JP5302599B2 - Backlight device - Google Patents

Description

  The present invention relates to a liquid crystal display device using a backlight device and a planar light source device, and more particularly to an LED backlight device and a liquid crystal display device in which a plurality of light emitting diodes (LEDs) are arranged.

  In recent years, liquid crystal display devices such as so-called liquid crystal televisions have been increased in size, and further, reduction in weight, thickness, and reduction in power consumption are desired for various applications such as wall hanging. The liquid crystal display device has a configuration in which a backlight, which is a backlight device, is disposed on the back surface of a liquid crystal panel. The backlight is provided with one or a plurality of point light sources or line light sources, and a diffusion plate for diffusing the light from the light sources to convert it into planar light.

  Conventionally, many cold cathode tubes, which are linear light sources, have been used as the light source of the backlight. Recently, research and development of backlights using LEDs have been actively conducted. The LED has a luminous efficiency per electric power equivalent to or higher than that of a cold cathode tube, and further reduction in power consumption is expected. Therefore, it is considered that a backlight using such an LED as a light source (hereinafter referred to as “LED backlight”) will be widely used in the future.

  However, the LED backlight has a problem that color unevenness occurs in the outer peripheral portion of the emission surface when three primary color LEDs are used. In addition to LED backlights, non-uniform luminance distribution may be required for backlights depending on the purpose of use. For example, in a large-sized liquid crystal television, there is a case where the brightness of the center of the screen is particularly bright or a case where it is desired to reduce power consumption by suppressing the brightness of a portion that may be dark.

As a means for solving the problem of uneven color and a means for realizing a non-uniform luminance distribution, a technique for arranging a plurality of LEDs with a non-uniform arrangement density on a substrate is disclosed in, for example, Patent Document 1. And Patent Document 2. There is a high possibility that such LED backlights in which the LED arrangement density is intentionally non-uniform will be adopted for various purposes in the future.
JP 2006-189665 A JP 2007-317423 A

  However, when the arrangement density of the light sources is non-uniform, there is a problem that luminance unevenness easily occurs in a portion corresponding to a region where the arrangement density of the light sources is low on the exit surface of the diffusion plate. This is because the irradiation area of each light source on the incident surface of the diffusion plate is constant, and in the portion corresponding to the region where the arrangement density of the light sources is low, the interval between the adjacent irradiation regions becomes wide. In order to obtain a high-quality image in a liquid crystal display device, it is desirable to suppress luminance unevenness on the exit surface of the diffusion plate as much as possible.

  The present invention has been made in view of this point, and an object thereof is to provide a backlight device and a liquid crystal display device that can reduce unevenness in luminance on the exit surface.

A backlight device according to one embodiment of the present invention is a backlight device used in a liquid crystal display device having a liquid crystal panel as a display screen, and a substrate having a facing portion disposed to face the back side of the liquid crystal panel. And a plurality of light emitting diodes arranged at a non-uniform arrangement density on the facing portion and light emitted from the plurality of light emitting diodes are incident, diffused to the incident light, and emitted to the liquid crystal panel side A diffusion plate; and a current supply unit that supplies current to the plurality of light emitting diodes to emit light that illuminates the liquid crystal panel to the plurality of light emitting diodes, and the current supply unit is a region of the facing unit a inner, the light emitting diode ambient temperature at a position close to the liquid crystal driver is positioned in a higher area of controlling the driving voltage of the liquid crystal panel, supplies a lower current, Emitting diodes supplied with a low current, disposed adjacent to the higher density other light-emitting diodes, light-emitting diode arrangement density is low position has a structure that emits light in the wide light distribution.

  According to the present invention, as the arrangement density is lower, the light emitted from the light source is more widely distributed, and the irradiation area on the diffusion plate is enlarged, so that uneven brightness on the emission surface can be reduced.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

(Embodiment 1)
FIG. 1 is a diagram showing a configuration of an LED backlight (backlight device) according to Embodiment 1 of the present invention. FIG. 1A is a schematic front view of an LED backlight, and FIG. 1B is a schematic side view of the LED backlight. This embodiment relates to, for example, an LED backlight that is used as a backlight in a liquid crystal display device, and in which a liquid crystal display is installed so that the screen is vertical, and the brightness above the screen is particularly high. is there. The vertical direction in FIG. 1 corresponds to the vertical direction in a state where a liquid crystal display using an LED backlight is installed, that is, the vertical direction of the screen.

  In FIG. 1, an LED backlight 100 includes a plurality of types of LEDs 110-1 to 110-6, a substrate 120 on which the LEDs 110-1 to 110-6 are disposed, and the light output side of the LEDs 110-1 to 110-6. It has mainly the diffusing plate 130 arranged. The LEDs 110-1 to 110-6 are, for example, white LEDs. The substrate 120 is a flat printed substrate using an insulating material such as glass epoxy resin. The diffusing plate 130 is a flat acrylic plate, and includes an incident surface 131 on which light emitted from the plurality of LEDs 110 is incident, and an emitting surface 132 disposed to face the incident surface 131. The diffusion plate 130 diffuses the light incident on the incident surface 131 by surface diffusion, internal diffusion, or a combination thereof, and emits the light from the output surface 132.

  The substrate 120 is disposed in parallel with the diffusion plate 130. The LEDs 110-1 to 110-6 have lenses for controlling the light distribution characteristics of the emitted light. The LEDs 110-1 to 110-6 are arranged in this order from the upper side of the diffusion plate 130 in the drawing, and are arranged more densely toward the upper side. Further, the LEDs 110-1 to 110-6 have a light distribution of light that is gradually increased in this order. That is, the LED 110 having a lower arrangement density has a wider light distribution. Here, “broad light distribution” means a state in which the spread distribution of emitted light is wide. The light distribution characteristic is arbitrarily set, for example, by adjusting the lens shape or refractive power of the LED 110.

  Here, the arrangement density of the uppermost LED 110-1 is Dh, the arrangement density of the lowermost LED 110-6 is D1, and the distance from the LED 110 to the incident surface 131 of the diffusion plate 130 (hereinafter referred to as “light source distance”). .) Is an example of a numerical value when T is set as follows.

Dh = 0.0064 [pieces / mm ^ 2] (average pitch in square arrangement is 12.5 mm)
Dl = 0.0016 [pieces / mm ^ 2] (average pitch in square arrangement is 20 mm)
T = 10 [mm]

  From the above numerical example, the average pitch of the lowermost LED 110-6 is 1.6 times larger than the average pitch of the uppermost LED 110-1.

  FIG. 2 is a diagram comparing the illuminance of the emitted light from the LED 110-1 and the illuminance of the emitted light from the LED 110-6. In FIG. 2, the horizontal axis indicates coordinates [mm] on the incident surface 131 of the diffusion plate 130, and the vertical axis indicates the illuminance on the incident surface 131 as a relative value with respect to the illuminance on the optical axis of each LED 110.

  As shown in FIG. 2, when the spread distribution 111 of the emitted light from the LED 110-1 and the spread distribution 112 of the emitted light from the LED 110-6 are compared, the spread distribution 111 of the emitted light from the LED 110-1 is compared with that of the LED 110-6. The spread distribution 112 of the emitted light is expanded about 1.6 times.

  As described above, in the present embodiment, the ratio of the average pitch between the LED 110-1 and the LED 110-6 and the ratio of the spread distribution between the LED 110-1 and the LED 110-6 are both 1.6 times. It has the structure which has done. That is, the light spreads according to the arrangement density of the LEDs 110. Therefore, luminance unevenness on the incident surface 131 of the diffuser plate 130 can be reduced.

  Further, since the external shape of the LED backlight 100 device is not particularly affected, the liquid crystal display device using the LED backlight 100 is advantageous in terms of design and production cost.

  In this embodiment, the ratio of the average pitch between the LED 110-1 and the LED 110-6 and the ratio of the spread distribution between the LED 110-1 and the LED 110-6 are both 1.6 times. However, the present invention is not limited to this. In short, it is sufficient if the ratio of the average pitch of the LEDs 110 and the ratio of the spread distribution of the light emitted from the LEDs 110 are substantially matched.

  Moreover, in this Embodiment, the direction of the high and low change of the arrangement density of LED110 is not limited to the said content. For example, even when the arrangement density is higher at the lower part of the diffusion plate 130, the luminance unevenness can be similarly reduced by selecting the type of the LED 110 such that the lower the arrangement density, the wider the light distribution. .

(Embodiment 2)
As an embodiment 2 of the present invention, an LED backlight configured to control the light emission amount of the LED will be described.

  FIG. 3 is a schematic configuration diagram showing the configuration of the LED backlight according to Embodiment 2 of the present invention.

  In FIG. 3, the LED backlight 200 has a plurality of LEDs 110 arranged with a uniform arrangement density in the horizontal direction and with a non-uniform arrangement density in the vertical direction. That is, the arrangement density distribution of the LEDs 110 is the same as that in the first embodiment. Further, the LED backlight 200 includes an LED driving unit 240 that controls the light emission amounts of the plurality of LEDs 110.

  The LED driving unit 240 controls a light emission amount of each LED 110 for each block according to an input control signal, with a plurality of LEDs 110 arranged in the horizontal direction as one block.

  With such a configuration, the light emission amount of the LED 110 can be controlled in conformity with the arrangement density distribution of the LEDs 110, and a desired luminance distribution can be obtained efficiently.

(Embodiment 3)
As a third embodiment of the present invention, a liquid crystal display device using the LED backlight according to the second embodiment will be described.

  FIG. 4 is a schematic configuration diagram showing the configuration of the liquid crystal display device according to Embodiment 3 of the present invention.

  In FIG. 4, the liquid crystal display device 300 includes the LED backlight 200 according to Embodiment 2 and a liquid crystal unit 350. The same parts as those in FIG. 3 are denoted by the same reference numerals, and description thereof will be omitted.

  The liquid crystal unit 350 is illuminated by the LED backlight 200 and controls the arrival state of the light emitted from the LED backlight 200 to the viewer side. The liquid crystal unit 350 includes a liquid crystal panel 351 and a liquid crystal driver 352.

  The liquid crystal panel 351 is a transmissive or transflective liquid crystal panel. The liquid crystal panel 351 transmits the light emitted from the LED backlight 200 and emits the transmitted light from the front surface as a display screen.

  The liquid crystal driver 352 controls the drive voltage for driving the liquid crystal panel 351 based on a video signal that is a digital signal indicating an image to be displayed on the display screen of the liquid crystal panel 351, thereby controlling the transmittance of the liquid crystal panel 351. Control. As a result of this control, the liquid crystal panel 351 displays an image.

  As described in Embodiment 2, the LED backlight 200 controls the light emission amount of the LED 110 for each block. On the other hand, the liquid crystal panel 351 cannot make the light transmittance zero. Therefore, by suppressing the light emission amount of the LED 110 to the minimum for each block, the black luminance that is the luminance of the black display portion of the screen can be reduced, and the contrast of the screen can be improved.

  As described above, according to the present embodiment, it is possible to display an image having a desired luminance distribution with no luminance unevenness with high contrast, and to reduce power consumption.

  In each of the embodiments described above, the case where the light source is an LED has been described. However, the present invention is not limited to this. For example, the present invention is also applied to a case where light sources are various point light sources such as semiconductor lasers, gas lasers, solid state lasers, fiber lasers and lamps, and various line light sources such as cold cathode tubes are arranged in a non-uniform distribution. Can do.

(Embodiment 4)
As a fourth embodiment of the present invention, a liquid crystal display device characterized by the arrangement of the liquid crystal driver and the operation of the LED driving unit will be described.

  FIG. 5 is a side view of the main part of the liquid crystal display device according to the fourth embodiment of the present invention, and corresponds to FIG. 1B of the first embodiment and FIG. 4 of the third embodiment. The same parts as those in FIG. 1B and FIG. 4 are denoted by the same reference numerals, and description thereof will be omitted.

  The liquid crystal display device 400 mainly includes a liquid crystal panel 351, a liquid crystal driver 352, and the LED backlight 200.

  In the present embodiment, the liquid crystal driver 352 is disposed in the vicinity of the upper end portion of the liquid crystal panel 351. In the description of this embodiment, “upper” means the upper side in the vertical direction of the display screen (hereinafter simply referred to as “vertical direction”), and in FIG. Corresponds to the above.

  Note that the liquid crystal driver 352 may be disposed in a place other than the above. For example, the liquid crystal driver 352 may be disposed in the vicinity of the lower end portion, the left end portion, or the right end portion of the liquid crystal panel 351, or may be disposed in other locations. In the description of this embodiment, “lower” means lower in the vertical direction, and “left” and “right” mean the horizontal direction of the display screen (hereinafter simply referred to as “horizontal direction”). Means left and right in

  In the LED backlight 200, the substrate 120 is disposed so as to face the diffusion plate 130 disposed on the back side of the liquid crystal panel 351, as in the first embodiment. The surface of the substrate 120 is a facing portion that faces the back surface of the liquid crystal panel 351, and the LEDs 110 a, 110 b, 110 c, 110 d, 110 e, and 110 f are substantially planar on the surface toward the back surface side of the diffusion plate 130. Is arranged. The diffuser plate 130 diffuses incident light and emits light from the emission surface toward the back surface of the liquid crystal panel 351. That is, the LED backlight 200 is a direct type LED backlight.

  In general, a direct type LED backlight has a sealed structure in which dust and dust are difficult to enter, but the LED backlight 200 may or may not have a sealed structure.

  The LED backlight 200 illuminates the liquid crystal panel 351 with light emitted from the LEDs 110a, 110b, 110c, 110d, 110e, and 110f. In the following description, when the LEDs 110a, 110b, 110c, 110d, 110e, and 110f are described without particular distinction, they are simply referred to as “LED 110”.

  The LED backlight 200 further includes an LED driving unit that drives the LED 110. The LED driving unit will be described later.

  Here, the LED 110 is a white LED, and is driven by a driving signal applied from an LED driving unit described later to emit white light. For example, when the LED 110 is an LED device mainly including a single color (for example, blue) LED and a phosphor, the LED 110 transmits light emitted from the single color LED to the phosphor when a drive signal is applied. It is comprised so that it may be whitened by the effect | action of.

  Note that the LED 110 may take other configurations such as a combination of LEDs of three colors of R (red), G (green), and B (blue).

  FIG. 6 is a diagram illustrating the arrangement of the LEDs 110 in the LED backlight 200.

The LEDs 110 arranged in the upper region 201a are arranged most densely, and the LEDs 110 arranged in the lowermost region 201c are arranged most sparsely and arranged in the region 201b located in the middle of them. The arranged LEDs 110 are arranged with a medium density. More specifically, in the vertical direction, the pitch d _ab between the LED 110a and the LED 110b is smaller than the pitch d _bc between the LED 110b and the LED 110c, and the pitch d _bc is the pitch d _cd between the LED 110c and the LED 110d. The pitch d _cd is smaller than the pitch d _de between the LED 110d and the LED 110e, and the pitch d _de is smaller than the pitch d _ef between the LED 110e and the LED 110f. In the horizontal direction, the pitch between the LEDs 110a is smaller than the pitch between the LEDs 110b, the pitch between the LEDs 110b is smaller than the pitch between the LEDs 110c, the pitch between the LEDs 110c is smaller than the pitch between the LEDs 110d, and the LED 110d. The pitch between the LEDs 110e is smaller than the pitch between the LEDs 110e, and the pitch between the LEDs 110e is smaller than the pitch between the LEDs 110f.

  LED110 has the structure by which the light radiate | emitted becomes wide light distribution, so that it goes below in the figure.

  FIG. 7 is a diagram for explaining an LED drive unit in the LED backlight 200, (a) is a circuit diagram showing an example of the configuration, and (b) is generated by the LED drive unit and supplied to the LED 110. It is a wave form diagram which shows an example of the drive signal which becomes.

  The LED drive unit 440 includes LED drive circuits 441a, 441b, 441c, 441d, 441e, and 441f. In the following description, when the LED driving circuits 441a, 441b, 441c, 441d, 441e, and 441f are described without particular distinction, they are simply referred to as “LED driving circuit 441”.

The LED drive circuit 441a as a current supply unit supplies a drive signal 451a having _a preset current value Ia to one of the LEDs 110a. The LED drive circuit 441b supplies a drive signal 451b having a current value _Ib to one of the LEDs 110b as a current supply unit. LED drive circuit 441c as a current supply section, the one of LED110c, supplies a driving signal 451c having a current value _{I c.} LED driving circuit 441d is as a current supply section, the one of LED110d, supplies a driving signal 451d having a current value _{I d.} The LED drive circuit 441e as a current supply unit supplies a drive signal 451e having a current value _Ie to one of the LEDs 110e. The LED drive circuit 441f serves as a current supply unit and supplies a drive signal 451f having a current value _If to one of the LEDs 110f.

Although not shown in FIG. 7A, the LED drive unit 440 includes the same number of LED drive circuits 441 as the LED 110 as current supply units. Each LED drive circuit 441 supplies a drive signal to one of the LEDs 110. By this configuration, each LED110a is supplied with driving signals 451a having a current value _{I a,} the LED110b is supplied with driving signals 451b having a current value _{I b,} each LED110c supply a driving signal 451c having a current value _{I c} are, each LED110d is supplied with driving signals 451d having a current value _{I d,} the LED110e is supplied with driving signals 451e having a current value _{I e,} each LED110f is supplied with driving signals 451f having a current value _{I f} .

Here, the current value _{I a} is smaller than the current value _{I b,} the current value _{I b} is smaller than the current value _{I c,} the current value _{I c} is smaller than the current value _{I d,} the current value _{I d} is the current value I _The current value I _e is smaller than the current value _If, which is smaller than _e . The duty ratio of each drive signal 451a, 451b, 451c, 451d, 451e, 451f is the same.

  In other words, a lower current is supplied to the LED 110 that is disposed higher and located closer to the liquid crystal driver 352.

  The current value of each LED 110 is optimally set based on the temperature distribution in the surface region 201 of the LED backlight 200. For example, in a region indicated as a high temperature region in the temperature distribution (for example, the region 201a) due to being positioned relatively upward or relatively close to the liquid crystal driver 352, the current value of the LED 110 Is set relatively low. In addition, the current value of the LED 110 is compared in the region (201c) indicated as the low temperature region in the temperature distribution, for example, because it is located relatively below or relatively far from the liquid crystal driver 352. Highly set. Here, these settings are performed so that the junction temperatures of all the LEDs 110 are equal.

  As a result, among the LEDs 110, the LED 110 that is disposed higher and located closer to the liquid crystal driver 352 emits light with lower luminance. Note that when such drive control is performed, there may be a difference in luminance between the individual LEDs 110. However, since the junction temperatures of all the LEDs 110 are equal, there is no difference in the progress of deterioration with time between the individual LEDs 110. Therefore, even if there is a difference in brightness between the LEDs 110, the balance of the brightness is maintained over a long period of time.

  Further, among the LEDs 110, those that are arranged at a higher position, are located closer to the liquid crystal driver 352, and are supplied with a lower current, are arranged at a higher density and adjacent to the other LEDs 110.

  Moreover, as for the LED backlight 200, the light emitted from the LED 110 is more widely distributed as the arrangement density is lower. Thereby, since the irradiation area | region in the entrance plane of the diffusion plate 130 is expanded, the brightness nonuniformity in the output surface of the diffusion plate 130 can be reduced.

  As a result, uniform luminance is realized over the entire display screen, and it is maintained unchanged over a long period of time.

  The current value I is the same, the duty ratio of the drive signal 451a is smaller than the drive signal 451b, the duty ratio of the drive signal 451b is smaller than the drive signal 451c, and the duty ratio of the drive signal 451c is smaller than the drive signal 451d. The same effect can be obtained by making the duty ratio of the drive signal 451d smaller than the drive signal 451e and making the duty ratio of the drive signal 451e smaller than the drive signal 451f.

  Next, a luminance correction method in the liquid crystal display device 400 will be described.

  FIG. 8 is a diagram for explaining a luminance correction method in the liquid crystal display device 400. Here, a case will be described as an example where the ambient temperature of the region located higher during the lighting of the LED 110 becomes higher.

  The LEDs 110 are arranged at a higher density as the arrangement position is higher. Even by adopting such an LED arrangement, it is possible to correct a difference in luminance reduction of the LED 110 caused by a difference in ambient temperature, and to make the luminance uniform over the entire display screen. This is possible even if drive signals having the same current value are supplied to all the LEDs 110.

  However, in the present embodiment, assuming that drive signals having the same current value are supplied to all the LEDs 110, the LED arrangement is determined so that the luminance in the upper region on the display screen is higher. And after employ | adopting such LED arrangement | positioning, LED110 is supplied with a lower electric current, so that an arrangement position is higher. Thereby, the brightness in the illumination area of the LED 110a (that is, the area of the display screen illuminated by the light emitted from all the LEDs 110a), the brightness in the illumination area of the LED 110b, the brightness in the illumination area of the LED 110c, and the illumination area of the LED 110d The brightness, the brightness in the illumination area of the LED 110e, and the brightness in the illumination area of the LED 110f are uniform.

  The effect of the brightness correction method shown in FIG. 8 will be described in more detail with reference to FIG. FIG. 9A shows an example of the relationship between ambient temperature and relative luminance for the LED backlight 200 in the initial state, and FIG. 9B shows the LED backlight 200 after use for a predetermined time (for example, 10,000 hours). An example of the relationship between the ambient temperature and the relative luminance is shown. In order to simplify the description, only the LEDs 110a and 110f are compared.

  Warm air gathers from the lower region around the LED 110a arranged in the upper region, and the temperature rises. This is because the liquid crystal display device 400 is generally used upright. Also, the fact that it is disposed near the liquid crystal driver 352 that generates heat during operation is a factor that increases the ambient temperature of the LED 110a compared to the LED 110f. Therefore, the brightness of the LED 110a itself is lower than that of the LED 110f.

  Further, the LED 110a is supplied with a current lower than that of the LED 110f (in the example of FIG. 8, the LED 110a is 8.5 mA and the LED 110f is 11 mA). This is also a factor that the luminance of the LED 110a itself is lower than that of the LED 110f.

  However, the LED 110a is arranged at a high density with the LED 110b (in the example of FIG. 8, the vertical distance (pitch) between the LEDs 110a and 110b is 8 mm), whereas the LED 110f is at a low density (the LED 110e in the example of FIG. 8). , 110f are arranged at a vertical interval (pitch) of 12 mm).

Therefore, in the initial state, the luminance in the illumination area of the LED 110a decreases relatively gradually as the ambient temperature of the LED 110a increases (curve C _a1 ), and the luminance in the illumination area of the LED 110f increases with the ambient temperature of the LED 110f. Then, the characteristic that it falls relatively remarkably (curve C _f1 ) is obtained.

In this case, when the LED backlight 200 is turned on, the ambient temperature of the LED 110a becomes 50 ° C., and the relative luminance in the illumination area of the LED 110a becomes B ₁ % (point P _a1 ). In addition, the ambient temperature of the LED 110f is 40 ° C., and the relative luminance in the illumination area of the LED 110f is also B ₁ % (point P _f1 ). Therefore, the luminance is uniform over the entire display screen.

When the accumulated usage time of the LED backlight 200 reaches a predetermined time, the luminance in the illumination area of the LED 110a decreases relatively slowly as the ambient temperature of the LED 110a increases (curve C _a2 ), and the illumination area of the LED 110f The characteristic that the brightness at is relatively remarkably lowered (curve C _f2 ) as the ambient temperature of the LED 110 _f rises is obtained. Here, when the curves C _a1 and C _f1 in FIG. 9A are compared with the curves C _a2 and C _f2 in FIG. 9B, the LEDs 110a and 110f both show deterioration in luminance over time. I understand.

In this case, when the LED backlight 200 is turned on, the ambient temperature of the LED 110a becomes 50 ° C., and the relative luminance in the arrangement region of the LED 110a becomes B ₂ % (point P _a2 ). Further, the ambient temperature of the LED 110f is 40 ° C., and the relative luminance in the arrangement region of the LED 110f is also B ₂ % (point P _f2 ). In other words, although the luminance is deteriorated with time in any region, the progress degree is the same, so the luminance uniformity is maintained over the entire display screen. This is because the deterioration of the LED 110 over time can be reduced by supplying a relatively low current to the LED 110 (the LED 110a in this example), which should be deteriorated over time due to the relatively high ambient temperature. This is because the progress was delayed.

  As described above, according to the present embodiment, a lower current is supplied to the LEDs 110 arranged in a region having a higher ambient temperature in the surface region 201 of the substrate 120 of the LED backlight 200. Thereby, the progress of deterioration with time of all the LEDs 110 provided in the LED backlight 200 is matched. Therefore, the luminance balance can be maintained over a long period of time over the entire display screen. Further, according to the present embodiment, the LED 110 is controlled so as to delay the deterioration with time (that is, with a relatively low current) with respect to the LED 110 that should be deteriorated with time relatively quickly due to the relatively high ambient temperature. Supply). Therefore, the lifetime of the LED backlight 200 can be extended.

  Further, according to the present embodiment, the light emitted from the LED 110 has a wider light distribution as the arrangement density is lower. Thereby, even if it employ | adopts the structure which changes arrangement density and extends lifetime as mentioned above, the brightness nonuniformity in the output surface of the diffusion plate 130 can be reduced.

  In this embodiment, the case where the ambient temperature of the upper region becomes higher is taken as an example, and the LEDs 110 arranged in the upper region are arranged at a higher density and are driven with a lower current. The configuration has been described. However, other configurations are possible.

  For example, when the liquid crystal driver 352 is disposed in the vicinity of the lower end portion of the liquid crystal panel 351 and the ambient temperature of the lower region becomes higher than the upper region, the LED 110 disposed in the lower region is Therefore, it is possible to adopt a configuration in which they are arranged at a higher density and driven with a lower current. In this configuration, the light emitted from the LED 110 may be made wider in the upper region.

  Further, when the liquid crystal driver 352 is disposed in the vicinity of the left end portion of the liquid crystal panel 351, and the ambient temperature of the left region becomes higher than that of the right region, the LED 110 disposed in the left region is Therefore, it is possible to adopt a configuration in which they are arranged at a higher density and driven with a lower current. In this configuration, the light emitted from the LED 110 may be made wider in the right region.

  Further, when the liquid crystal driver 352 is disposed in the vicinity of the right end of the liquid crystal panel 351, and the ambient temperature of the right region is higher than that of the left region, the LED 110 disposed in the right region is connected. Therefore, it is possible to adopt a configuration in which they are arranged at a higher density and driven with a lower current. In this configuration, the light emitted from the LED 110 may be made wider in the left region.

  In short, when the ambient temperature in a region near the liquid crystal driver 352 is higher than the ambient temperature in a region farther than that, the LEDs 110 arranged in the former region are arranged at a higher density and lower. A configuration driven by current can be adopted.

  The same thing as that of the liquid crystal driver 352 applies to a power supply unit, that is, a power supply circuit that supplies power to the liquid crystal driver 352, the LED drive circuit 441, and the like, and other heat generating members. This is because the power supply unit also generates heat. Therefore, the arrangement of the LEDs 110, the drive current value, and the light source distance can be determined according to the arrangement position of the power supply unit or the like.

  Further, even if there is a temperature distribution on the internal structure of the liquid crystal display device 400 such that the ambient temperature in the upper region does not become higher, the arrangement of the LEDs 110, the drive current value, and the The light source distance can be determined.

  In the present embodiment, the LED 110 is a white LED, but the same effect as described above can be obtained when the LED 110 is a combination of LEDs of R (red), G (green), and B (blue). The effect can be realized. In this case, in the high temperature region, a configuration is adopted in which more red LEDs having a large luminance decrease due to temperature are arranged than green LEDs and blue LEDs. Thereby, the balance of the color temperature can be maintained for a long time.

  In addition, when performing a backlight scan for improving the liquid crystal moving image performance by interlocking the lighting of the LED backlight 200 with the scanning of the image display of the liquid crystal panel 351, considering the fact that the pitch of the LEDs in the vertical direction is different, Therefore, it is necessary to control the lighting start time of the LED backlight 200.

  The backlight device and the liquid crystal display device according to the present invention are useful as a backlight device and a liquid crystal display device that can reduce luminance unevenness on the emission surface. For example, the backlight device and the liquid crystal display device according to the present invention are suitable for a thin and low power consumption large screen liquid crystal television.

(A) Schematic front view of LED backlight according to Embodiment 1 of the present invention, (b) Schematic side view of LED backlight according to Embodiment 1 of the present invention The figure which compared the illumination intensity of the emitted light of LED which has a different light distribution characteristic in Embodiment 1 of this invention The figure which shows the structure of the LED backlight which concerns on Embodiment 2 of this invention. The figure which shows the structure of the liquid crystal display device which concerns on Embodiment 3 of this invention. Side view of the principal part of the liquid crystal display device according to Embodiment 4 of the present invention. The figure which shows LED arrangement | sequence of the LED backlight which concerns on Embodiment 4 of this invention. (A) A circuit diagram showing a configuration of an LED drive unit according to Embodiment 4 of the present invention, (b) a waveform diagram showing a drive signal according to Embodiment 4 of the present invention. The figure which shows the brightness | luminance correction method which concerns on Embodiment 4 of this invention. (A) The figure which shows the relationship between ambient temperature and relative brightness | luminance about the LED backlight of the initial state which concerns on Embodiment 4 of this invention, (b) LED after predetermined time progress which concerns on Embodiment 4 of this invention Diagram showing the relationship between ambient temperature and relative brightness for backlight

Explanation of symbols

100, 200 LED backlight 110, 110a, 110b, 110c, 110d, 110e, 110f LED
120 Substrate 130 Diffusion plate 240, 440 LED drive unit 300, 400 Liquid crystal display device 350 Liquid crystal unit 351 Liquid crystal panel 352 Liquid crystal driver 441, 441a, 441b, 441c, 441d, 441e, 441f LED drive circuit

Claims (1)

A backlight device used in a liquid crystal display device having a liquid crystal panel as a display screen,
A substrate having a facing portion disposed facing the back side of the liquid crystal panel;
A plurality of light emitting diodes arranged at a non-uniform arrangement density in the facing portion;
A light diffusing plate that enters the light emitted from the plurality of light emitting diodes, diffuses the incident light, and emits the light to the liquid crystal panel side;
A current supply unit for supplying current to the plurality of light emitting diodes to emit light for illuminating the liquid crystal panel to the plurality of light emitting diodes;
The current supply unit supplies a lower current to the light emitting diodes disposed in a region where the ambient temperature is higher in a region close to the liquid crystal driver that controls the driving voltage of the liquid crystal panel in the region of the facing portion. And
Light-emitting diodes that are supplied with lower current are placed adjacent to other light-emitting diodes with higher density,
Light-emitting diode arrangement density is low position is one that emits light of wide light distribution,
Backlight device.

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