Abstract:
A back light module adopted for use in a dual panel display includes a plurality of external electrode fluorescent lamps (EEFLs) positioned between two liquid crystal display panels. Each EEFL has a first electrode and a second electrode, and the first electrodes and the second electrodes are respectively electrically connected in parallel.

Description:
BACKGROUND OF INVENTION  
       [0001]     1. Field of the Invention  
         [0002]     The present invention relates to a back light module adopted for use in a dual-sided display, and more particularly, to a back light module having a simplified structure.  
         [0003]     2. Description of the Prior Art  
         [0004]     With the development of liquid crystal display (LCD) technologies, LCD display panels have been widely applied to various consumer electronic products such as digital cameras, personal digital assistants, mobile phones, and flat TVs. A back light module, a key component in an LCD display, is installed in the back side of an LCD display panel for providing the LCD display panel with light.  
         [0005]     The back light module substantially includes a plurality of cold cathode fluorescent lamps (CCFL) arranged in parallel, and a combination of various optical components such as diffusion plates and prisms for providing the LCD display panel with a brilliant and even light source. Cold cathode fluorescent lamps have to be driven by a high AC voltage, and moreover, they have to be respectively driven by different inverters. If an inverter is used to drive a plurality of cold cathode fluorescent lamps, the ballast of the inverter cannot be maintained stable, which results in an uneven brightness of the cold cathode fluorescent lamps. As a result, each cold cathode fluorescent lamp requires independent conducting wires to connect to an inverter, and this limitation increases the difficulty in allocating internal components and in housing design of the LCD. For a single panel LCD, the inverters and the conducting wires can be hidden under the reflecting plate or the rear frame of the back light module without influencing the illumination of the back light module.  
         [0006]     However, for a dual-sided display, the allocation of the inverters and the conducting wires becomes a problem to be solved. The dual-sided display is composed of two parallel LCD display panels, and a back light module installed in between the LCD display panels. Therefore the back light module has to be open on both sides and a reflecting plate is not allowed. In such a case, the inverters and the conducting wires cannot be arranged under the reflecting plate, and have to be installed somewhere inside the back light module without influencing the illumination of the back light module. Generally, the conducting wires are positioned in the peripheral region of the display, nevertheless, this region is originally designed for other components, such as driving circuits of the display. In addition, since each cold cathode fluorescent lamp requires an inverter, the allocation of the internal components for the dual-sided display becomes more difficult.  
         [0007]     Please refer to  FIG. 1  and  FIG. 2 .  FIG. 1  is a top view of a conventional back light module  10  for use in a dual-sided display, and  FIG. 2  is a cross-sectional view of the back light module  10  shown in  FIG. 1 . As shown in  FIG. 1  and  FIG. 2 , the back light module  10  is positioned between parallel LCD display panels  20  for providing a light source for both of the LCD display panels  20 . The back light module  10  includes a frame  12 , and a plurality of cold cathode fluorescent lamps  14  (CCFL) fixed in the frame  12 . Each cold cathode fluorescent lamp  14  includes two electrodes  14 A and  14 B exposed outside the frame  12 . In addition, the back light module  10  further includes a plurality of inverters  16  corresponding to the cold cathode fluorescent lamps  14  for converting DC voltage into AC voltage. Each inverter  16  has two conducting wires  16 A and  16 B respectively connected to the electrodes  14 A and  14 B so as to provide the cold cathode fluorescent lamps  14  with proper driving voltages. Furthermore, the back light module  10  usually includes two diffusion plates  18 , each positioned between the cold cathode fluorescent lamps  14  and the respective LCD display panel  20  for scattering the light beams irradiated by the cold cathode fluorescent lamps  14 .  
         [0008]     As described, for the conventional back light module  10 , the same amount of inverters  16  as cold cathode fluorescent lamps  14  has to be installed to provide corresponding driving voltages. This increase in inverters means an increase in cost. Besides, redesigns for extra space for allocating the inverters  16  and the conducting wires  16 A and  16 B conflict with dimensional requirements of a small size display. In addition, the inverters  16  are high frequency components, and therefore an increase in the amount of inverters  16  generates increased electromagnetic interference.  
         [0009]     Therefore, any reduction in quantity of inverters for a dual-sided display would result in a more flexible design and effectively economize cost.  
       SUMMARY OF INVENTION  
       [0010]     It is therefore a primary objective of the present invention to provide a back light module having a simplified structure for solving the aforementioned problems.  
         [0011]     According to a preferred embodiment of the present invention, a back light module adopted for use in a dualsided display having two parallel LCD display panels is provided. The back light module includes a plurality of external electrode fluorescent lamps (EEFLs) positioned between the two LCD display panels. Each external electrode fluorescent lamp includes a first electrode and a second electrode. The first electrodes and the second electrodes are electrically connected in parallel separately.  
         [0012]     According to a preferred embodiment of the present invention, a back light module adopted for use in a dualsided display having two parallel LCD display panels is provided. The back light module includes a flat fluorescent lamp positioned between the two LCD display panels, where the flat fluorescent lamp is double-faced light source.  
         [0013]     Since the back light module of the present invention utilizes external electrode fluorescent lamps or a flat fluorescent lamp, which can be driven by a single inverter, to replace cold cathode fluorescent lamps as the light source of the dual display, the amounts of the inverters and conducting wires are reduced. This reduces the cost and avoids difficulty in designing dual-sided displays.  
         [0014]     These and other objectives of the present invention will no doubt become obvious to those of ordinary skill in the art after having read the following detailed description of the preferred embodiment that is illustrated in the various figures and drawings. 
     
    
     BRIEF DESCRIPTION OF DRAWINGS  
       [0015]      FIG. 1  is a top view of a conventional back light module for use in a dual-sided display.  
         [0016]      FIG. 2  is a cross-sectional view of the back light module shown in  FIG. 1 .  
         [0017]      FIG. 3  is a top view of a back light module according to a first preferred embodiment of the present invention  
         [0018]      FIG. 4  is a cross-sectional view of the back light module shown in  FIG. 3 .  
         [0019]      FIG. 5  is a schematic diagram illustrating another connection method of the electrodes.  
         [0020]      FIG. 6  is a top view of a back light module according to a second preferred embodiment of the present invention.  
         [0021]      FIG. 7  is a cross-sectional view of the back light module shown in  FIG. 6 .  
         [0022]      FIG. 8  is a top view of a flat fluorescent lamp. 
     
    
     DETAILED DESCRIPTION  
       [0023]     Please refer to  FIG. 3  and  FIG. 4 .  FIG. 3  is a top view of a back light module  50  according to a first preferred embodiment of the present invention, and  FIG. 4  is a cross-sectional view of the back light module  50  shown in  FIG. 3 . As shown in  FIG. 3  and  FIG. 4 , the back light module  50  is installed in between two parallel LCD display panels  60  for providing a light source for both of the LCD display panels  60 . The back light module  50  includes a frame  52 , and a plurality of external electrode fluorescent lamps (EEFLs)  54  fixed to the frame  52 . Each external electrode fluorescent lamp  54  includes two electrodes  54 A and  54 B exposed outside the frame  52 . In addition, the back light module  50  further includes an inverter  56  electrically connected to the electrodes  54 A and  54 B of the external electrode fluorescent lamps  54  through two conducting wires  56 A and  56 B so as to provide the external electrode fluorescent lamps  54  with proper driving voltages. It is noted that each external electrode fluorescent lamp  54  has an independent ballast (not shown), and thus all the external electrode fluorescent lamps  54  can be driven via the inverter  56 . The back light module  50  further includes two diffusion plates  58  respectively positioned between the external electrode fluorescent lamps  54  and the two LCD display panels  60  for scattering light generated by the external electrode fluorescent lamps  54 . In addition, other optical components, such as prisms and brightness enhancing films, can be installed in the back light module  50  where necessary.  
         [0024]     As shown in  FIG. 3  and  FIG. 4 , since the back light module  50  utilizes the external electrode fluorescent lamps  54  as a light source, and has a single inverter  56  to drive the external electrode fluorescent lamps  54 , the electrodes  54 A and  54 B can be respectively connected to the conducting wires  56 A and  56 B of the inverter  56  in a parallel manner. Accordingly, the amounts of conductive wires are reduced. In this embodiment, the electrode  54 A of each external electrode fluorescent lamp  54  is connected in parallel to the conducting wire  56 A through a conducting wire, and the electrode  54 B (not shown) of each external electrode fluorescent lamp  54  is connected in parallel to the conducting wire  56 B (not shown) through a conducting wire, so that the external electrode fluorescent lamps  54  can obtain an AC voltage from the inverter  56 . It is noted that the external electrode fluorescent lamps  54  are driven by the inverter  56  in a floating manner, which means the two electrodes  54 A and  54 B are driven by voltages out of phase. For example, if the driving voltage of the external electrode fluorescent lamps  54  is 1 KV, the floating driving method means the electrodes  54 A and  54 B are respectively provided with a +0.5 KV and a −0.5 KV AC voltage.  
         [0025]     The external electrode fluorescent lamps  54  can also be connected in another parallel manner. Please refer to  FIG. 5 , which is a schematic diagram illustrating another connection method of the electrodes  54 A. As shown in  FIG. 5 , the electrodes  54 A are connected in parallel with a metal electrode  59 . In practice, the electrodes  54 A (or  54 B) can be connected in either way illustrated in  FIG. 4  or  FIG. 5 .  
         [0026]     As described, since the back light module  50  utilizes the external electrode fluorescent lamps  54  as a light source, only an inverter  56  is required. Accordingly, the electrodes  54 A and  54 B respectively require a conducting wire or a metal electrode  59  to connect to the conducting wires  56 A and  56 B. Consequently, the amounts of inverters  56  and conducting wires are reduced.  
         [0027]     Please refer to  FIG. 6  and  FIG. 7 .  FIG. 6  is a top view of a back light module  70  according to a second preferred embodiment of the present invention, and  FIG. 7  is a cross-sectional view of the back light module  70  shown in  FIG. 6 . As shown in  FIG. 6  and  FIG. 7 , the back light module  70  is installed between two parallel LCD display panels  80  for providing a light source for both of the LCD display panels  80 . The back light module  70  includes a frame  72 , and a double-faced luminous flat fluorescent lamp  74  fixed to the frame  72 . The flat fluorescent lamp  74  includes two electrodes  74 A and  74 B. The back light module  70  further includes an inverter  76  connected to the electrodes  74 A and  74 B of the flat fluorescent lamp  74  through two conducting wires  76 A and  76 B so as to drive the flat fluorescent lamp  74 . The back light module  70  further includes two diffusion plates  78  respectively installed between the flat fluorescent lamp  74  and the two LCD display panels  80  for providing even illumination. In addition, other optical components, such as prisms and brightness enhancing films, can be installed in the back light module  50 .  
         [0028]     The flat fluorescent lamp  74  is implemented by various fluorescent lamps having a curved or a zigzag structure. Please refer to  FIG. 8 , which is a perspective view of the flat fluorescent lamp  74 . As shown in  FIG. 8 , the flat fluorescent lamp  74  is composed of a fluorescent lamp having a zigzag structure, and connected to the inverter (not shown) through the electrodes  74 A and  74 B. In addition, the flat fluorescent lamp  74  can be incorporated with a scattering plate (not shown) to improve light uniformity.  
         [0029]     It can be seen that the back light module  70  with a flat fluorescent lamp  74  installed is as efficient as several cold cathode fluorescent lamps. Consequently, the back light module  70  only requires a single inverter  76  to drive the flat fluorescent lamp  74 , and therefore reduce the quantities of the inverter  76  and the conducting wires.  
         [0030]     In comparison with the prior art, the back light module according to the present invention effectively reduces the amounts of inverters and conducting wires. As a result, the problems of allocating the inverters and conducting wires are solved, and the cost is accordingly reduced.  
         [0031]     Those skilled in the art will readily observe that numerous modifications and alterations of the device may be made while retaining the teachings of the invention. Accordingly, the above disclosure should be construed as limited only by the metes and bounds of the appended claims.