JP2007121927A - Backlight device, and liquid crystal display device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a backlight device capable of reducing the number of light emitting diodes needed to prevent unevenness of a light emission color on the whole device by increasing the light emission intensity of a fluorescent lamp and also preventing an electric power efficiency from being degraded owing to a decrease in parasitic capacitance of the fluorescent lamp. <P>SOLUTION: A radiation point of light that a light emitting diode 3 emitting the light to irradiate a liquid crystal panel 1 emits toward the liquid crystal panel 1 from the opposite direction from the liquid crystal panel 1 about the fluorescent lamp 2 is provided at a position shifted from a conductive part 51 of a back member 5 provided opposite the fluorescent lamp 2 away from the fluorescent lamp 2. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a backlight device used in a liquid crystal display device represented by, for example, a liquid crystal television, and more particularly to a backlight device including two types of light sources, a fluorescent tube and a light emitting diode.

  In general, a backlight device of a liquid crystal display device typified by a liquid crystal television uses a fluorescent tube having R (red), G (green), and B (blue) as primary colors. This fluorescent tube has the characteristic that the emission intensity of the red wavelength light is smaller than the emission intensity of the green or blue wavelength light, and the color purity of the emission color of the backlight device is not sufficient. The problem is that it affects the color reproducibility of the display image. Specifically, it is difficult for a liquid crystal display device to display pure red. Therefore, conventionally, two types of light sources, a fluorescent tube and a red LED (light emitting diode), are used together, and the emission intensity of the red wavelength light of the fluorescent tube is reinforced with a red LED, thereby improving the color purity of the emitted color. It is illustrated (for example, refer to Patent Document 1).

3A is a side sectional view of the conventional liquid crystal display device Z, and FIG. 3B is a front view showing a state in which the liquid crystal panel 21 and the diffusion plate 26 of the conventional liquid crystal display device Z are removed. .
As shown in FIG. 3, the conventional liquid crystal display device Z includes a liquid crystal panel 21 for displaying an image, a plurality of fluorescent tubes 22 arranged in the vertical direction, and a fluorescent tube 22 arranged between the fluorescent tubes 22. LED 23 for emitting red wavelength light, LED circuit board 24 on which a plurality of LEDs 23 are arranged and mounted, metal back member 25 to which LED circuit board 24 is fixed, fluorescent tube 22 and LED 23 And a diffusion plate 26 that diffuses the light.
In the liquid crystal display device Z configured as described above, red wavelength light is emitted from the LEDs 23 arranged between the fluorescent tubes 22 as shown in the dashed line in FIG. Since the emission intensity of the red wavelength light from the fluorescent tube 22 is reinforced and the color purity is improved, the color reproducibility of the display image in the liquid crystal display device Z is improved.

Further, it is generally known that a parasitic capacitance is generated between the fluorescent tube 22 and the back member 25, which varies depending on the separation distance. This parasitic capacitance is generated when a capacitor is formed by the plasma in the fluorescent tube 22 and the back member 25. The parasitic capacitance increases as the separation distance between the fluorescent tube 22 and the back member 25 decreases, and decreases as the separation distance increases.
Here, if the parasitic capacitance becomes too large, a leakage current from the fluorescent tube 22 becomes large, causing a problem that the fluorescent tube 22 does not emit light uniformly. If the parasitic capacitance becomes too small, the fluorescent tube This causes a problem that the leakage current from 22 becomes small and the power efficiency related to the light emission of the fluorescent tube 22 deteriorates. Therefore, the separation distance between the fluorescent tube 22 and the back member 25 is designed so that these problems do not occur.
JP 2004-39876 A

  By the way, since the LED 23 used to reinforce the light emission intensity of the fluorescent tube 22 is a light source having strong directivity, the range in which the light emission intensity of the fluorescent tube 22 can be reinforced is narrow. Therefore, there is a possibility that color unevenness may occur due to a change in the degree to which the light emission intensity of the fluorescent tube 22 is reinforced depending on where the light from the LED 23 reaches and where it does not reach. This problem can be improved by providing a large number of the LEDs 23 at short intervals between each of the fluorescent tubes 22, but providing a large number of the LEDs 23 is problematic because of high cost.

In addition, rather than providing a large number of the LEDs 23, it is conceivable that the LEDs 23 are provided at positions sufficiently separated from the fluorescent tube 22 to spread the light of the LEDs 23 even a little before reaching the liquid crystal panel 21. It is done. However, in such a configuration, as described above, the parasitic capacitance generated between the fluorescent tube 22 and the back member 25 is reduced, and the power efficiency related to the light emission of the fluorescent tube 22 is deteriorated. Arise.
Accordingly, the present invention has been made in view of the above circumstances, and an object of the present invention is to provide a light emitting diode necessary to reinforce the light emission intensity of the fluorescent tube and prevent color unevenness of the light emission color of the entire device. The present invention provides a backlight device and a liquid crystal display device including the backlight device that can reduce the number of light sources and prevent a reduction in power efficiency due to a decrease in parasitic capacitance of the fluorescent tube.

In order to achieve the above object, the present invention provides a fluorescent tube for irradiating light to the liquid crystal panel from behind the liquid crystal panel, and facing the liquid crystal panel from a direction opposite to the liquid crystal panel with respect to the fluorescent tube A light-emitting diode that emits irradiated light; and a conductive member disposed opposite to the fluorescent tube at a position spaced a predetermined amount in a direction opposite to the liquid crystal panel. The present invention is applied to a backlight device, and a radiation point of light emitted from the light emitting diode and applied to the liquid crystal panel protrudes in a direction away from the fluorescent tube rather than the conductive member. The backlight device is provided at a position.
Thus, by providing only the radiation point at a position protruding in a direction away from the fluorescent tube rather than the conductive member, the separation distance between the conductive member and the fluorescent tube is too large. Thus, the problem of a decrease in power efficiency that occurs can be prevented. In addition, according to the present invention, conventionally, light emitted from the same position as the conductive member toward the liquid crystal panel is directed from the position away from the fluorescent tube to the liquid crystal panel. Since the light is radiated, the light reaches the liquid crystal panel after being spread by an amount corresponding to the extended distance. Accordingly, it is possible to reinforce the light emission intensity of the fluorescent tube as uniformly as possible without increasing the number of light emitting diodes, and to prevent color unevenness on the liquid crystal panel.

Here, as a specific configuration for providing the radiation point at a position protruding in a direction away from the fluorescent tube with respect to the conductive member, the light emitting diode includes the conductive member, and the conductive member. It is conceivable that the rear member having a recessed portion recessed in a direction away from the fluorescent tube is disposed in the vicinity of the bottom portion of the recessed portion, and light is emitted from the vicinity of the bottom portion toward the liquid crystal panel.
Further, as another specific means, the light emitting diode is directed toward the inside of the depressed portion in the back member having the conductive member and a depressed portion that is depressed from the conductive member in a direction away from the fluorescent tube. It may be configured to irradiate light. As a result, the light emitted from the light emitting diode is reflected in the depression and irradiated toward the liquid crystal panel. That is, the radiation point is located in a pseudo manner at a position protruding in a direction away from the fluorescent tube with respect to the conductive member.
Further, by providing a member (second light reflecting member) having a high light reflectance on the inner wall of the depressed portion, the light emitted from the light emitting diode can be efficiently emitted to the liquid crystal panel. it can.

  Further, if a member having high light reflectance (first light reflecting member) is provided on the surface of the circuit board on which the light emitting diode is mounted, the light emitted from the fluorescent tube It can be efficiently reflected to the liquid crystal panel side.

By the way, it is preferable that the inner wall of the depressed portion is expanded from the bottom toward the liquid crystal panel in order to radiate the light of the light emitting diode toward the liquid crystal panel in a state where the light is spread as much as possible.
Furthermore, by making the inner wall of the depressed portion a curved surface, the light of the light emitting diode is emitted toward the liquid crystal panel in a more spread state.
As described above, the present invention provides a position where the radiation point of light emitted from the light emitting diode and applied to the liquid crystal panel protrudes in a direction away from the fluorescent tube rather than the conductive member. The present invention may be regarded as an invention of a liquid crystal display device including a backlight device provided in the above.

  According to the present invention, the distance between the conductive member and the fluorescent tube is too large by providing only the radiation point at a position protruding in a direction away from the fluorescent tube than the conductive member. Therefore, it is possible to prevent the problem of reduction in power efficiency caused by the above. In addition, according to the present invention, conventionally, light emitted from the same position as the conductive member toward the liquid crystal panel is directed from the position away from the fluorescent tube to the liquid crystal panel. Since the light is radiated, the light reaches the liquid crystal panel after the light is spread by an amount corresponding to the extended distance. Accordingly, it is possible to reinforce the light emission intensity of the fluorescent tube as uniformly as possible without increasing the number of light emitting diodes, and to prevent color unevenness on the liquid crystal panel.

Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings so that the present invention can be understood. The following embodiment is an example embodying the present invention, and does not limit the technical scope of the present invention.
1A is a side sectional view showing a schematic configuration of the liquid crystal display device X according to the embodiment of the present invention, and FIG. 1B is a diagram of a backlight device Y provided in the liquid crystal display device X. It is a front view.
First, a schematic configuration of the liquid crystal display device X according to the embodiment of the present invention will be described with reference to FIG.
As shown in FIG. 1, the liquid crystal display device X includes a liquid crystal panel 1 for displaying an image, a plurality of fluorescent tubes 2 for irradiating the liquid crystal panel 1 with light from behind the liquid crystal panel 1, Between each of the fluorescent tubes 2, a plurality of light emitting diodes 3 (hereinafter referred to as “LED 3”) that emit red wavelength light toward the liquid crystal panel 1 from a direction opposite to the liquid crystal panel 1 with respect to the fluorescent tube 2. ), A LED circuit board 4 on which a plurality of the LEDs 3 are arranged and mounted, a back member 5 to which the LED circuit board 4 is fixed, the fluorescent tube 2 and the light of the LED 3 are diffused to diffuse the liquid crystal panel X And a diffusing plate 6 for output toward the head. Here, a description will be given by taking as an example a method for enhancing the emission intensity of the red wavelength light of the fluorescent tube 2 by the LED 3 to increase the red color purity, but other colors such as blue or green Needless to say, the present invention can also be applied to increase the purity.
Here, as shown in FIG. 1B, among the components of the liquid crystal display device X, the fluorescent tube 2, the LED 3, the LED circuit board 4, the back member 5, etc. are connected to the liquid crystal display device X. The backlight device Y provided in is constructed. Further, the liquid crystal display device X includes components included in a general liquid crystal display device in addition to the illustrated components, for example, a control circuit and a power supply circuit, but the description thereof is omitted here.

  The back member 5 is made of a metal conductive portion 51 (conductive member) disposed opposite to the fluorescent tube 2 at a position spaced apart from the fluorescent tube 2 in a direction opposite to the liquid crystal panel 1 by a predetermined amount. 1) and a depressed portion 52 that is depressed in a direction away from the fluorescent tube 2 from the conductive portion 51, and the side cross section forms irregularities as shown in FIG. . The back member 5 may be configured by combining the conductive portion 51 and the depressed portion 52 as separate parts. Further, it may be integrally formed. Further, the back member 5 is configured integrally with the casing (not shown) of the liquid crystal display device X or as a separate member.

The conductive portion 51 reflects the light of the fluorescent tube 2 by a reflection sheet (not shown) provided on the surface of the conductive portion 51 on the fluorescent tube 2 side, and is parasitic between the conductive portion 51 and the fluorescent tube 2. It generates a capacity. In addition, even if the said electroconductive part 51 itself is not a metal electroconductive member, the said reflective sheet (not shown) provided in this electroconductive part 51 should just be electroconductive.
As described above, this parasitic capacitance changes depending on the distance between the conductive portion 51 and the fluorescent tube 2, and the size of the parasitic capacitance inhibits uniform light emission of the fluorescent tube 2. Or, there is a risk of reducing the power efficiency. Therefore, the conductive portion 51 is separated from the fluorescent tube 2 by a distance that allows the fluorescent tube 2 to emit light uniformly and does not reduce power efficiency.

  The depressed portion 52 has a bottom portion 52a for fixing the LED circuit board 4, and an inner wall 52b expanded from the bottom portion 52a toward the liquid crystal panel 1 side. Moreover, although not shown in figure, the reflection sheet (an example of the 2nd light reflection member) with a high reflectance of light is affixed inside the said inner wall 52b. Of course, the inner wall 52b itself may be composed of a member having high light reflectivity. Further, the inner wall 52b may be a curved surface like an inner wall 53 (see FIG. 2) of an embodiment described later.

By the way, as described above, since the LED 3 is a light source having a strong directivity, conventionally, a large number of the LEDs 3 are arranged, or the LED 3 is moved away from the liquid crystal panel 1 together with the conductive portion 51. The color unevenness of the light emission color as the whole apparatus of the liquid crystal display device X has been reduced. Therefore, on the other hand, the problem that the cost is increased by arranging a large number of the LEDs 3 and the problem that the parasitic capacitance is reduced and the power efficiency is lowered by moving the conductive portion 51 away from the liquid crystal panel 1. Was accompanied.
However, in the liquid crystal display device X according to the embodiment of the present invention, the distance between the conductive portion 51 and the fluorescent tube 2 is L1, and the distance between the LED 3 and the fluorescent tube 2 is L2. , L2> L1, L1 and L2 are individually set according to the cross-sectional concavo-convex shape of the back member 5, so that the above-mentioned problems are improved. This point will be described in detail below.

In the liquid crystal display device X, as shown in FIG. 1A, the LED 3 is attached to the bottom 52a by fixing the LED circuit board 4 to the bottom 52a of the depressed portion 52 of the back member 5. Has been placed. That is, the radiation point of the light emitted from the LED 3 and emitted toward the liquid crystal panel 1 is provided at a position (the bottom portion 52a) protruding in a direction away from the fluorescent tube 2 from the conductive portion 51. Will be.
Here, the broken line shown in the alternate long and short dash line in FIG. 1A is emitted from the LED 3 toward the liquid crystal panel 1 when the LED 3 is disposed at the same position as the conductive portion 51. Shows the light rays. On the other hand, the solid line shown in the alternate long and short dash line in FIG. 1A shows the case where the LED 3 is disposed on the bottom portion 52a protruding in a direction away from the fluorescent tube 2 rather than the conductive portion 51. A light beam emitted from the LED 3 toward the liquid crystal panel 1 is shown.
As is clear from FIG. 1A, the LED 3 is provided so as to protrude in a direction away from the fluorescent tube 2 rather than the conductive portion 51 as in the liquid crystal display device X according to the present embodiment. In the case, the light passing through the LED 3 is longer than the case where the LED 3 is provided at the same position as the conductive portion 51, so that the light spreads before reaching the liquid crystal panel 1. . In addition, since the inner wall 52a of the depressed portion 52 is expanded, the spread of the light is not hindered.
Therefore, variation in the reinforcement of the light emission intensity of the fluorescent tube 2 by the LED 3 is reduced, and color unevenness of light emitted from the entire apparatus is prevented. Therefore, it is possible to reduce the number of the LEDs 3.
In addition, as described above, the back member 5 has a concavo-convex shape in which L1 and L2 can be individually designed so that the separation distance L1 is smaller than the separation distance L2. The separation distance L1 can be designed so that a desired parasitic capacitance is generated between the conductive portion 51 and the fluorescent tube 2, and a reduction in power efficiency due to the parasitic capacitance becoming too large is prevented. Is possible. Further, since the back member 5 has a concavo-convex shape as shown in FIG. 1A, the total area is increased as compared with the case where it is formed in a flat plate shape (see FIG. 3), and heat dissipation in the backlight device Y is performed. The effect also increases.

Next, a liquid crystal display device X1 according to an embodiment of the present invention will be described with reference to FIG. 2A is a side sectional view showing a schematic configuration of the liquid crystal display device X1 according to the embodiment of the present invention, and FIG. 2B is a front view of the backlight device Y1 provided in the liquid crystal display device X1. FIG. In the liquid crystal display device X1, the same components as those of the liquid crystal display device X (see FIG. 1) are denoted by the same reference numerals, and description thereof is omitted.
As shown in FIG. 2, a liquid crystal display device X1 according to an embodiment of the present invention is different from the liquid crystal display device X in that a depressed portion 53 having a curved inner wall 53a is used instead of the depressed portion 52. 5, and the LED circuit board 4 is arranged in a state in which the LED 3 faces the direction in which the LED 3 emits light toward the depressed portion 53. The inner wall 53a is preferably a curved surface having a higher light diffusibility than a flat surface, but may be a flat surface. In addition, a reflective sheet (not shown, one example of a second light reflecting member) having a high light reflectivity is attached to the inner wall 53a as well as the inner wall 52a.
A reflective sheet 4a (an example of a first light reflecting member) having a high light reflectance is attached to the back surface of the LED circuit board 4, that is, the surface on the liquid crystal panel 1 side. Thereby, the light of the fluorescent tube 2 can be reflected not only to the conductive portion 51 but also to the reflection sheet 4a and radiated to the liquid crystal panel 1 side. The LED circuit board 4 is attached to the back member 5 by a screw or an engaging portion (not shown).

In the liquid crystal display device X1 configured as described above, the light emitted from the LED 3 is reflected by the inner wall 53a of the depressed portion 53 as indicated by a solid line in the dashed line in FIG. Irradiated toward the panel 1 side. At this time, the light radiated toward the liquid crystal panel 1 is L3 as the distance between the fluorescent tube 2 and the conductive portion 51 and L4 as the distance between the LED 3 and the bottom of the depressed portion 53. At this time, it can be considered that the light is radiated from the position P away from the fluorescent tube 2 by L3 + 2 × L4. That is, it can be considered that the radiant point of light irradiated toward the liquid crystal panel 1 protrudes in a direction away from the fluorescent tube 2 from the conductive portion 51.
The distance until the light radiated from the position P reaches the liquid crystal panel 1 is the light irradiated directly on the liquid crystal panel 1 side from the position of the conductive portion 51 (one point in FIG. 2A). Compared to the broken line of the chain line), the light reaches the diffusion plate 6 in a more expanded state, and the fluorescence by the LED 3 is increased without increasing the number of the LEDs 3. It is possible to reduce unevenness in the reinforcement of the light emission intensity of the tube 2 and prevent color unevenness of the light emitted as the entire apparatus. Of course, as with the liquid crystal display device X, it is possible to prevent the parasitic capacitance generated between the conductive portion 51 and the fluorescent tube 2 from becoming excessively large due to the concavo-convex shape of the back member 5. A configuration such as this can also be adopted.

(A) is a sectional side view which shows schematic structure of the liquid crystal display device which concerns on embodiment of this invention, (b) is a front view of the backlight apparatus which concerns on embodiment of this invention. (A) is a side sectional view showing a schematic configuration of a liquid crystal display device according to an embodiment of the present invention, (b) is a front view of a backlight device according to an embodiment of the present invention. (A) is a sectional side view of a conventional liquid crystal display device, and (b) is a front view showing a state in which a liquid crystal panel and a diffusion plate of the conventional liquid crystal display device are removed.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Liquid crystal panel 2 ... Fluorescent tube 3 ... LED (light emitting diode)
4 ... LED circuit board 4a ... reflective sheet 5 ... back member 6 ... diffuser plate 51 ... conductive part 52, 53 ... recessed part 52a ... bottom part 52b, 53a ... inner wall X, X1 ... liquid crystal display device Y, Y1 ... backlight device

Claims (8)

A fluorescent tube for irradiating the liquid crystal panel with light from behind the liquid crystal panel;
A light emitting diode that emits light emitted toward the liquid crystal panel from a direction opposite to the liquid crystal panel with respect to the fluorescent tube;
A conductive member disposed relative to the fluorescent tube at a position spaced a predetermined amount from the fluorescent tube in a direction opposite to the liquid crystal panel;
A backlight device comprising:
A back point in which a radiation point of light emitted from the light emitting diode and irradiated toward the liquid crystal panel is provided at a position protruding in a direction away from the fluorescent tube with respect to the conductive member. Light equipment. A back member having the conductive member and a recessed portion recessed in a direction away from the fluorescent tube from the conductive member;
2. The backlight device according to claim 1, wherein the light emitting diode is disposed in the vicinity of the bottom of the depressed portion of the back member, and emits light from the vicinity of the bottom toward the liquid crystal panel. A back member having the conductive member and a recessed portion recessed in a direction away from the fluorescent tube from the conductive member;
The backlight device according to claim 1, wherein the light emitting diode is irradiated with light toward the recessed portion. A circuit board on which the light emitting diode is mounted;
The backlight device according to claim 3, wherein a first light reflecting member having a high light reflectance is provided on a surface of the circuit board on the fluorescent tube side.   The backlight device according to claim 2, wherein a second light reflecting member having a high light reflectance is provided on an inner wall of the depressed portion.   The backlight device according to claim 2, wherein an inner wall of the depressed portion is expanded from the bottom toward the liquid crystal panel.   The backlight device according to claim 2, wherein an inner wall of the depressed portion is a curved surface.   A liquid crystal display device comprising the backlight device according to claim 1.

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