Patent Publication Number: US-2012044134-A1

Title: Liquid crystal display apparatus

Description:
TECHNICAL FIELD 
     The present invention relates to a liquid crystal display apparatus, and more particularly, to a liquid crystal display apparatus provided with a heat dissipation mechanism that dissipates heat generated by a heat generating part such as a semiconductor device and the like. 
     The present application claims priority to Japanese Patent Application No. 2009-108753 filed on Apr. 28, 2009. The entire contents of which are hereby incorporated by reference. 
     BACKGROUND ART 
     With the increase of the size of a liquid crystal panel and the like in recent years, the amount of heat generated by a heat generating part (typically, a power device such as a MOSFET and the like) such as a heat generating semiconductor device and the like that is used in a liquid crystal display apparatus is also on the rise. On the other hand, in order to realize a space saving for the depth of the liquid crystal display apparatus, reduction of the thickness (space saving) is being pursued. In such a thin type liquid crystal display apparatus, it is necessary to efficiently dissipate heat from the heat generating part. 
     Conventionally, as a measure to dissipate heat generated by a heat generating part such as a power device and the like, a heat dissipation plate  130  is attached to a heat generating part  120 , as shown in  FIG. 7 . However, since the heat dissipation plate  130  is only in contact with the heat generating part  120 , there is a problem of not achieving enough heat dissipation effect. 
     In Patent Document 1, a heat dissipation apparatus for heat generating parts that insures a heat dissipation area of the heat dissipation plate by making the cross section of the heat dissipation plate L shaped is disclosed as a technique in the art. Also, in Patent Document 2, a chassis that provides heat dissipation as a component of a plasma display panel (PDP) is disclosed. 
     RELATED ART DOCUMENTS 
     Patent Documents 
     Patent Document 1: Japanese Patent Application Laid-Open Publication No. 2001-203306 
     Patent Document 2: Japanese Patent Application Laid-Open Publication No. H11-233968 
     SUMMARY OF THE INVENTION 
     Problems to be Solved by the Invention 
     If a technique that increases heat dissipation effect by more efficiently utilizing the heat dissipation area of a heat dissipation plate and more efficiently dissipates heat generated by a heat generating part can be provided, this technique is useful. Also, it is preferable that a limited space be efficiently utilized by adopting a simple structure in order to increase the heat dissipation effect and that the structure can realize a liquid crystal display apparatus that is light and thin. 
     In view of the above, the present invention seeks to address the problems of the liquid crystal display apparatus provided with the heat generating part described above. An object of the present invention is to provide a liquid crystal display apparatus including a heat dissipation mechanism that can efficiently dissipate heat generated by a heat generating part generating a large amount of heat. 
     Means for Solving the Problems 
     In order to realize the object, a liquid crystal display apparatus provided by the present invention includes a liquid crystal panel that displays images, a backlight that irradiates light to the liquid crystal panel, a backlight chassis that supports the backlight, and a wiring substrate disposed on a rear side of the backlight chassis, wherein at least one heat generating part is electrically connected to the wiring substrate, and the heat generating part is mounted on to a heat dissipation plate that dissipates heat generated by the heat generating part. Here, the heat dissipation plate is configured so that a space between a region where the heat generating part is mounted on the heat dissipation plate and the wiring substrate is spatially separated and an air passage is formed therein, and at least a portion of the heat dissipation plate is attached to the backlight chassis so as to conduct the heat from the heat generating part to the backlight chassis through the heat dissipation plate. 
     In such a configuration of the liquid crystal display apparatus of the present invention, the air passage (that is, a space through which air can flow) is formed between the heat dissipation plate and the wiring substrate and the portion of the heat dissipation plate is attached to the backlight chassis. 
     Accordingly, because of this simple structure of forming the air passage between the heat dissipation plate and the wiring substrate, the surface area of the heat dissipation plate that can come in contact with the air can be increased in the liquid crystal display apparatus of the present invention. In addition, the heat generated by the heat generating part can be effectively dissipated in the air by the air going in and out of the air passage (the space portion). Further, because the portion of the heat dissipation plate is attached to the backlight chassis (typically, a metallic backlight chassis), the heat generated by the heat generating part can be dissipated through the heat dissipation plate. Furthermore, because heat is dissipated in the air from the backlight chassis also in a similar manner to the heat dissipation plate, the heat generated by the heat generating part can be dissipated even more efficiently and damages to the part itself due to a rise in temperature of the heat generating part can be prevented. 
     In a preferred embodiment of the liquid crystal display apparatus disclosed herein, a portion of the heat dissipation plate penetrates through the wiring substrate and is connected to a region of the backlight chassis directly underneath the wiring substrate. 
     In such a configuration of the liquid crystal display apparatus, the portion of the heat dissipation plate does not need to be attached to the area of the backlight chassis that is beyond the wiring substrate. That portion can be attached to the area of the backlight chassis with the are of the wiring substrate. Thus, the heat generated by the heat generating part can be dissipated efficiently utilizing a limited space. 
     In a preferred embodiment of the liquid crystal display apparatus disclosed herein, the heat dissipation plate is provided without physically touching the wiring substrate. 
     In such a configuration of the liquid crystal display apparatus, a heat dissipation plate does not have legs, and the heat dissipation plate does not need to be attached to the wiring substrate. Also, since the heat dissipation plate is completely separated from the wiring substrate, the surface area that comes in contact with the air is large and the heat generated by the heat generating part can be dissipated effectively in the air. Further, since the heat dissipation plate is attached to the backlight chassis, the heat generated by the heat generating part is conducted to the backlight chassis through the heat dissipation plate. The heat is dissipated also from the backlight chassis into the air in a similar manner to the heat dissipation plate. Thus, the heat generated from the heat generating part can be even more effectively dissipated. Also, the heat generated from the heat generating part is prevented from being conducted to the wiring substrate, and damages to the wiring substrate (and to a variety of electronic parts mounted on the wiring substrate) by the heat can be prevented before they occur. 
     In a preferred embodiment of the liquid crystal display apparatus disclosed herein, a cabinet enclosing the backlight chassis is disposed on the rear side of the backlight chassis, and the heat dissipation plate is attached to an inner surface of the cabinet facing the substrate. Also, it is configured so that a space between the region where the heat generating part is mounted on the heat dissipation plate and the cabinet is spatially separated and an air passage is formed therein. 
     In such a configuration of the liquid crystal display apparatus, a limited space can be effectively utilized by attaching legs of the heat dissipation plate to the cabinet even when there is no space for attaching the legs to the wiring substrate. In addition, stability of the heat dissipation plate can be maintained. Also, heat generated by the heat generating part is conducted to the cabinet through the heat dissipation plate and the heat is dissipated in the air from the cabinet. Further, since an air passage is also formed between the heat dissipation plate and the cabinet, the surface area of the heat dissipation plate that can come in contact with the air increases. Thus, the heat generated by the heat generating part can be dissipated in the air more effectively by the air going in and out of the air passage. 
     In a preferred embodiment of the liquid crystal display apparatus disclosed herein, the heat generating part mounted on the heat dissipation plate is a power device (for example, FET such as IGBT or MOSFET), and the wiring substrate to which the device is electrically connected is an inverter substrate. 
     Particularly because the inverter substrate for lighting the backlight takes up the majority of the power consumption, heat is likely to be generated and temperature rise of the power device (typically, a MOSFET) for driving a transformer is comparatively high. In such a configuration of the liquid crystal display apparatus, the heat generated by the power device such as a high heat generating MOSFET (Metal-Oxide-Semiconductor FET) and the like can be dissipated effectively. Thus, damages to the power device (MOSFET and the like) can be prevented. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic cross sectional view showing a configuration of a liquid crystal display apparatus according to an embodiment of the present invention. 
         FIG. 2  is a schematic exploded perspective view showing a configuration of a liquid crystal display apparatus according to an embodiment of the present invention. 
         FIG. 3  is a schematic cross sectional view along the line III-III in  FIG. 1  showing a configuration of a heat dissipation mechanism according to an embodiment of the present invention. 
         FIG. 4  is a schematic cross sectional view showing a configuration of a heat dissipation mechanism according to another embodiment of the present invention. 
         FIG. 5  is a schematic cross sectional view showing a configuration of a heat dissipation mechanism according to another embodiment. 
         FIG. 6  is a schematic cross sectional view showing a configuration of a heat dissipation mechanism according to another embodiment. 
         FIG. 7  is a schematic perspective view showing a heat dissipation mechanism using a conventional flat plate heat dissipation plate. 
     
    
    
     DETAILED DESCRIPTION OF EMBODIMENTS 
     With reference to the drawings, preferred embodiments of the present invention are described below. Here, matters necessary for embodying the present invention (for example, configuration of and method of constructing the liquid crystal panel, electric circuits related to drive method of light sources provided in the liquid crystal display apparatus and the like) that are outside of the matters particularly mentioned in the present specification can be taken as design matters to one of ordinary skill in the art based on conventional techniques. The present invention can be embodied based on the contents disclosed in the present specification and common techniques and knowledge in the art. 
     With reference to  FIGS. 1 to 3 , a liquid crystal display apparatus  1  provided with a heat dissipation mechanism  50  according to a preferred embodiment (Embodiment 1) of the present invention is described below.  FIG. 1  is a schematic cross sectional view showing a configuration of the liquid crystal display apparatus  1  according to an embodiment of the present invention.  FIG. 2  is a schematic exploded perspective view showing a configuration of a liquid crystal display apparatus body  5  according to an embodiment of the present invention.  FIG. 3  is a schematic cross sectional view taken along the line III-III of  FIG. 1  showing a configuration of the heat dissipation mechanism  50 . 
     In the following drawings, the same reference characters are assigned to the members and parts that have the same functionalities, and redundant descriptions may be omitted or simplified. Also, the dimensional relationships (length, width, thickness and the like) in each of the drawings do not necessarily reflect the actual dimensional relationships accurately. Also, in the following description, the side facing the viewer (that is, the side of the liquid crystal panel  10 ) in the liquid crystal display apparatus  1  is called “front” and “front side”, and the side not facing the viewer (that is, the side of the backlight apparatus  60 ) in the liquid crystal display apparatus  1  is called “back” or “back side”. 
     With reference to  FIGS. 1 and 2 , the configuration of the liquid crystal display apparatus  1  is described. As shown in  FIG. 1 , the liquid crystal display apparatus  1  is constituted by the liquid crystal display apparatus body  5  including the liquid crystal panel  10  and a cabinet  100  enclosing the display apparatus body  5 . The display apparatus body  5  is a term broadly encompassing devices, parts, members, and the like as a whole that are enclosed in the cabinet  100 . The display apparatus body  5  mainly includes the liquid crystal panel  10  and the backlight apparatus  60  that is the external light source disposed on the back side (bottom side in  FIG. 1 ) of the liquid crystal panel  10 . The liquid crystal panel  10  and the backlight apparatus  60  are integrally supported by being assembled with a bezel  30  or the like. 
     As shown in  FIG. 1  and  FIG. 2 , the liquid crystal panel  10  generally has a rectangular shape as a whole. In its central area, the liquid crystal panel  10  has a display area  15  where pixels are formed to display images. Also, this liquid crystal panel  10  has a sandwich structure constituted by a pair of translucent glass substrates  11  and  12  that are facing each other and a liquid crystal layer  13  encapsulated therebetween. Cutout portions from a large base material called mother glass are used in the manufacturing steps for the substrates  11  and  12 , respectively. Of the pair of substrates  11  and  12 , the one on the front side is a color filter substrate (CF substrate)  12  and the one on the back side is an array substrate  11 . Here, a sealing member  17  is provided on the periphery (periphery of the liquid crystal panel  10 ) of the substrates  11  and  12  so as to surround the perimeter of the display area  15  and seals the liquid crystal layer  13 . The liquid crystal layer  13  is constituted by a liquid crystal material including liquid crystal molecules. In such a liquid crystal material, the orientation of liquid crystal molecules is manipulated by the electric field that is applied between the substrates  11  and  12 , and therefore, the optical characteristics change. In the liquid crystal layer  13 , spacers (not shown) for securing the thickness (gap) of the layer  13  are disposed at a plurality of locations typically. Also, alignment films (not shown) that determine the orientation of liquid crystal molecules are formed on respective surfaces of the sides (inner sides) of both substrates  11  and  12  that are facing each other. On surfaces of the sides (outer sides) that are not facing each other, respective polarizing plates  18  and  19  are attached. 
     In the liquid crystal panel  10  disclosed herein, pixels for displaying images are arranged on the front side (the side facing the liquid crystal layer  13 ) of the array substrate  11 , and a plurality of source wires and gate wires (not shown) for driving the respective pixels are formed to exhibit lattice-like patterns. A thin film transistor (TFT), which is a switching device, and a (sub) pixel electrode are provided on each lattice region surrounded by such wires. The pixel electrode is typically made of ITO (Indium Tin Oxide), which is a transparent conductive material. A voltage corresponding to images is applied to these pixel electrodes through the source wire and through the thin film transistor at a prescribed timing. 
     On the other hand, on the CF substrate  12 , one of R (red), G (green), or B (blue) color filters is facing one of the pixel electrodes on the array substrate  11 . A black matrix that partitions the respective color filters and a common electrode (transparent electrode) that is formed uniformly on surfaces of the color filters and the black matrix are provided on the CF substrate  12 . 
     Also, as shown in  FIG. 2 , the source wires and the gate wires are connected to external driver circuits (driver ICs)  25  provided typically on the periphery of the liquid crystal panel  10 . The external driver circuits  25  are capable of supplying image signals and the like. 
     Here, the configuration of the pixels and the wiring itself of the electrodes may be similar to the case of manufacturing a conventional liquid crystal panel, and they do not characterize the present invention. Thus, any further detailed descriptions are omitted. 
     As shown in  FIG. 1  and  FIG. 2 , the backlight apparatus  60  as a backlight in the present embodiment is constituted by a plurality of linear light sources (for example, fluorescent tubes, typically cold cathode tubes)  62  and a metallic (for example, highly thermally conductive aluminum plate) backlight chassis  70  that supports the light sources  62 . The backlight chassis  70  has a box like shape with an opening facing the front side. Inside the chassis  70 , the light sources  62  are arranged in parallel. Between the chassis  70  and the light sources  62 , a reflective member  65  that efficiently reflects the light from the light sources  62  toward the viewer side is disposed. 
     Also, a plurality of sheet like optical members  67  are laminated and disposed in the opening of the chassis  70  so as to cover the opening. The optical members  67  are constituted by a diffusion plate, a diffusion sheet, a lens sheet, and a luminance increase sheet in this order from the side of the backlight apparatus  60 , for example. However, they are not limited to this combination and order. Further, a substantially rim shaped frame  68  is provided to the chassis  70  in order to support the optical members  67  by sandwiching them with the chassis  70 . 
     The liquid crystal display apparatus body  5  including the liquid crystal panel  10 , the backlight apparatus  60 , and the like as configured above is enclosed in a thin rim-like shaped (frame shaped) cabinet  100  that is made of a nonflammable, non-halogen series resin material, for example. 
     Next, with reference to  FIG. 1  and  FIG. 3 , the configuration of the heat dissipation mechanism  50  of the liquid crystal display apparatus  1  in the present embodiment is described. The heat dissipation mechanism  50  is generally constituted by the backlight chassis  70 , an inverter substrate (wiring substrate)  75 , a MOSFET (heat generating part)  90  that is a power device electrically connected to the wiring substrate  75 , and a heat dissipation plate  80 . 
     The inverter substrate (wiring substrate)  75  for mounting an inverter circuit and an inverter transformer (not shown), which is a step-up circuit for supplying power to each of the light sources  62 , are provided on the back side of the backlight chassis  70 . The inverter transformer includes an inverter (not shown), which converts a direct current voltage to a high frequency voltage, and a transformer (not shown), which steps up the high frequency voltage to a high voltage. Further, the inverter includes the MOSFET  90  that constitutes the switching device (power device). The MOSFET  90  is the electronic part corresponding to the heat generating part  90  in the present embodiment. 
     As show in  FIG. 3 , protrusions  72  for attaching the inverter substrate (wiring substrate)  75  are formed integrally with the backlight chassis  70  by press work on the rear side of the backlight chassis  70  (the surface on the back side of the backlight chassis  70 ). Also, the inverter substrate  75  is fixed to the backlight chassis  70  by mechanically fixing the inverter substrate  75  to the protrusion  72  using screws or the like. 
     On the inverter substrate  75 , the MOSFET  90  that is the heat generating part of the present embodiment is electrically connected to the inverter substrate  75  by fixing a lead wire  95  of the MOSFET  90  on the back side of the substrate  75  using soldering. Here, the lead wire  95  penetrates through the substrate  75 . However, fixing the lead wire  95  is not limited to penetrating through the inverter substrate  75 . The lead wire  95  may also be fixed on the front side of the substrate  75  using soldering. 
     Further, the MOSFET  90  is mounted on the heat dissipation plate  80  that dissipates the heat generated by the MOSFET  90 . The heat dissipation plate is formed using a material having a good heat conductivity, such as aluminum, copper, or iron. The heat dissipation plate is formed, for example, by extrusion molding, metallic molding or the like so that the cross sectional shape is a step-like shape. Here, the heat dissipation plate  80  of the present embodiment differs from the configuration in which the heat dissipation plate  130  on which a heat generating part  120  is mounted is attached to the wiring substrate  110  so that their respective surfaces are in close contact with each other as in a conventional technique shown in  FIG. 7 . Legs  85  of the heat dissipation plate  80  are attached to the inverter substrate  75  so as to form an air passage  87  by spatially separating the space between the region where the MOSFET  90  on the heat dissipation plate  80  is mounted and the inverter substrate  75 . This way, almost the entire back surface of the heat dissipation plate that was in close contact with the wiring substrate in the conventional technique is in contact with the air. Thus, the heat dissipation area of the heat dissipation plate increases and even more effective heat dissipation can be realized. 
     Further, a portion of the heat dissipation plate  80  is attached to the backlight chassis  70  by a screw  88  or the like. This way, the heat generated by the MOSFET  90  can be conducted to the backlight chassis  70  through the heat dissipation plate  80  and heat dissipation becomes possible also through the backlight chassis  70 . 
     Here, the air around the MOSFET (heat generating part)  90  is warmed by the heat generated by the MOSFET  90  and an updraft is generated by the chimney effect, as shown in  FIG. 1 . This way, the air flows in from an air intake  102  formed in the cabinet  100 , and the air is discharged through an air exhaust  104 . Thus, by forming the air passage  87  in the same direction as the updraft when the heat dissipation plate  80  is fixed to the backlight chassis  70 , even more efficient heat dissipation effect can be realized. Accordingly, the heat dissipation plate  80  is preferably attached to the backlight chassis  70  in the position that is parallel to the direction of the updraft. 
     Next, with reference to  FIG. 4 , Embodiment 2 is described.  FIG. 4  is a schematic cross sectional view showing a configuration of a heat dissipation mechanism  50 A of Embodiment 2 and corresponds to  FIG. 3  showing the heat dissipation mechanism  50  of Embodiment 1. 
     As shown in  FIG. 4 , the heat dissipation mechanism  50 A of Embodiment 2 differs from the heat dissipation mechanism  50  of Embodiment 1 in the attachment configuration of the heat dissipation plate. That is, in the present embodiment, a heat dissipation plate  80 A penetrates through an inverter substrate  75 A and is attached to a region of the backlight chassis  70  that is directly underneath the substrate  75 A by a screw  88  or the like. The space between the region where the MOSFET  90  is mounted on the heat dissipation plate  80 A and the inverter substrate  75  is spatially separated and an air passage  87  is formed therein. In such an attachment configuration of the heat dissipation plate  80 A, the heat generated by the MOSFET  90  can be effectively dissipated. Further, since the portion where the heat dissipation plate  80 A is attached to the backlight chassis  70  is within the area of the inverter substrate  75 A in the width direction, it is not necessary to newly secure a space for attaching the heat dissipation plate  80 A to the backlight chassis  70 . Thus, an efficient usage of the limited space is possible. 
     Next, with reference to  FIG. 5 , Embodiment 3 is described.  FIG. 5  is a schematic cross sectional view showing a configuration of a heat dissipation mechanism  50 B of Embodiment 3 and corresponds to  FIG. 3  showing the heat dissipation mechanism  50  of Embodiment 1. 
     As shown in  FIG. 5 , the heat dissipation mechanism  50 B in Embodiment 3 differs from the heat dissipation mechanisms  50  and  50 A of Embodiments 1 and 2 in that a heat dissipation plate  80 B is provided so as not to physically come in contact with the inverter substrate  75 . The space between the region where the MOSFET  90  is mounted on the heat dissipation plate  80 B and the inverter substrate  75  is spatially separated and the air passage  87  is formed therein. In this case, the heat dissipation plate  80 B having enough strength needs to be formed so that the end portion does not hang down by its own weight. In such an attachment configuration of the heat dissipation plate  80 B, the heat generated by the MOSFET  90  can be effectively dissipated. Further, because the heat dissipation plate  80 B does not require legs for mounting to the inverter substrate  75 , the space on the front surface of the substrate  75  can be effectively utilized. Furthermore, since the heat dissipation plate  80 B is only attached to the backlight chassis  70 , attachment becomes easy. 
     Next, with reference to  FIG. 6 , Embodiment  4  is described.  FIG. 6  is a schematic cross sectional view showing a configuration of a heat dissipation mechanism  50 C of Embodiment 4 and corresponds to  FIG. 3  showing the heat dissipation mechanism  50  of Embodiment 1. 
     As shown in  FIG. 6 , the heat dissipation mechanism  50 C of Embodiment 4 differs from the above described various embodiments in that a portion of the heat dissipation plate  80 C is attached to the backlight chassis  70  and other portions of the heat dissipation plate  80 C are attached to an internal surface (surface on the front side of the cabinet  100 ) of the cabinet  100 . That is, legs  85 C of the heat dissipation plate  80 C are attached to the internal surface of the cabinet  100  so that the space between the region where the MOSFET  90  is mounted on the heat dissipation plate  80 C and the cabinet  100  is spatially separated and an air passage  87 C is formed therein. Also, the space between the region where the MOSFET  90  is mounted on the heat dissipation plate  80 C and the inverter substrate  75  is spatially separated and the air passage  87  is formed therein. In such an attachment configuration of the heat dissipation plate  80 C, the heat generated by the MOSFET  90  can be effectively dissipated. Further, the heat generated by the MOSFET  90  is conducted to the cabinet  100  through the legs  85  of the heat dissipation plate  80 C. Thus, the heat can be dissipated also from the cabinet  100 . 
     Here, the heat dissipation plate  80 C may penetrate through the inverter substrate  75  and be attached to the backlight chassis  70  directly underneath the substrate  75  as described above. 
     Preferred embodiments of the present invention have been described as above. However, these descriptions are not limiting the scope of the present invention. Of course, there can be other variations, modifications and alternatives. 
     For example, the present invention can be applied to a power supply substrate and a main substrate attached to the rear side of the backlight chassis  70  as well. Also, fins can be formed on the heat dissipation plate in order to improve the heat dissipation effect. 
     INDUSTRIAL APPLICABILITY 
     According to the present invention, a liquid crystal display apparatus in which an air passage is formed between a heat dissipation plate and a wiring substrate and a portion of the heat dissipation plate is attached to a backlight chassis is provided. The liquid crystal display apparatus can dissipate heat generated by a heat generating part, which generates a large amount of heat, effectively in the air, because the surface area of the heat dissipation plate that can come in contact with the air is large. Also, the heat can be conducted to the backlight chassis through the heat dissipation plate. Therefore, damages to the heat generating part due to the rise in temperature of the part can be prevented before they occur. 
     DESCRIPTION OF REFERENCE CHARACTERS 
       1  liquid crystal display apparatus 
       5  liquid crystal display apparatus body 
       10  liquid crystal panel 
       11 ,  12  glass substrates 
       13  liquid crystal layer 
       15  display area 
       17  sealing member 
       18 ,  19  polarizing plates 
       25  external driver circuit 
       30  bezel 
       50 ,  50 A,  50 B,  50 C heat dissipation mechanisms 
       60  backlight apparatus 
       62  light source 
       65  reflective member 
       67  optical member 
       68  frame 
       70  backlight chassis 
       72  protrusion 
       75 ,  75 A inverter substrates (wiring substrates) 
       80 ,  80 A,  80 B,  80 C heat dissipation plates 
       85 ,  85 C legs 
       87 ,  87 C air passages 
       88  screw 
       90  MOSFET (heat generating part) 
       95  lead wire 
       100  cabinet 
       102  air intake 
       104  air exhaust 
       110  wiring substrate 
       120  heat generating part 
       130  heat dissipation plate