Latching relay in LED drive

Abstract

The invention relates to a switching device comprising an input for coupling to a driver, an output for coupling to a load, a latching relay coupled between the input and the output. The latching relay is arranged to be set in a first position wherein the latching relay is arranged to provide an electrical connection from the input to the output, and a second position wherein the latching relay is arranged to provide an electrical isolation between the input and the output. The switching device further comprising a controller adapted to set the latching relay in the first position and the second position. The controller is arranged to set the latching relay into the first position by providing a positive current pulse through a coil of the latching relay, and set the latching relay into the second position by providing a negative current pulse through the coil of the latching relay, receive an activation signal before or at the moment the driver is activated and to set the latching relay in the first position upon receiving the activation signal, and receive a deactivation signal after or at the moment the driver is deactivated and to set the latching relay in the second position upon receiving the deactivation signal.

Description

[0001] 2025PF80048

[0002] 1

[0003] Latching relay in LED drive

[0004] FIELD OF THE INVENTION

[0005] The invention relates to a switching device. The invention further relates to a system and a lighting system.

[0006] BACKGROUND OF THE INVENTION

[0007] In lighting systems, a driver is used to provide a regulated current and / or voltage to a lighting load. The lighting load may be coupled to a metal plate. The LEDs and especially the metal plate may form parasitic capacitances to ground. This results in a current path from the driver to the ground. Any so-called common mode current will flow through the LEDs. This effect is mostly present in the mains non-isolated drivers. The LEDs require only a small amount of current to emit light. This common mode current, may be large enough for the LEDs to emit light even when the driver is not active. The LEDs emit light, even when the driver is turned off. This effect is also referred to as after-glow effect, or glow-in-the-dark effect, due to light’s very low intensity. In standby or off mode of the lighting system, it is therefore desired to interrupt the common mode path so that the common mode current will not flow. This is currently done by a relay that is placed between the driver and the lighting load. The relay is controlled such that it provides a conductive path when the lighting system is active. During the off mode or standby of the lighting system, the relay is controlled to provide an electrical isolation between the driver and the lighting load. Keeping the relay in an active position, e.g., when providing the conductive path, requires energy. This amount of energy may provide a significant on efficiency, especially in low power lighting systems. It is desired to prevent the after-glow effect from occurring in a more energy efficient way.

[0008] SUMMARY OF THE INVENTION

[0009] It is an objective of the invention to provide a device that prevents after-glow in an energy efficient way.

[0010] To provide such solution, in a first aspect of the invention, a switching device is provided. The switching device comprises:2025PF80048

[0011] 2

[0012] - an input for coupling to a driver;

[0013] - an output for coupling to a load;

[0014] - a latching relay, coupled between the input and the output, wherein the latching relay is arranged to be set in:

[0015] - a first position wherein the latching relay is arranged to provide an electrical connection from the input to the output, and

[0016] - a second position wherein the latching relay is arranged to provide an electrical isolation between the input and the output,

[0017] the switching device further comprising a controller adapted to set the latching relay in the first position and the second position,

[0018] wherein the controller is arranged to:

[0019] - set the latching relay into the first position by providing a positive current pulse through a coil of the latching relay, and

[0020] - set the latching relay into the second position by providing a negative current pulse through the coil of the latching relay,

[0021] wherein the controller is arranged to:

[0022] -receive an activation signal before or at the moment the driver is activated and to set the latching relay in the first position upon receiving the activation signal, and

[0023] - receive a deactivation signal after or at the moment the driver is deactivated and to set the latching relay in the second position upon receiving the deactivation signal.

[0024] A switching device is provided that uses a latching relay between an output of a driver and a load. Opening the latching relay, the electrical connection between the driver and the load is interrupted and no current can flow through the latching relay. This means that also the undesired current that causes the undesired after-glow effect cannot flow. By using a latching relay instead of the commonly used holding relay, the power consumption of the switching device is kept as low as possible.

[0025] To control the latching relay properly, a dedicated controller is provided. This controller is arranged to provide a control signal to the coil of the latching relay. To improve the control of the latching relay further, the latching relay is set to the closed position upon receiving an activation signal. This signal is provided (just) before or at the moment the driver is activated. This means that the latching relay will be closed when no or a very small current will flow upon closing.2025PF80048

[0026] 3

[0027] In addition, a deactivation signal is provided, preferably at the same control input as for the activation signal, to open the latching relay upon receiving the deactivation signal. The deactivation signal is provided after or at the moment the driver is deactivated. This may allow the relay to act fast to provide a fast turn-off of the load. Alternatively, this may allow the relay switch a lower current than the nominal current that was provided to the load. By providing these activation ad deactivation signals, the latching relay can be controlled in a most energy optimized manner and allow the relay to be controlled such that an accurate prevention of an after-glow effect can achieved.

[0028] In a further example, the latching relay is a double pole single throw relay. Preferably, the latching relay is a double pole single throw relay. This means that the latching relay opens and closes two lines in a single action. The latching relay may then be used to connect and disconnect the positive connection the load and the negative connection to the load simultaneously. This provides an improved reduction of any undesired current flow that may result in an after-glow effect.

[0029] In a further example, the controller comprises a power circuit arranged to provide the positive current pulse and the negative current pulse.

[0030] The controller may be provided with a dedicated circuit that generates a positive current pulse and a negative current pulse to the coil of the latching relay. The positive current pulse sets the latching relay in the first, conductive, position and the negative current pulse sets the relays in the second, non-conductive, position.

[0031] In a further example, the controller comprises a capacitor coupled between the input and the coil.

[0032] A simple way of controlling the latching relay is to provide a capacitor between the input and the coil. When the driver starts to generate a current, at least a part of this current will flow from the input through the capacitor and therefore through the coil. This current has a positive polarity and will therefore set the relay in the first position. Eventually, the capacitor is charged and no current will flow anymore through the coil, resulting in no power consumption by the latching relay.

[0033] When the driver is deactivated, the current will decrease and eventually, the capacitor will discharge. This may be done via the output to the load or via the input to the driver. The current that then flows through the capacitor is a negative current, resulting in the latching relay to be set in the second position. Eventually, the capacitor is discharged and no current will flow anymore through the coil, resulting in no power consumption by the latching relay.2025PF80048

[0034] 4

[0035] In a further example, the controller is arranged to provide the positive current pulse repeatedly.

[0036] The controller may be arranged with dedicated control circuitry. Such circuitry may be arranged to provide a repeated positive current pulse to the coil. This repetition may be done until a current through the load has been detected. Alternatively, fixed amount of positive current pulses is provided to the coil to ensure the latching relay to be set to the first position. Such implementation provides a way to ensure that the latching relay switches to or stays at the first position. In another implementation, the repetition of the positive current pulse may be continuous, especially as long as the driver is active. In the event that the latching relay unintentionally switches to the second position, e.g. due to a shock, the repeated positive current pulse will set the latching relay back to the first position. The energy consumption created by these pulses remains significantly below the energy consumption of a holding relay.

[0037] In a further example, the controller is arranged to provide the negative current pulse repeatedly.

[0038] The controller may be arranged with dedicated control circuitry. Such circuitry may be arranged to provide a repeated negative current pulse to the coil. This repetition may be done until the controller gives the control to turn on the driver. Alternatively, fixed amount of positive current pulses is provided to the coil to ensure the latching relay to be set to the second position. Such implementation provides a way to ensure that the latching relay switches to or stays at the second position. In another implementation, the repetition of the negative current pulse may be continuous, especially as long as the driver is inactive. In the event that the latching relay unintentionally switches to the first position, e.g. due to a shock, the repeated negative current pulse will set the latching relay back to the second position.

[0039] In another example, a lighting system is provided. The lighting system comprises:

[0040] a driver;

[0041] a lighting load;

[0042] a switching device comprising:

[0043] - an input adapted to be coupled to the driver;

[0044] - an output adapted to be coupled to the load;

[0045] - a latching relay, coupled between the input and the output, wherein the latching relay is arranged to be set in:2025PF80048

[0046] 5

[0047] - a first position wherein the latching relay is arranged to provide an electrical connection from the input to the output, and

[0048] - a second position wherein the latching relay is arranged to provide an electrical isolation between the input and the output,

[0049] the switching device further comprising a controller adapted to set the latching relay in the first position and the second position,

[0050] wherein the controller is arranged to:

[0051] - set the latching relay into the first position by providing a positive current pulse through a coil of the latching relay, and

[0052] - set the latching relay into the second position by providing a negative current pulse through the coil of the latching relay.

[0053] A lighting system may especially benefit from using a switching device having a latching relay. Such lighting system further has a driver and a load. The driver is arranged to provide a regulated power to the load. A latching relay is placed in between the driver and the load. It is common practice to place at this location a common holding relay as this provides a simple way of control, as will be shown later. The power losses of such a relay have always been considered an acceptable necessity. However, as lighting systems start using less power for a similar light output, the power losses caused by the holding relay may become relevant. Therefore, the lighting system is provided with a switching device that has a latching relay. The latching relay can be set in at least two positions. In a first position, the latching relay is arranged to provide an electrical connection between the input to the output. In a second position, the latching relay is arranged to provide an electrical isolation between the input and the output. A controller is used to control the latching relay. The controller sets the relay in the first position by providing a positive current to the coil of the latching relay and in the second position by providing a negative current to the coil.

[0054] In another example, the controller is arranged to:

[0055] -receive an activation signal before or at the moment the driver is activated and to set the latching relay in the first position upon receiving the activation signal, and - receive a deactivation signal after or at the moment the driver is deactivated and to set the latching relay in the second position upon receiving the deactivation signal.

[0056] The controller may set the latching relay in the first position based on a received activation signal generated before or at the moment the driver is activated.

[0057] Similarly, the controller may set the latching relay in the second position based on a deactivation signal generated after or at the moment the driver is deactivated.2025PF80048

[0058] 6

[0059] In another example, a system is provided. The system comprises a driver, a load and a switching device according to any of the previous examples.

[0060] In another example, the driver is arranged to provide a regulated current or a regulated voltage to the lighting load.

[0061] Preferably, the driver is arranged to provide a regulated current or a regulated voltage to the load. A regulated current driver may also be referred to as a current source. A regulated voltage driver may be referred to as a voltage source. Depending on the lighting load, a regulated voltage or a regulated current may be required.

[0062] In another example, a switching current rating of the latching relay is lower that a maximum current that can be provided by the driver.

[0063] A latching relay with a relatively low current rating can be smaller and cheaper. By controlling the latching relay according to the invention, the latching relay may not need to switch any relevant currents and can therefore be designed with a relatively low maximum switching current rating.

[0064] In another example, the lighting load is thermally coupled to a heatsink, or a metal backplate of a luminaire.

[0065] Coupling the lighting load to a heatsink greatly improves the cooling performance of the lighting system. The cooling comes with the drawback of additional parasitic capacitance to ground. This greatly increases the current that may flow through the lighting load that may create the after-glow effect. The use of the latching relay prevents this current from flowing such that there is no after-glow effect. The invention therefore allows improved cooling without the negative side effect of after-glow.

[0066] BRIEF DESCRIPTION OF THE DRAWINGS

[0067] Examples of the invention will now be described with reference to the accompanying drawings, in which:

[0068] Fig. 1 shows an example of a circuit diagram of a common implementation of a holding relay.

[0069] Fig. 2 shows an example of a circuit diagram of a system having a latching relay.

[0070] Fig. 3 shows another example of a circuit diagram of a system having a latching relay.2025PF80048

[0071] 7

[0072] DETAILED DESCRIPTION OF THE EMBODIMENTS

[0073] The invention will be described with reference to the Figures.

[0074] 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.

[0075] Figure 1 shows an example of a common implementation of a lighting system. The lighting system has a driver 1, a lighting load LED and a holding relay Ul. The driver 1 is shown as a boost converter that has an inductor LI, switch Ml and diode DI to perform the boosting action. A rectifier Bl is provided to rectify the mains voltage Vmains and provide a rectified voltage to the boost converter. The driver 1 has an output that is coupled to an input of the holding relay UL The holding relay Ul has an output that is coupled to the lighting load LED. In this example, the relay is shown as a double pole single throw relay. Two connections to the load may be interrupted simultaneously. This prevents any undesired leakage current to flow through the lighting load LED. The holding relay Ul requires a constant energizing of the coil. In the circuits as commonly used, a very simple control is provided. The controller 2 for controlling the witch Ml of the boost converter requires a low voltage Vcc for proper operation. This low voltage Vcc is generated by an auxiliary power supply 3. This low voltage Vcc can also be directly provided to the coil of the holding relay UL By powering the controller 2, the holding relay Ul is also powered and the driver 1 can provide a current to the load LED. A switch can be provided in series with the coil to interrupt the coil current when the boost converter is set into a standby mode. The coil current is removed and the holding relay goes into its starting position, which in this example is in the off state.

[0076] Figure 2 shows an example of a lighting system using a latching relay UL A driver 1, similar to the driver 1 shown in Figure 1 may be used. The driver 1 has an output that is used to power the lighting load LED. The latching relay Ul is coupled between the output of the driver 1 and the load LED. In this example, the coil is powered via the output of the driver 1. A capacitor Cl is coupled between the output of the driver 1, and hence the input of the switching device, and the coil of the latching relay UL2025PF80048

[0077] 8

[0078] Activating the diver 1 causes a positive current pulse to flow through the coil, which causes the latching relay U1 to switch to the first position. The waveform of the positive current pulse is determined by the charging of the capacitor Cl. When the charging is done, i.e. the capacitor Cl has charged to the voltage provided by the driver 1, no current will flow anymore through the coil. The latching relay U1 is however latched in the first position and does not require any current through the coil anymore. The latching relay U1 therefore remains in the first position.

[0079] Deactivating the driver 1 causes a negative current pulse to flow through the coil, which causes the latching relay U1 to switch to the second position. The waveform of the negative current pulse is determined by the discharging of the capacitor Cl. When the discharging is done, i.e. the capacitor Cl has discharged, no current will flow anymore through the coil. The latching relay U1 is however latched in the second position and does not require any current through the coil anymore. The latching relay U1 therefore remains in the second position.

[0080] The capacitor Cl effectively causes a direct response to the activation and deactivation of the driver 1 for controlling the latching relay Ul.

[0081] Figure 3 shows another example of a lighting system using a latching relay Ul. A driver 1, similar to the driver 1 shown in Figure 1 may be used. The driver 1 has an output that is used to power the lighting load LED. The latching relay Ul is coupled between the output of the driver 1 and the load LED.

[0082] In this example, the coil of the latching relay Ul is powered by a controller 2. The controller 2 has an output that can provide a positive current pulse and a negative current pulse to the coil. The controller may further be used to control the driver 1. In this example, this is done by directly controlling the switch ML The controller 2 can provide additional functionality. The controller 2 can provide the positive current pulse more than once, preferably repeatedly. The controller 2 can also provide the negative current pulse more than once, preferably repeatedly. A dedicated power circuit may be provided in the controller 2 to allow a positive and negative current to be provided to the coil. A repetition of the positive current pulse and the negative current pulse may occur with a repetition rate of 10 Hz or lower. Preferably, the pulse duration has a duty cycle of less than 1 %. These parameters keep the control of the latching relay U 1 relatively simple and keep the power consumption to a minimum.

[0083] Another benefit of using a controller 2 for controlling the latching relay Ul is that the setting to first position and second position can be optimized. The controller 2 knows2025PF80048

[0084] 9

[0085] when the driver 1 is going to be activated e.g., the controller 2 also controls the driver 1. The controller 2 may provide a positive current pulse to the coil before or at the moment that the driver 1 is activated. The driver does not provide much current at this moment and therefore the latching relay U1 does not need to switch a significant current when switching to the first position. The controller 2 may also know when the driver 1 is going to be deactivated e.g., the controller 2 also controls the driver 1. The controller 2 may provide a negative current pulse to the coil after the moment that the driver 1 is deactivated. The driver does not provide much current at this moment anymore and therefore the latching relay U1 does not need to switch a significant current when switching to the second position.

[0086] In the examples provided, the load LED is shown as a lighting load. Any load other than a lighting load that may suffer from an undesired leakage current may also be used instead.

[0087] The lighting load may have a solid-state light source such as e.g., LEDs, laser diodes or a vertical -cavity surface-emitting laser, VCSEL.

[0088] In the examples provided, a single controller 2 is shown to control the switch Ml and the coil of the latching relay Ul. The controller 2 may therefore be a microcontroller, the controller 2 may however be comprised of multiple smaller controllers and also have discrete components.

[0089] In the examples provided, the latching relay Ul is shown as a double pole single throw relay. Other types of latching relays may also be used. A single pole single throw relay may also be used. This type of relay only interrupts one of the connections to the load LED and in some designs this may reduce the leakage current sufficiently.

[0090] In the examples provided, the driver 1 is shown as a boost converter. The driver may also use any other topology such as a buck converter, flyback converter, resonant LLC converter. This may depend on the design and requirements of the system.

[0091] 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

2025PF8004810CLAIMS:

1. A switching device comprising:- an input for coupling to an output of a driver (1);- an output for coupling to a load (LED);- a latching relay (Ul), coupled between the input and the output, wherein the latching relay (Ul) is arranged to be set in:- a first position wherein the latching relay (Ul) is arranged to provide an electrical connection from the input to the output, and- a second position wherein the latching relay (Ul) is arranged to provide an electrical isolation between the input and the output,the switching device further comprising a controller (2) adapted to set the latching relay (Ul) in the first position and the second position,wherein the controller (2) is arranged to:- set the latching relay (Ul) into the first position by providing a positive current pulse through a coil of the latching relay (Ul), and- set the latching relay (Ul) into the second position by providing a negative current pulse through the coil of the latching relay (Ul),- receive an activation signal before or at the moment the driver (1) is activated and to set the latching relay (Ul) in the first position upon receiving the activation signal, and- receive a deactivation signal after or at the moment the driver (1) is deactivated and to set the latching relay (Ul) in the second position upon receiving the deactivation signal.

2. The switching device according to claim 1, wherein the latching relay (Ul) is a double pole single throw relay.

3. The switching device according to any of the preceding claims, wherein the controller (2) comprises a power circuit arranged to provide the positive current pulse and the negative current pulse.2025PF80048114. The switching device according to any of the preceding claims, wherein the controller (2) comprises a capacitor (Cl) coupled between the input and the coil.

5. The switching device according to any of the claim 1 to 3, wherein the controller (2) is arranged to provide the positive current pulse repeatedly.

6. The switching device according to any of the claim 1 to 3 or claim 5, wherein the controller (2) is arranged to provide the negative current pulse repeatedly.7 A lighting system comprising:a driver (1);a lighting load (LED);the switching device according to any of the preceding claims.

8. The lighting system according to claim 7, wherein the controller (2) is arranged to:- receive an activation signal before or at the moment the driver (1) is activated and to set the latching relay (Ul) in the first position upon receiving the activation signal, and - receive a deactivation signal after or at the moment the driver (1) is deactivated and to set the latching relay (Ul) in the second position upon receiving the deactivation signal.9 A system comprising a switching device according to any of the claims 1 to 6, a driver (1) and a load (LED).

10. The system according to claim 9, wherein the system is a lighting system and the load (LED) is a lighting load.11 The lighting system according to claim 10, wherein the driver (1) is arranged to provide a regulated current or a regulated voltage to the lighting load (LED).2025PF800481212. The lighting system according to any of the claims 10 or 11, wherein a switching current rating of the latching relay (Ul) is lower that a maximum current that can be provided by the driver (1).

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

Images