Abstract:
An improved LED lamp tube and socket assembly intended for the replacement of fluorescent tube style lamps. The new lamp tube featuring a 3-pin end interface wherein a middle or center pin is connected to the LED tube&#39;s heat sink to prevent the potential for electrical fires and/or shocks following a failure event such as the LED array making electrical contact with the heat sink of the LED tube. An alternative embodiment bi-pin version of the invention is also disclosed.

Description:
FIELD OF THE INVENTION 
       [0001]    The invention relates to improved LED lamps and, in particular, to LED tube lamps which have one or more LEDs as light sources and which can replace a fluorescent tube. 
       BACKGROUND OF THE INVENTION 
       [0002]    Fluorescent lamps are widely used in different environments, such as in homes, offices and industry. Fluorescent lamps are more durable, economical and efficient than incandescent lamps, in which most of the electric power generates heat rather than light. In a conventional fluorescent lamp, the body is a straight tube with a length of about 20 to 60 inches. Fluorescent tubes are low-pressure mercury discharge lamps in which the inner surface of the tube is coated with a fluorescent material. The structure of a fluorescent tube is very simple which has likely contributed to their use for several decades. The lamp consists of an airtight glass tube containing a small amount of mercury, an inert gas, a fluorescent coating such as phosphor, as well as electrodes and a filament at each end of the lamp. At each end of the fluorescent tube, there is a cap with two symmetrically positioned contact pins, to which the electrodes on each side of the tube are connected. DC power to the fluorescent tube is provided via these contact pins. 
         [0003]    In order to provide a florescent tube with DC power an AC to DC power supply is used to convert AC line voltage (typically either 115 or 230 volts) to DC input current. The DC current is reduced by the power supply to a level suitable for use in a florescent tube. These power supplies are generally known within the lamp industry as ballasts. 
         [0004]    Unlike incandescent or newer light emitting diode (“LED”) lamps, fluorescent lamps will not illuminate or start simply by applying power to the lamp. The lamp requires a starting circuit. The circuit for a fluorescent tube lamp comprises a power supply (ballast) and a starter (capacitor or other switching device). Upon turning on a fluorescent lamp, the resistance through the tube is very high, and the electric current passes through the ballast, the electrodes on one side of the tube and a closed starter circuit. When passing through the electrodes, the current heats the filament, causing it to emit electrons which ionize the gas inside the tube. The ionized gas forms a current path through the tube. When, after a moment, the starter opens, a high voltage spike occur s between the electrodes which causes current conduction through the ionized gas in the fluorescent tube and thus switches on the lamp. Many types of starters are known in the art. 
         [0005]    Lighting systems based on LED light sources are a fairly new technology in the lighting field. LED&#39;s are desirable because they have substantially longer life and they use far less power than fluorescent tubes of equivalent output. LED replacement tubes for fluorescent lamps are of the same length and diameter of the fluorescent lamp they are intended to replace. LED replacement tubes typically comprise a number of LEDs to produce the desired light. The LEDs are disposed between a heat sink and a clear or translucent cover. The LEDs may be in a series or parallel circuit array. LEDs differ from fluorescent tubes in that only a power supply or ballast capable of converting high voltage AC line current to a relatively lower voltage DC input current to the LEDs is required. No starting circuit is required with LED lamps. 
         [0006]    In some types of LED tube lamps, the ballast is built into the lamp. In others, an external ballast is used. As LEDs have become more powerful and continue to gain in wattage, the need has become more critical to dissipate the heat generated by the LEDs. Therefore, in a typical LED tube used for replacing a fluorescent tube approximately ½ of the circumference of the LED tube comprises a metallic heatsink while the other half is clear or translucent for the transmission of light. The LED arrays are thermally, but not electrically, connected to the metallic heat sink. 
         [0007]    Government safety regulations require that lighting fixtures be constructed in such a way that when a fluorescent or LED tube is replaced, it is impossible for a user to come into contact with any parts at input voltage even if the lighting fixture were connected to line voltage. With fluorescent tubes, this requirement is met even if a fluorescent tube is replaced in such a way that only one set of contacts is in a tube end connector and a user touches the contacts on the side of the tube during installation. This requirement is met because even though input voltage may be present at the contacts, no current passes through the gas-filled fluorescent tube before the gas in the tube is ionized with a starting pulse. In other words, the gas in the fluorescent tube serves as an insulator in itself. The electric circuit of the fluorescent tube lighting fixture is such that generation of a starting pulse requires that both ends of the tube be connected to the contacts of the tube holder. 
         [0008]    The above however, is not true in the case of LED lights. In LED lights current conduction occurs through the tube at any time that one set of contacts is connected to input voltage. To solve this problem, manufacturers of LED tubes have equipped the lights with electronic switches where the switch opens and breaks the electrical circuit when voltage is detected at only one set of contacts. When voltage is detected at both sets of contacts, the switch closes and allows current to flow. 
         [0009]    In the present invention, the inventor has recognized that the safety features presently provided by manufacturers of LED tube lamps are inadequate because the metallic heat sink of the tube is not grounded. Under certain failure conditions, the LED arrays could inadvertently make electrical contact with the metallic heat sink causing a short circuit and a potential fire hazard. 
       SUMMARY OF THE INVENTION 
       [0010]    As discussed above, under certain failure conditions, input voltage or line voltage could inadvertently be applied to the metal heat sink of an LED tube style lamp causing a short circuit and a potential fire hazard because in such circumstances the printed circuit board and other electrical components within the tube can quickly overheat and catch fire. 
         [0011]    This failure condition may arise under several scenarios. For example, over time, the thermal insulation which thermally connects the LEDs with the heat sink may break down and allow an electrical connection to occur between the lamp the heat sink. Overheating of the lamp may accelerate this breakdown. In LED tubes where the ballast is incorporated in the tube, it must be insulated from the heat sink. Here again, the insulating material my break down over time and potentially expose the heat sink to line voltage. Moreover, LED tubes with relatively thin metallic heat sinks and plastic covers may be subject to flexing either during shipping or less than careful installation. Such flexing of the tubes could either break the thermal substrate of the LEDs and thus cause electrical contact with the heat sink or could damage the ballast and associated wiring in such a manner that electrical contact is made with the heat sink. 
         [0012]    The present invention solves the aforementioned problems by providing a ground pin on each side cap of the LED tube where the ground pins are connected to the heat sink and via the lamp sockets to an external ground. The grounding may be accomplished by use of tri-pin end caps for the LED tube, i.e. the end caps of the new lamp retain the outermost pins in their typical location as found in typical florescent lamp tubes. A third pin, however, is located in the middle of each end cap and this pin is connected with the ground terminal of the present invention end socket which in turn is connected to an external ground via a ground strap or metal ground lug. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0013]      FIG. 1  is a schematic view of an improved tri-pin LED replacement tube for a fluorescent tube and associated tri-pin socket and optional wiring box. 
           [0014]      FIG. 2  is a schematic view, partially cutaway, of the improved tri-pin LED replacement tube of  FIG. 1 . 
           [0015]      FIG. 3A  is a socket body for use with the tri-pin socket shown in  FIG. 1 . 
           [0016]      FIG. 3B  is a back cover for use with tri-pin socket shown in  FIG. 1 . 
           [0017]      FIG. 3C  is a ground plate for use with the tri-pin socket shown in  FIG. 1 . 
           [0018]      FIG. 3D  is ground strap for use with the tri-pin socket shown in  FIG. 1 . 
           [0019]      FIG. 3E  is a rivet for use with the tri-pin socket shown in  FIG. 1 . 
           [0020]      FIG. 4A  is a front view of the tri-pin socket of  FIG. 1 . 
           [0021]      FIG. 4B  is a side view of the tri-pin socket of  FIG. 1 . 
           [0022]      FIG. 4C  is a rear view of the tri-pin socket of  FIG. 1 . 
           [0023]      FIG. 5A  is a socket body for use with an alternative embodiment of the tri-pin socket shown in  FIG. 1 . 
           [0024]      FIG. 5B  is a back cover for use with an alternative embodiment of the tri-pin socket shown in  FIG. 1 . 
           [0025]      FIG. 5C  is a ground plate for use with an alternative embodiment of the tri-pin socket shown in  FIG. 1 . 
           [0026]      FIG. 5D  is a ground strap for use with an alternative embodiment of the tri-pin socket shown in  FIG. 1 . 
           [0027]      FIG. 5E  is a rivet for use with an alternative embodiment of with the tri-pin socket shown in  FIG. 1 . 
           [0028]      FIG. 6A  is a front view of an alternative embodiment of tri-pin socket of  FIG. 1 . 
           [0029]      FIG. 6B  is a side view of an alternative embodiment of the tri-pin socket of  FIG. 1 . 
           [0030]      FIG. 6C  is a rear view of an alternative embodiment of the tri-pin socket of  FIG. 1 . 
           [0031]      FIG. 7  is an alternative wiring box to the box shown in  FIG. 1  and is used when multiple LED tubes are used within the same lighting fixture. 
           [0032]      FIG. 8  shows a left end view of a light fixture, partially cutaway, showing the LED tube lamp, sockets and splitter box of the present invention as installed in the fixture, wherein a ground strap is used to ground the light. 
           [0033]      FIG. 9  shows right side view of a light fixture, partially cutaway, showing the LED tube lamp, sockets and splitter box of the present invention as installed in the fixture, wherein a ground strap is used to ground the light. 
           [0034]      FIG. 10  shows a left end view of a light fixture, partially cutaway, showing the LED tube lamp, sockets and splitter box of the present invention as installed in the fixture, wherein a ground lug is used to ground the light. 
           [0035]      FIG. 11  shows right side view of a light fixture, partially cutaway, showing the LED tube lamp, sockets and splitter box of the present invention as installed in the fixture, wherein a ground lug is used to ground the light. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0036]    The present invention will now be described more fully hereinafter with reference to the accompanying drawings, in which preferred embodiments of the invention are shown. The invention may, however, may be embodied in many different forms and should not be construed as being limited to the embodiments set forth herein. Rather these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art. Like numbers refer to like elements throughout. 
         [0037]    The field of the invention comprises all LED tube style lamps. With reference to  FIGS. 1 and 2 , the present invention improved LED lamp  10  comprises an LED tube style lamp  11  which has a metallic heat  12  sink on a portion of the lamp and a clear or translucent light emitting portion  14 . The LED lamp also includes an end cap  17  at each end of the lamp. Each end cap  17  includes three pins rather than the two pins of a conventional fluorescent lap. One pin  13  is a dummy pin which does not carry power and serves only to maintain compatibility with existing fluorescent lamp fixtures. A second pin  15  is a power pin and conducts current through the LED array. The third pin is a ground pin  16  which serves to connect the lamp&#39;s heat sink to an external ground. Methods of connecting the ground pin  16  to the lamp&#39;s heat sink are known in the art. 
         [0038]    With continued reference to  FIG. 1 , the present invention  10  includes tri-pin tube end sockets  18 . The tri-pin end sockets  18  are typically made from a high dielectric strength plastic as is known in the art. Coming off the center of the socket  18  is a ground strap  20 . The ground strap is electrically connected with the ground pin  16  when the lamp tube  11  is installed in the sockets. Additional detail regarding the present invention sockets  18  will be provided below. 
         [0039]    In LED lamps that use an internal ballast (not shown), it is necessary to run electrical wires carrying full AC line voltage to the internal ballast. Wires that carry full line voltage are generally several gauges larger than the input terminals on industry standard T8 and T5 type end sockets. Therefore, the present invention provides a wiring box  22  where wires  24  and  26  are AC line inputs which, for example, may be of 10 or 12 gauge in size. The wiring box reduces the size of the output wires  28  and  30  to a smaller gauge size, for example 18 or 20 gauge, suitable for use with the input terminals of the tri-pin sockets  18  which are based upon standard bi-pin T5 and T8 socket input terminals  42  (shown in  FIGS. 4A and 6A ). 
         [0040]    Referring now to  FIG. 2 , in the partial cutaway, LEDs  32  and the LED printed circuit board  34  are shown. Due to their high heat output, the LEDs must be thermally, but not electrically connected, to the heat sink. In any instance where the LEDs come into electrical contact with the heat sink a short circuit in LED array will arise and in the absence of a return ground path, heat may quickly build up in the lamp leading to a hazardous condition such as an electrical fire. 
         [0041]    Referring now to  FIGS. 3A through 3C  and  4 A through  4 D, the tri-pin end socket  18  of the present invention is a modified version of industry standard bi-pin T5 and T8 type sockets. The end sockets  18  are modified for use with a 3 pin LED tube type lamp of the present invention is shown. With particular reference to  FIGS. 3A through 3E , the new tri-pin end socket  18  comprises a socket body  36 , a back cover  50  a ground plate  44  a ground strap  20  having ring terminals  46  and  48  and a rivet  42  which connects the ground strap, ground plate and back cover to the socket body. 
         [0042]    Referring now to  FIGS. 4A through 4B , front, side and rear views of the present invention tri-pin socket  18  are shown. The new socket functions similarly to older bi-pin sockets in that when a light tube is placed into the socket and rotated the outermost pins are locked into place by hook shaped outer contacts  38 . What is different, however, is that in the new tri-pin socket, a ground plate  44  which includes a protruding section  45  is attached to the rear of the socket body  36  so that the ground or middle pin  16  of the lamp  11  makes contact with the ground plate  44 . Attached to the ground plate  44  is the ground strap  20  which when in use is attached to an external ground. 
         [0043]    With reference to  FIGS. 5A through 5E  and  5 A through  6 C, an alternative embodiment of the tri-pin socket  18  is disclosed. In this embodiment of the tri-pin socket  18  an angled ground lug  56  is used in place of the ground strap  20 . With particular reference to  FIGS. 5A through 5E , this alternative embodiment of the new tri-pin end socket  18  comprises a socket body  36 , a back cover  50  a ground plate  44 , the ground lug  56 , and a screw  52  which threadably connects the ground plate, ground lug, and back cover to the socket body. 
         [0044]    Referring now to  FIGS. 6A through 6B , front, side and rear views of the angled lug embodiment of the present invention tri-pin socket  18  are shown. Like the previous embodiment, the new socket functions similarly to older bi-pin sockets in that when a light tube is placed into the socket and rotated the outermost pins are locked into place by hook shaped outer contacts  38 . The difference, however, is that in the new tri-pin socket, a ground plate  44  which includes a protruding section  45  is attached to the rear of the socket body  36  so that the ground or middle pin  16  of the lamp  11  makes contact with the protruding portion  45  of the ground plate  44 , when the lamp tube is fully inserted into the socket. In this embodiment of the tri-pin socket  18 , the ground plate  44  is attached to the ground lug  56  via screw  52 . For those installations where a ground is available immediately under the socket, a ground screw  54  may be used to connect the tri-pin socket  18  to ground. 
         [0045]    With reference to  FIG. 7 , another embodiment of the wiring box  22  is shown. In this embodiment, the wiring box provides AC outputs for providing power to two LED tube arrays. The wiring box is used for LED lamp tubes that use an internal ballast (not shown). With an internal ballast, it is necessary to run electrical wires carrying full AC line voltage to the ballast. As mentioned above, wires that carry full AC line voltage (typically either 120 or 230 volts) are generally several gauges larger than the input terminals on industry standard T8 and T5 style end sockets. Therefore, the present invention provides a wiring box  22  where wires  24  and  26  are AC line inputs which, for example, may be of 10 or 12 gauge in size. The wiring box reduces the size of the two pairs of output wires  58  and  60  and  62  and  64  to a smaller gauge size, for example 18 or 20 gauge, suitable for use with the tri-pin sockets  18  which use standard size bi-pin T5 and T8 socket input terminals  42  (shown in  FIGS. 4A and 6A ). Because the wire runs from the wiring box to the internal ballast of the lamps are relatively short, they are capable of safely carrying line voltage over the short distance needed. Those skilled in the art will readily recognize that the wiring box  22  can be expanded to provide as many output leads as necessary to supply the number of tubes in a lamp array. 
         [0046]    In the exemplary embodiment, the tri-pin end sockets  18  are modified industry standard T5/T8 sockets which have standard input terminals requiring relatively small gauge wires. Those skilled in the art however, will understand that custom tri-pin sockets could readily be designed with input terminals capable of accepting a larger size wire gauge than the current standard for T5/T8 sockets. 
         [0047]    Referring now to  FIGS. 8 and 9 , the component parts of the present invention are shown installed in a light fixture  66 . The light fixture  66 , as shown in the figures, is cable of holding two LED lamp tubes  11 . The fixture  66  will typically be made of formed sheet metal such as steel or aluminum or other electrically conductive material, which in addition to holding the LED lamp tubes also provides a ground for the lamps. In the arrangement shown in  FIGS. 8 and 9 , two T5 or T8 style lamp sockets  18 , as modified to accept a third ground pin as taught by the present invention are shown at each end of the lamp fixture  66 . Installed within the sockets  18  are two LED lamp tubes  11 . The LED lamp tubes  11  are equipped with an internal ballast (not shown) and therefore require that AC line voltage be supplied to the terminals  42  of the lamp sockets  18 . 
         [0048]    To provide AC line voltage, the splitter box  22  is mounted to the underside of a top surface  70  of the light fixture  66 . AC line voltage (typically 120 or 230 volts) is introduced to the splitter box  22  via input leads  62  and  64 . These input leads will typically be of 10 to 12 gauge in size in typical household wiring. Since the input terminals  42  of the T5/T8 sockets  18  will typically accept wire gauges in of about 18 to 20 gauge, the splitter box includes an internal interconnection (not shown) which steps down the size of the electrical wiring to a size suitable for use with the sockets  18 . 
         [0049]    As taught by the exemplary embodiment for the sockets  18  of  FIGS. 3A through 4C , grounding of the heat sinks  12  of the LED lamp tubes  11  to the light fixture  66  is accomplished by means of the third ground pins  16  of the LED lamp tubes  11  making contact with the ground plates  44  of the modified T5/T8 sockets  18 . Grounding to the light figure is then accomplished by means of the ground straps  20  being attached to the light fixture, typically by means of screws. Thus, in light fixture  66  of  FIGS. 9 and 10 , four (4) ground straps  20 , i.e. one for each socket, are connected to the lamp fixture  66  at four locations on the fixture. 
         [0050]      FIGS. 10 and 11  are similar to  FIGS. 9 and 10 , with the exception that the alternative embodiment of the sockets  18  shown in  FIGS. 5A through 6C  is used. In this embodiment, grounding of the LED tube lamps is also accomplished by means of the ground pins  16  of the lamp tubes  11  making contact with the ground plates  44  of the modified T5/T8 socket. However, rather than using a ground strap, in the alternative embodiment of the sockets  18 , the ground plate  44  is electrically connected with a ground lug  56 , which is incorporated in the socket. The heat sinks  12  of the LED lamp tubes  11  may then be grounded to the lamp fixture via a screw which connects the ground lugs  56  to the light fixture  66 . Again, each individual socket is grounded to the light fixture. 
         [0051]    The foregoing detailed description and appended drawings are intended as a description of the presently preferred embodiments of the invention and are not intended to represent the only forms in which the present invention may be constructed and/or utilized. Those skilled in the art will understand that modifications and alternative embodiments of the present invention which do not depart from the spirit and scope of the foregoing specification and drawings, and of the claims appended below are possible and practical. It is intended that the claims cover all such modifications and alternative embodiments.