Lighting device

0001The invention relates to a lighting device, and in particular to a lighting device using high power sources, especially LEDs.

0002Prior art lighting devices having high power LEDs use relatively bulky heat sinks to cool the LEDs which also makes the overall lighting devices bulky. Additionally, the relatively ineffective heat dissipation often affects the reliability of the system. Document <patcit id="pcit0001" dnum="US6367949B"><text>US 6,367,949</text></patcit> discloses a lighting device according to the preamble of claim 1.

0003It is thus the object of the present invention to provide a more compact and reliable lighting device, in particular for high power light sources like LEDs.

0004The object is achieved by the lighting device according to claim 1. Advantageous embodiments are especially defined by the dependent claims.

0005The lighting device comprises a stack of functional layers such that the device can be arranged in a compact manner. Because of the shorter connections and solid attachment, reliability is improved. The functional layers (or sections) comprise at least (not necessarily in this order): <ul id="ul0001" list-style="dash" compact="compact"><li>an optics layer comprising at least one optical element like a lens, a collimator etc., to shape light emitted from the light source layer;</li><li>a light source layer comprising at least one light source, e.g., a LED or a laser diode, that is adapted to radiate light through the optics layer to an exterior;</li><li>a printed circuit board comprising an electronic driver to drive / control the lighting device; and</li><li>a cooling layer comprising at least one cooling element for cooling at least the light source(s).</li></ul>

0006The stack structure adds flexibility and design effectiveness because the layers may be independently customized or adjusted according to the system needs. Also, an excellent integration level is achieved.

0007Advantageously, the at least one light source comprises an LED array.

0008Advantageously, a primary optics is attached to the at least one light source, e. g., a lens attached on or after a light emitting face of the respective light source.

0009Advantageously, the optical element of the optics layer comprises a Fresnel structure common to the light sources.

0010The printed circuit board comprises a flexible layer to connect to at least one of the other functional layers. The flexible layer advantageously at least connects the electronic driver to the at least one light source.

0011The printed circuit board may advantageously comprise a lower / base insulation layer. In an alternative embodiment, the insulation layer may not be integrated with the printed circuit board.

0012To maintain a cost effective and reliable electrical connection, at least portions of the flexible layers are metallised.

0013To effectively cool at least the light source(s), the cooling layer comprises a metal heat sink and a fan for cooling the heat sink, i. e., an active heat sink. Advantageously, the heat sink comprises a bed of heat conduction / dissipation pins.

0014Advantageously, the heat sink is made of more than 95 % pure aluminium, preferably at least 99 % pure aluminium, and is advantageously made by high pressure molding, especially at a pressure above 800 bar, to improve thermal conductivity. The effective cooling enables a high brightness thanks to an increased thermal efficiency.

0015To effectively distribute heat away from the light sources, the at least one light source is directly attached to the heat sink.

0016The lighting system will schematically be described in more detail in the following non-limiting and exemplary embodiment. Where applicable, the same reference numbers are used for identical or similar components. <dl id="dl0001"><dt>FIG 1</dt><dd>shows a lighting device in a perspective view;</dd><dt>FIG 2</dt><dd>shows the lighting device of <figref idref="f0001">FIG 1</figref> in a top-down view;</dd><dt>FIG 3</dt><dd>shows the lighting device of <figref idref="f0001">FIG 1</figref> in a side view;</dd><dt>FIG 4</dt><dd>shows a layout of the printed circuit board in a top-down view;</dd><dt>FIG 5</dt><dd>shows a cut-out side view of the lighting system;</dd><dt>FIG 6</dt><dd>shows a heat sink of the lighting device in a bottom-up view; and</dd><dt>FIG 7</dt><dd>shows the heat sink of <figref idref="f0006">FIG 6</figref> in a side view.</dd></dl>

0017<figref idref="f0001">FIG 1</figref> shows a lighting device 1 without a housing for the sake of a better illustration. The lighting device comprises on top an optics layer 2 comprising a Fresnel structure. The optics layer 2 also functions as a protective front cover.

0018Below the optics layer 2 is arranged a light source layer 3 comprising three high power LEDs 4 that are covered by a primary optics including a respective collimator 5. Light emitted from the LEDs 4 is radiated through the respective primary optics / collimators 5 and then through the Fresnel structure of the optics layer 2 to the exterior. The Fresnel structure is common to all three LEDs. It comprises several Fresnel rings (2A) and a pillow structure (not shown) inside the rings 2A.

0019The lighting device 1 further comprises a printed circuit board 6 in turn comprising an electronic driver (not shown) to drive the lighting device 1, e. g., by controlling a LED current, or a fan speed (see below).

0020Further comprised is a cooling layer 7 in turn comprising a heat sink 17 (see <figref idref="f0006">FIG 6</figref>) and a fan 8 for active cooling of the LEDs 4. The heat sink 17 in turn comprises an aluminium base plate 14 and a bed of heat-dissipating pins 9 on its bottom side. The fan 8 is shown spaced apart from the heat sink 17, as it is its position within the housing. The fan 8 and the heat sink 17 are arranged one after the other / successively (superimposed). As it will be explained in more detail further below, the PCB 6 and the LEDs 4 are both directly mounted on the heat sink.

0021This superimposed stacked arrangement achieves a very compact and reliable lighting device 1.

0022<figref idref="f0002">FIG 2</figref> shows the lighting device 1 of <figref idref="f0001">FIG 1</figref> in a top-down view. The transparent optics (and protection) layer 2 gives view on the collimators 5 of the light source layer 3. The collimators 5, and thus the LEDs, are arranged in an angular three-fold symmetry around a centre point C and are - in this view - optically placed within the Fresnel structure.

0023<figref idref="f0003">FIG 3</figref> shows the lighting device 1 of <figref idref="f0001">FIG 1</figref> in a side view including exemplary dimensions. The Fresnel lens is 63 mm wide; while the optics layer 2 is slightly wider for reasons of subsequent assembly. The light source layer 3 is 19.9 mm high, and the PCB 6 is 1.3 mm high. The heat sink 17 with its metal base plate 14 and heat dissipation pins 9 is 15 mm high and spaced apart 12.60 mm from the fan 8 of height 15 mm and width 60 mm.

0024<figref idref="f0004">FIG 4</figref> shows a layout of the printed circuit board 6 in a top-down view. Because the LEDs 4 are arranged on the heat sink parallel to the PCB 6, the PCB 6 shows cut-outs 10 for receiving the LEDs 4. Flexible extensions 11 from the PCB 6 reach into the cut-outs 10.

0025<figref idref="f0005">FIG 5</figref> shows a cut-out side view of the lighting system in the vicinity of the flexible extensions 11. The printed circuit board 6 has a multilayer structure with at least a flexible layer 12 that includes the flexible extensions 11 and an insulating layer 13 to insulate the upper layer (s) 12, 16 from a metal base plate 14 of a heat sink. The LEDs 4 are also placed directly on the base plate for improved heat transfer.

0026The extension 11 of the flexible layer 12 is at least on its lower side covered by a copper film to contact the PCB 6 with the LEDs 4. The electrical contact between the flexible extension 11 and a respective LED 4 are achieved by using a bonding pad 15 and a suitable connection technique, e. g., soldering. Thus an electrical connection can be created between the LED 4, via the bonding pad 15 and the flexible extension 11 and flexible layer 12 to the wiring layer 16 which in turn is connected to electric and / or electronic components like an integrated driver circuit.

0027The insulating layer 13 may be made from the same material as the PCB laminates. This provides a sufficient electrical insulation between metal traces (wiring) at the bottom side of the wiring layer and the heat sink 14. In an alternative embodiment, the insulation layer may not be integrated in the printed circuit board.

0028This arrangement provides an easy to fabricate and reliable connection between the PCB 6 and other functional components 4. There are no other connection means needed. Because the shown design is susceptible to process automation of components and soldering, production and assembly costs can be reduced; this may be helped by the fact that multiple connections can made in the same step; i. e., that placing and soldering for all devices can be made at once. Also, for increased design flexibility, the PCB 6 can be placed on conductive surfaces thanks to its isolating bottom.

0029<figref idref="f0006">FIG 6</figref> shows a heat sink 17 of the lighting device in a bottom-up view. On the base plate 14 of the heat sink 17 is provided a bed made of the cylindrically shaped heat dissipation pins 9 in a substantially regular pattern. At some areas, pins are omitted to allow for through holes 18 to mount the heat sink 17, e.g. by screwing on. The base plate 14 also comprises recesses 19 at its periphery with a minimum radius of the outer contour of 0,5 mm.

0030The heat sink 17 is made of at least 99 % pure aluminium, and has been fabricated by high pressure molding at a pressure above 800 bar to improve thermal conductivity. The effective cooling enables a high brightness thanks to an increased thermal efficiency.

0031<figref idref="f0007">FIG 7</figref> shows the heat sink of <figref idref="f0006">FIG 6</figref> in a side view along the line A-A- of <figref idref="f0006">FIG 6</figref> with respective dimensions in mm.

List of reference numbers

0032<dl id="dl0002" compact="compact"><dt>1</dt><dd>lighting device</dd><dt>2</dt><dd>optics layer</dd><dt>2A</dt><dd>Fresnel ring</dd><dt>3</dt><dd>light source layer</dd><dt>4</dt><dd>light source</dd><dt>5</dt><dd>collimator</dd><dt>6</dt><dd>printed circuit board</dd><dt>7</dt><dd>cooling layer</dd><dt>8</dt><dd>fan</dd><dt>9</dt><dd>heat dissipation pin</dd><dt>10</dt><dd>cut-out</dd><dt>11</dt><dd>flexible extensions</dd><dt>12</dt><dd>flexible layer</dd><dt>13</dt><dd>insulating layer</dd><dt>14</dt><dd>base plate</dd><dt>15</dt><dd>bonding pad</dd><dt>16</dt><dd>wiring layer</dd><dt>17</dt><dd>heat sink</dd><dt>18</dt><dd>through hole</dd><dt>19</dt><dd>recess</dd><dt>C</dt><dd>centre point</dd></dl>