ESD Protection for Chip-Scale Packaged LEDs

Abstract

The present invention relates to a lighting device for coupling to an LED driver, the lighting device including a plurality of series connected LEDs arranged to form an LED string having a first end and a second end, a heat sink thermally coupled to the LED string, the heat sink being electrically conductive, a capacitor coupled between the first end of the LED string and the heat sink, and an electrical connection between the second end of the LED string and the heat sink.

Description

[Technical field]

[0001] The present invention relates to a lighting device.The present invention further relates to a lighting system. [Background technology]

[0002] Humans are very good charge generators, because they are insulators and touch many surfaces, generating static energy. By walking, humans generate static electricity, which slowly discharges to the ground. If a person carrying static electricity touches an electrical component, there is a great risk that the static electricity, i.e. the static charge, will be discharged to the electrical component, damaging or destroying it. This phenomenon is well known as electrostatic discharge (ESD).

[0003] According to the literature, the human body has an electrical equivalent circuit with a resistance of 1500Ω and a capacitance of 150pF. An ESD event can generate a lot of energy with high voltage and high current. If ESD damages the LED on the LED board, it becomes very difficult to estimate the lifespan of the LED board. ESD will weaken up the LED board and affect its reliability.

[0004] Most Chip Scale Package (CSP) LED boards do not have ESD protection.

[0005] Due to the lack of ESD protection or even if there is ESD protection, an additional risk of CSP LEDs is their susceptibility to surges. These surges occur, for example, when a large load is switched on or off in the mains grid. Surge is a representation of voltage and current that occurs for a very short time with high amplitudes in the range of 10 kV and 1 kA. Surge can last for example between 2.5 μs and 20 μs and contains a lot of energy in this short time. Surge also appears at the input of the LED driver that supplies power to the LED board. If there is no or insufficient surge protection provided by the LED driver, the surge can reach the LED board and damage the LEDs on the LED board by discharging the surge energy to the LED or the LED board.

[0006] It is desirable to prevent damage to LEDs from ESD and surges. Summary of the Invention [Problem to be solved by the invention]

[0007] It is an object of the present invention to provide a lighting device which is more resistant to surges and ESD. [Means for solving the problem]

[0008] To overcome this problem, in a first aspect of the present invention, there is provided an illumination device comprising: a plurality of series connected LEDs arranged to form an LED string having a first end and a second end; a heat sink thermally coupled to the LED string, the heat sink being electrically conductive; a capacitor coupled between the first end of the LED string and the heat sink; an electrical connection between the second end of the LED string and the heat sink; Includes.

[0009] By coupling both ends of the LED string to a conductive heat sink, the surge is returned to the source of the surge through a parasitic capacitive path from the LEDs through the heat sink. Since the heat sink is conductive and both ends of the LED string are coupled to it, it is not possible to directly couple both ends to the heat sink. One end of the LED string may be electrically coupled directly to the heat sink while the other end may be electrically coupled to the heat sink through a capacitor. If a surge reaches the LED string, for example through the LED driver, the surge is diverted directly to the heat sink through a capacitor or a direct connection and returns to the source of the surge. More details on this subject will be provided in the detailed description.

[0010] In a further example, the lighting device includes a printed circuit board (PCB), and the LED string and the capacitor are mounted on the PCB.

[0011] Preferably, the LEDs and the capacitors are mounted on a PCB. Preferably, the LEDs are chip-scale package (CSP) type LEDs, since these can be very well integrated on the PCB. Preferably, the capacitors are surface mounted device (SMD) capacitors, which may be made, for example, of ceramic. The use of a PCB for mounting the LEDs and the capacitors provides a robust and easy to make LED substrate that can be easily coupled to an LED driver.

[0012] In a further example, the LED string and capacitor are provided on one side of the PCB and the heat sink is provided on another side of the PCB.

[0013] A simple design for the lighting device is to have all the components on a single side of the PCB. The other side of the PCB can be used to include or be coupled to a heat sink. An example of such a heat sink is a conductive layer or copper plane on the PCB that can be placed on the other side of the heat sink. This plane can cover the entire other side of the PCB. Alternatively, this plane can have small interruptions while being electrically connected as a whole to prevent or reduce eddy currents flowing through this plane. Alternatively, the plane can be placed only under the heat source, which in this example is the LED. This could be, for example, that there is a plane under each LED, but each plane would be interconnected to provide a single electrically connected plane.

[0014] In a further example, the lighting device includes an electrical insulating and thermally conductive layer adapted to be coupled to the heat sink and to be coupled to the housing. To provide an optimal thermal path, it is preferable to thermally couple the LED to the housing so that the heat can be optimally transferred to the surroundings. Due to the different voltage levels and the fact that it is not good for the housing itself to have a voltage for human safety, electrical insulation needs to be provided between the heat sink, which can be directly coupled to one of the first or second ends of the LED string and therefore has this potential difference, and the housing. Equally important, this electric insulator needs to be able to provide good thermal coupling between the heat sink and the housing. This electrical insulation and good thermal coupling can be provided by a gap pad or a ceramic material. The gap pad is a soft material with good electrical insulation parameters and good thermal conductivity parameters.

[0015] In a further example, the electrical connection between the first end of the LED string and the heat sink includes a via from the first end of the LED string to the heat sink.

[0016] When the LEDs and capacitors are on one side of the PCB and the heat sink is on the other side of the PCB, the best way to transfer heat through the PCB is to use one or more vias. Preferably, more vias are used to optimize the heat transfer. These vias are called thermal vias. The vias are used to electrically connect the second end of the LED string and the heat sink. Therefore, the vias provide both electrical and thermal coupling between the second end and the heat sink.

[0017] In a further example, the capacitor is electrically coupled to the heat sink using vias.

[0018] The use of vias to electrically couple the capacitor to the heat sink is preferred as this connection provides the most optimal electrical connection as it is the shortest possible connection with as few parasitic effects as possible.

[0019] In a further example, the PCB is a ceramic PCB.

[0020] The use of ceramic PCBs brings further advantages. Ceramic PCBs are electrically insulating and have excellent thermal conductivity. As a result, fewer vias are required, since they need to provide at least electrical conductivity, but not thermal conductivity. Another advantage of using ceramics in PCBs is that the entire PCB can be used to spread heat across the surface of the PCB, and therefore also across the surface of the heat sink. This means that the LEDs acting as thermal hotspots have improved heat distribution across the PCB. In fact, the ceramic PCB and heat sink as a whole can be used to dissipate heat to the environment. This allows the PCB and heat sink not to be thermally connected to the housing, i.e., the heat sink can be disconnected from the housing.

[0021] In a further example, the heat sink is a single entity positioned to be thermally coupled to all LEDs of the plurality of LEDs.

[0022] Preferably the heat sink is a single copper plane that covers the other side of the PCB, i.e. the side without any components. In this way the heat sink is easy to make.

[0023] In a further example, the lighting device includes an additional capacitor and the heat sink is coupled to the ground return path via the additional capacitor.

[0024] If the heat sink is directly coupled to the ground return path with an additional capacitor, the surge or ESD will have a dedicated path for the current to flow. This provides more certainty as to how the current will flow compared to using parasitic capacitance from the surroundings, especially if there is no other path back to ground, i.e. there is no housing providing a path to ground.

[0025] In a further example, the heat sink includes a copper plane.

[0026] A copper plane is very easy to put on one side of a PCB.

[0027] In another example, a lighting system is provided that includes a lighting device and an LED driver for providing a regulated current to the lighting device.

[0028] Lighting systems such as lamps or luminaires benefit from protection against surges. Usually, the LED driver is directly connected to the power supply, where surges may occur. This LED driver may not be well protected against surges, because it may be designed to be small and cheap. According to the present invention, the LEDs of the lighting device are protected against surges, because the surges are bypassed from the LEDs. Furthermore, the LEDs are also better protected against ESD.

[0029] In another example, the LED driver is arranged to provide galvanic isolation between an input of the LED driver and an output of the LED driver, the output of the LED driver is coupled to the LED string, the input of the LED driver is coupled to a mains voltage supply, and the LED driver includes an isolation capacitor placed across the galvanic isolation.

[0030] The driver can be used to provide galvanic isolation. The lighting device is galvanically isolated from the power input. This allows the lighting device to be operated, for example, at safety extra-low voltage (SELV). This allows the user to touch the LED without the risk of receiving an electric shock. By touching the LED, the user introduces an ESD risk, which is reduced by the present invention. Typically, a Y-capacitor is placed across the galvanic isolation to reduce electromagnetic interference (EMI) generated by the LED driver. This capacitor allows a surge to cross the galvanic isolation barrier and damage the LED. By implementing the present invention, this surge bypasses the LED.

[0031] In another example, the lighting system includes a housing, which can be used to provide a total encapsulation of the LED driver and lighting device.

[0032] In another example, the housing is a conductive housing and the housing is coupled to ground.

[0033] A conductive housing, such as a metal housing, can be used to provide enclosure for the driver and lighting device, while also providing thermal benefits since metal is a good thermal conductor, and to provide human safety, the conductive housing is bonded to a protective earth. [Brief description of the drawings]

[0034] Examples of the present invention will now be described with reference to the accompanying drawings. [Figure 1] FIG. 1 shows an example of a conventional lighting system. [Diagram 2]Figures 2a, 2b and 2c show an example of a surge flowing through a lighting device. [Diagram 3] FIG. 3 shows an example of a layout of a lighting device according to the present invention. [Figure 4] FIG. 4 shows another example of a layout of a lighting device according to the invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0035] The present invention will now be described with reference to the figures.

[0036] It should be understood that the detailed description and specific examples, while indicating exemplary embodiments of the devices, systems and methods, are for purposes of illustration only and are not intended to limit the scope of the invention. These and other features, aspects and advantages of the devices and systems of the present invention will become better understood from the following description, the appended claims and the accompanying drawings. It should also be understood that the drawings are merely schematic and are not drawn to scale. It should also be understood that the same reference numerals are used to denote the same or similar parts throughout the drawings.

[0037] FIG. 1 shows an example of a commonly used lighting system. In FIG. 1, an LED driver 1 is used to provide regulated power to a lighting device 2. The driver is coupled to a power supply at its input. The power supply can be, for example, 230V 50Hz or 120V 60Hz. The LED driver 1 converts this power supply voltage to a desired output voltage and current so that the lighting device 2 provides a desired light output. The desired light output can be set by a user or can be pre-configured in the LED driver. The lighting device 2 comprises a number of LEDs coupled in a series configuration. These LEDs form an LED string 3. The LED string 3 has a first end 4 and a second end 5 at which the lighting device 2 is electrically coupled to the LED driver 1. The first end 4 is not electrically coupled to a heat sink 6. The second end 5 is coupled to the heat sink 6 via a parasitic capacitor Cpar. This circuit provides a very low grade of protection from surges or ESD.

[0038] A surge occurs at the power supply input. This can happen, for example, when a large load, such as an electric machine, a refrigerator or a washing machine, suddenly switches on or off. A large voltage and current spike is applied to the input of the LED driver 1. The LED driver 1 transfers this surge voltage to its output. This can happen in several ways. The surge can be supplied in differential mode or common mode. In a differential mode surge, the surge occurs between the line and neutral. In a common mode surge, the surge occurs between either the line or neutral and the protective earth, i.e. ground. In both situations, the surge is supplied either to the first end 4 or to the second end 5, and thus to the LEDs. In a differential mode surge situation, the surge flows from the first end 4 to the second end 5 or vice versa. In a common mode surge situation, the surge flows from either the first end 4 or to the second end 5 to the protective earth. Since the LED string 3 itself does not have a protective earth connection, the surge must find another path to the protective earth, which can be through the heat sink 6 as this acts as the largest available parasitic capacitance to the protective earth.

[0039] The first end 4 is coupled to the heat sink 6 through the first LED of the LED string 3. This means that a surge coming from the first end 4 will always flow through the first LED of the LED string 3. This will lead to damage to the first LED, even destruction of the first LED.

[0040] The second end 5 is only coupled to the heat sink 6 via a parasitic capacitance Cpar. However, this capacitance is insufficient to provide a low enough impedance to allow the entire surge to flow through the parasitic capacitance Cpar. This results in a portion of the surge flowing to the last LED of the LED string 3. This means that the surge coming from the second end 5 always flows through the last LED of the LED string 3. This leads to damage to the last LED, even destruction of the last LED.

[0041] ESD has similar behavior with respect to surges, but there is a big difference in where the source is located. A human body touching the lighting device 2 acts as the source. The human body can touch anywhere on the lighting device 2. Therefore, multiple current paths may be possible. Each ESD will discharge towards the heat sink 6, as each current path is directed towards the protective earth. It is therefore important that the LEDs are bypassed in any situation. In the example provided in FIG. 1, the first end 4 is only connected to the heat sink 6 via the top LED, which poses a risk of ESD damage at least to the top LED.

[0042] It is therefore desirable for lighting systems to be better protected against surges and ESD.

[0043] In figures 2a, 2b and 2c an example of a lighting device 2 according to the invention is shown and its functionality is explained.

[0044] The lighting device 2 comprises an LED string 3. In this example, six LEDs are coupled in series. It should be understood that any number of LEDs can be coupled in series. Furthermore, additional LEDs can be placed in parallel with the LED string 3 such that multiple LED strings can be formed or a single LED string 3 can have multiple parallel LEDs coupled in series.

[0045] The lighting device 2 may be coupled to an LED driver 1. A first end 4 may be used to connect a first output of the LED driver 1 to an input of the lighting device 2, i.e. the anode of the first LED of the LED string 3. A second end 5 may be used to connect a second output of the LED driver 1 to an output of the lighting device 2, i.e. the return side, i.e. the cathode of the last LED of the LED string 3. The LEDs may be mounted on a printed circuit board (PCB). This PCB may be an electrically non-conductive PCB. This PCB provides a platform for mounting the LEDs, capacitors and interconnects. LEDs consume a relatively large amount of power on a small surface. This means that a large amount of heat is generated that needs to be removed. For this purpose a heat sink 6 is used. The heat sink 6 is thermally and electrically conductive. In this example, the LEDs of the LED string 3 are mounted on one side of the PCB. The heat sink 6 is mounted on the other side of the PCB. A heat sink 6 may be arranged facing all the LEDs, for example on the other side of the PCB, to provide a heat sinking effect for all the LEDs. As in the lighting system of FIG. 1, there is a parasitic capacitive coupling between each LED and the heat sink 6. Each parasitic capacitance associated with this parasitic coupling is represented as a capacitance from the cathode of each LED to the heat sink 6. In this example, the parasitic capacitance is created by the pads (thermal or electrical connection pads) of the LEDs and the heat sink 6, which act as electrodes of the parasitic capacitance. The PCB is between the pads and the heat sink 6, and therefore acts as a dielectric for the parasitic capacitance. It is understood that the configurations can be slightly different but have the same effect. If a metal core printed circuit board (MCPCB) is used, the LEDs need to be electrically isolated from the MCPCB to avoid short circuits. An isolator for isolating the LEDs from the MCPCB acts as a dielectric for the parasitic capacitance.Similar to the situation in non-metal core PCBs, the pads and, in this case, the MCPCB, the heat sink 6 act as electrodes of the parasitic capacitance.

[0046] The heat sink 6 may be coupled to a housing 7, which may be electrically and thermally conductive. Due to the good thermal coupling between the LEDs and the housing 7, the heat generated by the LEDs can be transferred very efficiently to the surroundings.

[0047] During normal operation of the lighting system, the parasitic capacitance is harmless with regard to the safety of the LEDs, however in the event of a surge or electrostatic discharge (ESD) the situation is different and there is a risk of damaging the LEDs.

[0048] In Fig. 2a, a common mode surge is shown originating from the second end 5 and flowing through the heat sink 6 to ground. The surge will flow through the last parasitic capacitance, shown as the lowest parasitic capacitance in Fig. 2a. If this capacitance value is too low, as is the case in this example since the capacitance is a parasitic capacitance in the pF range, the current will also flow through the last LED and the parasitic capacitance at the anode of the last LED. The last LED will be damaged in the process by the surge, or at least a part of the surge, flowing backwards through the last LED.

[0049] To prevent a surge from the second end 5 to the heat sink 6 from damaging at least the last LED, a capacitor C byp is disposed between the second end 5 and the heat sink 6. This capacitance C byp provides enough capacitance to provide a low impedance path for the surge to flow to the heat sink 6 without flowing through any of the LEDs.

[0050] In this situation, it is assumed that the heat sink 6 itself provides enough parasitic capacitance to ground to provide a path for the surge to flow from the heat sink 6 to ground.

[0051] If the heat sink 6 is thermally coupled to the housing 7, the surge will flow from the heat sink 6 through a parasitic capacitive coupling to the housing 7 and ground. The housing 7 may be electrically coupled to ground to provide a low impedance path to ground.

[0052] Alternatively, instead of or together with the housing 7, a further capacitor C gnd can be coupled between the heat sink 6 and ground. In many situations, the LED driver 1 is powered by a supply voltage. The supply voltage is provided via the Line and Neutral inputs. In addition to these two inputs, an additional input may be provided, namely ground. Ground is sometimes also called Protective Earth, PE or Earth. The purpose of the ground connection is to electrically connect an otherwise floating metal part or surface to ground, so that a user is protected from electric shock if he touches the metal part or surface.

[0053] The ground connection can be provided to the lighting device 2 via the LED driver 1. In this case, a capacitive connection is provided via an additional capacitor C gnd A ground input can be established between the heat sink 6 using a ground terminal. This may not be sufficient to protect the user from an electric shock if touching the heat sink 6, but it does protect the LEDs from surges and ESD. To protect the user from an electric shock from the heat sink 6, a housing 7 can be provided that is electrically connected directly to ground. This electrical connection can be established by the same ground input as provided by the LED driver 1.

[0054] Figure 2b shows a lighting device 2 similar to Figure 2a. In Figure 2b, a common mode surge flows from the first end 4 to the heat sink 6. By electrically coupling the first end 4 to the heat sink 6, the surge bypasses the LEDs and flows directly to the heat sink 6. From there, the surge returns to ground, either directly or indirectly.

[0055] The surges depicted in Figures 2a and 2b are depicted as common mode surges that must return to ground.

[0056] In figure 2c a lighting device 2 is shown, which is similar to the lighting device of figures 2a and 2b. A surge occurs from the first end 4 to the second end 5 or vice versa.

[0057] The direct electrical connection of the first end 4 to the heat sink 6 and the capacitive connection of the second end 5 to the heat sink 6 provide a shunt path for high frequency currents such as surges. In fact, the LED string 3 is bypassed through the heat sink 6 when a transient such as a surge or ESD approaches the LEDs.

[0058] The use of a direct connection between the first end 4 and the heat sink 6 and a capacitive connection between the second end 5 and the heat sink 6 protects the LED string 3 from common mode and differential mode surges.

[0059] This circuit also improves the protection of the LEDs against ESD. ESD can occur if a user touches any of the LEDs anywhere in the LED string 3. ESD attempts to discharge the charge from the human body touching the LED to ground. This can occur even if the lighting device 2 is not connected to the LED driver 1. ESD follows the same discharge path as surges. If a user touches the first end 4 or the second end 5, the ESD is bypassed from the LED string 3 to the heat sink 6.

[0060] In FIG. 3, an example of a lighting device 2 according to the invention is shown. A side view of the lighting device 2 is shown, with LEDs mounted on a PCB. The LED string 3 is depicted as three LEDs coupled in series, with the first LED shown on the left and the last LED shown on the right. The LEDs are coupled together using a copper plane, which is provided on a first side of the PCB. The first end 4 is represented as a copper plane on the left, where an interconnection to the LED driver 1 can be made. The second end 5 is represented as a copper plane on the right, where another interconnection to the LED driver 1 can be made. The PCB can be made of any commonly used material. The material can be any of the following non-limiting list of examples: FR4, film substrate material for flexible PCBs, metal or ceramic. Preferably, the LEDs are covered with a coating 10 that prevents ESD from occurring at the LED itself. Still, ESD can occur at the first end 4 or the second end 5.

[0061] The use of ceramic PCBs, like the use of metal core PCBs, has the advantage that the PCB itself can act as a heat spreader due to its good thermal conductivity. In contrast to MCPCBs, ceramic is an electrically non-conductive material and therefore does not provide a plane for parasitic capacitance to the surroundings and therefore does not provide a ground. Furthermore, the LEDs and bypass capacitors C byp Components such as the LED and bypass capacitor C can be mounted directly on the ceramic PCB without the need for electrical insulators. This significantly improves the radiated EMI performance of the lighting device 2 compared to the MCPCB. bypis placed on one side of the PCB. On the other side of the ceramic PCB, a heat sink 6 is provided. The heat sink 6 does not need to be volumetric, since the ceramic PCB already provides good thermal spreading and conductance. A copper plane on the other side of the ceramic PCB may already be sufficient, but any other heat sink is also possible. A single copper plane may cover the whole other side of the ceramic PCB, but smaller planes are also possible to save on the amount of copper used. This copper plane, which also acts as a heat sink 6, is electrically coupled to the first end 4 and is connected to a bypass capacitor C. byp 3. The ceramic PCB is capacitively coupled to the second end 5 via a thermally coupled connector 6. Preferably, the ceramic PCB is decoupled from the housing 7, i.e. is not thermally coupled to the housing 7. This further reduces the parasitic coupling of the lighting device 2 to the environment and further improves the radiated EMI.

[0062] Preferably, the first end 4 is electrically coupled to the heat sink 6 using a via. The via is an interconnection through the PCB from the layer on which the first end 4 is located, in this example the first side of the PCB, to the heat sink. The via may also be a metallized through hole connection that electrically connects the first end 4 and the heat sink 6 directly. In the illustrated example, the bypass capacitor C byp is shown as an SMD capacitor on the same side as the LED. byp It will be apparent to those skilled in the art that the bypass capacitor C can be placed elsewhere. In this example, the bypass capacitor can be electrically coupled to the cathode of the last LED using a copper plane or trace. bypThe other end of the PCB can be coupled to a heat sink 6 using vias. Additional thermal vias can be used to improve the thermal coupling between both ends of the PCB. Depending on where these thermal vias are coupled, for example to the node between the first and second LEDs in the LED string 3, electrical insulation may be required between the thermal vias and the heat sink 6, since in this example the heat sink 6 is at the same potential as the first end 4. Using a ceramic PCB may omit the need for thermal vias due to the good thermal properties of ceramic materials.

[0063] The heat sink 6 may be thermally coupled to the housing 7 using a thermal pad 8. This thermal gap pad can be any material that can be used to provide a solid thermal connection between the heat sink 6 and the housing 7, such as, but not limited to, thermal paste, thermal tape, or gap filler.

[0064] The housing 7 is preferably electrically coupled to ground so that the housing is set to a safe potential.

[0065] FIG. 4 provides a detailed example of the present invention. A lighting device 2 is provided with an LED string 3 with three LEDs in series, which is provided on one side of a PCB. Furthermore, a first end 4 and a second end 5 are also provided on the same side of the PCB. The PCB may be made of ceramic, which provides good thermal contact to a heat sink 6. The LED string 3 is provided on one side and can be replaceable, which allows a user to select a desired PCB with a desired number of LEDs. The heat sink 6 may be a conductive plane, for example a copper plane. The heat sink 6 is coupled to a housing 7 by means of a thermal pad 8. The combination of the heat sink 6, the thermal pad 8 and the housing 7 can be an independent entity on which a PCB with the LED string 3 can be provided. The heat sink 6 protects the gap pad 8 from being damaged when the PCB is provided to the heat sink 6. If the heat sink 6 can be made flexible, the thermal coupling between the PCB and the heat sink can be optimized, i.e., air gaps are prevented or reduced.

[0066] In the example of Fig. 4, the connection between the first end 4 and the heat sink 6 is not made by a via. The connection is made by a wire or a bonding wire, which can be attached when the PCB is mounted to the heat sink 6. The bypass capacitor C byp is in this example a separate capacitor provided between the second end 5 and the heat sink 6. Again, a wire or bond wire is used to connect the bypass capacitor C byp to the second end 5 and to the heat sink 6.

[0067] In the example provided, the first end 4 is represented as a top connection between the LED driver 1 and the lighting device 2, and the second end 5 is represented as a bottom connection between the LED driver 1 and the lighting device 2. It should be understood that the first end 4 can be represented as a bottom connection between the LED driver 1 and the lighting device 2, and the second end 5 can be represented as a top connection between the LED driver 1 and the lighting device 2. This means, for example, that the capacitor C1 can be placed at the bottom end or at the top end.

[0068] The terms one side and the other side of a PCB refer to a PCB having only two sides. It should be understood that a PCB can have multiple layers, resulting in more than two sides. In the case of multiple layers, it is clear from the description that one side is a different layer than the other side.

[0069] In the examples provided, the first conductive element 6 is illustrated as a heat sink and the second conductive element 7 is illustrated as a housing. It should be understood that these should be considered as non-limiting examples and are used in the examples only for clarity. The heat sink is an example of a first conductive element 6. The first conductive element 6 may be, for example, an intermediate layer of conductive material. The housing is an example of a second conductive element 7. The second conductive element 7 may be, for example, a heat sink, preferably combined with an intermediate layer of conductive material.

[0070] Preferably, the first conductive element 6 is electrically isolated from the second conductive element 7 and / or from ground. Preferably, the second conductive element 7 is electrically coupled to ground.

[0071] Other variations to the disclosed embodiments can be understood by those skilled in the art, upon study of the drawings, the disclosure, and the appended claims, and can be implemented in practicing the claimed invention. In the claims, the word "comprise" does not exclude other elements or steps, and the indefinite articles "a" or "an" do not exclude a plurality. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage. Any reference signs in the claims should not be interpreted as limiting the scope.

Claims

1. 1. A lighting device for coupling to an LED driver, the lighting device comprising: a plurality of series connected LEDs arranged to form an LED string having a first end and a second end electrically coupled to the LED driver; a first conductive element thermally coupled to the LED string, the first conductive element being electrically isolated from ground; a second conductive element electrically coupled to ground and thermally coupled to the first conductive element; an electrical connection between the first end of the LED string and the first conductive element; a capacitor coupled between the second end of the LED string and the first conductive element; 13. A lighting device comprising:

2. 10. The lighting device of claim 1, wherein the lighting device includes a printed circuit board (PCB), and the LED string and the capacitor are mounted on the PCB.

3. 3. The lighting device of claim 2, wherein the LED string and the capacitor are provided on one side of the PCB and the first conductive element is provided on another side of the PCB.

4. 2. The lighting device of claim 1, wherein an electrical connection between the first end of the LED string and the first conductive element comprises a via from the first end of the LED string to the first conductive element.

5. The lighting device of claim 2 , wherein the capacitor is electrically coupled to the first conductive element using a via.

6. The lighting device of claim 2 , wherein the PCB is a ceramic PCB.

7. The lighting device of claim 1 , wherein the first conductive element is electrically decoupled from the second conductive element.

8. 10. The lighting device of claim 1, wherein the first conductive element is a single entity positioned to be thermally coupled to all LEDs of the LED string.

9. 10. The lighting device of claim 1, wherein the lighting device includes a further capacitor, and the first conductive element is coupled to a ground return path via the further capacitor.

10. The lighting device of claim 2 , wherein the first conductive element comprises a copper plane.

11. The lighting device according to claim 1 ; an LED driver for providing a regulated current to the lighting device; 2. A lighting system comprising:

12. 12. The lighting system of claim 11, wherein the LED driver is arranged to provide galvanic isolation between an input of the LED driver and an output of the LED driver, the output of the LED driver being coupled to the LED string and the input of the LED driver being coupled to a source of power supply voltage, the LED driver including an isolation capacitor disposed across the galvanic isolation.

13. The lighting system of claim 11 , wherein the second conductive element is a housing.

14. The lighting system of claim 13 , wherein the housing is coupled to ground.

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