JP2000206488A - Backlight device for liquid crystal panel - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a backlight device for a liquid crystal panel, providing an auxiliary light source turned on according to a lowering of an ambient temp. of a cold cathode discharge tube and making a beam incident on the liquid crystal panel. SOLUTION: A cold cathode discharge tube 30 is disposed on back side 11 of a liquid crystal panel 10 to make the beam incident on the liquid crystal panel 10, and an auxiliary light source 40 is disposed on the back side 11 of the liquid crystal panel 10 for making the beam incident on the liquid crystal panel 10, and a temp. sensor detects the ambient temp. of the cold cathode discharge tube 30. Then, a microcomputer controls the auxiliary light source unit 40 so as to increase and decrease the emitted light quantity of the auxiliary light source unit 40, according to the lowering and the increase of the detection temp. of the temp. sensor.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a backlight device for a liquid crystal panel applied to a liquid crystal display device.

[0002]

2. Description of the Related Art Conventionally, for example, in a backlight device of a liquid crystal panel of a liquid crystal display device for a car navigation system, a cold cathode discharge tube is arranged on the back side of the liquid crystal panel, and light is applied to the liquid crystal panel from the back side. Is made incident.

[0003]

By the way, in the above-mentioned backlight device, there is a problem that a phenomenon occurs in which the light incident on the liquid crystal panel is lower than usual at a low temperature such as winter. The cause of this phenomenon is that the luminous efficiency of the cold-cathode discharge tube decreases as the ambient temperature of the cold-cathode discharge tube decreases, as shown in FIG.

[0004] Specifically, a part of the mercury in the vapor state in the cold cathode discharge tube is solidified in accordance with a decrease in the ambient temperature of the cold cathode discharge tube, so that the mercury in the vapor state in the cold cathode discharge tube is reduced. Because. As a result, the radiation intensity of the ultraviolet light generated in response to the glow discharge between the two electrode portions of the cold cathode discharge tube decreases, so that the incident light from the cold cathode discharge tube to the liquid crystal panel decreases as described above.

On the other hand, a cold cathode discharge tube is heated by an electric heater at a low temperature so that mercury solidified in the cold cathode discharge tube is turned into a vapor state. Since it takes time to heat the tube, it is not possible to suppress a decrease in the amount of light from the cold cathode discharge tube to the liquid crystal panel immediately after the cold cathode discharge tube is turned on in a timely manner. In view of the above, the present invention provides a backlight device for a liquid crystal panel, which is provided with an auxiliary light source that is turned on in response to a decrease in the ambient temperature of the discharge tube to make light incident on the liquid crystal panel. The purpose is to:

[0006]

In order to achieve the above object, according to the first aspect of the present invention, there is provided an auxiliary light source (40) disposed on the back surface (11) of a liquid crystal panel to make light incident on the liquid crystal panel. ) And a temperature sensor (60) for detecting the ambient temperature of the discharge tube. The lighting control means (80, 220 to 350) controls the lighting of the auxiliary light source based on the temperature detected by the temperature sensor so as to compensate for the decrease in the light emission amount of the discharge tube. Light is incident on the liquid crystal panel according to the decrease. Therefore, by irradiating the liquid crystal panel with light from both the auxiliary light source and the discharge tube, it is possible to secure a sufficient amount of light to the liquid crystal panel regardless of a decrease in the amount of light emitted from the discharge tube.

Further, in the invention according to claim 2,
As in the first aspect, the lighting control means (8
0, 220 to 350) controls the lighting of the auxiliary light source based on the temperature detected by the temperature sensor so as to compensate for the decrease in the light emission amount of the discharge tube. For this reason, the auxiliary light source emits light to the liquid crystal panel according to a decrease in the amount of light generated by the discharge tube due to the temperature sensor. Therefore, a sufficient amount of light to the liquid crystal panel can be ensured irrespective of a decrease in the amount of light emitted from the discharge tube, as in the first aspect.

Further, in the invention according to claim 3,
The lighting control means controls lighting of the auxiliary light source so as to gradually reduce the amount of light emitted from the auxiliary light source in accordance with an increase in the temperature detected by the temperature sensor. Here, an increase in the temperature detected by the temperature sensor means an increase in the amount of light generated from the discharge tube. Therefore, the amount of light from the auxiliary light source to the liquid crystal panel increases as the amount of light emitted from the discharge tube decreases. Therefore, a stable light amount to the liquid crystal panel can be ensured irrespective of a decrease in the light emission amount of the discharge tube.

Further, in the invention according to claim 4,
The auxiliary light source has a light emitting diode (41a). Here, the light emission amount of the light emitting diode is less affected by a decrease in the ambient temperature than the discharge tube.
For this reason, the function as an auxiliary light source can be sufficiently exhibited without being affected by a decrease in the ambient temperature.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of the present invention will be described with reference to the drawings. (First Embodiment) FIGS. 1 and 2 show a first embodiment of a direct-type backlight device S for a liquid crystal panel 10 applied to a liquid crystal display device for a vehicle according to the present invention.

The backlight device S is provided along the back surface 11 of the liquid crystal panel 10, and as shown in FIG. 1, the backlight device S includes a case 20 having a substantially U-shaped cross section. The backlight device S includes a cold cathode discharge tube 30 and a diffusion sheet 50 housed in a case 20. Note that, in FIG. 1, reference symbol R indicates a reflector. As shown in FIG. 2, the cold cathode discharge tube 30 is formed in a substantially M shape, and the cold cathode discharge tube 30 extends along the back surface 11 of the liquid crystal panel 10 as shown in FIGS. It is arranged via a diffusion sheet 50. The cold cathode discharge tube 30 makes light incident on the diffusion sheet 50. The diffusion sheet 50 diffuses the incident light from the cold cathode discharge tube 30 and enters the liquid crystal panel 10 from the back surface 11 as planar light.

The backlight device S has an auxiliary light source unit 40 housed in the case 20. As shown in FIGS. 1 and 2, the auxiliary light source unit 40 includes three white light emitting diode mounting boards (hereinafter, referred to as white LED boards 41).
Each is electrically connected in series. Each of the white LED boards 41 is configured by electrically connecting a plurality (for example, 14) of white light emitting diodes 41a in series to a rectangular printed board 41b.

The reason why the white light emitting diode is used as the backlight of the auxiliary light source unit 40 is that the white light emitting diode 41a generates light of a color close to the color of the light from the cold cathode discharge tube 30. In addition to this,
This is because the light emitting action of the light emitting diode is less affected by its ambient temperature (low temperature) than that of the cold cathode discharge tube.

Specifically, in the cold cathode discharge tube, a part of the vapor state mercury in the cold cathode discharge tube is solidified as the ambient temperature decreases, so that the amount of light generated due to the decrease in the ambient temperature decreases. I do. In contrast, in the case of light emitting diodes,
Light is emitted by the coupling of electrons and holes at the PN junction of the semiconductor, but the coupling of electrons and holes is hardly affected by a decrease in the ambient temperature of the light emitting diode. For this reason, the light emission amount of the light emitting diode is hardly affected by a decrease in the ambient temperature.

Each of the white LED boards 41 has a light emitting portion of each of the white light emitting diodes 41a connected to the back surface 1 of the liquid crystal panel 10.
As shown in FIG. 2, each of the white LED substrates 41 is disposed along the longitudinal direction of the lower half of the cold cathode discharge tube 30 in the vertical direction. . When the temperature is low, the auxiliary light source unit 40 incidents light on the liquid crystal panel 10 from the back surface through the diffusion sheet 50 in an auxiliary manner.

Incidentally, each white LED board 41 is
The grounds arranged along the lower half of the M-shaped cold cathode discharge tube 30 in the vertical direction are based on the fact that the liquid crystal panel 10 is
When the M-shaped cold cathode discharge tubes 30 are arranged vertically,
The amount of light generated from the lower half of the C-shaped cold cathode discharge tube 30 is lower than that of the M-shaped cold cathode discharge tube 30 when the temperature is low.
It is because it becomes less.

Since the liquid crystal panel 10 is placed upright, the ambient temperature of the lower half of the M-shaped cold cathode discharge tube 30 is reduced by conduction of heat energy in the backlight device S using air as a medium. This is because the temperature becomes lower than the ambient temperature of the upper half of the M-shaped cold cathode discharge tube 30. Hereinafter, an electric circuit configuration for driving the liquid crystal panel 10 and the backlight device S will be described with reference to FIG.

The temperature sensor 60 is disposed directly below the cold cathode discharge tube 30 via a space (see FIG. 1). The temperature sensor 60 detects the temperature of the peripheral portion of the cold cathode discharge tube 30, and the temperature sensor 60 generates a signal (hereinafter, referred to as a temperature signal) indicating the detected temperature. The temperature signal indicates the luminous efficiency of the cold cathode discharge tube 30. The luminous efficiency means conversion efficiency between electric energy applied to the cold cathode discharge tube and light energy generated from the cold cathode discharge tube.

The microcomputer 70 includes a battery B
, And executes a computer program in accordance with the flowcharts shown in FIGS. 4 and 5. The LED drive circuit 80 drives the auxiliary light source unit 40 under the control of the microcomputer 70. The cold cathode drive circuit 90 is controlled by the microcomputer 70 to drive the cold cathode discharge tube 30. The liquid crystal drive circuit 100 drives the liquid crystal panel 10 under the control of the microcomputer 70.

The operation of the liquid crystal display device according to the first embodiment configured as described above will be described. The microcomputer 70 starts the computer program according to the flowcharts shown in FIGS. 4 and 5 when the ignition switch IG is turned on. In step 200, the cold cathode discharge tube 30 is turned on, and the cold cathode drive circuit 90 drives the cold cathode discharge tube 30 under the control of the microcomputer 70. Therefore, the cold cathode discharge tube 30 is turned on, and the light is incident on the liquid crystal panel 10 through the diffusion sheet 50 from the back surface.

Then, in step 210, the liquid crystal panel 1
0, and the liquid crystal driving circuit 100 is controlled by the microcomputer 70 to control the liquid crystal panel 10
Drive. As a result, the liquid crystal panel 10 performs a predetermined display. Next, at step 220, the temperature signal from the temperature sensor 50 is sampled. Hereinafter, sampling data obtained by the sampling is referred to as sampling data Tx.

Thus, at step 230, a comparison between the sampling data Tx and the first comparison data T1 is determined. Note that -20 ° C. is employed as the first comparison data T1, and the first comparison data T1 is stored in the ROM of the microcomputer 70 in advance. Then, in step 230, the sampling data Tx ≦ the first
If it is the comparison data T1, it is determined as YES, and in step 240, the duty ratio D1 (for example, 100%)
Is L as output data from the microcomputer 70.
It is output to the ED drive circuit 80.

As a result, the LED drive circuit 80 causes a current to flow into the auxiliary light source unit 40 based on the duty ratio D1 as output data from the microcomputer 70. Therefore, the auxiliary light source unit 40 emits light according to the current and emits light through the diffusion sheet 50 to the liquid crystal panel 10.
From the back side. Thereafter, the process of step 220 is performed.

Incidentally, as shown in FIG. 6, the duty ratio (%) means the ratio of the high-level period TH to the pulse signal period T0. Therefore, the amount of light generated from the auxiliary light source unit 40 decreases as the duty ratio decreases, as shown in FIG. The data of the duty ratio D1 is stored in the ROM of the microcomputer 70 in advance.
Is stored in

If it is determined in step 230 that the sampling data Tx> the first comparison data T1, the determination is NO, and in step 250, the comparison between the sampling data Tx and the second comparison data T2 is determined. The second
As the comparison data T2, -10 ° C. is adopted, and the second comparison data T2 is stored in the ROM of the microcomputer 70 in advance.

In step 250, if sampling data Tx ≦ first comparison data T2, YES
In step 260, the duty ratio D2 (for example, 80%) lower than the duty ratio D1 is output to the LED drive circuit 80 as output data from the microcomputer 70. As a result, the LED driving circuit 80
Causes a pulse current to flow into the auxiliary light source unit 40 based on the duty ratio D2 as output data from the microcomputer 70.

Accordingly, the auxiliary light source unit 40 emits light in response to the pulse current and makes the light incident on the liquid crystal panel 10 through the diffusion sheet 50 from the back surface. Thereafter, the process of step 220 is performed. The data of the duty ratio D2 is stored in the ROM of the microcomputer 70 in advance. If it is determined in step 250 that the sampling data Tx> the second comparison data T2, the determination is NO, and in step 270, the sampling data Tx
Is compared with the third comparison data T3.

The third comparison data T3 is 0 °
C, and the third comparison data T3 is stored in the ROM of the microcomputer 70 in advance.
Then, in step 270, the sampling data Tx ≦
If it is the third comparison data T3, YES is determined,
At step 280, a duty ratio D3 (for example, 70%) lower than the duty ratio D2 is output to the LED drive circuit 80 as output data from the microcomputer 70.

As a result, the LED drive circuit 80 causes a pulse current to flow into the auxiliary light source unit 40 based on the duty ratio D3 as output data from the microcomputer 70. Accordingly, the auxiliary light source unit 40 emits light in response to the pulse current and makes the light incident on the liquid crystal panel 10 from the back surface through the diffusion sheet 50. Thereafter, the process of step 220 is performed. The data of the duty ratio D3 is stored in the ROM of the microcomputer 70 in advance.

If it is determined in step 270 that the sampling data Tx> the third comparison data T3, the determination is NO, and in a step 290, the comparison between the sampling data Tx and the fourth comparison data T4 is determined. The fourth
20 ° C. is used as the comparison data T4,
The fourth comparison data T4 is stored in the ROM of the microcomputer 70 in advance.

If it is determined in step 290 that sampling data Tx ≦ fourth comparison data T4, YES
In step 300, the duty ratio D4 (for example, 55%) lower than the duty ratio D3 is output to the LED drive circuit 80 as output data from the microcomputer 70. As a result, the LED driving circuit 80
Causes a pulse current to flow into the auxiliary light source unit 40 based on the duty ratio D4 as output data from the microcomputer 70.

Therefore, the auxiliary light source unit 40 emits light in response to the pulse current and makes the light incident on the liquid crystal panel 10 through the diffusion sheet 50 from the back surface. Thereafter, the process of step 220 is performed. The data of the duty ratio D4 is stored in the ROM of the microcomputer 70 in advance. If it is determined in step 290 that the sampling data Tx> the fourth comparison data T4, the determination is NO, and in step 310, the sampling data Tx
Is compared with the fifth comparison data T5.

The fifth comparison data T5 is 40
° C, and the fourth comparison data T4 is stored in the ROM of the microcomputer 70 in advance. Then, in step 310, the sampling data T
If x ≦ the fifth comparison data T5, it is determined as YES, and in step 320, the duty ratio D5 (for example, 40%) lower than the duty ratio D4 is output from the microcomputer 70 to the LED driving circuit 80 as output data. Is output.

As a result, the LED drive circuit 80 causes a pulse current to flow into the auxiliary light source unit 40 based on the duty ratio D5 as output data from the microcomputer 70. Accordingly, the auxiliary light source unit 40 emits light in response to the pulse current and makes the light incident on the liquid crystal panel 10 from the back surface through the diffusion sheet 50. Thereafter, the process of step 220 is performed. The data of the duty ratio D5 is stored in the ROM of the microcomputer 70 in advance.

If it is determined in step 310 that the sampling data Tx> the fifth comparison data T5, the determination is NO, and in a step 330, the comparison between the sampling data Tx and the sixth comparison data T6 is determined. The sixth
As the comparison data T6, 60 ° C. is adopted,
The sixth comparison data T6 is stored in the ROM of the microcomputer 70 in advance.

If it is determined in step 330 that sampling data Tx ≦ sixth comparison data T6, YES
In step 340, the duty ratio D6 (for example, 20%) lower than the duty ratio D5 is output to the LED drive circuit 80 as output data from the microcomputer 70. As a result, the LED driving circuit 80
Causes a pulse current to flow into the auxiliary light source unit 40 based on the duty ratio D6 as output data from the microcomputer 70.

Therefore, the auxiliary light source unit 40 emits light in response to the pulse current and makes the light incident on the liquid crystal panel 10 via the diffusion sheet 50 from the back surface. Thereafter, the process of step 220 is performed. The data of the duty ratio D6 is stored in the ROM of the microcomputer 70 in advance. If it is determined in step 330 that the sampling data Tx> the sixth comparison data T6, the determination is NO, and in step 350, a light-off process is performed. As a result, the auxiliary light source unit 40 is controlled by the microcomputer 60 to turn off the LED drive circuit 80.

As described above, if the sampling data Tx (the ambient temperature of the cold cathode discharge tube 30) ≦ the sixth comparison data T6 (60 ° C.), the LED driving circuit 80
Drives the auxiliary light source unit 40 under the control of the microcomputer 70. For this reason, the auxiliary light source unit 40 makes light incident on the liquid crystal panel 10. Therefore, a sufficient amount of light to the liquid crystal panel 10 can be ensured regardless of a decrease in the amount of light emitted from the cold cathode discharge tube 30.

The duty ratio as output data from the microcomputer 70 to the LED drive circuit 80 decreases as the ambient temperature of the cold cathode discharge tube 30 increases. At the same time, the duty ratio is set to
It increases as the ambient temperature of 0 decreases. Here, an increase in the ambient temperature of the cold cathode discharge tube 30 means an increase in the amount of light generated from the cold cathode discharge tube 30, and a decrease in the ambient temperature of the cold cathode discharge tube 30 occurs in the cold cathode discharge tube 30. It means a decrease in the amount of light.

For this reason, the current from the LED drive circuit 80 to the auxiliary light source unit 40 decreases as the amount of light generated from the cold cathode discharge tube 30 increases. With this, LE
The current from the D drive circuit 80 to the auxiliary light source unit 40 is
It increases as the amount of light generated from the cold cathode discharge tube 30 decreases. Therefore, the liquid crystal panel 1 is
The amount of light to zero decreases with an increase in the amount of light from the cold cathode discharge tube 30 to the liquid crystal panel 10, while it increases with a decrease in the amount of light from the cold cathode discharge tube 30 to the liquid crystal panel 10 (see FIG. 8). In FIG. 8, reference numeral H indicates the luminous intensity of the auxiliary light source unit 40, and reference numeral K indicates the luminous intensity of the cold cathode discharge tube 30.

Therefore, the light quantity to the liquid crystal panel 10 can be sufficiently ensured irrespective of the fluctuation of the light emission quantity of the cold cathode discharge tube 30. Further, since the white light emitting diode 41a is employed as the backlight of the auxiliary light source unit 40 as described above, the auxiliary light source unit 40 generates light having a color close to the emission color of the cold cathode discharge tube 30. Therefore, when the auxiliary light source unit 40 is turned on, the liquid crystal panel 1
There is no sense of incongruity in the visual recognition of the display of 0.

As described above, the light emitting action of the light emitting diode 41a is less likely to be affected by the ambient temperature than the cold cathode discharge tube 30. For this reason, the auxiliary light source unit 40
Is generated without changing the amount of light as the ambient temperature decreases. Therefore, a sufficient amount of light to the liquid crystal panel 10 can be ensured irrespective of the low ambient temperature of the cold cathode discharge tubes 30. (Second Embodiment) FIGS. 9 and 10 show a second embodiment of the present invention.

In the second embodiment, as shown in FIGS. 9 and 10, the liquid crystal display device includes an edge-light type backlight device SA instead of the direct-type backlight device S. The backlight device SA is disposed along the back surface 11 of the liquid crystal panel 10 substantially as in the first embodiment. FIG. 9 is a cross-sectional view of the backlight device SA taken along line 9-9 shown in FIG.

The backlight device SA includes a case 20A having a substantially U-shaped cross section. The case 20A is mounted along the back surface 11 of the liquid crystal panel 10 at the annular opening 21 thereof. The backlight device SA has a case 2
The light guide plate 110 is provided together with the diffusion sheet 50 housed in 0A. The light guide plate 110 is disposed along the back surface 11 of the liquid crystal panel 10 through the opening 21 of the case 20A and the diffusion sheet 50 on the front surface 111 thereof.

The upper and lower incident end faces 1 of the light guide plate 110
When light is incident from 10a by both upper and lower cold cathode discharge tubes 30A, which will be described later, these lights are multiply reflected within the light guide plate 110 and propagated, and are finally diffused through the diffusion sheet 50 and become planar light. The light is emitted to the liquid crystal panel 10. The backlight device SA includes both upper and lower linear cold-cathode discharge tubes 30 </ b> A housed in a case 40. As shown in FIG. 9, the upper cold cathode discharge tube 30A is located between the upper incident end face 110a of the light guide plate 110 and the upper side wall 21 of the case 20A. 110 is provided along the upper incident end face 110a. The upper cold cathode discharge tube 30 </ b> A makes linear light incident on the upper incident end face 110 a of the light guide plate 110.

As shown in FIG. 9, the lower cold cathode discharge tube 30A is located between the lower incident end face 110a of the light guide plate 110 and the lower side wall 21 of the case 20A. The cathode discharge tube 30 </ b> A is disposed on the lower incident end face 1 of the light guide plate 110.
Arranged along 10a, linear light is incident on the lower incident end face 110a of the light guide plate 110. Backlight device SA
Has an auxiliary light source unit 40A. As shown in FIG. 9, the auxiliary light source unit 40A includes four white light emitting diode mounting boards (hereinafter, referred to as white LED boards 41A).
Each is electrically connected in series. Each of the white LED boards 41A is configured by electrically connecting a plurality of (for example, six) white light emitting diodes 41a in series to a triangular printed board 42b.

Each of the white LED boards 41A is arranged such that the light emitting portion of each of the white light emitting diodes 41a is connected to the back surface 1 of the light guide plate 110.
12, each of these white LED substrates 41A is located at each corner of the light guide plate 110, as shown in FIG. When the temperature is low, the auxiliary light source unit 40 </ b> A additionally enters light from the back surface 112 of the light guide plate 110 via the diffusion sheet 50.

Incidentally, the grounds for arranging the respective white LED substrates 41A at the respective corners of the light guide plate 110 are that the amount of light generated from the longitudinal end of the rod-shaped cold cathode discharge tube 30A is as follows when the temperature is low. This is because it is smaller than the central portion in the longitudinal direction. In the second embodiment, the temperature sensor 60
As shown in FIGS. 9 and 10, is disposed on the back surface of the light guide plate 110 via the diffusion sheet 50, and the temperature sensor 60 is located in the vicinity of the lower cold cathode discharge tube 30A. The cold-cathode tube circuit 90 drives both the cold-cathode discharge tubes 30A instead of the cold-cathode discharge tubes 30 described in the first embodiment, and the LED driving circuit 80 is an auxiliary light source unit described in the first embodiment. Auxiliary light source unit 40A instead of 40
Drive. Other configurations are the same as those of the first embodiment.

In the second embodiment constructed as described above, the microcomputer 70 turns on the ignition switch IG according to the flowcharts shown in FIGS. 4 and 5 substantially in the same manner as in the first embodiment. , Start the computer program. In step 200, a process of lighting both cold cathode discharge tubes 30 is performed, and both cold cathode driving circuits are controlled by the microcomputer 70 to drive both cold cathode discharge tubes 30A.

Therefore, both cold cathode discharge tubes 30A are
Light enters the light guide plate 110 from both upper and lower incident end faces 110a. Then, these lights are multiply reflected in the light guide plate 110 and propagated, diffused through the diffusion sheet 50, and emitted to the liquid crystal panel 10 as planar light. Thereafter, the processing of steps 200 to 330 is performed substantially in the same manner as in the first embodiment.

Therefore, substantially in the same manner as in the first embodiment, the sampling data Tx (lower cold cathode discharge tube 30A
If (the ambient temperature of the data) ≦ the sixth comparison data T6 (60 ° C.), the LED drive circuit 80A is controlled by the microcomputer 70 to drive the auxiliary light source unit 40A. For this reason, the auxiliary light source unit 40A is
Light enters the liquid crystal panel 10 via the diffusion sheet 10 and the diffusion sheet 50.

Accordingly, even though the ambient temperature of the lower cold cathode discharge tube 30A is low (60 ° C. or less), a sufficient amount of light to the liquid crystal panel 10 can be secured. Other effects are substantially the same as those of the first embodiment. In the second embodiment, an example in which the auxiliary light source unit 40A is disposed on the back surface 112 of the light guide plate 110 via the diffusion sheet 50 will be described.
0A may be provided along the end face of the light guide plate 110.

Further, in each of the above embodiments, the example in which the auxiliary light source unit has a white LED has been described. However, the present invention is not limited to this, and another backlight such as a discharge tube may be employed. In practicing the present invention, a hot cathode discharge tube, a fluorescent tube, or the like may be employed instead of the cold cathode discharge tube.

[Brief description of the drawings]

FIG. 1 is a sectional view showing a first embodiment of the present invention.

FIG. 2 shows a cold cathode discharge tube, an auxiliary light source unit,
It is a rear view showing a diffusion sheet and a liquid crystal panel.

FIG. 3 is a block diagram showing an electric circuit configuration of the first embodiment.

FIG. 4 is a flowchart showing a part of the operation of the microcomputer in FIG. 4;

FIG. 5 is a flowchart showing the rest of the operation of the microcomputer of FIG. 4;

FIG. 6 is a timing chart for explaining a duty ratio which is output data from a microcomputer to an auxiliary light source unit.

FIG. 7 is a timing chart showing a change in the amount of light generated from the auxiliary light source unit according to a change in the duty ratio.

FIG. 8 is a timing chart showing changes in luminous intensity of both the auxiliary light source unit and the cold cathode discharge tubes.

FIG. 9 is a sectional view showing a second embodiment of the present invention.

FIG. 10 is a rear view showing the cold cathode discharge tube, the auxiliary light source unit, the diffusion sheet and the light guide plate shown in FIG.

FIG. 11 is a timing chart showing luminous efficiency of a cold cathode discharge tube.

[Explanation of symbols]

10: liquid crystal panel, 11: back of liquid crystal panel, 30, 3
0A: cold cathode discharge tube, 40, 40A: auxiliary light source unit, 41a: white light emitting diode, 70: microcomputer, 100: light guide plate, 110: incident end face.

Claims (4)

[Claims] 1. A discharge tube (3) disposed on the back surface (11) side of a liquid crystal panel (10) and receiving light to the liquid crystal panel.
0) a backlight device for a liquid crystal panel comprising: an auxiliary light source (40) disposed on the back surface (11) side of the liquid crystal panel to make light incident on the liquid crystal panel; Temperature sensor to detect (60)
And a lighting control means (80, 220 to 350) for controlling lighting of the auxiliary light source so as to compensate for a decrease in the light emission amount of the discharge tube based on the temperature detected by the temperature sensor. Backlight device for panel. 2. A light guide plate (110) disposed along the back surface (11) of the liquid crystal panel (10) for making incident light incident on the liquid crystal panel from the back surface, and an incident end surface (110a) of the light guide plate. And a discharge tube (30A) disposed along the light guide plate and allowing light to enter the light guide plate from the incident end face thereof as the incident light, the backlight device for a liquid crystal panel being provided on the back surface (11) side of the liquid crystal panel. An auxiliary light source (40A) that is disposed to allow light to enter the liquid crystal panel; and a temperature sensor (60) that detects an ambient temperature of the discharge tube.
And a lighting control means (80, 220 to 350) for controlling lighting of the auxiliary light source so as to compensate for a decrease in the light emission amount of the discharge tube based on the temperature detected by the temperature sensor. Backlight device for panel. 3. The lighting control means controls the lighting of the auxiliary light source so as to gradually decrease the amount of light emitted from the auxiliary light source in accordance with an increase in the temperature detected by the temperature sensor. Or the backlight device for a liquid crystal panel according to 2. 4. The auxiliary light source comprises a light emitting diode (41).
2. The method according to claim 1, wherein the method comprises: a).
Or the backlight device for a liquid crystal panel according to 2.