Touch current prevention by flying y-cap

Abstract

The invention relates to a driver for driving a load. The driver comprises a primary side comprising a first input and a second input adapted to be coupled to a Line and a Neutral for receiving an input voltage, between the Line and Neutral, from a power source, a rectifier for rectifying the input voltage into a rectified input voltage, wherein the rectified input voltage is present at a first rectifier output and a second rectifier output, a switching circuit comprising a first switch and a second switch coupled in series and coupled between the first rectifier output and the second rectifier output, wherein a first node is at the interconnection of the first switch and the second switch, a secondary side comprising an output for providing an output voltage to the load, wherein the primary side and the secondary side are galvanically isolated from each other, a switched mode power converter for converting the rectified input voltage into the output voltage. The switched mode power converter comprises a transformer coupled between the primary side and the secondary side, a capacitor, wherein one end of the capacitor is coupled to the first node and another end of the capacitor is coupled to a further node at the secondary side. The driver comprises a controller for controlling the switching circuit, wherein the controller is arranged to control the switching circuit to close the first switch and open the second switch when the input voltage is negative, open the first switch and close the second switch when the input voltage is positive.

Description

[0001] Touch current prevention by flying Y-cap

[0002] FIELD OF THE INVENTION

[0003] The invention relates to a driver for driving a load. The invention further relates to a system.

[0004] BACKGROUND OF THE INVENTION

[0005] A load may be driven or powered by a driver. The driver provides a regulated power to the load. The load receives the required power for performing a desired operation e.g., emitting light. The load however will always convert some of the received power into heat. This heat needs to be removed in order for the load not to overheat. A heatsink is used for this purpose. The heatsink allows heat to be passed from the load to a location where the heat can be removed. This may be done by e.g., an airflow or water-cooling. The heatsink is therefore made of a thermally good conductive material. Such a material may be for example a metal such as aluminum or copper. Such material is however also electrically conductive and may pose a safety hazard. The heatsink is therefore normally coupled to a Protective Earth, PE, to provide additional human safety. The heatsink is electrically isolated from the load and therefore, a parasitic capacitance is formed between the load and the heatsink. The heatsink is also coupled to PE via a parasitic capacitance, or directly coupled to PE when a PE connection is present. The driver itself may also be placed in a metal housing, similarly, causing a parasitic capacitive coupling to PE or direct coupling to PE to be present. In any situation, a leakage current, or touch current, will flow from the input of the driver to the PE, resulting in undesired leakage currents. The leakage current does not necessarily have to result in a safety hazard, but too much leakage current will cause the circuit breaker to disengage and cause the system to fail. It is desired to provide a driver that will reduce the amount of leakage current to PE.

[0006] SUMMARY OF THE INVENTION

[0007] It is an objective of the invention to provide a driver that prevents or at least reduces the leakage current. To overcome this concern, in a first aspect of the invention, a driver is provided. The driver comprises: a primary side comprising: a first input and a second input adapted to be coupled to a Line and Neutral for receiving an input voltage, between the Line and Neutral, from a power source; a rectifier for rectifying the input voltage into a rectified input voltage, wherein the rectified input voltage is present at a first rectifier output and a second rectifier output, and a switching circuit comprising a first switch and a second switch coupled in series and coupled between the first rectifier output and the second rectifier output, wherein a first node is at the interconnection of the first switch and the second switch; a secondary side comprising an output for providing an output voltage to the load, wherein the primary side and the secondary side are galvanically isolated from each other; a switched mode power converter for converting the rectified input voltage into the output voltage; the switched mode power converter comprising: a transformer coupled between the primary side and the secondary side. a capacitor, wherein one end of the capacitor is coupled to the first node and another end of the capacitor is coupled to a further node at the secondary side; a controller for controlling the switching circuit, wherein the controller is arranged to control the switching circuit to: close the first switch and open the second switch when the input voltage is negative; open the first switch and close the second switch when the input voltage is positive.

[0008] The driver as proposed is used for driving a load while also providing a galvanic isolation between the input and the output. The galvanic isolation is present between a primary side and a secondary side of the driver. At the primary side, the driver receives an input voltage from e.g., mains. A first and second input may be provided to be coupled to a Line and Neutral of the input voltage. A rectifier rectifies the input voltage into a rectified input voltage. The driver has a switched mode power converter that converts the rectified input voltage into an output voltage that can be provided to the load. The switched mode power converter uses a transformer for the voltage conversion. The transformer is located across the galvanic isolation and provides energy transfer from the primary side to the secondary side. To provide a conducive path for high frequency disturbances generated at the primary side but reflected on the secondary side, a capacitor is placed across the galvanic isolation. This capacitor reduces the EMI generated by the switched mode power converter, but this however also causes an undesired low frequency current flowing from the Line or Neutral to any protective earth, PE, in the system. The capacitor is namely coupled with the PE via parasitic capacitances. The parasitic capacitance may be present for several reasons. As an example, the driver may be encased in a metal housing that is coupled to the PE for safety reasons. The parasitic capacitance then occurs between the driver and the housing. The parasitic capacitance is then present between the capacitors secondary side connection and PE. Alternatively, or additionally, the load may also be coupled to e.g., a metal heatsink also providing a parasitic coupling between the driver and the PE. The parasitic capacitance is then also present between the capacitors secondary side connection and PE. This interaction between the capacitor and the parasitic capacitance provide an undesired current path, that will cause an increase in current flowing through PE. If too much current flows through PE, the circuit breaker may become active, which is clearly undesired. This will be explained in more detail later on. The driver has an additional switching circuit that is configured to allow the capacitor to perform the EMI reduction, while keeping the current flow through the PE as low as possible. The switching circuit has a first switch and a second switch coupled in series between the first rectifier output and the second rectifier output. A first node is identified in between the interconnection of the first switch and second switch, The capacitor is coupled on one end to this first node. As mentioned before, the capacitor is also coupled on the other end to a further node present at the secondary side. By controlling the switching circuit in a specific way, the path for the touch current can be removed while the current path for the high frequency current to reduce the EMI can be maintained. The switches in the switching circuit are controlled such that the voltage that generates the touch current is kept as low as possible across the capacitor such that no or a very small touch current will flow through the capacitor. The polarity of the mains voltage i.e., the voltage between the Line and Neutral, determines which of the switches is closed and which is open. When the voltage between Line and Neutral is negative, the voltage at the Neutral is higher than the voltage at the Line, the first switch is closed and the second switch is opened. This results in a current loop provided from Neutral back to Neutral through the driver via the closed first switch and one of the diodes of the rectifier, effectively resulting in a very low voltage across the capacitor in the touch current path. Furthermore, the current path between the Neutral and the Line is blocked by opening the second switch. As long as one of the switches is closed, the high frequency current path is maintained allowing the main function of the capacitor, EMI reduction, to be still performed.

[0009] When the voltage between Line and Neutral is positive, the voltage at the Line is higher than the voltage at the Neutral, the first switch is open and the second switch is closed. This results in a current loop provided from Neutral back to Neutral through the driver via the second first switch and one of the diodes of the rectifier, effectively resulting in a very low voltage across the capacitor in the touch current path. Furthermore, the current path between the Line and the Neutral is blocked by opening the first switch. As long as one of the switches is closed, the high frequency current path is maintained allowing the main function of the capacitor, EMI reduction, to be still performed. It is an insight of the inventors that in order to keep the voltage in the current loop between Neutral and Neutral, and therefore effectively also the PE, through the driver as low as possible, preferably zero, no current will flow in this path and therefore any leakage current through the PE is kept as low as possible. The voltage is kept as low as possible by proving a very low impedance interconnection between the PE and Neutral via the driver using the switching circuit.

[0010] In a further example, the further comprises a protective earth connection.

[0011] An additional PE connection provides an additional safety protection for the driver by e.g., connecting the electrically conductive housing or heatsink parts of e.g., the load to the PE. This however also increase the parasitic capacitance between the PE and other circuitry and therefore also increases the touch current. The switching circuit however prevents any current from flowing regardless of the size of the parasitic capacitances. Therefore, a safe circuit can be provided without an increase of the touch current.

[0012] In a further example, the controller comprises a detection circuit adapted to generate a detection signal based on a low frequency current flowing through the capacitor, wherein the controller is arranged to use the detection signal for controlling the switching circuit.

[0013] In one example, the detection of whether the input voltage is positive or negative can be done by sensing the polarity of the current flowing through the capacitor. A detection circuit can be provided to the capacitor that detects a low frequency current through the capacitor, the polarity of this current is an indication of the polarity of the input voltage, preferably taking into account the phase-shift that may be caused by the capacitor. The detection circuit generates a detection signal based on this detection. The controller may then use this detection signal for controlling the switches in the switching circuit. The low frequency current is considered the current at which the touch current occurs. This is in the order of magnitude as the frequency of the input voltage. In the case of a mains voltage, this may be in the range of 50 Hz to 60 Hz. The high frequency current, this is flowing through the capacitor to reduce EMI, may the current that is generated by the switching behavior of the driver and may be in the order of 100 kHz and more. The high frequency current may be considered to be in the order of 1000 times, or more, higher than the frequency of the input voltage.

[0014] In a further example, the controller further comprises a detection circuit for detecting a polarity of the input voltage, wherein the controller is arranged to use the polarity of the input voltage for controlling the switching circuit.

[0015] A detection circuit can be used for detecting the polarity of the input voltage. This can be done by directly sensing the input voltage. The controller may use this detected polarity of the input voltage for controlling the switches in the switching circuit.

[0016] In a further example, the capacitor is a Y-cap.

[0017] For providing a galvanic isolation that meets the requirements of a human safe galvanic isolation, it is required for the capacitor to be a Y-cap.

[0018] In a further example, the switched mode power converter is a flyback converter.

[0019] Implementing the galvanic isolation, while using the capacitor, is preferably done by using a switched mode power converter being a flyback converter.

[0020] In a further example, the rectifier is a synchronous rectifier and the controller is further arranged to control the synchronous rectifier.

[0021] A synchronous rectifier may be used to improve the efficiency of the rectifier. Instead of diodes, active switches such as e.g., MOSFETs, are used. Instead of using the body diodes of the MOSFETs, the MOSFETs are closed such that the channel instead of the body diode is conductive, resulting in a very low conductive path. The control of these MOSFETs is relatively similar as the control of the switching circuit as the synchronous rectifier is also controlled based on the polarity of the input voltage. Therefore, the controller can be used to control the synchronous rectifier and the switching circuit in a simple and effective manner.

[0022] In a further example, the further node is coupled to the output.

[0023] The further node is preferably coupled to the output of the driver. This allows the capacitor to optimize its function for reducing the EMI. The load is coupled to the output. Therefore, the capacitor is also capable of providing EMI reduction for the load. In a further example, is coupled to a ground reference of the secondary side. Alternatively to coupling to the output of the driver, the second node may be coupled to the ground reference at the secondary side. This provides a more stable ground reference at the secondary side since the high frequency voltages at the secondary side ground reference are transferred back to the primary side.

[0024] In another example, a system is provided. The system comprises a driver according to any of the provided examples and the load.

[0025] In another example, the load is a lighting load, preferably an LED load.

[0026] A lighting load may be cooled using a large heatsink, The heatsink is made of a metal such as e.g., aluminum, which may be directly coupled to PE to provide a safe system. The size of the heatsink is the main determinant of the parasitic capacitance and therefore also the amount of touch current through the PE.

[0027] In another example, the load is thermally coupled to a metal heatsink.

[0028] Any load that generates undesired heat may be thermally coupled to a heatsink to lower its temperature. The heatsink is made of a thermally conductive material of which metals are mainly used for its robustness. This also results in electrically conductive heatsinks, that often require to be directly coupled to PE for safety. Alternatively, if safety can be guaranteed otherwise, there will always be a parasitic current path from the heatsink to the PE. The currents through such parasitic current path may be lower as when the heatsink is directly coupled to the PE, however the undesired touch current is still present.

[0029] In another example, the heatsink is electrically coupled to protective earth. Electrically coupling the heatsink to PE provides a safe operation of the system. It also provides the highest leakage current through PE and therefore, the invention provides a great benefit.

[0030] In another example, the system comprises a plurality of drivers according to any of the examples.

[0031] Multiple drivers provide multiple capacitors for EMI filtering and therefore also provide additional touch current through the PE. Each driver according to the examples reduce the total touch current, allowing more drivers to be placed in the system without generating to much touch current.

[0032] In another example, the plurality of drivers are arranged to drive a single load.

[0033] Using multiple drivers to drive a single load may be desired if the load is a very large load requiring a lot of power. A single driver design allows the driving of a single large load, while smaller loads can be driven with less drivers. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Examples of the invention will now be described with reference to the accompanying drawings, in which:

[0035] Fig. 1 shows an example of a circuit diagram of a conventional driver with load.

[0036] Fig. 2 shows an example of simplified circuit diagram of a conventional driver.

[0037] Fig. 3 shows an example of a circuit diagram of a driver with a load.

[0038] Fig. 4 shows another example of a circuit diagram of a driver with a load.

[0039] Fig. 5 shows an example of a simplified circuit diagram of a driver.

[0040] Fig. 6 shows another example of a simplified circuit diagram of the driver.

[0041] Fig. 7 shows another example of a simplified circuit diagram of the driver.

[0042] Fig. 8 shows another example of a circuit diagram of the driver.

[0043] Fig. 9 shows another simplified example of a circuit diagram of the driver.

[0044] Fig. 10 shows another simplified example of a circuit diagram of the driver.

[0045] DETAILED DESCRIPTION OF THE EMBODIMENTS

[0046] The invention will be described with reference to the Figures.

[0047] It should be understood that the detailed description and specific examples, while indicating exemplary embodiments of the apparatus, systems and methods, are intended 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 apparatus, systems and methods of the present invention will become better understood from the following description, appended claims, and accompanying drawings. It should also be understood that the Figures are merely schematic and are not drawn to scale. It should also be understood that the same reference numerals are used throughout the Figures to indicate the same or similar parts.

[0048] Figure 1 shows a circuit diagram of a conventional driver driving an LED load LED. The driver has an input for receiving an input voltage between the Line L and Neutral N. Preferably, the input voltage is a mains voltage with a voltage of 120 V or 230 V at 50 Hz or 60 Hz. A rectifier B 1 rectifies the input voltage into a rectified input voltage. The rectifier has two outputs where in between the rectified input voltage is provided. A capacitor C4 is provided to filter the rectified input voltage. A flyback converter is provided as a switched mode power converter. The flyback converter has a transformer Tl, a MOSFET M and a diode DI. The transformer has a primary side and a secondary side and splits the driver into a first part in the primary side and a second part in the secondary side. To reduce EMI of the switched mode power converter, a capacitive coupling is provided between the primary side and the secondary side. For this purpose, a capacitor Cy is provided between the primary side and the secondary side. The capacitor Cy allows any high frequency that is present at a ground reference at the secondary side to be coupled back to the primary side. A capacitor Cl is provided to stabilize a voltage at the output. A load LED is coupled to the output. The load LED requires cooling to prevent the load LED from overheating. This is normally done by providing a heatsink 3 that allows heat generated by the load LED to be transferred away. The heatsink is made of a metal, which has good thermal properties. However, metal also has good electrical characteristics. The heatsink is electrically conductive and there needs to be coupled to e.g., a protective Earth, PE. This results in the heatsink causing a large parasitic capacitance to be present between the heatsink and the load LED or the driver itself. The driver itself may be placed inside a housing that is made of metal. The housing may also be coupled to PE, providing additional parasitic capacitance to the PE. The parasitic capacitance Cp causes a low frequency current to flow from the Line or Neutral through the driver via the capacitance Cy and parasitic capacitance Cp to flow to PE.

[0049] Figure 2 shows a simplified circuit diagram of the driver as shown in Figure 1, where only the low frequency current path is shown for the leakage current. The rectifier is shown as four diodes DI, D2, D3 and D4. A leakage current may then flow from Line L, diode DI, capacitor Cy and parasitic capacitance Cp to PE. Alternatively, the current can flow from PE, parasitic capacitance Cp, capacitor Cy, C4 and diode D3 to the Line L.

[0050] A current flowing through PE is also referred to as a touch current or (earth) leakage current. For PE to be safe, a re si dual -current device (RCD) is used to disconnect the power to the driver in the event the leakage current is too large. If the leakage current is too large, something is wrong with the driver and a safe situation cannot be guaranteed anymore. This results obviously in an undesired situation that needs to be prevented.

[0051] The invention provides a circuit that blocks all or most of the aforementioned leakage current but allows the high frequency current to be still provided to the primary side.

[0052] Figure 3 shows an example of a driver. The driver is coupled to a load LED. The driver has a rectifier BL The rectifier receives an input voltage at the Line L and Neutral N connections. The rectifier B 1 rectifies the input voltage into a rectified input voltage. The rectified input voltage may be filtered by a capacitor C4 that is coupled across the outputs of the rectifier Bl. The rectified voltage is provided to a switching circuit having a series combination of a first switch SW1 and a second switch SW2. In this example, the switching circuit is directly coupled between the outputs of the rectifier B 1. It is to be appreciated that additional components can be placed between the output of the rectifier B 1 and the switching circuit. An example may be a filtering circuit such as e.g., a pi-filter. A controller 2 is used to control the first switch SW1 and the second switch SW2. A switched mode power converter is provided in the form of a flyback converter. The flyback converter has a transformer Tl, which has a primary side and a secondary side. The transformer Tl is used to galvanically separate the primary side from the secondary side. A MOSFET M is provided for providing the power conversion from the primary side to the secondary side. The MOSFET is controlled by a further controller 1. The aforementioned components are considered to be located on the primary side of the driver and are therefore galvanically isolated from the components on the secondary side.

[0053] On the secondary side, the secondary side of the transformer Tl is present. A diode D is used for the operation of the flyback diode. A capacitor Cl may be used to buffer the voltage at the output of the driver. The output of the driver may be coupled to the load LED.

[0054] A capacitor Cy is placed across the galvanic isolation. In this example, the capacitor is placed at one side at a first node that is present at the interconnection of the first switch SW1 and the second switch SW2. The capacitor Cy is coupled at another side at a location at the secondary side. In this example, the other side is coupled to the ground reference of the secondary side. The driver and / or load will always have a parasitic coupling to a PE, which may be in close vicinity. This coupling will result in undesired leakage currents through PE. When more drivers are used, more parasitic couplings to PE will occur, resulting in even more leakage currents. The controller 2 closes the first switch SW 1 and opens the second switch SW2 when the input voltage has a negative polarity. This means that the voltage at Neutral N is higher than the voltage at Line L. The controller 2 opens the first switch SW1 and closes the second switch SW2 when the input voltage has a positive polarity. This means that the voltage at Neutral N is lower than the voltage at Line L. The effect that is achieved by this switching will be explained later on in the application.

[0055] Figure 4 shows a similar example of a driver. The same circuitry is used as shown in Figure 3. An additional PE connection is provided. In this example, the PE is electrically coupled to the heatsink 3. The heatsink 3 is therefore at the same potential as the PE. Between the heatsink 3 and the load LED occurs a parasitic coupling resulting in the parasitic capacitance Cp between the heatsink 3 and the load LED. In this event, the leakage current will be even larger than in the situation described in Figure 3.

[0056] Figure 5 shows a simplified circuit diagram of the driver providing more focus on the current path for the leakage current. The rectifier Bl is shown as four diodes DI, D2, D3 and D4. The switching circuit has the first switch SW1 and the second switch SW2. The controller 2 is used to control the switching behavior of the first switch SW 1 and the second switch SW2. In essence, the controller 2 may control the switching behavior of the first switch SW1 and the second switch SW2 based on the polarity of the input voltage. How this is achieved will be explained in more detail later on.

[0057] Figure 6 shows an example of a configuration of the first switch SW1 and the second switch SW2. In this example, the controller 2 has opened the first switch SW1 and closed the second switch SW2. In this case, the input voltage has a positive polarity. This means that the leakage current wants to flow from Line L to Neutral N. The arrows in Figure 6 show the desired current path of the leakage current. It can also be seen that this current path is interrupted by the first switch SW1, which is open. The second switch SW2 is closed and provides a conductive path for the high frequency current so that EMI can remain to be reduced. The second switch SW2 and capacitor C4 do not provide any current path from Line to Neutral for the leakage current. The bottom node of the capacitor C4, which is also coupled to the anode of D4, has a voltage potential equal to Neutral minus the forward voltage of the diode D4. This effectively means that only the forward voltage of diode D4 is present across the capacitor Cy and parasitic capacitance Cp instead of the entire input voltage. The leakage current is therefore significantly reduced i.e., much closer to zero in the event of the input voltage having a positive polarity.

[0058] Figure 7 shows another example of a configuration of the first switch SW1 and the second switch SW2. In this example, the controller 2 has closed the first switch SW1 and opened the second switch SW2. In this case, the input voltage has a negative polarity. This means that the leakage current wants to flow from Neutral N to Line L. The arrows in Figure 7 show the desired current path of the leakage current. It can also be seen that this current path is interrupted by the second switch SW2, which is open. The first switch SW1 is closed and provides a conductive path for the high frequency current so that EMI can remain to be reduced. The first switch SW 1 and capacitor C4 do not provide any current path from Line to Neutral for the leakage current. The top node of the capacitor C4, which is also coupled to the cathode of D2, has a voltage potential equal to voltage at the Neutral plus the forward voltage of the diode D2. This effectively means that only the forward voltage of diode D2 is present across the capacitor Cy and parasitic capacitance Cp instead of the entire input voltage. The leakage current is therefore significantly reduced i.e., much closer to zero in the event of the input voltage having a negative polarity.

[0059] Figure 8 shows an example of a driver with a circuit for detecting the polarity of the input voltage. This is done by sensing the polarity of the leakage current flowing through the capacitor Cy. A detection circuit may be provided between the further node to which the capacitor Cy is coupled and the PE. This may result in an additional connection of the detection circuit to PE. Resistors R1 and R2 are used to sense the current flowing through the capacitor Cy. Preferably, most of the leakage current will flow through the series combination of resistor R1 and resistor R2 and not through the parasitic capacitance Cp. Capacitor C2 combined resistor R3 and capacitor C3 may be used to filter the signal from high frequency noise. The sensed voltage is either positive or negative, indication the current flow direction. A positive, low frequency, current indicates that the input voltage has a positive polarity and a negative voltage indicates that the input voltage has a negative polarity. The detection circuit use the detected polarity to generate a detection signal. Preferably, the phase shift that is caused by the capacitor Cy is taken into account. The controller 2 may then use the detection signal to control the switches accordingly so that the leakage current path may be directly interrupted.

[0060] Figure 9 shows another example of a driver with a circuit for detecting the polarity of the input voltage. This is done by directly sensing the input voltage. The AC mains voltage is in this example directly sensed form Line L and Neutral and provided to the controller 2. The controller 2 can therefore easily derive the polarity of the of the input voltage and therefore the switching circuit can be easily controlled. This way of detection allows an anticipation of the change of polarity as the zero crossing of the input voltage is the moment where the polarity changes. The leakage current can therefore be accurately and in a strict timing be blocked while keeping a good EMI reduction. In this example, a direct voltage measurement is shown. Alternatives are possible e.g., using a capacitive coupling for sensing the input voltage and the corresponding polarity.

[0061] Figure 10 shows another example of a simplified circuit diagram of a driver. The rectifier Bl has been modified by replacing the diodes by MOSFETs. Diode DI has been replaced by MOSFET Ml. Diode D2 has been replaced by MOSFET M2. Diode D3 has been replaced by MOSFET M3. Diode D4 has been replaced by MOSFET M4. The controller 2 is now also used for controlling the MOSFETs. Since the MOSFETs are controlled based on the same criteria as the first switch Ml and the second switch M2, namely the polarity of the input voltage is the determination of which MOSFETs are to be closed and opened, the controller 2 can be used to control all switches in a simple and convenient manner. An additional advantage of the use of a synchronous rectifier is that instead of the forward voltage of one of the diodes of the rectifier, the voltage drop of one of the MOSFETs is present across the capacitor Cy and parasitic capacitance Cp.

[0062] In the examples provided, a flyback converter is used as the switched mode power converter. It is clear that any switched mode power converter may be used that provides a galvanic isolation and also provides a capacitive path over this galvanic isolation.

[0063] In the examples provided, the capacitor Cy is preferably a Y-cap. The Y-cap type of capacitor provides an additional safety for the galvanic isolation because the Y-cap is designed such that if it fails, it fails in a safe way e.g., as an open.

[0064] In the examples provided, the first switch SW 1 and the second switch SW2 are preferably MOSFETs.

[0065] In the examples provided, the further node is coupled to the ground reference at the secondary side. The further node can also be coupled to the output of the driver or any other connection at the secondary side. The main function of the capacitor Cy can then still be to reduce the EMI.

[0066] The driver according to any of the examples may be used in a system. The system may have the driver according to any of the examples and the load LED. Preferably, the load LED is a lighting load and the system may be a luminaire or a lamp. In the event the load LED is relatively large, a plurality of drivers may be provided to drive the load. Preferably, the lighting load is an LED load.

[0067] By closing a switch, it is understood that the switch provides a conductive path. By opening the switch, it is understood that the switch does not provide a conductive path.

[0068] In the examples provided, the load is shown as an LED load, but the load can be any kind of load that is cooled using a heatsink, resulting is a parasitic coupling to PE.

[0069] Other variations to the disclosed embodiments can be understood and effected by those skilled in the art in practicing the claimed invention, from a study of the drawings, the disclosure, and the appended claims. In the claims, the word "comprising" does not exclude other elements or steps, and the indefinite article "a" or "an" does 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 construed as limiting the scope.

Claims

CLAIMS:

1. A driver for driving a load (LED), the driver comprising: a primary side comprising: a first input and a second input adapted to be coupled to a Line (L) and a Neutral (N) for receiving an input voltage, between the Line (L) and Neutral (N), from a power source; a rectifier (Bl) for rectifying the input voltage into a rectified input voltage, wherein the rectified input voltage is present at a first rectifier output and a second rectifier output; a switching circuit comprising a first switch (SW1) and a second switch (SW2) coupled in series and coupled between the first rectifier output and the second rectifier output, wherein a first node is at the interconnection of the first switch (SW1) and the second switch (SW2); a secondary side comprising an output for providing an output voltage to the load (LED), wherein the primary side and the secondary side are galvanically isolated from each other; a switched mode power converter for converting the rectified input voltage into the output voltage; the switched mode power converter comprising: a transformer (Tl) coupled between the primary side and the secondary side; a capacitor (Cy), wherein one end of the capacitor is coupled to the first node and another end of the capacitor (Cy) is coupled to a further node at the secondary side; a controller (2) for controlling the switching circuit, wherein the controller (2) is arranged to control the switching circuit to: close the first switch (SW 1) and open the second switch (SW2) when the input voltage is negative; open the first switch (SW1) and close the second switch (SW2) when the input voltage is positive.

2. The driver according to claim 1 further comprising a protective earth (PE) connection.

3. The driver according to any of the preceding claims, wherein the controller (2) comprises a detection circuit adapted to generate a detection signal based on a low frequency current flowing through the capacitor, wherein the controller (2) is arranged to use the detection signal for controlling the switching circuit.

4. The driver according to any of the claims 1 or 2, wherein the controller (2) further comprises a detection circuit for detecting a polarity of the input voltage, wherein the controller (2) is arranged to use the polarity of the input voltage for controlling the switching circuit.

5. The driver according to any of the preceding claims, wherein the capacitor (Cy) is a Y-cap.

6. The driver according to any of the preceding claims, wherein the switched mode power converter is a flyback converter.

7. The driver according to any of the preceding claims, wherein the rectifier (Bl) is a synchronous rectifier and the controller (2) is further arranged to control the synchronous rectifier.

8. The driver according to any of the preceding claims, wherein the further node is coupled to the output.

9. The driver according to any of the claims 1 to 7, wherein the further node is coupled to a ground reference of the secondary side.

10. A system comprising the driver according to any of the preceding claims and the load (LED).

11. The system according to claim 10, wherein the load (LED) is a lighting load, preferably an LED load.

12. The system according to any of the claims 10 or 11, wherein the load (LED) is thermally coupled to a metal heatsink (3).

13. The system according to claim 12, wherein the heatsink (3) is electrically coupled to protective earth (PE).

14. The system according to any of the claims 10 to 13 further comprising a plurality of drivers according to any of the claims 1 to 9.

15. The system according to claim 14, wherein the plurality of drivers are arranged to drive a single load (LED).

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