WO2012001593A2

WO2012001593A2 - Lighting device

Info

Publication number: WO2012001593A2
Application number: PCT/IB2011/052759
Authority: WO
Inventors: Henricus Marie Peeters; Rob Franciscus Maria Van Elmpt; Pieter Marnix Pieterse; Rogier Leo Emmanuel Nagelhout; Willibrordus Jurrianus Dijkman
Original assignee: Koninklijke Philips Electronics NV
Current assignee: Koninklijke Philips NV
Priority date: 2010-07-01
Filing date: 2011-06-23
Publication date: 2012-01-05
Anticipated expiration: 2013-01-01
Also published as: TW201207313A; WO2012001593A3

Abstract

There is provided a lighting device (100) comprising a printed circuit board, PCB, a light source (101) for emitting light mounted on the PCB, and a heat release member (105) for dissipating heat generated by the light source. The light source is thermally connected to at least one electrically and thermally conductive portion of the PCB by at least one contact, and the PCB is arranged such that an upper surface (108) of the PCB is arranged in thermal connection with an upper inner surface (116) of a cavity (115) arranged in the heat release member, while the light source is arranged in an aperture (118) of that cavity. Heat generated by the light source is transferred along a heat transfer path extending from the light source via the at least one contact and at least one thermally conductive portion to the heat release member via the interface formed by the upper surface of the PCB and the heat releasing member. Further, a corresponding light emitting system is provided.

Description

Lighting device

FIELD OF THE INVENTION

The present inventive concept generally relates to a lighting device comprising a light source and a heat release member for dissipating heat generated by the light source.

BACKGROUND OF THE INVENTION

In recent years the use of LED based lighting devices has increased and now extends over a wide variety of lighting applications. As the demand for high intensity lighting devices is large, the problem of removing heat produced in LED based lighting devices has to be attended to, in order to ensure a good performance, efficiency and high life expectancy of the lighting devices. Further, LED lighting devices are today interesting for use in demanding environments, like for instance green houses, in which artificial light is used to stimulate plant growth. The damp and warm environment in the green houses, in which the green house staff is working in the direct vicinity of the LED lighting devices, raises the need for attending to other demands like, in addition to the need for sufficient cooling, providing the LED lighting devices with sufficient insulation for electrical safety and ingress protection.

CN 201196403 Y discloses a light source module having a LED element mounted on a printed circuit board (PCB) arranged on a base made of aluminum alloy. A predefined gap is formed between the bottom surface of the PCB and the base. An insulating and heat conduction material such as silicone rubber and insulating gel or paste is filled between the bottom surface of the PCB and base. The surface of the PCB is filled with waterproof insulating cement.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide to an alternative and improved lighting device which provides a high safety in demanding environments, and which simultaneously provides an efficient cooling. A further object is to provide a method of providing such an improved lighting device. According to a first aspect of the invention, these and other objects are achieved with a lighting device comprising a printed circuit board, PCB, having an upper surface and a lower surface, the PCB further comprising at least one electrically and thermally conductive portion, a light source for emitting light mounted on the upper side of the PCB, the light source being thermally connected by at least one contact of the light source to the at least one electrically and thermally conductive portion, and a heat release member for dissipating heat generated by the light source. The heat release member comprises a cavity inside which the PCB is arranged such that the upper surface of the PCB is arranged in thermal connection with an upper inner surface of the cavity. The light source is arranged in an aperture of the cavity. The heat generated by the light source is transferred along a heat transfer path extending from the light source via at least one contact and at least one thermally conductive portion to the heat release member via the interface formed by the upper surface of the PCB and the heat release member.

Thereby, a lighting device in which a good cooling for the light source is provided while simultaneously providing ingress protection and easy assembly. As the PCB is arranged within the cavity of the heat release member, and more specifically is abutting the upper inner wall of the cavity, the lower surface of the PCB, which is typically in electrical connection with the mains, is separated from the heat release member and no separate mains insulation is therefore required which saves cost in the form of manufacturing steps and mounting time.

A further advantage is that with this configuration, the number of parts is minimized and each subpart can be manufactured using only standard technologies, thus no specific tooling and investments are required for the production of the lighting devices.

In addition, it is advantageous to arrange the PCB inside the cavity of the heat release member, which preferably is a metal housing, such that the metal housing fully enfolds the PCB and corresponding electronics, as this prevents from hazardous situations in case of fire. The life parts of the PCB will not drop down because the metal housing will not melt or break down at high temperature unlike e.g. a plastic housing.

According to an embodiment of the lighting device, the space between the light source and the heat release structure is filled with potting material. This may be done only on the top side to provide touch safety. Also electrical isolation between light sources arranged on the PCB, e.g. LEDs which may operate at high voltages, is provided by the insulator material of the PCB (e.g. glass reinforced epoxy) and from the topside by the potting material. Further, the space beneath the PCB may be filled up but this is not necessary for electrical safety. Thereby, any parts being connected to voltage present in the aperture of the heat release member, e.g. a light source contact which is not completely inserted in the PCB, or a part of the upper surface of the PCB which may be accessible through the aperture, are efficiently sealed off from the heat release member, which may be e.g. an aluminum structure. The potting material also seals the electrical parts from moist and dirt. Further, the potting provides an efficient ingress protection. The lighting device can therefore be made completely waterproof and more safe to handle from an electrical point of view. Further, as potting of the lighting device is restricted to a small, limited space, as for instance no potting on the back side of the PCB is required, the lighting device is easy to assemble and the total weight and cost of the final lighting device product is reduced.

According to an embodiment of the lighting device, the lower side of the PCB and the opposite inner side of the cavity has a predetermined separation for providing sufficient electrical insulation between the PCB and the heat release structure.

According to an embodiment of the lighting device, the lighting device further comprises a spring element arranged inside the cavity for clamping the PCB to the heat release element.

According to an embodiment of the lighting device, the lighting device further comprises an electrically insulating element arranged between the lower side of the PCB and the opposite inner side of the cavity. This has the advantage that the predetermined distance can be decreased, thus providing a thinner lighting device.

According to an embodiment of the lighting device, at least one of the electrically and thermally conductive portions are arranged on the upper surface of the PCB.

According to an embodiment of the lighting device, the contact is an electric contact or a heat transfer member of the light source.

According to an embodiment of the lighting device, the light source comprises at least one light emitting diode, LED.

According to an embodiment of the lighting device, the at least one LED is a surface mounted LED, SMD-LED.

According to an embodiment of the lighting device, the lighting device further comprises a cover member arranged over the light source.

According to an embodiment of the lighting device, the cover member is arranged to further providing an optical function. According to an embodiment of the lighting device, the optical function is arranged to be one of a collimating-, de-collimating, diffusing-, scattering-, and phosphor converting function.

According to a second aspect of the invention, there is provided a light emitting system comprising a plurality of lighting devices according to invention.

According to an embodiment of the light emitting system, at least two of the lighting devices are arranged having one of a common heat release member, and a common PCB and a common heat release structure. The PCBs are not in electrical connection with the heat release member such that the light sources are separated from each other, which allows for very high supply voltages for the lights sources and a high number of light sources arranged in the same light emitting system. Thus, the light emitting system is advantageous for high power lighting applications.

According to a third aspect of the present invention, there is provided a method for providing a lighting device comprising:

- providing a heat release member having a cavity and an aperture;

mounting a light source on a PCB;

inserting the PCB into the cavity such that the light source is arranged in the aperture;

clamping said PCB against the heat release member; and

- potting the light source into space defined by at least the PCB and the aperture.

Thereby a simple construction and assembly of a lighting device is achieved. It is noted that the invention relates to all possible combinations of features recited in the claims. BRIEF DESCRIPTION OF THE DRAWINGS

This and other aspects of the present invention will now be described in more detail, with reference to the appended drawings showing embodiment(s) of the invention.

Fig. 1 is a schematic illustrative cross-sectional side view of an embodiment of a lighting device according to the present inventive concept;

Fig. 2 is a schematic illustrative cross-sectional side view of an embodiment of a lighting device according to the present inventive concept;

Fig. 3 is a schematic illustrative cross-sectional side view of an embodiment of a lighting device according to the present inventive concept; Fig. 4 is a schematic illustrative cross-sectional side view of an embodiment of a lighting device according to the present inventive concept;

Fig. 5 is a schematic illustrative cross-sectional side view of a light emitting system according to the present inventive concept;

Fig. 6 is a schematic side view of a light emitting system according to the present inventive concept;

Fig. 7 is a schematic illustrative cross-sectional side view of an embodiment of a lighting device according to the present inventive concept; and

Fig. 8 is a schematic side view of a light emitting system according to the present inventive concept.

DETAILED DESCRIPTION

Embodiments of the present inventive concept will now be described more fully hereinafter with reference to the accompanying drawings, in which certain embodiments of the invention are shown. This invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided by way of example so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art. Like numbers refer to like elements throughout.

With reference to Fig. 1, which is a schematic illustration of an embodiment of a lighting device according to the present invention, the lighting device 100 comprises a light emitting diode (LED) 101 mounted on an upper side 107 of a printed circuit board (PCB) 106. The PCB 106 is a 4 layer FR4 having at least one electrically and thermally conductive portion 104 within its multilayer structure, which electrically and thermally conductive portion is a metal or a conductive polymer. Here the thermally conductive portions 104 are provided as copper layers of the PCB 106. The PCB may be made of any material conventionally used in the art, but is typically made of glass-epoxy.

The LED 101 is arranged having electrical contacts 110, 111, which each is thermally connected to at least one of the electrically and thermally conductive portions 104 of the PCB 106. Alternatively, the light source can comprise a plurality of LEDs. Further, the LED may be one or more surface mounted LEDs, SMD-LEDs, which is illustrated in Fig. 7, in which a lighting device 700 is arranged having an SMD-LED 701 mounted on a PCB 106 such that the electrical contacts 710, 71 lof the light source are in thermal and electrical contact with the PCB. For the purpose of thermally connecting the light source and the PCB, in alternative embodiments of the lighting device, heat transfer member are arranged on the light source. E.g. when the light source is a SMD-LED, a thermally conductive adhesive which is used for mounting of the component before soldering of the electrical contacts, will constitute a heat transfer member transferring heat produced in the SMD-LED to the PCB, which in turn may be arranged having a thermally conductive portion arranged at the heat transfer member (not shown).

The lighting device 100 further comprises a heat release member 105 for dissipating heat generated by the light source 101. The heat release member is made in any suitable material with acceptable thermal properties, e.g. aluminum, copper, magnesium, or a ceramic material. With the foregoing in mind, for simplicity, the heat release member in the exemplifying embodiments herein are all referred to as metal housing 105. The metal housing 105 is here a folded aluminum sheet. However, in alternative embodiments, the metal housing may be an extrusion profile.

The metal housing 105 is in principle arranged as a hollow metal box, comprising a cavity 115 and an aperture 118 arranged in an upper wall defining the cavity 115 of the metal housing 105. The metal housing 105 further comprises a vertically extending wall 128, which is arranged on its upper outer surface to encompass the aperture 118. Further, during assembly of the lighting device 100, the PCB 106 is introduced into the cavity 115 and arranged to abut on the upper inner surface 116, such that the upper surface 107 of the PCB is arranged in thermal connection with the inner surface 116 of the metal housing 105. The cavity 115 is arranged such that a predetermined distance is provided between lower inner side 117 of the metal housing 105 and the lower side 108 of the PCB 106, and to the electric contacts 110, 111, respectively, for providing sufficient electrical insulation between live parts on the backside 108 of the PCB 106 and the metal housing 105.

The PCB 106 is positioned such that the light source 101 is arranged in the aperture 118 and projecting into the space defined by the encompassing wall 128. Further, the PCB 106 is clamped with a spring element 127 which is inserted between the backside 108 of the PCB 106 and the lower inner surface 117 of the cavity 115 to maintain the position of the PCB 106. Spring element 127 is here a resilient plastic profile.

Space between the light source 101 and the metal housing 105, i.e. the space defined by the upper surface of the PCB 106, which is exposed through the aperture 118, the metal housing aperture 118 and the metal housing encompassing wall 128, is filled with potting material 109, which here is a two component poly urethane. The potting material may be selected from e.g. a variety of epoxies, and can be designed to fit specific requirements regarding thermal conductivity, water resistance etc.. Further, if there is a need for a potting material with high heat resistance or UV resistance, silicon may be used as potting material. In some applications it may be required to avoid discoloration of the potting material and e.g. a bright white surface is needed for light reflection, in which case a titanium oxide pigment may be used in the potting material. There are thermo setting potting materials, UV-curable potting materials and other types of potting materials, as the skilled person recognizes.

Once fully cured, the potting takes over the mechanical function of the spring element 127 by fixating the PCB 106 against the metal housing 105. The spring element 127 may subsequently optionally be removed from the lighting device 100 or be kept in place to provide an additional electric isolation making a flatter housing possible.

To provide a fully sealed lighting device, the metal housing is provided with a closing element (not shown) like a lid to close the cavity.

Heat generated by the light source 101 is transferred along a heat transfer path extending from the light source 101 via the electrical contacts 110, 111 and the electrically and thermally conductive portions 104 to the heat release member, i.e. metal housing 105, via the interface 116 formed by the upper surface 107 of the PCB and the heat releasing member.

In an embodiment of a lighting device 200 according to the present inventive concept, described with reference to Fig. 2, the lighting device 200 has a light source 101 mounted on a PCB 106, which PCB is arranged in a metal housing 105 and provided with insulating potting 109 in a similar manner as described above with reference to Fig. 1 for the lighting device 100. However, in the latter lighting device 200, the spring element 127 is replaced by an insulating piece of plastic foam 250. The piece of plastic foam 250 is used to clamp the upper surface 107 of the PCB 106 onto the inner surface 216 of the heat release structure, i.e. metal housing 105. The piece of plastic foam, or any other suitable material, is selected to in addition to clamping the PCB during the step of providing the potting material 109, to electrically seal the light source 101 and PCB 106, to provide electric insulation between, and isolation of, the back side 108 of the PCB 106 and the inner surface 117 of the metal housing 105. Thus, the cavity inside the metal housing 105 can be made flatter, than when not providing the piece of plastic foam250.

In an alternative embodiment, the plastic foam is provided into the cavity as a reactant filling up the cavity below the PCB, which reactant subsequently forms a foam which fully fills up the cavity and which is hardened underneath the PCB, pressing the PCB against the inner upper surface of the cavity in the metal housing. Further, in lighting device 200, at least one of the electrically and thermally conductive portions 104 of the PCB 106, i.e. here a copper layer, is provided on the top layer of the PCB 106 at the upper surface 107. The top copper layer 104, being both thermally and electrically conductive, must for safety reasons be separated with a correct safety distance from the life parts in the lighting device.

In an embodiment of a lighting device 300 according to the present inventive concept, described with reference to Fig. 3, the lighting device 300 has a light source 101 mounted on a PCB 106, which PCB is arranged in a metal housing 105 and provided with insulating potting 109 in a similar manner as described above with reference to Fig. 1 for the lighting device 100. However, in the latter lighting device 300, the spring element 127 is replaced by a leaf spring 350 made of metal. The leaf spring 350 presses the PCB 106 to the metal housing 105. Due to the leaf spring 350 being electrically conducing, the contact surface of the leaf spring 350 on back side 108 of the PCB 106 must be selected so as to maintain correct creepage- and clearance distances from live parts of the back side 108 of the PCB 106.

Fig. 4 illustrates an embodiment of a lighting device 400 according to the present inventive concept, further comprising a cover member 450 arranged over the light source 101. The cover member 450 may be provided during or subsequent to the step of potting the light source with potting material 109. Thereby, the cover member is attached into the potting material 109 during the subsequent hardening process. Alternatively, the metal housing 105, and in particularly the wall 128 encompassing the light source 101 may be arranged to receive the cover member 450. The cover member 450 is here a transparent piece of plastic, however glass is also suitable. The cover member 450 can be arranged on the lighting device 400 for additional protection of the light source 101 against dirt, pesticides and herbicides used in green houses, UV-radiation or to provide a surface which facilitates cleaning of the lighting device.

Further, the cover member 450 can be arranged to provide an optical function such that a collimating-, de-collimating, diffusing-, scattering-, and phosphor converting function. When providing a cover member comprising optical functionality, measures to align the optical cover with respect to the light sources are preferably taken during mounting. Further, the cover member 450 can be provided with a color filter or any suitable functional layer.

In an embodiment of the lighting device, the light source is a blue LED, and a remote phosphor layer, YAG phosphor, is provided on an inner side of the cover member. As is illustrated in Fig. 5, the present inventive concept is applicable to lighting devices comprising a plurality of light sources which are laterally separated. Here the light sources 101 are arranged on a common PCB 106, and is inserted into a common heat release structure 105, and subsequently potted with potting material 109 to be electrically insulated and protected from moist.

In an embodiment of a light emitting system, as illustrated in Fig. 6, the PCB with a plurality of LEDs 101 is mounted in a metal extrusion profile 105, which has an internal cavity (not visible) and an aperture 118 for exposing the light sources 101. Potting material 109 provides mechanical support and sealing of the light sources, as previously described above. An end portion 601 is arranged at an end of the extrusion profile 105 for sealing off the cavity. Thereby the metal housing fully enfolds the PCB and electronics avoids hazardous situations in case of fire. The life parts of the PCB will not drop down because the metal housing melts or breaks down at high temperature. The end portion 601 may further be arranged for providing the lighting system with supply voltage.

In an embodiment of the light emitting system 800 according to the present inventive concept, as illustrated in Fig. 8, several lighting devices 700, 700^', and 700^" are arranged in a common heat release structure 105. The heat release structure 105 is a light aluminum housing (heat sink) consisting of just one extrusion part, in which three separate PCBs with light sources (single or a e.g. a line of light sources as illustrated in Fig. 6) are arranged. This provides a very important feature of the present inventive concept, which is, fully enclosing the electrical parts by a metal housing. As illustrated in Fig. 8, the PCBs can be mounted at different angles which is advantageous for providing light in more than one direction.

The person skilled in the art realizes that the present invention by no means is limited to the preferred embodiments described above. On the contrary, many modifications and variations are possible within the scope of the appended claims.

Claims

CLAIMS:

1. Lighting device (100) comprising:

a printed circuit board, PCB, (106) having an upper surface (107) and a lower surface (108), said PCB further comprising at least one electrically and thermally conductive portion (104);

- a light source (101) for emitting light mounted on said upper side of said PCB, said light source being thermally connected by at least one contact (110, 111) of the light source to said at least one electrically and thermally conductive portion (104); and

a heat release member (105) for dissipating heat generated by said light source, said heat release member comprising a cavity (115) inside which said PCB is arranged such that said upper surface of said PCB is arranged in thermal connection with an upper inner surface (116) of said cavity, wherein said light source is arranged in an aperture (118) of said cavity;

wherein the heat generated by said light source is transferred along a heat transfer path extending from said light source via said at least one contact and said at least one electrically and thermally conductive portion to said heat release member via the interface formed by the upper surface of the PCB and the heat release member.

2. Lighting device according to claim 1, wherein space between said light source (101) and said heat release structure (105) is filled with potting material (109).

3. Lighting device according to claim 1 or 2, wherein said lower side (108) of said PCB (106) and the opposite inner side (117) of said cavity have a predetermined separation for providing sufficient electrical insulation between the PCB and the heat release member.

4. Lighting device according to anyone of the preceding claims, further comprising a spring element (127,350) arranged inside said cavity (115) for clamping said PCB (106) to said heat release element (105).

5. Lighting device according to claim anyone of claims 1 - 3, further comprising an electrically insulating element (250) arranged between said lower side (108) of said PCB (106) and the opposite inner side (117) of said cavity.

6. Lighting device according to anyone of the preceding claims, wherein at least one of the electrically and thermally conductive portions (104) are arranged on the upper surface (107) of the PCB (106).

7. Lighting device according to anyone of the preceding claims, wherein said contact is an electric contact (110, 111) or a heat transfer member of said light source (101).

8. Lighting device according to anyone of the preceding claims, wherein said light source comprises at least one light emitting diode, LED.

9. Lighting device according to claim 8, wherein said at least one LED is a surface mounted LED, SMD-LED.

10. Lighting device according to anyone of the preceding claims, further comprising a cover member arranged over the light source.

11. Lighting device according to claim 10, wherein said cover member is further arranged for providing an optical function.

12. Lighting device according to claim 11, wherein said optical function is arranged to be one of a collimating-, de-collimating, diffusing-, scattering-, and phosphor converting function.

13. Light emitting system comprising a plurality of lighting devices according to anyone of the preceding claims.

14. Light emitting system according to claim 13, in which at least two of the lighting devices are arranged having one of a common heat release structure, and a common PCB and a common heat release structure.

15. A method for providing a lighting device comprising:

providing a heat release member having a cavity and an aperture;

mounting a light source on a PCB;

inserting said PCB into said cavity such that the light source is arranged in said aperture;

lamping said PCB against said heat release member; and

potting said light source into space defined by at least said PCB and said aperture.