WO2012168845A1

WO2012168845A1 - Remote heat sink

Info

Publication number: WO2012168845A1
Application number: PCT/IB2012/052791
Authority: WO
Inventors: Benoit Georges Paul TOTHE
Original assignee: Koninklijke Philips Electronics N.V.
Priority date: 2011-06-06
Filing date: 2012-06-04
Publication date: 2012-12-13

Abstract

The invention relates to a cooling system comprising a heat sink made of thermally conductive material and comprising an open cavity (19) extending along a main axis. The heat sink further comprises: -a heat core (11) having an inner surface bounding a portion of the cavity (19); -a base plate (12), arranged in the cavity (19) to support a LED-based device (20), and extending transversally to the main axis; and -fins (15) being oriented from the heat core (11) to the base plate (12); wherein the base plate (12) is thermally linked to the heat core (11) such that at least one gap (14) is provided between the heat core (11) and the base plate (12),allowing some air to flow through this gap (14), between some fins (15). The invention further relates to a LED-based luminaire comprising said heat sink and a LED-based device (20).

Description

REMOTE HEAT SINK

FIELD OF APPLICATION

The invention relates to the field of LED-based systems, and more especially to the field of cooling systems usually provided within said LED-based systems. BACKGROUND OF THE INVENTION

Thermal dissipation of the heat produced by LED-based systems or devices is a key factor that limits the lumen output of an LED-based system.

Moreover, improvement at low cost of such heat dissipation is needed.

The most cost-effective, known solution for dissipating heat is the use of passive cooling systems, whose working principle is based on the association of thermally conductive material with LED-based devices. Efficiency of heat dissipation depends on the configuration and design of the cooling system, in particular some heat sinks, which has nevertheless to comply with the design and optical and electrical constraints of the LED- based device.

Thus, it is known to provide a thermally conductive heat sink to LED-based devices, comprising:

a central open cavity or through hole, typically cylindrical, extending along a main axis, in which the LED-based device is positioned;

a heat core bounding the cavity;

- a base plate arranged in the cavity to support the LED-based device, and extending transversely in the cavity from the heat core to the main axis; and

fins fixed to the outer surface of the heat core to increase the surface area of the heat sink that is in contact with air, thereby accordingly improving heat dissipation.

Due to the increase in intensity of the light emitted by the new type of LEDs, heat management challenges are increasing. And there is a need still to find more efficient, more compact, more reliable and cheaper heat management solutions to succeed in the design of high lumen output lighting solutions. SUMMARY OF THE INVENTION

The invention attempts to solve said problem by proposing a cooling system according to a cooling system comprising a heat sink made of thermally conductive material and comprising an open cavity extending along a main axis, the heat sink further comprising:

a heat core (11) having an inner surface bounding (or limiting) a portion of the cavity (19);

a base plate (12), arranged in the cavity (19) to support (or bear) a LED-based device (20), and extending transversely to the main axis; and

fins (15) being oriented from the heat core (11) to the base plate (12);

wherein the base plate (12) is thermally linked to the heat core (11) such that at least one gap (14) is provided between the heat core (11) and the base plate (12), allowing (some) air to flow through this gap (14), between part of the (or some) fins (15).

By spacing the base plate apart from the heat core, the gap thus created between them allows increasing significantly the possibility of an air flow within the cavity, and between the fins, thereby improving cooling. In particular air trapped between some of the fins is released by this additional air flow.

Moreover, this gap can be seen as a means for the removal of materials between the base plate and the heat core from known thermal solutions, which may lead to a decrease of the weight of the heat sink.

Moreover, the distance created between the base plate and the heat core allows using this new free space in the heat sink for other purposes (e.g. adding additional fins, lodging components inside this space, etc.).

Preferably, the cavity is a through hole enabling the user or assembler of the overall lighting system to access the cavity from both the rear side and the front side of the heat sink, thereby giving easy access to the LED-based device as well as to both sides of the base plate and to the interior part of the heat core. This through hole can also be useful for facilitating the cleaning of the heat sink (and especially of the fins).

According to an option, the gap separates entirely the base plate from the heat core. Alternatively, some mechanical structures, preferably made of thermal material, may be configured between the base plate and the heat core so as to form some openings or gaps therebetween.

The air flow between the heat core and the base plate, through the gap, is therefore maximized. According to another option, the cavity and the gap are both cylindrical. This design allows the air flow to be equally distributed within the heat sink, optimizing the cooling efficiency. In particular, the fins arranged around the main axis may be provided so as to further facilitate an equal cooling distribution.

Alternatively, the cavity and the gap may be differently configured, in order for instance to achieve different air flows in the heat sink or asymmetric cooling: this configuration may be useful if it is preferable to cool a warm area of the LED-based device more than a cold area and/or to cool fins in contact with warm air more than other fins in contact with cold air.

According to another option, the heat core and the base plate are thermally linked by at least one heat pipe. A heat pipe is typically a pipe having an internal liquid circuit that is successively heated and cooled depending on whether the water is located respectively close to a warm or a cold environment, thus increasing the transfer of heat between the base plate and the heat core (and potentially the fins). An advantage of a heat pipe is its good thermal conductivity in relation to its dimensions (especially its diameter), which allows providing the gap while keeping a satisfactory heat transmission between the base plate and the heat core. A heat pipe further is a cheap solution for performing such a thermal link between two parts of a system.

Alternatively or in combination, other means for thermally linking the base plate and the heat core may be chosen, e.g. any kind of element made of thermally conductive material. This element may be connected to the heat core and/or the base plate by using inserting, screwing, over-molding or soldering techniques. Another way to create the air flow gap between the base plate and the heat core is to start from a cavity comprising an elongated heat core attached to a base plate, and create openings by machining between the heat core and the base plate. The parts of the heat core that are not removed can form the said thermal link between the base plate and the heat core.

Optionally, said fins extend parallel to the main axis. Such a configuration may optimize the cooling efficiency, since the fins may extend in the general direction of the heat exchange or heat convection.

Optionally, some additional fins extend in the cavity: (i) from the heat core; and/or (ii) from the base plate.

These inner fins (i.e located in the cavity) allow increasing the cooling surfaces of the heat sink, while maintaining a good air flow (especially via said gap) and restricting the size of the outer fins (i.e. the fins being oriented from the outer surface of the heat core) and therefore the size of the heat sink.

Optionally, an active cooling device for causing an air flow is provided in the cavity, on the side of the base plate opposite to the LED-based device. In particular, this active cooling device is provided between the heat core and the base plate, and more particularly this active cooling device fits in the gap. This active cooling device might be a fan or another type of active cooling system. The presence of the cavity and said gap (which might increase the distance between the base plate and the heat core) allows lodging such an active cooling device inside the heat sink, and thus hiding this active cooling device from external view, leading to a lighting system that is esthetically more attractive. This embodiment can also lead to a more compact lighting system. Moreover, this active cooling device should increase the air flow and hence the cooling of the lighting system, especially through the gap.

Optionally, an LED-driving device for driving LEDs is provided in the cavity, on the side of the base plate opposite to the LED-based device. The presence of the cavity and said gap (which might increase the distance between the base plate and the heat core) allows lodging such an LED-driving device inside the heat sink. Accordingly: (i) the size of the LED-based device can be reduced, since a part of the electronics is now provided in a place other than the LED-based device; and/or (ii) this LED-driving device can be hidden from external view, leading to a lighting system that is esthetically more attractive. This embodiment can also lead to a more compact lighting system. Moreover, this LED-driving device can receive an additional air flow due to the proximity to the gap, and be cooled accordingly.

Optionally, the LED-based device comprises one or several LEDs attached directly or indirectly (e.g. via a circuit board) to the base plate and an optical member positioned in front of the LED(s), and at least a part of the fins are arranged so as to extend further at the level of the optical member.

According to another aspect, the invention proposes a LED-based luminaire comprising said heat sink and a LED-based device.

Optional embodiments of such a LED-based luminaire are recited in claims 13 through 16. BRIEF DESCRIPTION OF THE DRAWINGS

Other features and advantages of the invention appear from the following detailed description of one of its embodiments, given by way of non-limiting example, and with reference to the following drawings:

Fig. la shows a longitudinal cross-sectional view, with respect to a plane including a main axis XX', of a first embodiment of a lighting device according to the invention.

Fig. lb shows a perspective view of one half of the lighting device of Fig. 1, taken along a plane including the main axis XX'.

Fig. 2 shows a perspective view of one half of a second embodiment of a lighting device according to the invention, taken along to a plane including a main axis XX'.

Fig. 3 shows a longitudinal cross-sectional view of another embodiment of a lighting device according to the invention.

Fig. 4 shows a longitudinal cross-sectional view of another embodiment of a lighting device according to the invention.

Fig. 5 shows a longitudinal cross-sectional view of another embodiment of a lighting device according to the invention.

Fig. 6a shows a longitudinal cross-sectional view of a known lighting device, horizontally positioned.

Fig. 6b shows a longitudinal cross-sectional view of a lighting device according to FIG. 3, horizontally positioned.

Fig. 7a shows a longitudinal cross-sectional view of a known lighting device, vertically positioned.

Fig. 7b shows a longitudinal cross-sectional view of a lighting device according to Fig. 3, vertically positioned.

Fig. 8a shows a longitudinal cross-sectional view of a first known lighting device comprising active cooling.

Fig. 8b shows a longitudinal cross-sectional view of a second known lighting device comprising active cooling.

Fig. 8c shows a longitudinal cross-sectional view of a lighting device according to another embodiment of the invention, comprising active cooling. DETAILED DESCRIPTION OF THE INVENTION

FIG. la and lb show a first embodiment of a lighting device 100 according to the invention, comprising a LED-based device 20 and a heat sink 10.

The LED-based device 20 comprises at least one or several LEDs 21 which are directly or indirectly thermally linked to the heat sink 10. The LEDs 21 may be fixed to a circuit board 22. The circuit board 22 comprises circuitry and optionally some electronic components such as for example drivers and/or memories. The LED-based device 20 may further comprise at least one optical member 23 positioned on top of LEDs 21 and acting on the light beam shape, direction and/or density of energy output by the LEDs 21. In this example, the optical member 23 is represented by a collimator designed to guide the light outside the lighting device 100.

The heat sink 10 is made of thermally conductive material (e.g. aluminum alloys (e.g. ADC1, ADC10, A11050,...), copper, zamac, ceramics (A1N, A1203), thermal plastics and comprises an open cavity 19 (here a through hole 19) extending along an XX' axis, a heat core 11 whose inner surface limits a portion of the through hole 19, a base plate 12 arranged in the through hole 19 to support the LED-based device 20 and spaced apart from the heat core 11 by a gap 14, a heat pipe 13 thermally (and possibly mechanically) linking the base plate 12 to the heat core 19, fins 15 fixed to the heat core 11 and being oriented from the heat core 11 to the base plate 12 and optionally extending at the level of the optical member 23 (as depicted in FIG. la and lb).

The through hole 19 preferably extends with respect to a main axis XX', which can be the main optical axis of the LED-based device 20. Without any limitation, the through hole 19 may have a general cylindrical shape (e.g. having a circular, elliptical, square, rectangular cross-section) or a general tapered shape or any other appropriate shape for the design of the lighting device 100 and/or for cooling it. In the specific configuration of FIG. la and lb, the through hole 19 has a general cylindrical shape with a circular cross section - the circular cross-section might be particularly useful for use with spots and also advantageous because the design is compact for a symmetrical light distribution.

The heat core 11 extends generally with respect to the XX' axis, and comprises an inner surface 11 ' and an outer surface 11". If the through hole 19 is cylindrical, the inner surface 11 ' of the heat core 11, accordingly, might be cylindrical too, as depicted in FIG. la and lb. The inner surface 11 ' limits only a top portion of the through hole 19.

Fins 15 are oriented from the heat core 11 to the base plate 12. Preferably, the fins 15 are fixed to the outer surface 11" of the heat core 11. Fins 15 may be flat and thin blades or the like, arranged around the XX' axis. Fins 15 can be plane, extending parallel to the XX' axis, or slightly twisted. As an option, these fins 15 (as depicted in FIG. la and lb) further extend beyond the base plate 12, so as to surround at least a part of the optical member 23. Fins 15 may be arranged around the XX' axis according to a specific pitch with respect to one another. In the case of a cylindrical heat core 11 , fins can further extend radially from the outer surface 11 " of the heat core 11 , with respect to the XX' axis.

Size and shape of the base plate 12 can be determined by the size of the LED- based device 20, especially circuit board 22. The thickness of the base plate 12 is adjusted with regard to heat dissipation, weight, and cost considerations. Its thickness and geometry are also adjusted to have a good thermal transfer with the heat pipe 13. Base plate 12 is either only fixed to the heat core 11 via the heat pipe 13 (the base plate 12 and the LED-based device 20 are therefore suspended in the through hole 19) and/or fixed to some fins 15. For example, LED-based device 20 may be fixed (e.g. by screwing, clipping, sticking, and/or clamping) onto the base plate 12, and to the heat pipe 13 being fixed onto the base plate 20 (e.g. by soldering and/or pressing), after which the heat pipe 13 is fixed onto the heat core 11 (e.g. by soldering and/or pressing): in this case the heat pipe 13 ensures a good mechanical bond between the base plate 12 and the heat core 11. Other ways of interconnecting the heat pipe 13 / base plate 12 / heat core 11 / LED-based device 20 may nevertheless be used, such that the base plate 12 and the heat core 11 are sufficiently thermally linked together according to the invention.

The heat pipe 13 is provided between the base plate 12 and the heat core 11. A heat pipe is typically a pipe having an internal liquid circuit, which is successively heated and cooled depending on whether the water is located close to respectively a hot or a cold environment, thereby increasing the transfer of heat between the base plate 12 on one hand and the heat core 11 (and potentially the fins 15) on the other hand. Movement of the liquid in the circuit is caused by convection, and also some optional capillarity elements located inside the heat pipe 13 to counterbalance the force of gravity. The heat pipe 13 is preferably arranged in the through hole 19 such that the part of the through hole 19 above the base plate 12 is still accessible and not obstructed by the heat pipe 13. For this purpose, the heat pipe 13 may first extend transversally to the XX' axis through the base plate 12 up to the sides of the through hole 19 or up to the gap 14 (this is the first section 13' of the heat pipe 13), and secondly extends parallel to the XX' axis on sides of the though hole 19 parallel to the heat core 11 (this is the second section 13" of the heat pipe 13). Heat pipe 13 may be fixed in a different manner to the base plate 12 and the heat core 11. For example, the heat pipe 13 can be soldered to the base plate 12 and/or the heat core 11 with or without a groove provided into the base plate 12 and/or the heat core 11. Alternatively or in addition, the heat pipe 13 can be pressed into the base plate 12 and/or the heat core 11, inside a groove provided in the base plate 12 and/or the heat core 11.

In another embodiment, more than one heat pipe 13 may be provided between the base plate 12 and the heat core 11.

Additionally, some other mechanical reinforcement might be provided between the base plate 12 and the heat core 11, like e.g. a cage-structure.

By way of example, the following process for manufacturing a heat sink according to the invention is provided:

1. Manufacture the base plate 12;

2. Manufacture the heat pipe 13 + Bend the heat pipe 13 according to the heat sink dimensions and shape;

3. Mount the heat pipe 13 onto the base plate 12;

4. Manufacture the heat core 11;

5. Mount the heat pipe 13 onto the heat core 11;

- If the heat sink comprises some fins 16, 17 inside the through hole 19 (see e.g. FIGs. 2 and 3), then mount the heat pipe 13 outside the through hole 19;

- If the heat sink does not comprise fins 16, 17 inside the through hole 19, then mount the heat pipe 13 inside or outside the through hole 19;

6. Press fit the fins 15 onto the heat core 11.

FIG. 2 depicts another lighting device 100' similar to the lighting device 100 of FIG. lb, but additionally comprising inner lateral fins 16 extending from the inner surface 11 ' of the heat core 11. In this configuration the through hole 19 hosts these additional inner fins 16, thereby increasing the contact surface of the heat sink 10 with air while not significantly hampering the air flow.

FIG. 3 shows another lighting device 100" similar to the lighting device 100' of FIG. 2, but additionally comprising inner bottom fins 17 extending in the through hole 19 from the surface of the base plate 12 opposite to the surface of the base plate 12 receiving the LED-based device 20. In this configuration the through hole 19 hosts the additional inner lateral and bottom fins 16, 17, thereby increasing the contact surface of the heat sink 10 with air while not significantly hampering the air flow.

Another embodiment (not depicted) relates to another lighting device similar to the lighting device 100 of FIG. lb, but additionally comprising inner bottom fins 17 extending in the through hole 19 from the surface of the base plate 12 opposite to the surface of the base plate 12 receiving the LED-based device 20. In this configuration the through hole 19 hosts these additional inner bottom fins 17, thereby increasing the contact surface of the heat sink 10 with air while not significantly hampering the air flow.

As an alternative, or in combination with previous embodiments, the through hole 19 may further host LED-driving device 29 of the LEDs 21 of the LED-based device 20, the LED-driving device 29 being connected to the LED-based device 20 via connectors 28, as shown in FIG. 4. The LED-driving device 29 can be fixed to the inner surface of the heat core 11 and/or to the base plate 12 via fixation elements (e.g. attaching means, slots, etc.). As a first example, the LED-driving device 29 may be a plastic circuit board ("PCB") in a

(electrostatic) box or housing, screwed in the through hole 19 or clipped within the through hole if the inner surface of the heat core 11 is provided with complementary clipping elements. Alternatively, the LED-driving device 29 may be adhered to or potted inside the through hole 19 and provided with electrical insulation: the latter solution may be chosen if the LED-driving device 29 is a PCB with components (i.e. without a housing or a box protecting it). By providing at least a part of the LED-driving device 29 in the through hole 19 instead of within the LED-based device 20, the heat produced by this LED-driving device 29 is some distance apart from the base plate 12, causing the quantity of heat communicated to the base plate 12 to be reduced and this LED-driving device 29 to be positioned within the increased air flow. Furthermore, the separation of this LED-driving device 29 from the LED- based device 20 allows reducing the weight of the LED-based device 20, which is especially advantageous in the case that the assembly of LED-based device 20 and base plate 12 is suspended from the heat core 11 (via the heat pipe 13). Moreover, the design- and size- related constraints of the LED-driving device 29 are less important if it is positioned in the through hole 19 than in the LED-based device 20.

As an alternative to or in combination with previous embodiments, the through hole 19 may further host activatable cooling device 30, such as for example a fan. The presence of such an activatable cooling device 30 further increases the air flow within the heat sink 10, and especially through the gap(s) 14. Moreover, this activatable cooling device 30 is invisible to an external viewer, since it is hidden by the heat sink 10, leading to a lighting device 100 that is aesthetically more attractive.

FIG. 8c shows a LED-based luminaire 200, including a lighting device 100" according to the invention, comprising an activatable cooling device 30 positioned in the through hole 19, and more especially (in this case) in the portion of the through hole 19 bounded by the inner surface of the heat core 1 1, below the inner lateral fins 16 and above the optional inner bottom fins 17. Active cooling device 30 allows increasing the air flow by forcing the air to flow along an air path, especially via the gap 14. The LED-based luminaire 200 comprises a housing 60, made typically of electrically insulating material, lodging most of the lighting device 100" (which comprises through hole 19, heat sink 11, base plate 12, heat pipe 13, gap 14, outer fins 15, inner lateral fins 16, inner bottom fins 17 as discussed previously). This housing 60 comprises a front opening 61 on a front side, allowing light to be output through the optical member 23, and a rear opening 62 on a back side, allowing external air to communicate with the inner lateral fins 16 and the outer fins 15. The rear opening 62 may be annular, leaving a solid central disk covering a central portion of the through hole 19. The housing 60 may be made of two parts: a back housing 60' arranged to lodge the heat sink 10 and a front housing 60" arranged to lodge the optical member 23. The back housing 60' and the front housing 60" may be interconnected via an intermediate opening 63 arranged to receive the LEDs 21 therethrough.

FIGs. 6a and 6b depict how the heat dissipation is improved in a light device according to the invention (FIG. 6b) in comparison with a known light device (FIG. 6a) if they are positioned horizontally (i.e. the main axis XX' is perpendicular to the direction of gravity). It is to be noted that the two light devices are made of similar materials and have similar dimensions of the heat sinks 10, similar fins 15, and similar LED-based devices 20. Heat exchange is depicted in the FIGs by the arrows. For the known light device, heat exchange by convective heat transfer is limited as the orientation of the fins 15 is not in the gravity direction ("G") - indeed heat dissipated to the air via the bottom part of the light device is trapped between the bottom fins 15' (since hot air naturally travels upward) - leading to a low efficiency of the LEDs located close to the bottom fins 15' with respect to the efficiency of the LEDs located close to the upper fins 15". Now, the "opening" of the heat core 11 according to FIG. 6b, by providing a gap 14 between the heat core 11 and the base plate 12, allows releasing the trapped hot air through the heat sink 10, thereby creating furthermore an air flow as depicted by the arrow.

FIG. 7a and 7b depict how the heat dissipation is improved in a light device according to the invention (FIG. 7b) in comparison with a known light device (FIG. 7a) if the light devices are positioned vertically (i.e. the main axis XX' is parallel to the direction of gravity). It is to be noted that the two known light devices are made of similar materials and have similar dimensions of the heat sinks 10, similar fins 15, and similar LED-based devices 20. Heat exchange is depicted in the FIGs by the arrows. For the known light device, the heat exchange by convective heat transfer is performed principally via the fins 15 due to the elongated surface of the fins 15 in contact with air. Now, the "opening" of the heat core 11 according to FIG. 7b, obtained by providing a gap 14 between the heat core 11 and the base plate 12, allows creating a natural air flow (since hot air naturally travels upward) inside the light device, through (in this case) inner fins 16 (as depicted by the arrow). By spreading the cooling effect (?) throughout the heat sink 10, heat dissipation is improved.

FIG. 8a, 8b and 8c depict how the heat dissipation is improved in a light device according to the invention (FIG. 8c) in comparison with two known light devices (FIG. 8a and 8b). It is to be noted that the two known light devices have identical LED-based devices 20. Heat exchange is depicted in the FIGs by the arrows.

The first known light device (FIG. 8a) is a luminaire comprising a back housing 40 arranged to lodge an active cooling device 30 (e.g. a fan), a front housing 40' arranged to lodge the LED-based device 20, and a heat sink or radiator 10 positioned between the back housing 40 and the front housing 40'. In order to dissipate the heat by making the hot air flow out through the sides of the heat sink 10 (see heat exchange depicted by arrows in FIG. 8a), a gap 40" is to be provided between the back housing 40 and the front housing 40', allowing an external viewer to see the heat sink 10, which is not desirable for aesthetic reasons. Moreover, the cooling of such a heat sink 10 requires a powerful, cumbersome and noisy cooling system 30.

The second known light device (FIG. 8b) is a luminaire comprising a housing

40 arranged to accommodate an active cooling device 30 (e.g. a fan) and a heat sink 10 or radiator positioned between the active cooling device 30 and the LED-based device 20. This configuration allows dissipating the heat from the back side of the housing 40 to the front side of the light device, through openings 41 provided around the light output of the housing 40 (see heat exchange depicted by arrows in FIG. 8b). This second known light device needs to be wider than the first known device, since some additional space needs to be provided around the LED-based device 20, which is not desirable for aesthetic and practical reasons.

An LED-based luminaire 200 according to the invention, shown in FIG. 8c, has been previously described. Due to its specific configuration, the air flows through an air path between an air inlet (cool air), being the portion of the back opening 62 facing the inner lateral fins 16, and an air outlet (hot air), being the portion of the back opening 62 facing the outer fins 15. From the air inlet, air mostly flows successively via the inner lateral fins 16, via the fan 30, via the gap 14 and via the outer fins 15. The air flow may be improved by the presence of said inner bottom fins 17 located between the fan 30 and the air gap 14 in the air path. Heat dissipation is therefore mostly performed through the rear side of the LED-based luminaire 200. This configuration allows both hiding the active cooling device 30 from an external viewer and using an active cooling device 30 without a significant increase of the size of the luminaire 200 being required. Additionally, due to the proximity of the cooling device 30 to the LEDs 21 and the greater surface exchange (due to inner fins 16, 17) of the luminaire 200, the cooling device 30 may be smaller.

While the invention has been illustrated and described in detail in the drawings and foregoing description, such illustration and description are to be considered illustrative or exemplary and not restrictive; the invention is not limited to the disclosed embodiments, and the person skilled in the art can clearly adapt the teaching of the invention, especially as regards the remote heat core principle, to any other light configurations. In particular the lighting system does not necessarily comprise identical shapes of optical modules.

Other variations to the disclosed embodiments can be understood and effected by those skilled in the art in practicing the claimed invention, from a study of the drawings, the disclosure, and the appended claims. In the claims, the word "comprising" does not exclude other elements or steps, and the indefinite article "a" or "an" does not exclude a plurality.

Claims

CLAIMS:

1. Cooling system comprising a heat sink made of thermally conductive material and comprising an open cavity (19) extending along a main axis, the heat sink further comprising:

a heat core (11) having an inner surface bounding a portion of the cavity (19); - a base plate (12), arranged in the cavity (19) to support a LED-based device

(20), and extending transversely to the main axis; and

fins (15) being oriented from the heat core (11) to the base plate (12);

wherein the base plate (12) is thermally linked to the heat core (11) such that at least one gap (14) is provided between the heat core (11) and the base plate (12), allowing air to flow through this gap (14), between part of the fins (15).

2. Cooling system of claim 1, wherein the heat core (11) and the base plate (12) are thermally linked by at least one heat pipe.

3. Cooling system of claim 1, wherein some additional fins (16) extend in the cavity (19) from the heat core (11).

4. Cooling system according to any one of claims 1 to 3, wherein some additional fins (17) extend in the cavity (19) from the base plate (12).

5. Cooling system of claim 1, wherein an active cooling device (30) for generating an additional air flow is provided in the cavity (19), and is located on the side of the base plate (12) opposite to the LED-based device (20).

6. Cooling system of claim 5, wherein the active cooling device (30) fits in the gap (14).

7. Cooling system of claim 1, wherein the LED-based device (20) comprises at least one LED (21) attached directly or indirectly to the base plate (12) and an optical member (23) positioned in front of the LED(s) (21), and wherein at least a part of the fins (15) are arranged to extend at the level of the optical member.

8. Cooling system of claim 1, wherein the cavity (19) is cylindrical and the gap (14) is cylindrical.

9. Cooling system according to claim 1, wherein the gap entirely separates the base plate (12) and the heat core (11).

10. Cooling system according to claim 1, wherein the open cavity (19) is provided with two openings located at two opposite ends of the cavity (19) so as to form a through hole (19).

11. LED-based luminaire comprising a cooling system according to any one of claims 1 through 10 and a LED-based device (20), and further comprising:

an active cooling device for creating the air flow (30), provided in the cavity

(19) of the heat sink,

a housing (60) for lodging said heat sink and optionally the LED-based device

(20) ;

wherein the housing (60) comprises air opening(s) (62) to determine air inlet and air outlet.

12. LED-based luminaire of claim 12, wherein the air opening(s) (62) is (are) located on the side of the housing (60) opposite the side of the LED-based luminaire from which the light emanates.

13. LED-based luminaire of claim 12, further comprising inner fins (16) extending in the cavity (19) from the heat core (11), wherein the active cooling device (30) is positioned between these inner fins and the base plate (12), and wherein the air opening(s) are located such that the air flows first through the inner fins (16) and then to the fins (15) located outside the cavity (19).

14. LED-based luminaire of claim 14, further comprising internal fins (17) extending in the cavity (19) from the base plate (12), and located such that at least part of the air flowing between the inner fins (16) to the fins (15) located outside the cavity (19) passes through the internal fins (17).

15. LED-based luminaire of claim 11, further comprising a LED-driving device (29) for driving the LEDs (21) provided in the cavity (19), and being located on the side of the base plate (12) opposite to the LED-based device (20).