Abstract:
An LED-based light for replacing a conventional fluorescent light in an existing fixture is disclosed. The LED-based light includes an elongated housing, a heat sink extending substantially the length of the housing and having at least one integral retaining portion and a circuit board positioned on the heat sink and having a plurality of LEDs mounted thereon, wherein the at least one integral retaining portion is configured to secure the circuit board to the heat sink.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims priority to U.S. Provisional Application No. 61/526,875, filed Aug. 24, 2011, which is hereby incorporated by reference in its entirety. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The present invention relates in general to a light emitting diode (LED) based light, and in particular to a method and apparatus for mounting circuit boards in the LED light. 
       BACKGROUND 
       [0003]    Fluorescent tube lights are widely used in a variety of locations, such as schools and office buildings. Although conventional fluorescent bulbs have certain advantages over, for example, incandescent lights, they also pose certain disadvantages including, inter alia, disposal problems due to the presence of toxic materials within the glass tube. 
         [0004]    LED-based lights which can be used as one-for-one replacements for fluorescent tube lights have appeared in recent years. LED-based lights can be constructed with LEDs and other circuitry mounted on one or more circuit boards. LED-based lights can include a housing and a heat sink to dissipate heat produced by the LEDs contained therein. In some cases, the circuit board containing the LEDs is functionally attached to the heat sink or housing to prevent the circuit board from moving out of place. In some instances, these attachments may not be adequate. 
       SUMMARY 
       [0005]    Embodiments of an LED-based light for replacing a conventional fluorescent light in an existing fixture are disclosed herein. In one such embodiment, the LED-based light includes an elongated housing and a heat sink extending substantially the length of the housing. The heat sink has at least one integral retaining portion. The LED-based light also includes a circuit board positioned on the heat sink and having a plurality of LEDs mounted thereon. The at least one integral retaining portion is configured to secure the circuit board to the heat sink. 
         [0006]    Embodiments of a method of manufacturing an LED-based light are also disclosed herein. In one such embodiment, the method includes providing a heat sink having a longitudinally extending flat surface and at least one integral retaining portion extending away from the flat surface in an unengaged position and positioning a circuit board on the flat surface of the heat sink. The method also includes mounting a plurality of LEDs on the circuit board and engaging at least a portion of the at least one integral retaining portion of the heat sink to the circuit board such that the circuit board is secured to the heat sink. 
         [0007]    These and other embodiments will be described in additional detail hereafter. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0008]    The description herein makes reference to the accompanying drawings wherein like reference numerals refer to like parts throughout the several views, and wherein: 
           [0009]      FIG. 1  is a perspective view of an LED-based light with disengaged heat sink integral retaining portions in accordance with one embodiment; 
           [0010]      FIG. 2  is cross-section view of the LED-based light of  FIG. 1  along line A-A; 
           [0011]      FIG. 3  is cross-section view of an LED-based light with engaged heat sink integral retaining portions in accordance with another embodiment along a line similar to line A-A in  FIG. 1 ; 
           [0012]      FIG. 4  is a cross-section view of an LED-based light in accordance with another embodiment along a line similar to line A-A in  FIG. 1 ; 
           [0013]      FIG. 5  is a cross-section view of the LED-based light of  FIG. 4  along a line similar to line B-B in  FIG. 1 ; and 
           [0014]      FIG. 6  is a cross-section view of an LED-based light with intermittently engaged heat sink integral retaining portions in accordance with another embodiment along a line similar to line B-B in  FIG. 1 . 
       
    
    
     DETAILED DESCRIPTION 
       [0015]    Attaching the circuit board to the heat sink using screws, glue, tape, heat stakes, clips, or other types of fasteners can be both expensive and inadequate over time due to constant temperature changes affecting the attachments. Using one of these various attaching techniques can also reduce the effectiveness of a heat sink or disturb the functioning of the circuit board. 
         [0016]    Embodiments disclosed herein can simplify the design of LED-based lights by combining the heat sink function and the circuit board attachment function which can reduce cost and manufacturing assembly time and increase heat sink effectiveness. By engaging an integral retaining portion on the heat sink to the circuit board or other support, the circuit board can be held in place. Integral retaining portions of the heat sink can be engaged to the circuit board by crimping the integral retaining portions, for example walls or fins, on to the heat sink to overlap or extend over the circuit board and hold the circuit board in position against the heat sink. 
         [0017]      FIG. 1  illustrates an LED-based light  10  including a housing  12  with open ends, a heat sink  34 , a circuit board  14  positioned on the heat sink  34 , LEDs  16  mounted on the circuit board  14 , and a pair of end caps  23  (only one illustrated in  FIG. 1 ) on opposite ends of the housing  12 . At least one of the end caps  23  can carry at least one connector  22  to electrically connect the LEDs  16  to an existing fixture. Each end cap  23  can include two pins, though two of the total four pins can be “dummy pins” that do not provide an electrical connection. Alternatively, other types of end caps can be used, such as single pin end caps. Also, while the end caps  23  is shown as including a cup-shaped body, the end caps can have a different configuration (e.g., the end caps can be shaped to be press fit into the housing  12 ). 
         [0018]    The heat sink  34  has a flat surface extending longitudinally the length of the heat sink  34  with projections/integral retaining portions  36  such as walls or fins extending away (e.g., vertically) from opposite sides of the flat surface of the heat sink  34  in an unengaged position. The integral retaining portions may also extend in a different direction than vertically (e.g., extend outwardly from the heat sink). 
         [0019]    In the embodiment illustrated in  FIG. 1 , the integral retaining portions also extend the length of the heat sink. In other embodiments, the integral retaining portions may extend less than the full length of the heat sink. As shown, there are integral retaining portions on each side of the circuit board. In some embodiments, there may only be one integral retaining portion on one side of the circuit board. In other embodiments, there may be multiple distinct integral retaining portions along the length of the heat sink  34 . If there are multiple integral retaining portions, each may be distributed evenly along the length of the heat sink. In other embodiments the distribution may be uneven. In some embodiments, there may only be integral retaining portions on each side and each end of the heat sink  34 . Any suitable number and configuration of integral retaining portions may be used to suitably secure the circuit board to the heat sink  34 . 
         [0020]    In this embodiment of an LED-based light  10 , before assembly is completed, the integral retaining portions  36  on the heat sink  34  are not engaged with the circuit board  14  (i.e., in an unengaged position). The heat sink  34  in  FIG. 1  shows an example of how the integral retaining portions  36  can be structured before being engaged to the circuit board  14 . In addition to engaging the integral retaining portions  36  to the circuit board  14  as described in embodiments herein, the circuit board  14  of  FIG. 1  can be fastened to the heat sink  34  with screws, glue, heat stakes, or other structures so that circuit board  14  does not shift in location on the heat sink  34 . 
         [0021]      FIG. 2  shows a cross-section of  FIG. 1  at line A-A. In one embodiment, the heat sink  34  is a segment of thermally conductive metal of at least the same width as or wider than the circuit board  14  for dissipating heat generated by the LEDs  16  to the ambient environment. The heat sink  34 , before assembly, also has integral retaining portions  36  in the form of walls or fins that rise above the thickness of the circuit board  14 . The circuit board  14  has an LED-mounting side  14   a  and a primary heat transferring side  14   b  opposite the LED-mounting side  14   a.  The heat sink  34  can be designed so that the space between the integral retaining portions  36  on the heat sink  34  is roughly the width of the circuit board  14  so that the circuit board  14  fits between the integral retaining portions  36  on the heat sink  34  with little room for lateral movement. In another embodiment, the circuit board  14  can be designed so that it fits between the integral retaining portions  36  on the heat sink  34  with ample room for lateral movement. The placement of the circuit board  14  on the heat sink  34  can facilitate the integral retaining portions  36  engaging the circuit board  14 . 
         [0022]    Once the circuit board  14  is placed of the top flat surface of the heat sink  34  as shown in  FIG. 2 , the integral retaining portions  36  on the heat sink  34  can be engaged to the LED-mounting side  14   a  of the circuit board  14  as shown in  FIG. 3 . Engaging the integral retaining portions  36  of the heat sink  34  to the circuit board  14  can, for example, be accomplished by crimping the integral retaining portions  36  manually with any suitable artifact, e.g. with pliers, or can be done automatically by any known machine process, for example, pneumatic crimping. 
         [0023]    Further, the engagement, for example crimping, can be performed along the entire length of the heat sink  34  as shown in  FIG. 5  or at selected locations along the length of the heat sink  34  as shown in  FIG. 6 . It is not necessary to engage the entire length of integral retaining portions  36  to the circuit board  14 , only enough engagement to keep the circuit board  14  from shifting.  FIGS. 5 and 6  give two examples of how integral retaining portions  36  extending vertically from each side of the top flat surface of the heat sink  34  can be engaged to the LED-mounting side  14   a  of the circuit board  14 .  FIG. 5  illustrates that a single integral retaining portion  36  on each side of the heat sink  34  is crimped for the full length of the circuit board  14 .  FIG. 6  illustrates that a single integral retaining portion  36  on each side of the heat sink  34  is crimped at multiple locations along the circuit board  14 , in this case, between the spaced LEDs  16 . For example, the integral retaining portions  36  on the heat sink  34  shown in  FIGS. 5 and 6  can each be 3 mm high making it possible to crimp the integral retaining portions  36  to the circuit board  14  manually with pliers. Other dimensions of integral retaining portions  36  or number of integral retaining portions  36  can be engaged to the circuit board  14 . 
         [0024]      FIG. 4  illustrates a cross-section of an embodiment of an LED-based light  10  similar to the embodiment of  FIG. 1  at a line similar to line A-A with a portion of the housing  12  comprised of a lens  20  engaged to the heat sink  34 . In this embodiment, the lens  20  includes at two rounded-end integral retaining portions  39   a  and  39   b  on an interior surface that each engage a groove  40   a  and  40   b,  respectively on an outer surface of the heat sink  34 . The lens  20  can be made from polycarbonate, acrylic, glass, or another high-dielectric light transmitting material. The lens  20  can include light diffracting structures, such as dots, bumps, dimples, and other uneven surfaces formed on the interior or exterior of the lens  20 . A light diffracting film can be applied to the exterior of the lens  20  or placed between the lens  20  and heat sink  34 . The lens  20  can be formed of a material including light diffusing particles. The term “lens” as used herein means a light transmitting structure, and not necessarily a structure for concentrating or diverging light. 
         [0025]    The LED-based light  10  of  FIG. 4  also includes a cover  38  engaged to the heat sink  34  and forming a portion of the housing  12 . In this embodiment, the cover  38  includes at least one rounded-end integral retaining portion  42   a  and  42   b  on an interior surface that each engages a groove  44   a  and  44   b  on an outer surface of the heat sink  34 . Providing the cover  38  can allow the use of a highly thermally and electrically conductive heat sink  34 , e.g., an extruded aluminum heat sink  34 , because the dielectric properties of the cover  38  can reduce the shock hazard potential of capacitive coupling between the circuit board  14  and the heat sink  34 . Additionally, the cover  38  can provide structural support to the LED-based light  10 . Alternative forms of attachment of the lens  20  or cover  38  to the heat sink  34 , such as screws, highly thermally conductive adhesive tape, friction fit, or other attachments known to those of skill in the art are alternatively usable. 
         [0026]    Other suitable embodiments of LED-based light  10  including integral retaining portions  36  are also available. For example, although the integral retaining portions  36  are shown to extend the length of the heat sink  34 , one or more integral retaining portions may be included in the LED-based light  10  on one or both sides of the heat sink. For example, the LED-based light  10  may include a total of four projections that are a fraction of the length of the tube and are only located at each longitudinal end the heat sink  34 . Each projection can be, as discussed previously, structured so that it engages the circuit board to keep it in place. 
         [0027]    The above-described embodiments have been described in order to allow easy understanding of the invention and do not limit the invention. On the contrary, the invention is intended to cover various modifications and equivalent arrangements included within the scope of the appended claims, which scope is to be accorded the broadest interpretation so as to encompass all such modifications and equivalent structure as is permitted under the law.