Patent Publication Number: US-8115400-B2

Title: Backlight module

Description:
This application claims the benefit of priority based on Taiwan Patent Application No. 097103451 filed on Jan. 30, 2008, the disclosures of which are incorporated herein by reference in their entirety. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a backlight module, and more particularly, to an external electrode fluorescent lamp for use in a backlight module. 
     2. Descriptions of the Related Art 
     Because of making great progress in the manufacturing technology of the liquid crystal display (LCD), LCDs have many advantages such as light, thin, power-saving and radiation-less properties. Based on the above advantages, LCDs are widely used in various electrical products, for example, personal digital assistants (PDAs), notebook computers, digital cameras, digital camcorders, mobile telephones, computer monitors, and liquid crystal televisions. However, because the LCD panel cannot illuminate by itself, a backlight module is required to provide a light source for the LCD panel. The conventional backlight module has several cold cathode fluorescent lamps (CCFLs) as the light source to lighten the LCD panel. 
     A CCFL usually generates heat and hence leads to the nearby area at high temperature while emitting light. More particularly, as the required brightness of the LCD is gradually increasing, the increased brightness of the CCFL inevitably generates more heat, and the internal environmental temperature of the LCD is thus increased. Besides increase in heat, the driving voltage of the CCFLs also becomes higher. Consequently, the nearby environmental temperature of the CCFL would increase a lot, and thereby deteriorate the light emitting quality of the CCFL and the operating quality of the backlight module. 
     External electrode fluorescent lamps (EEFLs) are proposed to solve the problems mentioned above.  FIG. 1  is a schematic diagram illustrating the cross-sectional view of a prior art EEFL. The prior art EEFL requires two driving circuits. For example, in the embodiment of  FIG. 1 , one driving circuit includes a pair of inner electrodes  11  and  12  stretching into the glass tube  15 , and the other includes an outer electrode  13  surrounding the glass tube  15 . The inner surface of the glass tube  15  is coated with fluorescent material and the inner space of the glass tube  15  is filled with gas  16 . The gas  16  can be the mixture of some noble gases and Hg gas. When voltages are applied to the inner electrodes, the electrons are emitted from electrodes and bombard the Hg gas. Then, the excited Hg gas generates ultra-violet (UV) light when the Hg atoms transit from an excited state to a ground state. After the UV light then strikes the phosphor coated in the inner surface of the glass tube, visible light is hence emitted. Though EEFLs are proposed to solve the problems mentioned above, the working voltages of EEFLs are too high to result in a current leakage and the luminance of the lamp is reduced because the outer electrode  13  surrounding the lamp tube  15 . Accordingly, further improvements in the back light module are still required for the industry. 
     SUMMARY OF THE INVENTION 
     One objective of the present invention is to provide a backlight module with a new design for external electrode fluorescent lamps to reduce the start voltage and the current leakage thereof. 
     According to the above-mentioned objective, the backlight module includes a first lamp, a first voltage source, a second lamp, a second voltage source, a first external electrode, and a second external electrode. Both the first and the second voltage sources have a first terminal and a second terminal. The first voltage source is used to output a first voltage signal and electrically couples to the first terminal of the first lamp. The second voltage source is used to output a second voltage signal and electrically couples to the first terminal of the second lamp. Both the first external electrode and the second external electrode have a first terminal and a second terminal. The first terminal of the first external electrode electrically couples to the second voltage source and the first terminal of the second external electrode electrically couples to the first voltage source, wherein the first voltage signal and the second voltage signal are inverted. 
     The detailed technology and preferred embodiments implemented for the subject invention are described in the following paragraphs accompanying the appended drawings for people skilled in this field to well appreciate the features of the claimed invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Embodiments of the invention will be described with reference to the accompanying drawings in which: 
         FIG. 1  is a schematic diagram illustrating the cross-sectional view of a prior art EEFL; 
         FIG. 2  is a schematic diagram illustrating one preferred embodiment of the backlight module according to the present invention; 
         FIG. 3  is a schematic diagram illustrating one preferred embodiment of the backlight module according to the present invention; 
         FIG. 4  is a schematic diagram illustrating one preferred embodiment of the backlight module according to the present invention; 
         FIG. 5  is a schematic diagram illustrating one preferred embodiment of the backlight module according to the present invention; 
         FIG. 6(   a ) and  FIG. 6(   b ) are schematic diagrams illustrating the component configuration of the backlight module according to one preferred embodiment of the present invention; 
         FIG. 6(   c ) is a schematic diagram illustrating the component configuration of the backlight module according to one preferred embodiment of the present invention; 
         FIG. 7  is a schematic diagram illustrating the component configuration of the backlight module according one preferred embodiment of the present invention; 
         FIG. 8  is a schematic diagram illustrating various shapes of the external electrodes according one preferred embodiment of the present invention; and 
         FIG. 9  is a cross-sectional view of one preferred embodiment of the backlight module according to the present invention. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Refer to  FIG. 2 , which is a schematic diagram illustrating one preferred embodiment of the backlight module according to the present invention. The backlight module comprises a first lamp  21 , a second lamp  22 , a first voltage source  23 , a second voltage source  24 , a first external electrode  25 , and a second external electrode  26 . The first lamp  21  has a first terminal  211  and a second terminal  212 . The first voltage source  23  electrically couples to the first terminal  211  of the first lamp  21  for outputting a first voltage signal. The second lamp  22  has a first terminal  221  and a second terminal  222 . The second voltage source  24  electrically couples to the first terminal  221  of the second lamp  22  for outputting a second voltage signal. The first external electrode  25  has a first terminal  251  and a second terminal  252 , wherein the first terminal  251  of the first external electrode  25  electrically couples to the second voltage source  24 . The second external electrode  26  has a first terminal  261  and a second terminal  262 , wherein the first terminal  261  of the second external electrode  26  electrically couples to the first voltage source  23 . 
     Moreover, the second terminals  212 ,  222  of the first and the second lamps  21 ,  22  are grounded, and the second terminals  252 ,  262  of the first and the second external electrodes  25 ,  26  are floating. It is noted that the phase of the first voltage signal and the second voltage signal are preferably inverted. Since the first voltage signal and the second voltage signal are mutually inverted, the voltage difference between the first lamp  21  and the first external electrode  25  becomes larger. That is, the voltage difference between the first lamp  21  and the first external electrode  25  is the sum of the individual absolute amplitude of the first voltage signal and the second voltage signal. According to the configuration of the embodiment of the present invention, the voltages applied to the lamps can be lower than the conventional start voltages and hence reduce power consumption of the backlight module. 
     Please continue to refer to  FIG. 3 , which is a schematic diagram of another preferred embodiment of the backlight module according to the present invention. The backlight module of this embodiment, in  FIG. 3 , also comprises a first lamp  21 , a second lamp  22 , a first voltage source  23 , a second voltage source  24 , a first external electrode  25 , and a second external electrode  26 . The configuration of the abovementioned components in this embodiment is similar with that of the embodiment as shown in  FIG. 2 . It is noted that the second terminal  212  of the first lamp  21  connects to the second terminal  222  of the second lamp  22 . More specifically, the first and the second lamp  21 ,  22  together form a U shape. Compared with the conventional lamp, the U shape lamp provides more luminance because it has an extra portion formed by connecting the the second terminal  212  of the first lamp  21  and the second terminal  222  of the second lamp  22 . Similarly, the phase of the first voltage signal and the second voltage signal are preferably inverted for reducing the start voltage of the lamp and the power consumption as well. 
     Referring to  FIG. 4 , a schematic diagram illustrating one preferred embodiment of the backlight module according to the present invention is disclosed. The backlight module shown in  FIG. 4  has the similar components and configuration with the abovementioned embodiments. Compared with the abovementioned embodiments, the main difference of this embodiment is that two high-impedance circuits  41 ,  42  electrically couple to the second terminal  252  of the first external electrode  25  and the second terminal  262  of the second external electrode  26 , respectively. The high-impedance circuits  41 ,  42  optionally comprise passive components such as resistors, capacitors, inductors, or the combinations thereof. Owing to the high resistance of the high-impedance circuits  41 ,  42 , the second terminals  252 ,  262  of the first and the second external electrodes  25 ,  26  have an effect similarly to be floating. The phase of the first voltage signal and the second voltage signal are inverted. According to the configuration of the embodiment of the present invention, the voltages applied to the lamps can be lower than the conventional start voltages and hence the power consumption of the backlight module can be reduced. 
     Referring to  FIG. 5 , a schematic diagram illustrating one preferred embodiment of the backlight module according to the present invention is disclosed. The backlight module of this embodiment is also similar to that of the abovementioned embodiments. More specifically, the backlight module of this embodiment further comprises a third voltage source  51  and a fourth voltage source  52 . Furthermore, the third voltage source  51  electrically couples to the second terminal  212  of the first lamp  21  for outputting a third voltage signal and the fourth voltage source  52  electrically couples to the second terminal  222  of the second lamp  22  for outputting a fourth voltage signal. Preferably, there is a phase difference, such as, but not limited to, 180 degrees, between the first voltage signal and second voltage signal and between the first voltage signal and the third voltage, while there is no phase difference between the first voltage signal and fourth voltage signal. By adding the third voltage source  51 , the voltage difference between the first terminal  211  and the second terminal  212  becomes larger. That is, the voltage difference between the first terminal  211  and the second terminal  212  is the sum of the individual absolute amplitude of the first voltage signal and the second voltage signal. According to the configuration of the embodiment of the present invention, the voltages applied to the lamps can be lower than the conventional start voltages and hence reduce power consumption of the backlight module. 
     Please refer to  FIG. 6(   a ) and  FIG. 6(   b ), which are schematic diagrams illustrating the component configuration of the backlight module according to one preferred embodiment of the present invention. In this embodiment, the backlight module further comprises a lamp holder  61 , an electrode holder  62 , and a base support  63 . Specifically, the lamp holder  61  is used to fix the first lamp (not shown) or the second lamp (not shown), and the electrode holder  62  is disposed between the lamp holder  61  and the base support  63 . Refer to  FIG. 6(   c ), which is a schematic diagram illustrating the component configuration of the backlight module according to another preferred embodiment of the present invention. In this embodiment, the lamp holder  61 has an extending portion  64 , and the lamp holder  61  and the base support  63  are assembled by inserting the extending portion  64  into the lamp holder  61  through an opening of the first external electrode  25 . 
     Moreover, in the abovementioned embodiments, the first external electrode  25  and the second external electrode (not shown) both have elongated structures and the electrode holder  62  has an annular structure so that the electrode holder  62  is able to accommodate the first external electrode  25  or the second external electrode (not shown) therein. Further moreover, please refer to  FIG. 7 , in the preferred embodiment, the diameter of the first lamp  21  is greater than the width of the first external electrode  25  and the diameter of the second lamp (not shown) is greater than the width of the second external electrode so that the external electrode can be totally covered by the lamp from the top view. 
     It is noted that, in the abovementioned embodiments, the lamp fixed by the lamp holder is disposed above the external electrode so that lights emitted from the lamp won&#39;t be partially covered by the external electrode and the luminance of the lamp can be effectively increased. In a preferred embodiment, some reflective thin films can be coated on the outer surface of the external electrode to further increase the luminance of the lamp. The disadvantage of the prior art shown in  FIG. 1  that the luminance of the lamp is reduced can be improved. 
     The cross-sectional view of the external electrode can have many shapes as shown in  FIG. 8 , and the shape of the external electrode can be arbitrary chosen according to the real requirement. Refer to  FIG. 9 , which is a cross-sectional view of one preferred embodiment of the backlight module according to the present invention. The lamp holder  61  is used to fix the first lamp  21 , while the first external electrode  25  is disposed on the inner surface of the lamp holder  61 . More specifically, the first external electrode  25  can be a metal layer coated on the inner surface of the lamp holder  61 . Besides, in order to obtain better heat dissipation characteristics, the external electrode is preferably separated from the lamp for a predetermined interval. 
     The invention has been described in the context of several exemplary embodiments. However, it is to be understood that the scope of the invention is not limited to only the disclosed embodiments. On the contrary, the scope of the invention is intended to include various modifications and alternative arrangements within the capabilities of persons skilled in the art using presently known or future technologies and equivalents. The scope of the claims, therefore, should be accorded the broadest interpretation so as to encompass all such modifications and similar arrangements.