JP2002246193A - Electric field suppressing circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce electric field radiation which does not require components, such as shield fittings at a low cost, in a backlight for liquid crystals using an inverter. SOLUTION: In a secondary winding for driving a fluorescent lamp inside an inverter transformer, electric field radiation is reduced by canceling electric field radiation to each other due to a winding on the side generating an AC waveform for driving the fluorescent lamp and the generation of opposite phase waveform to that of the AC waveform for driving the fluorescent lamp.

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 using an inverter, and more particularly to a circuit for suppressing an electric field of a backlight for a liquid crystal using an inverter for reducing a radiated electric field generated by the inverter.

[0002]

2. Description of the Related Art In a liquid crystal display device using a backlight of a type in which a fluorescent lamp is turned on using an inverter, an unnecessary electric field is radiated mainly due to an AC waveform applied to the fluorescent lamp. There is a concern that this electric field radiation may affect the human body, and various organizations are working to suppress this, and the standard values are established by TCO, MPR-II, and the like. In Europe, in particular, there is a high level of safety awareness, and non-compliant products are not accepted by the market.

Conventionally, as a method of reducing this radiation,
The fluorescent lamp is shielded from the outside by the metal frame of the liquid crystal panel, the circuit and the board are shielded from the outside by the board shield metal fitting, and the connection cable connecting the circuit and the fluorescent lamp is shielded from the outside by covering with the cover metal fittings By doing so, a means has been taken to shield a portion where an AC waveform, which is a radiation source, flows to shield radiation of an electric field to the outside.

[0004]

However, as described in the above method, the exposed portions of the inverter transformer section of the inverter circuit and the connection cable to the fluorescent lamp in the liquid crystal panel, the fluorescent lamp, and the like are made of metal. It was necessary to shield using a board or the like. If this method cannot be performed due to difficulty in shielding due to structural problems or the like, a method of coating the cabinet with a conductive material may be considered, but this is not realistic because there is a problem with recycling. In addition, there is a problem that the cost and the number of assembling steps increase due to the necessity of preparing a shield metal separately.

According to the present invention, in a liquid crystal display device using a backlight, in which a fluorescent lamp is turned on using an inverter, an inverter which can reduce electric field radiation at a low cost without requiring parts such as shield fittings is provided. An object of the present invention is to provide an electric field suppressing circuit for a liquid crystal backlight used.

[0006]

According to the present invention, there is provided an electric field suppression device for a liquid crystal backlight using an inverter, which generates an AC waveform for driving a fluorescent lamp in an inverter transformer. A tap is inserted in the secondary winding for grounding, and the tap is grounded, thereby generating a waveform having the opposite phase to the AC waveform for driving the fluorescent lamp in the secondary winding, The method is characterized in that radiation corresponding to the voltage of a signal having a phase waveform is generated, thereby canceling a radiation electric field and reducing electric field radiation.

[0007]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The invention according to claim 1 of the present invention is directed to a liquid crystal backlight device for lighting a fluorescent lamp using an inverter circuit, the waveform having an opposite phase to an AC waveform for driving the fluorescent lamp. This is an electric field suppression circuit having a circuit for generating a voltage, and has an operation of generating a voltage waveform having an opposite phase to an AC waveform for driving a fluorescent lamp.

According to a second aspect of the present invention, in the electric field suppression circuit for a liquid crystal backlight using the inverter according to the first aspect, an AC waveform for driving a fluorescent lamp in the inverter transformer is generated. A tap is inserted in the secondary winding for causing the lamp to generate an AC waveform for driving the fluorescent lamp in the secondary winding by grounding the tap, and the fluorescent lamp is driven. This is an electric field suppression circuit having an inverter transformer having a winding that generates a waveform having a phase opposite to an AC waveform for generating a voltage waveform having a phase opposite to the AC waveform for driving a fluorescent lamp. . Hereinafter, embodiments of the present invention will be described with reference to the drawings.

(Embodiment 1) FIG. 1 shows an embodiment of an electric field suppressing circuit according to the present invention, and is a diagram showing a circuit configuration thereof. In FIG. 1, an inverter unit 1 converts a DC voltage into an AC voltage and outputs the AC voltage, applies the converted voltage to a fluorescent lamp 2 through a cable 12, and turns on the fluorescent lamp 2. The inverter transformer 3 is provided in the inverter 1 and boosts the voltage. When a switching voltage is generated in the primary winding 3c, the inverter transformer 3
An AC waveform is generated on the secondary winding 3a side, and an AC waveform having a phase opposite to that of the secondary winding 3a is generated on the secondary winding 3b side.

The cable 4 transmits an AC waveform generated from the winding 3b and radiates an electric field. The electric field radiation generated by the AC waveform transmitted to the fluorescent lamp 2 from the secondary winding 3a. , A circuit that radiates an electric field of opposite phase.

The cable 4 also emits an electric field having a phase opposite to that of electric field radiation generated by an AC waveform transmitted from the secondary winding 3a to the fluorescent lamp 2 on the substrate even when the cable 4 is used in a substrate pattern. This is possible if the signal is configured to flow.

Next, a specific example of the present invention will be described.

FIG. 1 shows an embodiment of an electric field suppressing circuit for a liquid crystal backlight using an inverter according to the present invention. The inverter unit 1 includes an inverter transformer 3, transistors 5 and 6 for resonance circuit switching, a base current setting resistor 7 for each of the transistors 5 and 6, a base current setting resistor 8, a transistor 5 and a transistor 6. It comprises a resonance capacitor 10 provided between the collector side and a ballast capacitor 9 provided between the output side of the inverter transformer 3 and the phosphor.

The inverter transformer 3 includes a transistor 5,
Primary winding by alternate switching of transistor 6
3c and the resonance capacitor 10 cause LC resonance, and the DC voltage supplied from the DC power supply 13 can be generated as an AC voltage in the secondary winding, and operates as a self-excited resonance inverter. Here, the secondary windings are 3a and 3b
And grounding the intersection point,
It is possible to generate AC waveforms of opposite phases in the secondary winding 3a and the secondary winding 3b.

The secondary winding 3a is connected to the fluorescent lamp 2 in the backlight of the liquid crystal panel 11 via a cable 12 via a ballast capacitor 9. The fluorescent lamp is turned on by an AC voltage and operates as a light source for the liquid crystal panel 11. I do. From this, the transformer 3, the ballast capacitor 9, the cable 12
Generates electric field radiation due to the AC waveform 12a. Here, by laying the cable 4 connected to the secondary winding 3b in the vicinity of the transformer 3, the ballast capacitor 9, and the cable 12, a reverse phase is provided in the vicinity of the transformer 3, the ballast capacitor 9, and the cable 12. Electric field radiation by the AC waveform 4a can be generated. Therefore,
Cable 4, transformer 3, ballast capacitor 9,
The mutual radiation electric fields of the cables 12 can cancel each other, and the effect of reducing the electric field radiation can be obtained at low cost without providing a shield fitting or a special circuit.

The effect of the cable 4 connected to the secondary winding 3b is increased as it is closer to the transformer 3, the ballast capacitor 9, and the cable 12 through which the phosphor driving signal flows. Although described as a cable, it is not limited to this. For example, it may be a pattern on a substrate.

[0017]

As described above, according to the electric field suppressing circuit of the present invention, in the electric field suppressing circuit of the backlight for the liquid crystal using the inverter, the electric field radiation can be performed at a low cost without requiring any parts such as a shield. The effect of reduction is obtained.

[Brief description of the drawings]

FIG. 1 is a diagram showing a circuit configuration which is an embodiment of an electric field suppression circuit of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Inverter part 2 Fluorescent lamp 3 Inverter transformer 4 Cable 5 Transistor 6 Transistor 7 Resistance 8 Resistance 9 Ballast capacitor 10 Resonance capacitor 11 Liquid crystal panel 12 Cable 13 DC power supply

Claims (2)

[Claims] 1. A liquid crystal backlight device for lighting a fluorescent lamp using an inverter circuit, comprising: a circuit for generating a waveform having an opposite phase to an AC waveform for driving the fluorescent lamp. circuit. 2. An inverter circuit comprising: a winding on a side for generating an AC waveform for driving a fluorescent lamp on a secondary winding; and a waveform having an opposite phase to the AC waveform for driving the fluorescent lamp. 2. The electric field suppression circuit according to claim 1, further comprising a transformer having a winding for generating a voltage, providing a tap on a secondary side of the transformer, and grounding the tap.