KR101137883B1 - backlight unit - Google Patents

Abstract

The present invention is to provide a backlight unit that can improve the brightness by reducing the current deviation input to each transformer to reduce the heat generation difference between the transformer, the backlight unit for achieving the above object is N fluorescent lamps arranged in one direction A lamp array unit including a plurality of blocks in units of one block; First and second current limiting elements connected to both ends of the fluorescent lamps, respectively; First and third transformers having a first output power line commonly connected to the first and second current limiting elements of the fluorescent lamps arranged in a first block; Second and fourth transformers in which a first output power line is commonly connected to the first and second current limiting elements of the fluorescent lamps arranged in a second block; First and second common mode choke coils having first output terminals connected to first and second input power lines of the first transformer and second output terminals connected to first and second input power lines of the second transformer, respectively. and; A first switching unit having an output terminal connected to each of the first and second input terminals of the first and second common mode choke coils; Third and fourth common mode choke coils having first output terminals connected to first and second input power lines of the third transformer, and second output terminals connected to first and second input power lines of the fourth transformer, respectively. and; And a second switching unit having an output terminal connected to each of the first and second input terminals of the third and fourth common mode choke coils.

Choke coil, transformer

Description

Backlight unit

1 is a perspective view of a direct type backlight unit according to the prior art;

2 is a view illustrating a power lead wire connected to a conventional light emitting lamp and a connector;

3 is a block diagram for parallel driving a backlight unit according to another conventional technology

4 is a configuration diagram for parallel driving of a backlight unit according to an embodiment of the present invention;

Explanation of symbols on the main parts of the drawings

41a, 41b: first and second electrodes 42: fluorescent lamp

43a, 43b: first and second power lead wires

44a, 44b: first and second current limiting elements

45a, 45b: first and second transformer

46a, 46b: first and second common mode choke coils

47: first switching unit

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a backlight unit, and more particularly, to a backlight unit capable of reducing current variation and reducing a difference in luminance and heat generation of a transformer.

CRT (Cathode Ray Tube), one of the commonly used display devices, is mainly used for monitors such as TVs, measuring devices, and information terminal devices.However, due to the weight and size of the CRT itself, Could not respond actively to demands.

Therefore, in the trend of miniaturization and light weight of various electronic products, CRT has a certain limit in weight and size, and is expected to replace the liquid crystal display (LCD) and gas discharge using electro-optic effects. Plasma Display Panels (PDPs) and Electro Luminescence Displays (ELDs) using electroluminescent effects are used. Among them, research on liquid crystal displays is being actively conducted.

In order to replace the CRT, liquid crystal display devices having advantages such as small size, light weight, and low power consumption have been actively developed. Recently, the liquid crystal display device has been developed enough to perform a role as a flat panel display device. As it is used for a monitor of a desktop computer and a large information display device, the demand for a liquid crystal display device is continuously increasing.

Since most of the liquid crystal display devices are light-receiving devices that display images by controlling the amount of light coming from the outside, a separate light source for illuminating the LCD panel, that is, a backlight unit, is necessary.                         

In general, the backlight unit used as the light source of the liquid crystal display device is a method of disposing a cylindrical fluorescent lamp, and is divided into an edge method and a direct method.

First, the edge method is that the lamp unit is installed on the side of the light guide plate for guiding the light, the lamp unit is a lamp that emits light, the lamp holder which is inserted at both ends of the lamp to protect the lamp and the outer peripheral surface of the lamp and one side It is provided with a lamp reflection plate fitted to the side of the light guide plate to reflect the light emitted from the lamp toward the light guide plate.

The edge method in which the lamp unit is installed on the side of the light guide plate is applied to a relatively small liquid crystal display device such as a monitor of a laptop computer and a desktop computer, and has good light uniformity and a long durability life. It is advantageous to thin the liquid crystal display device.

On the other hand, the direct method began to be developed mainly as the size of the liquid crystal display device became larger than 20 inches, and arranged a plurality of lamps in a row on the lower surface of the diffuser plate to direct light directly to the front of the LCD panel. will be.

The direct method is mainly used for a large screen liquid crystal display device requiring high luminance because the light utilization efficiency is higher than that of the edge method.

However, the liquid crystal display device adopting the direct method is used as a large monitor or a television, and it takes longer to use than a laptop computer, and the number of lamps is larger. It is more likely that a lamp that will not turn on will appear due to the failure and life of the lamp in the display.

The light source of the liquid crystal display device of the edge method and the direct method is EL (Electro Luminescence), LED (Light Emitting Diode), CCFL (Cold Cathode Fluorescent Lamp), HCFL (Hot Cathode Fluorescent Lamp), EEFL (External Electrode Fluorescent Lamp) ) Can be used.

Hereinafter, the backlight unit of the direct type according to the prior art will be described.

1 is a perspective view of a backlight unit of a direct method according to the prior art, Figure 2 is a view showing a power lead wire connected to a conventional light emitting lamp and connector.

As shown in FIG. 1, the backlight unit according to the related art includes a plurality of light emitting lamps 1, an outer case 3 for fixing and supporting the light emitting lamps 1, and the light emitting lamps ( Light scattering means 5a, 5b, 5c disposed between 1) and a liquid crystal panel (not shown).

The light scattering means (5a, 5b, 5c) is to prevent the shape of the light emitting lamp from appearing on the display surface of the liquid crystal panel and to provide a light source having an overall uniform brightness distribution, in order to enhance the light scattering effect A plurality of diffusion sheets, diffusion plates, and the like are disposed between the cells.

The inner surface of the outer case 3 is disposed with a reflector 7 so that the light emitted from the light emitting lamp 1 can be concentrated to the display unit of the liquid crystal panel, which is to maximize the utilization efficiency of the light.

The light emitting lamp 1 is composed of a cold cathode lamp (CCFL), as shown in FIG. 2, and electrodes 2 and 2a are disposed at both ends of a tube. When power is applied to 2 and 2a, the light is emitted, and both ends of the light emitting lamp 1 are fitted in grooves formed on both sides of the outer case 3 as shown in FIG.

Power leads 9 and 9a for transmitting power for driving the lamp are connected to both electrodes 2 and 2a of the light emitting lamp, and the power leads 9 and 9a are connected to a separate connector 11 to drive a drive circuit. Although connected to the furnace, a separate connector 11 is required for each light emitting lamp 1.

That is, as shown in FIG. 2, the power lead wire 9 connected to one electrode 2 of the light emitting lamp and the power lead wire 9a connected to the other electrode 2a are connected to one connector 11, and the power lead wire ( Any one of 9 and 9a is bent to the bottom of the outer case 3 and connected to the connector 11.

However, such a conventional backlight unit for a liquid crystal display device has a connector connected to a power supply lead of a light emitting lamp and connected to a driving circuit. Since the connector is individually required for each light emitting lamp, wiring is complicated and the purpose of reducing the thickness of the backlight unit is reduced. By connecting the connector to the connector by bending the power lead line, not only the work efficiency is lowered, but also a separate work is required for this, which increases the process time and decreases the productivity.

In addition, in order to connect the electrode and the connector, a hole penetrating the outer case must be drilled and both electrodes of the light emitting lamp must be inserted into the hole so that both electrodes of the light emitting lamp are exposed to the outside of the outer case. Falling and maintenance of the luminous lamp is difficult.                         

Next, a direct backlight unit according to another conventional technique will be described.

3 is a configuration diagram for parallel driving of a backlight unit according to another conventional technology.

In the backlight unit according to another conventional technology, as shown in FIG. 3, a plurality of fluorescent lamps 32 having first and second electrodes 31a and 31b disposed at both ends of a tube at predetermined intervals. The first and second power lead wires 33a and 33b for transmitting power are connected to the first and second electrodes 31a and 31b on both sides of the fluorescent lamp 32. First and second capacitors 34a and 34b are connected to the first and second power lead wires 33a and 33b of 32, respectively.

The driving of the plurality of fluorescent lamps 32 is controlled by using N or more (N is an integer of 2 or more) as one unit. Hereinafter, the driving of four fluorescent lamps as a unit will be described. .

The first capacitors 34a of the upper four fluorescent lamps 32 are commonly connected to the first output power line of the first transformer 35a, and the first capacitor 34a of the lower four fluorescent lamps 32 is common. Are commonly connected to the first output power line of the second transformer 35a. The second output power lines of the first and second transformers 35a and 35b are commonly grounded.

Input power lines of the first and second transformers 35a and 35b are connected to the switching unit 36.

The second capacitors 34b of the upper and lower fluorescent lamps 32 are commonly connected to the first output power line of the third and fourth transformers (not shown), and the second output power of the third and fourth transformers. The lines are common grounded.

Although not shown in the figure, the left and right have the same configuration based on the fluorescent lamp.

In the backlight unit configured as described above, the current from the switching unit 36 is divided into the first and second transformers 35a and 35b and the third and fourth transformers, and the fluorescent lamp is connected through the output power line of each transformer. Is passed on.

The backlight unit according to the related art has the following problems.

When several fluorescent lamps are connected to one transformer, and the current from the switching part is divided into the first, second transformer, and third and fourth transformers, the characteristic tolerance (amplification difference) at the time of manufacture of each transformer Therefore, a difference occurs in the amount of current (I1, I2) input through the input power line of each transformer. As a result, a deviation occurs in the output voltage output through the output power line of the transformer, and the deviation of the tube current applied to the fluorescent lamp is increased. This current deviation reduces the brightness uniformity of the backlight unit, and when a large amount of current is input to any one transformer, there is a problem of generating heat difference between the transformers.

The present invention has been made to solve the above problems, and an object of the present invention is to provide a backlight unit that can improve the brightness by reducing the current deviation input to each transformer and reduce the heat generation difference between the transformers.

According to an aspect of the present invention, there is provided a backlight unit including: a lamp array unit including a plurality of blocks using N fluorescent lamps arranged in one direction as a unit of a block; First and second current limiting elements connected to both ends of the fluorescent lamps, respectively; First and third transformers having a first output power line commonly connected to the first and second current limiting elements of the fluorescent lamps arranged in a first block; Second and fourth transformers in which a first output power line is commonly connected to the first and second current limiting elements of the fluorescent lamps arranged in a second block; First and second common mode choke coils having first output terminals connected to first and second input power lines of the first transformer and second output terminals connected to first and second input power lines of the second transformer, respectively. and; A first switching unit having an output terminal connected to each of the first and second input terminals of the first and second common mode choke coils; Third and fourth common mode choke coils having first output terminals connected to first and second input power lines of the third transformer, and second output terminals connected to first and second input power lines of the fourth transformer, respectively. and; And a second switching unit having an output terminal connected to each of the first and second input terminals of the third and fourth common mode choke coils.

The second output power supply lines of the first and second transformers and the second output power supply lines of the third and fourth transformers are respectively grounded in common.

The fluorescent lamp has first and second electrodes provided at both ends of a tube, and first and second power lead wires are connected to the first and second electrodes.                     

The first and second current limiting elements are characterized by consisting of a capacitor.

The first and second common mode choke coils may be configured by winding a coil having an inductance value high enough to neglect the resistance of the first and second transformers.

The first number of coils N1 wound in the direction of the first output terminal at the first input terminal of the first and second common mode choke coils, and the number of the second coils N2 wound in the direction of the second output terminal at the second input terminal are 1: It is characterized in that it is configured to have a ratio of 1.

The third and fourth common mode choke coils may be configured by winding a coil having an inductance value high enough to neglect the resistance of the third and fourth transformers.

The number of coils wound from the first input end of the third and fourth common mode choke coils toward the first output end and the number of coils wound from the second input end of the third and fourth common mode choke coils have a ratio of 1: 1. It is done.

Hereinafter, a backlight unit according to a preferred embodiment of the present invention will be described with reference to the accompanying drawings.

4 is a configuration diagram for parallel driving of a backlight unit according to an exemplary embodiment of the present invention.

In the backlight unit according to the exemplary embodiment of the present invention, as shown in FIG. 4, there is a lamp array unit including N fluorescent lamps 42 arranged in one direction as one block unit.

In this case, the plurality of fluorescent lamps 42 of the lamp array unit are provided with first and second electrodes 41a and 41b inside both ends of the tube, and the first and second electrodes (both sides of the fluorescent lamp 42) ( First and second power lead wires 43a and 43b are connected to 41a and 41b, and the first and second power lead wires connected to the first and second electrodes 41a and 41b of the fluorescent lamp 42. First and second current limiting elements 44a and 44b are connected to 43a and 43b, respectively. At this time, the first and second current limiting elements 44a and 44b are constituted by a capacitor.

In the above-described plurality of fluorescent lamps 42, N or more (N is an integer of 2 or more) are configured to receive driving voltages by one transformer on each side in units of one block. The case where a fluorescent lamp is comprised by one unit is demonstrated to an example.

For example, the first current limiting elements 44a of the four fluorescent lamps 42 corresponding to the first block 1 are commonly connected to the first output power line of the first transformer T1 45a. The first current limiting elements 44a of the four fluorescent lamps 42 corresponding to the second block 2 are commonly connected to the first output power line of the second transformer T2 45a. The second output power lines of the first and second transformers 45a and 45b are commonly grounded.

The first and second input power lines of the first transformer 45a are connected to first output terminals of the first and second common mode choke coils 46a and 46b, respectively. The first and second input power lines are connected to respective second output terminals of the first and second common mode choke coils 46a and 46b.                     

The first and second input terminals of the first and second common mode choke coils 46a and 46b are commonly connected to the output signal terminal of the first switching unit 47.

Although not shown in the figure, the left and right sides have the same configuration based on the fluorescent lamp. The second current limiting elements 44b of the four fluorescent lamps 42 located in the first and second blocks 1 and 2 Block are common to the first output power lines of the third and fourth transformers (not shown). The second output power lines of the third and fourth transformers are connected to a common ground, and the first and second input power lines of the third transformer are connected to the first output terminal of the third and fourth common mode choke coils. The first and second input power lines of the fourth transformer are connected to the second output terminal of the third and fourth common mode choke coils. The first and second input terminals of the third and fourth common mode choke coils are commonly connected to the output signal terminals of the second switching unit.

In the backlight unit configured as described above, the current from the first switching unit 47 is divided into the first and second transformers 45a and 45b, and the current from the second switching unit is transferred to the third and fourth transformers. It is divided and entered, and the driving voltage is transmitted to the fluorescent lamp through the output power line of each transformer.

In the above description, the common mode choke coil means that one signal enters two input terminals and comes out of two output terminals.

In this case, the first and second common mode choke coils 46a and 46b are disposed at the front ends of the first and second transformers 45a and 45b to compensate for the characteristic tolerances of the first and second transformers 45a and 45b. A coil having an inductance value high enough to neglect the resistance of the transformer, which is output through the first and second common mode choke coils 46a and 46b to be input to the first and second transformers 45a and 45b. The deviation of the currents I1 and I2 to be reduced as much as possible.

Here, the first number of coils N1 wound in the direction of the first output end from the first input end of the first and second common mode choke coils 46a and 46b, as shown in FIG. 4, and in the direction of the second output end from the second input end. The number of wound second coils N2, that is, N1: N2, is configured to have a ratio of 1: 1.

In addition, although not shown in the drawing, the third and fourth common mode choke coils have an inductance high enough to neglect the resistance of the transformer in front of the third and fourth transformers to compensate for the characteristic tolerances of the third and fourth transformers. By attaching a coil having a value, the deviation of each current output through the third and fourth common mode choke coils is reduced as much as possible.

In addition, the number of first coils wound from the first input end of the third and fourth common mode choke coils toward the first output end and the number of second coils wound from the second input end toward the second output end have a ratio of 1: 1.

In general, inverter refers to a device that converts DC power to AC power. In the DC-> AC conversion method, push-pull, half bridge, and full bridge methods are used. In the present invention, a full bridge method is used.

In addition, the present invention is configured in parallel to drive four fluorescent lamps per transformer.                     

The inverter of the present invention includes the first and second switching units, the first to fourth transformers, and the first to fourth common mode choke coils. A plurality of lamps can be driven using a transformer.

In the above description, only the configuration in which the fluorescent lamp is divided into the first and second blocks has been described. However, the fluorescent lamp may be configured to have more blocks according to the size of the screen.

It will be apparent to those skilled in the art that various modifications and variations can be made in the present invention without departing from the spirit of the invention.

Accordingly, the technical scope of the present invention should not be limited to the contents described in the above embodiments, but should be determined by the claims.

The backlight unit of the present invention as described above has the following effects.

First, the first and second common mode choke coils having an inductance value high enough to neglect the resistance of the transformer in front of the first and second transformers are attached, and are output through the first and second common mode choke coils. By reducing the deviation of the current coming out as much as possible, the current deviation input to each transformer can be reduced. This can improve the luminance unevenness problem of the lamp.

Second, since the current deviation input to each transformer can be reduced, it is possible to improve the heat generation difference between the transformer caused by a large amount of current input to any one transformer.

Claims (8)

A lamp array unit including a plurality of blocks using N fluorescent lamps arranged in one direction as one block unit; First and second current limiting elements connected to both ends of the fluorescent lamps, respectively; First and third transformers having a first output power line commonly connected to the first and second current limiting elements of the fluorescent lamps arranged in a first block; Second and fourth transformers in which a first output power line is commonly connected to the first and second current limiting elements of the fluorescent lamps arranged in a second block; First and second common mode choke coils having first output terminals connected to first and second input power lines of the first transformer and second output terminals connected to first and second input power lines of the second transformer, respectively. and; A first switching unit having an output terminal connected to each of the first and second input terminals of the first and second common mode choke coils; Third and fourth common mode choke coils having first output terminals connected to first and second input power lines of the third transformer, and second output terminals connected to first and second input power lines of the fourth transformer, respectively. and; A second switching unit connected to an output terminal of each of the first and second input terminals of the third and fourth common mode choke coils; And a second output power line of the first and second transformers and a second output power line of the third and fourth transformers are common grounded. delete The method of claim 1, The fluorescent lamp is provided with first and second electrodes in both ends of the tube, And a first and a second power lead wire are connected to the first and second electrodes. The method of claim 1, And the first and second current limiting elements comprise a capacitor. The method of claim 1, And a first impedance value due to inductances of the first and second common mode choke coils is relatively larger than a second impedance value due to resistance of the first and second transformers. The method of claim 1, The first number of coils N1 wound in the direction of the first output terminal at the first input terminal of the first and second common mode choke coils, and the number of the second coils N2 wound in the direction of the second output terminal at the second input terminal are 1: A backlight unit, characterized in that configured to have a ratio of one. The method of claim 1, And a third impedance value due to the inductance of the third and fourth common mode choke coils is relatively larger than a fourth impedance value due to the resistance of the third and fourth transformers. The method of claim 1, The number of coils wound from the first input end of the third and fourth common mode choke coils toward the first output end and the number of coils wound from the second input end of the third and fourth common mode choke coils have a ratio of 1: 1. Backlight unit.

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