Abstract:
A coin shaped light-emitting device is disclosed and includes a light-emitting member formed by encapsulating and wiring a plurality of LEDs on a thin substrate, a constant current controller for operating the light-emitting member in constant current and causing the light-emitting member to emit bright light, and a shell for enclosing the light. A water-resistant arrangement is further incorporated into the light-emitting device. A coin shaped spotlight is further disclosed and is formed by connecting a plurality of light-emitting devices in series, in parallel, or in another configuration. The spotlight has advantages of increased reliability, energy saving, and prolonged useful life.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of Invention 
         [0002]    The invention relates to LED (light-emitting diode) lights and more particularly to a coin shaped light-emitting device including LEDs and a coin shaped spotlight comprising a plurality of light-emitting devices with improved characteristics including increased reliability, energy saving, and prolonged useful life. 
         [0003]    2. Description of Related Art 
         [0004]    Conventionally, a spotlight employs a halogen bulb which has the disadvantages of consuming energy and generating high temperature in use. Recently, LED lights are gaining popularity due to its advantageous features including low energy consumption and sufficient brightness. Thus, halogen lamps are gradually replaced by LED lights. There is a type of LED light as a spotlight commercially available. The LED bulb has the shape of a halogen bulb. As such, the LED light including the LED bulb is relatively large. Further, rails for mounting LED lights are required. Furthermore, the LED bulb has a narrow operating voltage. That is, voltage is required to be highly stable. Hence, the LED light cannot operate normally if an external source of power is not stable (i.e., large voltage variations). This has the disadvantages of shortening its useful life, etc. 
         [0005]    Taiwanese Utility Model Patent No. M269,398 discloses a LED light comprising an array of a plurality of LEDs formed on a circuit board, a power supply circuit formed on a shell of the light, fin-shaped heat sinks, and a fan together for removing heat generated by the operating light. 
         [0006]    While the Taiwanese Patent can emit highly bright light rays, it has disadvantages the same as that described in the above first paragraph. Thus, continuing improvements in the exploitation of LED light are constantly being sought. 
       SUMMARY OF THE INVENTION 
       [0007]    It is therefore one object of the invention to provide a coin shaped light-emitting device comprising a coin shaped light-emitting member formed by encapsulating a plurality of LEDs, a constant current controller for operating the light-emitting member in constant current and causing the light-emitting member to emit bright light, and a shell for enclosing the light; and a coin shaped spotlight comprising a plurality of light-emitting devices. By utilizing the invention, a thin, stable spotlight is obtained. Further, the spotlight has the advantages including increased reliability, energy saving, and prolonged useful life. 
         [0008]    In one aspect of the invention, there is provided a coin shaped spotlight including a plurality of light-emitting devices each comprising a coin shaped light comprising a light-emitting member comprising a plurality of LEDs and a lens formed together by encapsulation; a constant current controller electrically connected to the light-emitting member for supplying a constant current; and an electrical connector electrically connected the constant current controller and the light-emitting member to a source of power; and a shell comprising a hollow cylindrical case; a cover releasably secured to one end of the case and comprising a central through hole; a hollow cylinder mounted within the case for fastening the light-emitting member, the constant current controller, and the connector together; and a fastener comprising a hollow first portion threadedly secured to the other end of the case, a hollow internal water-resistant member with wires passed through the water-resistant member and the case, and a hollow second portion threadedly secured to the other end of the first portion for fastening the water-resistant member in the first portion. 
         [0009]    In another aspect of the invention the constant current controller comprises parallel first and second constant current control circuits, each of the first and second constant current control circuits comprising an operational amplifier; a reference voltage source electrically connected to a first resistor which is in turn electrically connected to a negative terminal of the source of power so as to apply a reference voltage to a negative terminal of the operational amplifier via the first resistor and the reference voltage source; a sampling resistor interconnected a positive terminal of the source of power and a positive terminal of the operational amplifier so as to apply a sampling voltage to the positive terminal of the operational amplifier via the sampling resistor; and a switch adapted to conduct or cut off an output of either the first constant current control circuit or the second constant current control circuit based on a comparison result of the reference voltage and the sampling voltage. 
         [0010]    The above and other objects, features and advantages of the invention will become apparent from the following detailed description taken with the accompanying drawings. 
     
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0011]      FIG. 1  is a perspective view of a coin shaped light-emitting device according to the invention; 
           [0012]      FIG. 2  is an exploded perspective view of a coin shaped light-emitting device according to the invention; 
           [0013]      FIG. 3  is a circuit diagram of the LEDs; 
           [0014]      FIG. 4  schematically depicts wiring of the LED array; 
           [0015]      FIG. 5  is a plan view of the LED; 
           [0016]      FIG. 6  is a circuit diagram of the constant current controller; and 
           [0017]      FIGS. 7 ,  8 , and  9  schematically depict connections of first, second, and third preferred embodiments of coin shaped spotlight comprising a plurality of coin shaped light-emitting devices according to the invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0018]    Referring to  FIG. 2 , a coin shaped light-emitting device in accordance with the invention comprises a coin shaped light  1  and a shell  2  for enclosing the light  1 . The light-emitting device is adapted to operate in constant current and emit bright light. Thus, a spotlight including a plurality of series connected, parallel connected, or otherwise connected light-emitting devices the diameter thereof can be made as small as a coin. 
         [0019]    The light  1  comprises a light-emitting member  11 , a constant current controller  12 , and an electrical connector  13 . Each component is discussed in detailed below. 
         [0020]    The light-emitting member  11  comprises a disk shaped substrate  111  and a high power LED array  110 . A square lens  14  having four corner legs  141  mounted in four apertures  114  of the substrate  111 . Four LEDs  113  of the LED array  110  are mounted on a center of a top surface of the substrate  111  by encapsulation. Two opposite through holes  112  are formed on the substrate  111 . Two fasteners (e.g., screws)  15  are driven through the holes  112  into threaded holes  235  of a cylinder  23  for securing the substrate  111  to the cylinder  23 . 
         [0021]    The constant current controller  12  is electrically connected to both the light-emitting member  11  and the LED array  110 . As such, the LED array  110  is adapted to operate in constant current without being adversely affected by voltage variations of an external source of power. 
         [0022]    The connector  13  is electrically connected to the constant current controller  12  via two conductors  132  and comprises four terminals  131  for electrically connecting to one or two external sources of power. 
         [0023]    The shell  2  comprises a cylindrical case  21 , a cover  22 , the cylinder  23 , and a fastener  24 . Each component is discussed in detailed below. 
         [0024]    The case  21  comprises an externally threaded extension  211  (e.g., preferably male threads) projected from one end, a shoulder  213  at a joining portion of one end and the extension  211 , and internal threads  212  (e.g., preferably female threads) at the other end. 
         [0025]    The disk shaped cover  22  comprises a central through hole  221  having an inwardly extending rim  225 , and a disk shaped lens or a transparent disk  222  dimensioned to fit in the hole  221 , supported by the rim  225 , and secured thereto by a liquid impermeable adhesive. Preferably, the lens or disk  222  is formed of reinforced plastic, glass, or acrylic plastic. The cover  22  further comprises an annular flange  223  having internal threads  224  on its inner surface. A first sealing ring  220  is put on the shoulder  213 . A second sealing ring  226  is disposed under the rim  225  and against the top end  214 . The provision of the first and second sealing rings  220  and  226  can ensure a waterproof engagement of the cover  22  and the case  21  when the threads  224  are secured to the externally threaded extension  211 . 
         [0026]    The cylinder  23  comprises a body  231 , a bore  232 , a positioning member  233  of curved section extended downward from the body  231  and fitted within the case  21 , the threaded holes  235 , and a pin  234  driven through the positioning member  233  to fasten the connector  13 . 
         [0027]    The fastener  24  comprises a hollow first portion  241  including an externally threaded first element  244  at one end, an externally threaded second element  245  at the other end, the threads of the first element  244  being more dense than that of the second element  245 , a hexagonal flange (not numbered) disposed between the first element  244  and the second element  245 , an annular trough  248  on a joining portion of the first element  244  and the flange, an O-ring  249  fitted in the through  248 , and a knurled extension  246  projected downward from the second element  245 . 
         [0028]    The fastener  24  further comprises a cylindrical water-resistant member  243  tightly fitted in the knurled extension  246 . The water-resistant member  243  comprises two through holes  247  such that wires  251  are adapted to pass through the water-resistant member  243  and the case  21  to be electrically connected to the connector  13 . 
         [0029]    The fastener  24  further comprises a hollow, cylindrical second portion  242  having inner threads secured to the second element  245 . 
         [0030]    With the above water-resistant arrangement, the light-emitting device is substantially waterproof. 
         [0031]    Referring to  FIGS. 3 to 5 , two LEDs  113  are electrically connected together in series and the other two LEDs  113  are also electrically connected together in series by wiring. Further, one pair of the connected LEDs  113  are connected in parallel to the other pair of the connected LEDs  113 . Eventually, a thin high power LED array  110  is formed by encapsulation (see  FIG. 4 ). 
         [0032]    Referring to  FIG. 6 , the constant current controller  12  comprises first and second constant current control circuits  121  and  122  connected in parallel to the substrate  111  to supply the power to LED array  110 . The first constant current control circuit  121  comprises an operational amplifier  123 , a reference voltage source  124  electrically connected to a first resistor (R 1 )  125  which is in turn electrically connected to a positive terminal of a source of power such that a reference voltage can be applied to a negative terminal of the operational amplifier  123  via the first resistor  125  and the reference voltage source  124 , a sampling resistor (R 3 )  126  interconnected a negative terminal of the source of power and a positive terminal of the operational amplifier  123  such that a sampling voltage can be applied to the positive terminal of the operational amplifier  123  via the sampling resistor  126 , and a switch (e.g., preferably a transistor)  127  adapted to conduct or cut off an output of the first constant current control circuit  121  based on a comparison result of the reference voltage and the sampling voltage. 
         [0033]    Likewise, the second constant current control circuit  122  comprises an operational amplifier  123 ′, a reference voltage source  124 ′ electrically connected to a first resistor (R 2 )  125 ′ which is in turn electrically connected to a positive terminal of a source of power such that a reference voltage can be applied to a negative terminal of the operational amplifier  123 ′ via the first resistor  125 ′ and the reference voltage source  124 ′, a sampling resistor (R 4 )  126 ′ interconnected a negative positive terminal of the source of power and a positive terminal of the operational amplifier  123 ′ such that a sampling voltage can be applied to the positive terminal of the operational amplifier  123 ′ via the sampling resistor  126 ′, and a switch (e.g., preferably a transistor)  127 ′ adapted to conduct or cut off an output of the second constant current control circuit  122  based on a comparison result of the reference voltage and the sampling voltage. By configuring as above, the light  1  can always operate in constant current. 
         [0034]    Referring to  FIGS. 7 ,  8 , and  9 , connections of first, second, and third preferred embodiments of coin shaped spotlight are shown. The spotlight comprises a plurality of light-emitting devices including the light  1  and the shell  2 . As shown in  FIG. 7 , in the first preferred embodiment the light-emitting devices are connected in series with a source of power  25  via a cord  251 . As shown in  FIG. 8 , in the second preferred embodiment the light-emitting devices are connected in parallel with the source of power  25  via the cord  251 . As shown in  FIG. 9 , in the third preferred embodiment each of the light-emitting devices is electrically connected to the source of power  25  via a dedicated one of four cords  251 . 
         [0035]    To summarize, the invention provides a coin shaped light  1  including a light-emitting member  11  including a plurality of LEDs  113  electrically connected together to form a LED array  110  by encapsulation and wiring. Eventually the LED array  110  is formed on a top of the substrate  111  and then the lens  14  is mounted thereon by encapsulation. The constant current controller  12  is adapted to supply a constant input current. As a result, a coin shaped light  1  having characteristics of constant current, high power output, wide operating voltage, energy saving, and prolonged useful time is formed. 
         [0036]    To summarize, the invention further provides a light-emitting device including the light  1  and the shell  2 . The light-emitting device has a diameter of about 25 mm and a length of about 80 mm. 
         [0037]    To summarize, the invention yet further provides a coin shaped spotlight including a plurality of light-emitting devices which are connected in series, parallel, or otherwise connected together depending on applications. 
         [0038]    While the invention herein disclosed has been described by means of specific embodiments, numerous modifications and variations could be made thereto by those skilled in the art without departing from the scope and spirit of the invention set forth in the claims.