Patent Application
20090059131
This application claims priority under 35 U.S.C. §119 to Korean Patent Application No. 2007-0088467 filed in the Korean Intellectual Patent Office on Aug. 31, 2007, the contents of which are herein incorporated by reference in their entirety.
1. Field of the Invention
The present invention relates to a lamp and a liquid crystal display device having the same, and more particularly, to a low-cost and long-lifespan lamp and a liquid crystal display device having the same.
2. Description of the Related Art
Generally, liquid crystal display (“LCD”) devices display images by using electro-optical properties of liquid crystal. An LCD device includes an LCD panel and a backlight unit. The backlight unit supplies the LCD panel with the light necessary to display images.
The backlight unit includes a light source and an optical sheet. A cold cathode fluorescent lamp (“CCFL”) is often used as the light source.
Referring to
More specifically, the discharge tube 1 has a shape of a transparent tube whose both ends are sealed. The phosphor 2 is disposed on an inner wall of the discharge tube 1. The anode 3 and a cathode 4 are arranged at both ends of the discharge tube 1, respectively, to receive an AC voltage from an external inverter 6. The mixed gas 5, which contains neon (Ne), argon (Ar), and mercury (Hg), is injected in the discharge tube 1.
When a high voltage is applied between the anode 3 and cathode 1, the mixed gas 5 is converted into plasma to radiate ultraviolet rays. The ultraviolet rays excite the phosphor 2 to emit visible light.
The conventional lamp 10 employs Ni as its electrode material which is inexpensive, well-processed, and easily mass-produced.
However, metal atoms or molecules can be released from the anode 3 due to sputtering occurring when the lamp 10 is activated, and such atoms or molecules can be bonded with Hg in the discharge tube 1. As a result, Hg amalgam may be yielded, so that the brightness of the lamp can be lowered. Moreover, the lifespan of the lamp can be reduced because the anode 3 can be quickly worn out by sputtering.
Furthermore, a rise in temperature caused by the high voltage applied to the anode 3 cause a discrepancy in temperature between the anode 3 and cathode 4 resulting in movement of the Hg molecules. As the Hg molecules move toward the cathode 4, as shown in
An aspect of the present invention provides a lamp whose lifespan and brightness can be improved by employing a highly reliable metal as an electrode that is applied with a high voltage, and an LCD device having the same.
An exemplary embodiment of the present invention provides a lamp comprising: a discharge tube having an inner wall coated with a phosphor; a first electrode containing a first metallic material having a first sputtering rate provided at one end of the discharge tube and a second electrode containing a second metallic material having a second sputtering rate provided at the other end of the discharge tube, wherein the first sputtering rate is greater than the second sputtering rate.
The first electrode may be grounded, and the second electrode may be applied with a high voltage.
The first electrode may be formed of Ni or an alloy of Ni, and the second electrode may be formed of any one of niobium (Nb), molybdenum (Mo), tantalum (Ta), and tungsten (W).
The discharge tube may contain a mixed gas, a gas pressure of the mixed gas ranging from about 40 Torr to about 60 Torr.
Thermal conductivity of the second electrode may be higher than thermal conductivity of the first electrode.
A maximum allowable current of the first electrode may be about 8.5 mA, and a maximum allowable current of the second electrode may be about 10 mA.
Each of the first and second electrodes may be shaped as a cup whose inner side is recessed.
The discharge tube may be shaped as a letter “I” or “U”.
Another exemplary embodiment of the present invention provides a liquid crystal display device comprising: a liquid crystal display panel; and a lamp that supplies light to the liquid crystal display panel, the lamp comprising: a discharge tube having an inner wall coated with phosphor; a first electrode containing a first metallic material having a first sputtering rate provided at one end of the discharge tube; and a second electrode containing a second metallic material having a second sputtering rate provided at the other end of the discharge tube, wherein the first sputtering rate is greater than the second sputtering rate.
The liquid crystal display device may further comprise at least one inverter supplying a high voltage to the second electrode to drive the lamp.
A plurality of lamps may be provided at a rear surface of the liquid crystal panel.
The inverter may be provided to have the same number as the number of the lamps to separately drive the lamps.
The liquid crystal display device may further comprise a bottom chassis that receives the lamps, wherein the inverter is provided at a rear surface of the bottom chassis.
The liquid crystal display device may further comprise an optical sheet provided at an upper side of the lamps.
The lamps may be shaped as a letter “I” or “U”.
The liquid crystal display device may further comprise a light guide plate that guides light supplied from the lamp; an optical sheet provided at an upper side of the light guide plate; and a lamp cover that covers the lamp.
The present invention will become readily apparent by reference to the following detailed description when considered in conjunction with the accompanying drawings wherein:
Hereinafter, the present invention will be described in detail with reference to the accompanying drawings.
Referring to
More specifically, the LCD panel 30 includes a color filter substrate 31, a thin film transistor (“TFT”) substrate 32, and a liquid crystal layer interposed between the color filter substrate 31 and the TFT substrate 32. A color filter may be disposed at the color filter substrate 31, and TFTs are arranged on the TFT substrate 32. Sub-pixels are arranged in a matrix form on the LCD panel 30 and driven independently by the TFTs. The sub-pixels control the alignment of liquid crystal molecules by a voltage difference between a common voltage that is supplied to a common electrode and a pixel voltage that is supplied through the TFTs to a pixel electrode, and adjust light transmittance, thereby displaying images. The LCD panel 30 is a non-emission display element, so that the backlight unit 200 is necessary to emit light.
A panel driver is connected to the TFT substrate 32. The panel driver includes a gate driver 41, a data driver 43, a gate circuit film 42 on which the gate driver 41 is mounted, a data circuit film 44 on which the data driver 43 is mounted, and a printed circuit board (“PCB”) 45 on which driving elements such as a timing controller, etc. are arranged.
The gate driver 41 drives gate lines provided on the TFT substrate 32, and the data driver 43 drives data lines provided on the TFT substrate 32.
One side of the gate circuit film 42 is connected to the TFT substrate 32. One side of the data circuit film 44 is connected to the TFT substrate 32, and the other side thereof is connected to the PCB 45.
The gate and data circuit films 42 and 44 shown in
The backlight unit 200 includes a plurality of lamps 100, an optical sheet 60, and a reflective sheet 70. The optical sheet 60 may include a diffusion sheet, a prism sheet, and a protection sheet which are sequentially arranged on the lamps 100. The diffusion sheet diffuses light supplied from the lamps 100 to make the brightness of the light uniform. A plurality of prisms may be rigidly arranged on the prism sheet. The prism sheet collects the light diffused by the diffusion sheet in the direction of the rear surface of the LCD panel 30. In general, the prism sheet consists of two sheets. Most of the light that has passed through the prism sheet is directed perpendicularly to the LCD panel 30 and provides uniform distribution of brightness. The protection sheet prevents the prism sheet from scratching. The optical sheet 60 is received at a mold frame 50. The LCD panel 30 is seated and fixed at the upper part of the mold frame 50.
The lamps 100 may be arranged in a bottom chassis 80 to keep a constant distance from each other. The lamps 100 may be inserted and fixed in sockets 82 provided at opposite sides of the bottom chassis 80.
Two lamp sockets 82 are provided per lamp 100. The number of pairs of lamp sockets 82 are provided to have the same number as that of the number of lamps 100. The outer part of the lamp socket 82 is made of an insulation material to prevent short circuits between the lamps 100.
A top chassis 20 may be provided to cover the non-display region of the LCD panel 30 and fix the LCD panel 30. The top chassis 20 may be combined with the bottom chassis 80.
Referring to
More specifically, the discharge tube 101 is formed of a transparent material, such as glass, in the shape of the letter ‘I’. The phosphor 102 is disposed on the inner wall of the discharge tube 101. The phosphor 102 is made of a fluorescent material, including rare-earth elements such as yttrium (Y), cerium (Ce), terbium (Tb), etc. that can emit visible light by the illumination of ultraviolet rays. The mixed gas includes Hg, Ne, and Ar in the discharge tube 101.
The first electrode 103 may be provided at one of two ends of the discharge tube 101. The first electrode 103 may be connected to a first lead 106 that passes through the inner and outer wall of discharge tube 101. The first lead 106 may be grounded to connect the first electrode 103 to ground. Nickel (Ni) or its alloy that is inexpensive may be used for the first electrode 103. The current to be applied to the first electrode 103 may be limited within about 8.5 mA. When the current of more than about 8.5 mA is applied to the first electrode 103, a fuse included in an external inverter may be cut off.
The second electrode 104 may be provided at the other end of the discharge tube 101. The second electrode 104 may be connected to the high-voltage terminal of the external inverter through a second lead 107 that passes through the inner and outer wall of discharge tube 101, so that a high voltage may be applied to the second electrode 104. The external inverter converts a DC input voltage into an AC high voltage and supplies the AC high voltage to the second electrode 104. Accordingly, a high voltage of several ten or several thousand volts may be applied to the second electrode 104. In the exemplary embodiment of the present invention, the high voltage may be applied only to the second electrode 104. The current to be applied to the second electrode 104 may be limited to within about 10 mA. When a current of more than about 10 mA is applied to the second electrode 104, the temperature of the second electrode 104 may increase so that deterioration of the lamp 100 can advance, and the fuse included in the external inverter may be cut off to limit the deterioration. Accordingly, the current to be applied to the second electrode 104 may be limited to less than about 10 mA.
When a high voltage is applied between the first and second electrodes 103 and 104, a tube current flows from the second electrode 104 to the first electrode 103. Negative ions emitted from the first electrode 103 collide with particles of the mixed gas 105, so that a chain reaction is caused in the discharge tube 101, thus producing plasma. The phosphor 102 is excited by ultraviolet rays generated from the plasma to radiate visible light. In other words, an electric field is generated from the second electrode 104 to the first electrode 103. The negative ions excited from the mixed gas 105 while the plasma is generated move along the electric field. The negative ions move toward and collide against the second electrode 104 of positive polarity. When the negative ions collide against the second electrode 104, the second electrode 104 may become worn out. That is, sputtering may occur at the second electrode 104. Accordingly, the second electrode 104 may be formed of any one of niobium (Nb), tantalum (Ta), molybdenum (Mo), and tungsten (W) which is highly resistant to sputtering.
The sputtering-resistance properties of the electrode can be measured by testing a sample from the electrode for a prescribed time while prescribed conditions, such as acceleration voltage, acceleration current, incident angle, and gas pressure, are kept constant to calculate the sputtering rate by measuring the depth of holes created by the sputtering.
Table 1 shows the sputtering rate for Nb which was measured with respect to Ni under the same conditions as those of Ni.
As can be seen from Table 1, Nb has greater hardness and better sputtering resistance properties when compared to Ni. Accordingly, when Nb is employed for the second electrode 104, the lifespan of the electrode 104 is doubled since the Nb sputtering rate amounts to half the sputtering rate of Ni as measured under the same conditions as those of Ni. In addition, even if the amount of current applied to the lamp 100 increases, the lifespan can be lengthened compared to a case where Ni is used for the electrode 104.
When metals other than Nb, i.e. Ta, Mo, and W are used for the electrode 104, their sputtering rates are also smaller than that of Ni. Accordingly, when metals such as Ta, Mo, and W are employed for the second electrode 104, the sputtering-resistance properties can be improved compared to a case where Ni is used for the second electrode 104, so that the lifespan of the lamp 100 can be increased.
When the sputtering-resistance properties of the second electrode 104 are improved, the gas pressure can be lowered to improve the brightness of the lamp 100.
Referring to
More specifically, the slope of a curved line that indicates a relationship between the tube current and brightness becomes different depending on the gas pressure in the discharge tube 101. That is, when the gas pressure is 80 Torr, although the tube current increases, the increasing rate of brightness is relatively low, and therefore, the slope of the curved line gently increases. However, when the tube current increases while the gas pressure is 60 Torr or 40 Torr, the increasing rate of brightness is relatively higher. As a result, the curved line of tube current-brightness at lower pressure is increased with a larger slope than in the gas pressure of 80 Torr.
As the gas pressure increases while the gas pressure is less than the reference tube current (6 mA), the brightness of emissive light is correspondingly high. In the gas pressure of more than the reference tube current (6 mA), however, the lower gas pressure, the brighter the light emitted. In general, because the tube current supplied to the lamp 100 is more than the reference tube current (6 mA), the gas pressure may be kept lower in the discharge tube 101 to emit brighter light. Accordingly, the gas pressure may be kept in the range from about 40 Torr to about 60 Torr.
More specifically, as the gas pressure becomes higher in the discharge tube 101, the collision of molecules of mixed gas is increased in the course of generation of plasma, so that the temperature of the discharge tube 101 is raised. At the temperature of more than a prescribed temperature (e.g., 35° C.), vaporized Hg absorbs ultraviolet rays, so that as the temperature increases, the brightness may be decreased as shown in
When the gas pressure is less than about 40 Torr in the discharge tube 101, the density of gas is decreased and therefore the collision of molecules of mixed gas is reduced, thus increasing mean free path (“MFP”) of negative ions. Accordingly, the energy of the negative ions colliding against the second electrode 104 is increased. As such, when the MFP of negative ions is increased, the second electrode 104 may be more rapidly worn out by the negative ions colliding with the second electrode 104, thereby lessening the lifespan of the lamp 100.
In addition, when the gas pressure is less than about 40 Torr and therefore the MFP is higher so that the energy of colliding against the second electrode 104 is increased, the temperature of the second electrode 104 is higher, which may increase the temperature difference between the first and second electrodes 103 and 104. Accordingly, the gas pressure may be kept higher than about 40 Torr in the discharge tube 101.
When the gas pressure is 40 Torr, the MFP of negative ions is larger than in 60 Torr, and therefore, the energy of negative ions colliding against the second electrode 104 is increased. Accordingly, a metal such as Nb, Ta, Mo, and W may be used to guarantee a minimum specified period of lifespan even when the second electrode 104 is under the gas pressure of 40 Torr.
As the gas pressure of the discharge tube 101 is lower, the voltage applied to the second electrode 104 may be correspondingly lowered according to an exemplary lamp 100 of the present invention.
Referring to
As a result, the power consumption of the lamp 100 may be improved by about 5% to 6% at the gas pressure of 40 Torr compared to where the gas pressure is 60 Torr in the same brightness. Therefore, the efficiency of the lamp 100 may be improved by about 10%. As such, the gas pressure may be 40 Torr.
More heat may be generated at the second electrode 104 under the gas pressure of 40 Torr than under the gas pressure of 60 Torr. In particular, in a single side driving type where a high voltage is applied only to the second electrode 104, more heat is generated at the second electrode 104 than at the first electrode. When the temperature is higher at the second electrode 104 than at the first electrode 103, a discrepancy occurs at the temperature of the discharge tube 101, so that malfunctions such as pink discharges may be created. Therefore, such a discrepancy between the first and second electrodes 103 and 104 may be removed. Accordingly, the second electrode 104 may be formed of any one of Nb, Ta, Mo, and W, which has good thermal conductivity. A metal such as Nb, Ta, Mo, and W is higher in thermal conductivity than Ni, so that heat generated from the second electrode 104 may be dissipated to the outside more rapidly. As a consequence, Hg is inclined toward the first electrode 103 in the discharge tube 101, so that the pink discharge can be prevented.
The first and second electrodes 103 and 104 may be shaped as cups to make the effective area larger, thus improving the reliability of electrodes. As shown in
In addition, as the length of the second electrode 104 is longer, the lifespan of the lamp 100 may be correspondingly increased. That is, when the length of the second electrode 104 increases, the time which it takes for the second electrode 104 to wear out is lengthened, so that the lifespan of the lamp 100 may be extended.
Referring to
More specifically, the bottom chassis 80 includes a plurality of connection holes 81 that pass through the bottom chassis 80 to connect the inverters 90 with the lamps 100. The connection holes 81 are provided to go through the region where the lamp sockets 82 shown in
The number of the inverters 90 may be the same as that of the lamps 100 to supply tube currents to the lamps 100. The inverters 90 are arranged parallel with each other along the long side of the inverter PCB 91. The inverter PCB 91 is arranged at the rear surface of the bottom chassis 80. The inverter PCB 91 is placed at a part of the rear surface of the bottom chassis 80 where the second electrode 104 is provided so that the second electrode 104 of the lamp 100 can be easily coupled with the inverter 90. The first electrode 103 of the lamp 100 may be connected to the ground of the inverter 90, or connected directly to the bottom chassis 80.
Referring to
In addition, since the first and second electrodes 103 and 104 are both provided at one side of the LCD device, the length of a wire that connects the first electrode 103 to the ground may be reduced.
Referring to
The light guide plate 140 is provided at the rear surface of the LCD panel 30. The light guide plate 140 whose incident surface faces the lamp 100 converts a line-type light source to a surface-type light source and supplies the surface-type light source from the incident surface to the LCD panel 30. The light guide plate 140 includes a plurality of grooves or protrusions each of which is shaped as the letter “V” to guide the light through refraction or reflection from its incident side to another side that is opposite to the incident side.
The lamp cover 130 covers the outer surface of the lamp 100 to protect the lamp 100 from external physical impacts. And, the lamp cover 130 improves optical usage efficiency by reflecting the light from the lamp 100 to the incident surface of the light guide plate 140.
The backlight unit 200 may further include an optical sheet 60 and a reflective sheet 70 to make the light supplied from the light guide plate 140 uniform and improve the optical efficiency.
The optical sheet 60 includes a diffusion sheet, a prism sheet, and a protection sheet which are sequentially stacked on the light guide plate 140. The reflective sheet 70 that is provided at the rear surface of the light guide plate 140 reflects light from the lower part of the light guide plate 140 to the light guide plate 140.
The lamp 100 is identical to that shown in
The backlight unit 200 further includes inverters (not shown in
As mentioned above, the backlight unit according to an exemplary embodiment of the present invention and the LCD device having the same, may reduce the cost of lamp usage by employing a metal such as Nb, Ta, Mo, and W for the second electrode that is applied with high voltage and Ni for the first electrode that is grounded.
Additionally, since the metal such as Nb, Ta, Mo, and W may be used for the second electrode that is applied with high voltage, the probability for the electrode wearing out may be reduced, so that the lifespan of the lamp can be extended.
Moreover, the gas pressure of the mixed gas injected in the discharge tube is reduced, so that the brightness may be increased and power consumption may be lessened.
In addition, since the thermal conductivity of the second electrode is higher than that of the first electrode, thermal balance of the lamp may be kept constant, so that pink discharges can be prevented.
Although the present invention has been described with reference to certain exemplary embodiments thereof, it will be understood by those skilled in the art that a variety of modifications and variations may be made to the present invention without departing from the spirit or scope of the present invention defined in the appended claims, and their equivalents.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2007-0088467 | Aug 2007 | KR | national |
