Lighting device comprising at least one light-emitting diode and vehicle headlight

#The invention relates to an illumination device in accordance with the precharacterizing clause of patent claim 1 and to a vehicle headlight having at least one such illumination device.

#Such an illumination device has been disclosed, for example, in EP-A 1 298 382. This specification describes an illumination device having two or more light-emitting diodes which are arranged on a heat sink and optics as well as an electrical module for operating the light-emitting diodes. This illumination device is envisaged for use in a vehicle and as a replacement for a conventional incandescent lamp.

#It is the object of the invention to provide a generic illumination device which makes possible reliable mounting in a vehicle headlight, with a defined physical position and alignment with respect to the headlight optics.

#The invention will be explained in more detail below with reference to a few preferred exemplary embodiments. In the drawing:

#FIG. 1 shows a plan view of the front of an illumination device in accordance with the first exemplary embodiment of the invention,

#FIG. 2 shows a plan view of the rear of the illumination device in accordance with the first exemplary embodiment of the invention,

#FIGS. 1 and 2 show the illumination device in accordance with the first exemplary embodiment. This illumination device has a heat sink 1 having a mounting surface 10 in the form of a circular disk and parallel cooling ribs 11, 12, 13, 14, 15, 16 which extend perpendicularly with respect to the mounting surface 10. The heat sink 1 is in the form of an integral aluminum die-cast part. The outer contour of the heat sink 1 essentially corresponds to that of a circular cylinder, apart from the cavities between the cooling ribs 11 to 16 and the latching tabs 17, 18, 19, which are part of a bayonet-type lock between the illumination device and a vehicle headlight. The three latching tabs 17, 18, 19 are arranged equidistantly along the circumference of the circular-cylindrical mounting surface 10 at a distance of 120 degrees. They point radially outwards. The two latching tabs 17, 18 have the same design but are arranged in mirror-symmetrical fashion with respect to the diameter of the mounting surface 10, which runs centrally through the third latching tab 19. The latching tab 19 has a different shape than the first latching tab 17 and the second latching tab 18 in order to ensure a definite orientation and installed position of the illumination device in the vehicle headlight. The two cooling ribs 11 and 16 arranged outside have a profile 11a or 16a on their outer surface in order to ensure that they can be gripped better on actuation of the bayonet-type lock. Next to the latching tab 19, the mounting surface 10 has a depression 102 in order to provide space for mounting a lateral contact-pressure spring 103, which acts perpendicularly with respect to the axis of the rotary movement of the bayonet-type lock. The contact-pressure spring 103 is arranged between the latching tab 19 and the spring ring 101. It is hidden in the illustration in FIG. 1 by the latching tab 19.

#A carrier plate 2, for example a so-called metal-core printed circuit board, for in total five light-emitting diode chips 3 (also referred to as LED chips) is fixed on the mounting surface 10 of the heat sink 1. The metal-core printed circuit board 2 is a metal plate which is provided with electrical insulation, for example made from ceramic. Conductor tracks 21 are arranged on the electrical insulation of the metal-core printed circuit board 2 for the purpose of making electrical contact with the LED chips 3. The carrier plate or metal-core printed circuit board 2 ensures electrical insulation between the metallic heat sink 1 and the LED chips 3. The carrier plate 2 is anchored, for example mechanically, on the mounting surface 10 of the heat sink 1 by means of a clamping fit in a cutout in the heat sink 1 or by means of a latching connection or with the aid of an adhesive compound. In order to align and mount the carrier plate 2 in the correct position on the mounting surface 10 of the heat sink 1, two holes, for example, can be introduced into the mounting surface 10, in each case one appropriately shaped pin on the underside of the carrier plate 2 engaging in said holes. These holes can also define the alignment and installed position of the carrier plate 2 with respect to the latching tabs 17 to 19. The five light-emitting diode chips 3 are arranged in a row on the carrier plate 2 and are surrounded by the walls of a so-called casting trough 4 such that the row comprising the five light-emitting diode chips 3 is arranged on the bottom of the casting trough 4. The casting trough 4 is partially filled with a transparent casting compound covering the light-emitting diode chips 3 which contains, for example, two different fluorescent materials in order to convert the wavelength of some of the electromagnetic radiation generated by the light-emitting diode chips 3 such that the illumination device emits white light during its operation. Such fluorescent materials are described, for example, in WO 98/12757. The surface 4a, which faces the light-emitting diode chips 3, of the walls of the casting trough 4 is designed such that they reflect the electromagnetic radiation emitted by the light-emitting diode chips 3. The light-emitting diode chips 3 are, for example, thin-film light-emitting diode chips, whose basic principle is described, for example, in the document I. Schnitzer et al., Appl. Phys. Lett. 63 (16), Oct. 18, 1993, 2174-2176. The five light-emitting diode chips 3 form, together with the casting compound and the fluorescent materials integrated therein, five light-emitting diodes. The term light-emitting diode also includes those diodes which, during operation, emit electromagnetic radiation from the ultraviolet or infrared wavelength range which is converted into electromagnetic radiation from the visible wavelength range by suitable conversion means.

#The carrier plate 2 has four holes 22, in each case one appropriately matching pin 52 of primary optics 5 (depicted in FIG. 4), which serve the purpose of reducing the divergence of the electromagnetic radiation emitted by the light-emitting diode chips 3, or a holder for the primary optics 5 engaging in said holes 22. As a result, the primary optics 5 are fixed on the carrier plate 2 by means of the pins 52 and its installed position and orientation with respect to the carrier plate 2 and thus also with respect to the latching tabs 17 to 19 is fixed. The holes 22 are preferably arranged such that they fit over corresponding holes in the mounting surface 10 of the heat sink 1 such that the pins 52 of the primary optics 5 are passed through the holes 22 in the carrier plate 2 and engage in the abovementioned holes in the heat sink 1. As a result, in addition to the primary optics 5, the carrier plate 2 is also fixed to the heat sink 1 and aligned by means of the aligning pins 52. In this case, no separate means are required for the carrier plate 2 for the purpose of fixing it on the mounting surface 10 of the heat sink 1. In order to set the distance of the primary optics 5 above the light-emitting diode chips 3 located therebeneath to the correct value, one or more spacers can be provided between the primary optics 5 and the carrier plate 2 or the mounting surface 10, said spacers limiting the penetration depth of the pins 52 in the holes 22. The primary optics are a compound optical concentrator which is of similar design to the optical concentrator 5 of the exemplary embodiment of the invention depicted in FIG. 4. One end of this optical concentrator 5 engages in the casting trough 4 and is coupled optically to the light-emitting diode chips 3 by means of Canada balsam, for example. The optical concentrator 5 focuses the light generated by the light-emitting diode chips 3 such that it emerges from the end side 51, which is remote from the light-emitting diode chips 3, of the concentrator 5 with reduced divergence. The optical concentrator 5 is, for example, a compound parabolic concentrator (CPC) or a compound elliptic concentrator (CEC) or a compound hyperbolic concentrator (CHC). The primary optics 5 are arranged in a well defined position and orientation with respect to the light-emitting diode chips 3 on the heat sink 1 or on the carrier plate 2. The primary optics 5 match the optics of the vehicle headlight (secondary optics).