Patent Publication Number: US-2010109535-A1

Title: Light-emitting device

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This Non-provisional application claims priority under 35 U.S.C. §119(a) on Patent Application No(s). 097142959 and 098112376 filed in Republic of China on Nov. 6, 2008 and Apr. 14, 2009, the entire contents of which are hereby incorporated by reference. 
     BACKGROUND OF THE INVENTION 
     1. Field of Invention 
     The present invention relates to a light-emitting device. 
     2. Related Art 
     Light-emitting diode (LED) is one of semiconductor elements. In the beginning, most of light-emitting diodes were used as indicator lights and light sources for outdoor display boards. Due to the advantages of high luminous power, long lifetime, and breakage-resistance, which conventional light sources barely have, light-emitting diode is praised as the innovative type of light source in the 21st century. 
     Generally speaking, the control methods of devices using light-emitting diodes as a light source can be classified into two types: constant voltage control and constant current control. As shown in  FIG. 1A , the conventional light-emitting device  1 A, controlled by constant voltage, includes a light-emitting diode module  11 , a capacitor  12 , a plurality of resistors  13  and a constant voltage source  14 . For the constancy of voltage signals inputted into light-emitting diodes, designers usually have to use capacitors with high capacitance values or more complicated rectification circuits to stabilize the voltage; however, it increases the production cost. 
     Although the circuit of constant voltage control is easier to design, the constant voltage control cannot provide a stable current. Light-emitting diodes depend on the combination of electrons and holes to release excess energy in the form of light so as to achieve luminant effect. However, current variation imposes a great influence on the illuminating properties of light-emitting diodes. In other words, the constant voltage control cannot accurately control the illuminating properties of light-emitting diodes. 
     In contrast, as shown in  FIG. 1B , another conventional light-emitting device  1 B controlled by constant current includes a light-emitting diode module  11 , a capacitor  12 , a plurality of resistors  13 , a constant current source  15  and a detecting unit  16 . Although the constant current control can provide a stable current for a light-emitting diode, in practical applications, it has to use resistors  13  as current limiting elements to absorb the power variations which are resulted from the variations of electric properties and to overcome the current variations generated from the differences among light-emitting diodes. Consequentially, it causes additional power loss. 
     However, either the conventional light-emitting device controlled by constant voltage or by constant current, it needs a supply unit for providing a stable current. Thus, it is an important issue to provide a light-emitting device, which can be driven by a variable power source without additional power loss on current limiting elements, to increase the operation efficiency of power. 
     SUMMARY OF THE INVENTION 
     In view of the foregoing, the present invention provides a light-emitting device driven by a variable power source without additional power loss in current limiting elements to increase the operation efficiency of power. 
     To achieve the above, a light-emitting device in accordance with the present invention includes a light-emitting diode module, a detecting circuit and a control circuit. The light-emitting diode module receives a variable voltage and includes a plurality of light-emitting diode units in series. The detecting circuit detects a light state of at least one of the light-emitting diode units of the light-emitting diode module and outputs at least a control signal. The control circuit includes a plurality of switch units and at least a control unit. The switch units are connected to each other in series, and each of the switch units is electrically connected to the corresponding light-emitting diode unit. The control unit adjusts the amount and/or the light state of the on-state light-emitting diodes in the corresponding light-emitting diode unit via each of the switch units in accordance with the control signal. 
     To achieve the above, a light-emitting device in accordance with the present invention includes a light-emitting diode module, a detecting circuit and a control circuit. The light-emitting diode module receives a variable voltage and includes a plurality of light-emitting diode units in series. The detecting circuit detects a light state of at least one of the light-emitting diode units of the light-emitting diode module and outputs at least a control signal. The control circuit includes a plurality of switch units and at least a control unit. The switch units are connected to each other in parallel, and each of the switch units is electrically connected to the corresponding light-emitting diode unit. The control unit adjusts the amount and/or the light state of the on-state light-emitting diodes in the corresponding light-emitting diode unit via each of the switch units in accordance with the control signal. 
     As mentioned above, the light-emitting device in accordance with the present invention adjusts the amount and/or the light state of the on-state light-emitting diodes in the light-emitting diode module via the control circuit. In comparison with the prior art, the present invention can operate the light-emitting diode module in a default state by changing the amount and/or the light state of the on-state light-emitting diodes so as to become a light-emitting device, which can be driven by a variable power source without additional power loss in current limiting elements and, meanwhile, increase the operation efficiency of power. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention will become more fully understood from the detailed description and accompanying drawings, which are given for illustration only, and thus are not limitative of the present invention, and wherein: 
         FIG. 1A  is a schematic figure of a conventional light-emitting device controlled by constant voltage; 
         FIG. 1B  is a schematic figure of a conventional light-emitting device controlled by constant current; 
         FIG. 2  is a schematic figure of a light-emitting device of a preferred embodiment of the present invention; 
         FIG. 3  is a schematic figure of a light-emitting device of a preferred embodiment of the present invention; 
         FIGS. 4A to 4D  are schematics figures of different aspects of the light-emitting device of a preferred embodiment of the present invention; and 
         FIGS. 5A and 5B  are schematics figures of a light-emitting device of a preferred embodiment of the present invention and the alternative-current voltage corresponding to the light-emitting device. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The present invention will be apparent from the following detailed description, which proceeds with reference to the accompanying drawings, wherein the same references relate to the same elements. 
     As shown in  FIG. 2 ,  FIG. 2  is a schematic figure of a light-emitting device in accordance with a preferred embodiment of the present invention. The light-emitting device  2  includes a light-emitting diode module  21 , a detecting circuit  22  and a control circuit  23 . 
     The light-emitting diode module  21  includes a plurality of light-emitting diode units  211  in series, and the light-emitting diode units  211  include at least a light-emitting diode respectively. The light-emitting diode module  21  is used to receive a variable voltage V. 
     In this embodiment, the variable voltage V can be an alternative-current voltage or a direct-current voltage. The variable voltage V is a voltage, which can change its own level along with the time periodically or randomly, and refers to the inconstant voltage. In more detailed, the aforementioned alternative-current voltage can be the well-known commercial power, which is an alternative current in the range from 90V to 250V, or an alternative current outputted from a power converter. Otherwise, the aforementioned direct-current voltage includes a voltage generated from a battery, a battery jar or an alternative-current voltage via a rectification circuit. However, variations of the outputted voltage levels are generated from the increase of usage period of the battery and the battery jar. And the direct-current voltage generated via the rectification circuit still has nipples. Therefore, in practice, this sort of the direct-current voltage level varies with the time yet. 
     The detecting circuit  22  detects a light state of the light-emitting diode module  21  and then outputs a control signal S C . In one example, the detecting circuit  22  can include a resistor, a light detector, a photodiode, an induction coil, an electromagnetic induction element or a magnetoelectric induction element. In one example, the means of connecting the detecting circuit  22  to the light-emitting diode module  21  can be used by coupling or by electrical connection in accordance with the selected detecting circuit  22 . Additionally, the detecting circuit  22  can be an integrated circuit. 
     Otherwise, types of the light state of the light-emitting diode module described herein are, for example, the current value, the voltage value, the electric power, the luminous intensity and/or the luminous power of the light-emitting diode module. In other words, in one example, various types of the detecting circuit  22  can be used in accordance with needs of products or practical designs. 
     The control circuit  23  is electrically connected to the light-emitting diode module  21 , and adjusts the amount and/or the light state of the on-state light-emitting diodes in the light-emitting diode module  21  in accordance with the control signal Sc. In one example, the control circuit  23  can be a digital control circuit or an analog control circuit, and at least one of the light-emitting diode units  211  in the light-emitting diode module  21  is not controlled by the control circuit  23 . Additionally, in the present embodiment, the control circuit  23  can be an integrated circuit. 
     Moreover, as shown in  FIG. 3 , the light-emitting device of the present invention is further described herein. A light-emitting diode module  31  of a light-emitting device  3  includes a first light-emitting diode unit  311  and a second light-emitting diode unit  312  connected to each other in series. In the present embodiment, the light-emitting diode module  31  receives a variable voltage V to drive the first light-emitting diode unit  311  and the second light-emitting diode unit  312 . 
     Otherwise, in one example, the light-emitting diodes of the first light-emitting diode unit  311  and the second light-emitting diode unit  312  can be connected in series first and then connected in parallel, and/or connected in parallel first and then connected in series. 
     A detecting circuit  32  is electrically connected to the second light-emitting diode unit  312 , and detects the value of the current flowing through the second light-emitting diode unit  312  to generate a control signal Sc. In the present embodiment, the detecting circuit  32  includes a resistor. 
     A control circuit  33  includes a switch unit  331  and a control unit  332 . The switch unit  331  is electrically connected to the second light-emitting diode unit  312 . The control unit  322  is electrically connected to the switch unit  331  and the detecting circuit  32 , and receives the control signal Sc generated by the detecting circuit  32 . In one example, the switch unit includes a bipolar junction transistor (BJT) or a field effect transistor (FET). 
     In the present embodiment, the control unit  322  controls the switch unit  331  to switch between on-state and off-state by determining whether the control signal Sc is weaker than a default value. Practically, the control circuit  33  can cut off or conduct the second light-emitting diode unit  312  to operate the light-emitting diode module  31  with a default current value in accordance with the control signal Sc. 
     To be noticed, in the present embodiment, the first light-emitting diode unit  311  is not controlled by the control unit  33 , and the detecting circuit  32  is a real-time detecting circuit. Herein, as above mentioned that the first light-emitting diode unit  311  is not controlled by the control unit  33  refers to whether the first light-emitting diode unit  311  emits light is controlled by the power source and, meanwhile, the operation of the control circuit  33  does not influence whether the first light-emitting diode unit  311  emits light. However, the electrical connection still exists between the first light-emitting diode unit  311  and the control unit  33 . 
     In the aforementioned hardware architecture, the present invention can operate the light-emitting diode module in a default state by altering the amount and/or the light state of the on-state light-emitting diodes. Therefore, a power supply of the light-emitting device is not limited to provide a stable current. 
     Otherwise, in one example, the architecture between the detecting circuit and the control circuit can be various aspects in accordance with different needs. As shown in  FIGS. 4A to 4D , four exemplary application architectures of the detecting circuit and the control circuit are illustrated. 
     As shown in  FIG. 4A , a light-emitting diode module  41  of a light-emitting device  4 A includes a plurality of the light-emitting diode units  411  connected in series, and a control circuit  43 A includes a plurality of switch units  431  and a control unit  432 . Each of the switch units  431  is electrically connected to the corresponding light-emitting diode unit  411 , respectively, and each of the switch units  431  is mutually connected in parallel. 
     In one example, the control unit  432  can include a shifting register and a comparator. The shifting register is electrically connected to each of the switch units  431 , respectively. The comparator is electrically connected to the shifting register and the detecting circuit  42 , respectively, and receives the control signal generated by the detecting circuit  42 . The control circuit  432  can cut off or conduct each of the light-emitting diode units  411  to operate the light-emitting diode module  41  with a default current value by determining whether the control signal is weaker than a default value through the comparator. 
     Moreover, as shown in  FIG. 4B , the difference between the light-emitting devices  4 B and  4 A is that each of the switch units  431  of a control circuit  43 B is mutually connected in series and electrically connected between two light-emitting diode units  411  to control the conduction path of the current. 
     Additionally, as shown in  FIG. 4C , in one non-limiting embodiment, for providing clear illustration, the light-emitting diode module has, for example, three light-emitting diode units. 
     A light-emitting device  4 C includes a first detecting unit  421  and a second detecting unit  422 . The first detecting unit  421  is electrically connected to a first light-emitting diode unit  412 , and detects the light state of the first light-emitting diode unit  412 . The second detecting unit  422  is electrically connected to a second light-emitting diode unit  413 , and detects the light state of the second light-emitting diode unit  413 . 
     A control circuit includes a first switch unit  433 , a second switch unit  434 , a first control unit  435  and a second control unit  436 . The first switch unit  433  is electrically connected to the first light-emitting diode unit  412 . The first control unit  435  adjusts the amount and/or the light state of the on-state light-emitting diodes in the first light-emitting diode unit  412  in accordance with the light state of the first light-emitting diode unit  412 . 
     Otherwise, the second switch unit  434  is electrically connected to the second light-emitting diode unit  413 . The second control unit  436  adjusts the amount and/or the light state of the on-state light-emitting diodes in the second light-emitting diode unit  413  in accordance with the light state of the second light-emitting diode unit  413 . 
     In the present embodiment, the control unit adjusts the amount and/or the light state of the on-state light-emitting diodes in the light-emitting diode units in accordance with the light state of the aforementioned light-emitting diode units detected by the detecting unit. In other words, the control unit adjusts the light-emitting diode unit in accordance with the control signal outputted by the detecting unit in the same group. 
     As shown in  FIG. 4D , a light-emitting diode module of the light-emitting device  4 D includes a first light-emitting diode unit  412 , a second light-emitting diode unit  413  and a third light-emitting diode unit  414 . 
     A detecting circuit  42  includes a first detecting unit  421  and a second detecting unit  422 . The first detecting unit  421  is electrically connected to the first light-emitting diode unit  412 , and detects the light state of the first light-emitting diode unit  412 . The second detecting unit  422  is electrically connected to the second light-emitting diode unit  413 , and detects the light state of the second light-emitting diode unit  413 . 
     A control circuit  43  includes a first switch unit  433 , a second switch unit  434 , a first control unit  435  and a second control unit  436 . In the present embodiment, the first switch unit  433  is electrically connected to the second light-emitting diode unit  413 . The first control unit  435  is electrically connected to the first detecting unit  421  and the first switch unit  433 , respectively, and adjusts the amount and/or the light state of the on-state light-emitting diodes in the second light-emitting diode unit  413  in accordance with the light state of the first light-emitting diode unit  412 . 
     Moreover, the second switch unit  434  is electrically connected the third light-emitting diode unit  414 . The second control unit  436  is electrically connected to the second detecting unit  422  and the second switch unit  434 , respectively, and adjusts the amount and/or the light state of the on-state light-emitting diodes in the third light-emitting diode unit  414  in accordance with the light state of the second light-emitting diode unit  413 . 
     Therefore, in the present embodiment, the control unit adjusts the amount and/or the light state of the on-state light-emitting diodes in the light-emitting diode unit in accordance with the light state of another light-emitting diode unit detected by the detecting unit. To be noticed, the another light-emitting diode unit described herein is a light-emitting diode unit connected to the light-emitting diode unit detected by the detecting unit in series directly or indirectly. In other words, the control unit adjusts the light-emitting diode unit in accordance with the control signal outputted by the detecting unit from the previous group. 
     As shown in  FIG. 5A  and  FIG. 5B , a method of adjusting the amount of the light-emitting diodes used while a light-emitting device  5  is operated via alternative-current voltage is further described. Additionally, in the present embodiment, the current flowing through all of the light-emitting diode units is, for example but not limited to, a constant current (80 mA). 
     As shown in  FIG. 5B , in the present embodiment, the variable voltage V is an alternative-current voltage. Furthermore, the variable voltage V can be separated into four divisions from low to high voltage. During the first division R 1 , the duty of the light-emitting diode module is 85%; during the second division R 2 , the duty of the light-emitting diode module is 70%; during the third division R 3 , the duty of the light-emitting diode module is 50%; and during the forth division R 4 , the duty of the light-emitting diode module is 25%. 
     As shown in  FIG. 5A , a light-emitting diode module  51  of the light-emitting device  5  includes four light-emitting diode units  511 A,  511 B,  511 C and  511 D mutually connected in series. The light-emitting diode units  511 A,  511 B and  511 C respectively include four, three and two light-emitting diodes connected in parallel. 
     The control circuit  53  includes a first switch unit  531 A, a second switch unit  531 B, a third switch unit  531 C, a first control unit  532 A, a second control unit  532 B and the third control unit  532 C. Each of the switch units  531 A to  531 C, is electrically connected to the corresponding light-emitting diode units  511 A to  511 D, respectively, and each of the switch units  531 A to  531 C is mutually connected in series. 
     The detecting circuit  52  includes a first detecting unit  521 A, a second detecting unit  521 B and a third detecting unit  521 C. Each of the detecting units (the first detecting unit  521 A, the second detecting unit  521 B and the third detecting unit  521 C) is coupled with the light-emitting diode units  511 A to  511 C, respectively, and electrically connected to the control units (the first control unit  532 A, the second control unit  532 B and the third control unit  532 C), respectively, to detect variations of the voltage level of the variable voltage V. 
     During the voltage level of the variable voltage V is in the first division R 1 , the light-emitting diode unit  511 A emits light in accordance with the received variable voltage V; during the voltage level of the variable voltage V is in the second division R 2 , the first detecting unit  521 A outputs the control signal to the first control unit  532 A to cut off the first switch unit  531 A so as to conduct the light-emitting diode units  511 A and  511 B; during the voltage level of the variable voltage V is in the third division R 3 , the first detecting unit  521 A and the second detecting unit  521 B output the control signals to the first control unit  532 A and the second control unit  532 B respectively to cut off the first switch unit  531 A and the second switch unit  531 B so as to conduct the light-emitting diode units  511 A to  511 C; and during the voltage level of the variable voltage V is in the forth division R 4 , each of the detecting unit  521 A to  521 C outputs the control signal to each of the control units  532 A to  532 C respectively to cut off the first switch unit  531 A, the second switch unit  531 B and the third switch unit  531 C so as to conduct the light-emitting diode units  511 A to  511 D. 
     In other words, during the voltage level is in the first division R 1 , the current flowing through each of the light-emitting diodes of the light-emitting diode unit  511 A is 20 mA; during the voltage level is in the second division R 2 , one added current flowing through each of the light-emitting diodes of the light-emitting diode unit  511 B is 26.6 mA; during the voltage level is in the third division R 3 , another added current flowing through each of the light-emitting diodes of the light-emitting diode unit  511 C is 40 mA; and during the voltage level is in the forth division R 4 , the other added current flowing through the light-emitting diodes of the light-emitting diode unit  511 D is 80 mA. Meanwhile, the ratio of the output power among the light-emitting diode units  511 A to  511 D is 17:18.62:20:20. 
     In one example, the light-emitting device can further include a capacitor or adjust the amount of the light-emitting diodes connected in series in each of the light-emitting diode units in order to extend the duties of the first division and second division. It results in the relative ratio of the duty of each division being 100%, 75%, 50% and 25%, and then causes the output power ratio of each of the light-emitting diode units becoming 20:20:20:20. 
     In the hardware architecture as shown in  FIG. 5A , the present invention can enable each of the light-emitting diode units to have similar or identical output powers by changing the amount of the on-state light-emitting diodes in each of the light-emitting diode units. 
     Moreover, it is also possible for the detecting units  521 A to  521 C to detect the average light power of the light-emitting diode units  511 A to  511 C and outputs a control signal to each of the control units  532 A to  532 C respectively to control the switch unit  531 A to  531 C so as to control the outputting light power of the light-emitting diode units  511 A to  511 C, and to keep the total outputting light power of the light-emitting diode module  51  at a controlled and limited level. 
     Moreover, it is worth mentioning that the amount of the light-emitting diodes used in each of the light-emitting diode units is not limited in accordance with the present invention. And, at least one of the light-emitting diode units is not controlled by the control circuit. In addition, the light-emitting device of the present invention can be used as a backlight source or a lighting device, and applied to fields like mobile communication, transportation lighting and general lighting as well. 
     In summary, the light-emitting device of the present invention can adjust the amount and/or the light state of the on-state light-emitting diodes in a light-emitting diode module by a control circuit. In comparison with the prior art, the present invention can operate the light-emitting diode module in a default state by changing the amount and/or the light state of the on-state light-emitting diodes so as to become a light-emitting device, which can be driven by a variable power source without additional power loss in current limiting elements and, meanwhile, increase the operation efficiency of power. 
     Although the invention has been described with reference to specific embodiments, this description is not meant to be construed in a limiting sense. Various modifications of the disclosed embodiments, as well as alternative embodiments, will be apparent to persons skilled in the art. It is, therefore, contemplated that the appended claims will cover all modifications that fall within the true scope of the invention.