Hot-swap protection circuits for lighting products

Abstract

The present invention relates to a protection circuit for protecting a load, the protection circuit comprising: an input node adapted to be couplable to an SMPS, a bleeder coupled between the input node and a return node, a first output node adapted to be coupled to the input node and a load, a second output node adapted to be coupled to the load, the second output node being couplable between the first output node and the second output node, an impedance coupled between the second output node and the return node, a switch coupled in parallel with the impedance, and a controller adapted to control the switch and the bleeder, the controller adapted to activate the bleeder and open the switch when a voltage across the impedance is above a threshold, and the controller adapted to deactivate the bleeder and close the switch when a voltage across the impedance is below the threshold.

Description

[Technical Field]

[0001] The present invention relates to a protection circuit.The present invention further relates to a driver.The present invention further relates to a lighting system. [Background technology]

[0002] A lighting system can be divided into several components. These components can fail and need to be replaced. For a circular economy, it is desirable that all components can be replaced without the need to replace non-defective components. A lighting system may have a driver configured to supply regulated power, i.e., regulated voltage and / or current, to a load. A lighting system also has a load, which may be a lighting load. A lighting load is usually a separate module that can be placed on a single printed circuit board (PCB). This PCB with the lighting load can need to be replaced without the need to replace the driver.

[0003] Although it is recommended to power down a lighting system before performing maintenance on it, it is common to perform maintenance on a powered lighting system. It is particularly convenient to perform maintenance without powering down the system in lighting systems that use safety extra-low voltage (SELV) drivers. Not all drivers and lighting loads can accommodate, for example, “hot swapping” an LED board, i.e., replacing an LED board in an LED driver that is still powered on. When an LED board is removed from a powered LED driver, the LED driver’s output voltage rises to the maximum limit of the LED driver, which for non-SELV LED drivers may be several hundred volts, and for SELV drivers, it may be lower than the SELV limit (60 Vdc). Reconnecting the LED board to a driver operating at its maximum output voltage results in high surge currents due to the mismatch between the driver’s output voltage and the LED board’s design voltage. These high surge currents may assert protection circuits within the LED driver or permanently damage the LED driver and / or LED board. Summary of the Invention [Problem to be solved by the invention]

[0004] It is an object of the present invention to provide a protection circuit that allows hot swapping of a load when connected to a power source without risking damage to said load. [Means for solving the problem]

[0005] To solve this problem, in a first aspect of the present invention, there is provided a lighting system for protecting a load, the lighting system comprising: a switched mode power supply (SMPS) adapted to provide a regulated current to an input node; Load and a protection circuit for protecting the load, the protection circuit comprising: - said input node adapted to be coupled to said switched mode power supply; - a bleeder coupled between the input node and a return node; a first output node adapted to be coupled to the input node and to a load; a second output node adapted to be coupled to the load, the load being couplable between the first output node and the second output node; an impedance coupled between the second output node and the return node; a switch coupled in parallel with said impedance; a controller adapted to control the switch and the bleeder, the controller adapted to activate the bleeder and open the switch when the voltage across the impedance is above a threshold, and the controller adapted to deactivate the bleeder and close the switch when the voltage across the impedance is below the threshold.

[0006] The protection circuit has an input node that can be coupled to a driver. The protection circuit can be directly coupled to the output of the switched mode power supply (SMPS) using the input node. A bleeder is coupled between the input node and a return node. The bleeder is used to provide a path for current supplied by the SMPS to return to the SMPS. A first output node is coupled to the input node and allows the load to be connected to the protection circuit. A second output node is provided, the second output node also coupled to the load. The load can be coupled between the first output node and the second output node. An impedance is coupled between the second output node and the return node. A switch is provided in parallel with this impedance. The switch is capable of shunting the impedance. A controller is used to control the switch and the bleeder. The controller can receive a feedback signal from the impedance in the form of a voltage across the impedance.

[0007] Unless disconnected from the power source, the SMPS continues to operate. When the load is disconnected, the current that should be supplied to the load can no longer flow, causing the voltage at the output of the SMPS to increase, and therefore the voltage at the first output node. The SMPS is protected from excessive voltage and limits the voltage to a level above its normal operating voltage. Connecting a load directly to this higher voltage would cause a current surge to flow through the load, potentially damaging it. If the voltage across the impedance exceeds a threshold, the current through the load is deemed too high to close the shunt switch. Closing the shunt switch would result in an even higher current, potentially damaging the load. If the voltage across the impedance is below the threshold, the current is below the desired current level, and closing the switch would not result in too much current flowing through the load. Therefore, the controller closes the switch and turns off the bleeder when the voltage across the impedance is below the threshold. In that case, the bleeder is also turned off since its function is no longer needed. The main function of the bleeder is to discharge any capacitance at the first output node so that the voltage at the first output node drops from the overvoltage protection voltage level to or near the normal operating voltage. When the voltage across the impedance is above the threshold, the switch is open and the bleeder is turned on.

[0008] In a further example, the lighting system further comprises a voltage sensing circuit for sensing a voltage across the impedance.

[0009] Preferably, a voltage sensing circuit is used to sense the voltage across the impedance, which may be used to provide a feedback signal to the controller based on the sensed voltage across the impedance.

[0010] In a further example, the bleeder comprises a series arrangement of a resistor and a switching element.

[0011] A simple bleeder may include a switching element, which may be controlled by the controller, coupled in series with a resistor, and opening and closing the bleeder to form a current path from the input node to the return node.

[0012] In a further example, the impedance has a resistance of at least 1 kΩ.

[0013] Preferably, the resistance of the impedance is not too low, as too low a resistance may cause too much current to flow through the load even when the switch is open. A relatively large resistance, for example between 1 kΩ and 10 kΩ, allows the current to be limited sufficiently to avoid damaging the load and provides a voltage across the impedance that can be easily detected.

[0014] In another example, the resistance of the impedance is greater than the resistance of the load.

[0015] To be able to reduce the excess voltage supplied by the SMPS as quickly as possible without risking damage to the load, it is desirable for the impedance to have a higher resistance than the load, which reduces the current through the load sufficiently so that the surge current does not harm the load.

[0016] In another example, the amplitude of the current drawn by the bleeder is greater than the amplitude of the current through the load.

[0017] Preferably, the bleeder draws a majority of the current so that the total current drawn allows the voltage at the input node of the protection circuit to decrease to a normal voltage level as quickly as possible.

[0018] In another example, the load is a lighting load.

[0019] Preferably, the load to be protected in the lighting system is the lighting load, which is most susceptible to current surges and therefore will benefit most from the proposed protection circuit.

[0020] In another example, the lighting load comprises a solid-state light source.

[0021] The light source is preferably a semiconductor light source because these types of light sources are very energy efficient. Examples of desirable semiconductor light sources are light emitting diodes (LEDs), laser diodes (LDs), and vertical cavity surface emitting lasers (VCSELs).

[0022] In another example, the load and the protection circuitry are configured on a first, single PCB, and the SMPS is configured on a second, different PCB.

[0023] The load and the protection circuit may reside on a single PCB. In that case, replacing the load may also result in replacing the protection circuit. The protection circuit may be mated with the load. In this case, the load and the protection circuit are always together, ensuring that the load is always protected when replaced.

[0024] In another example, the load is adapted to be swapped while keeping the SMPS in an operational mode.

[0025] Preferably, the load can be hot swapped while the driver is in an operational mode. The driver is configured to supply current to the first output node, i.e., to the load, even when the load is disconnected. This can result in an increase in voltage at the first output node, creating a risk to a load that should be coupled between the first output node and the second output node.

[0026] In another example, the SMPS is configured to operate in an overvoltage protection mode during the exchange of the load.

[0027] When the driver is operational and unable to supply current to the load, the voltage exceeds an overvoltage level. In that case, it is desirable for the driver to operate in voltage control mode to prevent the voltage at the input node of the protection circuit from rising any further. Once the overvoltage problem has been resolved, i.e., the load is properly connected and the voltage has returned to normal operating voltage levels, the driver can operate in current regulation mode.

[0028] In another example, the protection circuit prevents current from flowing through the load when the voltage supplied by the SMPS exceeds a threshold.

[0029] It may occur that the overvoltage level may exceed a voltage level that causes the current to become too high and thus may damage the load, even if precautions are taken. In this case, it may be desirable to have all current flow through the bleeder and not through the load. This may be done by including an additional switch configured to disconnect the impedance so that no current can flow through the impedance and the switch. In this case, it may be desirable for the voltage at the input node to be sensed and supplied to the controller. When the voltage drops below the overvoltage threshold, the impedance can be reconnected and the voltage across the impedance can be used as a feedback signal for the controller.

[0030] In another example, the bleeder remains inactive as long as the load is disconnected from the SMPS.

[0031] Turning off the bleeder when the load is disconnected prevents any unnecessary power loss. Although the load is not connected, the driver still supplies voltage to the input node of the protection circuit. Therefore, when the bleeder is active, it introduces losses and serves no purpose. The bleeder is mainly effective when a load is connected to an active driver. [Brief explanation of the drawings]

[0032] Examples of the invention will now be described with reference to the accompanying drawings, in which: [Figure 1] 1 shows an example of an electrical diagram for a lighting system. [Figure 2a] 1 shows an example graph of the voltage at the input node and the load current. [Figure 2b] 1 shows an example graph of the current supplied by the SMPS over time. [Figure 2c] 10 shows an example of a graph of bleeder current over time. [Figure 3a] 3 shows an example graph of the voltage at the input node and the load current during start-up. [Figure 3b] 1 shows an example graph of the current supplied by the SMPS at start-up. [Figure 3c] 10 shows an example graph of the bleeder current during start-up. DETAILED DESCRIPTION OF THE INVENTION

[0033] The present invention will be described with reference to the drawings.

[0034] 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, 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 schematic only 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.

[0035] FIG. 1 shows an exemplary circuit diagram of a lighting system including a protection circuit. The protection circuit includes an input node In that can be connected to the output of an SMPS 3. The protection circuit can include a bleeder 1 that can be used to provide a current path between the input node In and a return node Return. The bleeder 1 can include a resistor R1 coupled in series with a switching element M1. The switching element M1 can be any type of switching element that allows the resistor R1 to be coupled between the input node In and the return node Return. Preferably, the switching element M1 is a MOSFET or a bipolar transistor. The protection circuit can further include a controller 2 for controlling the bleeder 1. This can be done by providing a control signal from the controller 2 to a control gate of the switching element M1. The protection circuit can further include a first output node Out1 to which a load LED can be coupled. A second output node Out2 can be provided to couple to the load LED such that the load LED is coupled between the first output node Out1 and a second output node Out2. The second output node Out2 is further coupled to a switch M2 and an impedance R3. Similar to the switching element M1, the switch M2 is a MOSFET or a bipolar transistor. The switch M2 and the impedance R3 are arranged in parallel with each other. The switch M2 and the impedance R3 may be coupled to a return node Return on opposite sides. The controller 2 may control the switch M2 by providing a control signal to the control gate of the switch M2.

[0036] In the illustrated example, the load LED is shown as a light-emitting diode. The load LED can be any type of load that may be susceptible to current surges and may be hot-swapped from the SMPS 3. When directly connected to an active SMPS 3, the LED may suffer from current surges. The LED die itself may be damaged, substantially shortening the LED's lifespan. Other lighting loads, such as laser diodes or lasers, are even more susceptible to current surges. Devices other than lighting loads may also be susceptible to current surges. The controller 2 is configured to control the bleeder 1 and switch M2 based on the voltage across the impedance R3. Preferably, a voltage sensing circuit R2 is provided to sense the voltage across the impedance R3. The voltage sensing circuit R2 is shown as a single resistor disposed across the second output node Out2. The voltage sensing circuit R2 may output a feedback signal to the controller 2. Other examples of the voltage sensing circuit may be possible. For example, the voltage sensed across the impedance R3 may need to be reduced so that the controller 2 can receive an appropriate feedback signal. Another option may be to introduce galvanic isolation, and an optocoupler may be used. The voltage sensed across impedance R3 flows through the load LED and is therefore a measure of the amplitude of the current flowing through the impedance. If the current through the impedance exceeds a defined current threshold, the voltage across impedance R3 exceeds the voltage threshold. The current threshold may be set to a current higher than the nominal current set for the load LED. In that case, the voltage sensed across impedance R3 may exceed the voltage threshold to provide an indication that the current through the load LED is too high. In that case, controller 2 may decide to activate bleeder 1 so that current flows not only through the load LED but also through bleeder 1. The current may be too high because the voltage provided by SMPS3 is significantly greater than the nominal or forward voltage of the load LED. This may be because the load LED is disconnected from SMPS3, for example.The SMPS 3 is configured to supply a regulated current to its output and to the input node of the protection circuit. In the illustrated example, the SMPS 3 is shown as a boost converter having an inductor L1, a switch M3, and a diode D1. A controller 4 is used to control the SMPS 3. The controller 4 may control the SMPS 3 based on a voltage and / or current feedback signal supplied to the input node In. A capacitor C1 may be applied to reduce the voltage ripple present at the output of the SMPS 3. If no load is provided for the SMPS 3, the current supplied by the SMPS 3 cannot flow through the load but instead flows through parasitic capacitance to ground and other capacitances to ground, such as the capacitor C1. This causes the voltage at the output of the SMPS 3 to rise indefinitely. To protect the circuit from overvoltage, the SMPS 3 is usually equipped with an overvoltage protection circuit. When the voltage increases above the protection threshold, the SMPS regulates its output to maintain this voltage level as long as the load connection remains open. When a new or the same load LED is connected to the SMPS 3, current may begin to flow through the load LED. If precautions are not taken, the current through the load LED may exceed the maximum current rating of the load LED. Impedance R3 is provided in series with the load LED and configured to prevent the current through the load from exceeding the maximum current rating of the load LED. Impedance R3 may have a resistance of, for example, at least 1 kΩ. The current causes a voltage drop across impedance R3, allowing controller 2 to detect that the load has been connected or reconnected. Controller 2 responds to this detection by enabling bleeder 1. Activation of bleeder 1 discharges capacitor C1 or any other parasitic capacitance. Bleeder 1 may be configured to draw a current greater than the nominal current of the load LED. This allows bleeder 1 to ensure that the voltage at input node In is reduced when bleeder 1 is activated. When the voltage at input node In decreases, the current through the load LED also decreases because the voltage approaches the nominal voltage level. Therefore, the voltage across impedance R3 also decreases.The voltage across the impedance eventually drops below the threshold. Controller 2 turns off bleeder 1 when the voltage across impedance R3 drops below the threshold. The voltage at input node In has reached a safe operating voltage where there is no risk of current surges through the load. To prevent any further losses from occurring, impedance R3 can be shunted by switch M2.

[0037] The protection circuit can be configured in various ways. The protection circuit may be part of the driver. The driver may include the SMPS3 and the protection circuit. The driver allows safe hot swapping of the load LEDs without requiring any changes to the design of the SMPS3. The driver may also include a rectifier circuit B1 to provide a rectified DC voltage. The driver may be coupled to the mains voltage.

[0038] The protection circuit may be located near the load LED. In the example of a lighting load, the protection circuit may be located on the same PCB as the lighting load. The SMPS 3 may be part of the driver that powers the lighting load. The driver may be a separate module. The protection circuit and lighting load on a single PCB may be separate modules. The protection module and lighting load are preferably located as a chip-on-board (COB) module. The driver may be any driver currently available on the market and may not require any modifications. The single PCB with the lighting load and protection circuit can be connected to the driver by the installer while the driver is operating safely. When connected, the lighting load in series with impedance R3 forms the only conductive path for current from the driver, so very low current is drawn by the driver and no arcing occurs between the driver or the connection pins of the single PCB with the lighting load and protection circuit. When connected, current flows through impedance R3, causing the voltage across impedance R3 to exceed a threshold. Controller 2 responds to this moment by activating bleeder 1, causing more current to be drawn from SMPS 3.

[0039] 2a, 2b, and 2c show example graphs illustrating the behavior of current and voltage during a hot swapping event. The values ​​of voltage, current, and time can be chosen arbitrarily and may depend on the design of the system.

[0040] Figure 2a shows a graph of the bus voltage (the voltage at input node In) over time when the protection circuit becomes active. Figure 2a also shows the current through the load LED. At 1 second, the voltage at input node In is at its maximum value, approximately 60 V. This is the point at which the load LED is coupled to the output of active SMPS2. At this point, bleeder 1 is activated by controller 2. The current drawn by bleeder 1 reduces the voltage at input node In1. This also results in a voltage drop across impedance R3. Impedance R3 is chosen to have a high resistance so that the current through the load LED is very low when the bleeder is active. This current is a small fraction of the nominal load current and can remain below 1 mA. At 1.01 seconds, the voltage across impedance R3 drops below the threshold, which occurs when the voltage at input node In is approximately 50 V. Controller 2 then turns off bleeder 1 and activates switch M2. Impedance R3 is shunted by switch M2, allowing a larger current to flow through the load LED. In this example, the current through load R3 rises to approximately 400 mA.

[0041] FIG. 2b shows the driver current, which is the current supplied by SMPS3 when the protection circuitry becomes active. At 1 second, bleeder 1 becomes active because this is the point at which the load LED is coupled to the active SMPS3 output. Bleeder 1 is configured to draw approximately 480 mA of current. SMPS3 and the capacitor at input node In supply this current. SMPS3 may not be able to supply such a large current, so the remaining current is supplied by the capacitor at input node In. This causes the voltage at input node In to drop, which can be seen in FIG. 2a. Controller 2 keeps bleeder 1 active until the voltage across impedance R3 drops below the threshold, which occurs at 1.01 seconds. After this point, controller 2 deactivates the bleeder, and the current that should be supplied by SMPS3 and the capacitor at input node In becomes zero. Because controller 2 also closes switch M2, the current does not actually go to zero. Therefore, current flows through the load LED. The current amplitude supplied to the load LED may correspond to the current supplied by the SMPS 3. In this example, the current through the load is approximately 400 mA.

[0042] Figure 2c shows the bleeder current drawn by bleeder 1. The bleeder is turned on at 1 second because this is the point at which the load LED is coupled to the output of active SMPS3. The current drawn by the bleeder may remain approximately constant or may decrease over time, as shown in Figure 2c. At 1.01 seconds, controller 2 turns off bleeder 1, and no more current is drawn by bleeder 1.

[0043] FIG. 3a shows a graph of the bus voltage (the voltage at input node In) over time as SMPS3 starts up with a load LED connected. At 6.9 seconds, SMPS3 starts up and supplies voltage V_bus to input node In. In this example, the load LED is a lighting load, more specifically, a solid-state lighting load. The voltage at input node In increases over time but remains below the forward voltage of the load LED. While the voltage at input node In increases, current does not flow through the load LED, and therefore through impedance R3, so controller 2 disables bleeder 1 and closes switch M2. When the voltage at the input node In reaches the forward voltage of the load LED, current begins to flow. This occurs when the voltage at input node In reaches approximately 50 V. The current through the load LED rises to approximately 400 mA. It is assumed that SMPS3 startup is complete at 8.9 seconds.

[0044] Figure 3b shows the current supplied by SMPS3 to its output over time. During start-up, which occurs between 6.9 and 8.9 seconds, the voltage at the output of SMPS3 rises rapidly because the load cannot draw current as long as the voltage at input node In is lower than the forward voltage of the load LED. Shortly after 6.9 seconds, the voltage at input node In increases to exceed the forward voltage of the load. The load LED begins to conduct, allowing current to be supplied to the load LED by SMPS3. In the example shown, the current increases linearly as SMPS3 regulates it. In other examples, the current may increase at a different rate, for example, logarithmically. The current continues to increase until it reaches the current level to which SMPS3 is designed to regulate it. In this example, the SMPS is designed to supply approximately 400 mA of current.

[0045] Figure 3c shows the bleeder current drawn by bleeder 1 during start-up of SMPS 3. Preferably, bleeder 1 is inactive throughout the start-up period of SMPS 3 and therefore draws no current.

[0046] Impedance R3 may have a low resistance, e.g., a sense resistor on the order of milliohms or ohms, or may have a relatively large resistance on the order of hundreds of ohms to several kiloohms. Using a low resistance may be desirable to keep the voltage across the impedance within a preferred range. A higher impedance allows impedance R3 to act as surge protection while also providing a voltage within the desired range to controller 2 or voltage sensing circuit R2.

[0047] Those skilled in the art can understand and effect other variations to the disclosed embodiments in practicing the claimed invention, from a study of the drawings, the specification and the appended claims. In the claims, the word "comprises" does not exclude other elements or steps, and the singular 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 interpreted as limiting the scope.

Claims

1. an SMPS adapted to provide a regulated current to an input node; Load and a protection circuit for protecting the load, the protection circuit comprising: the input node adapted to be coupled to the SMPS; a bleeder coupled between the input node and a return node; a first output node adapted to be coupled to the input node and to a load; a second output node adapted to be coupled to the load, the load being couplable between the first output node and the second output node; an impedance coupled between the second output node and the return node; a switch coupled in parallel with the impedance; a controller adapted to control the switch and the bleeder, the controller is adapted to activate the bleeder and open the switch when a voltage across the impedance is above a threshold, and the controller is adapted to deactivate the bleeder and close the switch when a voltage across the impedance is below the threshold.

2. 10. The lighting system of claim 1, further comprising a voltage sensing circuit for sensing a voltage across the impedance.

3. 3. The lighting system according to claim 1, wherein the bleeder comprises a series arrangement of a resistor and a switching element.

4. 4. A lighting system according to any one of the preceding claims, wherein the impedance has a resistance of at least 1 kΩ.

5. 5. A lighting system according to any one of claims 1 to 4, wherein the resistance of the impedance is greater than the resistance of the load.

6. 6. A lighting system according to any one of the preceding claims, wherein the amplitude of the current drawn by the bleeder is greater than the amplitude of the current through the load.

7. 7. The lighting system according to claim 1, wherein the load is a lighting load.

8. The lighting system of claim 7 , wherein the lighting load comprises a solid-state light source.

9. 9. A lighting system according to any one of claims 1 to 8, wherein the load and the protection circuit are arranged on a first, single PCB and the SMPS is arranged on a second, different PCB.

10. 10. A lighting system according to any one of the preceding claims, wherein the load is adapted to be replaced whilst keeping the SMPS in an operational mode.

11. 11. The lighting system of claim 1, wherein the SMPS is configured to operate in an overvoltage protection mode during replacement of the load.

12. 12. A lighting system according to any one of claims 1 to 11, wherein the protection circuit prevents current from flowing through the load when the voltage supplied by the SMPS exceeds a threshold value.

13. 13. The lighting system of any one of claims 1 to 12, wherein the bleeder remains inactive as long as the load is disconnected from the SMPS.

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