Back light unit

Details Back light unit Back light unit

2003-04-25

2004-09-28

Wong, Don (Department: 2821)

Electric lamp and discharge devices: systems

Plural power supplies

Plural cathode and/or anode load device

C362S227000, C362S097200

Reexamination Certificate

active

06798150

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a back light unit for a liquid crystal display device, and more particularly, to power lines connected between lamps and an inverter in a back light unit for a liquid crystal display device.
2. Discussion of the Related Art
The CRT (Cathode Ray Tube) display technology, which is employed in a wide variety of applications—such as TV receivers, instruments, computer monitors, and information terminals—cannot meet the requirements of reduced size and weight needed for electronic goods due to weight and size of the CRT itself. Thus, the CRT display has certain limitations in the trend of reducing size and weight of electronic goods in view of weight and size of the CRT.
Of the types of displays that are expected to replace CRTs, liquid crystal displays (LCD) using an electro-optical effect, plasma display panels (PDP) using gaseous discharge, EL displays (Electro Luminescence Display) using an electro luminescence effect, and the like, have been researched. Among these, the LCD display has been the most actively researched. As such, in order to replace CRTs, development of the LCDs has been successful in reducing size, weight, and power consumption of the displays. Accordingly, LCDs are becoming increasingly used as flat displays for not only monitors in laptop computers, but also monitors in desktop computers and large sized information displays.
Since most LCDs are light receptive devices in which control of a light provided from outside the device is required for displaying a picture, a separate light source for providing the light to an LCD panel (i.e., a back light unit) is required. In general, the back light unit used as the light source of the LCD is a cylindrical lamp arranged in an edge light type or a direct type.
In the edge light type, a lamp unit is place at a side of a light plate that guides the light, wherein the lamp unit is provided with a lamp for emission of the light, lamp holders inserted in both sides of the lamp for protection of the lamp, and a lamp reflecting plate inserted in a side surface of the light plate to surround an outside surface of the lamp for reflecting the light from the lamp toward the light plate. The edge light type, with the lamp unit provided to the side surface of the light plate, is employed in comparatively small sized LCDs—such as laptop computers and desk top computers—having good uniformity of light, long lifetime, and easy fabrication with thin dimensions.
On the other hand, the direct type is more commonly used as size of the LCD becomes larger greater than 20 inches with a priority given thereto. The direct type is provided with a plurality of lamps arranged on a line under a diffuse plate for directing the light to a front surface of the LCD panel, directly. Because the direct type has a light utilization efficiency higher than that of the edge light type, the direct type is employed in large sized LCDs.
A related art back light unit will be described with reference to the attached drawings.
FIG. 1
illustrates a perspective view of a related art direct type back light unit,
FIG. 2
illustrates a plan view of a first related art lamp arrangement,
FIG. 3
illustrates a back view of a back light unit having inverters for applying electrical signal to the lamps in the arrangement of
FIG. 2
, and
FIG. 4
illustrates a plan view of a second related art lamp arrangement.
Referring to
FIGS. 1 and 2
, the related art back light unit is provided with a plurality of lamps
1
, an outside case
3
for holding and supporting the lamps
1
, and light scattering means
5
a
,
5
b
, and
5
c
between the lamps
1
and an LCD panel (not shown). The light scattering means
5
a
,
5
b
, and
5
c
is provided with a plurality of diffusion sheets and diffusion plates between the lamps
1
and the LCD panel for enhancing a light scattering effect to prevent the lamps from being shown on a screen of the LCD and providing a uniform luminance distribution. There is a reflection plate
7
on an inside surface of the outside case
3
for directing the light from the lamps
1
only to the display part of the LCD panel.
The lamp
1
is a cold cathode fluorescent lamp (CCFL) provided with electrode parts
2
a
and
2
b
at opposite ends of an inside of a tube, each connected to a power line
9
a
or
9
b
. Opposite ends of the lamp
1
are inserted in holes formed in opposite surfaces of the outside case
3
. When a voltage is provided to the electrode parts
2
a
and
2
b
through the power lines
9
a
and
9
b
, the lamp
1
emits the light. The voltage provided to the power lines is supplied from an inverter
30
provided in one side part of back of the outside case
3
, as shown in FIG.
3
. In the power lines
9
a
and
9
b
, there are a high voltage power line
31
and a low voltage power line
32
depending on voltages provided thereto. That is, the high voltage power line
31
and the low voltage power line
32
from opposite ends of the lamp
1
are connected to one/the other terminals of the inverter
30
connector for receiving voltages.
To minimize electrical influences on the LCD panel and external devices, a length of the high voltage power line
31
is shorter than a length of the low voltage power line
32
. In the related art direct type back light unit, a length of the lamp
1
is substantially equal to a length of a front light emission surface of the back light unit. Therefore, the larger the size of the light emission surface, the longer the length of the lamp
1
. For an example, currently an LCD with a size over 30-40 inches requires a length of the lamp longer than 700 mm.
Thus, the longer the length of the lamp not only is fabrication of the lamp more difficult, but also assembly of the lamp with the back light unit is more difficult and susceptible to an external impact damage. Moreover, a luminance of the lamp becomes non-uniform. Thus, picture quality deterioration (EMI: Electro Magnetic Interference) occurs due to instability and electronic influence from the driving circuit of the LCD because high turn-on and sustaining voltages are required.
Due to such a problem, in some direct type back light units, as shown in
FIG. 4
, the lamps
40
are arranged in a height direction of the light emission surface. In this instance, the electrode parts
42
a
and
42
b
are provided at opposite ends of an inside of each tube of the lamp
40
, and the power lines
43
a
and
43
b
are connected to the electrode parts
42
a
and
42
b
, respectively. A reflection plate
41
is provided behind the lamps
40
.
However, the arrangement of the lamps
40
in the height direction of the light emission surface causes mercury inside of the tubes of the lamp
40
to gather to a bottom thereof due to gravity. As a result, performance of the lamp
40
is deteriorated if the back light unit is used for a long time.
SUMMARY OF THE INVENTION
Accordingly, the present invention is directed to a back light unit that substantially obviates one or more of the problems due to limitations and disadvantages of the related art.
An object of the present invention is to provide a back light unit which can improve an efficiency of a lamp, and permits an effective wiring arrangement for the lamps.
Additional features and advantages of the invention will be set forth in the description which follows, and in part will be apparent from the description, or may be learned by practice of the invention. The objectives and other advantages of the invention will be realized and attained by the structure particularly pointed out in the written description and claims hereof as well as the appended drawings.
To achieve these and other advantages and in accordance with the purpose of the present invention, as embodied and broadly described, a back light unit having a light emission surface comprises a plurality of lamps each having first and second ends, each lamp disposed substantially only in one of an integer (n) number regions of the light emission surface, wherein the regions div

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