Patent Publication Number: US-2010109562-A1

Title: Backlight module and light-emitting device thereof

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a backlight module and light-emitting device thereof, and more particularly to a direct backlight module and an edge-type backlight module and light-emitting device thereof. 
     2. Description of the Related Art 
     With numerous applications of liquid crystal display (LCD) for electronic apparatuses, such as televisions, monitors, personal computers, mobile phones, and PDAs, demand for backlight modules of LCDs continues to increase. Because the liquid crystal in an LCD does not emit any light itself, the liquid crystal requires a backlight module to provide a uniform and high brightness light source, so that the LCD can display images clearly and sharply. Therefore, the performance of the backlight module can affect the display quality of the display directly. As a result, the backlight module is one of the most important parts of the LCD. 
     Generally, backlight module types include side-edge backlight modules and direct backlight modules.  FIG. 1  shows a pictorial decomposition diagram of a conventional direct backlight module  10 , wherein the backlight module  10  utilizes a cold cathode fluorescent lamp (CCFL) as a light source. The backlight module  10  comprises an inverter  11 , a rear frame  12 , a reflecting plate (not shown) positioned on the rear frame  12 , a plurality of parallel lamps  13 , a diffuser plate  14 , and a plurality of optical films  15 . The optical films  15  comprise a diffusion film  151  and a convergent film  152  for diffusing and modifying the direction of the light source, respectively. The optical films  15  and the diffuser plate  14  are positioned above the lamps  13  and diffuse the light emitted by the lamps  13  uniformly to an LCD. The reflecting plate positioned on the rear frame  12  is used to reflect the light emitted by the lamps  13  so as to raise the utilization rate of the light. Two electrodes arranged at opposite ends of the respective lamps  13  are driven by a high voltage provided by the inverter  11 . Because the lamps contain mercury, an environmentally unfriendly material, current direct backlight modules are gradually shifting to use of light emitting diodes (LEDs) in place of the conventional CCFL as a light source. 
       FIG. 2  shows a top view of a conventional side-edge backlight module  20 , wherein the backlight module  20  utilizes LEDs as a light source. The backlight module  20  comprises a carrying frame  21 , a light source  22 , an electrical connector  23 , a carrier  24 , a light guiding plate  25 , and a driving board  26 . The light source  22  has a plurality of LEDs  221  positioned on the carrier  24 . The electrical connector  23 , positioned on the carrier  24 , comprises a plurality of input terminals connected to a voltage source and used to receive driving signals of the plurality of LEDs  221 . The carrier  24  is positioned on the inner surface of the carrying frame  21 , and one side of the carrier  24  contacts an inner surface  211  of the carrying frame  21 . The light source  22  is positioned adjacent to one side  251  of the light guiding plate  25  so that the light can incident to the light guiding plate  25  from the light incident surface  251  beside the light guiding plate  25 . As shown in  FIG. 2 , the driving board  26  is positioned adjacent to another side of the light guiding plate  25  and configured to output the driving signals of the plurality of LEDs  221 . 
       FIG. 3A  shows a top view of a conventional light emitting device  30  of a direct backlight module, wherein the light emitting device  30  utilizes LEDs as a light source. The light emitting device  30  comprises a carrier  31 , a plurality of LEDs  32 , an electrical connector  33 , and a driving board  34  (not shown). The plurality of LEDs  32  are positioned on a top surface of the carrier  31  and configured to diffuse the light via a diffuser plate above the carrier to provide a uniform surface light source for an LCD. A light reflective film is formed on the top surface of the carrier  31  to reflect the light emitted by the LEDs  32 . The driving board  34  is positioned on the bottom surface of the carrier  31  and configured to output the driving signals of the LEDs  32 . 
       FIG. 3B  shows a conventional driving board  34 . The driving board  34  comprises a printed circuit board (PCB)  35 , an electrical connector  36 , and a driving unit  37 . The driving unit  37  comprises a boost circuit  371 , an LED driving circuit  372 , and a passive component area  373 . The boost circuit  371  is configured to adjust a supply voltage to a voltage required by the backlight module  30 , and the LED driving circuit  372  is configured to generate the driving signals. The passive component area  373  is configured to position a plurality of passive components, such as resistors, capacitors, and diodes so as to set the control parameters of the LED driving circuit  372 . The driving signals of the LEDs  32  are outputted to the electrical connector  33  on the top surface of the carrier  31  via the electrical connector  36  with connecting lines. 
     The light emitting device  30  in  FIG. 3A  and the backlight module  20  in  FIG. 2  require a boost circuit to convert voltages. The boost circuit is implemented by an inductor, active devices, and a control circuit driving the active devices. Said components require space and thus need to be positioned on the extra driving boards  34  and  26 . In addition, U.S. Patent Publication No. 20060092346 provides an LED backlight unit and a liquid crystal display device having the same. Referring to  FIG. 3C , the LED backlight unit comprises a control unit PCB  170  and a light emitting unit PCB  150 . A plurality of LEDs  120  and drive components are mounted together on the light emitting unit PCB  150 , and PWM signals for controlling the LEDs  120  are outputted from the control unit PCB  170 . The requirement of the driving boards  34 ,  26  and the control unit PCB  170  not only incurs additional material and assembling costs in production, but also demands consideration of the disposition of the wires when an operator connects carriers with driving boards or with the extra control unit PCB. Therefore, these conventional structures cannot meet the requirement of miniaturized structures of the market. On the basis of the above, there is a need for a direct backlight module and an edge-type backlight module and light-emitting device thereof for solving the problems mentioned above. 
     SUMMARY OF THE INVENTION 
     An aspect of the present invention is to provide a light emitting device of a backlight module. 
     According to one embodiment of the present invention, the light emitting device of the backlight module comprises a carrier, an electrical contact, a light emitting diode (LED) driving circuit, and a plurality of LEDs. The carrier comprises a surface, and the electrical contact is electrically connected to a voltage source for providing a voltage potential substantially equal to that of the voltage source. The LED driving circuit comprises at least one driving component electrically connected to the electrical contact, and the plurality of LEDs electrically connected between the electrical contact and the LED driving circuit. The electrical contact, the LED driving circuit, and the plurality of LEDs are all positioned on the surface of the carrier. 
     Another aspect of the present invention is to provide a light emitting device of a backlight module comprising a plurality of light emitting strips. 
     According to one embodiment of the present invention, the light emitting strip comprises a carrier, an electrical contact, a light emitting diode (LED) driving circuit, and a plurality of LEDs. The carrier comprises a surface, and the electrical contact is electrically connected to a voltage source for providing a voltage potential substantially equal to that of the voltage source. The LED driving circuit comprises at least one driving component electrically connected to the electrical contact, and the plurality of LEDs electrically connected between the electrical contact and the LED driving circuit. The electrical contact, the LED driving circuit, and the plurality of LEDs are all positioned on the surface of the carrier. 
     Yet another aspect of the present invention is to provide a direct backlight module. 
     According to one embodiment of the present invention, the direct backlight module comprises a diffuser plate and a light emitting device positioned under the diffuser plate. The light emitting device comprises a carrier, an electrical contact, a light emitting diode (LED) driving circuit, and a plurality of LEDs. The carrier comprises a surface, and the electrical contact is electrically connected to a voltage source for providing a voltage potential substantially equal to that of the voltage source. The LED driving circuit comprises at least one driving component electrically connected to the electrical contact, and the plurality of LEDs electrically connected between the electrical contact and the LED driving circuit. The electrical contact, the LED driving circuit, and the plurality of LEDs are all positioned on the surface of the carrier. 
     Yet another aspect of the present invention is to provide a side-edge backlight module. 
     According to one embodiment of the present invention, the side-edge backlight module comprises a light guiding plate and a first light emitting device. The light guiding plate comprises a first side, a second side, a third side, and a fourth side, and the first light emitting device is positioned adjacent to the first side of the light guiding plate. The first light emitting device comprises a carrier, an electrical contact, a light emitting diode (LED) driving circuit, and a plurality of LEDs. The carrier comprises a surface, and the electrical contact is electrically connected to a voltage source for providing a voltage potential substantially equal to that of the voltage source. The LED driving circuit comprises at least one driving component electrically connected to the electrical contact, and the plurality of LEDs electrically connected between the electrical contact and the LED driving circuit. The electrical contact, the LED driving circuit, and the plurality of LEDs are all positioned on the surface of the carrier. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention will be described according to the appended drawings in which: 
         FIG. 1  shows a pictorial decomposition diagram of a conventional direct backlight module; 
         FIG. 2  shows a top view of a conventional side-edge backlight module; 
         FIG. 3A  shows a top view of a conventional light emitting device of a direct backlight module; 
         FIG. 3B  shows a conventional driving board; 
         FIG. 3C  shows a conventional LED backlight unit; 
         FIG. 4  illustrates a light emitting device of a direct backlight module according to one embodiment of the present invention; 
         FIG. 5  illustrates a light emitting device of a direct backlight module according to another embodiment of the present invention; 
         FIG. 6  illustrates a light emitting device of a side-edge backlight module according to one embodiment of the present invention; 
         FIGS. 7A-7E  illustrate a side-edge backlight module according to a variety of embodiments of the present invention; 
         FIG. 8  illustrates a circuit diagram of the light emitting devices according to one embodiment of the present invention; and 
         FIG. 9  illustrates a circuit diagram of the light emitting devices according to another embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       FIG. 4  illustrates a light emitting device  40  of a direct backlight module according to one embodiment of the present invention. The light emitting device  40  comprises a carrier  41 , an electrical contact  42 , an LED driving circuit  43 , and a plurality of LEDs  44 . A first surface of the carrier  41  is configured to carry the light emitting device  40 . A diffuser plate is positioned above the first surface for providing a uniform surface light source to an LCD by diffusing the light of the light emitting device  40 . 
       FIG. 5  illustrates a light emitting device  50  of a direct backlight module according to another embodiment of the present invention. The light emitting device  50  comprises a plurality of light emitting strips  51 - 54 . Each of the light emitting strips  51 - 54  comprises a carrier  510 , an LED driving circuit  513 , and a plurality of LEDs  512 . Referring to  FIG. 5 , the light emitting strip  51  further comprises an electrical contact  511  positioned on a first surface of the carrier  510  for providing a voltage source of the light emitting device  50 . With the increasing size of the LCD, additional light emitting strips can be added as needed based on the size of the LCD. 
       FIG. 6  illustrates a light emitting device  60  of a side-edge backlight module according to one embodiment of the present invention. The light emitting device  60  comprises a carrier  61 , an electrical contact  62 , an LED driving circuit  63 , and a plurality of LEDs  64 . The carrier comprises first and second surfaces, wherein the first surface is configured to carry the light emitting device  60  and the second surface, positioned opposite to the first surface, contacts a contact surface of a rear frame. Such contact can be implemented by cohering the second surface to the rear frame with a thermal interface material or other adhesive. 
       FIGS. 7A-7E  illustrate a side-edge backlight module  70  according to a variety of embodiments of the present invention. The backlight module  70  comprises a light guiding plate  72  and a first light emitting device  71 . The light guiding plate  72  has a first side, a second side, a third side, and a fourth side. As shown in  FIG. 7A , the first light emitting device  71  is positioned adjacent to any side of the light guiding plate  72  and emits light to the light guiding plate  72 , and thus the light guiding plate  72  provides a uniform and bright surface light to an LCD by emitting the light. 
     For LCDs of various size requirements, different sides of the light guiding plate  72  can be positioned by at least two light emitting devices based on the size of the LCD. According to one embodiment of the present invention, as shown in  FIGS. 7B and 7C , the backlight module  70  comprises two sets of light emitting devices, wherein the first light emitting device  71  is positioned adjacent to the first side of the light guiding plate  72 , and the second light emitting device  73  is positioned adjacent to the second side of the light guiding plate  72 . The second side in this embodiment is parallel or perpendicular to the first side. According to another embodiment of the present invention, the backlight module  70  in  FIG. 7D  comprises three sets of light emitting devices, wherein the first, second, and third light emitting devices  71 ,  72 , and  73  are positioned adjacent to the first, second, and third sides of the light guiding plate  72 , respectively. The second side in this embodiment is parallel to the first side, and the third side is perpendicular to the first side. According to yet another embodiment of the present invention, the backlight module  70  in  FIG. 7E  comprises four sets of light emitting devices, wherein the first, second, third, and forth light emitting devices  71 ,  72 ,  73 , and  74  are positioned adjacent to the four sides of the light guiding plate  72 . 
     The carriers in  FIGS. 4-6  can be a single layer or multi-layers of an elongated PCB, and a reflecting film disposed covering the carriers so as to enhance the emitting efficiency of the LEDs. The electrical contacts  42 ,  511 , and  62  are configured to provide voltage sources of the light emitting devices, wherein each of the electrical contacts  42 ,  511 , and  62  can be an electrical connector, a solder joint, or a pad. The LED driving circuits  43 ,  513 , and  63  are electrically connected to the LEDs  44 ,  512 , and  64  so as to transmit driving signals of the LEDs  44 ,  512 , and  64 . The LED driving circuits  43 ,  513 , and  63  comprise driving components  431 ,  514 , and  631  and passive components  432 ,  515 , and  632 , wherein the driving components  431 ,  514 , and  631  can be either unpackaged dies or packaged chips, and the passive components  432 ,  515 , and  632  can be a capacitor, a resistor, a diode, or combinations. In the embodiment, the unpackaged die is used to reduce the overall thickness and the occupied area of the light emitting device. In addition, the LED driving circuits  43 ,  513 , and  63  further comprise an active component, such as a switching component implemented by a MOSFET or a diode. The passive components  432 ,  515 , and  632  or the active components are electrically connected to the driving components  431 ,  514 , and  631 , and the LED driving circuits  43 ,  513 , and  63  are positioned on the first surface of the carriers. 
     In one embodiment of the present invention, the LEDs  44 ,  512 , and  64  can be dies emitting white light. In another embodiment of the present invention, the LEDs  44 ,  512 , and  64  can be dies emitting red, green, blue, other color or combinations light. The LEDs  44 ,  512 , and  64  are respectively positioned on the first surface of the carriers  41 ,  510 , and  61 , and the numbers and arrangement can be varied according to the requirement of the LCD. The term “positioned” as used above refers to a method in which the LEDs  44 ,  512 , and  64  and the carriers  41 ,  510 , and  61  are connected via surface mount, flip-chip, bump, or wire bonding. After the connecting process, an encapsulating material is applied to the LEDs  44 ,  512 , and  64  and the driving components  431 ,  514 , and  631 , thereby protecting the components from pollution, humidity and other environmental impurities. 
       FIG. 8  illustrates a circuit diagram of the light emitting devices  40 ,  50 , and  60  according to one embodiment of the present invention. Referring to  FIG. 8 , a light emitting row  81  is composed of a plurality of LEDs  84  connected in series, and the light source of the light emitting devices  40 ,  50 , and  60  are composed of a plurality of light emitting rows  81  connected in parallel. In the embodiment, a first terminal of each light emitting row  81  is connected to a constant voltage V B . The electrical contacts  42 ,  511 , and  62  connected to a voltage source provide the constant voltage V B  via a filter circuit or a linear regulator, and the electrical contacts  42 ,  511 , and  62  do not raise the voltage potential of the constant voltage V B  via an additional boost circuit. A second terminal of each light emitting row  81  is connected to an output terminal of a driving unit  82  via a resistor R 2 , and the resistor R 2  is used to increase a voltage drop. 
       FIG. 9  illustrates a circuit diagram of the light emitting devices  40 ,  50 , and  60  according to another embodiment of the present invention. Referring to  FIG. 9 , three sets of the light emitting row  81  are connected in parallel to form a light emitting unit. A first terminal is connected to the constant voltage V B  via a resistor R 3 , and a second terminal is connected to the output terminal of the driving unit  82 . Therefore, each output terminal of the driving unit  82  can control one set or a plurality of sets of the light emitting row  81 . 
     Referring to  FIG. 8 , the driving unit  82  can be a sixteen-channel constant current driver for the LED lighting, and provides the PWM control effect by sinking constant current from LED clusters with a minimum pulse width. The driving unit  82  has a plurality of output terminals OUT 1 -OUT 16 , a voltage source terminal VDD, a ground terminal GND, a control terminal R ext , and an enable terminal OE. A voltage source V DD  and a ground potential provide voltage potential to the inner chip of the driving unit  82 . The control terminal R ext  is connected to a resistor R 1  for adjusting the current through the light emitting row  81  so as to control the brightness of the light emitting row  81 . The enable terminal OE is connected to the voltage source terminal VDD so as to enable outputs of the output terminals OUT 1 -OUT 16 . Alternatively, the enable terminal OE is coupled to a PWM signal from a system control unit mounted onto the same board with the driving unit  82  so as to perform the PWM control function, i.e., function as a dimming control. The driving components  82  are positioned on the two sides of the first surface of the carrier or positioned uniformly or non-uniformly on the first surface of the carrier. The term “electrically connected” in the content refers to a method in which wires are connected in a layout via the lines of the first surface, the second surface, or a middle layer between the first and second layers. 
     In contrast with the prior art, the LED driving circuit and the LEDs are positioned close together on one surface of the carrier; therefore, the LED driving circuit can easily monitor the heat generated by the LEDs and the carrier, and if needed perform over-temperature protection to reduce risk of overheating damage. Also, as mentioned before, the present invention requires no additional boost circuit including a boost inductor, and thus can reduce the PCB area requirement, material cost, and assembly cost in production. 
     The above-described embodiments of the present invention are intended to be illustrative only. Numerous alternative embodiments may be devised by those skilled in the art without departing from the scope of the following claims.