L3are equal to each other. Alternatively, however, the width Wy1of the connection plate314A in the row L1and the width Wy3of the connection plate314A in the row L3may be different from each other.

As illustrated inFIG. 21, the positions of the LEDs312in one of two adjacent rows are offset in the second direction x with respect to the positions of the LEDs312in the other row. This arrangement can suppress the accumulation of heat in the vicinity of the cathode of each LED312. In this example, the positions of the LEDs312in one row are offset with respect to the positions of the LEDs312in the other row by a half distance of the interval of the LEDs312. Thus, the LEDs312in the row L2are each located on a straight line passing through an intermediate position of two LEDs312arranged in the respective rows L1and L3.

FIG. 22is a graph schematically showing temperature distributions along the line C-C′ illustrated inFIG. 21. InFIG. 22, the solid lines T1, T2, and13individually represent temperature distributions caused by heat from the LEDs312in the row L1, the LEDs312in the row L2, and the LEDs312in the row L3. The dashed line Tt represents a temperature distribution caused by heat from the LEDs312in all the rows. Note that, the line C-C′ is the line passing on the cathode side of the LEDs312.

As represented by the solid lines T1, T2, and T3ofFIG. 22, in the temperature distributions caused by heat from the LEDs312in the respective rows L1, L2, and L3, the temperature becomes the highest at positions P1, P2, and P3at which the LEDs312are arranged, and the temperature decreases in accordance with the distances from the positions P1, P2, and P3. As described above, the width of the connection plate314B is larger than the width of the connection plate314A. Thus, as represented by the solid line T2, the temperature distribution caused by heat from the LEDs312in the row L2is lower as a whole than the temperature distributions caused by heat from the LEDs312in the rows L1and L3. Consequently, in the temperature distribution caused by heat from the LEDs312in all the rows represented by the dashed line Tt, the increase in temperature can be suppressed particularly in the vicinity of the positions P2at which the LEDs312in the row L2are arranged.

The number of rows composed of the LEDs312and the connection plate314A or314B is not limited to three, and the circuit board311may include a larger number of rows. For example, four rows may be formed on the circuit board311. In this case, the width in the first direction y of the connection plates314B included in two middle rows is larger than the width in the first direction y of the connection plates314A included in two rows on both sides. In this case, the widths in the first direction y of the connection plates314B included in the two middle rows may be equal to each other. With this, the temperature of the LEDs312included in the two middle rows becomes uniform easily.

FIG. 23is a plan view illustrating a modified example of the circuit board311. Note that, points different from the example illustrated inFIG. 21are mainly described below, and the other points are the same as in the example ofFIG. 21.

In the example ofFIG. 23, the circuit board311includes five rows L1, L2, L3, L4, and L5as rows composed of the LEDs312and the connection plate314A,314B, or314C. InFIG. 23, the rows L1and L5are two rows on both sides, that is, two rows on edge sides, and the rows L2, L3, L4are rows between the rows L1and L5.

The connection plates314A,314B, and314C arranged in the five rows L1, L2, L3, L4, and L5are larger in accordance with the distances from the two rows L1and L5on both sides. In other words, the connection plates314B in the rows L2and L4are larger than the connection plates314A in the rows L1and L5, and the connection plate314C in the middle row L3is larger than the connection plates314B in the rows L2and L4. This arrangement can effectively suppress the accumulation of heat in the vicinity of the cathode of the LED312in the middle row L3.

In this example, widths Wy2and Wy4of the connection plates314B in the first direction y are larger than widths Wy1and Wy5of the connection plates314A in the first direction y. A width Wy3of the connection plate314C in the middle row L3in the first direction y is larger than the widths Wy2and Wy4of the connection plates314B in the first direction y. On the other hand, widths Wx2, Wx3, and Wx4of the connection plates314B and314C in the second direction x are equal to widths Wx1and Wx5of the connection plates314A in the second direction x. In other words, also in this example, the connection plates314B and314C each have a shape obtained by extending the connection plate314A in the first direction y. Further, similarly toFIG. 21, the positions of the LEDs312in one of two adjacent rows are offset in the second direction x with respect to the positions of the LEDs312in the other row by a half distance of the interval of the LEDs312.

FIG. 24is a plan view illustrating a second modified example of the circuit board311. Note that, points different from the example illustrated inFIG. 21are mainly described below, and the other points are the same as in the example ofFIG. 21.

Heat of the LED312is spread in a concentric manner from terminals (that is, the cathode and the anode). As described above, the temperature is higher in particular on the cathode side. Accordingly, in the example ofFIG. 24, the shape of the connection plate is appropriately designed so that the radius of a maximum circle T (two-dot chain line T inFIG. 24) that can be assumed on the connection plate and is centered at the terminals of the LED312may be larger than that in the case of a rectangular connection plate.

Specifically, the circuit board311ofFIG. 24includes a plurality of connection plates314A-2and314B-2arranged in the second direction x together with the plurality of LEDs312. Each of the connection plates314A-2and314B-2includes two edge portions314b-2located on both sides in the second direction x. The cathode and the anode of the LED312are connected to the edge portions314b-2. Each of the connection plates314A-2and314B-2includes protrusion portions314a-2protruding in the first direction Y in plan view to the edge portion314b-2side. Such shapes of the connection plates314A-2and314B-2can increase the radius of the maximum circle T that can be assumed on the connection plates and is centered at the terminals of the LED312. In this example, each of the connection plates314A-2and314B-2includes an edge314c-2along the second direction x. The two protrusion portions314a-2are formed on the opposite side of the edge314c-2. In this example, the protrusion portions314a-2are triangular in plan view.

Also in this example, the positions of the LEDs312in one of two adjacent rows are offset in the second direction x with respect to the positions of the LEDs312in the other row by a half distance of the interval of the LEDs312. The protrusion portion314a-2of the connection plate314A-2or314B-2in one row overlaps with the protrusion portion314a-2of the connection plate314A-2or314B-2in the other row in the second direction x. In other words, the protrusion portion314a-2of the connection plate314A-2or314B-2in one row is fitted into a recess portion formed between two protrusion portions314a-2of the connection plate314A-2or314B-2in the other row. This arrangement can suppress the enlargement of the width of the circuit board311in the first direction y.

In the example ofFIG. 24, the circuit board311has four rows L1, L2, L3, and L4as rows composed of the plurality of LEDs312and the plurality of connection plates314A-2or314B-2. The two rows L1and L4on both sides include the connection plates314A-2, and the two middle rows L2and L3include the connection plates314B-2. The connection plates314A-2and the connection plates314B-2are arranged so that the protrusion portions314a-2thereof overlap with each other in the second direction x. The connection plates314B-2in the row L2and the connection plates314B-2in the row L3are arranged so that the edges314c-2thereof are opposed to each other in the first direction y.

Also in the example ofFIG. 24, similarly to the example ofFIG. 21, the connection plates314B-2arranged in the two middle rows L2and L3each have a larger area than those of the connection plates314A-2arranged in the two rows L1and L4on both sides. Specifically, the width of the connection plate314B-2in the first direction y is larger than that of the connection plate314A-2. The width of the connection plate314B-2in the second direction x is equal to that of the connection plate314A-2. In other words, the connection plate314B-2has a shape obtained by extending the connection plate314A-2in the first direction y. Thus, a maximum width WyB and a minimum width of the connection plate314B-2in the first direction y are larger than a maximum width WyA and a minimum width of the connection plate314A-2, respectively. In this example, each of the connection plates314A-2and314B-2includes the protrusion portions314a-2on the edge portion314b-2side. Thus, the widths of the connection plates314A-2and314B-2in the first direction y are the maximum widths WyA and WyB at the two edge portions314b-2connected to the LED312. Those widths are gradually decreased in accordance with the distance from the edge portions314b-2and become the minimum at the center in the second direction x.

FIG. 25is a plan view illustrating a third modified example of the circuit board311. Note that, points different from the example illustrated inFIG. 24are mainly described below, and the other points are the same as in the example ofFIG. 24.

The circuit board311ofFIG. 25includes a connection plate314A-3and a connection plate314B-3that correspond to the above-mentioned connection plates314A-2and314B-2, respectively. Each of the connection plates314A-3and314B-3includes two edge portions314b-3each connected to the LED312. Each of the connection plates314A-3and314B-3includes protrusion portions314a-3that correspond to the above-mentioned protrusion portions314a-2on the edge portion314b-3side. Thus, also in this example, the radius of the maximum circle that can be assumed on the connection plates and is centered at the terminals of the LED312can be increased. The protrusion portion314a-3in this example is trapezoidal, and includes an edge314d-3along the second direction x and an edge314e-3extending obliquely from the edge314d-3.

Also in this example, the positions of the LEDs312in one of two adjacent rows are offset in the second direction x with respect to the positions of the LEDs312in the other row by a half distance of the interval of the LEDs312. The protrusion portion314a-3of the connection plate314A-3or314B-3in one row overlaps with the protrusion portion314a-3of the connection plate314A-3or314B-3in the other row in the second direction x. In other words, the protrusion portion314a-3is located to be fitted into a recess portion formed between two protrusion portions314a-3included in the connection plate314A-3or314B-3in an adjacent row.

In the example ofFIG. 25, the circuit board311has four rows L1, L2, L3, and L4. The two rows L1and L4on both sides include the connection plates314A-3, and the two middle rows L2and L3include the connection plates314B-3. The connection plates314A-3in the row L1and the connection plates314B-3in the row L2are arranged so that the protrusion portions314a-3thereof overlap with each other in the second direction x. Similarly, the connection plates314B-3in the row L3and the connection plates314A-3in the row L4are arranged so that the protrusion portions314a-3thereof overlap with each other in the second direction x. The connection plates314B-3in the row L2and the connection plates314B-3in the row L3are arranged so that edges314c-3thereof are opposed to each other.

Also in the example ofFIG. 25, similarly to the above-mentioned connection plate314B-2, the connection plate314B-3has a shape obtained by extending the connection plate314A-3in the first direction y. Thus, the maximum width and the minimum width of the connection plate314B-3in the first direction y are larger than the maximum width and the minimum width of the connection plate314A-3, respectively. The width of the connection plate314B-3in the second direction x is equal to that of the connection plate314A-3.

FIG. 26is a plan view illustrating a fourth modified example of the circuit board311. Note that, points different from the example illustrated inFIG. 25are mainly described below, and the other points are the same as in the example ofFIG. 25.

The circuit board311ofFIG. 26includes a plurality of connection plates314A-4and314B-4. Each of the connection plates314A-4and314B-4includes two edge portions314b-4and314f-4each connected to the LED312. The cathode of the LED312is connected to the edge portion314b-4, and the anode of the LED312is connected to the edge portion314f-4. Each of the connection plates314A-4and314B-4includes a protrusion portion314a-4that corresponds to the above-mentioned protrusion portion314a-3only on the edge portion314b-4side. Thus, in this example, the radius of the maximum circle that can be assumed on the connection plates and is centered at the cathode terminal of the LED312can be further increased. Note that, also the protrusion portion314a-4in this example is trapezoidal in plan view similarly to the above-mentioned protrusion portion314a-3.

Also in this example, the positions of the LEDs312in one of two adjacent rows are offset in the second direction x with respect to the positions of the LEDs312in the other row by a half distance of the interval of the LEDs312. The protrusion portion314a-4of the connection plate314A-4and the protrusion portion314a-4of the connection plate314B-4overlap with each other in the second direction x.

Also in the example ofFIG. 26, the circuit board311has four rows L1, L2, L3, and L4. The two rows L1and L4on both sides include the connection plates314A-4, and the two middle rows L2and L3include the connection plates314B-4. The connection plates314A-4in the row L1and the connection plates314B-4in the row L2are arranged so that the protrusion portions314a-4thereof overlap with each other in the second direction x. Similarly, the connection plates314B-4in the row L3and the connection plates314A-4in the row L4are arranged so that the protrusion portions314a-4thereof overlap with each other in the second direction x. The connection plates314B-4in the row L2and the connection plates314B-4in the row L3are arranged so that edges314c-4thereof along the second direction x are in proximity to each other.

Also in the example ofFIG. 26, similarly to the example ofFIG. 21, the connection plates314B-4arranged in the two middle rows L2and L4each have a larger area than those of the connection plates314A-4arranged in the two rows L1and L4on both sides. Specifically, the connection plate314B-4has a shape obtained by extending the connection plate314A-4in the first direction y, and the width of the connection plate314B-4in the first direction y is larger than that of the connection plate314A-4. The width of the connection plate314B-4in the second direction x is equal to that of the connection plate314A-4.

As described above, in the liquid crystal display device301, the plurality of connection plates314A,314A-2,314A-3, and314A-4arranged in the row(s) between two rows on both sides among three or more rows are larger than the plurality of connection plates314B,314C,314B-2,314B-3, and314B-4arranged in the two rows on both sides. Consequently, heat of the LEDs312arranged in the row (s) between the two rows on both sides can be efficiently released. In particular, the connection plates314A,314A-2,314A-3, and314A-4are larger than the connection plates314B,314C,314B-2,314B-3, and314B-4in width in the first direction y. Consequently, there is no need to decrease the arrangement density of the LEDs312arranged in the middle row (s) as compared to the arrangement density of the LEDs312arranged in the two rows on both sides. As a result, the brightness of the backlight unit310can be enhanced easily.

Note that, in the above description, the first direction y is the vertical direction of the backlight unit310, and the second direction x is the horizontal direction of the backlight unit310. Alternatively, however, the first direction may be defined as the horizontal direction of the backlight unit310, and the second direction may be defined as the vertical direction of the backlight unit310. In this case, the circuit board311is a board elongated in the vertical direction, and is arranged at a horizontal center portion of the backlight unit310.

Further, in the above description, the plurality of connection plates314A to314B-4have equal widths in the second direction x. Alternatively, however, the connection plates314B,314C,314B-2,314B-3, and314B-4that form one or a plurality of middle rows may be larger in width in the second direction x than the connection plates314A,314A-2,314A-3, and314A-4that form two rows on both sides. In other words, the arrangement density of the LEDs321may be decreased in the middle row (s) than in the two rows on both sides.

Further, in the liquid crystal display device301, the regions A and B on both sides of the circuit board311are larger than the circuit board311in width in the first direction y. Alternatively, however, the connection plates described above may be applied to a liquid crystal display device in which the circuit board311is located at a center portion in the first direction y but the regions A and B are smaller than the circuit board311in width in the first direction y.

By incorporating the liquid crystal display device301, a television receiver configured to receive television broadcast radio waves to display a video and output sound can be constructed. An exemplary television receiver is described below.

FIG. 27is an exploded perspective view of a television receiver according to one embodiment of the present application.FIG. 28is a front view illustrating members arranged behind the reflection sheet313of the television receiver illustrated inFIG. 27.FIG. 29is a side view of the television receiver illustrated inFIG. 27.FIG. 30is a schematic view illustrating a vertical cross-section of the television receiver illustrated inFIG. 27.

The television receiver includes the liquid crystal display panel320having a landscape-oriented screen. The aspect ratio of the screen of the television receiver (ratio of horizontal dimension and vertical dimension) is 16:9. The front side of the liquid crystal display panel320(image display side) is supported by a front frame341, and the rear side thereof is supported by a mold frame342. The television receiver includes the backlight unit310overlapping with the liquid crystal display panel320.

The liquid crystal display panel320, the front frame341, the mold frame342, and the backlight unit310are housed in a cabinet including a front cabinet333and a back cabinet331. The front cabinet333is formed of a resin, and the back cabinet331is formed of coated iron. The cabinets331and333are supported by a stand353including a mount355and a leg354. As illustrated inFIG. 29, switches357are arranged on side surfaces of the cabinets331and333.

A cover351is mounted behind the lower portion of the back cabinet331. Speakers356and a circuit board352are arranged inside the cover351. The circuit board352includes a tuning circuit (tuner) for selecting a particular frequency radio wave from among various frequency radio waves.

The backlight unit310includes the reflection sheet313as described above. The reflection sheet313is arranged so that the recessed surface thereof faces the liquid crystal display panel320. Portions of the reflection sheet313excluding the bottom portion313eare spaced apart from the back cabinet331toward the front (seeFIG. 19andFIG. 30). The upper portion313aand the lower portion313bare located so as to sandwich the plurality of LEDs312. The circuit board352is arranged in a lower space between the reflection sheet313and the back cabinet331(seeFIG. 30).

The circuit board311is located on the opposite side of the reflective sheet313with respect to the liquid crystal display panel320, and overlaps with the reflective sheet313. The width of the circuit board311in the vertical direction is half or less of the length of the liquid crystal display panel320in the vertical direction. As described above, the plurality of LEDs312(seeFIG. 19) are arranged behind substantially the center of the liquid crystal display panel320, and are mounted on the circuit board311. The LEDs312are arranged in three rows in the horizontal direction in a staggered manner.

The circuit board311is fixed onto the back cabinet331. For example, the circuit board311is fixed directly onto the back cabinet331. For example, the circuit board311is fixed onto the back cabinet331by screws. Further, as in the example described herein, the circuit board311may be fixed onto the back cabinet331via the radiator plate332. For example, the circuit board311is fixed by screws onto the radiator plate332made of metal such as aluminum, and the radiator plate332may be fixed onto the back cabinet331.

The circuit board311and the reflective sheet313are in proximity to the back cabinet331. Consequently, thinning of the television receiver can be attained. Specifically, in the related-art backlight structure, the circuit board for mounting LEDs thereon is fixed onto a back frame (not shown) of the liquid crystal display device made of iron or aluminum, and a board for mounting thereon a power supply for driving the LEDs and a timing controller for controlling gate signal lines and drain signal lines of the liquid crystal display panel is arranged outside the back frame, followed by arranging the back cabinet further outside. Thus, the distance between the optical sheets and the LEDs in the backlight unit as well as the distance between the back frame and the back cabinet is necessary, with the result that the thickness of the liquid crystal display device is undesirably large. In this embodiment, on the other hand, the circuit board311and the radiator plate332are held in contact with each other, and the radiator plate332and the back cabinet331are fixed to each other by screws. Consequently, there are no other necessary distances than a distance Zd (seeFIG. 30) between the optical sheets321and the circuit board311, and hence the television receiver is thinned.

Thinning of the television receiver is attained also by the arrangement of the circuit board352including a power supply circuit, a video circuit, a tuning circuit (tuner), and a timing circuit for the liquid crystal display panel320. Specifically, the upper portion313aand the lower portion313bof the reflection sheet313are curved in the direction away from the back cabinet331, and hence a wide space can be obtained between the reflection sheet313and the back cabinet331. Further, the circuit board352including the power supply circuit, the video circuit, the tuning circuit (tuner), and the timing circuit for the liquid crystal display panel320is housed in the lower portion of the television receiver in a compact manner. This eliminates the need of providing a space for housing the power supply circuit and the like between the circuit board311and the back cabinet331.

As the circuit board311, a printed wiring board can be used. As described above, the backlight unit310has the regions A and B devoid of the light sources. The vertical length of each of the regions A and B is larger than the vertical length of the circuit board311. Thus, as illustrated inFIG. 28, a vertical dimension YL of the circuit board311is ⅓ or less of a vertical dimension YH of the liquid crystal display panel320.

As described above, the lens315is arranged on each LED312, and the pair of the LED312and the lens315constructs one point light source S (seeFIG. 19). The point light source S is mounted on the circuit board311, and protrudes to the front side of the bottom portion313eof the reflection sheet313(seeFIG. 20) through a hole formed in the bottom portion313e. The plurality of point light sources S are arranged in at least three rows in the horizontal direction of the screen. The overall vertical width of the plurality of point light sources S is half or less of the vertical length of the liquid crystal display panel320.

The point light source S emits light not only in the direction perpendicular to the circuit board311but also in other directions. Light intensity of the light source S is higher in other directions than in the direction perpendicular to the circuit board311. The lens315expands the light emitted from the LED312more in a viewing direction than in the front direction.FIG. 31shows such a light intensity distribution (directivity characteristics) of the point light source S.FIG. 32is a graph showing a result of measuring the intensity of light emitted from the lens315, specifically, the illuminance of the point light source S. Note that, e represents an angle formed by the direction perpendicular to the circuit board311and the light output direction.

One feature of the television receiver described herein resides in that the entire screen is bright and the uniformity of brightness of the entire screen is high even though the vertical dimension YL of the circuit board311is reduced to be ⅓ or less of the vertical dimension YH of the liquid crystal display panel320.

A related-art television receiver includes a plurality of circuit boards each having a plurality of light emitting diodes mounted thereon, and the overall size of the plurality of circuit boards conforms to the size of the liquid crystal display panel. The circuit boards and the LEDs mounted on the circuit boards are laid out so that brightness may not vary even in a region between the circuit boards. Specifically, in order to prevent the positions of the individual LEDs from being optically recognized, a large number of LEDs are used and the interval between the LEDs is set to be small.

In the example described herein, the interval between two lenses315located farthest away from each other in the vertical direction is ⅓ or less of the dimension YH of the liquid crystal display panel320. To reduce cost, the LED312and the lens315are set to have the dimensions not protruding outside of the circuit board311.

In this example, the dimension YL of the circuit board311, or the distance between an upper edge of the lens315in the top row and a lower edge of the lens315in the bottom row is ⅓ or less of the dimension YH of the liquid crystal display panel320. In this way, the number of LEDs312is reduced more than hitherto, and the cost may be significantly reduced. Because the lens315and the reflection sheet313are used, the liquid crystal display panel320that is bright and has a natural brightness distribution can be obtained even when the number of LEDs312is reduced.

In this embodiment, the overall width of the upper portion313aand the lower portion313bof the reflection sheet313is set to have a length obtained by subtracting the dimension YL of the circuit board311from the dimension YH of the liquid crystal display panel320. When the sum of the width of the upper portion313aand the width of the lower portion313bis ½ or more of the dimension YH, the brightness distribution of the screen becomes smoother, and the number of LEDs312can be significantly reduced to reduce the cost. In other words, the cost can be reduced by setting the reflective region including the upper portion313aand the lower portion313bto be larger than the region in which the point light sources S are arranged.

Light emitted from the LED312is expanded by the lens315. The LED315has such light distribution characteristics that light intensity is higher in the oblique direction than in the direct front direction. With the lens315mounted on each of the plurality of LEDs312, in a space from the circuit board311to the optical sheets321(seeFIG. 19), the intensity of radiation light directed in the vertical direction is larger than the intensity of radiation light directed in the direct front direction. Part of light emitted from the lens315to the front passes through the optical sheets321to be displayed as an image through the liquid crystal display panel320. The rest of the light emitted to the front is reflected on the optical sheets321and the reflection sheet313to be emitted also in the direction oblique to the front. Part of light emitted obliquely in the vertical direction through the lens315passes through the outer peripheral portion of the liquid crystal display panel320through the optical sheets321. Another part of the light emitted obliquely is reflected on the reflection sheet313to be directed to the optical sheets321.

Brightness performance of the television receiver described herein is as follows. When the brightness measured on the front surface is 100%, the brightness at the outer peripheral portion is about 30%. The ratio of the central brightness of the liquid crystal display panel320to the average brightness is 1.65. However, the upper portion313aand the lower portion313bof the reflection sheet313are gently curved, and hence the brightness gently varies from the circuit board311in the vertical direction. As described above, there is no point at which the brightness abruptly varies, and hence a high-quality image can be provided. The fact that the smooth brightness distribution can be obtained even when the ratio of the central brightness to the average brightness is 1.65 or more means that the number of LEDs312can be reduced to decrease the width of the circuit board311. Note that, in the structure in which light radiation to the front surface of the liquid crystal display panel320is blocked, the center of the liquid crystal display panel320is dark. To address this, the light emission characteristics of the individual point light source S including the LED312and the lens315are set to have a predetermined output also in the direct front direction.

The back cabinet331serves as the outermost surface of the television receiver. The circuit board311is fixed onto the radiator plate332by screws, and heat of the LEDs312is released from the connection plates314A and314B of the circuit board311(seeFIG. 21) and the radiator plate332. Note that, when the brightness of the television receiver is low, that is, when the amount of heat released from the LEDs312is small, the circuit board311may be fixed directly onto the back cabinet331without using the radiator plate332. In this case, heat dissipation of the LED312is performed only by the circuit board311, but even by the heat dissipation effects of the circuit board311itself and the connection plates314A and314B arranged on the circuit board311, the temperature of the connection portions of the LEDs312can be suppressed.

Next, a process of manufacturing the television receiver is described. A bracket334for wall hanging is mounted on an inner side of the back cabinet331formed by coating a member made of iron. The bracket334reinforces the strength of the back cabinet331. The bracket334has a screw hole formed therein. The screw hole is used to hook a screw fixed on the wall. After the bracket334is mounted, the radiator plate332is fixed on the inner side of the back cabinet331.

Next, the circuit board311having the LEDs312mounted thereon is mounted on the radiator plate332. The lens315is capped on the LED312, and is fixed by an adhesive, for example. When heat resistance of the connection portion of the LED312has a margin, the circuit board311may be mounted directly on the back cabinet331. In this case, the circuit board311is coated in advance with a white resist so that the surface of the circuit board311may easily reflect light emitted from the LED312. Next, the reflection sheet313is mounted on the circuit board311. The optical sheets321such as a diffusion sheet and a prism sheet having a thickness of 1.5 mm to 3 mm are arranged in front of the reflection sheet313.

Next, the optical sheets321are fixed by the mold frame342, which is made of a resin material and divided into four pieces. The liquid crystal display panel320is arranged in front of the optical sheets321. The front frame341formed of iron is arranged on the front side of the liquid crystal display panel320, which is used to prevent a magnetic wave from the driver IC and fix the liquid crystal display panel320.

To finally complete the television receiver, the front cabinet333made of a resin material is mounted on the surface of the front frame341, and a power supply circuit for supplying power to a control circuit, a timing control circuit, and a video circuit for the LEDs312, an external connection terminal, and the like are arranged under the cabinets331and333, followed by mounting the protective cover351made of a resin.

Note that, the embodiments described above are specific examples for describing the present invention, and the present invention is not intended to be limited to the embodiments. For example, in the embodiments, the lens is provided on the front surface of the light emitting diode, but the lens is not always necessary if light emitted from the light emitting diode is sufficiently diffused. In the embodiments, the liquid crystal display device is structured to have only a single light emitting diode substrate at the lateral center of the liquid crystal display device, but may be structured to have two or more light emitting diode substrates that are arranged side by side in the lateral direction thereof. Further, the number and arrangement of the light emitting diodes and the number, shape, and arrangement of other members are not limited to the ones described in the embodiments, and an appropriate number, shape, and arrangement are intended to be optimized as necessary.