Abstract:
An arrangement of a multiplicity of LEDs, drive circuitry, and supporting structure to form a replacement for standard fluorescent tubes without the need to rewire or remove the magnetic or electronic ballasts in use in standard fluorescent fixtures.

Description:
RELATED APPLICATION DATA 
       [0001]    This application is a continuation application of U.S. patent application Ser. No. 11/361,656, filed Feb. 23, 2006 entitled “Circuit Devices Which Include Light Emitting Diodes, Assemblies Which Include Such Circuit Devices, and Methods for Directly Replacing Fluorescent Tubes,” which is incorporated herein by reference in its entirety. This application claims the benefit and priority of U.S Provisional Application Ser. No. 60/657,100 filed Feb. 28, 2005 entitled “Fluorescent Replacement Using Light Emitting Diodes,” which is incorporated herein by reference in its entirety. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The present invention relates to a circuit device for providing energy to a series of light emitting diodes and an assembly including such circuit devices and light emitting diodes. The present invention relates to a light emitting diode (LED) assembly for direct replacement of a tubular fluorescent light bulb. 
       BACKGROUND 
       [0003]    The widespead use of fluorescent tubes for general purpose lighting has several drawbacks. One significant drawback is their use of rare-earth and other toxic phosphors to generate light. This provides a problem when tubes which have ceased to function require disposal. The phosphors can present a toxic waste situation which must be dealt with. Also, because the envelope of the tube is thin glass, the potential for accidental breakage, with attendant problems of scattering toxic material, is high. For this reason, in food-related and other industries where potential contamination is a risk, special plastic protective sleeves are required to be placed on all fluorescent tubes. A drawback to the use of these sleeves is that they trap heat generated by the tube and increase the operating temperature of the tube which decreases the useful life of the device. 
         [0004]    The ballasts used in fluorescent fixtures present an inductive load to the line resulting in a lower than unity power factor. While fluorescent lighting is longer lasting and more efficient than incandescent bulbs, the tubes have a short life relative to solid state lighting devices. Based on an eight hour per day use, LED lighting will have an average usable life ten times that of a fluorescent light source. 
         [0005]    With the introduction of high current, high output LEDs, the use of these devices in general purpose lighting has become feasible. One area of general lighting which could benefit from this technology is fluorescent lighting. Heretofore, tubes meant to accomplish this were unable to work with standard magnetic or electronic ballasts, and required replacement or complete rewiring of the lighting fixture. 
       SUMMARY OF THE DISCLOSURE 
       [0006]    In one implementation, an LED lighting device for replacing a fluorescent tube in a fluorescent lighting fixture having fluorescent fixture connectors and one or more of a standard fluorescent ballast and a magnetic fluorescent ballast is provided. The LED lighting device includes a plurality of light emitting diodes; a pair of contact pins at each end of the lighting device, said contact pins configured for mating with the fluorescent fixture connectors of the fluorescent lighting fixture; and drive circuitry connected with said plurality of light emitting diodes and at least one contact pin of said pair of contact pins, said drive circuitry configured to provide an operating current to said plurality of light emitting diodes and to operate with a standard fluorescent ballast and a magnetic fluorescent ballast such that the lighting device is operable when connected to a fluorescent lighting fixture having a standard fluorescent ballast and operable when connected to a fluorescent lighting fixture having a magnetic fluorescent ballast. 
         [0007]    In another implementation, an LED lighting device is provided. The LED lighting device includes a plurality of light emitting diodes; a pair of end caps, each of said pair of end caps disposed at an end of the lighting device; a male bi-pin fluorescent fixture connector disposed on each of said pair of end caps, each male bi-pin fluorescent fixture connector configured to mate with a fluorescent fixture connector of a fluorescent fixture having a standard electronic fluorescent ballast and to mate with a fluorescent fixture connector of a fluorescent fixture having a magnetic fluorescent ballast; and drive circuitry connected with at least one contact pin of said male bi-pin fluorescent fixture connectors and said plurality of light emitting diodes, said drive circuitry configured to provide an operating current to said plurality of light emitting diodes when said at least one contact pin is connected to a fluorescent fixture having a standard electronic fluorescent ballast and to provide an operating current to said plurality of light emitting diodes when said at least one contact pin is connected to a fluorescent fixture having a magnetic fluorescent ballast. 
         [0008]    In yet another implementation, an LED lighting device is provided. The LED lighting device includes a pair of end caps, each of said pair of end caps disposed at an end of the lighting device; a housing extending between said pair of end caps; a plurality of light emitting diodes arranged in a single row between said pair of end caps, said housing comprising a plurality of fins extending radially outward from three sides of said plurality of light emitting diodes; a male bi-pin fluorescent fixture connector disposed on each of said pair of end caps, each male bi-pin fluorescent fixture connector configured to mate with a fluorescent fixture connector of a fluorescent fixture having a standard fluorescent ballast and to mate with a fluorescent fixture connector of a fluorescent fixture having a magnetic fluorescent ballast; and drive circuitry connected with at least one contact pin of said male bi-pin fluorescent fixture connectors and said plurality of light emitting diodes, said drive circuitry configured to provide an operating current to said plurality of light emitting diodes when said at least one contact pin is connected to a fluorescent fixture having a standard fluorescent ballast and to provide an operating current to said plurality of light emitting diodes when said at least one contact pin is connected to a fluorescent fixture having a magnetic fluorescent ballast. 
         [0009]    In still another implementation, a circuit arrangement is provided. The circuit arrangement provides the proper drive to a multiplicity of LEDs, connected in a series string, by deriving the drive from standard magnetic or electronic ballast and commonly used fluorescent fixture wiring. Another circuit provides the capability of operation with any fixture wiring variation. Yet another circuit provides protection against the ballast generating a high “strike” voltage in the event that an LED fails open. Still another embodiment is shown which provides dimming capability for the light. Still yet another embodiment shows the interface circuitry for remotely dimming the LED light. 
         [0010]    In yet still another implementation, no glass or other easily breakable materials are utilized and no toxic substances are used. Therefore, there is no need for heat trapping protective sleeves or other covering devices to be used. A further implementation provides for means to remove the heat generated by the LEDs and thereby increase the useful life of the devices. In still a further implementation, the filter capacitance at the input offsets, to some degree, the inductive load presented by the ballast and bring the input power factor closer to unity. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS  
         [0011]    For the purpose of illustrating the invention, the drawings show aspects of one or more embodiments of the invention. However, it should be understood that the present invention is not limited to the precise arrangements and instrumentalities shown in the drawings, wherein: 
           [0012]      FIG. 1  is a plan view of the final assembly of an embodiment of the invention. 
           [0013]      FIG. 2  is a cross-sectional view of one end-cap of the assembly. 
           [0014]      FIG. 3  is a cross-sectional view of the LED mounting and heat sink. 
           [0015]      FIG. 4  is a schematic diagram of a basic embodiment of circuit elements and LEDs 
           [0016]      FIG. 5  is a schematic diagram of an embodiment providing an arrangement of circuit elements to accommodate differing versions of fixture wiring. 
           [0017]      FIG. 6  is a schematic diagram of a circuit which protects the circuit elements against damage from ballast-generated, high voltage “strike” voltages. 
           [0018]      FIG. 7  is a schematic diagram of an embodiment providing dimming capability. 
           [0019]      FIG. 8  is a schematic diagram of an embodiment providing interface circuitry for remote dimming of the device. 
       
    
    
     REFERENCE NUMERALS IN THE DRAWINGS 
       [0020]      10  Contact Pin 
         [0021]      20  End Cap 
         [0022]      30  Heat Sink 
         [0023]      40  Bridge Rectifier 
         [0024]      45  Bus Wire 
         [0025]      50  Input Capacitor 
         [0026]      55  Input Circuit Board 
         [0027]      60  LED 
         [0028]      70  LED Circuit Board 
         [0029]      90  Thermally Conductive Isolator 
         [0030]      100  Shut Down Triac 
         [0031]      110  Overvoltage Sense Zener Diode 
         [0032]      120  Current Setting Resistor 
         [0033]      125  Control Circuit Board 
         [0034]      130  NPN Power Transistor 
         [0035]      140  Base Drive Resistor 
         [0036]      150  Diode 
         [0037]      200  N Channel MOSFET 
         [0038]      210  P Channel MOSFET 
         [0039]      220  Microprocessor 
         [0040]      240  Voltage Regulator 
         [0041]      250  Input Zener Diode 
         [0042]      260  Filter Capacitor 
         [0043]      270  Capacitor 
         [0044]      280  Base Drive Resistor 
         [0045]      290  NPN Transistor 
         [0046]      300  Diode 
         [0047]      310  Resistor 
         [0048]      320  NPN Transistor 
         [0049]      330  Resistor 
         [0050]      340  Diode 
         [0051]      350  Resistor 
         [0052]      360  PNP Transistor 
         [0053]      370  Zener Diode 
         [0054]      380  Interface Device 
       DETAILED DESCRIPTION  
       [0055]    Referring now to the drawings,  FIG. 1  shows a plan view of an embodiment of the present invention. A multiplicity of LEDs  60  are mounted to the LED circuit board  70  and attached to two end caps  20 . This assembly is mounted to heat sink  30  which also acts as a protective housing. The end caps  20  are fitted with contact pins  10 , spaced such that they mate with standard fluorescent fixture connectors. The overall length of the assembly is equivalent to that of a standard fluorescent tube. 
         [0056]      FIG. 2  is a cross-sectional of an end cap  20 . Contact pins  10  are physically and electrically connected to the input circuit board  55  upon which are mounted the rectifier bridge  40  and capacitor  50 . The input circuit board  55  is physically and electrically connected to the control circuit board  125  by bus wires  45 . The shut down triac  100 , overvoltage sense Zener diode  110 , and current setting resistor  120  are mounted on control circuit board  125 . These components are from the embodiment shown in  FIG. 6  and are used for illustrative purposes only. As would be known to anyone skilled in the art, the components for any of the embodiments shown could be mounted to this board. 
         [0057]      FIG. 3  is a cross sectional view of the LED mounting and heat sink. The LEDs  60  are mounted to LED circuit board  70 . This assembly is affixed to the heat sink  30  with thermally conductive isolator  90  such as T -Flex  210 , manufactured by Thermagon, or other such materials well known to anyone skilled in the art. Heat sink  30  consists of an aluminum extrusion coated with a material such as Powder Coat 10225 manufactured by The Eastman Company or other similar materials well known to anyone skilled in the art. This material, while being highly reflective to visible light has a high emissivity for infra-red. Conversely, the coating used on standard fluorescent fixtures, while being highly reflective to visible light, is an excellent absorber of infra-red. This combination permits heat sink  30  to effectively couple heat generated by the LEDs to the large area of the fluorescent fixture. 
         [0058]    The operation of example LED drive circuits within the present invention will now be described in detail while referencing the embodiments of  FIGS. 4 through 8 . All of the drive circuits presented herein make use of the constant current characteristic of standard and magnetic ballasts. By choosing LEDs which require a current of this magnitude, the need for additional constant current drive circuitry is eliminated. 
         [0059]      FIG. 4  shows one type of drive for the LED string. A multiplicity of LEDs  60  is connected as a series string. The primary AC power is brought to the circuit by contact pins  10 . The input voltage is rectified by bridge rectifier  40  and filtered by capacitor  50 . The rectified, filtered voltage is then connected to the series string of LEDs  60 . The embodiment shown in  FIG. 4  will operate with the most common wiring configuration of fluorescent fixtures.  FIG. 5  shows the preferred embodiment for input power conditioning. A second bridge rectifier and filter capacitor are added to those shown in  FIG. 4 . The embodiment of  FIG. 5  allows the present invention to operate in any fluorescent fixture wired in accordance with prevailing electrical codes. 
         [0060]    Should an LED in the series string fail as an open circuit, the ballast will sense that there is no current flowing and apply a high voltage “strike” voltage. This would normally cause the fluorescent tube to light. A “strike” voltage could cause serious damage to other components. To prevent this, the drive circuit shown in  FIG. 6  is used. As shown, shut down triac  100  is connected across the power input to the LEDs  60 . If a “strike” voltage occurs, overvoltage sense Zener diode  110  conducts current. At a current set by current setting resistor  120 , a voltage sufficient to trigger shut down triac  100  into conduction will appear at its gate terminal. This shunts the voltage across the LED string and prevents possible catastrophic failure of other circuit elements. 
         [0061]      FIG. 7  is the same embodiment shown in  FIG. 4  with a dimming capability provided by the addition of an NPN transistor  130 , a base drive resistor  140 , and diode  150 . A pulse width modulated (PWM) signal is applied to the base of NPN transistor  130  through base drive resistor  140 . This causes NPN transistor  130  to shunt the drive current to LEDs  60 . By switching NPN transistor  130  on and off at a rate sufficiently high to prevent flicker, the apparent brightness of the LEDs  60  will vary as the on to off time ratio of NPN transistor  130  is varied. Diode  150  prevents NPN transistor  130  from discharging capacitor  50 . 
         [0062]      FIG. 8  shows an embodiment which provides a remotely controlled dimming capability. The interface device  380 , which could be an infra-red, rf, or other type of receiver, sends command signals to microprocessor  220 . Operating voltage for microprocessor  220  and interface device  380  is provided by a low voltage regulator consisting of input Zener diode  250 , voltage regulator  240 , filter capacitor  260 , and capacitor  270 . The output of microprocessor  220  provides a drive signal to a level shifting and gate drive circuit consisting of resistors  280 ,  310 ,  330 , and  350 , NPN transistors  290  and  320 , PNP transistor  360 , P channel MOSFET  210 , diodes  300  and  340 , and Zener diode  370 . The gate drive signal is applied to N channel MOSFET  200 . By switching N channel MOSFET  200  on and off, in the same manner as recited above for NPN transistor  130 , the apparent brightness of LEDs  60  can be varied. 
         [0063]    It will be apparent to anyone skilled in the art that the embodiment of  FIG. 8  could be modified to control two strings of LEDs. By selecting warm white (low color temperature) for one string and cool white (high color temperature) for the other, that by varying the intensity of the strings with relation to each other, the resultant, effective color temperature could be controlled. 
         [0064]    Although the description above contains specific heat sink, mounting, and assembly designs, these should not be construed as limiting the scope of the invention but as merely providing an illustration of the currently preferred embodiment. 
         [0065]    Further, although various circuit configurations have been shown and described above there are numerous variations which can be used with the present invention, the specific design of which will be evident to one skilled in the art given the detailed description herein. 
         [0066]    Thus, although the present invention has been described in relation to particular embodiments therof, many other variations and modifications will become apparent to those skilled in the art. It is preferred, therefore, that the present invention be limited not by the specific disclosure herein, but only by the appended claims.