Patent Publication Number: US-9429302-B2

Title: Lighting system with thermal management system having point contact synthetic jets

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     The present application is a continuation of, and claims priority to, U.S. patent application Ser. No. 12/908,948, filed Oct. 21, 2010, the disclosure of which is incorporated herein by reference. 
    
    
     GOVERNMENT LICENSE RIGHTS 
     This invention was made with Government support under contract number DE-FC26-08NT01579 awarded by The United States Department of Energy. The Government has certain rights in the invention. 
    
    
     BACKGROUND OF THE INVENTION 
     The invention relates generally to lighting systems, and more particularly to lighting systems having thermal management systems. 
     High efficiency lighting systems are continually being developed to compete with traditional area lighting sources, such as incandescent or florescent lighting. While light emitting diodes (LEDs) have traditionally been implemented in signage applications, advances in LED technology have fueled interest in using such technology in general area lighting applications. LEDs and organic LEDs are solid-state semiconductor devices that convert electrical energy into light. While LEDs implement inorganic semiconductor layers to convert electrical energy into light, organic LEDs (OLEDs) implement organic semiconductor layers to convert electrical energy into light. Significant developments have been made in providing general area lighting implementing LEDs and OLEDs. 
     One potential drawback in LED applications is that during usage, a significant portion of the electricity in the LEDs is converted into heat, rather than light. If the heat is not effectively removed from an LED lighting system, the LEDs will run at high temperatures, thereby lowering the efficiency and reducing the reliability of the LED lighting system. In order to utilize LEDs in general area lighting applications where a desired brightness is required, thermal management systems to actively cool the LEDs may be considered. Providing an LED-based general area lighting system that is compact, lightweight, efficient, and bright enough for general area lighting applications is challenging. While introducing a thermal management system to control the heat generated by the LEDs may be beneficial, the thermal management system itself also introduces a number of additional design challenges. 
     BRIEF DESCRIPTION OF THE INVENTION 
     In one embodiment, a lighting system is provided. The lighting system, comprises a housing structure and a light source configured to provide illumination visible through an opening in the housing structure. The lighting system further comprises a thermal management system configured to cool the lighting system and comprising a plurality of synthetic jet devices secured within the housing structure by a plurality of contact points. The lighting system further comprises driver electronics configured to provide power to each of the light source and the thermal management system. 
     In another embodiment, a lighting system comprising an array of light emitting diodes and a thermal management system is provided. The array of light emitting diodes (LEDs) is arranged on a surface of a lighting plate. The thermal management system is arranged above the array of LEDs, and comprises a heat sink having a base and a plurality of fins extending therefrom and a plurality of synthetic jets. Each of the plurality of synthetic jet devices is arranged to produce a jet stream between a respective pair of the plurality of fins, wherein the plurality of synthetic jet devices are coupled to the lighting system at a plurality of contact points. 
     In another embodiment, there is provided a lighting system, comprising a light source, a housing structure and a plurality of synthetic jet structures. The housing structure comprises a plurality of slots. Each of the plurality of synthetic jet devices is configured to engage at least one of the plurality of slots. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       These and other features, aspects, and advantages of the present invention will become better understood when the following detailed description is read with reference to the accompanying drawings in which like characters represent like parts throughout the drawings, wherein: 
         FIG. 1  is block diagram of a lighting system in accordance with an embodiment of the invention; 
         FIG. 2  illustrates a perspective view of a lighting system, in accordance with an embodiment of the invention; 
         FIG. 3  illustrates an exploded view of the lighting system of  FIG. 2 , in accordance with an embodiment of the invention; 
         FIG. 4  illustrates a cross-sectional view of a portion of a thermal management system of a lighting system, in accordance with an embodiment of the invention; and 
         FIG. 5  illustrates a perspective view of the light source illustrating packaging details of a portion of the thermal management system, in accordance with an embodiment of the invention. 
     
    
    
     DETAILED DESCRIPTION 
     Embodiments of the invention generally relate to LED-based area lighting systems. A lighting system is provided with driver electronics, LED light source and an active cooling system, which includes synthetic jets arranged and secured into the system in a manner which optimizes actuation of the synthetic jets and air flow through thereby providing a more efficient lighting system than previous designs. In one embodiment, the lighting system fits into a standard 6″ (15.2 cm) halo and leaves approximately 0.5″ (1.3 cm) between the lamp and halo. Alternatively, the lighting system may be scaled differently, depending on the application. The presently described embodiments provide a lighting source, which produces approximately 1500 lumens (lm) with a driver electronics efficiency of 90%, and may be useful in area lighting applications. The thermal management system includes synthetic jet cooling which provides an air flow in and out of the lighting system, allowing LED junction temperatures to remain less than 100° C. for the disclosed embodiments. 
     Advantageously, in one embodiment, the lighting system uses a conventional screw-in base (i.e., Edison base) that is connected to the electrical grid. The electrical power is appropriately supplied to the thermal management system and to the light source by the same driver electronics unit. In one embodiment, the LEDs of the light source are driven at 500 mA and 59.5 V while the synthetic jets of the thermal management system are driven with less than 200 Hz and 120 V (peak-to-peak). The LEDs provide a total of over 1500 steady state face lumens, which is sufficient for general area lighting applications. In the illustrated embodiments described below, synthetic jet devices are provided to work in conjunction with a heat sink having a plurality of fins, and air ports, to both actively and passively cool the LEDs. As will be described, the synthetic jet devices are excited with a desired power level to provide adequate cooling during illumination of the LEDs. 
     As described further below, the synthetic jets are arranged vertically with regard to the lighting surface. The synthetic jets are arranged parallel to one another and are configured to provide sufficient air flow to cool the light source. The synthetic jets are arranged to provide air flow across fins of a heat sink. In order to provide increased airflow, while minimizing vibrations transferred to the housing of the lighting system, a unique packaging configuration of the synthetic jets is provided. In accordance with embodiments disclosed herein, the synthetic jets are secured to housing structures of the lighting system by a contact point attachment technique. 
     As used herein, “contact point attachment” refers to securing an object, here a synthetic jet device, to a structure, here a housing structure, at multiple points of engagement along a periphery of the object. Each point of engagement encompasses a limited length along the periphery. As used herein, the term “point” connotes a discrete area of contact that is minimized when compared to the periphery of the object, as a whole. For instance, each “contact point” wherein a portion of the periphery of the synthetic jet is secured to the structure, holds the object along a length that is less than 10% of the total length of the periphery. More specifically, for a circular synthetic jet, the periphery of the synthetic jet is engaged at each contact point for a length that is less than 10% of the circumference of the synthetic jet device. Thus, as used herein, the term “contact point” refers to a region of contact that is less than 10% of the circumference of the synthetic jet device. In contrast, a securing mechanism that contacts and holds a synthetic jet device at a single contact region that is greater than 10% of the circumference (or total length of the periphery for a non-circular device) is not considered a “contact point,” but rather would be an entire contact region, or the like. In one embodiment, each synthetic jet is held in place at three contact points. By securing each synthetic jet utilizing a point contact configuration, rather than clamping large peripheral areas of the synthetic jet, movement of the synthetic jet is not unnecessarily restrained, thereby allowing maximization of membrane deflection, and thus increased air flow. Further, point contacts provide minimal vibration transfer from the synthetic jet to the housing of the lighting system, which is generally desirable. Because the disclosed embodiments provide at least three contact points for securing each of the synthetic jets within the lighting system, mechanical stability of the synthetic jets is not compromised. 
     Referring now to  FIG. 1 , a block diagram illustrating a lighting system  10  in accordance with embodiments of the present invention is illustrated. In one embodiment, the lighting system  10  may be a high-efficiency solid-state down-light luminaire. In general, the lighting system  10  includes a light source  12 , a thermal management system  14 , and driver electronics  16  configured to drive each of the light source  12  and the thermal management system  14 . As discussed further below, the light source  12  includes a number of LEDs arranged to provide down-light illumination suitable for general area lighting. In one embodiment, the light source  12  may be capable of producing at least approximately 1500 face lumens at 75 lm/W, CRI&gt;80, CCT=2700 k-3200 k, 50,000 hour lifetime at a 100° C. LED junction temperature. Further, the light source  12  may include color sensing and feedback, as well as being angle control. 
     As will also be described further below, the thermal management system  14  is configured to cool the LEDs such that the LED junction temperatures remain at less than 100° C. under normal operating conditions. In one embodiment, the thermal management system  14  includes synthetic jet devices  18 , heat sinks  20  and air ports  22  which are configured to work in conjunction to provide the desired cooling and air exchange for the lighting system  10 . As will be described further below, the synthetic jet devices  18  are arranged and secured utilizing a point attachment technique which advantageously maximizes air flow production and synthetic jet stability, while minimizing vibration transfer to the housing of the lighting system  10 . 
     The driver electronics  16  include an LED power supply  24  and a synthetic jet power supply  26 . In accordance with one embodiment, the LED power supply  24  and the synthetic jet power supply  26  each comprise a number of chips and integrated circuits residing on the same system board, such as a printed circuit board (PCB), wherein the system board for the driver electronics  16  is configured to drive the light source  12 , as well as the thermal management system  14 . By utilizing the same system board for both the LED power supply  24  and the synthetic jet power supply  26 , the size of the lighting system  10  may be advantageously minimized. In an alternate embodiment, the LED power supply  24  and the synthetic jet power supply  26  may each be distributed on independent boards. 
     Referring now to  FIG. 2 , a perspective view of one embodiment of the lighting system  10  is illustrated. In one embodiment, the lighting system  10  includes a conventional screw-in base (Edison base)  30  that may be connected to a conventional socket that is coupled to the electrical power grid. The system components are contained within a housing structure generally referred to as a housing structure  32 . As will be described and illustrated further with regard to  FIG. 3 , the housing structure  32  is configured to support and protect the internal portion of the light source  12 , the thermal management system  14 , and the driver electronics  16 . 
     In one embodiment, the housing structure  32  includes a cage  34 , having air slots  36  there through. The cage  34  is configured to protect the electronics board having the driver electronics  16  disposed thereon. The housing structure  32  further includes a thermal management system housing  38  to protect the components of the thermal management system  14 . The thermal management system housing  38  many include air slots  39 . In accordance with one embodiment, the thermal management system housing  38  is shaped such that air ports  22  allow ambient air to flow in and out of the lighting system  10  by virtue of synthetic jets in the thermal management system  14 , as described further below. Further, the housing structure  32  includes a faceplate  40  configured to support and protect the light source  12 . As will be described and illustrated in  FIG. 3 , the faceplate  40  includes an opening which is sized and shaped to allow the faces of the LEDs  42  and/or optics, of the light source  12 , to be exposed at the underside of the lighting system  10  such that when illuminated, the LEDs  42  provide general area down-lighting. In an alternative embodiment illustrated and described with reference to  FIG. 4 , the housing structure may also include a trim piece surrounding the faceplate  40  to provide further heat transfer to cool the lighting system  10 , as well as provide certain ornamental attributes. As further illustrated in the embodiment described with reference to  FIG. 4  below, the shape of the thermal management system housing  38  may vary. 
     Turning now to  FIG. 3 , an exploded view of the lighting system  10  is illustrated. As previously described and illustrated, the lighting system  10  includes a housing structure  32  which includes the cage  34 , the thermal management system housing  38 , and the faceplate  40 . When assembled, the housing structure  32  is secured by screws  44  configured to engage the cage  34 , the thermal management system housing  38 , and a holding mechanism such as a plurality of nuts (not shown). In one embodiment, the faceplate  40  is sized and shaped to frictionally engage a base of the lighting system  10 , and/or secured by another fastening mechanism such as additional screws (not shown). An opening  48  in the faceplate  40  is sized and shaped such that the LEDs  42  positioned on the underside of the light source  12  may be visible to the opening  48 . The light source  12  may also include fastening components, such as pins  50  configured engage an underside of the thermal management system  14 . As will be appreciated, any variety of fastening mechanisms may be included to secure the components of the lighting system  10 , within the housing structure  32 , such that the lighting system  10  is a single unit, once assembled for use. 
     As previously described, the driver electronics  16  which are housed within the cage  34  include a number of integrated circuit components  52  mounted on a single board, such as a printed circuit board (PCB)  54 . As will be appreciated, the PCB  54  having components mounted thereto, such as the integrated circuit components  52 , forms a printed circuit assembly (PCA). Conveniently, the PCB  54  is sized and shaped to fit within the protective cage  34 . Further, the PCB  54  includes through-holes  56  configured to receive the screws  44  such that the driver electronics  16 , the thermal management system housing  38 , and the cage  34  are mechanically coupled together. In accordance with the illustrated embodiment, all of the electronics configured to provide power for the light source  12 , as well as the thermal management system  14  are contained on a single PCB  54 , which is positioned above the thermal management system  14  and light source  12 . Thus, in accordance with the present design, the light source  12  and the thermal management system  14  share the same input power. 
     In the illustrated embodiment, the thermal management system  14  includes a heat sink  20  having a number of fins  58  coupled to a base  60  via screws  62 . As will be appreciated, the heat sink  20  provides a heat-conducting path for the heat produced by the LEDs  42  to be dissipated. The base  60  of the heat sink  20  is arranged to rest against the backside of the light source  12 , such that heat from the LEDs  42  may be transferred to the base  60  of the heat sink  20 . The fins  58  extend perpendicularly from the base  60 , and are arranged to run parallel to one another. 
     The thermal management system  14  further includes a number of synthetic jet devices  18  which are arranged adjacent to the fins  58  of the heat sink  20 . As will be appreciated, each synthetic jet device  18  is configured to provide a synthetic jet flow across the faceplate  40  and between the fins  58  to provide further cooling of the LEDs  48 . Each synthetic jet device  18  includes a diaphragm  64  which is configured to be driven by the synthetic jet power supply  26  such that the diaphragm  64  moves rapidly back and forth within a hollow frame  66  to create an air jet through an opening in the frame  66  which will be directed through the gaps between the fins  58  of the heat sink  20 . 
     As will be described in greater detail with regard to  FIG. 4 , the thermal management system housing  38  includes molded slots within the housing structure that are configured to engage the synthetic jet devices  18  at two contact points. By providing molded slots in the thermal management system housing  38 , the synthetic jet devices  18  may be accurately positioned within the housing  38 . To further secure the synthetic jet devices  18  within the thermal management system housing  38 , a bridge  68  may be provided. The bridge  68  is configured to engage each synthetic jet device  18  at one contact point. Accordingly, in the present embodiment, once assembled, each synthetic jet device  18  is secured within the lighting system  10  at three contact points. 
     The thermal management system  14  and the unidirectional airflow created by these synthetic jet devices  18  will be described further below with respect to  FIG. 4 . It should be noted that while the thermal management system housing  38  of  FIG. 3  includes bowed sides that extend beyond the edges of the cage  34  to provide increased openings for the air flow through the ducts  22 , in certain embodiments, such a bowed design may be eliminated. For instance, as will be illustrated with reference to  FIG. 4 , the size of the ducts  22  may be reduced such that sides of the thermal management system housing  38  extend linearly from the edge of the cage  34  to provide a uniform structure. The slots  39  may be designed to provide sufficient air flow through the lighting system  10  to allow a reduction in the size of the ducts  22 . 
     Referring now to  FIG. 4 , a partial cross-sectional view of the lighting system  10  is provided to illustrate certain details of the thermal management system  14 , as well as to illustrate the alternative embodiment of the thermal management system housing  38  described above. As previously discussed, the thermal management system  14  includes synthetic jet devices  18 , heat sink  20 , air ports  22 , and slots  39  in the thermal management system housing  38 . The base  60  of the heat sink  20  is arranged in contact with the underlying light source  12 , such that heat can be passively transferred from the LEDs  42  to the heat sink  20 . The array of synthetic jet devices  18  is arranged to actively assist in the linear transfer of heat transfer, along the fins  58  of the heat sink  20 . In the illustrated embodiment, each synthetic jet device  18  is positioned between the recesses provided by the gaps between the parallel fins  58 , such that the air stream created by each synthetic jet device  18  flows through the gaps between the parallel fins  58 . The synthetic jet devices  18  can be powered to create a unidirectional flow of air through the heat sink  20 , between the fins  58 , such that air from the surrounding area is entrained into the duct through one of the ports  22 A and the slots  39 A on one side of the thermal management system housing  38  and warm air from the heat sink  20  is ejected into the ambient air through the other port  22 B and slots  39 B on the other side of the thermal management system housing  38 . The unidirectional airflow into the port  22 A and slots  39 A, through the fin gaps, and out the port  22 B and slots  39 B is generally indicated by airflow arrows  70 . Advantageously, the unidirectional air flow  70  prevents heat buildup within the lighting system  10 , which is a leading cause for concern in the design of thermal management of down-light systems. In alternative embodiments, the air flow created by the synthetic jet devices  18  may be radial or impinging, for instance. In addition, the thermal management system may further include a trim plate  73 . The trim plate  73  may be conductive and may be directly coupled to the heat sink  20  to provide further heat transfer from the lighting system  10 , radially into the ambient air. The presently described thermal management system  14  is capable of providing an LED junction temperature of less than 100° C. at approximately 30 W of heat generation. 
     As will be appreciated, synthetic jets, such as the synthetic jet devices  18 , are zero-net-massflow devices that include a cavity or volume of air enclosed by a flexible structure and a small orifice through which air can pass. The structure is induced to deform in a periodic manner causing a corresponding suction and expulsion of the air through the orifice. The synthetic jet device  18  imparts a net positive momentum to its external fluid, here ambient air. During each cycle, this momentum is manifested as a self-convecting vortex dipole that emanates away from the jet orifice. The vortex dipole then impinges on the surface to be cooled, here the underlying light source  12 , disturbing the boundary layer and convecting the heat away from its source. Over steady state conditions, this impingement mechanism develops circulation patterns near the heated component and facilitates mixing between the hot air and ambient fluid. 
     In accordance with one embodiment, each synthetic jet devices  18  has two piezoelectric disks, excited out of phase and separated by a thin compliant wall with an orifice. This particular design has demonstrated substantial cooling enhancement, during testing. It is important to note that the synthetic jet operating conditions should be chosen to be practical within lighting applications. The piezoelectric components are similar to piezoelectric buzzer elements. The cooling performance and operating characteristics of the synthetic jet device  18  are due to the interaction between several physical domains including electromechanical coupling in the piezoelectric material used for actuation, structural dynamics for the mechanical response of the flexible disks to the piezoelectric actuation, and fluid dynamics and heat transfer for the jet of air flow  70 . Sophisticated finite element (FE) and computational fluid dynamics (CFD) software programs are often used to simulate the coupled physics for synthetic jet design and optimization. 
     The package that holds the synthetic jet device  18  within the lighting system  10  should orient the synthetic jet devices  18  for maximum cooling effectiveness without mechanically constraining the motion of the synthetic jet. Advantageously, the synthetic jet devices  18  are secured within the lighting system  10  utilizing contact point attachment techniques. As will be more clearly illustrated with reference to  FIG. 5 , each synthetic jet device  18  is held in place by contact points  72 . In the illustrated embodiments, there are three contact points at which the synthetic jet device  18  is secured to a structure of the lighting system, such as the thermal management system housing  38  or the bridge  68 . By minimizing the contact area, the synthetic jet devices are not unnecessarily restrained within the lighting system  10 . 
     Referring now to  FIG. 5 , a schematic view of a portion of the lighting system  10  is shown to illustrate the contact point attachment techniques used to secure the synthetic jet devices  18  within the lighting system  10 , in accordance with embodiments of the invention. As illustrated, the thermal management system housing  38  includes a base bracket  74 . In the illustrated embodiment, the base bracket  74  is a molded portion of the thermal management system housing  38 . However, in alternative embodiments, the base bracket  74  may be a separate piece. The base bracket  74  includes base slots  76  configured to securely receive the synthetic jet devices  18 . Specifically, the base bracket  74  includes two base slots  76  to engage each synthetic jet device  18 . In the illustrated embodiment, the base bracket  74  is configured to receive six synthetic jet devices  18 . During assembly, the synthetic jet devices  18  may be slid into the base slots  76 . In one embodiment, the base slots  76  have tapered edges to help guide the synthetic jet device  18  into place. The base slots  76  are only slightly wider than the thickness of the synthetic jet devices  18 , at the base of each base slot  76 . Further, the base slots are just deep enough to restrain the synthetic jet device  18  in place, without affecting the ability of the synthetic jet device to be fully actuated. Advantageously, because each of the base slots  76  is molded into the base bracket  74 , which may in turn be molded into the thermal management system housing  38 , as illustrated, the positioning of each respective synthetic jet device  18  is precisely defined with respect to the heat sink  20  to provide maximum cooling. 
     Once the synthetic jet devices  18  are positioned within the base slots  76 , the bridge  68  may be snapped into a slot  78  in the housing  38 . As will be appreciated, the bridge  68  includes a snapping mechanism (not illustrated) to allow the bridge to be mechanically coupled to the housing  38 . The bridge  68  includes a number of bridge slots  80 . Each bridge slot  80  is tapered and positioned to engage a synthetic jet device  18  at a third contact point  72 . Accordingly, the bridge  68  provides a locking mechanism to securely hold each synthetic jet device  18  within the lighting system  10 , such that vibration during actuation, or other movement of the lighting system  10  will not loosen the synthetic jet devices  18 . Advantageously, the bridge  68  is a single structure utilized to hold the entire set of synthetic jet devices  68  in place. Using a single piece of material for the bridge  68  provides a simple, repeatable, robust, easily manufacturable and cost effective way of securing the synthetic jet devices  18  to the base bracket  74 . Further, by utilizing a contact point attachment technique, as described herein, provides improved cooling efficiency, without requiring additional driving power and without significant increase in noise. 
     Additionally, a soft gel such as silicone (not shown) may be applied to each of the three contact points  72  to reduce vibrational noise and to further affix each synthetic jet device  18  within the lighting system  10 , such that the synthetic jet devices  18  do not rotate within the slots  76  and  80 . Further, by using a mounting gel in conjunction with the slotted base bracket  74  and slotted bridge  68 , the required holding force may be reduced. 
     This written description uses examples to disclose the invention, including the best mode, and also to enable any person skilled in the art to practice the invention, including making and using any devices or systems and performing any incorporated methods. Further details regarding the driver electronics and the light source may be found in U.S. patent application Ser. No. 12/711,000, entitled LIGHTING SYSTEM WITH THERMAL MANAGEMENT SYSTEM, which was filed on Feb. 23, 2010 and is assigned to General Electric Company, and is hereby incorporated by reference herein. The patentable scope of the invention is defined by the claims, and may include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims if they have structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements with insubstantial differences from the literal languages of the claims.