JPH07262815A - Back light unit - Google Patents

Abstract

PURPOSE:To provide a back light unit having an excellent brightness uniformity. CONSTITUTION:A slender and a small diameter of fluorescent lamp 2 is set to a flat lamp house 6 having an upper side opening, and the fluorescent lamp 2 is fixed and held in the lamp house 6 by a holder 11, while the fluorescent lamp 2 is lighted at least by a high-frequency inverter lighting circuit 14 of 15kHz or higher. In such a back light unit 18, the fluorescent lamp 2 is fixed and held to the lamp house 6 by the insulating holder 11.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention has a light-reflecting surface formed on an inner wall thereof, and a light-transmitting diffuser plate is provided in an opening of a lamp house having a light source lamp housed therein, and the light-transmitting diffuser plate is arranged on an upper surface side of the lamp house. The present invention relates to a direct-type backlight unit that uniformly illuminates a display panel from the back surface, and more particularly to a backlight unit for a liquid crystal display device in which a long and narrow fluorescent lamp is used as a light source lamp for high frequency lighting.

[0002]

2. Description of the Related Art A backlight used in a liquid crystal display device of this type has a narrow and small diameter as a light source because of a demand for a thinner display device, a larger display surface, higher brightness, and lower power consumption. The ones that use fluorescent lamps are the mainstream, and the light from the lamp house that houses the fluorescent lamps is used as a light transmission diffuser plate by arranging the fluorescent lamps on the end surface of the light guide plate to guide the light to the surface side. There is a direct-lighting type that allows the light to pass through, and both have advantages and disadvantages. However, the direct-lighting type has a higher light extraction efficiency than the edge-light type and is suitable for high-luminance display.

3 to 6 are a perspective view and a cross-sectional view showing a schematic structure of such a direct-type backlight unit.

That is, the backlight unit 1 has an elongated fluorescent lamp 2 having a small diameter, for example, a bent portion 2
It is composed of a light emitting part 3 which houses a U-shaped fluorescent lamp of a book, and a lighting circuit part 5 incorporating a circuit component 4 for lighting the fluorescent lamp 2 of the light emitting part 3 at a high frequency. It has an integrated structure in which and are integrally connected.

The light-emitting portion 3 has two U-shaped fluorescent lamps 2 arranged side by side in a concave lamp house 6 having an upper opening.
A light transmission diffusion plate 7 is arranged on the opening of the lamp house 6. The lamp house 6 forms the lower surface and the inner wall of the side wall so as to reflect light, and reflects the light from the fluorescent lamp 2 toward the light transmitting / diffusing plate 7. For example, an aluminum plate is white-painted, A silver vapor deposition sheet with a mirror surface is attached to form the inner wall surface with good light reflectivity. on the other hand,
The light transmitting / diffusing plate 7 is made of an acrylic resin plate or the like, diffuses and transmits the light of the fluorescent lamp 2 and emits diffused light to the surface,
The liquid crystal display device 9 arranged on the upper surface side is uniformly illuminated.

Further, in the light emitting section 3, the fluorescent lamps 2 are arranged in the lamp house 6 at predetermined intervals so that a predetermined brightness uniformity can be obtained.
For example, as shown in FIG. 5, the side wall 6a along the optical axis of the fluorescent lamp 2 is formed in a taper shape that expands upward, or the position of sticking the silver vapor deposition sheet 10 stuck to the inner surface of the lamp house 6 is regulated. Then, the light reflectivity of the inner surface of the lamp house 6 is adjusted.

Further, the long and thin fluorescent lamp 2 has a tip portion 2a in which the bulb wall surface is locked by a claw 11 formed by cutting and raising a side wall 6b surface on the tip side of the lamp house 6.
The rear end side passes over the notch 12 formed in the side wall 6c surface on the rear end side of the lamp house 6, and the rear end portion 2b is fixedly supported by the lamp socket 13 of the lighting circuit unit 5 described later.

The lighting circuit section 5 is composed of an inverter case 16 in which a circuit board 4 in which an inverter lighting circuit 14 for lighting the fluorescent lamp 2 by an inverter and a lamp socket 13 of the fluorescent lamp 2 are incorporated is housed. Then, the front end portion of the case 16 is integrally coupled to the lamp house 6 with a screw 17 or the like.

In the backlight unit 1 thus constructed, when the fluorescent lamp 2 is turned on, a part of the light is directly reflected and the rest is reflected on the inner surface of the lamp house 6 and projected on the light transmission diffusion plate 7, The light is diffused by the light transmission diffusion plate 7, and the diffusion plate 7
The liquid crystal display device 9 arranged above is uniformly illuminated.

[0010]

By the way, the direct-type backlight unit 1 using the elongated and small-diameter fluorescent lamp 2 as the light source in this way has a bulb of the fluorescent lamp 2 supported by a fixture such as a nail 11 for fixing the lamp. A structure is adopted in which the wall surface is locked and the fluorescent lamp 2 is supported at a predetermined position in the lamp house 6, but at high frequency lighting, one end side from the claw 11 part that locks and supports the bulb wall surface of the fluorescent lamp 2 is slightly. In some cases, the luminance was lowered and the luminance uniformity of the light emitting section 3 could not be obtained.

Therefore, the arrangement position of each fluorescent lamp 2 in the lamp house 6 is adjusted, or the attachment position of the silver vapor deposition sheet 10 to be attached to the inner surface of the lamp house 6 is adjusted. However, it was difficult to obtain a good luminance uniformity of the light emitting section 3.

Therefore, the present invention has been made in view of the problem of adjusting the brightness uniformity of the backlight unit, and it is possible to eliminate the decrease in brightness in the supporting portion of the fluorescent lamp by the supporting member with a simple structure, which is favorable. It is an object of the present invention to provide a backlight unit that can obtain a brightness uniformity.

[0013]

Means for Solving the Problems The present inventor has made the following conclusions as a result of examining the cause of the decrease in brightness occurring at one end side of the locking support portion of the fluorescent lamp of the backlight unit. is there. That is, the fluorescent lamp 2 used in the backlight unit 1 is extremely thin and thin with a bulb outer diameter of 3 to 5 mm and a bulb length of 150 to 250 mm, for example. 14 is a high voltage of several hundreds of volts to several hundreds of thousands of volts. Therefore, as shown in FIG. 2, when the electrodes at both ends of the fluorescent lamp 2 are connected to the inverter lighting circuit 14 to be lit, the claw 11 that fixedly supports the fluorescent lamp 2 has a high frequency of the inverter through the bulb wall. A high voltage is applied, and a leak current i flows through the claw 11 through the valve wall, and as a result, the claw 11 part has a low voltage side (earth side) 14b.
The luminance of the portion is lower than that of the portion from the claw 11 to the high voltage side 14a. From the claw 11 to the low pressure side 14b
The decrease in the luminance is hardly visible when the lighting frequency of the inverter lighting circuit 14 is less than 15 KHz, but it is clearly visible when the lighting frequency is 15 KHz or more, and the normal 40
It was found that a luminance difference of several% or more occurs at ˜50 KHz and the luminance uniformity of the light emitting unit 3 is reduced. Therefore, according to the present invention, the supporting tool for supporting the bulb wall of the long and thin fluorescent lamp 2 is made of an insulating member so as to prevent the leakage current leaking to the supporting portion via the bulb wall. Then, specifically, the configuration is as follows. That is, in the backlight unit of the present invention, an elongated fluorescent lamp having a small diameter is arranged in a flat lamp house having an upper opening, and a part of the fluorescent lamp is supported by a supporting tool, and the fluorescent run is 15 KHz or more. In the backlight unit that is turned on at a high frequency, the supporting member is characterized in that a portion in contact with the bulb wall surface of the fluorescent lamp is made of an insulating member. Further, the backlight unit of the present invention is characterized in that the support member is formed by fitting a resin tube on a metal claw formed by cutting and raising the lamp house.

[0014]

In the elongated and thin fluorescent lamp, the wall surface of the bulb is supported by the lamp house by the insulating support. In this case, even if the fluorescent lamp is turned on by a high-frequency, high-voltage inverter of 15 KHz or more, since the bulb wall surface is supported by the insulating support, the leakage current leaking from the bulb wall surface is small,
The decrease in brightness on the low pressure side of the support portion is eliminated.

[0015]

Embodiments of the present invention will now be described in detail with reference to the drawings.

FIG. 1 is a cross-sectional view showing a main structure of a backlight unit 18 for a liquid crystal display device according to the present invention.

Similar to the conventional backlight unit 1, this backlight unit 18 uses an elongated fluorescent lamp 2 having a small diameter as a light source, and an integral type in which a light emitting section 3 and a lighting circuit section 5 are integrally connected. With the structure, the inverter lighting circuit 14 has a relatively high frequency with high brightness and high efficiency,
For example, the lighting frequency is set to 42 KHz.

Then, like the backlight unit 1, two U-shaped fluorescent lamps 2 are arranged side by side in a lamp house 6 formed by forming an aluminum plate into a flat concave shape having an upper opening, and are arranged side by side on the opening. The light transmitting / diffusing plate 7 is arranged to configure the light emitting unit 3. Further, the fluorescent lamp 2 is arranged in the lamp house 6 at a predetermined position while being regulated, and a side wall 6a of the lamp house 6 along the optical axis of the fluorescent lamp 2 is formed in a tapered shape that expands upward, although not shown. Alternatively, the silver vapor deposition sheet 10 is attached to the inner surface of the lamp house 6 so that the light emitting unit 3 can obtain a predetermined luminance uniformity.

Further, in the fluorescent lamp 2, the tip portion (U-shaped bent portion) 2a is locked to a claw (support tool) 11 formed by cutting and raising the side wall 6b surface of the lamp house 6 on the tip side. The rear end side passes through the notch 12 formed in the side wall 6c surface on the rear end side of the lamp house 6, and the rear end portion 2b is supported by the lamp socket 13 of the lighting circuit unit 5.

In this backlight unit 18,
The difference from the backlight unit 1 is that the resin-made insulating tube (insulating member) 19 is covered on the claw 11 that supports the bulb wall surface of the fluorescent lamp 2, and this insulating tube 19
It is only the point that the bulb wall surface of the fluorescent lamp 2 is supported via the above, and the other configuration is the same as that of the backlight unit 1. Therefore, the same components are shown in FIGS.
The same reference numerals are given and the description thereof is omitted.

In the backlight unit 18 thus constructed, both electrodes of the fluorescent lamp 2 are lit by the inverter lighting circuit 14 by applying high frequency and high voltage in the same manner as in FIG. At this time, the claw 11 supporting the fluorescent lamp 2 is covered with the insulating tube 19 to prevent a leak current from leaking from the bulb wall surface to the metal (aluminum plate) lamp house 6. Therefore, it is possible to prevent the luminance from the low voltage side 14b from the claw 11 part to be lower than that from the high voltage side 14a from the claw 11 part.

Therefore, in the backlight unit 18, variations in the brightness uniformity due to the difference in the brightness distribution of the fluorescent lamp 2 are suppressed, and a good brightness uniformity is obtained in the light emitting section 3.

In this regard, the present inventor has found that the bent portion of a U-shaped fluorescent lamp having a bulb outer diameter of 3 mm and a bulb length of 220 mm has a thickness of 1.
When it was supported by a supporting tool (cutting claw of an aluminum plate) covered with a 5 mm silicon tube and connected to a high-frequency lighting circuit with a frequency of 45 KHz and a secondary voltage of 1200 V and turned on, a decrease in brightness was visually recognized. .

In the above embodiment, the supporting member for supporting the bulb wall surface of the fluorescent lamp 2 is formed by the claw 11 which is formed by cutting and raising the lamp house 6, and the insulating tube 19 is fitted to this. Any form of insulating support can be similarly applied as long as it is an insulating support that does not cause leakage through the wall surface of the bulb by the application of high frequency and high voltage to the lighting circuit. Further, when the surface of the support is covered with an insulating member, it is preferable that the support has flexibility or elasticity.

Further, although the U-shaped fluorescent lamp is used as the fluorescent lamp 2, it can be similarly applied to a straight tube-shaped or curved tube-shaped lamp. Further, the backlight unit 18 has an integrated structure in which the light emitting unit 3 and the lighting circuit unit 5 are integrally connected, but the backlight unit 18 can be applied to a structure in which the light emitting unit 3 and the lighting circuit unit 5 are separately configured.

[0026]

As described in detail above, according to the present invention,
Since the surface of the support that comes into contact with the wall surface of the bulb of the fluorescent lamp is made of an insulating member, the problem of reduced brightness due to current leakage during lighting of the fluorescent lamp can be solved, and the brightness uniformity is excellent. A backlight unit for a liquid crystal display device can be provided.

[Brief description of drawings]

FIG. 1 is a sectional view showing an example of a backlight unit for a liquid crystal display device of the present invention.

FIG. 2 is an operation explanatory diagram of a conventional backlight unit for a liquid crystal display device.

FIG. 3 is a perspective view showing a configuration example of a backlight unit for a conventional liquid crystal display device.

FIG. 4 is a sectional view taken along the line AA of FIG.

FIG. 5 is a sectional view taken along line BB of FIG.

6 is a sectional view taken along the line CC of FIG.

[Explanation of symbols]

 2 Fluorescent lamp 6 Lamp house 11 Claw (support) 14 Inverter lighting circuit 18 Backlight unit 19 Resin tube (insulating member)

Claims (2)

[Claims] 1. A slender lamp house having a flat upper surface opening,
A small-diameter fluorescent lamp is arranged, a part of the fluorescent lamp is supported by a supporting tool, and the fluorescent run is 15 KH.
In the backlight unit which is turned on at a high frequency of z or higher, the supporting unit is configured such that a portion of the supporting member that comes into contact with a bulb wall surface of the fluorescent lamp is made of an insulating member. 2. The backlight unit according to claim 1, wherein the support member is formed by fitting a resin tube on a metal claw formed by cutting and raising the lamp house.