JPH0580333A - Back light unit - Google Patents

Abstract

PURPOSE:To provide the back light unit which is decreased in unequal brightness by simple constitution. CONSTITUTION:The brightness of fluorescent tubes CFL1, CFL2 consisting of plural pieces is adjusted by the length of cables CL1, CL2 connecting the respective fluorescent tubes and a packaging substrate or capacity means CB1, CB2 provided on the cables CL1, CL2 so as to be nearly equaled. Then, the fluctuations in the brightness characteristics of the fluorescent tubes CFL1, CFL2 can be adjusted by the voltage losses in the floating capacity by the length of the cables and the floating capacity including the capacity means CB1, CB2 added thereto and, therefore, the screening thereof can be omitted.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a backlight unit, and more particularly to a technique effective when used in a liquid crystal display device.

[0002]

2. Description of the Related Art In a conventional barite unit,
When two cold cathode discharge tubes (hereinafter sometimes simply referred to as CFL) are driven to be driven by a drive circuit (power supply board), the luminance characteristics of the cold cathode discharge tubes have a large variation of about 30%, so We select and assemble the complete set of. Regarding the backlight unit, there is, for example, Japanese Patent Application No. 63-165202.

[0003]

As described above, a plurality of Cs are used.
When a backlight unit is formed using FL, it is necessary to select those having uniform characteristics, and there is a problem that it takes time for selection. The cold cathode discharge tube requires a high voltage of about 400 V at a high frequency such as about 30 KHz in order to be lit. The inventor of the present application pays attention to the fact that the stray capacitance of the cable cannot be ignored at such a high frequency, and the loss seen from the drive circuit side cannot be ignored, and the variation in the characteristics of the cold cathode discharge tube is adjusted by utilizing this. I thought to do. The purpose of this invention is
An object of the present invention is to provide a backlight unit having a simple structure and reduced brightness unevenness. The above and other objects and novel features of the present invention will be apparent from the description of this specification and the accompanying drawings.

[0004]

The outline of the representative one of the inventions disclosed in the present application will be briefly described as follows. That is, the length of the cable connecting each fluorescent tube and the mounting board is adjusted by the capacitance means provided in the cable so that the brightness of the plurality of fluorescent tubes becomes substantially equal.

[0005]

According to the above-mentioned means, it is possible to adjust the variation in the brightness characteristic of the fluorescent tube due to the voltage loss in the stray capacitance due to the cable length and the stray capacitance including the added capacitance means, so that the selection is omitted. it can.

[0006]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a schematic configuration diagram of an embodiment of a backlight unit according to the present invention. In this embodiment, the cold cathode discharge tubes CFL1 and CFL2 are arranged in parallel on the left and right to serve as a light source of one backlight unit. The cold cathode discharge tubes CFL1 and CFL2 are not subjected to the selection of the brightness characteristics before assembly, and the cable C
It is connected to the CFL power supply by L1 and CL2. CF
The power supply for L is also called an inverter, and is supplied with a DC power supply at a high frequency of about 30 KHz and about 400 V.
Generates an alternating voltage. This AC voltage is output via the ballast capacitors CB1 and CB2.

In this embodiment, the cables CL1 and C are
In L2, tubular rings LN1 and LN2 made of a conductor are provided by bundling the cables on the high voltage side and the ground potential side.
In this state, the cold cathode discharge tubes CFL1 and CFL2 are turned on, and the cold cathode discharge tube CFL1 (or CF with a smaller brightness)
The length L1 (or L2) of the tubular ring corresponding to L2) is shortened.

FIG. 2 shows an equivalent circuit diagram of FIG. The output voltage Vo of the inverter is supplied to CFL1 and CFL2 via ballast capacitors CB1 and CB2. The cable connecting these CFL1 and CFL2 to the power source has a stray capacitance CF as shown by the dotted line in the figure.
1 and CF2 are present. These stray capacitances CF1 and CF
2 is inserted in series with the ballast capacitors CB1 and CB2, and divides the output voltage Vo according to its capacitance ratio. That is, the ballast capacitors CB1 and CB2
Of the stray capacitances CF1 and C
By adjusting the capacitance value of F2, a pair of CFL1 and CFL
It is possible to adjust the voltages VT1 and VT2 applied to the second circuit.

Since the driving voltage has a high frequency such as about 30 KHz as described above, the lengths L1 and L2 of the tubular rings LN1 and LN2 provided by bundling the cables are set to a simple structure. It is possible to add a relatively large stray capacitance corresponding to the above. Accordingly, even if the assembled pair of CFL1 and CFL2 have variations in luminance characteristics, the tubular rings LN1, LN
By adjusting the lengths L1 and L2 of 2, the applied voltage VT1,
The brightness can be set to be substantially the same by adjusting VT2. In this embodiment, the stray capacitance is positively used, and the stray capacitance increases in accordance with the length of the connection cable, so that the adjustment can be performed depending on the length of the connection cable.

It is not a good idea to provide the tubular rings LN1 and LN2 from the beginning of assembling the backlight unit. This is because, in this embodiment, a pair of CFL1 and CFL assembled by causing a voltage loss due to stray capacitance.
This is because the variation of the luminance characteristic of No. 2 is corrected and the luminance is reduced. Therefore, at the beginning of assembling the backlight unit, when the tubular rings LN1 and LN2 are not provided and the LEDs are turned on and the brightness varies, the length of the cable corresponding to the brighter cold cathode discharge tube is lengthened, or The tubular ring as described above is provided to increase the stray capacitance in the connection cable and cause a voltage loss with respect to the output voltage Vo of the inverter. With this configuration, the luminance loss can be minimized because the luminance adjustment can be performed according to the darker luminance.

FIG. 3 is a schematic sectional view of an embodiment of a backlight unit to which the present invention is applied.
This figure is a schematic cross-sectional view of the backlight unit cut in the thickness direction, and the connection cable and the CFL power source are omitted. This also applies to FIGS. 4 and 5 described later. CFL1 and C sandwiching the light guide plate
FL2 is arranged. A diffusion plate is provided on the front surface of the light guide plate, and the back surface of the liquid crystal display panel is arranged on top of it. CFL1 and CFL2 are contained in a semi-cylindrical reflector, and the reflected light is directed to the light guide plate.

FIG. 4 is a schematic sectional view of another embodiment of the backlight unit to which the present invention is applied. CFL1 and CFL2 are arranged to sandwich the light guide plate.
The light guide plate has a tapered surface so that the central portion is thin. A diffusion plate is provided opposite to the light guide plate, and the back surface of the liquid crystal display panel is placed on top of the diffusion plate. CFL1 and CFL2 are contained in a semi-cylindrical reflector, and the reflected light is directed to the light guide plate.

FIG. 5 is a schematic sectional view of still another embodiment of the backlight unit to which the present invention is applied. In this embodiment, CFL1 and CFL2 are symmetrically arranged in a symmetrical chamber surrounded by a reflection plate, and a pattern for blocking specific light is formed on the color curtain. A diffuser plate is superimposed on this light curtain.

In this embodiment, since the lighting brightness of CFL1 and CFL2 can be made substantially uniform, by the left and right of the reflection plate, the light guide plate, the light curtain and the diffusion plate as described above,
It is possible to obtain a backlight in which the brightness is uniform over the entire surface.

The effects obtained from the above embodiment are as follows. That is, the cable length is adjusted by connecting the cold cathode discharge tube and the mounting board on which the driving circuit for lighting the cold cathode discharge tube is mounted, or the simple structure of providing the capacitance means provided in the cable Therefore, it is possible to adjust the variation in the luminance characteristics of the cold cathode discharge tube in response to the voltage loss in response to the substantial increase in the stray capacitance, so that the selection can be omitted.

Although the invention made by the present inventor has been specifically described based on the embodiments, the invention of the present application is not limited to the embodiments and various modifications can be made without departing from the scope of the invention. Needless to say. For example, the number of cold cathode discharge tubes may be three or more. There may be a plurality of mounting boards on which the CFL power supply is mounted, corresponding to each. Further, a ground potential may be applied to the tubular ring or a conductor equivalent thereto to obtain a stray capacitance. The cold cathode ray tube may be a fluorescent tube that requires a high voltage at a relatively high frequency as described above. The present invention can be widely applied to various display devices as a backlight unit.

[0017]

The effects obtained by the typical ones of the inventions disclosed in the present application will be briefly described as follows. That is, the cable length is adjusted by connecting the cold cathode discharge tubes and the mounting board on which the drive circuit for lighting the cold cathode discharge tubes is mounted, or a simple structure of providing a capacitance means provided in the cable is used. It is possible to adjust the variation in the luminance characteristics of the cold cathode discharge tube in response to the voltage loss corresponding to the substantial increase of the stray capacitance.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram showing an embodiment of a backlight unit according to the present invention.

FIG. 2 is an equivalent circuit diagram of FIG.

FIG. 3 is a schematic sectional view showing an embodiment of a backlight unit to which the present invention is applied.

FIG. 4 is a schematic cross-sectional view showing another embodiment of the backlight unit to which the present invention is applied.

FIG. 5 is a schematic sectional view showing still another embodiment of the backlight unit to which the present invention is applied.

[Explanation of symbols]

CFL1, CFL2 ... Cold cathode discharge tubes, CB1, CB2 ...
Ballast capacitors, LN1, LN2 ... tubular ring, C
L1, CL2 ... Connection cable, CF1, CF2 ... Stray capacitance.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Hitoshi Suzuki, 3300 Hayano, Mobara-shi, Chiba, Hitachi, Ltd. Mobara factory (72) Inventor Takayuki Iura, 3300, Hayano, Mobara-shi, Chiba, Hitachi Ltd., Mobara, Hitachi, Ltd.

Claims (1)

[Claims] 1. A fluorescent tube comprising a plurality of fluorescent tubes, and a mounting board on which a drive circuit for lighting and driving the fluorescent tube comprising a plurality of the fluorescent tubes is mounted. A backlight unit which is adjusted by a length of a cable connecting the fluorescent tube and the mounting board or a capacitance means provided on the cable.