JP2006208510A - Display device using discharge lamp lighting device, and liquid crystal display device having backlight attached thereto - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a display device using a discharge lamp lighting device, which is made not to increase power consumption while improving luminance uniformity, and a liquid crystal display device having a backlight attached thereto. <P>SOLUTION: In the display device equipped with three or more lamps arranged on the rear face side of a display panel, the discharge lamp lighting device to turn on the respective lamps, and a reflection plate to reflect light from the lamps in a direction toward the display panel, a current flowing through the lamp arranged on an edge portion side of the reflection plate in a vertical direction is set to be larger than a current flowing through the lamp arranged on a center portion in the vertical direction. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a display device using a discharge lamp lighting device and a backlit liquid crystal display device, and is used as a backlit display panel such as a liquid crystal television or a liquid crystal monitor or a backlit signboard. is there.

  In recent years, there has been a market demand for development of a liquid crystal panel such as a liquid crystal display device, particularly a liquid crystal television forming a large screen, and space saving or power saving by making the entire device thin. Such a liquid crystal display device usually has a configuration in which polarizing plates are mounted on a light incident side and a light emission side of a liquid crystal panel in which a liquid crystal layer is sandwiched between a pair of glass substrates. That is, an image is displayed by modulating the polarization state of linearly polarized light incident on the liquid crystal panel by the liquid crystal layer.

  At present, a transmissive liquid crystal display device is the mainstream among the liquid crystal display devices. In this transmissive liquid crystal display device, illumination from the back side of the liquid crystal panel is necessary, and the backlight device is an indispensable component.

  Further, the size of the display screen of the liquid crystal panel is currently 12 to 15 type, which is used in a large quantity as a display screen for personal computers. As a backlight device for a liquid crystal panel of this size, a so-called side edge type is currently widely used.

  A liquid crystal display device employing this side-edge type backlight device has a basic structure as schematically shown in FIG. In this liquid crystal display device, a pair of straight tube type lamps b and b are arranged as light sources on the back side of the liquid crystal panel a at positions corresponding to both sides of the liquid crystal panel a, and an acrylic product is provided between the lamps b and b. The light guide plate c is disposed. On the side of the light guide plate c facing the liquid crystal panel a, a polarizing reflection film e is disposed with a diffusion plate d interposed therebetween, while a reflection film f is disposed on each of the lamps b and b. The lamps b and b, the light guide plate c, the diffusion plate d, the polarization reflection film e, and the reflection film f constitute a backlight device.

  In this backlight device, light from the lamps b and b is incident on the light guide plate c directly or through the reflective film f. The light incident on the light guide plate c is converted into a uniform surface light source by the diffusion plate d and polarized to a single light by the polarization reflection film e. This single-polarized light is incident on the liquid crystal panel a and modulated by the input signal, thereby being displayed as an image on the display screen of the liquid crystal panel a.

  Such a side edge type backlight device is suitable for a 12-15 type display screen as described above. However, a display device such as a 28-inch liquid crystal television or the like has some problems in the side edge type.

Normally, the brightness of the monitor screen of the personal computer is the order of 120~200cd / m ^2, it is necessary to screen luminance of 400~600cd / m ² for use as a television. However, in the side-edge type, when the liquid crystal panel a is large, it is impossible to simply increase the number of lamps b and b. It is difficult to make it brighter and there is a limit to the brightness of the liquid crystal screen.

  Therefore, a direct-type backlight system using a fluorescent lamp such as a straight tube or a U-shaped tube is used as a backlight device for large liquid crystal panels, and the screen brightness is increased by increasing the number of fluorescent lamps used according to the screen size. It makes it possible to brighten. In the case of using a plurality of fluorescent lamps in such a direct type backlight system, uniformity of surface luminance has been a problem.

  FIG. 13 is a diagram in which the luminance distribution in a normal backlight device is measured, and it can be seen that the luminance at the edge and the center of the screen is different. Regarding the end portion in the vertical direction, it is considered that the light from the reflection plate decreases as the distance from the end portion increases. Therefore, as a means for improving the uniformity as the surface brightness, a configuration as disclosed in JP-A-6-258639 has been proposed.

  In the backlight system described in JP-A-6-258639, a fluorescent lamp is arranged in a lamp space formed by a reflector and a diffuser. The center arrangement pitch of the light emission straight tube portion of the fluorescent lamp is set to 1.2 to 2.5 times the thickness of the lamp space, and the lamp from the reflector to the center of the light emission straight tube portion of the fluorescent lamp. The space height is set to 1/2 or less of the thickness. As a result, the brightness on the diffusion plate is made uniform without special processing of the reflection plate and the diffusion plate.

However, in the backlight device having the conventional structure as described above, the backlight power is increased by increasing the display area and increasing the display area. Here we compare the large backlight and the backlight of a typical notebook computer. Taking a 14.1-inch display screen as an example of a notebook personal computer and assuming that the screen brightness is 150 cd / m ² , if the display screen of a large LCD TV is 42-inch size and 450 cd / m ² screen brightness, the screen brightness The ratio is about 3 times, and the area ratio is about 9 times. When simply comparing the power consumption of the backlight, the 42 type size is 27 times. Therefore, if the power consumption of the backlight of the 14.1 type notebook personal computer is 10 W, the power consumption of the backlight is greatly increased to 270 W in the 42 type liquid crystal television. Such an increase in power consumption of the backlight device causes an increase in the temperature of the backlight device, which causes a decrease in the reliability of the liquid crystal panel. In addition, when the ambient temperature of the lamp rises and exceeds the optimum temperature of the lamp, the light emission efficiency may decrease and the screen brightness may decrease.

  There is JP-A-2002-82626 as a prior art for solving these problems. According to this publication, the backlight device is composed of a plurality of straight tube fluorescent lamps arranged on the back side of the display panel, a reflector, and a display panel, and the distance between each straight tube fluorescent lamp is set at the center of the display screen of the display panel. The brightness at the center of the screen is improved by setting the screen to be narrower at the screen and wider toward the edge of the display screen. As a result, the power consumption can be reduced when the luminance at the center of the screen is equal to the case where the lamps are arranged at equal intervals.

However, naturally, the brightness difference between the center of the screen and the brightness at the edge of the screen is large, so if the brightness at the center of the screen is the same as when the lamps are equally spaced, the brightness at the edge of the screen will be low, The edge of the screen becomes dark as a liquid crystal television or display panel, making it difficult to see details in the image.
Japanese Patent Laid-Open No. 6-258639 JP 2002-82626 A

  The present invention has been devised to solve the above-described points, and the object of the present invention is to use a discharge lamp lighting device that does not increase power consumption while improving luminance uniformity. An object of the present invention is to provide a display device and a liquid crystal display device with a backlight.

  In order to solve the above problems, the present invention, as shown in FIG. 1, includes three or more lamps 1 arranged on the back side of the display panel, a discharge lamp lighting device for lighting each of the lamps 1, a lamp In a display device including a reflection plate 2 that reflects light 1 toward the display panel, the light flows through a lamp disposed on the vertical end of the reflection plate 2 as shown in FIGS. The current is set to be larger than the current flowing through the lamp disposed in the central portion in the vertical direction.

  According to the present invention, it is possible to provide a display device in which the luminance distribution on the light emitting surface is made uniform without increasing power consumption.

Example 1
At present, an inverter circuit for a cold cathode lamp as shown in FIG. 2 is often used as a lighting device for a backlight device. First, the circuit configuration of the lighting device will be described with reference to FIG. As the inverter circuit HB1, a half bridge circuit is configured by switching elements Q1a and Q2a made of FETs and capacitors C3a and C4a. The primary sides of the leakage transformers T1a and T2a are connected as the output of the half bridge circuit. Lamps La1 and La2 are connected to secondary sides of the leakage transformers T1a and T2a, respectively, and capacitors C5a and C6a are connected in series with the lamps La1 and La2, respectively. The inverter circuit HB2 has a similar configuration.

  IC1 is a control IC for the inverter circuits HB1 and HB2. Here, ROHM BD9884FV is used. The basic operation of the IC 1 is to drive a switching element connected to the outside at a high frequency of several tens of kHz to perform a so-called inverter operation, and to detect a lamp current as a load of the inverter circuit by a lamp current detection means (resistor etc.). Then, control is performed so that the set constant current is obtained. In addition, the lamp connection detecting means (resistor, capacitor, etc.) detect the lamp connection failure, etc., and when the lamp connection is poor, the inverter operation is stopped. It is possible to output a so-called Fail signal that is a High signal output.

  The half-bridge circuit HB1 of this circuit has a leakage current caused by flowing a high-frequency current to the primary side of the leakage transformers T1a and T2a by causing the switching elements Q1a and Q2a to alternately perform on / off operations at a high frequency of several tens of kHz by the IC1. A voltage corresponding to the transformer turns ratio is generated on the secondary side of the transformers T1a and T2a, the leakage transformers T1a and T2a and the capacitors C5a and C6a resonate, and a substantially sinusoidal high-frequency current is supplied to the lamps La1 and La2. Keep the lamp lit stably.

  The other half-bridge circuit HB2 performs the same operation with the same configuration as the half-bridge circuit HB1, and keeps the lamps La3 and La4 lit.

  That is, in the configuration of FIG. 2, the lighting control of the four lamps is performed by the IC1. Here, for example, taking a backlight device of a 32-inch liquid crystal television as an example, some 32-inch backlight devices usually have 16 cold cathode lamps. That is, in order to construct a 32-inch backlight device, four sets are required in the case of the circuit configuration of FIG.

  Usually, the lamp current is set to the same value for all 16 lamps. Here, when the screen brightness was measured, it was as shown in FIG. From this, it can be seen that the vertical brightness is lower than the center of the screen. Thus, in the first embodiment, the luminance difference between the central portion of the screen and the upper and lower end portions is reduced.

  FIG. 1 shows a schematic configuration diagram of the backlight device of the first embodiment viewed from the side. Sixteen lamps 1 are arranged in parallel in the vertical direction in parallel with the reflector 2. Further, a diffusing plate 3 and an optical sheet 4 are arranged in the light emission direction of the lamp 1, and substantially planar light is incident on the liquid crystal panel 5.

  Here, FIG. 3 is a conceptual diagram of the set value of the lamp current and the distribution of the screen brightness in the backlight device. That is, the lamp current is increased toward the upper and lower ends of the screen rather than the central portion of the screen having high luminance. By increasing the lamp current toward the upper and lower ends of the screen, it is possible to increase the luminance of the upper and lower ends of the screen, which tends to be low in the past.

  Here, when the lamp current at the end is increased, the power consumption increases. For example, if the lamp power per lamp when the lamp current is uniform is 6 W, the total backlight device is 6 W × 16 lamps = 96 W. Assuming that the lamp power when the lamp current at the end is increased is 7 W at the end, and the average is about 6.5 W, the total lamp power at this time is 6.5 W × 16 = 104 W. As a result, the lamp power consumption is increased by 8 W. Therefore, heat generation from the lamp and heat generation from the lighting device increase. As a result, the ambient temperature of the space in which the lamp is housed increases, so that the optimum temperature of the luminous efficiency of the lamp may be exceeded. In that case, the temperature tends to be high at the center of the screen in the space in which the lamp is stored. For this reason, the lamp arranged at the center of the screen does not reach the optimum temperature, and the luminance decreases (see the solid line of the luminance distribution in FIG. 3). When the brightness at the center of the screen is lower than the others on a television, it is felt dark as visibility.

  Therefore, as shown in FIG. 4, the current flowing through the lamp arranged at the center of the screen is made smaller than the current of the conventional example, and the ambient temperature is lowered by suppressing the heat generation of the lamp itself arranged at the center of the screen, thereby improving the luminous efficiency. Is prevented from falling. For example, if the lamp power at the center of the screen is 5.5 W, the average is about 6 W, which is the same as when the lamp current is uniform.

  In this way, at the edge of the screen, the current flowing through the lamp is increased to increase the brightness, and at the center of the screen where the temperature tends to be high, the lamp current is decreased to suppress heat generation and not to reduce the luminous efficiency. By doing so, the luminance of the screen can be made uniform while keeping the average luminance the same as the conventional one while preventing the power consumption of the backlight device from increasing (see the solid line of the luminance distribution in FIG. 4).

  In order to set the lamp current as shown in FIG. 4, in the circuit diagram shown in FIG. 2, the so-called resonant capacitors of the capacitors C5a, C5b, C6a, and C6b are changed for each lamp, and the lamps flowing to the respective lamps. The current can be adjusted.

  In addition, since the circuit shown in FIG. 2 is for four lamps, in the backlight device shown in FIG. 1, by setting the lamp current for every four lamps as shown in FIG. If the uniform case is 6 mA, the lamp current setting for each circuit is set to one. For example, the upper four of the backlight device is 6.5 mA, the lower four are 5.5 mA, and the lower four are also The same effect can be obtained even if the setting is 5.5 mA and the lower 4 wires are set to 6.5 mA.

  In this embodiment, the half-bridge method has been described as an example of the inverter. However, any circuit that allows a high-frequency current to flow through the lamp may be used. For example, a full-bridge method may be used.

(Example 2)
FIG. 6 shows a conceptual diagram of the second embodiment. FIG. 6 is a diagram in which the setting of the lamp current on the lower side in the vertical direction in the backlight device is further increased from the upper side in the vertical direction with respect to the conceptual diagram of the lamp current setting in the first embodiment.

  Usually, since the backlight device is installed vertically, the internal temperature of the backlight device is higher on the upper side and lower on the lower side. Therefore, naturally, the lamp ambient temperature is lower on the lower side, so that it tends to be difficult to obtain luminance. In this embodiment, the lamp current is set higher to increase the lower luminance.

  FIG. 7 shows a circuit diagram of this embodiment. In the circuit of FIG. 7, R7b in the circuit of FIG. 2 is replaced with an impedance Z composed of resistors R15 and R16 and the thermistor TH1. Since the resistance value of the thermistor TH1 varies depending on the ambient temperature, the impedance Z is set to be smaller than R7a by installing this circuit below the backlight device. Therefore, IC1 controls the switching element so that the voltage detected by impedance Z becomes the same value as the voltage detected by R7a. Therefore, the current flowing through lamps La3 and La4 increases, and the brightness of lamps La3 and La4 increases. Become.

  With this configuration, the use of a temperature compensation element such as a thermistor makes it possible to achieve uniform brightness. Moreover, it is good also as a structure which enlarges a lower lamp current by providing a temperature sensor in the lower side of a backlight apparatus.

(Example 3)
A basic structural diagram of this embodiment is shown in FIG. In the structure of FIG. 8, the lamp arrangement of FIG. 1 is gradually narrowed from the center to the upper and lower ends rather than at equal intervals. For example, they are arranged in the order of P1, P2, P3, P4, P5, P6, P7 in the order of 38 mm, 37 mm, 36 mm, 35 mm, 34 mm, 33 mm, and 32 mm. As a result, the brightness is increased because the lamp interval is narrowed at the upper and lower ends. Therefore, it is possible to make the luminance uniform as a screen.

  Here, P1> P2>...> P6> P7. However, when attention is paid to the luminance at the upper and lower ends of the screen, for example, P1 = P2 =... = P5> P6 = P7. The configuration may be narrower than that.

  In the third embodiment, the luminance can be made more uniform by combining the first and second embodiments.

Example 4
FIG. 9 shows a basic structural diagram of this embodiment. FIG. 9 shows different types of lamps 1a and 1b instead of the lamp 1 of FIG. Here, the lamp 1a and the lamp 1b are lamps having different light output characteristics such as luminance and luminous flux. In general, it is said that when the lamp diameter is reduced, the luminance is increased, and when the lamp diameter is increased, the luminous flux is increased.

  That is, in FIG. 9, a lamp with a large lamp diameter is arranged at the center of the screen of the backlight device, and a lamp with a small lamp diameter is arranged at the upper and lower ends. By doing so, the luminance at the top and bottom of the screen decreases as shown in FIG. 13 with the same lamp diameter, whereas the luminance at the upper and lower ends can be increased. Therefore, the brightness of the screen is made uniform. Further, by arranging a lamp with a large luminous flux in the center part, it is possible to compensate for the luminous flux as compared with the case where all the lamps are made to have high brightness.

  In addition, it is conceivable that the electric characteristics (lamp voltage, lamp current) of the lamp differ for different inverters for lighting the lamp. Therefore, it is preferable to control every lamp or every four lamps by installing the circuits shown in FIGS. 2 and 7 on the back side of the backlight device in accordance with the number of lamps.

(Example 5)
As the lamp of the backlight device, a lamp with a high voltage of several hundred to several kV (depending on the lamp length) and a lamp current of several mA is often used. FIG. 10 is a schematic diagram for explaining the difference in brightness between the lamp installation state and the high pressure side and low pressure side of the lamp 1. Here, there is a parasitic capacitance Cs between the housing 6 and the lamp 1. When the lamp 1 is lit by the lighting device 7, the current flowing through the parasitic capacitance Cs becomes a leakage current from the lamp. The leakage current is proportional to the potential difference between the lamp 1 and the housing 6, and the lamp becomes brighter toward the high pressure side 12 of the lamp 1, and becomes darker due to the influence of the leakage current when the pressure is low. Therefore, as shown in FIG. 13, the luminance is high on the left side which is the high voltage side, and the luminance is low on the right side which is the low voltage side.

  In the fifth embodiment, attention is paid to the leakage current between the lamp 1 and the housing 6 to reduce the luminance difference between the high voltage side and the low voltage side. FIG. 11 shows a basic structural diagram of the fifth embodiment. FIG. 11 is a view of the backlight device as viewed from above.

  According to the structure of FIG. 11, the distance H1 between the high pressure side and the housing 6 by the lamp 1 and the distance H2 between the low pressure side and the housing 6 are not equal, and the distance H3 between the high pressure side by the lamp 1 and the diffusion plate 3 is also the same. The distance H4 between the low pressure side and the diffusion plate 3 is also not equal. That is, the shape of the housing 6 is configured so that H1> H2, and the arrangement of the lamps 1 is also set such that H3> H4. With this configuration, the difference in luminance between the high voltage side and the low voltage side of the lamp 1 can be reduced, and luminance uniformity can be achieved as a screen.

  In addition, by combining the fifth embodiment and the first to fourth embodiments, it is possible to achieve uniform brightness on the top and bottom and left and right of the screen without increasing the power consumption.

It is a sectional side view of Example 1 of this invention. It is a circuit diagram of Example 1 of the present invention. It is explanatory drawing which shows the lamp current and luminance distribution of Example 1 of this invention. It is explanatory drawing which shows the lamp current and luminance distribution of the example of improvement of Example 1 of this invention. It is explanatory drawing which shows the lamp current and luminance distribution of one modification of Example 1 of this invention. It is explanatory drawing which shows the lamp current and luminance distribution of Example 2 of this invention. It is a circuit diagram of Example 2 of the present invention. It is a sectional side view of Example 3 of the present invention. It is a sectional side view of Example 4 of the present invention. It is principle explanatory drawing of Example 5 of this invention. It is sectional drawing seen from the top of Example 5 of this invention. It is a schematic block diagram of the liquid crystal display device which employ | adopted the conventional backlight device of the side edge type | mold system. It is explanatory drawing which shows the luminance distribution of a prior art example.

Explanation of symbols

1 Lamp 2 Reflector 3 Diffuser 4 Optical Sheet 5 Liquid Crystal Panel

Claims (6)

Three or more lamps arranged on the back side of the display panel;
A discharge lamp lighting device for lighting each of the lamps;
In a display device comprising a reflector that reflects the light of the lamp toward the display panel,
A display using a discharge lamp lighting device, characterized in that a current flowing through a lamp disposed on an end portion side in the vertical direction of the reflector is set larger than a current flowing through a lamp disposed in a central portion in the vertical direction. apparatus. The discharge lamp lighting device according to claim 1, further comprising a temperature compensation element in the discharge lamp lighting device or the display device, wherein the output of the discharge lamp lighting device can be adjusted by the temperature compensation element. Display device. 3. The discharge lamp lighting according to claim 1, wherein a distance between the lamps is set so as to be wide at a center portion in the vertical direction of the display device and narrow toward an end portion side in the vertical direction. A display device using the device. 4. The lamp according to claim 1, which has at least two kinds of lamps having different light output characteristics, and the lamp arranged on the end side in the vertical direction of the reflecting plate is the center in the vertical direction of the reflecting plate. A display device using a discharge lamp lighting device, characterized in that the lamp is brighter than a lamp arranged in a section. 5. The discharge lamp lighting according to claim 1, wherein a distance between the reflector and the lamp and a distance between the display panel and the lamp at one end of the lamp connected to the high-voltage output side of the discharge lamp lighting device are the discharge lamp lighting. A display device using a discharge lamp lighting device, wherein the distance between the reflector and the lamp at the other end of the lamp connected to the low-voltage output side of the device and the distance between the display panel and the lamp are larger . A liquid crystal display device with a backlight, wherein the display panel of the display device using the discharge lamp lighting device according to claim 1 is a liquid crystal panel.

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