JPH08122776A - Backlight for liquid crystal television - Google Patents

Abstract

PURPOSE: To provide a backlight for a liquid crystal television reduced in the radiation noise of a backlight inverter, high in efficiency, more uniform in luminance distribution and suitable for a large screen. CONSTITUTION: This backlight is constituted of a fluorescent tube 1 having such a shape that a tube terminal part 1A is in an opposite direction to a tube central part 1B like a U-shape or a square U-shape, and a backlight inverter where the secondary winding of a boosting transformer 2 is divided to two winding parts 2A and 2B whose midpoint is connected to the ground and ballast capacitors 3 and 4 are provided at both ends. Then, high voltage having different polarity is impressed on both terminals of the fluorescent tube.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a backlight for a liquid crystal television, and more particularly to a structure of a fluorescent tube and an inverter used in a liquid crystal television having a relatively large screen size to make the screen brightness uniform and reduce noise.

[0002]

2. Description of the Related Art Conventionally, as a backlight inverter for a liquid crystal television, a self-excited oscillation type inverter as shown in FIG. 3 has been used. One of the secondary side of the step-up transformer 12 is connected to the ground, one of both terminals of the fluorescent tube 11 is connected to the ground, and the other is connected to the high voltage side via the ballast capacitor 13. When a fluorescent tube for a liquid crystal television having a size of 5 inches or more is lit with such a configuration, the output voltage of the step-up transformer 12 is 4000 because the tube length is long.
A high voltage of ~ 5000 V pp is required. The drive frequency is generally in the range of 20 KHz to 80 KHz.

[0003]

The liquid crystal television backlight having such a structure has the following problems.

Since the same wave number is high at a high voltage, leakage is large, and the brightness of the fluorescent tube is brightest on the high voltage side of the fluorescent tube and dark on the ground side, as shown in FIG. In FIG. 3, the brightness of the fluorescent tube 11 becomes dark as 11a, 11b, and 11c. Therefore, in display area 14, part A is brighter than part C,
In the areas B and D, uneven brightness occurs because the area B is much brighter.

Because of the high voltage, the radiated electromagnetic wave becomes large, and it is necessary to shield the panel and the backlight with a film having a transparent nesa film or the like. Therefore, it is difficult to simplify the structure.

Because of the high voltage, it is easy to discharge and it is necessary to increase the clearance between the high voltage part wiring pattern and other parts or patterns, resulting in poor space efficiency.

Leakage due to capacitive coupling in the step-up transformer winding due to high voltage and high frequency is large, and since the fluorescent tube is long, leakage between the fluorescent tube and other parts is large, resulting in poor efficiency.

The present invention aims to remedy such problems.

[0009]

A backlight for a liquid crystal television according to the present invention has at least a fluorescent tube and a backlight inverter for driving the fluorescent tube, and the fluorescent tube is U-shaped or U-shaped. The terminal part is a fluorescent tube having a shape opposite to the central part of the tube, and the backlight inverter is a self-oscillation type inverter, and the secondary winding of the step-up transformer is divided into two winding parts 2a and 2b. An inverter having a configuration in which a point is connected to the ground and ballast capacitors are provided at both ends, and high voltages having different polarities are applied to both terminals of the fluorescent tube.

[0010]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a block diagram of an inverter and a fluorescent tube showing an embodiment of the present invention. The fluorescent tube 1 has a U-shape or a U-shape, and the tube terminals 1a and 1b and the tube central portion 1 are provided.
b is in the opposite direction.

The inverter is a self-excited oscillation type inverter whose oscillation frequency is determined by the step-up transformer 2, the ballast capacitors 3 and 4 and the collector coupling capacitor 5 of the transistors 6 and 7. The secondary winding of the step-up transformer is an inverter that is divided into two winding portions 2a and 2b, the middle point of which is connected to the ground, and ballast capacitors are provided at both ends. Base resistors 8 and 9 of the transistor of FIG.
The feedback winding 2c of the step-up transformer can be made one by using three terminals. High voltages having different polarities and equal values are applied to both terminals of the fluorescent tube.

In a backlight using such a combination of an inverter and a fluorescent tube, both ends of the tube are brightened with the same brightness as shown in FIG. 2, and the central part of the tube is at the potential of the virtual ground, so the brightness is dark. Become. Therefore, FIG.
At the ends 1a and 1c of the fluorescent tube have the same brightness,
b becomes darker. This means that the brightness of the A and C parts of the display area 10 approximates to each other, and the brightness difference between the B and D parts is higher than that of the conventional inverter drive using a U-shaped fluorescent tube. Is getting less.

Since the fluorescent tube cannot be shaped like a square U, it will be used as a U-shape, but in actual assembly, the U-shaped fluorescent tube will be combined with a light guide plate to form an edge light system. Is used for a thin type backlight, and the U-shaped type is used for a type of backlight arranged on the lower surface of the diffusion plate to be used together with the reflection plate, but the object and effect of the present invention do not change even if the structure is different.

Conventionally, it has been practiced to divide the secondary winding of a transformer to generate a plurality of voltages and to use a single transformer as a power source for a plurality of components. The combination of fluorescent tubes has achieved an unprecedented effect.

In order to maximize the effects of the present invention,
Aligning the inductance of the split windings of the transformer,
This is to devise the structure and layout so that the wiring length from the step-up transformer to the fluorescent tube terminal does not differ greatly.

[0016]

As described above, according to the present invention, the following effects can be realized by combining the shape of the fluorescent tube and the inverter.

The uneven brightness of the backlight can be improved.

The peak voltage of the transformer ground reference is half that of a fluorescent tube of the same size, which reduces radiated electromagnetic noise and reduces the need for a shield member such as a film with a transparent nesa film between the panel and the backlight, which was required in the past. It becomes unnecessary and the structure is simplified.

The gap between the high-voltage wiring pattern and other parts or patterns can be made smaller than before, and space efficiency is improved.

Leakage due to high voltage is reduced, and the efficiency of the step-up transformer is improved. In addition, the step-up transformer can be made smaller and thinner.

[Brief description of drawings]

FIG. 1 is a configuration diagram of an inverter and a fluorescent tube showing an embodiment of the present invention.

FIG. 2 is a luminance distribution diagram of the fluorescent tube according to the configuration of the present invention.

FIG. 3 is a configuration diagram of a conventional inverter and a fluorescent tube.

FIG. 4 is a luminance distribution diagram of a fluorescent tube having a conventional configuration.

[Explanation of symbols]

 1. Fluorescent tube 2. Step-up transformer 3. Ballast capacitor 4. Ballast capacitor

Claims (1)

[Claims] 1. At least a fluorescent tube and a backlight inverter for driving the fluorescent tube are provided, and the fluorescent tube is U-shaped or U-shaped so that the tube end portions 1A and 1C are opposite to the tube central portion 1b. The backlight inverter is a self-oscillation type inverter, and the secondary winding of the step-up transformer 2 is divided into two winding portions 2a and 2b, and the middle point is connected to the ground. A backlight for a liquid crystal television characterized in that it is an inverter having ballast capacitors 3 and 4 at both ends, and high voltages having different polarities are applied to both terminals of a fluorescent tube.