Abstract:
An illumination device for a display device has cold cathode tube lamps capable of being driven in parallel, a first holding member having holders equivalent in number to the number of the cold cathode tube lamps and each holding one end of each lamp, a second holding member having holders equivalent in number to the number of the cold cathode tube lamps and each holding the other end of each lamp and an electric power source device. Harness lines connected to one end of the electric power source device and the first holding member are interconnected at multiple points, and harness lines connected to the other end of the electric power source device and the second holding member are interconnected at multiple points. This reduces uneven brightness. The illumination device for a display device can be used as backlight for a liquid crystal TV.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to an illuminating device for a display device (hereinafter, “display-device illuminating device”), and to a display device. More particularly, the present invention relates to a display-device illuminating device provided with a plurality of lamps that can be driven in parallel, and also relates to a display device. 
     2. Description of the Related Art 
     Common cold cathode lamps used as light sources for display devices have a non-linear negative impedance characteristic, and accordingly cannot be driven in parallel. Thus, each cold cathode lamp is generally provided with a separate power supply circuit. This configuration, however, is costly since it requires as many power supply circuits as there are cold cathode lamps, and also is disadvantageous in terms of size reduction, weight reduction, and cost reduction. 
     Moreover, common cold cathode lamps used as light sources for display devices are connected to power supply circuits via harness leads (also simply called leads) and connectors. Therefore, their fitting is troublesome, resulting in poor assembly efficiency with display-device illuminating devices employing cold cathode lamps; likewise their removal also is troublesome, resulting in poor replacement efficiency at the time of replacement of cold cathode lamps, and in poor disassembly efficiency at the time of discarding of display-device illuminating devices employing cold cathode lamps. 
     Known as lamps free from such disadvantages are external electrode fluorescent lamps (EEFLs) (see, e.g., JP-A-2004-31338 and JP-A-2004-39264), and the cold cathode lamps for which the present applicant applied for a patent (see WO 2006/051698 A1). 
     An external electrode fluorescent lamp is, in terms of an equivalent circuit, a serial circuit with a capacitor connected to each end of a negative resistance, and has a nonlinear positive impedance characteristic; external electrode fluorescent lamps can therefore be driven in parallel. On the other hand, a circuit comprising a cold cathode lamp disclosed in WO 2006/051698 A1, a first power feeding member, and a second power feeding member, wherein the cold cathode lamp is fed with electric power from a power supply device via the first and second power feeding members, is, in terms of an equivalent circuit, a serial circuit with a capacitor connected to at least one end of a negative resistance, and therefore has a nonlinear positive impedance characteristic; thus the cold cathode lamp disclosed in WO 2006/051698 A1 can be driven in parallel. 
     These lamps, as discussed above, can be driven in parallel, and can be fed with electric power via holders made out of a resilient metal member (e.g. spring steel), with the holders, under the resilience thereof, pinching and holding end portions of the lamps. This construction is advantageous in terms of easy fitting and removal of the lamps. 
     As shown in  FIG. 8 , in a display-device illuminating device employing such lamps as discussed above that can be driven in parallel, one end of each lamp  11  is held with a holder  12  provided on a first holding member  13 , and the other end of each lamp  11  is held with a holder  14  provided on a second holding member  15 . The lamps  11  are each supplied with an alternating-current voltage having a frequency of several tens of kilohertz from a power supply device  16  via the first holding member  13  and the second holding member  15 . There are provided as many of each of the holders  12  and  14 , which are made out of a resilient metal member (e.g. spring steel) as there are lamps. An A-A′ section of the second holding member  15  shown in  FIG. 8  is as shown in  FIG. 9A , and a B-B′ section of the second holding member  15  shown in  FIG. 8  is as shown in  FIG. 9B . Note that the shape of the first holding member  13  is similar to that of the second holding member  15 . 
     In the configuration shown in  FIG. 8 , as in other known art (e.g., see JP-A-2003-36723), a connecting point of the first holding member  13  and a harness lead  17 , which is connected to one end of a power supply device  16 , is provided at a bottom end portion of the first holding member  13 , and a connecting point of the second holding member  15  and a harness lead  18 , which is connected to the other end of the power supply device  16 , is provided at a bottom end part of the second holding member  15 . Therefore, the influence of a voltage drop resulting from an ohmic loss is greater the closer a lamp is located to the top of the first holding member  13  and the second holding member  15 ; thus the closer a lamp is located to the top of the first holding member  13  and the second holding member  15 , the smaller the lamp current therethrough. This results in uneven brightness. 
     SUMMARY OF THE INVENTION 
     To overcome the above problems, preferred embodiments of the present invention provide a display-device illuminating device that offers more even brightness and provide a display device including such a display-device illuminating device. 
     A display-device illuminating device according to a preferred embodiment of the present invention includes a plurality of tube lamps capable of being driven in parallel, a first holding member having as many holders as there are tube lamps, the holders holding first ends of the tube lamps, and a power supply device, and is provided with two or more connecting points of harness leads connected to a first end of the power supply device and the first holding member. 
     With this configuration, the difference among the distances from the connecting points of the harness leads connected to one end of the power supply device and the first holding member to each of the tube lamps can be reduced, and thus it is possible to obtain more even brightness. For example, in a case where the connecting points of the harness leads connected to one end of the power supply device and the first holding member are provided at the top and bottom ends of the first holding member, the difference among the distances from the connecting points of the harness leads connected to one end of the power supply device and the first holding member to each of the tube lamps is halved compared with in the configuration shown in  FIG. 8 . 
     In a case where the tube lamps capable of being driven in parallel are such that their other ends can be held directly with holders, there may be additionally provided a second holding member having as many holders as there are tube lamps, the holder holding the other ends of the tube lamps, and two or more connecting points of the harness leads connected to the other end of the power supply device and the second holding member. 
     In the display-device illuminating device according to a preferred embodiment of the present invention with the above described configuration, it is preferable that the lengths of the harness leads provided between one end of the power supply device and the first holding member are equal. In a case where the above-mentioned second holding member is provided, it is preferable that the lengths of the harness leads provided between the other end of the power supply device and the second holding member are equal. 
     This configuration helps to eliminate the difference among the lamp currents through the individual lamps owing to the ohmic loss across the harness leads. 
     In the display-device illuminating device according to a preferred embodiment of the present invention with the above described configuration, the first holding member may be replaced with a first power feeding portion having as many first power feeding members as there are tube lamps, the first power feeding members being conductive members that do not make contact with the tube lamps, and the circuit formed by the tube lamps and the first power feeding member may form, in terms of an equivalent circuit, a serial circuit with a capacitor connected to one end of a negative resistance. In a case where the display-device illuminating device according to a preferred embodiment of the present invention with the above described configuration is provided with the second holding member, the second holding member may be replaced with a second power feeding portion having as many second power feeding members as there are tube lamps, the second power feeding members being conductive members that does not make contact with the tube lamps, and the circuit formed by the tube lamp, the first power feeding member, and the second power feeding member may form, in terms of an equivalent circuit, a serial circuit with a capacitor connected to each end of a negative resistance. 
     A display device according to a preferred embodiment of the present invention (e.g. a television receiver) preferably includes any of the above described display-device illuminating devices. 
     According to various preferred embodiments of the present invention, it is possible to realize display-device illuminating devices with more even brightness and display devices provided therewith. 
     These and other features, elements, steps, characteristics and advantages of the present invention will become more apparent from the following detailed description of preferred embodiments of the present invention with reference to the attached drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a diagram showing an example of the configuration of a display-device illuminating device according to a preferred embodiment of the present invention. 
         FIG. 2A  is a diagram showing a sectional shape of a second holding member provided in the display-device illuminating device shown in  FIG. 1 . 
         FIG. 2B  is a diagram showing a sectional shape of a second holding member provided in the display-device illuminating device shown in  FIG. 1 . 
         FIG. 3  is a diagram showing another example of the configuration of a display-device illuminating device according to a preferred embodiment of the present invention. 
         FIG. 4  is a diagram showing yet another example of the configuration of a display-device illuminating device according to a preferred embodiment of the present invention. 
         FIG. 5A  is a diagram showing an example of the configuration of a tube lamp provided in a display-device illuminating device according to a preferred embodiment of the present invention. 
         FIG. 5B  is a diagram showing an example of the configuration of a holder provided in a display-device illuminating device according to a preferred embodiment of the present invention. 
         FIG. 5C  is a diagram showing an example of the configuration of a display-device illuminating device according to a preferred embodiment of the present invention. 
         FIG. 6A  is a diagram showing another example of the configuration of a tube lamp provided in a display-device illuminating device according to a preferred embodiment of the present invention. 
         FIG. 6B  is a diagram showing another example of the configuration of a holder provided in a display-device illuminating device according to a preferred embodiment of the present invention. 
         FIG. 7  is a diagram showing an exploded perspective view of a liquid crystal television receiver which is one example of a display device according to a preferred embodiment of the present invention. 
         FIG. 8  is a diagram showing an example of the equivalent circuit of a conventional display-device illuminating device. 
         FIG. 9A  is a diagram showing a sectional shape of a second holding member provided in the display-device illuminating device shown in  FIG. 8 . 
         FIG. 9B  is a diagram showing a sectional shape of a second holding member provided in the display-device illuminating device shown in  FIG. 8 . 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Preferred embodiments of the present invention will be described below with reference to the accompanying drawings. One example of a configuration of a display-device illuminating device according to a preferred embodiment of the present invention is shown in  FIG. 1 . 
     The display-device illuminating device shown in  FIG. 1  includes a plurality of tube lamps  1  that can be driven in parallel; a first holding member  3  that has as many holders  2  as there are tube lamps, the holders  2  holding one ends of the tube lamps  1  respectively; a second holding member  5  that has as many holders  4  as there are tube lamps, the holders  4  holding the other ends of the tube lamps  1  respectively; and a power supply device  6 . The lamps  1  are each supplied with an alternating-current voltage having a frequency of several tens of kilohertz from the power supply device  6  via the first holding member  3  and the second holding member  5 . There are provided as many of each of the holders  2  and  4 , which are made out of a resilient metal member (e.g. spring steel) as there are lamps. An A-A′ section of the second holding member  5  shown in  FIG. 1  is as shown in  FIG. 2A , and a B-B′ section of the second holding member  5  shown in  FIG. 1  is as shown in  FIG. 2B . Note that the shape of the first holding member  3  is similar to that of the second holding member  5 . 
     The display-device illuminating device shown in  FIG. 1  includes an optical sheet; and an illuminating unit; that is provided with the first holding member  3 , and the second holding member  5 , that has the tube lamps fitted on a front surface thereof, and that has the power supply device  6  arranged at a rear surface thereof. This results in a construction in which the optical sheet covers the front surface of the illuminating unit with the tube lamps  1  fitted thereon. 
     A first end of a harness lead  7  is directly electrically connected to one end of a power supply device  6  and a second end of the harness lead  7  is directly electrically connected to one end of the first holding member  3  at the top end of the first holding member  3 . The harness lead  7  includes a middle portion  7   a  that is directly connected to the first end and the second end of the harness lead  7 . A first end of a harness lead  7 ′ is directly electrically connected to the one end of the power supply device  6  and a second end of the harness lead  7 ′ is directly electrically connected to another end of the first holding member  3  at the bottom end of the first holding member  3 . The harness lead  7 ′ includes a middle portion  7   a ′ that is directly connected to the first end and the second end of the harness lead  7 ′. Also, a first end of a harness lead  8  is directly electrically connected to a second end of the power supply device  6  and a second end of the harness lead  8  is directly electrically connected to one end of the second holding member  5  at the top end of the second holding member  5 . The harness lead  8  includes a middle portion  8   a  that is directly connected to the first end and the second end of the harness lead  8 . A first end of a harness lead  8 ′ is directly electrically connected to the second end of the power supply device  6  and a second end of the harness lead  8 ′ is directly electrically connected to another end of the second holding member  5  and a harness lead  8 ′at the bottom end of the second holding member  5 . The harness lead  8 ′ includes a middle portion  8   a ′ that is directly connected to the first end and the second end of the harness lead  8 ′. 
     With this configuration, the difference among the distances from the connecting points of the first holding member  3  and the harness leads  7  and  7 ′, which are connected to one end of the power supply device  6 , to one ends of the tube lamps  1  is approximately halved as compared with the difference, in the configuration shown in  FIG. 8 , among the distances, from the connecting point of the first holding member  13  and the harness lead  17 , which is connected to one end of a power supply device  16 , to one ends of the tube lamps  11 , and, the difference among the distances from the connecting points of the second holding member  5  and the harness leads  8  and  8 ′, which are connected to the other end of the power supply device  6 , to the other ends of the tube lamps  1  is approximately halved as compared with the difference, in the configuration shown in  FIG. 8 , among the distances, from the connecting points of the second holding member  15  and the harness lead  18 , which is connected to the other end of the power supply device  16 , to the other ends of the tube lamps  11 , and thus the difference of the lamp-current in the tube lamps  1  is reduced. In this way, it is possible to obtain more even brightness. 
     Note that, the positions of the connecting points of the first holding member  3  and the harness leads  7  and  7 ′, which are connected to one end of the power supply device  6 , and the positions of the connecting points of the second holding member  5  and the harness leads  8  and  8 ′, which are connected to the other end of the power supply device  6 , may be modified as the configuration shown in  FIG. 3 . In this configuration, the difference among the distances from the connecting points of the first holding member  3  and the harness leads  7  and  7 ′, which are connected to one end of the power supply device  6 , to one ends of the tube lamps  1  is reduced approximately to one-fourth as compared with the difference, in the configuration shown in  FIG. 8 , among the distances from the connecting point of the first holding member  13  and the harness lead  17 , which is connected to one end of the power supply device  16 , to one ends of the tube lamps  11 , and the difference among the distances from the connecting points of the second holding member  5  and the harness leads  8  and  8 ′, which are connected to the other end of the power supply device  6 , to the other ends of the tube lamps  1  is reduced approximately to one-fourth as compared with the difference, in the configuration shown in  FIG. 8 , among the distances from the connecting point of the second holding member  15  and the harness lead  18 , which is connected to the other end of the power supply device  16 , to the other ends of the tube lamps  11 . Thus, it is possible to obtain still more even brightness. 
     The number of connecting points of the first holding member  3  and the harness lead, leads that are connected to one end of the power supply device  6 , and the number of connecting points of the second holding member  5  and the harness lead, leads that are connected to the other end of the power supply device  6 , are not restricted to two, and, for example, three of each may be provided as shown in  FIG. 4 . The larger the number of connecting points, the more even the brightness obtained, but simultaneously the larger the number of harness leads, lessening the effect of the reduction in the number of harness leads owing to parallel driving. Preferably, with this taken into consideration, the number of connecting points is determined. 
     In a case where the material of the first holding member and the second holding member has a higher specific resistance than the material of the harness leads, for example, in a case where the material of the harness leads is copper (with a specific resistance of 1.55×10 −8  Ω·m at 0° C.), and the material of the first holding member and the second holding member is bronze (with a specific resistance of 13.6×10 −8  Ω·m at 0° C.), or in a case where the shape of the first holding member and the second holding member is such as to have a higher resistance than the shape of the harness leads, the influence of the ohmic loss across the harness leads on the lamp current through each of the lamps is small; thus, even in a configuration where, as in the display-device illuminating device shown in  FIG. 1 , the lengths of the harness leads  7  and  7 ′ are different and the lengths of the harness leads  8  and  8 ′ are different, more even brightness can be obtained. 
     However, in order to prevent the lamp current through each lamp from varying as a result of the ohmic loss across the harness leads, it is preferable, in the configurations shown in  FIG. 1 ,  FIG. 3  and  FIG. 4 , that the lengths of the harness leads provided between one end of the power supply device  6  and the first holding member  3  be equal, and the lengths of the harness leads provided between the other end of the power supply device  6  and the second holding member  5  be equal. 
     A description will now be given of examples of the configuration of the tube lamps  1  and the holders  2  and  4  provided in the display-device illuminating device shown in  FIG. 1 . 
     One example of the configuration of the tube lamps  1  and the holders  2  and  4  provided in the display-device illuminating device according to a preferred embodiment of the present invention are a cold cathode lamp having a sectional structure as shown in  FIG. 5A  and a holder as shown in  FIG. 5B . 
     The cold cathode lamp shown in  FIG. 5A  has internal electrodes  22  and  23  inside a glass tube  21 . Portions of the internal electrodes  22  and  23  penetrate and protrude out of the glass tube  21 , and serve as an electrode terminal. In this configuration, the interior of the glass tube  21  is air-tight. The inner wall of the glass tube  21  is coated with a fluorescent substance. Inside the air-tight glass tube  21 , neon and argon are preferably sealed therein in a ratio of 95:5, 80:20, etc. such that the overall pressure inside the glass tube  21  is, for example, approximately 10.7×10 3  to 5.3×10 3  Pa (≈80 to 40 Torr), and in addition several milligrams of mercury is enclosed. In some cases, xenon is sealed in instead of mercury. 
     In the cold cathode lamp shown in  FIG. 5A , an external electrode  24  is provided on an internal electrode  22 -side end portion of the glass tube  21 , and the protruding portion of the internal electrode  22  and the external electrode  24  are soldered together with solder  26 ; an external electrode  25  is provided on an end portion on the internal electrode  23 -side of the glass tube  21 , and the protruding portion of the internal electrode  23  and the external electrode  25  are soldered together with solder  27 . Specific implementations of the external electrodes  24  and  25  include metal paste, metal foil, metal cap, and the like. As long as the electrical connection between the protruding portion of the internal electrode  22  and the external electrode  24  is sufficiently secured, the solder  26  may be omitted; as long as the electrical connection between the protruding portion of the internal electrode  23  and the external electrode  25  is sufficiently secured, the solder  27  may be omitted. 
     The holder shown in  FIG. 5B  is a resilient metal member  28 A coated with an insulating layer  28 B, and pinches and holds the external electrode of the cold cathode lamp shown in  FIG. 5A  under the resilience of the resilient metal member  28 A. The insulating layer  28 B coated on the resilient metal member  28 A has simply to be formed such that the resilient metal member  28 A and the external electrode of the cold cathode lamp does not make direct contact with each other. 
     As shown in  FIG. 5C , instead of the holder  2 , a first power feeding member  2 ′ which is a conductive member that does not make contact with the external electrode  24  of the cold cathode lamp may be used, and instead of the holder  4 , a second power feeding member  4 ′ which is a conductive member that does not make contact with the external electrode  24  of the cold cathode lamp may be used, and the illuminating unit may be provided with a holding portion which holds the cold cathode lamp such that the external electrode  24  of the cold cathode lamp and the first power feeding member  2 ′ form a capacitor, and that the external electrode  25  of the cold cathode lamp and the second power feeding member  4 ′ define a capacitor. In other words, the first holding member  3  may be replaced with a first power feeding portion  3 ′ provided with as many first power feeding members  2 ′ as there are cold cathode lamps  21 , the first power feeding members  2 ′ each being a conducting member that does not make contact with the external electrode  24  of the cold cathode lamp; the second holding member  5  may be replaced with a second power feeding portion  5 ′ provided with as many second power feeding members  4 ′ as there are cold cathode lamps, the second power feeding members  4 ′ each being a conducting member that does not make contact with the external electrode  25  of the cold cathode lamp; and the circuit defined by the cold cathode lamp  21 , the first power feeding member  2 ′, and the second power feeding member  4 ′ may be, in terms of an equivalent circuit, a serial circuit with a capacitor connected to each end of a negative resistance. However, this implementation suffers from the problem that the interelectrode distance of the capacitor defined by the external electrode  24  of the cold cathode lamp and the first power feeding member and the interelectrode distance of the capacitor defined by the external electrode  25  of the cold cathode lamp and the second power feeding member are unstable, and the problem that there may occur electric discharge between the external electrode  24  of the cold cathode lamp  21  and the first power feeding member  2 ′, and between the external electrode  25  of the cold cathode lamp and the second power feeding member  4 ′. Thus, the configuration, which includes a resilient metal member  28 A coated with an insulating layer  28 B shown in  FIG. 5B  is preferable for use as the first power feeding member  2 ′ and the second power feeding member  4 ′. 
     Another example of the configuration of the tube lamps  1  and the holders  2  and  4  provided in the display-device illuminating device according to a preferred embodiment of the present invention are a cold cathode lamp with a section structure as shown in  FIG. 6A  and a holder shown in  FIG. 6B . Such elements shown in  FIGS. 6A and 6B  as find their counterparts in  FIGS. 5A and 5B  are identified by common reference signs, and no detailed description of them will be repeated. 
     In the cold cathode lamp shown in  FIG. 6A , an insulating layer  29  is disposed on the external electrode  24 , an insulating layer  30  is disposed on the external electrode  25 , a strip-ring-shaped counter electrode  31  is disposed on the insulating layer  29 , and a strip-ring-shaped counter electrode  32  is disposed on the insulating layer  30 . The external electrode  24  as a whole is covered with the glass tube  21  and the insulating layer  29 , and the external electrode  25  as a whole is covered with the glass tube  21  and the insulating layer  30 . 
     Moreover, in the cold cathode lamp shown in  FIG. 6A , a ring-shaped projecting portion  31 A is disposed on the strip-ring-shaped counter electrode  31  to ensure electrical connection between the counter electrode  31  and the holder shown in  FIG. 6B , and a ring-shaped projecting portion  32 A is disposed on the strip-ring-shaped counter electrode  32  to ensure the electrical connection between the counter electrode  32  and the holder shown in  FIG. 6B . 
     The holder shown in  FIG. 6B  is a resilient metal member  28 A, and pinches and holds the projecting portion of the counter electrode of the cold cathode lamp shown in  FIG. 6A  under the resilience of the resilient metal member  28 A. 
     An external electrode fluorescent lamp may be used instead of the cold cathode lamp shown in  FIG. 6A . 
     In both of the two examples of configuration described above, the circuit defined by the tube lamp  1  and the holders  2  and  4  is, in terms of an equivalent circuit, a serial circuit composed of a negative resistance, a capacitor connected to one end of the negative resistance, and a capacitor connected to the other end of the negative resistance. 
     Also in a case where the circuit defined by the tube lamp  1  and the holders  2  and  4  is, in terms of an equivalent circuit, a serial circuit composed of a negative resistance and a capacitor connected to one end of the negative resistance (for example, in a case where the tube lamp  1  and the holders  2  and  4  are the cold cathode lamp with the sectional structure shown in  FIG. 5A , a holder with the structure shown in  FIG. 5B , and a holder with the structure shown in  FIG. 6B ), preferred embodiments of the present invention are applicable. In a case where each lamp is configured as the cold cathode lamp with the sectional structure shown as  FIG. 5A  but with the external electrode  25  and the solder  27  omitted, the second holding member  5  may be omitted, and the other end of the power supply device  6  may be connected with the end portion of the internal electrode  23  by a harness lead. 
     A display-device illuminating device according to a preferred embodiment of the present invention may, for example, be provided with a plurality of units including, for example, the tube lamps  1 , the first holding member, the second holding member  5 , the power supply device  6 , and the harness leads  7 ,  7 ′,  8 , and  8 ′ shown in  FIG. 1 . In this way, it is possible to adapt to large-screen display devices easily. 
     A display device according to a preferred embodiment of the present invention includes a display-device illuminating device according to another preferred embodiment of the present invention as described above and a display panel. Specific implementations of a display device according to various preferred embodiments of the invention include, for example, a transmission liquid crystal display device using a display-device illuminating device according to a preferred embodiment of the present invention as a backlighting unit and having a liquid crystal display panel provided at the front side thereof. 
       FIG. 7  shows an example of an exploded perspective view of a display device according to a preferred embodiment of the present invention in a case where it is a liquid crystal television receiver. A transmission liquid crystal display portion  43 , a tuner  44 , and a power supply  45  are enclosed in between a front cabinet  41  and a rear cabinet  42 , and the rear cabinet  42  is held on a stand  46 . The transmission liquid crystal display portion  43  uses the display-device illuminating device according to a preferred embodiment of the present invention as a backlighting unit, and has the liquid crystal display panel provided at the front side thereof. 
     Display-device illuminating devices according to a preferred embodiment of the present invention can be applied as devices for various display devices, including backlights for liquid crystal television receivers. 
     While preferred embodiments of the present invention have been described above, it is to be understood that variations and modifications will be apparent to those skilled in the art without departing the scope and spirit of the present invention. The scope of the present invention, therefore, is to be determined solely by the following claims.