FR2944855A1 - LED LIGHTING DEVICE INCORPORATING IMPROVED MEANS FOR ENHANCED THERMAL DISSIPATION - Google Patents

Abstract

The object of the invention is a lighting device comprising on the one hand a flat plate (32) on which a plurality of LEDs (34) are arranged, said plate (32) comprising a plate (36) made of a material electrically insulating with a so-called upper layer (38) of a conductive material at its upper surface, forming an electrical circuit with two terminals for each LED, characterized in that the plate (32) comprises at its lower surface a layer (40) said lower a thermally conductive material, and a plurality of holes between the terminals, sealed by a weld of a thermally conductive material so as to connect said layers (38, 40) of conductive material each forming a thermal bridge between the two layers (38, 40) in contact with the lower surface of the LEDs.

Description

LED LIGHTING DEVICE INCORPORATING IMPROVED MEANS FOR ENHANCED THERMAL DISSIPATION

The present invention relates to an LED lighting device. According to an embodiment illustrated in FIGS. 1A and 1B, a lighting device comprises a plate 10 of LED 12 fixed on a support 14 and surmounted by a transparent cover 16, subsequently called optical, which processes the LEDs' light beams. 12 projected towards the area to be illuminated. The plate 10 is in the form of a plate 18 made of an electrically and thermally insulating material with an upper surface at which a layer 20 made of a conductive material, generally made of copper, forming an electrical circuit and with a surface is provided. lower directly in contact with the support 14 ensuring the heat dissipation. Each LED comprises a first terminal 22 and a second terminal 24 connected by welds 22 'and 24' respectively to the anode and to the cathode of the electrical circuit formed by the layer 20. The service life of the electrical components and in particular the LEDs is strongly related to the operating temperature. Also, the invention aims to provide an LED lighting device whose design promotes the evacuation of the heat produced by the LEDs to significantly increase the life of said lighting device. To this end, the invention ob der jet a lighting device comprising firstly a plane plate on which are disposed a plurality of LEDs, said plate comprising a plate of an electrically insulating material with at its surface an upper layer of a conductive material, forming an electrical circuit with for each two-terminal LED, characterized in that the plate comprises at its lower surface a so-called lower layer of a thermally conductive material, and a plurality of holes between terminals sealed by a weld of a thermally conductive material so as to connect said conductive material layers each forming a thermal bridge between the two layers, in contact with the lower surface of the LEDs. Other features and advantages will become apparent from the following description of the invention, a description given by way of example only, with reference to the appended drawings in which: FIG. 1A is a sectional view of a lighting device according to the prior art, - Figure 1B is a top view of an LED on a support of a lighting device according to the prior art, - Figure 2 is a section of a lighting device according to FIG. 3A is a top view of a plate according to the invention before the implantation of an LED; FIG. 3B is a bottom view of a plate according to the invention; FIG. 4 is a perspective view of a first variant of a lighting device according to the invention; FIG. 5 is a sectional view of the lighting device of FIG. 4; FIG. in perspective of an extruded element according to the variant of the invention illustrated in FIG. 4 used as a heat sink, FIG. 7 is a view illustrating an assembly of several lighting devices according to the invention, FIG. 8 is a section of another variant of a lighting device according to the invention, FIG. 9A. is a top view of another variant of a lighting device according to the invention, - Figure 9B is a section of the lighting device illustrated in Figure 9A, - Figure 10 is a diagram illustrating a source. According to another variant of the invention, FIGS. 11A and 11B are front views illustrating the two parts forming the male part of the lighting device of FIG. 10, FIG. 12 is a side view illustrating the part of FIG. 10 of the lighting device of FIG. 10, FIGS. 13A and 13B are front views illustrating the two parts forming the female part of the lighting device of FIG. 10, FIG. 14 is a side view illustrating the female part of the lighting device of figu 10, and FIG. 15 is a front view illustrating the connection means of the lighting device of FIG. 10. In FIG. 2, an LED lighting device is shown at 30. The lighting device 30 comprises a flat plate 32 on which a plurality of LEDs 34 are arranged. Preferably, the plate 32 comprises LEDs reported along lines, for example thirty LEDs, six lines of five LEDs. However, the invention is not limited to this arrangement of LEDs. According to the invention, the plate 32 comprises a plate 36 of electrically insulating material with at its upper surface a layer 38 of a conductive material, generally copper, forming an electrical circuit and at its lower surface a layer 40 at least one thermally conductive material, preferably copper.

Each LED 34 comprises in the lower part a substantially square plate 42 with at two opposite edges of the substantially rectangular terminals 44 extending over the entire edge. In parallel, the upper layer 38 comprises for each LED two rectangular terminals 46 capable of cooperating with the terminals 44 of the LED. According to the invention, for each LED, the plate 32 comprises between the terminals 46, below the LED, a plurality of through holes 48 capable of connecting the two layers 38 and 40 of conductive material. Preferably, these holes 48 have a reduced diameter less than or equal to 0.5 mm.

According to one embodiment, these holes 48 are arranged along two lines parallel to the greatest length of the terminals 46. Advantageously, the plate comprises holes 48 at each end of the terminals 46. For each terminal 46, the holes 48 are arranged according to forms of C (or inverted C).

When the terminals 44 of the LEDs are soldered to the terminals 46 of the plate 32, the holes 48 are clogged with the solder in an electrically and thermally conductive material. In this way, each welded hole 48 forms a thermal bridge between the two conducting layers 38, 40 of the plate in contact with the lower surface of the LEDs and close to said surface. This configuration ensures efficient heat transfer between the LEDs and the area below the plate 32. The holes 48 should be small enough in diameter to be clogged when soldering the LEDs. However, they must have a diameter sufficient to be clogged by the weld. According to another characteristic of the invention, the plate 32 comprises, in the vicinity of the LEDs, orifices 50 passing through with metallized side walls to ensure thermal transfer between the two conductive layers 38 and 40 of the plate 32. According to one embodiment, the orifices 50 are arranged in at least one line provided at each end of the terminals 46, as illustrated in FIG. 3A.

According to one embodiment, the orifices have a diameter greater than 0.5 mm to ensure heat transfer between the area above the plate 32 and the area below. Preferably, as illustrated in FIG. 3B, the lower layer 40 which covers almost the entire surface of the plate comprises for each LED at least one thermal barrier 52 between the holes 48 and the orifices 50 to limit the propagation of heat during LED soldering. Advantageously, for each LED, the lower layer 40 comprises a thermal barrier 52 or several heat barriers placed end to end surrounding the LED. For this purpose, the lower layer 40 comprises cutouts and areas without conductive material forming thermal barriers. This configuration makes it possible to limit the risks of closing the orifices 50 during the welding of the LEDs so as not to alter their functions. The illumination device 30 includes, for the treatment of the light beams emitted by the LEDs, a substantially transparent cover 54 called optical which covers the LEDs. This optic 54 comprises a front wall disposed between the LEDs 34 and the area to be illuminated with an outer surface oriented towards the area to be illuminated and an inner surface facing the LEDs 34 and a peripheral wall providing the connection between the optic 54 and the plate 32 so as to confine the LEDs in a substantially sealed enclosure. Advantageously, the peripheral wall comprises a flange capable of providing a bearing surface capable of being pressed against the plate 32 and at the level of which may be formed a peripheral groove adapted to receive a peripheral seal to ensure a better seal. The geometric shapes of the optics are not defined because they are the subject of a specific patent application.

According to another characteristic of the invention, the optic 54 and the plate 32 form a cavity 55 which is preferably filled with a heat-transfer liquid promoting heat exchange between the LEDs 34 and the upper face of the plate 32. Preferably the cavity is filled with silicone oil. This solution promotes heat exchange between the LEDs and the upper face of the plate 32, preserves the welds and improves the optical properties. In addition, the lighting device may comprise a reservoir for the coolant connected to the cavity 55 by a valve to compensate for variations in the volume of the coolant in said cavity 55. In addition or alternatively, the cavity 55 may comprise a filling tip. According to another characteristic of the invention, the lighting device 30 comprises a volume of balls 56 made of ceramic, preferably glass, in direct contact or via at least one conductive plate with the lower layer of the platinum 32. Advantageously, the balls 56 have a diameter of the order of 5 mm. The ceramic beads 56 absorb some of the calories evacuated by the plate 32 and promote heat exchange between said platen and the external environment. According to another characteristic of the invention, the lighting device comprises a support 58 pressed against the lower surface of the plate 32 to ensure the heat dissipation. The presence of the lower layer 40 of a heat-conducting material which extends over almost the entire surface of the plate 32 ensures optimized heat transfer between the plate 32 and the support 58 ensuring the heat dissipation. According to simplified variants, the support 58 is in the form of a plate as illustrated in FIGS. 9A, 9B and 10.

According to other variants illustrated in FIGS. 4 to 8, the support 58 comprises an extruded element 60. According to an embodiment illustrated in FIGS. 4 to 7, the extruded element 60 has parallel sections to the constant plate 32 comprising an elongated hollow body 62 with a frame-shaped section defining a recess 64 and with a plurality of fins 66 on the outside. The body 62 comprises a top bearing surface 68. The support 58 also comprises a first plate 70 made of a thermal transfer promoting material placed under the plate 32, the dimensions of which are such that said first plate 70 comes into contact with the upper bearing surface 68 and a second plate 72 made of a material promoting heat transfer plated under the first plate 70 whose dimensions are such that said second plate 72 is housed in the recess 64. The plates 70 and 72 each have a thickness of about 3 mm to obtain a thermal inertia The plates 70 and 72 promote the thermal transfer of the LED support plate 32 towards the extruded element 60. The plate 32 comprises at least one circuit board for powering the LEDs and thermal bridges under each LED 34 to provide thermal transfer of the LEDs 34 to the plates 70 and 72. The extruded member 60 comprises means for securing the optic and the first plate 70. According to one embodiment, the optic 54 comprises at its rim a plurality of through holes which coincide with passage holes formed at the first plate 70, screws being screwed into housings 74 formed at the extruded element 60 thus ensuring the retention of the optical 54 and the first plate 70. To promote heat dissipation the extruded member 60 comprises fins 66 at the four sides of the hollow and elongate body 62. The extruded member 60 comprises two types of fins 66. Some fins 66.1 have only one heat dissipation function while other fins 66.2 have an additional function ensuring the assembly of several lighting devices 30 as illustrated. in Figure 7.

The fins 66.1 have a section which gradually tapers towards their end and are corrugated in order to increase the surface of the fins and therefore the heat exchange surface. The fins 66.2 have a profile substantially identical to the fins 66.1 with at the end a thickening 76 reducing the spacing with the fin 15 adjacent. The fins 66 are distributed in the following manner on each side of the extruded element 60 in the clockwise direction. The first fin is a fin-type fin 66.2 with an excess thickness 76 oriented towards the second fin, also of the fin type 66.2, with an excess thickness 76 oriented towards the first fin. The last fin is also a wing fin type 66.2 with a thickening 76 oriented in the same way as the first fin. For the long sides of the extruded member 60, all the other fins are blades of the fin type 66.1. For the narrow sides of the extruded member 60, the third fin is of wing type 66.2 with a thickness of 76 oriented in the same manner as the first fin, the other fins being winglets of the fin type 66.1. To increase the exchange surface at the corners of the extruded member 60, the first fin on each side comprises three star-shaped secondary fins 78 whose lengths are adapted to favor the assembly of the lighting devices. As illustrated in FIG. 7, to assemble two lighting devices, the last fin of the first lighting device is disposed between the two first fins of the second lighting device, the last fin of the second lighting device being disposed between the first two fins of the first lighting device. The lighting device comprises a power supply secured to the free face of the second plate 72 and housed in the recess 64. This supply makes it possible to supply the LEDs. According to one characteristic of the invention, as illustrated in FIG. 5, the duct formed by the extruded element 60 is closed at a first end by the plate 32 of the LEDs or one of the plates 70 and at the other end by of the resin 80, the recess 64 being filled with balls 56 which increase the thermal inertia and promote the thermal transfer of the LED support towards the extruded element 60. To reinforce the seal, a plate with a peripheral seal can be pressed against the bearing surface 82 of the extruded element. Preferably, the amount of beads 56 is sufficient to flood the components of the power supply and that the resin 80 does not touch the components. According to another variant illustrated in FIG. 8, the extruded element 60 has sections perpendicular to the constant plate 32 comprising an elongated hollow body 86 with a tube-shaped section delimiting a recess 88 and with a plurality of outside elements. The plate 32 is secured and pressed to a flat surface provided between the fins 90. A plate 92 is inserted into the recess 88 and supports the power supply of the LEDs. The recess 88 is filled with ceramic balls 56 and the tube 86 is closed at each end by plates.

This embodiment provides an elongated lighting device. According to an embodiment illustrated in FIGS. 9A and 9B, the support 58 is in the form of a plate with, at a first surface, a plate 32 of LED covered with an optic 54, a volume containing ball 56 being provided at the opposite surface. The support 58 also comprises a recess adjacent to the optic 54 at which the power supply of the LED trapped in a chamber filled with balls 56 secured to the support 58 is provided. This configuration makes it possible to obtain a lighting device thick.

According to another variant illustrated in FIGS. 10, 11A, 11B, 12, 13A, 13B, 14, 15, it is possible to envisage a support 58 in two dismountable parts, the first part supporting a plate 32 and an optic 54 and the second part comprising means for dissipating heat comprising a volume of glass balls 56, the two parts being connected using a connection system. According to the embodiment illustrated in FIG. 10, the second part also comprises a frame or casing 94 supporting means 96 for dissipating heat as well as means 98 for supplying the LEDs. Preferably, the housing 94 comprises means for securing it to a support. Generally, the housing 94 comprises a housing 100 in which are placed the means 98 for feeding the LEDs embedded in glass balls. According to one embodiment, the means 96 for dissipating the heat are in the form of fins arranged around the housing 94. According to one characteristic of the invention, the two parts of the support 58 are connected via a dismountable type connection system 102 having an electrical connection and a thermal connection.

The electrical connection comprises a first portion 104 connected to the LED support and a second portion 106 connected to the housing 94, as illustrated in FIG. 10. According to the example illustrated in FIG. 10, the first portion 104 corresponds to the plug of FIG. a connection capable of fitting into the second portion 106 which corresponds to the socket. The invention is not limited to this arrangement, the plug being connectable to the housing and the socket to the LED support. According to the invention, the housing 94 comprises a surface 108 facing a surface 110 of the LED support.

Thus, according to the illustrated example, the housing 94 comprises a plate 112 connected to said housing 94, one of the surfaces of which corresponds to the surface 108. Preferably, this plate 112 is made of a thermally conductive material, for example metal. Advantageously, the means 96 for dissipating heat are connected to this plate 112. The rest of the housing 94 is preferably made of a thermally insulating material. In parallel, the LED support comprises a plate 114 fixed at the rear face of the printed circuit supporting the LEDs. Means are provided for transferring the heat emitted by the LEDs to this plate 114. According to the invention, the thermal connection comprises a first male part 116 connected to the LEC support) illustrated in FIGS. 11A, 11B, 12 and 15 and a second so-called female portion 118 connected to the housing 94 illustrated in Figures 13A, 13B, 14 and 15, the parts 116 and 118 being made of a heat conductive material. The male part 116 comprises at least one surface capable of being in contact with at least one surface of the female part 118 to ensure the heat transfer and in addition to the locking / unlocking means for keeping the two surfaces flat against each other. 'other.

According to an embodiment illustrated in FIGS. 11A, 11B, 12, 13A, 13B and 14, the male part 116 comprises two stacked plates, a disc 120 (FIG. 11A) interposed between the plate 114 and another disc 122 (FIG. 11B ) having at the periphery at least one notch 124 projecting. Preferably, the disk 122 comprises three protruding notches 124 disposed at 120 °, as shown in FIG. 11B. The plate 114, the disk 120 and the disk 122 are interconnected by any appropriate means, for example by three screws, to ensure the heat transfer between the LED support, the plate 114, the disks 120, 122.

The disc 122 has a diameter d1 equal to or slightly greater than the diameter of the disc 120 between the notches 124 and a diameter D1 greater than d1 at the notches 124. In addition, the female part 118 comprises two plates, a ring 126 (FIG. 13B ) interposed between the plate 112 and another ring 128 (Figure 13A) having at least one hollow recess 130. Preferably, the ring 128 comprises three hollow recesses 130 to 120 °, as shown in Figure 13A. The provision of recessed and protruding notches 124 and 130 is not limited to that described. Thus, the thermal connection can be made with one or more notches arranged with different angles. These notches can be arranged according to the geometry selected according to the needs according to the applications. Preferably, the ring 126 has an inside diameter D2 slightly greater than D1. The ring 128 has a diameter equal to or slightly smaller than D2 at the recessed notches 130 and a diameter d2 greater than d1 and less than D1 between the recessed notches 130. The recessed notches 130 have shapes adapted to allow the protruding notches 124.

According to another characteristic of the invention, the disk 122 corresponds to the recess of the ring 128. Thus, by cutting a disk whose outer diameter is equal to that of the ring 128 according to the profile of its central recess, the disk 122 and the ring 128 are simultaneously obtained. This configuration makes it possible to optimize the material and makes it possible to be sure that the disk 122 will pass through the ring 128. The plate 112, the rings 126 and 128 are connected by any appropriate means, for example by three screws, to ensure the heat transfer between the housing 94, the plate 112 and the rings 126, 128.

The rings 126, 128 and the disks 120 and 122 have substantially the same thicknesses. To obtain the assembly of the male and female parts and in this way of the LED support, the disk 122 is inserted into the recess of the ring 128 by arranging the projecting notches 124 to the right of the recessed notches 130. disc 122 is in the plane of the ring 126, a slight rotation is made along an axis 132, as illustrated in Figure 15. Thus, the projecting notches 124 of the disc 122 is immobilized by the portions of the ring 128 provided between the recessed notches 130 to obtain a locking of the thermal connection. To unlock the thermal connection, it is necessary to make a slight rotation in the opposite direction to release the protruding notches 124. When the thermal connection is in the locked position, the free surface A of the disc 122 is in contact with the free surface A ' of the plate 112 and the free surface B of the ring 128 is in contact with the free surface B 'of the plate 94 to ensure efficient heat transfer between the LED holder and the means 96 for dissipating heat. The expansion phenomena reinforce the contact between said surfaces which reinforces the heat transfer.

According to a variant of the invention, the plug 104 of the electrical connection comprises a cylinder whose axis coincides with the axis of rotation 132 of the thermal connection. In parallel, the socket 106 of the electrical connection comprises a bore whose axis coincides with the axis of rotation 132 which receives the plug 104. The cylinder and the bore comprise two zones which cooperate to ensure electrical continuity. According to another variant, the first part of the electrical connection comprises at least one stud 136 (shown in dashed lines in FIG. 10), the end of which is flush with the surface A, arranged on a circle of radius R and center 132. Generally, one can provide several pads 136. In addition, the second portion of the electrical connection comprises at least one pad 138 (shown dotted in Figure 10) whose end is flush with the surface A ', disposed on a circle of radius R and center of the axis of rotation 132, the pads 138 and 136 being arranged to face each other and provide electrical continuity when the connection device is in the locked state. However, other technical solutions can be envisaged for the electrical connection. The invention reduces maintenance costs, because when the quality of lighting is affected by the number of LEDs no longer working, it is sufficient to change only the LED support, the LEDs and the male parts of the thermal connections. and the electric. Unlike the systems of the prior art, the supply means and the means for dissipating heat are retained which reduces maintenance costs.

The thermal and electrical connections do not affect the operation of the light source because they ensure on the one hand the electrical continuity, and on the other hand, an effective heat transfer between the LEDs and the means for dissipating heat.

Claims (12)

REVENDICATIONS1. Lighting device comprising firstly a flat plate (32) on which a plurality of LEDs (34) are arranged, said plate (32) comprising a plate (36) of an electrically insulating material with at its upper surface a so-called upper layer (38) made of a conductive material, forming an electric circuit with two terminals (46) for each LED, characterized in that the plate (32) comprises at its lower surface a layer (40) called a lower layer (40). a thermally conductive material, and a plurality of holes (48) between the terminals (46), sealed by a weld of thermally conductive material so as to connect said layers (38, 40) of conductive material each forming a thermal bridge between the two layers (38, 40) in contact with the lower surface of the LEDs. 2. Lighting device according to claim 1, characterized in that the plate (32) comprises near the LEDs orifices (50) passing through metallized side walls to ensure heat transfer on both sides of the plate. (32). 3. Lighting device according to claim 2, characterized in that the orifices (50) have a diameter greater than or equal to 0.5 mm. 4. Lighting device according to claim 2 or 3, characterized in that the lower layer (40) covers almost the entire surface of the plate and comprises for each LED at least one thermal barrier (52) between the holes (48). and the orifices (50) for limiting the propagation of heat. 5. Lighting device according to any one of the preceding claims, characterized in that it comprises a volume of beads (56) ceramic, preferably glass, in direct contact or through at least one plate thermally conductive with the lower layer (40) of the plate (32). 6. Lighting device comprising an optic (54) covering the LEDs and delimiting a cavity (55) according to any one of the preceding claims, characterized in that said cavity (55) contains a heat transfer fluid promoting heat exchange between the LED (34) and the upper face of the plate (32). 7. Lighting device according to any one of the preceding claims, characterized in that it comprises a support (58) pressed against the lower surface of the plate (32) to provide heat dissipation. 8. Lighting device according to claim 7, characterized in that the support (58) comprises an extruded element (60) with a hollow body delimiting a recess (64, 88) with a plurality of fins on the outside ( 66, 90). 9. Lighting device according to claim 8, characterized in that the extruded element (60) comprises constant sections parallel to the plate (32). 10. Lighting device according to claim 8, characterized in that the extruded element (60) comprises constant sections perpendicular to the plate (32). 11. Lighting device according to any one of claims 8 to 10, characterized in that the recess (66, 90) contains beads (56) of ceramic. 12. Lighting device according to any one of claims 8 to 11, characterized in that the support (58) comprises two removable parts, a first part supporting the plate (32) and a second comprising means for dissipating heat. .