Abstract:
A backlight module is provided. The backlight module comprises a light source and a back bezel. The light source includes at least one high voltage electrode terminal. The back bezel is positioned at a rear portion of the light source. The back bezel is formed with at least an opening at a lower portion thereof. At least a part of the opening faces a rear portion of the high voltage electrode terminal. The back bezel is capable of changing the temperature distribution of the light source to allow more lamps operate under a better working temperature, thereby stabilizing the operational quality of the backlight module and prolonging its service life.

Description:
[0001]    This application claims priority to Taiwan Patent Application No. 095132688 filed on Sep. 5, 2006, the disclosures of which are incorporated herein by reference in their entirety. 
       CROSS-REFERENCES TO RELATED APPLICATIONS 
       [0002]    Not applicable. 
       BACKGROUND OF THE INVENTION 
       [0003]    1. Field of the Invention 
         [0004]    The present invention relates to a backlight module. More particularly, the present invention relates to a backlight module with little current leakage and with a greater portion of light source within a certain temperature range to enhance performance. 
         [0005]    2. Descriptions of the Related Art 
         [0006]    Liquid Crystal Display (LCD) technologies have developed rapidly in recent years. Consequently, many electronic devices, such as Personal Digital Assistants (PDAs), laptops, digital cameras, mobile phones, computer monitors, and LCD TVs, comprise LCD panels. To display images, an LCD uses the light source from a backlight module. Thus, the quality of an LCD is directly related to the quality of the light source from the backlight module. 
         [0007]    According to the position of the light source, backlight modules are categorized into two types: edge types and direct types. Lamps of an edge-type backlight module are equipped on the sides of the LCD panel. The light emitted by the lamps is transmitted to the light guiding panel equipped behind the LCD panel. Then, using the light guiding panel as a medium, incident lights are guided into the light guiding panel for reflection and refraction. 
         [0008]    The direct-type backlight module comprises a back bezel, a reflection panel, a plurality of lamps, a diffusion plate, and optical films. The back bezel forms a container holding the reflection panel. The lamps are arranged in front of the reflection panel inside the container. The diffusion panel and the optical films are disposed in front of the lamps, wherein the optical films comprise a prism sheet, a diffuser, and a brightness enhancement film. The LCD panel is disposed in front of the optical films. 
         [0009]    In the direct-type backlight module, drivers are required for supplying the high voltages to the two electrode terminals. For example, drivers provide +1 KV and −1 KV to the two electrode terminals, respectively, to provide the proper current for lighting. The emitted light processed by the reflection panel, diffusion plate, and optical films are then projected onto the LCD. 
         [0010]    Because the back bezel is usually made of conducted metal, parasitic capacitance or stray capacitance is usually generated between the electrode terminals and the back bezel when high voltage is supplied to the lamp. Unfortunately, the currents supplied to the lamps by the drivers leak to the back bezel, which greatly reduces the lighting performance. Since the received current is less than the expected current, the lighting performance of the back bezel degrades. In addition, because hot air rises, the lamps disposed at the upper portion of the backlight module are further affected by high temperature. As a result of the large temperature gap between the upper and lower areas of the backlight module, the lighting performance is further reduced, shortening the life of the lamps. 
         [0011]    According to the aforementioned descriptions, a method that reduces the leakage current of a direct-type backlight module and to change the temperature distribution of lamps to increase lighting performance and lifetimes of lamps is still a critical industrial issue. 
       SUMMARY OF THE INVENTION 
       [0012]    An object of the present invention is to provide a backlight module. The backlight module comprises a light source and a back bezel. The light source includes a high-voltage electrode terminal formed at one end thereof. The back bezel is positioned behind the light source. The back bezel is provided with an opening formed at a lower portion of the back bezel, in which the opening is formed to face at least part of the first high-voltage electrode terminal. 
         [0013]    Another object of the present invention is to provide a backlight module that comprises a plurality of linear light source units and a back bezel. The linear light source units are arranged substantially in parallel to one another. Each of the linear light source units has a first high-voltage electrode terminal formed at one end thereof. The back bezel is positioned behind the linear light source units and is provided with a first opening formed at a lower portion of the back bezel. The first opening faces at least part of the first high-voltage electrode terminals. 
         [0014]    Another object of the present invention is to provide a backlight module. The backlight module comprises a light source and a back bezel. The light source includes a first high-voltage electrode terminal that corresponds to a predetermined range of preferred operating temperature. The predetermined range has a lower-bound temperature, usually between 65° C. to 75° C. The first high-voltage electrode terminal has an actual operating temperature lower than the lower-bound temperature. The back bezel is disposed behind the light source. The back bezel has a first portion which is formed with an opening to face at least part of the first high-voltage electrode terminal. 
         [0015]    A further object of the present invention is to provide a backlight module that comprises a plurality of linear light source units and a back bezel. The linear light source units are arranged substantially in parallel to one another and correspond to a predetermined range of preferred operating temperature. The predetermined range has a lower-bound temperature. Each of the linear light source units has a first high-voltage electrode terminal formed at one end thereof. At least one of the first high-voltage electrode terminal has an actual operating temperature lower than the lower-bound temperature. The back bezel is disposed behind the light source. The back bezel has a first portion which is formed with a first opening to face at least part of the first high-voltage electrode terminal that has an actual operating temperature lower than the lower-bound temperature. 
         [0016]    With the aforementioned arrangement, the present invention is capable of reducing the parasitic capacitance and the leakage current of a specific lower portion of the back bezel. At the same time, the lighting performance and the temperature of the light sources at the specific portion are increased accordingly. Thus, more lamps operate in the range of the preferred operating temperatures. Temperature distribution of the lamps is more evenly. With temperature of the lamps being evenly distributed, the backlight module has better quality and a longer lifetime. 
         [0017]    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 
         [0018]      FIG. 1A  illustrates a side view of the relationship between the lamps and the back bezel of the first embodiment; 
           [0019]      FIG. 1B  illustrates a front view of the first embodiment; 
           [0020]      FIG. 1C  illustrates a back view of the first embodiment; 
           [0021]      FIG. 2  illustrates a back view of a second embodiment; 
           [0022]      FIG. 3  illustrates the distribution of the lamp temperatures; and 
           [0023]      FIG. 4  illustrates the comparison between the lamp temperatures of a back bezel with openings to a back bezel without openings. 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0024]    The principle of the present invention is to control the amount of current leakage from part of the lamps of a backlight module so that more lamps operate in a predetermined range of a preferred operating temperature and the distribution of the lamp temperatures is more uniform. In addition, the brightness of the backlight module is increased and distributed more evenly. 
         [0025]    The relationship between current leakage and parasitic capacitance can be expressed with the following equation: 
         [0000]        I   S =2π f*C   S   *V   L , 
         [0000]    wherein I S  represents the value of the current leakage, C S  represents the values of the parasitic capacitance, f represents the frequency of the alternating voltage provided by a lamp driver to a high voltage electrode terminal of a light source, and V L  represents a voltage value supplied to the high voltage electrode terminal of the light source of the lamp driver. According to the above equation, I S  is proportional to f, C S , and V L . Thus, decreasing the frequency of the alternating voltage f, the parasitic capacitance C S , the voltage V L  or a combination thereof can decrease current leakage, I S . 
         [0026]    Decreasing current leakage, I S , by decreasing the frequency of the alternating voltage, f, requires to adjust the LCD, to avoid display distortion. Decreasing current leakage, I S , by reducing the voltage V L  faces an obstacle. That is, the voltage V L  relates to the size of a light source. A longer or thinner light source requires a higher voltage V L . However, light source sizes are limited, so reducing the voltage V L  requires new light sources, adding cost. As a result, reducing current leakage by reducing the parasitic capacitance is a more efficient approach. The factors that affect the parasitic capacitance C S  between a high voltage electrode terminal and a back bezel include the following: the dielectric parameter ε of the material between the high voltage electrode of the light source and the back bezel, the size of the overlapped area S between the high voltage electrode of the light source and the back bezel, and the distance d between the high voltage electrode of the light source and the back bezel. These relationships can be represented by the following equation: 
         [0000]    
       
      
       Cs=ε*S/d.  
      
     
         [0027]    According to the above equation, Cs is proportional to ε and S and inversely proportional to d. Thus, reducing current leakage I S  by reducing C S  requires the reduction of the overlapped area S or the increase of the distance d. However, increasing the distance d would increase the volume of the backlight module, which does not produce thinner or smaller LCDs. Consequently, the present invention reduces the overlapped area S to reduce current leakage I S . The reduction of the overlapped area S is achieved by forming openings in the back bezel which correspond to the high voltage electrode terminals of the lamps with insufficient temperatures. 
         [0028]    Because hot air rises, the lamps disposed in the upper portions of the back bezel have higher temperatures. In contrast, lamps disposed in the lower portions of the back bezel often have temperatures lower than the required temperatures. To make the hot air flow to lower temperature regions, openings are often formed at the lower portion of the back bezel, which corresponds to lamps with insufficient temperatures Thus, the air flow to the cooler region of the back bezel distributes the temperatures between the portions more evenly. 
         [0029]      FIG. 1A  illustrates a side view of a first embodiment of the present invention, which is a backlight module  1 . The backlight module  1  comprises eight Cold Cathode Fluorescent Lamps (CCFLs)  11 - 18  and a back bezel  19 . The eight CCFLs are disposed in front of the back bezel  19  (the arrow points to the front). 
         [0030]      FIG. 1B  illustrates a front view of the first embodiment. Each CCFL comprises three parts: a first high voltage electrode terminal, a second high voltage electrode terminal, and a light source unit. That is, the first CCFL  11  comprises a first high voltage electrode terminal  111 , a second high voltage electrode terminal  112 , and a light source unit  113 . The second CCFL  12  comprises a first high voltage electrode terminal  121 , a second high voltage electrode terminal  122 , and a light source unit  123 . The third CCFL  13  comprises a first high voltage electrode terminal  131 , a second high voltage electrode terminal  132 , and a light source unit  133 . The fourth CCFL  14  comprises a first high voltage electrode terminal  141 , a second high voltage electrode terminal  142 , and a light source unit  143 . The fifth CCFL  15  comprises a first high voltage electrode terminal  151 , a second high voltage electrode terminal  152 , and a light source unit  153 . The sixth CCFL  16  comprises a first high voltage electrode terminal  161 , a second high voltage electrode terminal  162 , and a light source unit  163 . The seventh CCFL  17  comprises a first high voltage electrode terminal  171 , a second high voltage electrode terminal  172 , and a light source unit  173 . The eighth CCFL  18  comprises a first high voltage electrode terminal  181 , a second high voltage electrode terminal  182 , and a light source unit  183 . 
         [0031]      FIG. 1C  illustrates a back view of the first embodiment. The lower portion of the back bezel  19  comprises two first openings  175 ,  185  and two second openings  174 ,  184 . The first opening  175  corresponds to the first high voltage electrode terminal  171  of the seventh CCFL  17  and the first opening  185  corresponds to the first high voltage electrode terminal  181  of the eighth CCFL  18 . Similarly, the second opening  174  corresponds to the second high voltage electrode terminal  172  of the seventh CCFL  17  while the second opening  184  corresponds to the second high voltage electrode terminal  182  of the eighth CCFL  18 . Since the shapes of the first openings  175 ,  185  and two second openings  174 ,  184  are oval-shaped, they partially correspond to the first high voltage electrode terminal and the second high voltage electrode terminals. 
         [0032]    The aforementioned openings are formed at the lower portion of the back bezel, which shows that the overlapped area S between the high-voltage electrode terminals of light sources and the back bezel is reduced. Thus, the parasitic capacitance C S  and the current leakage I S  between the back bezel and the high voltage electrode terminals of the light sources are reduced. The lighting performance of the light sources is consequently increased. Furthermore, the lighting quality of the lower portion of the back bezel is increased and the distribution of the light source temperatures in the upper and lower portion is more even. As a result, the lamp life is increased. 
         [0033]    The shapes, sizes, numbers, and positions of the first openings and the second openings are not limited by the aforementioned description. The only requirement is for the first and second openings formed in the lower portion of the back bezel  19  to face the rear of the high voltage electrode terminals. An opening can be formed completely or partially behind the high voltage electrode terminal. 
         [0034]    In addition, the aforementioned 8 CCFLs can be replaced with External Electrode Fluorescent Lamps (EEFLs) or any other fluorescent lamps that require a driver. Further, the CCFLs can be replaced by a Cold Cathode Flat Fluorescent Lamp (CCFFL) or any other flat fluorescent lamps that require a driver. 
         [0035]      FIG. 2  illustrates a back view of a second embodiment of the present invention, which is a backlight module  2 . The backlight module  2  comprises 8 CCFLs (not shown) and a back bezel  29 . The back bezel  29  comprises two first openings  263 ,  283  and two second openings  273 ,  284 , that correspond to the first high voltage electrode terminals of two CCFLs and the second high voltage electrode terminals of two other CCFLs, respectively, wherein the first opening  283  and the second opening  284  correspond to the same CCFL. 
         [0036]    Similarly, the shapes, sizes, numbers, and positions of the first openings and the second openings are not limited to the aforementioned description. The only requirement is for the first and second openings formed at the lower portion of the back bezel  29  to face the high voltage electrode terminals so that current leakage I S  is reduced. The first and second opening can partially or completely face the first and second high voltage electrode terminals. In addition, the CCFLs can be replaced by EEFLs, CCFFLs, or any other fluorescent lamps that require a driver. 
         [0037]      FIG. 3  illustrates the distribution of the lamp temperatures, wherein the horizontal axis represents the lamp temperatures and the vertical axis represents relative brightness. The four curves represent the lamp currents set at 4 mA, 6 mA, 8 mA, and 10 mA, respectively. From  FIG. 3 , it is obvious that the range of preferred operating temperatures, i.e. to achieve the best relative brightness, is between 65° C. and 75° C. That is, in this range, the relative brightness of lamps is highest and evenly distributed. Since the object of the present invention is to increase the lighting performance and the life of the lamps, more lamps with actual operating temperatures in the range of the preferred operating temperatures are required. Thus, regardless of the lamp diameters, if more lamps operate between 65° C. and 75° C., the lighting performance will be increased, thermal energy will be diffused more evenly, and the lifetime of the lamps will be increased. 
         [0038]      FIG. 4  shows a comparison between the surface temperatures of the lamps corresponding to a back bezel with openings and a back bezel without openings, wherein the horizontal axis represents the temperature of the surfaces of the lamps and the vertical axis represents the relative upper positions and lower positions of the back bezel. Specifically, because each of the two backlight module comprises 16 CCFLs, the number on the vertical axis corresponds to the positions of every two CCFLs. Furthermore, the back bezel with openings has eight openings facing the two high voltage electrode terminals of each of the lowest four CCFLs. 
         [0039]    In  FIG. 4 , the curve with triangles represents the back bezel without openings, while the curve with rectangles represents the back bezel with openings. The dotted lines  41 ,  42  show that the surface temperatures of the lamps are around 65° C. and 75° C., respectively. 
         [0040]    According to  FIG. 4 , the surface temperatures of the lamps in the back bezel with openings are higher than those in the back bezel without openings. The average temperature from the first point to the fourth point increases about 0.4° C., while the average temperature from the fifth dot to the eight dot increases about 1.4° C. As shown in this figure, more lamps will operate normally, or more specifically, in the range of preferred operating temperatures, in the back bezel with openings. Furthermore, the differences between the temperatures of the lamps in the lower and upper portion are reduced. As a result, the distribution of the temperatures of the lamps is more uniform. This statement is supported by the fact that the curve between 65° C. to 75° C. of the back bezel with opening is longer than that of back bezel without opening. Furthermore, the lifetime of the lamps are prolonged. 
         [0041]    In addition to the temperatures, the brightness values of the lamps are described in the following tables. Table 1 and Table 2 show the average brightness values of the light sources of the back bezels without opening and with openings, respectively. The experimental conditions are similar to those conditions set in deriving the results drawn in  FIG. 4 . Each of the tables comprises 81 numbers and each of the numbers corresponds to a position on the back bezel of the backlight module. For example, the number 5712 of Table 1 corresponds to the left-upper position of the back bezel. Other numbers in Table 1 and Table 2 are interpreted using a similar approach. 
         [0042]    In Table 1, the average brightness value from the first row to the fourth row is 6447 nit, while the average brightness value from the sixth row to the ninth row is 6175 nit. In Table 2, the average brightness value from the first row to the fourth row is 6450 nit, while the average brightness value from the sixth row to the ninth row is 6222 nit. From the numbers, it is obvious that the average brightness value of a back bezel with openings is higher than that of a back bezel without openings. In addition, the increased value in the lower portion of the back bezel is even more convincing. The values also show that when a back bezel has openings in its lower portion, the brightness values of the upper portion and of the lower portions are closer in values. Thus, the back bezel is in a better state and the lifetime of the back bezel is increased. 
         [0000]    
       
         
               
             
               
               
               
               
               
               
               
               
               
             
           
               
                 TABLE 1 
               
               
                   
               
               
                 Average brightness of the back bezel without opening (Nit) 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                 5712 
                 6101 
                 6218 
                 6240 
                 6241 
                 6255 
                 6035 
                 6101 
                 5722 
               
               
                 6040 
                 6430 
                 6560 
                 6575 
                 6611 
                 6576 
                 6426 
                 6362 
                 5992 
               
               
                 6250 
                 6620 
                 6718 
                 6673 
                 6836 
                 6815 
                 6744 
                 6583 
                 6217 
               
               
                 6408 
                 6761 
                 6842 
                 6770 
                 6937 
                 6928 
                 6842 
                 6663 
                 6286 
               
               
                 6345 
                 6732 
                 6763 
                 6783 
                 6843 
                 6798 
                 6688 
                 6628 
                 6248 
               
               
                 6303 
                 6654 
                 6744 
                 6731 
                 6779 
                 6770 
                 6495 
                 6512 
                 6149 
               
               
                 6154 
                 6533 
                 6604 
                 6613 
                 6636 
                 6628 
                 6400 
                 6299 
                 5972 
               
               
                 5837 
                 6163 
                 6245 
                 6213 
                 6308 
                 6321 
                 6214 
                 6060 
                 5661 
               
               
                 5330 
                 5658 
                 5701 
                 5627 
                 5769 
                 5774 
                 5722 
                 5540 
                 5163 
               
               
                   
               
             
          
         
       
     
         [0000]    
       
         
               
             
               
               
               
               
               
               
               
               
               
             
           
               
                 TABLE 2 
               
               
                   
               
               
                 Average brightness of the back bezel with opening at its lower portion 
               
               
                 (Nit) 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                 5704 
                 6100 
                 6215 
                 6233 
                 6249 
                 6254 
                 6047 
                 6105 
                 5716 
               
               
                 6035 
                 6432 
                 6551 
                 6580 
                 6609 
                 6579 
                 6426 
                 6355 
                 5991 
               
               
                 6251 
                 6642 
                 6736 
                 6687 
                 6844 
                 6816 
                 6743 
                 6584 
                 6217 
               
               
                 6402 
                 6780 
                 6850 
                 6792 
                 6948 
                 6939 
                 6842 
                 6660 
                 6276 
               
               
                 6363 
                 6746 
                 6790 
                 6801 
                 6862 
                 6803 
                 6697 
                 6610 
                 6263 
               
               
                 6332 
                 6714 
                 6795 
                 6777 
                 6827 
                 6802 
                 6530 
                 6535 
                 6182 
               
               
                 6209 
                 6591 
                 6655 
                 6652 
                 6682 
                 6664 
                 6431 
                 6320 
                 5991 
               
               
                 5923 
                 6245 
                 6336 
                 6264 
                 6361 
                 6366 
                 6258 
                 6095 
                 5692 
               
               
                 5431 
                 5747 
                 5766 
                 5685 
                 5817 
                 5810 
                 5760 
                 5570 
                 5188 
               
               
                   
               
             
          
         
       
     
         [0043]    From the aforementioned descriptions, the formation of openings at the lower portion of the back bezel reduces current leakage and parasitic capacitance and increases temperatures. The principle behind choosing opening positions is to choose positions that can reduce the area of the back bezel behind the high voltage electrode terminal. When there is almost no metal behind the high voltage electrode terminal, the parasitic capacitance at the electrode is almost zero. According to other experiments, this method increases the lamp temperature about 5° C. to 7° C. Thus, the lighting performance of the light source is increased, while the voltage provided to the light source by the light driver becomes more stable. Furthermore, part of the hot air flows to the openings and increases the temperatures of the corresponding lamps which makes the temperatures and brightness values of the upper and lower portions be more uniform. In summary, it is more beneficial to have openings in the lower portion of the back bezel as compared to a back bezel without openings, openings in the upper portion or openings along the whole back bezel. 
         [0044]    The above disclosure is related to the detailed technical contents of the present invention and inventive features thereof. People skilled in this field may proceed with a variety of modifications and replacements based on the teachings and suggestions of the invention as described without departing from the characteristics thereof. Nevertheless, although such modifications and replacements are not fully disclosed in the above descriptions, they have substantially been covered in the following claims as appended.