Patent Application
20070279906
The invention relates to LED lamps and, more specifically, to mounting arrangements for such lamps.
Light emitting diodes (or LEDs) are meeting with an increasing success in their use as lighting sources, i.e. as lamps. This applies particularly to so-called high-flux (HF) LEDs. A significant advantage of LED lamps lies i.a. in the possibility of grouping together several LED sources having different emission wavelengths characteristics with the ensuing possibility of selectively varying the chromatic characteristics of the resulting lighting radiation thus produced.
Proper heat sinking of such LED-based lighting sources is a key requirement to preserve the operating life time of the LEDs for a long time. Direct coupling of high-flux LEDs onto a metal heat sink and accessible (that is, unshielded) heat sink operation in open air for thermal dissipation by convection are strongly preferred. Accessible heat sink operation means that the heat sink and the LED side, that is the secondary side of the transformer feeding the LED source(s), are accessible so that they can be safely touched by a user during operation. The heat sink that the LED side of the LED lamp must thus properly insulated by satisfying the requirements in terms of creepage/clearance distances, insulation resistance and dielectric strength dictated by safety standards such as SELV-rated insulation, SELV being an acronym for Safety Extra Low Voltage.
The need is therefore felt for a properly insulated (e.g. SELV-rated) systems for LED lamps, this being particularly the case for self-ballasted high-flux LED lamps supplied from an AC line, such as the common household mains voltage.
The object of the invention is to provide a fully satisfactory response to that need.
According to the invention, that object is achieved by means of an arrangement having the features set forth in the claims that follow. The claims are an integral part of the disclosure of the invention provided herein.
The arrangement described herein is adapted to provide a self-rated insulation system for a self-ballasted high-flux LED lamp supplied from an AC line by providing a number of significant advantages. These include, i.e.:
The invention will now be described, by way of example only, by referring to the enclosed figure of drawing, which represents a general sectional view of a mounting arrangement as described herein.
In the annexed figure of drawing, reference 10 designates as a whole a lighting source (i.e. a “lamp”) including at least one light emitting diode (LED), and, preferably, a plurality of LEDs 12 as the generating source of the lighting radiation. Typically, the LEDS 12 are of the high-flux (HF) type and are fed via an electronic driver 14.
The lamp 10 is essentially includes a support body 16 onto which the LED sources 12, the driver 14 and a number of components associated therewith are mounted as better detailed in the following.
These components are at least partly enclosed within a casing 18. In a preferred embodiment as described herein the casing has a shape somewhat reminiscent of the shape of a conventional light bulb with the LED sources 12 at its distal end and the driver 14 at its proximal end, respectively.
As clearly visible in the drawing, the body 16 is partitioned into two sections, namely a high-voltage (HV) section 16a and a low-voltage (SELV) section 16b. The two sections 16a, 16b may be separated by a gap 20 extending along a non-rectilinear path. Typically, one of the two sections 16a, 16b, preferably the section 16a, includes a protruding portion 160 extending into a corresponding recess 162 in the other section 16b to a produce a mating relationship between the two board sections 16a, 16b.
Typically, the LED sources 12 are carried by a board 22 and are directly mounted on a heat conductive metal (e.g. aluminium, light-alloy) heat sink 24. The heat sink 24 has a hollow domed-shaped section 24a opening towards the driver 14 with the interposition of insulating (e.g. plastics) layer forming a barrier or shield 26. The layer 26 is typically in the form of a cap mounted (e.g. by snap-fit engagement) onto the protrusion 160 of the high-voltage section 16a of the body 16 in order to at least partly surround the transformer 14 carried thereby.
Finally, reference 28 indicates a twisted wire pair connecting the secondary winding of the transformer 10 to the LED sources 12. The wiring 28 extends through corresponding holes 28a and 28b provided in the barrier 26 and in the heat sink 24, respectively. Using a twisted pair for the wiring 28 provides an improved radio frequency interference (RFI) behaviour and is also advantageous because only two wire solderjoints, in the place of four, must be soldered to achieve the proper connection.
In a preferred embodiment of the arrangement described herein, the driver 14 includes a fly-back transformer whose secondary winding is comprised of a triple-insulation wire. Preferably, the secondary winding of the transformer is not soldered in correspondence with the transformer bobbin: a so-called “floating” connection is thus preferred in order to minimize (and notionally dispense with) creepage/clearance requirements. Typically, the transformer is an insulation transformer that keeps 6 mm creepage/clearance and 4 kV insulation between the high-voltage and the low-voltage sections of the circuit (in the case of 230 V ac line voltage).
The LED lamp arrangement described herein is thus partitioned into sections:
The high-voltage section 16a and the low-voltage section 16b referred to in the foregoing are separated by an insulation barrier. This is essentially provided by the insulation transformer 14 and the plastic barrier 26 mounted thereon.
The barrier 26 is preferably comprised of plastic body essentially in the form of a cap adapted to achieve mechanical connection of the two sections of the arrangement while ensuring (possibly together with the gap 20, if present) the desired degree of separation. The size of the hole 28a through the cap 26 can be kept to a minimum value for the wiring 28 to pass therethrough.
The arrangement described herein achieves an optimal coupling of the light source body section 16b towards the heat sink 24 which is conductive and must be accessible (i.e. freely touchable) during operation. Consequently, this section of the “lamp” plus the heat sink 24 are properly insulated, e.g. SELV-rated. The arrangement disclosed is intended to be supplied directly from the mains voltage whereby the SELV requirements (creepage/clearance distances, insulation resistance, dielectric strength) are very strong. The arrangement described herein meets these requirements without any appreciable negative impact on miniaturization, costs of materials and assembly, reliability in large-scale production.
Of course, without prejudice to the underlying principles of the invention, the details and embodiments may vary, even significantly, with respect to what has been described and shown just by way of example, without departing from the scope of the invention as defined by the annexed claims.
| Number | Date | Country | Kind |
|---|---|---|---|
| 06425372 | May 2006 | EP | regional |
