Abstract:
The present invention provides an alternating current light-emitting diode (AC LED), which uses a light compensation layer disposed on the light-emitting surface of the AC LED. The materials of the light compensation layer can be phosphorescent or fluorescent materials. The light-emitting mechanism is mainly the light-emitting mechanism of electron-hole pairs in a triplet state. By absorbing light of the AC LED, the flashes occurred when the power of the AC LED alters from a positive half-cycle to a negative one can be compensated. Thereby, the AC LED can emit light full-timely.

Description:
FIELD OF THE INVENTION 
       [0001]    The present invention relates generally to a light-emitting diode (LED), and particularly to an alternating current (AC) LED. 
       BACKGROUND OF THE INVENTION 
       [0002]    Although traditional incandescent lamps are cheap, they suffer the drawbacks of low efficiency, high power consumption, and short lifetime. As for fluorescent lamps, they bring about pollution problems owing to mercury contained in their waste. 
         [0003]    LEDs own the properties of endurable light emitting, long lifetime, lightness, and low power consumption. Besides, they also have other advantages, such as cold operation capability, broad operating temperature ranges, at least 100 thousand hours of lifetime, and even containing no hazard materials such as mercury. Thereby, LEDs indeed are ideal next-generation light sources. 
         [0004]    In general, LEDs are extensively applied to white-light illuminating apparatuses, indicators, automobile signal lights, automobile headlamps, flashlights, backlight modules of LCD, light sources of projectors, outdoor displaying units, and so forth. However, transformers and rectifiers are required for these applications. These extra circuitries increase manufacturing costs of lamps, occupy additional space and thus affecting their looks, and produce additional heat, which deteriorate long-term safety of lamps, let alone the lifetime limitations of the extra circuitries shorten the lifetime of lamps, making LEDs&#39; long-lifetime advantage in vain. 
         [0005]    According to the stable development of optoelectronic technology, companies in the world all invest a great deal of resources to the development of relevant technologies. In Jan. 26, 2005, product announcement by Seoul Semiconductor Co., Ltd of Korea and III-N Technology of US reveal that commercialization of AC LEDs must be developed in a global scale. In the development of AC light-emitting microchip technology, there exists a bridge AC LED structure that solved the problem, occurred in the early time of AC LED development, of unable to emit light in both positive and negative alternating cycles (full-time light emitting). It adopted the design concept of Wheatstone bridge to improve the problem that only a half during the cycle can contribute to light emitting. However, because the rectifying devices of the bridge AC LED structure use AC light-emitting microchips directly, it will result in two drawbacks. First, because the endurance of reverse biases for a single rectifying device (a single AC light-emitting microchip) is inferior, the amount of adopted rectifying devices cannot be reduced. In other words, multiple AC light-emitting microchips have to be connected in series with the Wheatstone bridge for sharing the reverse bias applied by AC power. Taking the 110V grid for example, the peak voltage of the reverse bias applied by AC power us approximately 156V (110×√2). Thereby, 20 AC light-emitting microchips on the path of the positive and negative half-waves of AC signals are needed for sharing the reverse bias and avoiding reverse-bias breakdown. Consequently, the total amount of required rectifying devices is approximately 20×2=40 (AC light-emitting microchips on the path of the positive and negative half-waves of AC signals). Meanwhile, the number of the AC light-emitting microchips used for emitting light is reduced to 110V/3.1V (the enabling voltage of each AC light-emitting microchip)−20 (the number of AC light-emitting microchips used for rectifying)=15. It is known that the number of AC light-emitting microchips used for rectifying is much greater than that for emitting light. In addition, because the amounts of power consumption for both type of light-emitting devices (AC light-emitting microchips) are identical, the proportion of input power wasted on rectifying devices will remain high, resulting in inferior overall efficiency. Secondly, although the light-emitting area, compared to the design of earlier AC LEDs, has increased, there are still numerous rectifying devices wasting the overall light-emitting area owing to incapability of emitting light during reverse biases. Accordingly, the problem of full-time light emitting for an AC LED has become the most crucial issue in the field. 
       SUMMARY 
       [0006]    An objective of the present invention is to provide an AC LED, which uses a light compensation layer disposed on the light-emitting surface of the AC LED. Thereby, the AC LED is able to emit light full-timely. 
         [0007]    In order to achieve the objective described above, the present invention provides an AC LED, which uses a light compensation layer disposed on the light-emitting surface of the AC LED. The materials of the light compensation layer can be phosphorescent or fluorescent materials. The light-emitting mechanism is mainly the light-emitting mechanism of electron-hole pairs in a triplet state. By absorbing light of the AC LED, the flashes occurred when the power of the AC LED alters from a positive half-cycle to a negative one can be compensated. Thereby, the AC LED can emit light full-timely. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0008]      FIG. 1  shows a structural schematic diagram according to a preferred embodiment of the present invention; 
           [0009]      FIG. 2A  shows cycles of power according to a preferred embodiment of the present invention; 
           [0010]      FIG. 2B  shows the relation between cycles of power and light intensity according to a preferred embodiment of the present invention; 
           [0011]      FIG. 2C  shows a schematic diagram of reduced flashes according to a preferred embodiment of the present invention; 
           [0012]      FIG. 3  shows a structural schematic diagram according to another preferred embodiment of the present invention; 
           [0013]      FIG. 4  shows a structural schematic diagram according to another preferred embodiment of the present invention; 
           [0014]      FIG. 5  shows a structural schematic diagram according to another preferred embodiment of the present invention; and 
           [0015]      FIG. 6  shows a structural schematic diagram according to another preferred embodiment of the present invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0016]    In order to make the structure and characteristics as well as the effectiveness of the present invention to be further understood and recognized, the detailed description of the present invention is provided as follows along with embodiments and accompanying figures. 
         [0017]    The present invention solves the problem of flashes occurred in the prior art when the power of an AC LED alters from a positive half-cycle to a negative one. The present invention provides a light compensation layer to make an AC LED emit light full-timely. 
         [0018]      FIGS. 1 ,  2 A,  2 B, and  2 C show a structural schematic diagram, cycles of power, the relation between cycles of power and light intensity, and a schematic diagram of reduced flashes, respectively, according to a preferred embodiment of the present invention. As shown in the figures, the present invention provides an AC LED structure, which comprises an AC LED  10  and a light compensation layer  20 , which is disposed on the light-emitting surface of the AC LED  10 . 
         [0019]    When the power alters from a positive half-cycle to a negative one (as shown in  FIG. 2A ), the AC LED flashes at the point Q as shown in  FIG. 2B . The present uses the light compensation layer to absorb light from the AC LED, and emit light when a positive half-cycle alters to a negative one and thus compensating the light intensity at flashes as shown at the point P of  FIG. 2C . Accordingly, the AC LED can emit light full-timely, eliminating the drawback of flashes caused by the property of AC power. 
         [0020]    Besides, the AC LED can be a red, blue, green, white, ultraviolet, or any combination of the above AC LED. The light compensation layer  20  is not the fluorescent or phosphorescent layer of a white (blue LED adopts Yag or Tag) or other-color LED used for converting light of the LED into a specific light. The light compensation layer  20  according to the present invention is used as a compensation mechanism for compensating the specific light when the LED flashes. 
         [0021]    The material of the light compensation layer  20  is chosen from the group consisting of yellow phosphorescent powders, red phosphorescent powders, and any combination of the above, for example, ZnS, CaS, SrAl 2 O 4 , CaAl 2 O 4 , CaSrS, Sr 4 Al 14 O 25 , and coordination compounds containing Pd. 
         [0022]    For instance, if blue LED chip is used, it is required to use yellow fluorescent powders for light conversion to mix the blue LED and produce white light. On the other hand, the light compensation layer  20  according to the present invention can be chosen from the group consisting of yellow phosphorescent powders, green phosphorescent powders, red phosphorescent powders, yellow fluorescent powders, green fluorescent powders, red fluorescent powders, and any combination of the above. According to design purpose, the light compensation layer  20  can emit any color of light at the transient moments of flashes. 
         [0023]      FIG. 3  shows a structural schematic diagram according to another preferred embodiment of the present invention. As shown in the figure, the structure and light compensation layer according an embodiment of a practical AC LED  10  are used for description. The AC LED  10  comprises a first lateral LED chip  100  and a second lateral LED chip  200 . The first lateral LED chip  100  comprises a first electrode  110  and a second electrode  120 ; the second lateral LED chip  200  comprises a third electrode  210  and a fourth electrode  220 . The first and second lateral LED chips  100 ,  200  are reversely disposed on a substrate  300 . The second and fourth electrodes  120 ,  220  are disposed on the substrate  300 , respectively. The first electrode  110  is connected electrically with the fourth electrode  220 ; the second electrode  120  and the third electrode  210  are connected to an AC power supply  30 . If a package layer  400  of the AC LED  10  contains light conversion materials  410 , the light compensation layer  20  is disposed on or under (not shown in the figure) the package layer  400 , so long as the side being the light-emitting surface of the AC LED  10 . On the contrary, if the package layer  400  of the AC LED  10  contains no light conversion materials  410 , the package layer  400  can be combined with the light compensation layer  20  (not shown in the figure). 
         [0024]      FIG. 4  shows a structural schematic diagram according to another preferred embodiment of the present invention. As shown in the figure, the structure and light compensation layer according an embodiment of a practical AC LED  10  are used for description. The AC LED  10  comprises a first lateral LED chip  100  and a second lateral LED chip  200 . The first lateral LED chip  100  comprises a first electrode  110  and a second electrode  120 ; the second lateral LED chip  200  comprises a third electrode  210  and a fourth electrode  220 . The first and second lateral LED chips  100 ,  200  are disposed on a substrate  300 . The first electrode  110  is connected electrically with the fourth electrode  220 ; the second electrode  120  and the third electrode  210  are connected to an AC power supply  30 . If a package layer  400  of the AC LED  10  contains light conversion materials  410 , the light compensation layer  20  is disposed on or under (not shown in the figure) the package layer  400 , so long as the side being the light-emitting surface of the AC LED  10 . On the contrary, if the package layer  400  of the AC LED  10  contains no light conversion materials  410 , the package layer  400  can be combined with the light compensation layer  20  (not shown in the figure). 
         [0025]    If an ultraviolet (UV) LED chip is used, the light compensation layer  20  according to the present invention can be chosen from the group consisting of red phosphorescent powders, green phosphorescent powders, blue phosphorescent powders, red fluorescent powders, green fluorescent powders, blue fluorescent powders, and any combination of the above. According to design purpose, the light compensation layer  20  can emit white light during light emitting of the UV LED. 
         [0026]      FIG. 5  shows a structural schematic diagram according to another preferred embodiment of the present invention. As shown in the figure, the structure and light compensation layer according an embodiment of a practical AC LED  12  are used for description. The AC LED  12  comprises a first lateral LED chip  102  and a second lateral LED chip  202 . The first lateral LED chip  102  comprises a first electrode  112  and a second electrode  122 ; the second lateral LED chip  202  comprises a third electrode  212  and a fourth electrode  222 . The first and second lateral LED chips  102 ,  202  are reversely disposed on a substrate  300 . The second and fourth electrodes  122 ,  222  are disposed on the substrate  300 , respectively. The first electrode  112  is connected electrically with the fourth electrode  222 ; the second electrode  122  and the third electrode  212  are connected to an AC power supply  30 . In addition, the first and second lateral LED chips  102 ,  202  are UV LED chips. If a package layer  402  of the AC LED  12  contains light conversion materials  412 , the light compensation layer  20  is disposed on or under (not shown in the figure) the package layer  402 , so long as the side being the light-emitting surface of the AC LED  12 . On the contrary, if the package layer  402  of the AC LED  12  contains no light conversion materials  412 , the package layer  402  can be combined with the light compensation layer  20  (not shown in the figure). 
         [0027]      FIG. 6  shows a structural schematic diagram according to another preferred embodiment of the present invention. As shown in the figure, the structure and light compensation layer according an embodiment of a practical AC LED  12  are used for description. The AC LED  12  comprises a first lateral LED chip  102  and a second lateral LED chip  202 . The first lateral LED chip  102  comprises a first electrode  112  and a second electrode  122 ; the second lateral LED chip  202  comprises a third electrode  212  and a fourth electrode  222 . The first and second lateral LED chips  102 ,  202  are disposed on a substrate  300 . The first electrode  112  is connected electrically with the fourth electrode  222 ; the second electrode  122  and the third electrode  212  are connected to an AC power supply  30 . In addition, the first and second lateral LED chips  102 ,  202  are UV LED chips. If a package layer  402  of the AC LED  12  contains light conversion materials  412 , the light compensation layer  20  is disposed on or under (not shown in the figure) the package layer  402 , so long as the side being the light-emitting surface of the AC LED  12 . On the contrary, if the package layer  402  of the AC LED  12  contains no light conversion materials  412 , the package layer  402  can be combined with the light compensation layer  20  (not shown in the figure). 
         [0028]    Besides, the relative positions of the light conversion materials and light compensation layers in  FIGS. 3 to 6  can be interchanged arbitrarily or be combined to a single layer. This is well known to a person having ordinary skill in the art, and will not be described in more details. 
         [0029]    Accordingly, the present invention conforms to the legal requirements owing to its novelty, nonobviousness, and utility. However, the foregoing description is only embodiments of the present invention, not used to limit the scope and range of the present invention. Those equivalent changes or modifications made according to the shape, structure, feature, or spirit described in the claims of the present invention are included in the appended claims of the present invention.