Patent Publication Number: US-2007109809-A1

Title: Backlight module

Description:
FIELD OF THE INVENTION  
      The present invention generally relates to backlight modules, and, particularly, to a backlight module for a liquid crystal display (LCD) device.  
     DISCUSSION OF THE RELATED ART  
      Most liquid crystal display (LCD) devices are passive devices in which images are displayed by controlling an amount of light inputted from an external light source. Thus, a separate light source (for example, backlight module) is generally employed for illuminating an LCD panel.  
      Generally, a backlight module should have good optical illumination and optical uniformity so as to improve the LCD devices&#39; display effect, such as color contrast, optical brightness, and so on.  
      Referring to  FIG. 1 , a typical backlight module  10  is disposed below a LCD panel  16 . The backlight module  10  includes a housing  11 , a plurality of lamps  13  disposed in the housing  11  in a parallel manner, a diffusion sheet  14  disposed above the lamps  13 , and an optical sheet  15  disposed above the diffusion sheet  14 . The housing  11  is a plastic housing, and can also be replaced by a metallic casing. The diffusion sheet  14  is configured for uniformly diffusing the light emitted from the lamps  13 , thus, a brightness of the LCD panel  14  would be more uniform. The diffusion sheet  14  is made of transparent resin materials such as polyester (PET) and polycarbonate (PC). The thickness of the diffusion sheet  14  ranges from 0.11 centimeters to 0.15 centimeters. The optical sheet  15  is configured for collimating the emitted light, thereby improving the brightness of light illumination. The optical sheet  15  is also made of transparent resin materials such as polyester (PET) and polycarbonate (PC).  
      Light emitted from the lamps  13  pass through the diffusion sheet  14  and the optical sheet  15 , improving the optical brightness and optical uniformity of the LCD panel  16 . However, the lamps are generally not completely identical due to differences developed during manufacturing process. If all of the lamps are driven by the same electric current or voltage, the lamps  13  will illuminate at different variations. Therefore, the optical brightness and optical uniformity of the backlight module  10  will be affected, and accordingly a desired display property of the LCD panel  16  will be reduced.  
      What is needed, therefore, is a backlight module which can improve the optical brightness and optical uniformity.  
     SUMMARY  
      The present invention provides a backlight module. The backlight module includes a casing, a light guide plate disposed in the casing, a plurality of lamps arranged to illuminate the light guide plate, a plurality of image sensors configured for detecting illumination of corresponding lamps, a digital processor configured for processing signals generated by the image sensors, and a plurality of lamp driving loops configured for receiving feedback signals generated by the digital processor and adjusting a lamp current voltage outputted by a lamp driving loop for each lamp, so as to get an uniform illumination of each lamp.  
      Other advantages and novel features will become more apparent from the following detailed description of preferred embodiments when taken in conjunction with the accompanying drawings.  
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
      Many aspects of the backlight module can be better understood with reference to the following drawings. The components in the drawings are not necessarily drawn to scale, the emphasis instead being placed upon clearly illustrating the principles of the backlight module. Moreover, in the drawings, like reference numerals designate corresponding parts throughout the several views.  
       FIG. 1  is a schematic, cross-sectional view of a conventional backlight module;  
       FIG. 2  is a schematic, isometric view of a backlight module according to a first embodiment;  
       FIG. 3  is a schematic, cross-sectional view taken along the line  111 - 111  of  FIG. 2 ;  
       FIG. 4  is a partially isometric view of the backlight module without a casing and reflecting plate of  FIG. 2 ;  
       FIG. 5  is a schematic, functional connecting chart of the backlight module of  FIG. 2 ; and  
       FIG. 6  is a schematic, functional connecting chart of a backlight module according to a second embodiment. 
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS  
      Reference will now be made to the drawings to describe preferred embodiments of the present backlight module, in detail.  
      Referring to  FIGS. 2 through 4 , in a first preferred embodiment, a backlight module  20  includes a casing  21 , a light guide plate  26  disposed in the casing  21 , a reflecting plate  22 , a plurality of lamps  23 A,  23 B,  23 C, and  23 D, at least one optical sheet  25 , and a plurality of image sensors  20 A,  20 B,  20 C, and  20 D. The reflecting plate  22  is disposed between the casing  21  and the light guide plate  26 . The lamps  23 A,  23 B,  23 C, and  23 D are disposed within the light guide plate  26 , for example, the lamps  23 A,  23 B,  23 C, and  23 D are disposed in a plurality of receiving hole (not labeled) defined in the light guide plate  26 . The receiving hole can also be replaced by a plurality of receiving channel defined in one side of the light guide plate  26 . The at least one optical sheet  25  is disposed above the light guide plate  26 . The image sensors  20 A,  20 B,  20 C, and  20 D are configured for detecting illumination of the corresponding lamps  23 A,  23 B,  23 C, and  23 D. The backlight module  20  defines a plurality of through holes  29  below the lamps  23 A,  23 B,  23 C, and  23 D; the through holes  29  are configured to run through the reflecting plate  22 , the light guide plate  26 , and the casing  21 . Each of the through hole  29  corresponds to one of the lamps  23 A,  23 B,  23 C, and  23 D. The image sensors  20 A,  20 B,  20 C, and  20 D are disposed below the casing  21  and aims at the through holes  29  correspondingly.  
      The lamps  23 A,  23 B,  23 C, and  23 D are tubular fluorescent lamps, such as cold cathode fluorescent lamps (CCFLs). The total number of the lamps  23 A,  23 B,  23 C, and  23 D are also not limited to this embodiment, and the disposing manner for the lamps  23 A,  23 B,  23 C, and  23 D can also be in other manners, such as being disposed in the casing  21 .  
      The optical sheet  25  is selected from one of a diffusing sheet, and a brightness enhancement sheet. The backlight module  20  may also include a plurality of optical sheets  25  according to the actual requirement.  
      The total number and the disposing manner of the image sensors  20 A,  20 B,  20 C, and  20 D corresponds to the total number and the disposing manner of the lamps  23 A,  23 B,  23 C, and  23 D so as to detect the illumination of the corresponding lamps  23 A,  23 B,  23 C, and  23 D. The image sensors  20 A,  20 B,  20 C, and  20 D may also be disposed at any positions in the backlight module  20 , and at such positions the image sensors  20 A,  20 B,  20 C, and  20 D can effectively detect the illuminations of the lamps  23 A,  23 B,  23 C, and  23 D corresponding without interfering with the light emitted from the lamps  23 A,  23 B,  23 C, and  23 D. The image sensors  20 A,  20 B,  20 C, and  20 D can be selected from a group comprising of a photo diode, a charge couple device, a photoelectric crystal, a photosensitive resistance, and a combination thereof.  
      Referring to  FIG. 5 , the backlight module  20  further includes a digital processor  3  electrically connected to the image sensors  20 A,  20 B,  20 C, and  20 D, and a plurality of lamp driving loops  32 A,  32 B,  32 C, and  32 D electrically connecting with the lamps  23 A,  23 B,  23 C, and  23 D respectively. The digital processor  30  is configured for processing signals generated by the image sensors  20 A,  20 B,  20 C, and  20 D. The lamp driving loops  32 A,  32 B,  32 C, and  32 D are configured for receiving feedback signals generated by the digital processor  30  and adjusting a lamp current or voltage outputted by each driving loop  32 A,  32 B,  32 C, and  32 D for each of the lamps  23 A,  23 B,  23 C, and  23 D, thus each of the lamps  23 A,  23 B,  23 C, and  23 D illuminates uniformly.  
      When each of the lamps  23 A,  23 B,  23 C, and  23 D is driven by the lamp current or voltage outputted by each driving loop  32 A,  32 B,  32 C, and  32 D, each of the lamps  23 A,  23 B,  23 C, and  23 D are illuminated; each of the image sensors  20 A,  20 B,  20 C, and  20 D detects the illumination of each of the lamps  23 A,  23 B,  23 C, and  23 D and generates a corresponding signal. The signals generated by the image sensors  20 A,  20 B,  20 C, and  20 D are then sent to the digital processor  30 . The signals are compared with a required average value, and then the digital processor  30  sends the corresponding feedback signals to the lamp driving loops  32 A,  32 B,  32 C, and  32 D. The lamp driving loops  32 A,  32 B,  32 C, and  32 D adjust the lamp current or voltage that drives each of the lamps  23 A,  23 B,  23 C and  23 D according to the corresponding feedback signals so that each of the lamps  23 A,  23 B,  23 C, and  23 D illuminates corresponding to the required average value.  
      The backlight module  20  further includes an alarm unit  34  connected with the digital processor  30 . If one of the image sensors  20 A,  20 B,  20 C, and  20 D detects the corresponding illumination and generates a corresponding signal lower than the required average value and such corresponding signal continues over a certain time period, the alarm unit  34  will raise an alarm and further outputs a control signal so that the digital processor  30  cuts off the corresponding signal and the corresponding lamp driving loops  32 A,  32 B,  32 C, and  32 D turn off the lamps  23 A,  23 B,  23 C, and  23 D correspondingly.  
      The alarm raised by the backlight module  20  is one of a sound, a flash, and an image. The continuing time of the corresponding signal is selected according to an actual requirement.  
      Referring to  FIG. 6 , in a second preferred embodiment, the backlight module (not shown) is substantially the same as the backlight module  20  in the first embodiment. The difference is that the backlight module has a plurality of amplifiers  58 A,  58 B,  58 C, and  58 D electrically connecting the image sensors  20 A,  20 B,  20 C, and  20 D to the digital processor  30 . The amplifiers  58 A,  58 B,  58 C, and  58 D are configured for amplifying the signal generated by the image sensors  20 A,  20 B,  20 C, and  20 D according to an illumination of the lamps  23 A,  23 B,  23 C and  23 D. Therefore, the signal can be more accurately compared with the required average value so that the lamps  23 A,  23 B,  23 C, and  23 D can better controlled. The required average value is selected according to an actual requirement.  
      It is to be understood, however, that even though numerous characteristics and advantages of the present embodiments have been set forth in the foregoing description, together with details of the structures and functions of the embodiments, the disclosure is illustrative only, and changes may be made in detail, especially in matters of shape, size, and arrangement of parts within the principles of the invention to the full extent indicated by the broad general meaning of the terms in which the appended claims are expressed.