Patent Publication Number: US-2011069502-A1

Title: Mounting Fixture for LED Lighting Modules

Description:
BACKGROUND OF THE INVENTION 
     Light emitting diodes (LEDs) are an important class of solid-state devices that convert electric energy to light. Improvements in these devices have resulted in their use in light fixtures designed to replace conventional incandescent and fluorescent light sources. The LEDs have significantly longer lifetimes and, in some cases, significantly higher efficiency for converting electric energy to light. 
     Individual LEDs generate too little light for many applications that are currently based on incandescent or fluorescent light sources; hence, an LED light source that is intended to replace one of these conventional sources typically includes a plurality of LEDs that are mounted on a substrate such as a metal-core printed circuit board. The electrical connections are provided by soldering wires to pads on the circuit board or inserting a connector into a mating connector on the circuit board. In addition to electrical connections, the LEDs often require a thermal connection to a heat sink and heat-radiating structure that transfers the heat generated by the LEDs to the surrounding environment. 
     The thermal connections between the heat-dissipating structure and the LED module have been implemented in many different configurations. In general, the schemes involve attaching a heat-conducting surface in the module to the heat-dissipating structure using a thermally conductive medium to reduce the thermal resistance of the heat-conducting path and a mechanical connection to bond the module to the heat-conducting structure. In some systems, the module is attached by a thermally conductive adhesive to the heat-conducting structure. Thermally conductive tape or thermally conducting epoxy have been used to make the thermal connections. In other schemes, the module is attached to the heat-dissipating structure using screws. 
     While these methods are effective in providing thermal and electrical connections, these connection schemes complicate the replacement of the module. Field replacement of LED modules can be costly in many applications. If the module is located in a sign that is not easily reached by personnel, unsoldering leads and/or detaching the module from the heat-dissipating structure can impose significant costs which detract from the use of LEDs in many applications. In addition, the number of different mounting schemes makes it difficult to implement a standardized module scheme that can be used with a large variety of light modules. 
     In addition, many applications require the LED module to be located in a structure that includes secondary optics that operate on the light generated by the module. Schemes based on gluing the module to the heat sink in the field present challenges when precise registration of the LEDs relative to an external optical system is required. 
     Hence, it would be advantageous to provide an LED-mounting fixture that provides good heat dissipation while providing easy field replacement of the LED module and precise positioning of the LEDs relative to external optics. 
     SUMMARY OF THE INVENTION 
     The present invention includes a mounting fixture comprising a base having a cavity adapted to receive a module having a light-emitting device mounted thereon, a cover, first and second power contacts that provide electrical connections to the light-emitting device, a spring and a closure. The base has a heat-conducting surface. The cover has a window positioned to allow light from the light-emitting device to pass through the window. The first and second power contacts have first and second portions, respectively, adapted to receive external power connections on an outer surface of the mounting fixture. The spring forces the module against the heat-conducting surface when the base is in a closed position relative to the cover, the module being manually removable from the base when the cover is in an open position relative to the base. The closure reversibly attaches the base to the cover. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  illustrates a mounting fixture  10  that is bonded to a heat-dissipating structure. 
         FIGS. 2 and 3  illustrate a module  23  that mates with mounting fixture  10  shown in  FIG. 1 . 
         FIG. 4  is a cross-sectional view of a mounting fixture in which the cover is attached to the base via a plurality of clips. 
         FIG. 5  is a cross-sectional view of a mounting fixture  50  having detent pins on the base surface of the cavity that holds the module. 
         FIG. 6  is a cross-sectional view of a portion of the base of mounting fixture with a portion of an LED module in place according to another aspect of the current invention. 
         FIG. 7  is a cross-sectional view of a portion of the base of mounting fixture with a portion of an LED module in place according to another aspect of the current invention. 
         FIG. 8  is a cross-sectional view of a mounting fixture according to another embodiment of the present invention. 
         FIG. 9  illustrates an embodiment of the present invention in which the base is formed from a recess in the heat-radiating element. 
         FIG. 10  is a cross-sectional view of a portion of heat-dissipating element  110  with a module  120  in base  111 . 
         FIG. 11  is an exploded view of a light source according to another embodiment of the present invention. 
         FIG. 12  is a bottom view of the cover shown in  FIG. 11 . 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS OF THE INVENTION 
     The manner in which the present invention provides its advantages can be more easily understood with reference to  FIGS. 1-3 , which illustrate an LED-mounting fixture according to one embodiment of the present invention and a module that mates with that mounting fixture. Refer first to  FIG. 1 , which illustrates a mounting fixture  10  that is bonded to a heat-dissipating structure  31  that includes a plurality of fins  32  that facilitate the transfer of heat from structure  31  to the surrounding environment. Mounting fixture  10  includes a base  11  that is bonded to heat-dissipating structure  31  in a manner that assures good thermal conduction between the bottom surface of base  11  and structure  31 . For example, base can be adhesively bonded to heat-dissipating surface  31  using a heat-conducting epoxy or other thermal conductive medium. In general, base  11  is constructed from a good heat-conducting material such as a metal. 
     Refer now to  FIGS. 2 and 3 , which illustrate a module  23  that mates with mounting fixture  10 . Module  23  includes a printed circuit board  21  on which a plurality of LEDs shown at  22  are mounted. Printed circuit board  21  includes a metal core that transfers the heat generated by the LEDs to a heat transfer surface  27  on the backside of printed circuit board  23  as shown in  FIG. 3 . Heat transfer surface  27  is typically a metal pad that is in good thermal contact with the metal core of printed circuit board  23 . When module  23  is inserted in mounting fixture  10 , heat transfer surface  27  is in thermal contact with base  11 . In one aspect of the present invention, the thermal contact is enhanced by coating heat transfer surface  27  with a suitable heat-conducting medium. 
     Module  23  includes detents  24  that mate with corresponding pins  13  on cover  16  of mounting fixture  10 . The detents and corresponding locating pins assure that module  23  is properly positioned in mounting fixture  10  such that LEDs  22  are at a predetermined position relative to window  17 . Module  23  is powered through contacts  25  which make connection with a corresponding pair of contacts  14  shown in  FIG. 1 . Contacts  14  are preferably spring loaded so that a positive force is applied between contacts  25  and  14  when cover  16  is closed. This force insures good electrical contact between the contacts and also forces heat transfer surface  27  on the bottom surface  26  of module  23  against the bottom of base  11  to reduce the thermal resistance of the module-mounting fixture interface. 
     Cover  16  is hingedly connected to base  11  by hinge  18 . When closed, cover  16  is held in place by latch  19 . The force provided by contacts  14  forces cover and base away from each other and maintains the pressure needed for good electrical connections and heat conduction. 
     Window  17  can be implemented as an opening in cover  16  or be covered in a transparent material. In the former case, the LEDs are further cooled by contact with the surrounding environment. Window  17  can also be surrounded with a gasket  15  of compliant material that provides a seal around the LEDs that prevents debris from entering the interior of mounting fixture  10  when the upper and lower sections of mounting fixture  10  are in their closed configuration. If the compliant material is resilient, the gasket  15  also increases the force of contact between heat transfer surface  27  and base  11  of mounting fixture  10  when it is in a compressed state. 
     It should be noted that the bottom surface of base  11 , or a portion thereof, could be missing to provide direct contact between heat transfer surface  27  and the top surface of structure  31 . Such an arrangement provides improved heat transfer, since the intervening material is not present. 
     The above-described embodiments utilize an arrangement in which the two sections of the mounting fixture are hingedly connected to one another. However, other arrangements can be utilized. Refer now to  FIG. 4 , which is a cross-sectional view of a mounting fixture in which the cover is attached to the base via a plurality of clips.  FIG. 4  also illustrates an embodiment in which the bottom surface of base  31  includes an opening that allows the module to rest on an underlying heat-dissipating surface that is not part of mounting fixture  30 . 
     Mounting fixture  30  includes a plurality of clips that are attached to base  31 . Exemplary clips are shown at  33  and  34 . The clips are sufficiently compliant to allow cover  32  to be placed over base  31  and then moved into the closed position shown in  FIG. 4 . Detent pins such as pins  35  and  36  engage module  41  to position module  41  within mounting fixture  30 . In one aspect of the invention, the detent pins are spring loaded such that the detent pins provide a downward force that presses module  41  against the bottom surface of base  31  to provide improved heat transfer between heat transfer surface  42  and the bottom surface of base  31 . 
     Detent pins can also be located on the base surface of the mounting fixture. Refer now to  FIG. 5 , which is a cross-sectional view of a mounting fixture  50  having detent pins on the base surface of the cavity that holds the module. Pins such as pin  54  fit into mating recesses  53  in module  51 . Heat is transferred to the surface of section  61  through heat transfer surface  52  that is forced against the surface when section  62  is attached to section  61  via clips  63  and  64 . The force is provided by compliant members such as members  65  and  66  that contact the upper surface of module  51 . Members  65  and  66  can be constructed from metallic springs that also function as conductors for making electrical contact with module  51 . Alternatively, the mechanism for forcing module  51  against the surface of section  61  could be provided by a spring mechanism that is separate from the power contact that electrically connects module  51  to the mounting fixture. 
     Refer now to  FIG. 6 , which is a cross-sectional view of a portion of the base of a mounting fixture according to one embodiment of the present invention with a portion of an LED module in place according to another aspect of the current invention. In this embodiment, one of the electrical contacts is utilized both as a detent pin and an electrical contact. The electrical contact is made by a spring  81  that is connected to an electrical trace  83  that is insulated from surface  73  by an insulating layer  82 . Contact  72  is connected electrically to a plurality of LED dies  77  that are mounted on heat sink  87 . Springs such as spring  85  force module  71  against surface  73  when section  84  is attached. 
     In this embodiment, the dies are powered by connections on the top surfaces of the dies, and the bottom surfaces of the dies are insulated from heat sink  87 . The dies are connected in series by wire bonds and to contact  72  by conductors  78  and  79 . In this embodiment, the heat sink acts as a second power terminal and is connected to heat conduction surface  74  by a conductor  80  that passes through the module. Surface  73  acts as the second electrical contact in this embodiment. 
     Refer now to  FIG. 7 , which is a cross-sectional view of a portion of the base of a mounting fixture according to one embodiment of the present invention with a portion of an LED module in place according to another aspect of the current invention. In this embodiment, both of the electrical contacts are utilized both as a detent pin and an electrical contact. In particular, the dies are connected in series between contacts  72  and  91 . A vertical conductor shown at  92  provides the connection to contact  91 . The dies are mounted on a heat sink  95  that is insulated from the dies. Heat sink  95  is thermally connected to heat-conducting surface  94  by a heat conductor  93 , which is typically constructed from metal. 
     The cover of the mounting fixture can also include additional optical elements for processing the light generated by the LEDs on the enclosed module. Refer now to  FIG. 8 , which is a cross-sectional view of a mounting fixture according to another embodiment of the present invention. Mounting fixture  110  includes a base  111  and a cover  101 . An LED  115  on enclosed module  116  is positioned under an optical element  104  that focuses, or otherwise processes, the light generated by LED  115 . The optical element may be part of cover  101  or attached to cover  101  with the aid of an optical mount  102 . Since the same base can be used with multiple covers, the optical elements can be customized for each application without requiring a special mounting fixture for each application. 
     Refer again to  FIG. 1 . While the mounting fixture is shown as being separate from heat-dissipating element  31 , embodiments in which the mounting fixture is an integral part of some other structure, such as heat-dissipating element  31 , can also be constructed. For example, the base of the mounting fixture could be a molded recess in a surface of the heat-dissipating element. 
     The manner in which power is connected to the mounting fixture from an external source so as to power the module contained therein will, in general, depend on the location of the power contacts. For example, in the embodiment shown in  FIG. 1 , the power contacts are on the moveable element  16 . Accordingly, connections for power are more conveniently implemented on the surface of member  16  that is exposed when member  16  is in its closed position. The contacts can be provided by extending contacts  14  through member  16  and providing a connection or solder pad for the external power leads. If the power contacts are on the bottom surface of the mounting fixture as shown in  FIG. 7 , the contacts can be provided on an exposed edge of the bottom portion of the mounting fixture. 
     The embodiments shown in  FIG. 1  utilize a base that is separate from the heat-radiating element. However, embodiments in which the base is formed from a recess in the heat-radiating element can also be constructed. Refer now to  FIG. 9 , which illustrates an embodiment of the present invention in which the base is so formed. Base  111  is a recess in heat-dissipating element  110 . Pins  112  are molded into heat-dissipating element  110  and serve to position the module in base  111  by engaging matching recesses in the bottom of the module. In this embodiment, the power contacts for the module are on the bottom surface of the module and connect to contacts  113  and  114  that mounted on an insulating layer  117  that is bonded to the bottom surface of the base. Contacts  113  and  114  are connected by insulating traces to contacts  115  and  116  that are mounted on an outer surface that can be accessed to make connections to the module once the module is placed in the recess and covered. The contacts can be formed on a flexible printed circuit substrate. 
     Refer now to  FIG. 10 , which is a cross-sectional view of a portion of heat-dissipating element  110  with a module  120  in base  111 . Cover  121  fits into the recess in base  111  and is held in place by rotating clips such as clip  125 . Clip  125  rotates about a pin  126  so as to retain cover  121  in the recess. Pin  126  can be molded into heat-dissipating element  110 . Spring members  122  and  123  force module  120  against the bottom surface of the recess to assure good thermal contact between heat-conducting surface  124  and heat-dissipating element  110 . The spring members can be constructed from a compressible material such as foam rubber that is bonded to the underside of cover  121 . 
     The above-described embodiments utilize pins or other positioning protrusions to maintain the position of the module in the base of the section during operation. However, other positioning mechanisms could be utilized. Any form of protrusion that engages a matching recess could be utilized, one of the two elements being associated with the mounting fixture and the other with the module. For example, seal  15  shown in  FIG. 1  could engage a matching recess in module  21  to hold module  21  in place. In addition, if module  21  has dimensions that match those of the recess in the base, the sides of the module could provide the needed positioning. Positioning mechanisms that do not depend on the specific size of the recess have the advantage of allowing a range of module sizes to be accommodated in a single mounting fixture. To simplify the discussion of such various forms of positioning mechanisms, the term pin is defined to cover any form of protrusion that defines the position of the module when engaged with a complementary recess. 
     The above-described embodiments utilize various forms of catches to hold the cover in place with respect to the base such that an internal spring mechanism can force the module against the bottom of the base to provide heat conduction and reliable electrical conduction for powering the module. However, other attachment mechanisms could be utilized. For example, the cover could be screwed to the base. The catch mechanisms have the advantage of providing reversible attachment without requiring any special tools, and hence, have advantages in systems requiring field replacement of a module. 
     In the above-described embodiments, the base includes a recess into which the module is placed. However, the recess is optional. Refer now to  FIG. 11 , which is an exploded view of a light source according to another embodiment of the present invention. Light source  150  includes a heat-dissipating structure  151  that has a planar surface  156  on which module  155  is in contact during the operation of light source  150 . A cover section  152  having the power connections and detents that engage module  155  is provided. Cover  152  is attached to heat-dissipating structure  151  by fasteners such as screw  154 . 
     In one aspect of the invention, cover  152  includes hinges  153  that allow cover  152  to rotate upward such that module  155  can be accessed after cover  152  is attached to heat-dissipating structure  151 . However, embodiments in which cover  152  lacks such hinges could also be constructed. 
     Cover  152  is forced downward onto surface  156  by securing an additional fastener  157 , which could also be a screw as shown or other form of catch mechanism as described above. Contacts  168  are then forced against contacts  163  on cover  152  and module  155  is then positioned under window  161 . 
     Refer now to  FIG. 12 , which is a bottom view of cover  152 . Cover  152  includes one or more spring mechanisms that force module  155  against surface  156  and assure that good electrical contacts are made between conductors  163  within cover  152  and the corresponding contacts  168  on module  155  when cover  152  is secured in place. In one aspect of the invention, conductors  163  include a separate spring mechanism for assuring good electrical contact. These springs will also force module  155  against surface  156 ; however, additional springs can be utilized to assure good thermal contact. For example, window  161  could be surrounded by a compressible gasket  162  as described above or the detent pins  164  could be compressible. 
     Conductors  163  are connected to a connector  153  on the outer surface of cover  152  by conductors on the inside of cover  152 . Connector  153  mates with a corresponding cable in the light source controller to power light source  150 . 
     It should be noted that cover  152  could be supplied with module  155  by the manufacturer of module  155 . In such a system, the luminaire manufacturer would supply heat-dissipating structure  151 . 
     The above-described Summary of the Invention and embodiments of the present invention have been provided to illustrate various aspects of the invention. However, it is to be understood that different aspects of the present invention that are shown in different specific embodiments can be combined to provide other embodiments of the present invention. In addition, various modifications to the present invention will become apparent from the foregoing description and accompanying drawings. Accordingly, the present invention is to be limited solely by the scope of the following claims.