JP2011086535A - Backlight unit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a backlight unit capable of suppressing occurrence of luminance unevenness due to leakage current.
SOLUTION: A case 1 having a conductive bottom portion, a lighting circuit 3 provided in the case 1, and a pair of electrodes 44a and 44b are provided at both ends of a glass tube 41, and a pair of electrodes 44a, 44b is provided with a discharge lamp 4 arranged in the case 1 so that electric power is supplied from the lighting circuit 3, and a pair of electrodes 44a and 44b and an electric electrode are provided on the outer surface of the glass tube 41 of the discharge lamp 4. It is characterized in that electrically connected conductors 45 are formed.
[Selection] Figure 1

Description

  The present invention relates to a backlight unit used in a liquid crystal display device or the like.

  Since a liquid crystal display device such as a liquid crystal television does not emit liquid crystal itself, a backlight unit is used as a light source. The backlight unit is as shown in FIG. 7 and includes a case 101, a reflection sheet 102, a lighting circuit 103, a cold cathode fluorescent lamp 104, and the like. As shown in FIG. Is arranged along the bottom of the case 101 and connected to the lighting circuit 103.

  Since the case 101 of such a backlight unit is desired to have high strength and excellent workability, metal is often used at present. However, when the case 101 is made of a metal material, as shown in FIG. 9, the potential difference between the metal and the lamp becomes large, and a leakage current is generated. This leakage current is also mentioned in Japanese Patent Laid-Open No. 2006-39487 (hereinafter referred to as Patent Document 1). When the influence of the leakage current becomes large, the light emission in the tube axis direction of the cold cathode fluorescent lamp 104 becomes non-uniform and the backlight emits non-uniformly.

JP 2006-39487 A

  Patent Document 1 attempts to reduce leakage current by providing an insulating member on a lower frame so that the distance between the lamp and the frame used as a lamp is not more than a certain distance even when the lamp is bent. However, when the lamp comes into contact with the insulating member, the temperature is lowered only at that portion, so that it is impossible to suppress the occurrence of luminance unevenness due to the deviation of mercury. In addition, when an insulating member is newly provided, the number of parts increases and the configuration becomes complicated.

  The objective of this invention is providing the backlight unit which can suppress generation | occurrence | production of the brightness nonuniformity by leakage current.

  In order to achieve the above object, the backlight unit of the present invention comprises a case having a conductive bottom, a lighting circuit provided in the case, and a pair of electrodes at both ends of the glass tube. A discharge lamp disposed in the case so that electric power is supplied from the lighting circuit to the pair of electrodes, and an outer surface of the glass tube of the discharge lamp is provided with the pair of electrodes. An electrically connected conductor is formed.

  According to the present invention, it is possible to suppress the occurrence of luminance unevenness due to leakage current.

The figure for demonstrating the backlight unit of the 1st Embodiment of this invention. The figure for demonstrating the voltage distribution of the backlight unit of FIG. The figure for demonstrating the backlight unit of the 2nd Embodiment of this invention. The figure for demonstrating the voltage distribution of the backlight unit of 2nd Embodiment. The figure for demonstrating the other example of a backlight unit. The figure for demonstrating the voltage distribution of the backlight unit of FIG. The figure for demonstrating the conventional backlight unit. The figure for demonstrating arrangement | positioning / connection of each member of the conventional backlight unit. The figure for demonstrating the voltage distribution of the backlight unit of FIG.

(First embodiment)
Hereinafter, a backlight unit according to an embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a diagram for explaining a backlight unit according to a first embodiment of the present invention.

  The backlight unit of the present embodiment is a direct type backlight unit, and its container is constituted by a case 1. The case 1 is shown only at the bottom and the entire structure is omitted, but like the case 101 in FIG. 1, it has a bottomed opening shape having a bottom and a side and is made of a metal such as SUS. . A reflective sheet 2 having high reflectivity such as white resin is provided on the inner side of the case 1. Although not shown, on the opening side of the case 1, an optical surface material such as a diffusing plate and a diffusing sheet and a lid having an opening that fits the case 1 are arranged.

  A lighting circuit 3 is disposed on the back side of the case 1. The lighting circuit 3 is a circuit called a so-called inverter that outputs a high frequency composed of components such as a transistor, an inductor, a transformer, and a capacitor.

  Inside the case 1, a plurality of cold cathode fluorescent lamps 4 are arranged in parallel as discharge lamps. The cold cathode fluorescent lamp 4 includes a glass tube 41 as a main part. The glass tube 41 is made of, for example, borosilicate glass. Mercury and a rare gas are sealed inside the glass tube 41. As the rare gas, xenon, krypton, argon, neon, helium and the like can be used singly or in combination of two or more, and a neon-argon mixed gas is preferable. The sealing pressure is preferably 5 to 50 torr. A phosphor layer 42 made of a three-wavelength phosphor is applied to the inner surface of the glass tube 41.

  A pair of lead wires 43 a and 43 b made of, for example, Kovar are sealed at both ends of the glass tube 41 and led out to the inside and outside of the glass tube 41. Electrodes 44a and 44b are connected to the lead wires 43a and 43b led into the glass tube 41 so as to face each other. Here, since the lighting circuit 103 has a so-called single high voltage type circuit configuration, one end side of the discharge lamp is set to the ground potential. In this example, the electrode 44b is set to the ground potential (low voltage side), and the electrode 44a is set to the high voltage side.

  A conductor 45 is formed on the outer surface of the glass tube 41. The conductor 45 is formed so as to straddle the pair of electrodes 44a and 44b along the tube axis direction of the glass tube 41, and both ends thereof are connected to the lead wires 43a and 43b. Thus, unless the conductor 45 and the electrodes 44a and 44b are electrically connected, the effect of suppressing the leakage current cannot be obtained. The conductor 45 preferably has a resistance value of 10 MΩ or more and 1000 MΩ or less. In order to set the resistance value of the conductor 45 to such a suitable value, the material, the film thickness, and the coating width may be adjusted. In the present embodiment, ITO (indium-tin oxide alloy) is thinly applied to almost the entire outer surface of the glass tube 41.

  Here, luminance unevenness when a high frequency voltage is applied to the backlight unit of the present embodiment (example) and the conventional backlight unit (conventional example) not including the conductor 45 as shown in FIG. Were tested. As a result, the luminance unevenness in the tube axis direction of the lamp was confirmed in the conventional example, but it was not confirmed in the example, and the luminance was more uniform in the example.

  The reason why the uneven brightness is improved in the embodiment is that the leakage current is suppressed. The influence of leakage current and the like will be described with reference to FIGS. FIG. 2 is a diagram for explaining the voltage distribution of the embodiment and FIG. 9 is a diagram for explaining the voltage distribution of the conventional backlight unit. The vertical axis indicates the voltage, and the horizontal axis indicates the position between the electrodes. The positive voltage region indicates that the electrode 44a is an anode, and the negative region indicates that the electrode 44b is a cathode. In addition, the solid line indicates the positive column portion of the lamp being lit, the dotted line indicates the conductor portion, and the alternate long and short dash line (matches the horizontal axis) indicates the voltage of the case portion.

As can be seen from FIG. 9, in the conventional backlight unit, since the electrode 1044b is at the ground potential, the voltage of the positive column portion decreases from the high-voltage side electrode 1044a side toward the low-voltage side electrode 1044b side. Become. The large voltage change in the vicinity of the cathode is due to the influence of the cathode fall voltage. Moreover, the voltage of the case 101 part is 0V in any part. Since the positive column portion and the case have such a relationship, a large potential difference is generated between the positive column portion and the case portion during lighting, and a stray capacitance is generated between the glass tube 1041 and the case 101 as shown in FIG. C _{1 to} C ₃ occur, and leakage currents L _{1 to} L ₃ are generated. As a result, the lamp currents I _{1 to} I ₃ change in the tube axis direction of the glass tube 1041, and a luminance difference occurs in the tube axis direction.

  On the other hand, in the example, the voltage of the positive column part and the case part is the same as the conventional example, but the voltage lowering from the high voltage side electrode 44a side to the low voltage side electrode 44b side by the conductor 45. It is formed on the conductor portion. Since the conductor 45 is interposed between the glass tube 41 and the case 1, a leakage current from the positive column portion is generated between the conductor portion. However, as is clear from FIG. 2, since the potential difference between the positive column portion and the conductor portion is small, the occurrence of leakage current is very small. Therefore, the change in the lamp current in the tube axis direction of the glass tube 41 is It becomes small and the nonuniformity of the brightness | luminance of a pipe-axis direction can be suppressed.

  Here, the resistance value of the conductor 45 is preferably 10 MΩ or more. This is because if the resistance value is too low, the current flowing through the conductor 45 increases and the power loss is reduced. To suppress the power loss to about 2% or less of the power supplied to the lamp, the conductive The resistance value of the body 45 is preferably 10 MΩ or more. The resistance value of the conductor 45 is desirably 1000 MΩ or less. This is because if the resistance value is too high, the effect of suppressing the leakage current is reduced.

  The leakage current affects the lamp length, lamp voltage, frequency, and the distance between the glass tube and the bottom. Specifically, if the lamp length is 800 mm or more, the lamp voltage is 1500 V or more, the frequency is 30 kHz or more, and the distance between the glass tube and the bottom is 5 mm or less, the leakage current increases. The invention is particularly effective.

  Therefore, according to the present embodiment, the outer surface of the glass tube 41 of the discharge lamp 4 is extended between the pair of electrodes 43a and 43b and electrically connected to the pair of electrodes 43a and 43b. Since the conductor 45 is formed, the leakage current of the lamp that is lit is reduced, so that the occurrence of uneven brightness can be suppressed.

  Further, by setting the resistance value of the conductor 45 to 10 MΩ or more and 1000 MΩ or less, it is possible to suppress the leakage current while suppressing the decrease in efficiency as much as possible.

(Second Embodiment)
FIG. 3 is a diagram for explaining a backlight unit according to the second embodiment of the present invention. About each part of subsequent embodiment, the same part as each part of 1st Embodiment is shown with the same code | symbol, and the description is abbreviate | omitted.

  In the second embodiment, the electrodes 44a and 44b are placed on the high voltage side by the lighting circuits 31 and 32, and the so-called dual high voltage type configuration is used in which pulses having the same phase are supplied. The voltage distribution in this case is as shown in FIG. 4, and the change in luminance due to the leakage current is from one electrode to the approximate center in the tube axis direction of the lamp, that is, half the length of the first embodiment. The occurrence of uneven brightness can be suppressed.

  In addition, this invention is not limited above, For example, you may change as follows.

  The case 1 may be formed by, for example, forming a metal reflective film on the inner surface of the resin case 1, and may be any structure as long as the bottom of the case 1 has conductivity.

  The discharge lamp 4 may be an outer surface electrode fluorescent lamp or a hot cathode fluorescent lamp, and may have a bent shape such as an L shape, a C shape, or a U shape.

  The conductor 45 may be IZO, ZnO, SnO or the like. Further, the formation range does not have to be the entire circumference of the outer surface of the glass tube 1, and may be a half or a quarter of the circumference, or a strip-like conductor extended along the tube axis. Good. In that case, it is desirable that at least a part is located between the bottom of the case 1 and the outer surface of the glass tube 41. The conductor 45 is not limited to a film-like material, and may be a metal wire such as nickel or SUS formed in a spiral shape.

  As shown in FIG. 5, a voltage having the same phase as the voltage applied to the cold cathode fluorescent lamp 4 may be applied to the bottom of the case 1 by the lighting circuit 33. In this case, as shown in FIG. 6, in the voltage distribution of the backlight unit, the voltage at the case portion becomes high and the potential difference from the positive column portion becomes small, so that the leakage current can be reduced and luminance unevenness can be suppressed. Incidentally, in this example, it is not necessary to provide the conductor 45, and only this configuration can be expected to suppress the leakage current. The output voltage of the lighting circuit 33 is preferably about half of the voltage applied to the cold cathode fluorescent lamp 4. In this structure, the case 1 is made of an insulating member such as PET (polyethylene terephthalate), silver is deposited instead of the reflective sheet 2, and the silver layer and the lighting circuit 33 are connected to apply a voltage. It is desirable that the case 1 is configured so as not to get an electric shock even if it is directly touched.

DESCRIPTION OF SYMBOLS 1 Case 2 Reflective sheet 3 Lighting circuit 4 Cold cathode fluorescent lamp 41 Glass tube 42 Phosphor layer 43a, 43b Lead wire 44a, 44b Electrode 45 Conductor

Claims (2)

A case having a conductive bottom portion, a lighting circuit provided in the case, and a pair of electrodes provided at both ends of the glass tube so that electric power is supplied to the pair of electrodes from the lighting circuit. And a discharge lamp disposed in the case,
A backlight unit, wherein a conductor electrically connected to the pair of electrodes is formed on an outer surface of the glass tube of the discharge lamp.   The backlight unit according to claim 1, wherein a resistance value of the conductor is 10 MΩ or more and 1000 MΩ or less.

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