JP2002164185A - Illumination device, backlight device and liquid crystal display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an illumination device that prevents leak current between the cold-cathode tube and the reflector, lowering of brightness by leak current between the both cold-cathode tubes and the shortening of the life of the cold- cathode tube when plural cold-cathode tubes are lighted at the same time, and a backlight device and a liquid crystal device using the illumination device. SOLUTION: The illumination device which illuminates the light guiding plate 3 for supplying backlight to the liquid crystal panel is comprised of plural cold-cathode tubes 2 and an inverter 1 that drives the cold-cathode tubes 2 arranged adjoined to each other out of plural cold-cathode tubes 2 by a drive voltage of same frequency, same phase and same size.

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 illuminating a liquid-phase panel from behind, which is used for a display device of a personal computer, a liquid crystal monitor, and a liquid crystal display device such as a liquid crystal television. Also,
The present invention also relates to a liquid crystal display device using a backlight device.

[0002]

2. Description of the Related Art In recent years, flat panel displays have been widely applied because they are flat, have no depth, and are lightweight. Among them, liquid crystal displays are used in a wide variety of applications, and their application to projectors, video cameras, portable information terminals, notebook personal computers (PCs) and the like is particularly well known. One example is a liquid crystal monitor shown in FIG. The liquid crystal monitor 100 includes a cold-cathode fluorescent tube (hereinafter, referred to as a “cold-cathode tube”) 2 and an inverter 101 for driving the cold-cathode tube 2, which are arranged around the liquid crystal panel 6.

In general, a liquid crystal display is provided with a separate light source because the liquid crystal itself does not emit light, and display is performed by controlling the transmittance of light from the light source. Therefore, it is necessary to provide a backlight device for illuminating from the back of the liquid crystal panel in order to secure the screen luminance to some extent and to ensure better display quality.

FIG. 20 shows an example of a conventional backlight device. As shown in the figure, the backlight device 111 illuminates the liquid crystal panel 6 from the back. The mainstream of the backlight device uses a fluorescent tube luminous body such as the cold cathode tube 2. As a structure of the backlight device, a cold cathode tube 2 as a light source is disposed immediately below a diffusion plate 210 as shown in FIG. 21 and a reflector 4 is disposed on the back of a liquid crystal lighting device to efficiently illuminate the diffusion plate 5. There is known a "direct light type" which illuminates the diffusion plate 5 by irradiating light from the side surface of the light guide plate 3 with the cold cathode tube 2 as shown in FIG. In the case of the edge light type, a reflector 4 is arranged around the cold cathode tube 2 so that light from the cold cathode tube 2 is efficiently incident on the light guide plate 3. A reflection sheet is disposed on the back surface of the light guide plate 3 so as to efficiently illuminate the diffusion plate 5.

In general, in a backlight device, a cold cathode tube having a cold cathode structure in which electrodes for discharge have no heater is used. Since the cold-cathode tube has a cold-cathode structure, the discharge starting voltage for starting discharge and the sustaining voltage for maintaining discharge are very high. In general, a cold-cathode tube used in a 14-inch class liquid crystal display has a discharge sustaining voltage of 800 Vrms and a discharge starting voltage of 130 Vrms.
About 0 Vrms is required.

[0006] The demand for smaller and more efficient liquid crystal displays also requires smaller and more efficient backlight devices, and it is necessary to increase the light use efficiency and reduce the power consumption.

In order to increase the conversion efficiency of an inverter for a backlight device, it is necessary to improve the conversion efficiency of a step-up transformer. For this purpose, the operating frequency is set higher, and the frequency is further increased from 40 kHz to 60 kHz. When the operating frequency is increased, the light use efficiency of the cold-cathode tube is increased, so that it is desirable even when viewed from the entire backlight device.

[0008]

However, for example, in the case of the edge light system shown in FIG. 22, an optical system for effectively collecting the light emitted from the fluorescent tube in the target direction around the cold cathode tube 2 is provided. A reflector 4 is provided.
In order to increase the reflectance of the light from the light source, the reflector 4 is formed by depositing a metal having a high reflectance such as silver or aluminum on a plastic film. The reflector 4 is grounded for safety.

As shown in FIG. 23, since the reflector 4 is disposed over the entire length of the cold cathode tube 2, a large stray capacitance 11 is generated between the cold cathode tube 2 and the reflector 4.
For example, a stray capacitance of about 10 pF is generated, and a leakage current generated through this stray capacitance has a frequency of 60 kHz and a voltage of 8
In the case of 00 Vrms, it is about 3 mA, which is a value that cannot be ignored even from the viewpoint of the discharge current of the cold cathode tube 2 of 6 mA.

As described above, on the secondary side of the inverter for the backlight device, in addition to the high voltage, the frequency is high as described above, and the leakage current leaking through the stray capacitance becomes relatively large. Since such a leakage current is not caused by the luminance, it is not only a useless current but also supplied to the inverter as reactive power, so that the circuit can be downsized,
This is one of the factors that hinder high efficiency. Furthermore, if the size of the liquid crystal display is increased and the lighting start voltage and the lighting maintenance voltage are increased due to the lengthening of the cold cathode tubes 2, the voltage is increased.
It is thought that this leakage current will increase further.

Further, when a plurality of cold-cathode tubes are arranged close to each other in a conventional liquid crystal backlight device with an increase in the size of a liquid crystal screen, the following problem occurs. That is, since each CCFL is lit with a drive voltage having a different frequency and a different phase, leakage current between adjacent CCFLs and interference such as beats are likely to occur. There is a problem that the brightness of the cold-cathode tube varies when the tube is turned on.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems, and provides a lighting device for reducing a stray capacitance generated between a cold-cathode tube and a reflector or a leakage current due to a stray capacitance between cold-cathode tubes. The purpose is to do. Another object of the present invention is to provide a liquid crystal lighting device that can be turned on without causing a decrease in efficiency due to an increase in the size of a liquid crystal screen and without being affected by interference between cold cathode tubes. Another object of the present invention is to provide a liquid crystal display device which is small and consumes less power.

[0013]

A first illuminating device according to the present invention is an illuminating device for illuminating an object to be illuminated, comprising a plurality of cold cathode tubes for emitting light for illuminating the object to be illuminated; A cold-cathode tube driving device for driving the cold-cathode tube at high frequency.
The cold-cathode tube driving device drives the cold-cathode tubes arranged in close proximity,
Driving is performed with driving voltages having substantially the same phase, substantially the same voltage, and substantially the same frequency.

A second illuminating device according to the present invention is an illuminating device for illuminating an object to be illuminated, wherein a plurality of cold cathode tubes for emitting light for illuminating the object to be illuminated, and the cold cathode tubes are illuminated with high frequency And a cold-cathode tube driving device. The cold-cathode tube driving device has a drive voltage input to one of the electrodes of the cold-cathode tube and a drive voltage input to the other of the electrodes of the cold-cathode tube having substantially the same phase.
It is controlled so as to differ by 80 °.

In the above illuminating device, the CCFL driver may be composed of a piezoelectric transformer, and a plurality of CCFLs connected to the CCFL driver may be connected in series.

Further, the cold-cathode tube driving device may turn on the cold-cathode tube using a resonance operation of a leakage inductor of the step-up transformer and a capacitor connected in parallel to the cold-cathode tube. Are connected in series.

The shape of the cold cathode tube may be U-shaped or L-shaped.

[0018] In the above-mentioned lighting device, the lighting device may include two L-shaped cold cathode tubes and a cold cathode tube driving device for driving the two L-shaped cold cathode tubes at high frequency. Two L
In order to illuminate the object to be illuminated from four directions with the C-shaped cold cathode tubes, one of the L-shaped cold cathode tubes is arranged along two adjacent sides of the illuminated object, and the other of the cold cathode tubes is connected Preferably, it is arranged along the remaining two sides of the light plate. It is preferable that the cold-cathode tube driving device is disposed on the back surface of the light emitting surface of the illuminated body.

A third illuminating device according to the present invention is an illuminating device for illuminating an object to be illuminated, wherein a plurality of cold cathode tubes for emitting light for illuminating the object to be illuminated and a lamp for lighting the cold cathode tubes are provided. And a plurality of cold-cathode tube driving devices provided for each of the cold-cathode tubes and configured by a piezoelectric transformer. The lead wire connected to the high-voltage side terminal of the cold-cathode tube is wired along the periphery of the illuminated body, and the lead wire connected to the low-voltage side terminal of the cold-cathode tube is connected to the central portion of the illuminated body. It is wired to pass near. The plurality of cold cathode tubes are driven at substantially the same drive frequency.

It is preferable that the cold-cathode tube driving device is constructed using a piezoelectric transformer having balanced output characteristics.

The cold-cathode tube driving device may turn on the cold-cathode tube by using a resonance operation of a leakage inductor of the step-up transformer and a capacitor connected in parallel to the cold-cathode tube.

When a reflector is provided around the cold cathode tube, it is preferable that the reflector is not grounded.

A backlight device according to the present invention includes the above-described illumination device, and further includes, as an object to be illuminated, a light guide plate for emitting light illuminated by the illumination device onto a surface. Then, another illuminated body is illuminated from the back by the light emission of the light guide plate.

A liquid crystal display device according to the present invention includes the above-mentioned backlight device and a liquid crystal display panel as another illuminated object.

[0025]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of a lighting device, a backlight device and a liquid crystal display device according to the present invention will be described below in detail with reference to the accompanying drawings.

(Embodiment 1) A first embodiment of a backlight device according to the present invention will be described with reference to FIGS.

FIG. 1 is a plan view of the backlight device according to the first embodiment. As shown in FIG. 1, the backlight device includes a lighting device including an inverter 1 and a cold cathode tube 2, and a light guide plate 3. The cold cathode tubes 2 are arranged along two long sides around the light guide plate 3 and illuminate the light guide plate 3 from two directions on the long side of the light guide plate 3. The inverter 1 is arranged on one of the short sides of the light guide plate 3 or on the back surface of the light guide plate 3. The other short side of the light guide plate 3 is used for leading a lead wire.

FIG. 2 is a diagram showing a part of the configuration of the liquid crystal display device. In FIG. 2, the backlight device further includes a reflector 4. In addition, a diffusion plate 5 and a liquid crystal panel 6 are further added to this backlight device to constitute a liquid crystal display device. FIG. 3 is a cross-sectional view of the backlight device shown in FIG. 2 taken along a plane orthogonal to the longitudinal direction. That is, in FIG. 3, the cold cathode tube 2 extends in a direction perpendicular to the paper surface.

The cold-cathode tube 2 is turned on by the high-voltage power output from the inverter 1. Light emitted from the illumination device (cold cathode tube 2) is efficiently radiated by the reflector 4 to the light guide plate 3 made of acrylic resin or the like. The light guide plate 3 propagates light in a plane direction. The reflection sheet 7 is also attached to the back surface of the light guide plate 3, whereby the light from the cold cathode tubes 2 is effectively illuminated on the liquid crystal panel 6 through the diffusion plate 5.

The operation of the backlight device configured as described above will be described. The inverter 1 is an electromagnetic transformer type inverter as shown in FIG. 4 and includes a driving unit 20 driven by a DC power supply to generate an AC signal, and an electromagnetic transformer T. Generally, in the case of an electromagnetic transformer type inverter, a ballast capacitor C is connected in series with the cold cathode tube 2 on the secondary side, and limits a current flowing into the cold cathode tube 2. The voltage input to the primary side of the electromagnetic transformer T is multiplied by the number of turns and taken out from the secondary side as high-voltage power. The extracted high-voltage power is applied to the cold cathode tube 2, and the cold cathode tube 2 is turned on. At this time, as shown in FIG. 5, a stray capacitance 11 exists between the reflector 4 and the cold-cathode tube 2, which causes a leakage current (leakage current).

Returning to FIG. 1, two cold cathode tubes 2 are connected in series, and two sets of the cold cathode tubes 2 connected in series are electrically connected in parallel to the inverter 1. I have. These cold-cathode tubes 2 are operated at 30 kHz to 200 kHz.
The lamp is lit at a high frequency to improve the lamp efficiency.

FIG. 6 is a diagram showing a driving waveform of the cold cathode tubes 11 and a waveform of a potential difference between the respective cold cathode tubes 11. FIG.
In (c), (d) and (e), the horizontal axis of the waveform is arbitrary. FIG. 6A shows a voltage waveform of a driving voltage (hereinafter, referred to as “first driving voltage”) applied to one set of the cold cathode tubes 2, and FIG. 6B shows another set of the cold cathode tubes. 2 shows a voltage waveform of a drive voltage (hereinafter, referred to as a “second drive voltage”) applied to the second drive voltage. When each set of the cold cathode tubes 2 is driven to have the same amplitude, frequency, and phase between the first drive voltage and the second drive voltage, as shown in FIG. The potential difference between one set of cold cathode tubes and the other set of cold cathode tubes is 0V. However, when the phase is shifted by 60 ° between the first drive voltage and the second drive voltage, as shown in FIG. 6D, between one set of cold cathode tubes and another set of cold cathode tubes. (Correctly, a potential difference occurs when there is a phase shift). Further, when the frequency shifts between the first drive voltage and the second drive voltage, a potential difference as shown in FIG. 6E is generated, and the luminance becomes inconsistent. However, in practice, the driving voltage is slightly different due to variations in the characteristics of the cold cathode fluorescent lamp.

In the backlight device of this embodiment,
The inverter 1 has substantially the same phase with respect to the two sets of the cold cathode tubes 2,
The drive voltage is controlled so that voltages having substantially the same voltage and substantially the same frequency are applied. Here, substantially the same phase, substantially the same voltage and substantially the same frequency are used when the drive voltage phase, the voltage value, and the frequency are not exactly the same, but they are almost the same if they are substantially the same. This is because an effect can be obtained. By such control, the potential difference between the two sets of cold cathode tubes 2 is reduced as shown in FIG.
As shown in (c), the value becomes zero, thereby reducing the occurrence of leakage current due to the floating capacitance 11 between the reflector 4 and the cold cathode tube 2.

The backlight device according to the present embodiment having the above-described configuration and drive has the following advantages. (1) To drive at substantially the same voltage, substantially the same frequency, and substantially the same phase,
Leak current can be reduced. (2) Since the leakage current between the cold cathode tubes 2 arranged close to each other is small, the brightness of the cold cathode tubes 2 can be made substantially uniform. (3) Since the leak current is small, the consumption of the electrodes of the cold cathode tube 2 is small, and the life of the cold cathode tube 2 can be extended. (4) Since the leak current is small, the efficiency of the inverter 1 can be increased.

An example of the result of verifying the characteristics of the backlight device of the present embodiment will be described. For example, the diameter of the cold cathode tube 2 is 2.
When the light guide plate 3 is 15 inches in size and the lighting frequency of the cold cathode tube 2 is 6 mm, the length is 280 mm, and the lighting frequency of the cold cathode tube 2 is 60 kHz, the input power required to flow the rated current of the cold cathode tube 2 of 6 mA is 9.3 W. Was. Further, with regard to luminance, it was possible to light the cold cathode fluorescent lamp 2 with substantially uniform luminance.

When the cold-cathode tube 2 is turned on without considering the phase, frequency and voltage as in the prior art, the electric power required to flow the same rated current of 6 mA is 10.2 W. Further, the brightness of the cold cathode tube was sparse.

That is, by using the backlight device of the present embodiment, it is possible to reduce or prevent a leak current between the cold cathode tubes due to a voltage difference between the cold cathode tubes, thereby improving the luminous efficiency. . As a result, the life of the cold cathode tube electrodes can be prolonged, the luminance can be made uniform, and the efficiency of the inverter circuit can be increased.

In the backlight device of this embodiment,
The piezoelectric transformer type inverter shown in FIG.
It is also possible to use an inverter that turns on the cold-cathode tube using a resonance operation such as a resonance type electromagnetic inverter shown in FIG. In such a resonance type circuit, the output voltage of the inverter is lower than that of an inverter using a ballast capacitor when the cold-cathode tube is turned on, so that not only the leakage current can be reduced, but also the effect is large in terms of safety.

The liquid crystal display device shown in FIG.
Since the backlight device of the present embodiment, which has high lamp efficiency and improved durability, is incorporated as the lighting means, the efficiency and the life of the liquid crystal display device can be improved.

Further, in this embodiment, four cold cathode tubes 2 connected in series two by two
Has been described, the present invention is not limited to this, and it is sufficient if two or more cold cathode tubes are arranged in parallel.

Further, as described above, since the cold cathode fluorescent lamp 2 becomes longer and the lighting sustaining voltage becomes higher or the lighting frequency becomes higher, the leakage current becomes a serious problem.
In particular, when the cold-cathode tube 2 having a length of 280 mm or more is turned on, the effect of reducing or preventing the leakage current is increased by performing the above-described control in the present embodiment. Further, when the present invention is applied to a backlight device used in a large liquid crystal display device having a size of 15 inches or more, the effect is further enhanced.

(Embodiment 2) A backlight apparatus according to a second embodiment of the present invention will be described with reference to FIGS.

FIG. 8 is a plan view of a backlight device according to the second embodiment. In FIG. 8, a backlight device includes a lighting device including an inverter 1 and a cold cathode tube 2,
And a light guide plate 3. The cold cathode tubes 2 are arranged along the long side of the light guide plate 3 so as to illuminate the light guide plate 3 from two directions on the long side of the light guide plate 3. The inverter 1 is arranged on one of the short sides of the light guide plate 3 or on the back surface of the light guide plate 3. The other short side of the light guide plate 3 is used for leading a lead wire.

The difference from the first embodiment is that the high-frequency voltage applied to the cold-cathode tube 2 has opposite phases at the two electric terminals of the cold-cathode tube 2. That is, the voltage applied to one terminal A1 of the inverter 1 and the voltage applied to the other terminal A
2 have opposite phases. Such an inverter that outputs opposite-phase voltages at the two electric terminals can be realized by, for example, connecting a step-up transformer and a cold cathode tube as shown in FIG.

FIG. 9A is a diagram illustrating the connection of a cold cathode tube to an inverter using a piezoelectric transformer. In the inverter 1, a driving unit 20 drives a piezoelectric transformer 21. FIG. 9B is a diagram for explaining the connection of the cold cathode tubes to the resonance type electromagnetic inverter. The inverter 1 drives the electromagnetic transformer T by the drive unit 20, and the leakage inductance of the electromagnetic transformer T and the capacitor C The cold cathode tube 2 is driven by utilizing the resonance of. Conventionally, an unbalanced output from an inverter in which one of the secondary electrodes of the transformer is grounded as shown in FIG. 7 is applied to the cold cathode tube. On the other hand, in the present embodiment, a balanced output, which is an output from an inverter whose secondary side electrode of the transformer is not grounded as shown in FIG. That is, substantially symmetric voltages having opposite polarities are applied to both electrodes of the cold cathode tube 2. Thereby, the lighting voltage of the cold cathode tube can be reduced. That is, since a positive voltage and a negative voltage are applied to both ends of the cold cathode tube 2, respectively, if a voltage of one half of the voltage value in the first embodiment is applied as a voltage applied to one electrode, the cold cathode tube 2 Has the same value as in the first embodiment, the lighting voltage can be reduced.

Next, a comparison of the leak current is performed. FIG. 10 is a diagram illustrating a leak current in the backlight device according to the first embodiment, and FIG. 11 is a diagram illustrating a leak current in the backlight device according to the present embodiment. In the first embodiment, the potential of one electrode terminal of the cold-cathode tube 2 becomes high and the other potential is a low voltage of about several volts, so that a large amount of leakage current mainly occurs on the high-voltage side. Therefore, the brightness of the cold-cathode tubes 2 is different, and an optimal design of the light guide plate 3 is required for uniform light emission. However, with the driving voltage of the balanced type output as in the present embodiment, the cold cathode fluorescent lamp 2
, The leak currents of the respective cold cathode tubes 2 become substantially equal as shown in FIG. 11, so that the brightness between the cold cathode tubes 2 becomes substantially uniform.

That is, the backlight device of the present embodiment has the following advantages as compared with the first embodiment. (1) The output voltage may be halved. (2) Leakage current can be reduced because the wiring portion has a low voltage. (3) The applied voltage is lower than in the past, and safety design is easy. (4) The luminance becomes uniform.

An example of the result of verifying the characteristics of the backlight device of the present embodiment will be described. For example, the diameter of the cold cathode tube 2 is 2.
When the light guide plate 3 has a size of 15 inches, the lighting frequency of the cold cathode tube 2 is 60 kHz, and the current flowing through the cold cathode tube is 6 mA (current contributing to light emission), the voltage across the cold cathode tube 2 Was 600 Vrms, and the required input power was 9.1 W. As the leak current decreases, the inverter efficiency is improved. Also, with regard to luminance, one set of cold-cathode tubes could be lit almost uniformly.

The voltage between both ends of the cold-cathode tube in the first embodiment is 1
Since it was 200 Vrms, it can be seen that the applied voltage can be reduced.

That is, by using the backlight device of this embodiment, the voltage applied to the cold cathode fluorescent lamp can be reduced, and the leakage current between the cold cathode fluorescent light and the reflector or the leakage current between the cold cathode fluorescent lamps can be reduced. Alternatively, the luminous efficiency can be improved. As a result, the durability of the electrodes of the cold-cathode tube can be improved, the luminance can be made uniform, and the efficiency of the inverter circuit can be increased.

By applying the backlight device of this embodiment, which has a high lamp efficiency and a long life, to the liquid crystal display device, the efficiency and the life of the liquid crystal display device can be increased. .

Further, in the present embodiment, a case has been described where four cold cathode tubes are connected in series two by two and electrically connected in parallel to the inverter. However, the present invention is not limited to this. However, it is only necessary that two or more cold cathode tubes are arranged in parallel.

Further, as described above, the length of the cold-cathode tube increases, and the leakage current becomes a serious problem due to the increase in the lighting sustaining voltage or the increase in the lighting frequency. When the above-mentioned cold cathode fluorescent lamp is turned on, it is possible to reduce or prevent the leakage current by using the drive control of the present invention.

Further, when used in a backlight device used in a large liquid crystal display device having a size of 15 inches or more, the effect is further enhanced.

(Embodiment 3) A third embodiment of the backlight device according to the present invention will be described with reference to FIG.
In FIG. 12, the backlight device includes a lighting device including an inverter 1 and a cold cathode tube 30, and a light guide plate 3. The cold cathode tube 30 has a U-shape, is arranged so as to surround the light guide plate 3, and illuminates the light guide plate 3 from three directions. The inverter 1 is arranged on the end surface of the light guide plate 3 where the cold cathode tubes 2 are not arranged or on the back surface of the light guide plate 3.

The difference from the second embodiment is that the cold cathode tube 30
Has a U-shape, and the other configurations are the same. The output of the inverter 1 is also a balanced output.

The cold cathode tube 30 is turned on by the high-voltage power output from the inverter 1. Light emitted from the cold cathode tube 30 is efficiently illuminated by the reflector onto the light guide plate 3 made of acrylic resin or the like. The light guide plate 3 propagates light in a plane direction. The reflection sheet 7 is also provided on the back surface of the light guide plate 3.
Is formed so as to uniformly illuminate the liquid crystal panel with light from the cold cathode tube through the diffusion plate.

In FIG. 12, a U-shaped cold cathode tube 30 is formed.
Are electrically connected to the inverter 1. The lamp efficiency is improved by lighting the cold-cathode tube 30 at a high frequency of 30 kHz to 200 kHz.

In the backlight device shown in FIG.
The cold-cathode tube 30 is driven from its two terminals by high-voltage power whose phases differ by approximately 180 °.

This backlight device has a single cold-cathode tube as compared with the first and second embodiments, so that the lighting start voltage and the lighting maintenance voltage can be reduced, and the safety design and the leakage This has the advantage that the current can be reduced.

An example of verification results of the characteristics of the backlight device of the present embodiment will be described. For example, the diameter of the cold cathode tube 30 is 3.0 mm, the length is 800 mm, and the size of the light guide plate 3 is 1
When the lighting frequency of the cold-cathode tube 30 was 4 inches and the frequency was 60 kHz, the input power required for flowing the rated current 8 mA of the cold-cathode tube 30 was 10.2 W. Further, it was possible to light the cold cathode tube 30 with substantially uniform luminance. Also,
At this time, the applied voltage of the cold cathode tube 30 was 500 Vrms (the potential difference between both ends was 1000 Vrms).

That is, by using the backlight device configured as described above, it is possible to reduce or prevent a leak current between the fluorescent tubes due to a voltage difference between the cold cathode tubes 30, thereby improving the luminous efficiency. Can be performed. as a result,
It is also possible to extend the life of the cold cathode tube electrodes, make the luminance uniform, and increase the efficiency of the inverter circuit.

By incorporating the backlight device of the present embodiment having high lamp efficiency and long life into the liquid crystal display device, the efficiency and long life of the liquid crystal display device can be achieved.

Further, in the present embodiment, the case where one U-shaped cold cathode tube is connected has been described, but the present invention is not limited to this, and two or more U-shaped cold cathode tubes are connected. The same effect can be obtained even when a C-shaped cold cathode tube is arranged.

Also, as shown in FIG. 13, the same effect as the U-shaped cold cathode tube 30 can be obtained with the L-shaped cold cathode tube 31.

Further, as shown in FIG. 14, an L-shaped cold cathode tube 31 is disposed so as to illuminate from four sides of the light guide plate 3.
The inverter 40 may be arranged on the back surface. Even in such a case, the same effect as in the case of the above-described U-shaped cold cathode tube 30 can be obtained.

Further, as described above, the length of the cold-cathode tube increases, and the leakage current becomes a serious problem due to the increase in the lighting sustaining voltage or the increase in the lighting frequency. Therefore, in particular, the length of the cold-cathode tube is 280 mm. When lighting the above-mentioned cold cathode tubes, by using the cold cathode tubes of the present embodiment,
The effect of reducing or preventing leakage current is great. One more
When used in a lighting device used in a large liquid crystal display device of 5 inches or more, a greater effect can be obtained.

(Embodiment 4) A backlight apparatus according to a fourth embodiment of the present invention will be described with reference to FIG.
In FIG. 15, the backlight device includes an inverter 50.
And a light guide plate 3. The cold cathode tubes 2 are arranged along the long side of the light guide plate 3 so as to illuminate the light guide plate 3 from two directions on the long side. The inverter 50 is arranged on one of the short sides of the light guide plate 3 or on the back surface of the light guide plate 3. Inverter 50 and cold cathode tube 2
And are electrically connected by lead wires 55a and 55b. The lead wire 55a connected between the high-voltage side of the cold-cathode tube 2 and the inverter 50 is wired such that its length is as short as possible. The lead wire 55b connected to the low-voltage side terminal of the cold cathode tube 2 is wired so as to be as far away from the cold cathode tube 2 as possible. For example, the lead wire 55a
Is wired along the outside of the light guide plate 3 and leads 55
b is wired on the back surface of the light guide plate 3 so as to pass near the center thereof, whereby a sufficient distance between the lead wire 55b and the cold cathode tube 2 can be secured.

In the backlight device configured as described above, the lead wire 55b and the cold cathode fluorescent lamp 2 are different from the conventional backlight device.
Are isolated, so leakage current during that period can be reduced.
There is an advantage.

An example of the results of verifying the characteristics of the backlight device configured as described above will be described. For example, the diameter of the cold cathode tube 2 is 2.6 mm, the length is 280 mm, the size of the light guide plate 3 is 15 inches, and the lighting frequency of the cold cathode tube 2 is 60 kHz.
In the case of the present lighting device, the current flowing through the cold-cathode tube was 5.8 mA and 5.9 mA. In addition, when the conventional backlight device was used at the same input power, the current flowing through the cold-cathode tube was 5.6 mA, 5.6 mA, and the leakage current was reduced.

By using the backlight device configured as described above, the leakage current between the cold cathode tube and the lead wire can be reduced or prevented, and the luminous efficiency can be improved. As a result, the life of the cold cathode tube electrode is extended,
Further, the efficiency of the inverter circuit can be improved.

Further, in the backlight device of the present embodiment, the cold cathode is utilized by utilizing a resonance operation such as a piezoelectric transformer type inverter shown in FIG. 7A or a resonance type electromagnetic inverter shown in FIG. 7B. When an inverter that lights a tube is used, the output voltage of the inverter is lower than that of an inverter that uses a ballast capacitor when the cold-cathode tube is turned on. large.

By using the above-described backlight device for a liquid crystal display device, the efficiency and long life of the liquid crystal display device can be achieved.

Further, in the present embodiment, the description has been given with respect to two cold cathode tubes, but the present invention is not limited to this. Should be fine.

FIG. 16 shows another example of the backlight device according to the present embodiment. The difference from the embodiment shown in FIG. 16 is that the low-voltage side lead wire 55b is connected to terminals (B1, B2) provided near the center of one side of the circuit board of the inverter 1. The high-voltage output terminals (A1, A2) of the inverter 1 are arranged on the other side adjacent to one side of the circuit board of the inverter 1, from which the cold cathode tubes 2 and the lead wires 5 are connected.
It is electrically connected at 5a. By providing the terminals on the circuit board in this manner, the low-voltage terminals (B1, B2)
And the high voltage output terminals (A1, A2) can be separated by a predetermined distance. The low-voltage side lead wire 55 b is wired away from the cold cathode tube 2. Thus, lead wire 5
By wiring 5b, it is possible to easily separate the high voltage part and the low voltage part of the circuit, not only to prevent the leakage current, but also to alleviate the problem of the spatial distance and the circular distance due to the high voltage, to reduce the size of the inverter, and to further reduce the size of the inverter. Can improve safety.

Further, as described above, the length of the cold-cathode tube becomes longer, and the lighting sustaining voltage becomes higher, or the lighting frequency becomes higher. As a result, the leakage current becomes a serious problem. When the cathode tube 2 is turned on, the effect of reducing or preventing the leak current is great by using this embodiment.

Further, when used in a backlight device used in a large liquid crystal display device having a size of 15 inches or more, an even greater effect can be obtained.

(Embodiment 5) A backlight device according to a fifth embodiment of the present invention will be described with reference to FIGS.

FIG. 17 is a plan view of a backlight device according to the fifth embodiment. In FIG. 17, the backlight device includes an inverter 1, a cold cathode tube 2, a light guide plate 3, and reflectors 60 and 61. The reflectors 60 and 61 are arranged around the cold cathode tube 2, and are configured to efficiently irradiate the light from the cold cathode tube 2 to the light guide plate 3. Reflectors 60, 6
1 is not grounded and is not electrically connected to either.

FIG. 18 is a view for explaining a leakage current due to a stray capacitance between the cold cathode tube and the reflector. In the conventional backlight device, as shown in FIG. 18, the reflectors 4a and 4b are electrically connected to the ground. Therefore, there is a problem of leakage current due to the stray capacitance. Here, the high voltage power and the leak current applied to the cold cathode tube 2 are shown. In FIG. 18, two cold cathode tubes 2a, 2b
Are electrically connected in series, and voltages different in phase by approximately 180 ° are applied to the terminals of the cold cathode tubes 2a and 2b to which the cold cathode tubes 2a and 2b are not connected.

The operation when sine waves having phases different from each other by 180 ° around the ground are input will be described with reference to FIG. First, in the state of FIG. 18A (the flow of the leak current at this time corresponds to the solid arrow), the cold cathode fluorescent lamp 2a
Since the current flows out of the reflector 4a, the brightness of the tube decreases as the potential decreases. On the other hand, the cold cathode tube 2
In b, since current flows from the reflector 4b,
The brightness increases as the potential decreases. In the state of FIG. 18B (the flow of the leak current at this time corresponds to the dashed arrow), on the contrary, the current flows from the reflector 4a into the cold cathode tube 2a, and from the cold cathode tube 2a. Reflector 4a
The current starts to flow. Thus, the reflectors 4a, 4b
Is grounded to the ground, a leak current flows through the reflectors 4a and 4b and the ground.

Therefore, in this embodiment, the leakage current can be reduced or prevented by using the reflector in an electrically floating state without grounding the reflector.

Further, by using the reflector in an electrically floating state, it is possible to prevent a decrease in luminance due to a leak current as described above.

The backlight device configured as described above has the following advantages. (1) The leakage current can be reduced or prevented. (2) The brightness of the cold cathode tube can be made substantially uniform. (3) Since the leakage current is small, the consumption of the electrodes of the cold cathode tube is small, and the life of the cold cathode tube can be extended. (4) Since the leakage current is small, the efficiency of the inverter can be increased.

An example of the results of verifying the characteristics of the backlight device configured as described above will be described. For example, the diameter of the cold cathode tube 2 is 2.6 mm, the length is 280 mm, the size of the light guide plate 3 is 15 inches, and the lighting frequency of the cold cathode tube 2 is 60 kHz.
In the case of (1), the input power was 10 W when the reflector was grounded and the current flowing through the cold cathode tube was 6 mA. Further, the brightness of the cold cathode tube was sparse.

When the reflector was not grounded, the power required to flow the same rated current of 6 mA was 9.1 W.

By using the backlight device configured as described above, the leak current due to the reflector can be reduced or prevented, and the luminous efficiency can be improved. As a result, the life of the cold cathode tube electrodes can be prolonged, the luminance can be made uniform, and the efficiency of the inverter circuit can be increased.

In this embodiment, the cold-cathode tube is turned on using a resonance operation such as a piezoelectric transformer inverter shown in FIG. 9A or a resonance type electromagnetic inverter shown in FIG. 9B. It can be realized using either of the inverters.

The liquid crystal display device incorporating the backlight device shown in FIG. 17 can achieve the efficiency and long life of the liquid crystal display device.

Further, in the present embodiment, a case has been described in which four cold cathode tubes connected in series two by two are electrically connected in parallel to the inverter. The present invention is not limited to this, and it is sufficient if two or more cold cathode tubes are arranged in parallel.

Further, as described above, the length of the cold-cathode tube becomes longer, and the leakage current becomes a serious problem due to a higher lighting sustaining voltage or a higher lighting frequency. When the above-mentioned cold cathode fluorescent lamp is turned on, a great effect can be obtained in reducing or preventing leakage current by using the backlight device of the present embodiment. Further, when used in a backlight device used in a large liquid crystal display device having a size of 15 inches or more, an even greater effect can be obtained.

[0092]

According to the illuminating device of the present invention, the arrangement and the drive control of the cold-cathode tubes are driven at substantially the same phase, substantially the same voltage, and substantially the same drive frequency to reduce or prevent the leakage current. be able to. As a result, it is possible to improve the brightness of the cold-cathode tube and prevent the cathode from being consumed, thereby extending the life. Further, also in a backlight device and a liquid crystal display device using the lighting device, miniaturization, high luminance, and long life can be realized.

Further, by driving the cold-cathode tube with a boosting transformer capable of balanced output, the voltage at both ends of the cold-cathode tube can be reduced, and the leak current can be further reduced.

As described above, according to the illumination device of the present invention, a highly reliable and high-brightness backlight device,
A liquid crystal display device can be provided, and the effect is very large in practical use.

[Brief description of the drawings]

FIG. 1 is a plan view of a backlight device according to a first embodiment of the present invention.

FIG. 2 is a perspective view of the backlight device according to the first embodiment of the present invention.

FIG. 3 is a cross-sectional view of the backlight device according to the first embodiment of the present invention.

FIG. 4 is a diagram showing connection with a cold cathode tube in an inverter using a ballast capacitor.

FIG. 5 is a diagram illustrating a stray capacitance between a cold cathode tube and a reflector.

FIG. 6 is a diagram illustrating a driving voltage to the cold cathode tubes and a potential difference between the cold cathode tubes.

FIG. 7 is a diagram illustrating another example of the connection between the cold cathode tubes and the boosting transformer in the first embodiment of the present invention.

FIG. 8 is a plan view of a backlight device according to a second embodiment of the present invention.

FIG. 9 is a diagram for explaining a method of connecting a cold cathode tube and a step-up transformer for realizing a balanced output.

FIG. 10 is a diagram illustrating stray capacitance and leakage current of the backlight device in Embodiment 1.

FIG. 11 is a diagram illustrating stray capacitance and leakage current of a backlight device in Embodiment 2.

FIG. 12 is a plan view of a backlight device (including a U-shaped cold cathode tube) according to a third embodiment of the present invention.

FIG. 13 is a plan view of a backlight device (including an L-shaped cold cathode tube) according to a third embodiment of the present invention.

FIG. 14 is a plan view of a backlight device (including two L-shaped cold cathode tubes) according to a third embodiment of the present invention.

FIG. 15 is a plan view of a backlight device (part 1) according to a fourth embodiment of the present invention.

FIG. 16 is a plan view of a backlight device (part 2) according to a fourth embodiment of the present invention.

FIG. 17 is a plan view of a backlight device (including a non-grounded reflector) according to a fifth embodiment of the present invention.

FIG. 18 is a diagram illustrating a leak current between a cold cathode tube and a reflector.

FIG. 19 is a diagram showing a liquid crystal monitor according to the related art.

FIG. 20 is a diagram showing a liquid crystal display device according to the related art.

FIG. 21 is a diagram showing a direct-type backlight device (illumination device) according to the related art.

FIG. 22 is a diagram illustrating an edge light type backlight device (illumination device) according to the related art.

FIG. 23 is a diagram for explaining stray capacitance in the related art.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1,101 Inverter 2, 2a, 2b Cold-cathode tube (cold-cathode fluorescent tube) 3 Light guide plate 4, 4a, 4b Reflector 5 Diffusion plate 6 Liquid crystal panel 7 Reflection sheet 10, 20 Driving part 11 Floating capacitance 21 Piezoelectric transformer 30 L-shaped cold cathode tube 55a, 55b, 214 Lead wire 100 LCD monitor 111 Backlight device

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Kojiro Okuyama 1006 Kadoma Kadoma, Osaka Prefecture Matsushita Electric Industrial Co., Ltd. 72) Inventor Katsunori Morikiki 1006 Kazuma Kadoma, Kadoma City, Osaka Prefecture F-term in Matsushita Electric Industrial Co., Ltd. HA10

Claims (13)

[Claims] 1. An illumination device for illuminating an object to be illuminated, comprising: a plurality of cold cathode tubes for emitting light for illuminating the object to be illuminated; and a cold cathode tube driving device for illuminating the cold cathode tube at a high frequency. The cold-cathode tube driving device drives the cold-cathode tubes arranged close to each other with a drive voltage having substantially the same phase, substantially the same voltage, and substantially the same frequency. 2. An illumination device for illuminating an object to be illuminated, comprising: a plurality of cold cathode tubes for emitting light for illuminating the object to be illuminated; and a cold cathode tube driving device for illuminating the cold cathode tube at high frequency. The cold-cathode tube driving device controls the driving voltage input to one of the electrodes of the cold-cathode tube and the driving voltage input to the other of the electrodes of the cold-cathode tube so that the phases are different from each other by approximately 180 °. A lighting device, comprising: 3. The cold-cathode tube driving device comprises a piezoelectric transformer, and a plurality of cold-cathode tubes connected to the cold-cathode tube driving device are connected in series. 3. The lighting device according to 2. 4. The cold-cathode tube driving device turns on a cold-cathode tube using resonance operation of a leakage inductor of a step-up transformer and a capacitor connected in parallel to the cold-cathode tube. The lighting device according to claim 1 or 2, wherein the plurality of cold cathode tubes connected are connected in series. 5. The lighting device according to claim 2, wherein the cold cathode tube has a U-shape. 6. The lighting device according to claim 2, wherein the shape of the cold cathode tube is L-shaped. 7. An L-shaped cold-cathode tube comprising: two L-shaped cold-cathode tubes; and a cold-cathode tube driving device for driving the two L-shaped cold-cathode tubes at high frequency; One of the L-shaped cold cathode tubes is arranged along two adjacent sides of the object to be illuminated to illuminate the object to be illuminated from four directions by the cathode tube, and the other of the cold cathode tubes is the other of the light guide plate. The lighting device according to claim 2, wherein the lighting device is arranged along two sides, and the cold cathode tube driving device is arranged on a back surface of a light emitting surface of the illuminated body. 8. The lighting device according to claim 5, wherein the cold-cathode tube driving device is configured using a piezoelectric transformer having balanced output characteristics. 9. The cold-cathode tube driving device turns on the cold-cathode tube using a resonance operation of a leakage inductor of the step-up transformer and a capacitor connected in parallel to the cold-cathode tube. The lighting device according to any one of claims 5 to 7. 10. A reflector is provided around the cold cathode tube,
3. The reflector according to claim 2, wherein the reflector is not grounded.
The lighting device according to claim 1. 11. A lighting device for illuminating an object to be illuminated, wherein: a plurality of cold cathode tubes for emitting light for illuminating the object to be illuminated; and a plurality of cold cathode tubes provided for lighting the cold cathode tubes. And, comprising a plurality of cold cathode tube driving device, constituted by a piezoelectric transformer, a lead wire connected to a high voltage side terminal of the cold cathode tube along the periphery of the illuminated object A lead wire that is wired and connected to a terminal on the low voltage side of the cold-cathode tube is wired so as to pass near the center of the illuminated body, and the plurality of cold-cathode tubes are each driven at substantially the same drive frequency. A lighting device, comprising: 12. The lighting device according to claim 1, further comprising:
A backlight device, comprising: a light guide plate for emitting light illuminated by the lighting device onto a surface, and illuminating another illuminated object from the back by the light emission of the light guide plate. 13. A liquid crystal display device comprising: the backlight device according to claim 12; and a liquid crystal display panel as the another object to be illuminated.