Patent Publication Number: US-8523410-B2

Title: Light source device with thermal dissipating members

Description:
TECHNICAL FIELD 
     The present invention relates to a light source device, and particularly to a light source device including a light emitting element such as an LED and including therein a circuit unit for lighting the light emitting element. 
     BACKGROUND ART 
     As a solid-state light emitting element such as an LED increases in temperature during light emission, its light emitting efficiency and life decrease. Also, some of electronic components of a circuit unit for lighting the solid-state light emitting element are damaged or decrease their life due to thermal effects. 
     In view of this, there is a need for efficient dissipation of heat generated by the LED and the circuit unit. Patent Literature 1 discloses a light source device including a case composed of a cylindrical body, which is made of a material having excellent thermal conduction properties such as aluminum, whose hollow part is partitioned by a plate member made of the same material as the cylindrical body. The plate member is fixed to the cylindrical body in such a state where an edge part of the plate member is folded back in a predetermined width so as to bring an outer circumferential surface of the folded-back edge part into close contact with an internal circumferential surface of the cylindrical body. 
     On one of surfaces of the plate member, an LED module is mounted, which is composed of a print substrate on which an LED is mounted. On the other surface of the plate member, a circuit unit is housed in the hollow part of the case. 
     According to the light source device having the above structure disclosed in the Patent Literature 1, heat generated by the LED module during lighting is dissipated via the plate member and the cylindrical body. On the other hand, heat generated by the circuit unit is conducted to the cylindrical body by radiation, convection within the hollow part, or the like, and then is dissipated from an outer surface of the cylindrical body. 
     CITATION LIST 
     Patent Literature 
     
         
         [Patent Literature 1] Japanese Patent Application Publication No. 2009-117342 
         [Patent Literature 2] Japanese Patent Application Publication No. 2002-75011 
       
    
     SUMMARY OF INVENTION 
     Technical Problem 
     However, the above light source device causes the following problem because the cylindrical part functioning as a thermal dissipation member is shared between the LED module and the circuit unit. 
     In the case where the circuit unit during lighting generates a higher heat than that of the LED module for example, most of heat conducted from the circuit unit to the cylindrical body is internally conducted beyond a part of the cylindrical body where the plate member is fixed. This decreases thermal dissipation properties of the cylindrical body for dissipating heat conducted from the LED module. 
     In view of the above problem, the present invention aims to provide a light source device capable of eliminating thermal effects between a light emitting module and a circuit unit as much as possible so as to ensure thermal dissipation properties of the light emitting module and the circuit unit. 
     Solution to Problem 
     In order to achieve the above aim, the present invention provides a light source device comprising: a light emitting module; a first thermal dissipation member onto which the light emitting module is attached; a circuit unit configured to light the light emitting module; and a second thermal dissipation member that has the circuit unit housed therein, wherein a thermal insulation member is inserted between the first thermal dissipation member and the second thermal dissipation member. 
     Also, the first thermal dissipation member is bowl-shaped and has a flat bottom, the second thermal dissipation member includes a cylindrical part, the thermal insulation member is plate-like, the light emitting module is attached onto an inner surface of the bottom of the first thermal dissipation member, the circuit unit is housed in the cylindrical part of the second thermal dissipation member, and the thermal insulation member is inserted between an outer surface of the bottom of the first thermal dissipation member and one of ends of the cylindrical part of the second thermal dissipation member. 
     In this case, the cylindrical part may be circular cylindrical, and the thermal insulation member may be discoid. 
     Furthermore, the second thermal dissipation member includes a small circular cylindrical part that extends from the other end of the cylindrical part, is smaller in diameter than the cylindrical part, and the small circular cylindrical part has a base attached thereto that is electrically connected to the circuit unit. 
     Also, the thermal insulation member has formed therein at least one through-hole passing through in a thickness direction thereof, and the first dissipating member and the second dissipating member are fastened to each other via a fastening member inserted into the through-hole. 
     Advantageous Effects of Invention 
     According to the light source device relating to the present invention having the above structure, heat generated by the light emitting module during lighting is conducted to the first thermal dissipation member onto which the light emitting module is attached. Then, the heat is distributed throughout the first thermal dissipation member to be dissipated from a surface of the first thermal dissipation member. On the other hand, heat generated by the circuit unit is conducted to the second thermal dissipation member by radiation, convection within the case, or the like. Then, the heat is distributed throughout the second thermal dissipation member to be dissipated to an ambient space through the outer circumferential surface of the second thermal dissipation member. In this case, the thermal insulation member is inserted between the first thermal dissipation member and the second thermal dissipation member. This prevents, as much as possible, conduction of heat generated by the light emitting module to the second thermal dissipation member and conduction of heat generated by the circuit unit to the first thermal dissipation member. Accordingly, it is possible to eliminate thermal effects between the light emitting module and the circuit unit as much as possible so as to ensure thermal dissipation properties of the light emitting module and the circuit unit which are provided for the member light emitting module and the circuit unit, respectively. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a perspective view of an LED lamp relating to an embodiment. 
         FIG. 2  is an exploded perspective view of the LED lamp. 
         FIG. 3  is a longitudinal sectional view of the LED lamp. 
         FIG. 4  is a cross-sectional view of a case constituting an LED lamp relating to a modification. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     The following describes an embodiment of the present invention with reference to the drawings. 
       FIG. 1-FIG .  3  are a perspective view, an exploded perspective view, and a longitudinal sectional view of an LED lamp  10  as an example of a light source device, respectively. Note that the scale ratio between members differs among  FIG. 1-FIG .  3  and  FIG. 4  which is later described. Also, part of members is shown without being cut in  FIG. 3 . Furthermore, in the drawings, a dashed line represents a lamp axis J, and a direction, which is parallel to the lamp axis J and is indicated by an arrow X, is toward the front side of the LED lamp  10  and is also a lighting direction. 
     (Schematic Structure) 
     The LED lamp  10  is used as a substitute for a halogen bulb having a reflecting mirror. That is, the LED lamp  10  has a similar outer appearance to a halogen bulb having a reflecting mirror, as shown in  FIG. 1 . Also, the LED lamp  10  includes a base  26 , and includes therein a circuit unit  22  ( FIG. 2  and  FIG. 3 ). The LED lamp  10  is used by being attached to lighting equipment to which a halogen bulb having a reflecting mirror should be attached. 
     As shown in  FIG. 2 , the LED lamp  10  includes, in addition to the circuit unit  22  and the base  26 , a body  12 , a light emitting module  14 , an optical member  16 , a front cover  18 , a thermal insulation member  20 , and a case  24 . 
     (Body) 
     The body  12  is bowl-shaped, and has a cylindrical part  28  and a bottom  30 . The cylindrical part  28  increases in diameter from the back to the front. The bottom  30  is discoid (plate-like), and closes the back end of the cylindrical part  28 . In other words, the body  12  is bowl-shaped, and has the bottom  30  that is flat. The cylindrical part  28  has a circular cross-section taken along a plane perpendicular to the lamp axis J, and has (that is, the body  12  has) a central axis that coincides with the lamp axis J. 
     Note that the bottom  30  is not limited to be discoid. Alternatively, the bottom  30  may be, for example, in the shape of an elliptical plate, a rectangular plate, or a polygonal plate. 
     The bottom  30  of the body  12  has an inner surface  30   a  onto which the light emitting module  14  is attached. The body  12  is made of a metal having excellent thermal conduction properties such as aluminum, and functions as a thermal dissipation member (first thermal dissipation member) for exclusively dissipating heat generated by the light emitting module  14 . Note that, the body  12  may be made of a resin or ceramic having excellent thermal conduction properties. Also, the body  12  has housed therein an optical member  16 . The use of a light transmissive material for the body  12  allows light irradiation of the body  12  itself and light irradiation toward the back side of the body  12 . This improves the quality of the outer appearance of the LED lamp  10  in use. 
     The cylindrical part  28  has an annular flange  32  at the end of an opening thereof, which extends in a direction perpendicular to the lamp axis J. 
     The front cover  18  is attached to the body  12  via claws  34  engaging with the flange  32 . Furthermore, the flange  32  has a plurality of protrusions  36  on the back surface thereof at intervals in a circumferential direction thereof. Provision of the protrusions  36  prevents idle rotation of the front cover  18  relative to the body  12 . That is, when the front cover  18  rotates about the lamp axis J, the claws  34  abut with the respective protrusions  36 . Accordingly, the front cover  18  does not rotate relative to the body  12  anymore. Note that an arbitrary number of the protrusions  36  may be provided. 
     (Light Emitting Module) 
     The light emitting module  14  includes a module substrate  38  and an LED unit  40  mounted substantially at the center on the module substrate  38 , and is mounted substantially at the center on the inner surface  30   a  of the bottom  30  of the body  12 . The LED unit  40  includes, for example, a unit substrate  42 , LED chips  44  mounted on the unit substrate  42 , a phosphor provided on the LED chips  44 , and a semispherical sealing member  46  sealing the LED chips  44 . The LED chips  44  are each, for example, an InGaN LED chip emitting blue light, and the phosphor is an yellow-green phosphor. With this structure, part of blue light emitted from the LED chips  24  is converted to yellow-green light by the phosphor, and the converted yellow-green light and remaining unconverted part of the blue light are mixed so as to be emitted as white light. 
     (Optical Member) 
     The optical member  16  is, for example, made of a translucent material such as a transparent acrylic resin, and includes a lens part  48  in the shape of a substantially conical frustum and an outer edge part  50  in the shape of a substantially annular plate, which are integrally molded. The outer edge part  50  extends along a circumferential surface of the lens part  48 . 
     The lens part  48  is positioned at substantially the center of the body  12  and toward the front side of the light emitting module  14 . The lens part  48  has a concave  52  that is substantially circular cylindrical at a back end thereof. By fitting the sealing member  46  of the LED unit  40  into the concave  52 , the position of the optical member  16  relative to the LED unit  40  is determined. 
     Light emitted from the light emitting module  14  mainly enters the lens part  48  through the concave  52 , passes through the lens part  48 , and is extracted to the outside of the body  12  from the front surface of the lens part  48 . The course of the light emitted from the light emitting module  14  changes while the light passes through the lens part  48 . Specifically, the emitted light is focused by the lens part  48  thereby to be a spotlight similar in light distribution properties to light emitted from a halogen bulb having a reflecting mirror. Note that the front surface of the lens part  48  has been subjected to light diffusion process so as to be provided with a plurality of convexes and concaves for diffusing emitted light. 
     The outer edge part  50  is positioned toward the back of the front cover  18  so as to close the opening of the body  12 . The front surface of the outer edge part  50  and the back surface of the front cover  18  are in face-to-face contact with each other. Since the circumferential unit  32  and the front cover  18  are in surface contact with each other, heat conducted to the optical member  30  easily escapes through the front cover  18 . This allows heat generated by the LED unit  40  to efficiently release from the front cover  18  to the outside via the optical member  16 . In the case where the front cover  18  is translucent, a small amount of light leaked from the optical member  16  can pass through the front cover  18 . This produces an effect of light irradiation of the whole front surface of the lamp. 
     (Front Cover) 
     The front cover  18  includes, for example, a main part  56  and a circumferential wall  58 . The main part  56  is in the shape of an annular plate, and has a light emission window  54  that is substantially circular. The circumferential wall  58  is in the shape of a short cylinder, and extends toward the back side from an outer circumferential edge of the main part  56 . Note that the shape of the front cover  18  is not limited to the above shape, and may be any shape in accordance with the shape of the opening  11  of the body  12 . 
     The front cover  18  is made of a non-translucent resin material such as white PBT (polybutylene terephthalate). PBT is a preferable material for the front cover  18  because having a high thermal resistance, a moderate elasticity, and an excellent weather resistance. The resin that constitutes the front cover  18  is not limited to PBT, and may be acrylic, PC (polycarbonate), or the like. Also, the front cover  18  is not limited to be white, and may have any color. The front cover  18  may be transparent or translucent. 
     The circumferential wall  58  is provided with the plurality of claws  34  at intervals in the circumferential direction thereof. For example, the claws  34  are provided at regular intervals near a back end edge of an inner circumferential surface of the circumferential wall  58  in the inner circumferential direction of the circumferential wall  58 , so as to project toward the lamp axis J. Note that an arbitrary number of the claws  34  may be provided. 
     The main part  56  is provided with holes  62  at positions corresponding to the respective claws  34 . Provision of the holes  62  allows resin-molding of the front cover  18  having a complicated shape with use of a simple mold composed of a smaller number of parts. 
     The front cover  18  forces the optical member  16  backward. This brings the front cover  18  and the outer edge part  50  in face-to-face contact with each other, and makes the lens part  48  to abut with the light emitting module  14 . This controls the movement of the optical member  16  backward and forward, thereby to prevent the positional shift and backlash of the optical member  16 . 
     (Thermal insulation Member) 
     The thermal insulation member  20  is discoid, has substantially the same size as the bottom  30  of the body  12 , and has thermal insulation properties literally. Here, a member having a thermal conductivity of less than 10 W/mK is defined as having thermal insulation properties, and a member having a thermal conductivity of 10 W/mK or higher is defined as having thermal conduction properties. Accordingly, the thermal insulation member  20  is made of a member having a thermal conductivity of less than 10 W/mK, and the body  12  that is the first thermal dissipation member and the case  24  that is the second thermal dissipation member are each made of a member having a thermal conductivity of 10 W/mK or higher. 
     The thermal insulation member  20  is, for example, made of a synthetic resin such as PBT, PET, PC, and PPS. 
     The thermal insulation member  20  is inserted between the body  12  that is the first thermal dissipation member and the case  24  that is the second member so as to insulate the body  12  and the case  24 . 
     The thermal insulation member  20  also has a function of electrically insulating the circuit unit  22  and the body  12 . 
     In the above example, the thermal insulation member  20  has substantially the same size as the bottom  30  of the body  12 , as shown in  FIG. 3 . That is, the thermal insulation member  20  has substantially the same diameter as the bottom  30 . Alternatively, the thermal insulation member  20  may have a diameter larger than the diameter of the bottom  30  such that the circumferential edge of the thermal insulation member  20  protrudes outside the bottom  30 . Further alternatively, the thermal insulation member  20  may have a diameter smaller than the diameter of the bottom  30  such that the circumferential edge of the thermal insulation member  20  is positioned entirely inside the circumferential edge of the bottom  30 . 
     In the case where the bottom  30  of the body  12  is not discoid as described above, the thermal insulation member  20  may be in the shape of an elliptic plate, a square plate, a polygonal plate, or the like, in accordance with the shape of the bottom  30  of the body  12 . 
     (Circuit Unit) 
     The circuit unit  22  includes, for example, a lighting circuit that is provided with a rectifier circuit that rectifies an AC power supplied from a commercial power source to a DC power and a voltage adjustment circuit that adjusts a voltage value of the DC power rectified by the rectifier circuit. The circuit unit  22  is electrically connected to the base  26  and the LED unit  40 , receives power from lighting equipment (not illustrated) via the base  26 , and causes the LED chips  44  of the LED unit  40  to emit light. 
     The circuit unit  22  is composed of a circuit board  64  and a plurality of electronic components  66  mounted on the circuit board  64 , and is housed in the case  24 . 
     (Case) 
     The case  24  is made of a material having electrical insulating properties and thermal conduction properties. The case  24  is, for example, made of a resin to which a heat conductive filler has been added, a ceramic having a high thermal conductivity, or the like. The case  24  functions as a thermal dissipation member (second thermal dissipation member) dissipating heat generated by the circuit unit  22  housed in the case  24 . 
     The case  24  includes a large circular cylindrical part  68 , a small circular cylindrical part  70  that is smaller in diameter than the large circular cylindrical part  68 , and a taper cylindrical part  72  connecting the large circular cylindrical part  68  and the small circular cylindrical part  70 . The large circular cylindrical part  68  has a flange  68   a  extending in a diameter direction thereof on the edge of an opening thereof. 
     The case  24  has three bulged-out portions  74  that each protrude along an internal wall thereof in the axis direction thereof to form a semicircular cylindrical shape. The case  24  has three pilot holes  76  for screws  82  at respective thicker portions within a range from the respective bulged-out portions  74  to the flange  68   a  ( FIG. 2 ). 
     As shown in  FIG. 3 , most parts of the circuit unit  22  are housed in the large circular cylindrical part  68 . 
     Note that the shape of the large circular cylindrical part  68  is not limited to be a circular cylindrical shape, and may be other cylindrical shape. In the case where the bottom  30  of the body  12  and the thermal insulation member  20  are each not discoid as described above, the large circular cylindrical part  68  may be in the shape of an elliptic cylinder, a square cylinder, a polygonal cylinder, or the like, in accordance with the shape of the bottom  30  of the body  12  and the thermal insulation member  20 . 
     (Base) 
     The base  26  is a member for allowing the LED lamp  10  attached to lighting equipment to receive power from a socket (not illustrated). The base  26  is an E11 base, which is one type of Edison bases, in the present embodiment. Alternatively, the base  26  may not be especially limited to this type. The base  26  is substantially circular cylindrical, and includes a shell  78  whose outer circumferential surface functions as a male screw and an eyelet  80 . The base  26  is attached to the small circular cylindrical part  70  by being fit onto the small circular cylindrical part  70 . 
     (Assembly of Light Source Device) 
     The case  24  in which the circuit unit  22  is housed, the thermal insulation member  20 , the body  12 , and the light emitting module  14  are assembled by being fastened to one another via a plurality of screws  82  (three screws  82 , in the present embodiment). The screws  82  are each a tapping screw. The number of the screws  82  may be one. The number of each of cuts  38   a , through-holes  30   c , through-holes  20   a , and pilot holes  76 , which are described later, is adjusted depending on the number of the screws  82 . 
     As shown in  FIG. 2 , the bottom  30  of the body  12  is provided with the plurality of through-holes  30   c  for fastening the screws  82  and a wiring hole (not illustrated) for wiring. Also, the thermal insulation member  20  is provided with the plurality of through-holes  20   a  and a wiring hole  20   b . Furthermore, the module substrate  38  of the light emitting module  14  is provided with the plurality of U-shaped cuts  38   a . The screws  82  are inserted through the cuts  38   a  of the module substrate  38 , the through-holes  30   c  of the body  12 , and the through-holes  20   a  of the thermal insulation member  20  in this order. Then, the screws  82  are further inserted into the pilot holes  76 . This forms a female screw in each of the pilot holes  76 , thereby to integrally assemble the body  12 , the light emitting module  14 , the thermal insulation member  20 , and the case  24 . 
     Moreover, a wiring (not illustrated) of the light emitting module  14  is inserted through the case  24  via the wiring hole (not illustrated) provided on the bottom  30  of the body  12  and the wiring hole  20   b  of the insulation member  20 , so as to be electrically connected to the circuit unit  22 . The flange  68   a  of the case  24  has a recess  68   c  on an internal circumferential surface thereof, which communicates with an internal space of the case  24 . The wiring passes through the recess  68   c , and this determines a predetermined position of the light emitting module  14  in the case  24 . 
     Note that the screws  82  are each not limited to a tapping screw. Alternatively, a general machine screw may be used. In the case where such a machine screw is used, a female screw to be engaged with the machine screw needs to be formed instead of the pilot hole  76 . 
     Further alternatively, other fastening member may be used such as a rivet. 
     According to the LED lamp  10  having the above structure, heat generated by the light emitting module  14  during lighting is conducted to the body  12  that is the first thermal dissipation member onto which the light emitting module  14  is attached. Then, the heat is dissipated from the surface of the body  12 . On the other hand, heat generated by the circuit unit  22  is conducted to the case  24  that is the second thermal dissipation member by radiation, convection within the case  24 , or the like. Then, the heat is dissipated to an ambient space through the outer circumferential surface of the case  24  or to lighting equipment to which the LED lamp  10  is attached via the base  26 . 
     In this case, the thermal insulation member  20  is inserted between the body  12  and the case  24 . This prevents, as much as possible, conduction of heat generated by the light emitting module  14  to the case  24  and conduction of heat generated by the circuit unit  22  to the body  12 . Accordingly, it is possible to eliminate thermal effects between the light emitting module  14  and the circuit unit  22  as much as possible, thereby to ensure thermal dissipation properties of the light emitting module  14  and the circuit unit  22 . 
     [Modification] 
       FIG. 4  is a cross-sectional view of a case  90  constituting an LED lamp relating to a modification. The LED lamp relating to the modification has the same structure as the LED lamp  10  excepting the case. Accordingly, description of the structure excepting the case is omitted. 
     Also, the case  90  has the same structure as the case  24  ( FIG. 3 ) excepting that the case  90  includes a metal cylinder  94  described later. Thus, components of the case  90  shown in  FIG. 4 , which are substantially the same as those of the case  24 , have the same referential numerals as those of the case  24 . Accordingly, description thereof is omitted. 
     The case  90  is composed of a main part  92  made of a synthetic resin and the metal cylinder  94 . 
     In the case where a case for housing a circuit unit is made of a synthetic resin, abnormal heat generation by the circuit unit due to some defect might partially melt the case to create a hole in the case. Such a state where the case has the hole is visible as a modified outer appearance of the LED lamp, and this makes a user to feel anxious. 
     In view of this, there is a demand for an LED lamp whose outer appearance is not modified (that is, any modified part is invisible) due to abnormal heat generation by a circuit unit. 
     In response to the demand, there has been proposed to cover, with a metal cylinder, an outer circumference (a part where a hole might be created) of a case made of a synthetic resin. However, just covering leads to the increase in size of the LED lamp by the size of a space between the metal cylinder and the resin case. Although, on the contrary, there has been proposed to downsize the resin case, a problem occurs such as an insufficient space for housing the circuit unit. 
     In view of this, according to the case  90  of the LED lamp relating to the modification, when the main part  92  is injection-molded, insert-molding is performed such that the metal cylinder  94  is partially embedded in the main part  92  so as to be connected to each other. 
     That is, the case  90  for housing the circuit unit  22  is composed of the main part  92 , which is made of a synthetic resin and has a cylindrical part, and the metal cylinder  94  which is partially embedded in the body  92  by insert-molding and has a circular cylindrical part covering an outer circumferential surface of the cylindrical part in close contact with the outer circumferential surface. 
     By covering the main part  92  with the metal cylinder  94  connected thereto by insert-molding, the metal cylinder  94  comes in close contact with the outer circumferential surface of the main part  92  with no space therebetween. This makes it possible to prevent the increase in size of the case resulting from providing the metal cylinder. 
     Also, since the parts of the metal cylinder  94  (one end part of the circular cylindrical part and the other end part of the circular cylindrical part that is folded back inward) is embedded in the main part  92 , the metal cylinder  94  is prevented from dropping out from the main part  92 . Furthermore, the metal cylinder  94  is integrally assembled with the main part  92 . This requires less trouble compared with a case where a metal cylinder is joined to a main part using adhesive. 
     The metal cylinder  94  preferably has excellent thermal conduction properties in order to ensure thermal dissipation properties, and is made of aluminum for example. 
     INDUSTRIAL APPLICABILITY 
     The light source device relating to the present invention is, for example, preferably usable as a substitute for a halogen bulb having a reflecting mirror. 
     REFERENCE SIGNS LIST 
     
         
         
           
               10  LED lamp 
               12  body 
               14  light emitting module 
               20  thermal insulation member 
               22  circuit unit 
               24  case