WO2021079311A1

WO2021079311A1 - Led lighting device with overvoltage protection system

Info

Publication number: WO2021079311A1
Application number: PCT/IB2020/059933
Authority: WO
Inventors: Matteo CASALINO; Enrico PONS; Pietro COLELLA; Riccardo TOMMASINI
Original assignee: Politecnico Di Torino
Priority date: 2019-10-24
Filing date: 2020-10-22
Publication date: 2021-04-29
Also published as: IT201900019755A1

Abstract

The present invention relates to a LED lighting device (200), comprising: - a first plate of dielectric material (201) comprising a first face (201a) and a second face (201b), said first plate (201) comprising at least one electric circuit (300) and at least one LED module (105a, 105b, 105c) located on the first face (201a) of the first plate (201), said at least one LED module (105a, 105b, 105c) comprising a positive pole and a negative pole; - a second plate of electrically conductive material (202) comprising a first face (202a) and a second face (202b), said second plate (202) being electrically connected to the negative pole of said at least one LED module (105a, 105b, 105c), said first face (202a) of the second plate (202) facing, at least partly, towards the second face (201b) of the first plate (201). The peculiar feature of said LED lighting device (200) lies in the fact that it comprises a third plate (203) of dielectric material facing, at least partly, towards the second face (202b) of the second plate (202). The present invention further relates to a lighting apparatus for outdoor use, comprising a containment enclosure (101) made of metallic material, a support (102) made of metallic material and adapted to support the containment enclosure (101) at a predetermined height, and a LED lighting device (200).

Description

LED LIGHTING DEVICE WITH OVERVOLTAGE PROTECTION SYSTEM

DESCRIPTION

The present invention relates to a LED lighting device equipped with an overvoltage protection system according to the preamble of claim 1; in particular, the present invention falls within the field of LED lighting devices for street lighting applications in urban or suburban environments.

Although characterized by high energetic efficiency, the LED lighting devices known in the art are typically affected by high overvoltage sensitivity; in particular, in the street lighting field, this characteristic is particularly problematical, since such devices are often subject to strong atmospheric overvoltages. As a consequence, the average life of LED devices is considerably reduced, resulting in increased costs and complexity incurred for maintaining street lighting systems based on such devices. For this reason, it is necessary to resort to protection methods and systems capable of insulating and protecting the LED device also from strong atmospheric overvoltages.

According to techniques known in the art, in Class I devices (i.e. with Class I specifications according to the EN 60598-1:2015-14 CEI standard) equipped with a grounding connection, the LED lighting device can be protected by directly inserting a voltage discharger between the active parts of the LED lighting device and the protection conductor (i.e. in common mode configuration). In Chinese patent application CN204464990, this protection is achieved by connecting, in parallel with the LED device, a plurality of dischargers and capacitors; such a solution requires the presence of a grounding terminal, and therefore can only be used in Class I LED devices. In Chinese patent application CN201636674, the protection system is realized by using, in a suitable configuration, zinc-oxide varistors, overvoltage suppressor diodes and inductors; in this case as well, the use of the grounding terminal limits the use of the protection system to Class I LED devices.

Protection and insulation of Class II LED lighting devices (i.e. with Class II specifications according to the EN 60598-1:2015-14 CEI standard) is more problematical; in fact, the insulation techniques described above with reference to Class I devices are not directly applicable to Class II devices in that, by definition, the latter have no grounding connection. According to techniques known in the art (i.e. according to Art. 3.7.2 of the 34-156:2016-06 CEI Guide), overvoltage protection of a Class II LED lighting device can be accomplished by using a capacitive protection impedance disposed between the negative supply of the LED module and the metallic enclosure (also defined as containment enclosure in the present description) of the LED lighting device; in addition, further protection can be attained by reinforcing the insulation between the circuit of the LED device and the accessible internal (i.e. the heatsink) and external (i.e. the external containment enclosure of the lighting device) metallic parts. Such solutions have many drawbacks. For example, the insertion of a capacitive impedance in a Class II LED device often requires the execution of a number of high-precision soldering steps; therefore, installing the LED lighting body into the containment enclosure turns out to be a complex and costly task.

In this frame, it is the main object of the present invention to provide a LED lighting device which is so designed as to overcome the drawbacks of prior-art LED lighting devices. In particular, it is one object of the present invention to provide a Class II LED lighting device capable of ensuring efficient protection against atmospheric overvoltages. It is a further object of the present invention to provide a Class II LED device which is simple to manufacture and easy to install.

The LED lighting device of the present invention comprises a first plate of dielectric material; said first plate may be substantially flat and may comprise a first face and a second face. The dielectric material may be copper-plated vetronite or, more in general, fiberglass; the first plate may comprise an electric circuit comprising, for example, a plurality of conductive tracks etched on the dielectric material. Said electric circuit may comprise an AC/DC converter (also referred to as power supply unit in the present description) and a plurality of protection elements. The first plate may also comprise, on the first face thereof, one or more LEDs; said one or more LEDs may be connected, usually in series, into a single module (also referred to as LED module in the present description) by means of, for example, the conductive tracks of the electric circuit etched on the dielectric material of the first plate. As is known, a LED (Light Emitting Diode), also referred to as light emitting diode in the present description, is an electronic component widely used in the lighting technology for making lighting devices; a LED, or a LED module, is usually powered by direct electric current or voltage through a positive current or voltage input (also referred to as positive pole in the present description) and a negative current or voltage input (also referred to as negative pole in the present description). The LED lighting device of the present invention further comprises a second plate of electrically conductive material (e.g. aluminium), used as a heat sink for dissipating the heat produced by the electric circuit and the LEDs comprised in the first plate of dielectric material. Said second plate may be substantially flat and may comprise a first face and a second face; in order to promote the dissipation of the heat produced by the first plate, the second plate of electrically conductive material faces towards the first plate of dielectric material so as not to affect the light emission of the LEDs. For example, the first face of the second plate of electrically conductive material may face towards the second face of the first plate of dielectric material; in particular, the first face of the second plate of conductive material may overlap, being preferably in direct contact therewith, the second face of the first plate of dielectric material. Moreover, according to one aspect of the present invention, the second plate of electrically conductive material comprises an electric connection to the negative pole of one LED or of the LED module. The LED lighting device of the present invention further comprises a third plate of dielectric material; said third plate may be substantially flat and may comprise a first face and a second face. According to a further aspect of the present invention, the first face of the third plate of dielectric material may face towards the second face of the second plate of electrically conductive material. In particular, the first face of the third plate of dielectric material may overlap, being preferably in direct contact therewith, the second face of the second plate of electrically conductive material. In this way, the first, second and third plates are mutually overlapping (i.e. the second plate of electrically conductive material is interposed between the first and third plates). The first plate and the third plate may be made of the same type of dielectric material; alternatively, the first plate may be made of a first dielectric material, and the third plate may be made of a second dielectric material.

According to a further aspect of the present invention, the above-described LED lighting device may be comprised in a lighting apparatus for outdoor use (e.g. a street lighting apparatus). Said lighting apparatus for outdoor use may comprise a containment enclosure made of metallic material, a support made of metallic material and adapted to support the containment enclosure at a predetermined height, and a LED lighting device as previously described herein. The LED lighting device may be arranged within the containment enclosure so that the second face of the third plate of dielectric material faces towards a substantially flat portion of the containment enclosure; preferably, the second face of the third plate may be directly in contact with the surface of the containment enclosure. According to techniques known in the art, the support and the containment enclosure may be configured to ensure electric continuity between themselves.

In order to achieve the above-mentioned objects, the present invention provides a LED lighting device incorporating the features set out in the appended claims, which are an integral part of the present description. Further objects, features and advantages of the present invention will become apparent in the light of the following detailed description and of the annexed drawings, provided merely by way of non-limiting example, wherein:

- Figure 1 schematically shows a LED lighting device with a system capacitance (Cs);

- Figure 2 schematically shows a LED lighting device according to the present invention;

- Figure 3 schematically shows the electric circuit of a LED lighting device according to the present invention;

- Figure 4 schematically shows an exploded view of a LED lighting device according to the present invention.

Referring now to the annexed drawings, in Figure 1 reference numeral 100 designates as a whole a LED lighting device comprising a power supply unit 103, one or more light emitting diodes 105a, 105b and 105c electrically connected in series (also referred to as LED module 105a, 105b and 105c in the present description), and a system capacitance (Cs) 104. According to techniques known in the art, said system capacitance (Cs) 104 may be realized by means of a capacitive impedance electrically connected to the negative pole of the LED module 105a, 105b, 105c and to the containment enclosure 101 of the lighting device. Said containment enclosure

101 is usually a hollow body internally comprising a housing, consisting of a substantially flat surface, for the LED device. The containment enclosure 101 may comprise a support 102; the support 102 and the containment enclosure 101 may be configured in such a way as to ensure electric continuity between themselves. For example, the containment enclosure 101 may be installed on the support 102 in a manner such that the metallic parts of the support 102 will be directly in contact with the metallic parts of the containment enclosure; alternatively, the support 102 and the containment enclosure 101 may be inseparable and made as a one metallic body. Said support 102 may also be installed directly in contact with the ground or, alternatively, may comprise a grounding terminal 106; in both cases, the support

102 will be at the electric potential of the ground. In the absence of any overvoltages, this capacitive protection impedance will behave like an open circuit; in this case, the presence of the capacitive impedance will not affect by any means the normal operation of the power supply unit 103 and of the LED module 105a, 105b and 105c. Conversely, when an atmospheric overvoltage occurs, the impedance will decrease and will allow the lightning current to flow towards the external containment enclosure 101 of the lighting device 100 and then towards the support 102 that is at the electric potential of the ground; in this manner, the power supply unit 103 and the LED module 105a, 105b, 105c will be protected against the atmospheric overvoltage.

In Figure 2, reference numeral 200 schematically designates a LED lighting device according to one aspect of the present invention. The LED lighting device 200 comprises a substantially flat first plate 201 of dielectric material, in turn comprising an electric circuit 204 and a LED module 105a, 105b, 105c. As shown in Figure 2, the LED module 105a, 105b, 105c is so arranged as to emit light in a predefined direction; to this end, the LED module 105a, 105b, 105c is located on the surface of one of the two faces of the first plate. The LED lighting device 200 further comprises a substantially flat second plate 202 of electrically conductive material (e.g. aluminium). In the absence of any overvoltage, the main function of the second plate 202 is to dissipate the heat produced by the electric circuit 204 and by the LED module 105a, 105b, 105c. For this reason, the second plate 202 is disposed substantially parallel to that face of the first plate which does not carry the LED module 105a, 105b, 105c; in order to maximize heat dissipation, the second layer 202 of electrically conductive material may overlap the first layer 201, being preferably in direct contact therewith. The LED lighting device 200 may further comprise a containment enclosure 101 and a support 102. As previously described, said support 102 may be installed in direct contact with the ground or, alternatively, may comprise a grounding terminal 106; in both cases, the support 102 will be at the electric potential of the ground. The containment enclosure 101 and the support 102 are usually made of metallic materials characterized by high electric conductivity, and are configured to ensure electric continuity between themselves.

The basic idea of the present invention is to generate a system capacitance (C_s) for the LED lighting device 200 without the use of any additional electronic devices and without the need for high-precision soldering steps during the installation process. For this purpose, according to one aspect of the present invention, the second plate of electrically conductive material is configured in such a way as to behave, in combination with a portion of the containment enclosure 101, like a capacitor with parallel flat faces.

According to one aspect of the present invention, the second plate 202 is electrically connected to the negative pole of the LED module 105a, 105b, 105c. Moreover, in order to create a capacitor by means of the plate 202 and the containment enclosure 101, the LED lighting device 200 comprises a substantially flat third plate 203 of dielectric material. In this way, when the LED lighting device 200 is positioned in the housing of the containment enclosure 101, said third plate 203 is configured to face towards the second layer 202 of electrically conductive material, thus being interposed between the second layer 202 and the containment enclosure 101.

In this way, the second plate of electrically conductive material 202, the third plate of dielectric material 203 and the containment enclosure 101 form a capacitor (also referred to as composite capacitor in the present description) with substantially flat and substantially parallel faces, characterized by a system capacitance (C_s), operating in a way similar to above-described protection impedance. This means that in the absence of any overvoltage the composite capacitor will behave like an open circuit, so as not to impair the regular operation of the LED lighting device 200. Conversely, when an atmospheric overvoltage occurs, the composite capacitor will allow the lightning current to flow towards the external containment enclosure 101 of the lighting device 100 and then towards the support 102 that is at the electric potential of the ground; in this manner, the power supply unit 103 and the LED module 105a, 105b, 105c will be protected against the atmospheric overvoltage. In order to ensure sufficient protection against environmental overvoltages, the system capacitance (C_s) of the composite capacitor must be assessed appropriately. This operation can be carried out in accordance with techniques known in the art, by suitably adjusting at least one of the following parameters:

- area A of the second plate 202 of electrically conductive material;

- relative dielectric constant e_G (i.e. relative electric permittivity) of the dielectric material of the third plate 203;

- distance d between the second plate 202 and the containment enclosure 101. The dielectric material of the third plate 203 may be, for example, any one of the following:

- glass;

- thermally conductive insulating silicone (e.g. Sil-Pad®);

- polyester film, e.g. BoPET (biaxially-oriented polyethylene terephthalate,

Mylar®, Melinex®, and Hostaphan®);

- fiberglass;

- cellulose acetate.

As shown in Figure 3, according to a further aspect of the present invention, the circuit 204, which is comprised in the first plate 201 of dielectric material, may comprise an AC/DC converter 103 (also referred to as direct current or voltage power supply unit or, more simply, power supply unit) comprising a phase input 301, a neutral input 302, a positive direct voltage output 303 (i.e. the positive pole of the DC circuit) and a negative direct voltage output 304 (i.e. the negative pole of the DC circuit). Preferably, said AC/DC converter may be functionally connected to the circuit 204 via electric connections (e.g. electric wires), so that it can be located at any distance from the first plate 201. In order to supply power to at least one LED 105a or to a LED module 105a, 105b, 105c, the outputs 303 and 304 of the power supply unit 103 are electrically connected to the positive pole and the negative pole of a LED 105a or a LED module 105a, 105b, 105c. In order to ensure further protection against atmospheric overvoltages, the electric circuit 204 comprises also three varistors 305, 306, 307; as is known, a varistor is an electronic component for overvoltage protection which is comparable to a variable-resistance resistor. In particular, the resistance value of a varistor can be determined so as to decrease rapidly when the voltage across its terminals exceeds a given threshold value. The varistor 305 protects the power supply unit on the input side from overvoltages occurring across the phase input 301 and the neutral input; the varistor 306 protects the power supply unit on the input side from overvoltages occurring across the neutral input 302 and the negative pole of the DC system (for example, the varistor 306 may be connected to the second plate 202). The varistor 307 protects the power supply unit on the output side and the LED module 105a, 105b, 105c from induced overvoltages across the positive direct voltage output 303 of the power supply unit 103 (or the positive pole of the LED module 105a, 105b, 105c) and the negative pole of the DC system; to this end, the varistor 307 may be connected to the positive direct voltage output 303 of the power supply unit 103 and, even indirectly, to the grounding terminal (for example, the varistor 306 may be connected to the second plate 202).

Figure 4 shows an exploded view of an embodiment of the present invention. In particular, the first plate 201 comprises a first face 201a, in turn comprising an electric circuit 204 and a LED module 105a, 105b, 105c. The second plate 202 of electrically conductive material comprises a first face 202a and a second face 202b; the first face 202a faces the second face 201b of the first plate 201, overlapping it or being directly in contact with it. In this manner, the second plate of electrically conductive material is so arranged as not to affect the light emission of the LED module 105a, 105b, 105c. Finally, according to one aspect of the present invention, the LED lighting device 200 comprises a third plate of dielectric material interposed between the metallic plate 202 and the containment enclosure 101. Preferably, the first plate 201, the second plate 202, the third plate 203 and the area 101a of the containment enclosure 101 facing towards the third plate 203 may be substantially flat.

The LED lighting device described herein by way of example may be subject to many possible variations without departing from the novelty spirit of the inventive idea; it is also clear that in the practical implementation of the invention the illustrated details may have different shapes or be replaced with other technically equivalent elements. It can therefore be easily understood that the present invention is not limited to the above-described LED lighting device, but may be subject to many modifications, improvements or replacements of equivalent parts and elements without departing from the inventive idea, as clearly specified in the following claims.

* * * * * * * * *

Claims

1. LED lighting device (200), comprising: a first plate of dielectric material (201) comprising a first face (201a) and a second face (201b), said first plate (201) comprising at least one electric circuit (300) and at least one LED module (105a, 105b, 105c) located on the first face (201a) of the first plate (201), said at least one LED module (105a, 105b, 105c) comprising a positive pole and a negative pole; a second plate of electrically conductive material (202) comprising a first face (202a) and a second face (202b), said second plate (202) being electrically connected to the negative pole of said at least one LED module (105a, 105b, 105c), said first face (202a) of the second plate (202) facing, at least partly, towards the second face (201b) of the first plate (201); said LED lighting device (100, 200) being characterized in that it further comprises a third plate (203) of dielectric material facing, at least partly, towards the second face (202b) of the second plate (202).

2. LED hghting device (200) according to claim 1, wherein said first plate is made of a first dielectric material and said third plate is made of a second dielectric material.

3. LED lighting device (200) according to each one of the preceding claims, wherein said first plate (201), said second plate (202), and said third plate (203) are, at least partly, overlapping.

4. LED lighting device (200) according to each one of the preceding claims, wherein the second face (201b) of the first plate (201) is directly in contact with the first face (202a) of the second plate (202), and wherein said third plate (203) is directly in contact with the second face (202b) of the second plate (202).

5. LED lighting device (200) according to each one of the preceding claims, further comprising a containment enclosure (101) made of electrically conductive material, said containment enclosure comprising a substantially flat area (101a) facing towards the third plate (203) of dielectric material, said containment enclosure (101) being so arranged as to form a system capacitance (104) in combination with said second plate of conductive material (202).

6. LED lighting device (200) according to claim 5, wherein the third plate (203) of dielectric material is anchored to the containment enclosure (101).

7. LED lighting device (200) according to claims 5 or 6, wherein said containment enclosure (101) further comprises a support (102) made of electrically conductive material, said support (102) being in electric continuity with said containment enclosure (101).

8. LED lighting device (200) according to each one of the preceding claims, wherein said electric circuit (204) comprises: a direct current power supply unit (103) adapted to supply power to said at least one LED module (105a, 105b, 105c), said power supply unit (103) comprising: a first phase input (301); a second neutral input (302); a first positive direct voltage output (303); a second negative direct voltage output (304); a first varistor (305) adapted to connect said first phase input (301) to said second neutral input (302); a second varistor (306) connected to said second neutral input (302) and said second plate of conductive material (202); a third varistor (307) connected to said first positive direct voltage output (303) and said second plate of conductive material (202).

9. Lighting apparatus for outdoor use, comprising a LED lighting device (200) according to each one of claims 1-8.