GB2479423A

GB2479423A - LED lamp with heat removal body

Info

Publication number: GB2479423A
Application number: GB1016909A
Authority: GB
Inventors: Norbertus Plechelmus Engelberts; Henk Geert Jan Rompelman; Yusuf Umar Jeggels; Martijn Jeroen Dekker; Alexander Paul Johannus De Visser
Original assignee: Lemnis Lighting Patents Holding BV
Current assignee: Lemnis Lighting Patents Holding BV
Priority date: 2010-04-09
Filing date: 2010-10-07
Publication date: 2011-10-12
Also published as: WO2011124386A1; GB201016909D0

Abstract

An LED lamp 100 has a heat dissipation structure 1 for removing heat from one or more LEDs in the lamp 100. The heat removal structure 1 has a central heat dissipation body (11, fig 2A,B) and cooling ribs 13 formed as a single integrated piece. The central body (11, fig 2A,B) has an outer side for accommodating the LEDs and an opposing inner side. The cooling ribs 13 have first and second ends (13a, fig 2A, 13b, fig 2B), the first ends (13a, fig 2A) connected to the central body (11, fig 2A). The cooling ribs 13 extend from the central heat dissipation body (11, fig 2A) and away from the inner side of the central body (11, fig 2A) to partially enclose an interior space and define open channels for heat convection flow into and out from the interior space over the surfaces of the cooling ribs.

Description

HEAT DISSIPATION STRUCTURE, LED LAMP AND METHOD OF

MANUFACTURING A HEAT DISSIPATION STRUCTURE

BACKGROUND OF THE INVENTION

1. Field of the Invention

[0001] The present invention relates to a heat dissipation structure and to a light emitting diode (LED) lamp comprising such heat dissipation structure. Additionally, the present invention relates to a method of manufacturing a heat dissipation structure.

2. Description of the Related Art

[0002] Light emitting diodes, or LEDs, are semiconductor elements that convert electricity into light. Nowadays, LEDs are widely used as light sources in lamps.

These LED lamps are very efficient in that they emit more light per watt and have a longer lifetime than an incandescent light. Furthermore, LEDs are less susceptible to environmental conditions than fluorescent lights.

[0003] The performance of LEDs is influenced by their temperature when in operation. The performance of the LED generally decreases with increasing temperature. Therefore, it is desirable to effectively cool LEDs by using a fan or by mounting the LEDs on a heat sink structure. In many applications, the use of fans is impractical or undesirable due to their size, cost, noise etc. Additionally, heat sinks are desired which are compact but able to dissipate sufficient heat from LEDs.

[0004] Many LED applications relate to so-called retrofit applications, in which existing light sources such as incandescent lights are replaced by LEDs. In such retrofit applications there is typically no space to accommodate cooling fans as the formerly used light sources did not use a fan. The use of heat sinks in such retrofit applications is more complex due to the additional requirement that the heat sink needs to fit within the available infrastructure, e.g. in a conventional fitting.

[0005] The presently known measures to provide heat dissipation from LEDs in an LED lamp are in need of improvement to enable the use of higher power LEDs in LED lamps, particularly in retrofit applications. Conventional heat sink structures are also highly dependent on the orientation of the LED lamp. Heat dissipation may be sufficient if the LED lamp is used in a preferred orientation, e.g. a vertical orientation with the bulb facing downwards or upwards. However, in many applications the LED lamp cannot function optimally because its orientation is such that sufficient heat cannot be removed from the LEDs. As a result, existing LED lamp designs have required the use of lower power LEDs and the applications for these LED lamp designs are limited.

SUMMARY OF THE INVENTION

[0006] It is desirable to provide a heat sink for LED lamps that provides sufficient heat dissipation to enable the use of higher power LEDs generating higher light outputs, and for use independent of the orientation of the LED lamp. For this purpose, the invention relates to a heat dissipation structure for removing heat from one or more LEDs, the heat assembly comprising a central heat dissipation body and a plurality of cooling ribs, the central body and cooling ribs being formed as a single integrated piece, wherein: the central body comprises an outer side for accommodating the LEDs and an opposing inner side, the cooling ribs each have a first end and a second end, the first ends being connected to the central body and the second ends being disposed distant from and facing the inner side of the central heat dissipation body, and the cooling ribs extend in a radial direction outwardly from the central heat dissipation body and in an axial direction away from the inner side of the central body to partially enclose an interior space and define open channels permitting heat convection flow into and out from the interior space over the surfaces of the cooling ribs. By using this heat dissipation structure heat generated by the LEDs is effectively removed independent of the orientation of the structure. The openness of the structure allows for both convective air flow in a direction substantial parallel to the ribs as well as convective air flow in a direction substantially perpendicular to the ribs. Additionally, the structure is limited in size, adds little weight and is easy to manufacture, which makes it suitable for many LED applications, including many retrofit LED applications.

[0007] The first ends of adjacent cooling ribs may be spaced apart so that the channels between the cooling ribs are open ended in a direction towards the LEDs.

Due to the spacing, more air can flow into and out from the interior space and permits a greater convection flow. Furthermore, the removal of heat conductive material may increase the radius of curvature of the air flow. A large radius of curvature of the air flow is desirable as it keeps the air flow in contact with the cooling ribs in a laminar flow regime. For similar reasons, the second ends of adjacent cooling ribs may be spaced apart as well.

[0008] The average width of a cooling rib may be substantially the same as the average spacing between two adjacent ribs. This ratio between width and spacing provides a good trade-off between convection flow and surface area.

[0009] In some embodiments of the invention, the number of cooling ribs is in the range of 8 -15. With such number of cooling optimal results with respect to performance in different orientations of the heat dissipation structure have been obtained. A greater number of ribs may cause too much material blocking the flow.

Having fewer ribs may create openings between the ribs that are too large to develop an optimal convection flow into and out from the interior space.

[0010] The ribs may protrude above the plane extending from the surface of the central heat dissipation body arranged for accommodation of the LEDs, i.e. the outer surface. This arrangement provides ribs with more surface area that may be used in a vertical orientation, i.e. longer channels, and a horizontal orientation, i.e. more surface area across which the cooling fluid can flow. If a bulb is in place, the bulb surface may help to guide the flow into and out of the interior space.

[0011] In some embodiment of the invention, the structure further comprises a holding structure for keeping the second ends of the cooling ribs together. The use of the holding structure provides a more rigid structure. The holding structure may be made of an electric insulating material. The use of such material reduces the risk of short-circuiting and enhances the safety of the structure, which may be of significant importance if used in retrofit LED applications. Additionally, or alternatively, the material used to make the holding structure may be made of a material that is heat conductive. The holding structure may help to improve the heat dissipation capacity of the heat dissipation structure with respect to the heat generated by the LEDs.

Furthermore, the holding structure may remove heat generated by other components, e.g. electric components in circuitry for driving the LEDs.

[0012] In some embodiments of the invention, the structure further comprises a further heat dissipation body located inside the interior space and arranged for heat conductive connection to inner side of the central heat dissipation body. The further heat dissipation body may be used for further heat removal from the LED5.

Additionally, the further heat dissipation body may be arranged for the removal of heat generated by other components, for example heat generated by electronic circuitry for driving the LEDs.

[0013] In one embodiment, the central heat dissipation body, the cooling ribs and the further heat dissipation body are made out of a single piece. This reduces the thermal resistance between the two heat dissipation bodies to permit greater heat transfer along the length of the ribs.

[0014] In some other embodiments, the further heat dissipation body comprises a surface facing the inner side of the central heat dissipation body that can be placed against a complementary surface at the inner side of the central heat dissipation body, and the surface of the two bodies can be fixated by one or more fastening elements. These embodiments allow for a more modular construction which enables a more flexible adaptation of the structure. To reduce the thermal resistance, a heat conductive paste may be provided between the opposing surfaces of the two bodies.

[0015] In some embodiments, the ribs have a thickness of more than 2 mm. This thickness reduces the thermal resistance of the ribs and increases the ribs' ability to transfer heat from the central heat dissipation body along the length of the ribs. An additional advantage is that a thick rib has an increased surface area that may be used for heat dissipation purposes.

[0016] In some embodiments, the thickness of the ribs at the first end is greater than the thickness at the second end. A thick rib at the first end helps to further reduce thermal resistance of the rib and increase heat transfer along the rib. The thickness at the second end is preferably less to facilitate a larger air flow in that region further away from the LEDs. A suitable rib shape which addresses this trade-off between thermal resistance and heat convection is a wedge-like shape.

[0017] In some embodiments of the invention at least one of the ribs comprises an indent in an outwardly facing surface. The indent provides additional surface area that may be used for heat dissipation purposes. Additionally, less material is used, which saves material cost and reduces the weight of the heat dissipation structure.

[0018] The rib may further comprise a hole for connecting the outwardly facing surface of the at least one rib with the indent. The presence of the hole allows for an additional laminar convection flow option within the heat dissipation structure.

Additionally, more surface area is made available for heat dissipation. Finally, further material is saved, which reduces material cost and further reduces the weight of the structure.

[0019] Embodiments of the invention further relate to a LED lamp comprising a fitting for connecting the lamp to an electrical source, a heat dissipation structure as described above; and one or more LEDs mounted on the outer side of the central heat dissipation body of the heat dissipation structure. The LED lamp may be a retrofit lamp. Furthermore, the LED lamp may be positioned in different orientations.

The one or more LEDs may be placed on a metal core printed circuit board [0020] Finally, embodiments of the invention relate to a method of manufacturing a heat dissipation structure comprising providing a thermally conductive two-dimensional structure comprising a central portion and a plurality of elongated strips extending outwards from the central portion; forming a heat dissipation structure as mentioned above by performing one or more stamping actions on the two-dimensional structure. In order to obtain some embodiments of the heat dissipation structure, the method further comprises: providing a holding structure; and placing the holding structure in contact with the second ends of the cooling ribs such that the holding structure keeps the second ends of the cooling ribs together.

BRIEF DESCRIPTION OF THE DRAWINGS

[0021] FIG. I schematically shows an embodiment of a LED lamp according to the invention; [0022] FIGS. 2a, 2b schematically show a top view and a side view of a heat dissipation structure according to an embodiment of the invention; [0023] FIG. 3A shows an exploded view of a cross-section of a LED lamp according to an embodiment of the invention; [0024] FIG. 3B shows a cross-sectional perspective view of a LED lamp of FIG. 3A after assembly; [0025] FIGS. 4A, 4B and 5 schematically show LED lamps according to other embodiments of the invention; and [0026] FIGS. 6A-6D schematically show different stages of a method of manufacturing a heat dissipation structure as shown in FIG. 2A according to an embodiment of the invention.

DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

[0027] The following is a description of certain embodiments of the invention, given by way of example only.

[0028] FIG. I schematically shows an embodiment of a LED lamp 100 according to the invention. The LED lamp 100 comprises a light source comprising one or more LEDs (not shown) covered with a transparent bulb 5. The LED lamp 100 further comprises a fitting 3 for connection to a power source. The LED lamp 100 also comprises a heat dissipation structure 1 for removing heat from the one or more LEDs.

[0029] FIGS. 2a, 2b schematically show a top view and a side view of a heat dissipation structure according to one embodiment of the invention. The heat dissipation structure comprises a central heat dissipation body 11 and a plurality of cooling ribs 13. The central heat dissipation body 11 has an outer side (shown in FIG. 2A) arranged for accommodating one or more LEDs, and an inner side. The cooling ribs 13 extend outwardly from the central heat dissipation body 11.

[0030] The cooling ribs 13 have a first end 13a connected to the central heat dissipation body 11 so as to form a single integrated piece, i.e. the body 11 and the ribs 13 are made out of one piece. A single integrated piece reduces thermal resistance caused by an imperfect connection between the two bodies, and improves the heat flow from the central heat dissipation body 11 to the cooling ribs 13.

[0031] The cooling ribs 13 further have a second end 13b. The second ends 13b of the cooling ribs 13 are grouped together in a plane distant from and facing the inner side of the central heat dissipation body 11 such that the cooling ribs and the central heat dissipation body enclose an interior space with open channels and facilitate laminar heat convection air flow from outside the structure into the interior space and back out of the interior space. This cooling flow into and out of the structure and over the surfaces of the ribs 13 greatly enhances heat transfer from the heat sink to the air or other cooling fluid.

[0032] A laminar flow means that a fluid such as air flows in parallel layers without disruption or turbulence between the layers. A laminar fluid flow which is flowing over a surface with smooth contours will tend to follow the contours and remain in contact with the surface. In this case the term refers to the movement of an air (or other cooling fluid) layer along the heat dissipation structure, in particular the ribs 13, without losing the connection with the structure. The air layer flows over and remains in contact with the surface of the ribs and heat can be transferred effectively from the ribs to the air layer. To further enhance air flow in the laminar flow regime, the surface of the ribs 13 is preferably a smooth surface. Furthermore, the ribs 13 may have a shape with contours without or with a minimal number of angles.

[0033] The heat dissipation structure enables heat dissipation by radiation and heat convection. The arrangement of the cooling ribs 13 is such that air may flow through as a laminar flow in substantially all orientations of the heat dissipation structure.

Conventional designs often function as a thermal "chimney" with a solid heat sink structure which permits good convection flow and heat transfer when the chimney is oriented vertically but relatively poor convection flow and heat transfer in other orientations. The design with cooling ribs reduces the surface area of the heat sink but the loss of cooling area is more than compensated for by improved convection flow and consequent improved heat transfer from the heat sink to the air or other cooling fluid. Compared to conventional designs with solid heat sink structures and maximized heat sink surface area, the cooling ribs design also benefits from lighter weight and lower cost of material since the heat sink includes less material.

[0034] The laminar air flow allows effective heat transfer from the heat dissipation structure, in particular from the cooling ribs 13 to the air. Even if the driving force, i.e. the temperature difference between the air and the cooling ribs 13, is very small, effective cooling may be achieved.

[0035] The heat dissipation structure is made of a material with sufficient thermal conductivity, preferably more than 200 W/mK. Values for heat conductivity for metals used for heat sinks are generally in a range of 100-385 W/mK, and more particularly in a range of about 150 up to 250-300 W/rnK. However, also electrically insulating materials with a heat conductivity in the range of 1-10 W/mK can be used for some applications.

[0036] Furthermore, the structure can be efficiently made using a stamping process, a casting process, or an injection molding process, and the materials may be selected for suitability for these processes. Examples of suitable materials include, but are not limited to, metals with good thermal conductivity such as aluminum for stamping or casting, and high thermal conductivity plastics that can be shaped by means of injection molding.

[0037] As can be seen in the embodiment shown in FIG. 2A, the first ends 13a of adjacent cooling ribs 13 are spaced apart, so that the channels formed between the ribs are open at the "top" end towards the LEDs. As a result, more air can flow along the channels and over the surfaces of the cooling ribs with less resistance.

Furthermore, the removal of heat conductive material to form the open channels increases the radius of curvature of the air flow at this location. The radius of curvature at a point in the air flow is defined as the radius of the osculating circle at that point, where the osculating circle is the circle whose center lies on the inner normal line and whose curvature is the same as that of the given curve at that point.

[0038] A large radius of curvature of the air flow is desirable as it keeps the air flow in contact with the cooling ribs 13 in a laminar flow regime. If the radius of curvature is too small, vortices may develop which creates turbulence, increase flow resistance and reduce heat transfer. If the radius of curvature is too small the heat convection flow may be stalled, reducing the convection flow and heat transfer.

[0039] Having more space between ribs permits greater flow of air into and out from the interior space and greater convection flow. However, a more open structure generally reduces the surface area of the ribs that is used for the heat dissipation.

Experiments have indicated that a good tradeoff between convection flow and surface area can be obtained if the width of the cooling ribs is substantially the same as the spacing between two adjacent ribs. However, reducing the width of the ribs too much reduces the strength of the structure, can make the lamp more difficult to handle, and affects the aesthetic appearance of the lamp. In the embodiment shown in FIG. 1, the ratio between rib width and spacing is about 3:1 on average, and this has been found to yield satisfactory results. A preferred range for the average ratio between rib width and spacing is thus from 1:1 to 4:1.

[0040] For similar reasons as discussed with reference to the first ends 13a of the ribs 13, the second ends 13b of adjacent cooling ribs 13 may be spaced apart. To create a large radius of curvature in the air flow at many locations throughout the heat dissipation structure, adjacent cooling ribs 13 are spaced apart over their entire length.

[0041] The cooling ribs may define channels 17 between the ribs 13 which permit cooling air flow into and out of the interior space, the flow in contact with both interior and exterior surfaces of the cooling ribs 13. The presence of channels 17 having a length that is substantially longer than its width promotes laminar air flow over the surfaces of the cooling ribs 13. The laminar air flow may be substantially parallel to the cooling ribs 13, in particular if the LED lamp has a vertical orientation. In a horizontal orientation of the LED lamp, the channels are oriented across the flow.

The laminar air flow will then move into and out of the interior space and generally contact several ribs 13. Due to the elongated channels more air can flow across the ribs which enhances the convection flow of the air and the heat dissipation of the structure.

[0042] The channels 17 may be open at the side of the central heat dissipation body 11. Having gaps at that location may again enlarge the radius of curvature of the air flow. Furthermore, the volume of the air flow may increase as well as there is less flow resistance.

[0043] Optimal results with respect to performance in different orientations of the heat dissipation structure have been obtained with a structure having 8-15 cooling ribs 13. Without wishing to be bound by theory, a greater number of ribs 13 is believed to disturb the development of an optimal laminar convection flow pattern. A greater number of ribs leads to more material blocking the flow. To compensate for this increase of blocking material, an increase of the number of ribs 13 may be accompanied by a reduction in rib width, in particular at the first ends, to maintain a minimal accessibility to the enclosed space. However, such width reduction may slightly increase thermal resistance between the central heat dissipation body 11 and the cooling ribs 13. Again without wishing to be bound by theory, having fewer ribs 13 is considered to be less advantageous as well. If the width of the ribs 13 is not amended, openings between the ribs may be too large to develop an optimal laminar flow through the heat dissipation structure. If the width of the ribs 13 is increased due to the fewer number of ribs, the amount of heat conductive material is believed to provide too much air blockage. Consequently, again, the air flow through the heat dissipation structure may be less then optimal.

[0044] As shown in FIG. 2B, the cooling ribs 13 may protrude above the plane extending from the surface of the central heat dissipation body 11 arranged for accommodation of the LEDs. Ribs 13 rising higher than the outer side of the central heat dissipation body 11 increases the surface area of the ribs 13 suitable for heat dissipation. Furthermore, in particular if a glass bulb 5 is in place, the protrusion of the ribs 13 may allow the formation of an additional or extended heat convection channel through which a laminar air flow can be facilitated that stays in contact with the rib for a longer period of time. Preferably, the shape of the protruded ribs 13 is such that the air flow has a large radius of curvature.

[0045] The thickness of the structure at the location where the central heat dissipation body 11 passes into the first ends I 3a of the ribs 13 can be selected on the basis of the desire to obtain a minimal thermal resistance. The selection of a thickness is dependent on the material of the heat dissipation structure. For example, for a heat dissipation structure material with a heat conductivity of at least W/mK, e.g. 229 W/mK, a thickness of 2 mm or more minimizes thermal resistance.

[0046] The ribs 13 also have a preferred thickness. For aluminum ribs, the preferred thickness of more than 2 mm. If the ribs are made of copper, slightly smaller ribs, e.g. with a thickness of 1.5 mm or more, may be desirable to save material cost and weight. Such thickness provides the rib 13 with an increased cross-sectional area to reduce the thermal resistance of the ribs and increase heat transfer from the central body along the length of the ribs, and an increased surface area that may be used for heat dissipation purposes. Preferably, the thickness of the ribs 13 at the first end 13a is greater than the thickness at the second end 13b. A thick rib 13 at the first end helps to further reduce thermal resistance and increase heat transfer along the rib 13. The thickness at the second end 13b is preferably less to facilitate a larger air flow in that region further away from the heat source (the LED5). A suitable rib shape which addresses this trade-off between thermal resistance and heat convection is a wedge-like shape.

[0047] The heat dissipation structure may further comprise a holding structure 15 for keeping the second ends 13b of the cooling ribs 13 together. The heat dissipation structure may be manufactured in a stamping process. In such process, the ribs 13 are bent inwards during the process, and may act as springs. The holding structure is then arranged to hold the second ends 13b of the ribs 13 inwards against the spring tension to keep the desired form of the heat dissipation structure. The holding structure 15 may be made of an electric insulating material to minimize hazards for consumers and minimize risks related to electronic malfunctioning e.g. a short-circuit.

[0048] Preferably, the holding structure 15 is made of a heat conductive material.

The holding structure 15 would then further increase the surface area of heat dissipating material. Moreover, the holding structure 15 can contribute to removal of heat generated by electronic components used to drive the LEDs. As a result, these components may operate at a lower temperature which may improve their performance and/or efficiency.

[0049] As shown in the embodiment of FIG. 2B, the holding structure 15 may comprise notches 16 at positions that coincide with the channels 17. These notches may provide additional surface area for cooling, in particular when the holding structure is made of a heat conductive material.

[0050] FIG. 3A shows an exploded view of a cross-section of a LED lamp 200 according to an embodiment of the invention. FIG. 3B shows a cross-sectional perspective view of a LED lamp 200 of FIG. 3A after assembly.

[0051] The LED lamp 200 comprises a central heat dissipation body 11 as shown in FIG. 1, and further comprises an inner heat dissipation body 19. The inner heat dissipation body 19 is located inside the interior space 21. The inner heat dissipation body 19 is arranged for heat conductive connection to the central heat dissipation body 11. The further heat dissipation body 19 can serve as an additional heat removal body for heat generated by the one or more LEDs 30. Furthermore, the further heat dissipation body 19 may facilitate removal of heat generated by electronic circuitry 40 used for driving the one or more LEDs 30.

[0052] The dimensions of the further heat dissipation body 19 are such that the spacing between the further heat dissipation body 19 and the ribs 13 is sufficient to avoid stagnation of heat flow within the interior space 21. Due to the openness of the interior space 21, and the structure of the ribs 13 radiation heat coming from the further heat dissipation body 19 may effectively be transferred out of the interior space 21.

[0053] The LEDs 30 in LED lamp 200 are mounted on a heat conductive substrate 31 that is attached to the central heat dissipation body 11. The heat conductive substrate may be a thermally conductive ceramic layer or a metal core printed circuit board (MCPCB) or similar structure.

[0054] The inner heat dissipation body 19 may be a heat conductive tube.

Connection of the tube with the inner side of the central heat dissipation body 11 may be established by using fastening elements like screws 18. That is, the tube may comprise a surface facing the inner side of the central heat dissipation body 11 that can be placed against a complementary surface at the inner side of the central heat dissipation body 11. The opposing surfaces of the two bodies 11, 19 are then fixated against each other by using one or more screws 18. Instead of screws 18 other fastening elements like bolts and nuts may be used as well. To further reduce thermal resistance caused by an imperfect connection between the bodies 11, 19, heat conductive paste may be used during the fastening process so that the heat conductive paste is provided between the opposing surfaces of the two bodies.

[0055] In another embodiment, the central heat dissipation body 11 and the inner heat dissipation body 19 are welded together, for example by means of brazing. In yet another embodiment, both bodies 11, 19 are made of a single piece of material.

[0056] FIGS. 4A, 4B and 5 schematically show LED lamps 300a, 300b and 400 respectively according to other embodiments of the invention. These embodiments comprise a central heat dissipation body and cooling ribs 13 partially enclosing an interior space with open channels 17 formed between the ribs to permit air flow into and out from the interior space as in the embodiments described above.

[0057] The side surfaces of the ribs 13 in the lamps 300a, 300b have a wedge-like shape. Additionally, the outwardly facing surface of the ribs 13 comprises an indent 23. The indent increases the surface area of the rib 13. As a result of the indent 23 less heat conductive material needs to be used to construct the rib 13 which reduces the material cost and the weight of the ribs 13.

[0058] In LED lamps 300a and 300b, near the first end of the ribs 13, the ribs 13 are provided with holes 25a, 25b. In the LED lamp 300a, the holes 25a connect the outwardly facing surface of ribs 13 and the interior space to increase the air flow into and out of the interior space. Although not shown, such holes 25a may be provided in other embodiments, e.g. in an embodiment as shown in FIG. 1, as well.

[0059] In the LED lamp 300b, the holes 25b facilitate a laminar convective air flow (represented by the arrow in FIG. 4B) between the outwardly facing surface of ribs 13 and corresponding indents 23. Besides the use to further improve the flow characteristics of the heat dissipation structure, the use of holes 25a, 25b reduces the material cost and weight even further.

[0060] The LED lamps 100, 300 show ribs 13 that are broader at the first end and narrower at the second end. However, the ribs may have different dimensions and shapes, for example as shown for LED lamp 400. In this LED lamp 400, the ribs are equally wide at both ends, while the width of the ribs is at its maximum in the middle.

[0061] Furthermore, embodiments of the invention can be used for a variety of LED lamps, including LED lamps with different fittings 3.

Example

[0062] The design as discussed with reference to FIGS. 2A and 2B was tested with a horizontal and a vertical orientation with the bulb facing downwards. The heat dissipation structure was made of aluminum. The central heat dissipation body accommodated a metal core printed circuit board (MCPCB) provided with 4 blue LEDs and 2 red LEDs. Temperatures were measured at the following locations: on top of the MCPCB at a center position between the LEDs (point #1), at the surface of the central heat dissipation body adjacent to the MCPCB (point #2), near the first end of a rib (point #3), and near a second end of a rib (point #4).

[0063] Furthermore, the ambient temperature was measured for both orientations.

During the experiment with vertical orientation, the ambient temperature was 21.7 °C. The experiment with horizontal orientation was performed with an ambient temperature of 21.6 °C.

[0064] The results of the experiments are reproduced in table I provided below.

Table I Temperature in degrees Celsius at different points heat dissipation structure for different orientations.

Measurement point T (°C) horizontal orientation T (°C) vertical orientation #1 73.8 74.8 #2 65.9 66.6 #3 61.9 61.7 #4 60.7 61.3 [0065] As follows from table 1, the heat dissipation structure shows a comparable performance independent of orientation.

[0066] FIGS. 6A-6D schematically show different stages of a method of manufacturing a heat dissipation structure as shown in FIG. 2A according to an embodiment of the invention.

[0067] First, as shown in FIG. 6A, a flat two-dimensional structure is provided, e.g. by a first stamping action in which the structure is stamped from a metal sheet as a single piece. The 2D-structure comprises a central portion 50 and a plurality of elongated strips 60 extending outwards from the central portion 50.

[0068] Then a second stamping action is performed which results in the structure shown in FIG. 6B. As compared to the structure in FIG. 6A, the central portion 50 of the structure is elevated and forms a cover 52.

[0069] Next, a third stamping action is performed which results in the structure shown in FIG. 6G. As compared to the structure in FIG. 66, a portion of the elongated strips 60 is elevated creating a circular moat-like structure 62. Although.

FIG. 6C further shows that the cover now comprises a number of apertures, these apertures are not used for heat dissipation but merely serve the purpose for electrical connection of the LEDs to be mounted at a later stage of the procedure.

[0070] Finally, a fourth stamping action forms the structure shown in FIG. 6D (which is similar to the one shown in FIG. 2A). The cover 52 now corresponds to the central heat dissipation body 11 while the strips 60 correspond to ribs 13.

[0071]To avoid that the ribs 13 due to spring action move back towards a position somewhere between the one shown in FIG. 6C and the one shown in FIGS. 6D and 2A, the method of manufacturing a heat dissipation structure may further comprise providing a holding structure such as holding structure 15 in FIG. 2B. The holding structure is then placed in contact with the second ends of the cooling ribs such that the holding structure keeps the second ends of the cooling ribs together.

[0072] The invention has been described by reference to certain embodiments discussed above. It will be recognized that these embodiments are susceptible to various modifications and alternative forms well known to those of skill in the art.

Claims

WHAT IS CLAIMED IS: 1. A heat dissipation structure (I) for removing heat from one or more LEDs (30), the heat assembly comprising a central heat dissipation body (11) and a plurality of cooling ribs (13), the central body and cooling ribs being formed as a single integrated piece, wherein: the central body comprises an outer side for accommodating the LEDs and an opposing inner side, the cooling ribs each having a first end (13a) and a second end (13b), the first ends being connected to the central body and the second ends being disposed distant from and facing the inner side of the central heat dissipation body, and the cooling ribs extend in a radial direction outwardly from the central heat dissipation body and in an axial direction away from the inner side of the central body to partially enclose an interior space (21) and define open channels (17) permitting heat convection flow into and out from the interior space over the surfaces of the cooling ribs.
2. The structure of claim 1, wherein the first ends of adjacent cooling ribs are spaced apart so that the channels between the cooling ribs are open ended in a direction towards the LEDs.
3. The structure of claim I or claim 2, wherein the second ends of adjacent cooling ribs are spaced apart.
4. The structure of claim 2 or claim 3, wherein the width of a cooling rib at the first end is substantially the same as the spacing between two adjacent ribs.
5. The structure of any one of the preceding claims, wherein the number of cooling ribs is in the range of 8 -15.
6. The structure of any one of the preceding claims, wherein the ribs protrude above the plane extending from the surface of the central heat dissipation body arranged for accommodation of the LEDs.
7. The structure of any one of the preceding claims, further comprising a holding structure (15) for keeping the second ends of the cooling ribs together.
8. The structure of claim 7, wherein the holding structure is made of an electric insulating material.
9. The structure of claim 7 or claim 8, wherein the holding structure is made of a heat conductive material.
10. The structure of any one of the preceding claims, further comprising a further heat dissipation body (19) located inside the interior space and arranged for heat conductive connection to inner side of the central heat dissipation body.
11. The structure of claim 10, wherein the central heat dissipation body, the cooling ribs and the further heat dissipation body are made out of a single piece.
12. The structure of claim 10, wherein the further heat dissipation body comprises a surface facing the inner side of the central heat dissipation body that can be placed against a complementary surface at the inner side of the central heat dissipation body, and the surface of the two bodies can be fixated by one or more fastening elements.
13. The structure of claim 12, wherein a heat conductive paste is provided between the opposing surfaces of the two bodies.
14. The structure of any one of the preceding claims, wherein the ribs have a thickness of more than 2 mm.
15. The structure of any one of the preceding claims, wherein the thickness of the ribs at the first end is greater than the thickness at the second end.
16. The structure of any one of the preceding claims, wherein at least one of the ribs comprises an indent (23) in an outwardly facing surface.
17. The structure of the immediately preceding claim, wherein the rib further comprises a hole (25b) for connecting the outwardly facing surface of the at least one rib with the indent (23).
18. An LED lamp (100, 200, 300a, 300b, 400) comprising: -a fitting (3) for connecting the lamp to an electrical source; -a heat dissipation structure according to any one of the preceding claims; and -one or more LEDs (30) mounted on the outer side of the central heat dissipation body of the heat dissipation structure.
19. The lamp of claim 18, wherein the one or more LEDs are placed on a metal core printed circuit board (31).
20. A method of manufacturing a heat dissipation structure comprising: -providing a thermally conductive two-dimensional structure comprising a central portion and a plurality of elongated strips extending outwards from the central portion; -forming a heat dissipation structure according to any one of claims I -6 by performing one or more stamping actions on the two-dimensional structure.
21. The method of claim 20, wherein the method further comprises: -providing a holding structure; and -placing the holding structure in contact with the second ends of the cooling ribs such that the holding structure fixedly locates the second ends of the cooling ribs.