JP4123817B2 - Backlight system - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a configuration for improving the efficiency of an inverter circuit in a liquid crystal display device using a backlight, which is used for image display in a computer, a television receiver or the like.
[0002]
[Prior art]
In recent years, many liquid crystal display devices have been used in display devices such as television receivers and computers. In the backlight system of the liquid crystal display device, as a typical example, a direct type in which a backlight is arranged on the back of the liquid crystal panel and a backlight on the side of the liquid crystal panel, and the emitted light of the backlight is transmitted to the liquid crystal panel. There is a sidelight system in which light is reflected on the back surface and transmitted through a liquid crystal panel.
[0003]
In order to illuminate the cold cathode fluorescent lamp of the backlight system at the normal time, an AC power supply of nearly 1000 V is required, and the voltage becomes higher at the start of lighting. For this reason, a step-up transformer is provided to generate a high voltage. In addition, there is an increasing demand for thinner and higher brightness backlight systems, and miniaturization / thinning is indispensable due to the efficiency of inverter circuits.
[0004]
Here, a schematic diagram of a backlight system of a conventional liquid crystal display device is shown in FIG. Reference numeral 1 denotes a cold cathode fluorescent lamp having electrodes 5 at both ends. A reflector called a reflector (not shown) is provided around the cold-cathode fluorescent lamp 1, and metal such as metal-based aluminum is generally used as the material for improving the reflection efficiency. . However, the stray capacitance 9 is generated between the cold cathode fluorescent lamp 1 and the reactor, and the current flows as a leakage current, so that the efficiency of the inverter circuit of the drive circuit of the cold cathode fluorescent lamp 1 is deteriorated.
[0005]
Therefore, as described in Japanese Patent Laid-Open No. 6-148633, an insulating layer is provided on the inner surface of the reactor to suppress the leakage current, thereby improving the efficiency of the inverter circuit. In that case, since the effect of the stray capacitance is reduced, the efficiency of the inverter circuit is increased, but the lighting start voltage is also increased, so that there is a problem that the step-up transformer becomes larger and becomes an expensive inverter circuit. .
[0006]
[Problems to be solved by the invention]
In order to solve the above-described problems, the present invention provides a backlight system for a liquid crystal display device, which normally suppresses leakage current by separating the reflector from GND, and connects the reflector to GND at the start of lighting. It is excellent in that the lighting start voltage can be reduced.
[0007]
[Means for Solving the Problems]
In order to solve the above problems, the present invention is configured such that a reflector provided around a cold cathode fluorescent lamp is connected to GND only at the start of lighting.
[0008]
Thereby, according to the present invention, it is excellent in that the efficiency of the inverter circuit and the lighting start voltage can be reduced.
[0009]
DETAILED DESCRIPTION OF THE INVENTION
The present invention is a circuit characterized in that the efficiency of an inverter circuit is improved in a backlight system of a liquid crystal display device. Specifically, the reflector is connected to GND only at the start of lighting.
[0010]
Hereinafter, the backlight system of the present invention will be described with reference to FIG. In each figure, the same number is given to the same element as the described component.
[0011]
(Embodiment 1)
FIG. 1 is a diagram showing a configuration example of a backlight system according to the present invention. The configuration of the backlight in FIG. 1 includes a cold cathode fluorescent lamp 1, a reflector 2, a transistor 3, and an ON / OFF control signal 4. In the cold cathode fluorescent lamp (lamp) 1, an AC voltage is applied between electrodes by a drive circuit (not shown) including an inverter, whereby electrons in the cold cathode fluorescent lamp 1 are accelerated toward the electrodes, and mercury electrons. Light is generated by causing a discharge by colliding with the light. At the start of lighting, it is necessary to apply a voltage higher than the normal voltage between the electrodes.
[0012]
However, when the reflector 2 is connected to the GND, stray capacitance is generated between the cold cathode fluorescent lamp 1 and the reflector 2, and current flows as a leakage current at the normal point, so that the efficiency of the inverter deteriorates. Therefore, by separating the reflector 2 from GND, the leakage current flowing through the stray capacitance is suppressed.
[0013]
In order to reduce the lighting start voltage at the start of lighting, the transistor 3 connected to the reflector is turned on at the lighting start timing, and a stray capacitance is generated between the reflector 2 and the cold cathode fluorescent lamp 1 to flow a leakage current. Thus, the electrons are accelerated from the electrode toward the reflector, and the cold cathode fluorescent lamp 1 is turned on by colliding with mercury atoms.
[0014]
The transistor 3 is controlled to be turned on or off according to the control signal 4. The control signal 4 is a signal that changes according to the operation of the drive circuit that applies an AC voltage between the electrodes of the cold cathode fluorescent lamp 1 and turns on the transistor 3 at the timing of starting the cold cathode fluorescent lamp 1.
[0015]
Therefore, the leakage current can be suppressed during normal lighting, and the lighting start voltage can be reduced at the start of lighting, so that the efficiency of the inverter circuit is improved.
[0016]
As described above, this embodiment is excellent in that the efficiency of the inverter circuit can be improved and the inverter circuit can be reduced in size and thickness.
[0017]
【The invention's effect】
According to the present invention, an excellent effect can be obtained in that the efficiency of the inverter circuit is improved and the inverter circuit is reduced in size and thickness by connecting the reflector to the GND only at the start of lighting as described above.
[Brief description of the drawings]
FIG. 1 is a configuration diagram of a backlight system according to an embodiment of the present invention. FIG. 2 is a configuration diagram of a conventional backlight system.
1 Cold Cathode Fluorescent Lamp 2 Reflector 3 Transistor 4 Control Signal 5 Electrode 6 Electron 7 Mercury Electron 8 Discharge 9 Floating Capacity

Claims (1)

A backlight system for a liquid crystal display device, comprising: a cold cathode fluorescent lamp that is turned on or off; a reflector that is provided around the cold cathode fluorescent lamp; and a switching means that is provided between the reflector and GND. Means connect the reflector to GND only at the start of lighting of the cold cathode fluorescent lamp.

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