Surge protection circuit

Abstract

A surge protection circuit for a DC power supply. The voltage clamp circuit is connected between the power supply terminal and the protective ground terminal. The voltage clamp circuit is configured to reduce its impedance when a voltage across it exceeds a threshold voltage. The active switch is configured to control an electrical parameter of the voltage clamp circuit such that an impedance of the voltage clamp circuit restores to a high when the voltage across the protection ground terminal decreases again. In one embodiment, an active switch is connected between a positive power supply terminal and a negative power supply terminal. In another embodiment, there is another recoverable component in series with the voltage clamping circuit and having a rated voltage that is less than the rated voltage of the voltage clamping circuit, and the active switch is connected in parallel with the recoverable component.

Description

Technical Field

[0001] The present invention relates to the field of surge protection. Background Art

[0002] There are various types of drivers for driving or powering electrical devices such as lighting devices. Surge protection circuits are often provided for use with such drivers in order to protect the electrical devices from surge voltages.

[0003] Some existing surge protection circuits designed for AC power sources include a voltage clamping circuit between the AC power terminals and protective ground. When a voltage surge occurs, the voltage across the voltage clamping circuit exceeds the breakdown voltage. This causes the voltage clamping circuit to become conductive and clamp the voltage at the power terminals to the clamping voltage. After the surge, the voltage across the voltage clamping circuit must drop below the recovery threshold voltage in order to reset the voltage clamping circuit for future use. For AC power sources, this is achieved through the natural zero crossing of the AC power supplied to the power terminals.

[0004] With the development of technology, surge protection on the DC side is also preferred. Figure 5 A known circuit using a voltage clamping circuit with a DC power supply is shown. The normal output voltage of the DC power supply is only 28V, which is low enough to reset the voltage clamping circuit. However, such a surge protection circuit cannot be used with a DC power supply whose output voltage during normal operation is generally greater than the recovery threshold voltage. For example, in an LED driver, the output voltage provided by the DC power supply (e.g., between V+ and V-) can be several hundred volts, and the corresponding voltage between V+ and protective ground (GND) is also high, making it impossible to reset the voltage clamping circuit.

[0005] Therefore, unless reset, the voltage clamp circuit cannot protect against surge voltages. Consequently, there is a continuing desire to improve the operation and / or performance of surge protection circuits, and in particular, to provide a surge protection circuit that can be used with DC power supplies. More specifically, there is a need for a technique that can reset a voltage clamp circuit used with a high-voltage DC power supply, where the rated voltage of the DC power supply is too high to reset the voltage clamp circuit on its own.

[0006] US5436786A1, GB2542789A and JP2015211602A disclose a parallel bypass component, which is used to bypass a related surge protection component to restore the surge protection component to an off state. Summary of the Invention

[0007] The present invention is defined by the claims.

[0008] The proposed invention overcomes the aforementioned issues by using an additional active switch to reset the voltage clamp circuit at the end of a surge voltage (i.e., when the voltage across the voltage clamp circuit drops below the breakdown voltage). For example, the active switch can prevent current from flowing through the voltage clamp circuit at the end of a surge voltage, thereby resetting the voltage clamp circuit. Alternatively, the active switch can limit the voltage across the voltage clamp circuit at the end of a surge voltage, thereby resetting the voltage clamp circuit. This provides a technique for implementing surge protection using widely available surge protection circuit components and high-voltage DC-link designs.

[0009] Therefore, the proposed method overcomes the previously unsolved problem of surge protection for DC power supplies.

[0010] According to an example of one aspect of the present invention, a surge protection circuit for use between a DC power source and a load is provided.

[0011] The surge protection circuit includes a power terminal, a protective ground terminal, and a voltage clamping circuit. The power terminal is configured to be connected between a DC power source and a load, wherein the power terminal is one of the following: a positive power terminal of a surge protection circuit (200, 300) configured to be connected between a positive output of the DC power source and a positive input of the load, and a negative power terminal of a surge protection circuit (200, 300) configured to be connected between a negative output of the DC power source and a negative input of the load. The protective ground terminal is different from the positive terminal and the negative terminal and is configured to be connected to a protective ground. The voltage clamping circuit is connected between the power terminal and the protective ground terminal and is adapted to: in response to a voltage across the voltage clamping circuit exceeding a surge threshold voltage, reduce the impedance of the voltage clamping circuit to a low impedance and clamp the voltage across the voltage clamping circuit, and in response to an electrical parameter across the voltage clamping circuit falling below a recovery threshold, restore to a high impedance.

[0012] There are two implementations. First, the surge protection circuit further includes a control circuit including an active switch connected between the positive power supply terminal and the negative power supply terminal and configured to limit an electrical parameter across the voltage clamp circuit to below a recovery threshold when operated. The control circuit is adapted to operate the active switch to short-circuit the DC power supply after the voltage exceeding the surge threshold voltage ends, thereby restoring the voltage clamp circuit to a high impedance.

[0013] The method provides a technique that achieves one or both of the following functions: actively pulling voltage and / or current at the output to reset the voltage clamping circuit; and creating a fault at the output of the DC power supply to trigger the DC power supply's inherent protection mechanism to limit its output power, thereby resetting the voltage clamping circuit.

[0014] This embodiment is particularly suitable for DC power supplies with such inherent protection mechanisms. For example, the DC power supply may have undervoltage protection or overcurrent protection. Active circuits can create such undervoltage or overcurrent, thereby stopping or interrupting normal operation of the DC power supply.

[0015] Second, the surge protection circuit further includes a control circuit, the control circuit including a restorable component connected in series with the voltage clamping circuit; and an active switch connected in parallel with the restorable component, wherein the restorable component has a rated voltage that is less than the rated voltage of the voltage clamping circuit, and the control circuit is configured to operate the active switch to restore the voltage clamping circuit to high impedance by: closing the active switch to bypass the restorable component and restoring the restorable component to a high impedance state; and then opening the active switch to thereby cut off current through the voltage clamping circuit.

[0016] This provides a reliable and rapid forced recovery technique for a voltage clamp circuit. This embodiment does not rely on the DC power supply to limit its output to reset the voltage clamp circuit, as in the previous embodiment, but instead actively shuts down the voltage clamp circuit. Therefore, it does not require the DC power supply to have inherent protection mechanisms and is compatible with a wider variety of DC power supplies. Preferably, a recoverable component with a smaller rated voltage is easier to shut down than a voltage clamp circuit with a higher rated voltage.

[0017] The present disclosure provides a mechanism for providing surge protection to a load powered by a DC power source.

[0018] The voltage clamp circuit is configured to be triggered when the voltage supplied to the load (e.g., a common-mode voltage) exceeds a surge threshold voltage. When triggered, the impedance of the voltage clamp circuit drops or decreases. The voltage clamp circuit can be designed to restore to its original (higher) impedance when an electrical parameter through or across the voltage clamp circuit (e.g., a voltage across the voltage clamp circuit or a current through the voltage clamp circuit) drops below a recovery threshold (e.g., the voltage across the voltage clamp circuit drops below a second (lower) threshold voltage).

[0019] It is recognized that for DC power supplies, the normal power (sometimes referred to as the rated power) supplied to the load by the DC power supply may provide electrical parameters that exceed the recovery threshold. This effect is particularly pronounced in high-voltage scenarios, such as when powering lighting modules. Therefore, under normal conditions, the voltage clamping circuit cannot restore its original impedance even after the surge voltage ends.

[0020] The proposed method utilizes an active switch that is configured to limit the current through, or the voltage across, the voltage clamping circuit for a period of time after the surge voltage ends. This effectively deactivates or resets the voltage clamping circuit. This provides a mechanism for providing surge voltage protection using a voltage clamping circuit with a DC power supply.

[0021] A voltage exceeding the surge threshold voltage may be caused by a surge voltage. The surge voltage may be caused by a surge in AC power from a DC power source. Alternatively, the surge voltage may be injected by lightning or another electrostatic discharge between the DC power source and the load, for example, if lightning strikes the power line to the load.

[0022] The electrical parameter across the voltage clamp circuit can be a voltage or a current. For example, when the voltage across the voltage clamp circuit is below a second threshold voltage, which is lower than the surge threshold voltage, the voltage drops below a recovery threshold. In some alternative examples, the current across the voltage clamp circuit can drop below the recovery threshold when the current through the voltage clamp circuit is below a first threshold current.

[0023] Methods for appropriately configuring or designing a voltage clamp circuit for this purpose will be clear to those skilled in the art based on the teachings of this application.These methods provide a technique for defining or controlling how to reset or restore a voltage clamp circuit.

[0024] The voltage clamping circuit may include at least one of the following: a voltage clamping component configured to clamp the voltage across the voltage clamping component in response to the voltage across the voltage clamping circuit exceeding a surge threshold voltage, optionally clamping the voltage across the voltage clamping component to a non-zero clamping voltage; and a conductive component configured to become conductive in response to the voltage across the voltage clamping circuit exceeding the surge threshold voltage. Both components can act as a voltage clamping circuit by themselves. However, they are particularly advantageous when both are formed into a voltage clamping circuit to perform fast surge protection (via the conductive component) while reducing the risk of sudden changes in the voltage supplied to the load via the voltage clamping component. The voltage clamping component is typically a varistor, and more commonly a metal oxide varistor (MOV). The conductive component is typically a gas discharge tube (GDT). Note that other components may also be used.

[0025] The control circuit may further include a detection component configured to sense a current passing through the voltage clamp circuit. The control circuit may be configured to operate the active switch in response to the sensed current. For example, the control circuit may operate the active switch when the sensed current rises above a second threshold current. This approach provides a simple technique for detecting when the voltage clamp circuit is activated, thereby detecting the current flowing therethrough and, therefore, when the voltage clamp circuit needs to be reset.

[0026] The control circuit can be configured to cease operating the active switch in response to the sensed current falling below a second threshold current. In a particularly preferred example, the control circuit is configured to cease operating the active switch when the sensed current falls to zero. This method provides a technique for deactivating the active switch when the function of resetting the voltage clamp circuit is no longer required (i.e., when the voltage across the voltage clamp circuit may have fallen below the surge threshold voltage and the surge has ceased).

[0027] The control circuit may further include a delay circuit configured to delay the sensed current through the voltage clamp circuit; and the control circuit is configured to operate (and optionally stop operating) the active switch in response to the delayed sensed current. This increases the robustness of the surge protection circuit and reduces the likelihood that the voltage clamp circuit will be triggered by noise in the circuit.

[0028] The control circuit can be configured to operate the active switch in response to the delayed sensed current rising above a first value; and to cease operating the active switch in response to the delayed sensed current falling below a second value. This approach provides a simple and reliable mechanism for controlling the operation of the active switch. The first value and the second value can be the same or different.

[0029] The detection assembly may include a first winding connected in series with a voltage clamping circuit; and a second winding magnetically coupled to the first winding to generate a current in response to current flowing through the voltage clamping circuit. The control circuit may be adapted to operate an active switch in response to the generated current. This approach provides a low-cost yet accurate mechanism for sensing current passing through the voltage clamping circuit. This technique also electrically isolates the control of the active switch from the voltage clamping circuit, reducing the likelihood of accidental triggering of the active switch. Furthermore, inrush currents themselves are typically too large to safely control the active circuit, so the windings implement downconversion.

[0030] The power terminal may be a positive power terminal configured to be connected between a positive output of the DC power supply and a positive input of the load.The power terminal may alternatively be a negative terminal.

[0031] The surge protection circuit may further include a negative power terminal configured to be connected between a negative output of the DC power source and a negative input of the load.

[0032] A lighting module is also provided, comprising: a surge protection circuit as disclosed herein; a load, wherein the load comprises an LED lighting load; and a housing for the LED lighting load, wherein the housing is configured to be connected to a protective ground. The LED lighting load and the housing may have a parasitic leakage path along which the lighting load breaks down when a voltage, optionally a surge voltage, supplied to the LED lighting load relative to the protective ground exceeds a breakdown voltage. The proposed technique is particularly advantageous when used to provide surge protection for a load that, if a surge voltage occurs, would have a parasitic leakage path that could damage the load or pose a danger to individuals near the load.

[0033] The surge threshold voltage is preferably lower than the breakdown voltage. This allows the surge protection circuit to be adapted to prevent the voltage supplied to the LED lighting load from reaching the breakdown voltage, thereby preventing the lighting module from breaking down at the parasitic leakage path. This technique advantageously provides a more reliable lighting module, for example, one that is less susceptible to damage from any surge voltage.

[0034] A lighting arrangement is also provided, comprising: a lighting module as disclosed herein; and a DC power supply, wherein a positive output of the DC power supply is connected to a positive input of a load via a positive terminal of a surge protection circuit, and a negative output of the DC power supply is connected to a negative input of the load via a negative terminal of the surge protection circuit. The DC power supply is configured to be operable in an operating mode in which the DC power supply is adapted to generate a rated power at the power supply terminal that is capable of producing an electrical parameter above a recovery threshold across the voltage clamping circuit.

[0035] After the voltage exceeds the surge threshold voltage and the active switch is not operated, the DC power supply can be operated in the operating mode. Therefore, the present application provides compatibility between the voltage clamping circuit and the DC power supply on the DC side, and the DC side can also be protected by the well-developed voltage clamping circuit with only the additional simple control circuit proposed by the present application. This is very low cost and very reliable.

[0036] In some examples, the DC power supply is configured to provide a first supply voltage at the positive terminal and a second supply voltage at the negative terminal, the first supply voltage being greater than the second supply voltage. The control circuit can be connected between the positive terminal and the negative terminal.

[0037] The control circuit can be configured to short-circuit the DC power supply, wherein the DC power supply is adapted to switch from an operating mode to a protection mode upon the short circuit and reduce the power on the positive output to a power lower than the rated power, wherein the lower power is adapted to generate an electrical parameter across the voltage clamping circuit that is lower than a recovery threshold so as to restore the voltage clamping circuit to high impedance.

[0038] This method utilizes the protection mode of the DC power supply to improve surge protection.

[0039] These and other aspects of the invention will be apparent from and elucidated with reference to the embodiment(s) described hereinafter. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] For a better understanding of the invention, and to show more clearly how it may be carried into effect, reference will now be made, by way of example only, to the accompanying drawings, in which:

[0041] Figure 1 The figure shows the existing surge protection circuit on the AC input side;

[0042] Figure 2 A proposed surge protection circuit according to one embodiment of the present invention is illustrated;

[0043] Figure 3 Another proposed surge protection circuit according to another embodiment of the present invention is illustrated;

[0044] Figure 4 illustrates a lighting arrangement utilizing the proposed surge protection circuit; and

[0045] Figure 5 The figure shows a conventional surge protection circuit suitable for the DC side of a low DC voltage. DETAILED DESCRIPTION

[0046] The present invention will be described with reference to the accompanying drawings.

[0047] It should be understood that the detailed description and specific examples, while indicating exemplary embodiments of the devices, systems, and methods, are for illustrative purposes only and are not intended to limit the scope of the present invention. These and other features, aspects, and advantages of the devices, systems, and methods of the present invention will be better understood from the following description, the appended claims, and the accompanying drawings. It should be understood that the drawings are merely schematic and not drawn to scale. It should also be understood that the same reference numerals are used throughout the drawings to indicate the same or similar components.

[0048] The present invention provides a surge protection circuit for a DC power supply. A voltage clamping circuit is connected between a power terminal and a protective ground terminal. The voltage clamping circuit is configured to reduce its impedance when a voltage across the voltage clamping circuit exceeds a threshold voltage. When the voltage across the protective ground terminal decreases again, an active switch is configured to control an electrical parameter of the voltage clamping circuit so that the impedance of the voltage clamping circuit returns to a high value.

[0049] Embodiments are based on the recognition that using a voltage clamp circuit in a DC-based system means that the voltage across the voltage clamp circuit may never decrease sufficiently to allow the impedance of the voltage clamp circuit to recover after a surge voltage in the DC-based system itself. This means that even after the surge voltage ends, the voltage clamp circuit will freewheel and continue to conduct due to the normal / rated output power of the DC-based system. Using an active switch forces the voltage clamp circuit to return to a higher impedance, thereby reducing or preventing conduction of the voltage clamp circuit after the surge voltage ends and resetting the voltage clamp circuit for future surge protection.

[0050] Figure 1 The figure shows a conventional surge protection circuit 100 used between an AC power source 191 and a load 192. For the sake of clarity, the structure and operation function of the surge protection circuit 100 will be described below.

[0051] AC power supply 191 provides a positive output L (live) and a negative output N (neutral). It should be understood that in practice, AC power supply 191 provides a different output between positive and negative outputs that cyclically or periodically changes polarity in the form of a sine wave.

[0052] For example, the load 192 may include a rectifying arrangement 192 (here a bridge rectifier), a driver circuit 195, a heat sink and / or housing 198, and an LED lighting load 199 (comprising one or more LEDs). The load is connected to the positive and negative outputs of the AC power source 191 to be powered therefrom.

[0053] For various loads, it is important to keep the maximum voltage supplied to them below the maximum allowable voltage. For example, if an LED lighting load includes an insulating dielectric layer, damage to the insulating dielectric layer (caused by the high voltage supplied to the LED lighting load) or damage to the LED will cause failure. Therefore, the surge protection circuit 100 is an important component for improving the reliability of the load 192.

[0054] The surge protection circuit 100 includes a first power terminal 111 configured to be connected between an AC power source 191 and a load 192. In the example shown, the first power terminal 111 is a positive power terminal connected between a positive output L of the AC power source 191 and a positive input 192A of the load 192.

[0055] The surge protection circuit 100 further includes a protective ground terminal 115 configured to be connected to a protective ground GND.

[0056] The surge protection circuit 100 includes a first voltage clamping circuit VDR1, G1 connected between a first power terminal 111 and a protective ground terminal 115. The first voltage clamping circuit includes a voltage clamping component VDR1 and a conductive component G1.

[0057] The voltage clamping component VDR1 is configured to clamp a maximum voltage across the voltage clamping component to a (non-zero) clamping voltage.

[0058] An example of a suitable voltage clamping component is a varistor, such as a metal oxide varistor (MOV). When the voltage across the varistor exceeds the varistor threshold voltage, it breaks down and conducts electricity while clamping the voltage across it to a non-zero voltage, such as to the varistor threshold voltage.

[0059] Another example of a voltage clamping component is a Zener diode arranged such that the breakdown voltage of the Zener diode serves as the clamping voltage.

[0060] Other suitable examples will be apparent to those skilled in the art.

[0061] The conductive component G1 is any suitable component that becomes conductive (ie, reduces its impedance to a low impedance) when a voltage across the conductive component exceeds a conductive component threshold voltage.

[0062] One example of a suitable conductive component is a gas discharge tube (GDT).When the voltage across the gas discharge tube exceeds the breakdown voltage of the GDT, it becomes conductive, causing the voltage across the conductive component to drop significantly, such as to zero or near zero (eg, effectively negligible).

[0063] Another example of a suitable conductive component is a thyristor surge protection device (TSPD) or thyristor surge suppressor (TSS).The effective function of a TSPD / TSS is similar to that of a GDT, but relies on a different mechanism.

[0064] Other suitable examples (eg involving transistor-based arrangements) will be apparent to those skilled in the art.

[0065] In use, when a surge voltage occurs between the AC line and a protective ground (e.g., between line L and the protective ground wire), this surge voltage is applied across the voltage clamping circuit VDR1, G1 (i.e., the common-mode voltage at the power supply terminal 111). Typically, the parasitic impedance of a non-conductive gas discharge tube is much higher than that of an MOV varistor. Therefore, the surge voltage is primarily applied to the gas discharge tube and exceeds the threshold voltage of the conductive component G1. This component rapidly enters a low-voltage conductive state, thereby turning on. Consequently, the voltage across the conductive component drops to a second clamping voltage.

[0066] After the conductive component is turned on, the voltage across the conductive component drops rapidly. This increases the voltage across the voltage clamping component. This causes the voltage clamping component to clamp the voltage across the voltage clamping component (and the entire voltage clamping circuit) to the clamping voltage.

[0067] In this manner, the residual voltage presented to the load is determined by the clamping voltage (across the voltage clamping component) and a second clamping voltage (which is very low or negligible) across the conductive component.

[0068] When the surge voltage has passed or ends, the voltage across the line and neutral points is a normal AC sinusoidal voltage. When the AC sinusoidal voltage crosses zero at the first power terminal 111, the voltage across the voltage clamping circuit VDR1 and G1 also drops to a very low potential, allowing the voltage clamping circuit to reset itself to a high impedance. The conductive component G1 and the voltage clamping component VDR1 will automatically exit the low-voltage conductive state and increase their impedance.

[0069] It will be appreciated that an electrical parameter (eg, voltage and / or current) across the voltage clamp circuit VDR1 , G1 needs to drop below a recovery threshold in order for the voltage clamp circuit to exit the low voltage / low impedance conductive state and increase its impedance.

[0070] The surge protection circuit also includes a second voltage clamping circuit VDR2, G1 between the second power supply terminal 112 and the protective ground terminal 115. If a surge occurs between the neutral point N and the protective ground GND, the varistor VDR2 and the GDT G1 will trigger. The operation of the second voltage clamping circuit is similar / identical to that of the first voltage clamping circuit and is not described for the sake of simplicity.

[0071] It has been recognized herein that such existing surge protection devices are designed for use with AC power supplies only. More specifically, the switching off of the voltage clamping circuit (ie, the increase in impedance) relies on the natural zero crossing of the AC signal provided by the AC power supply.

[0072] like Figure 5As shown, placing a voltage clamp circuit on the DC side is known. The normal DC voltage is 28V, which can be low enough to reset the voltage clamp circuit. However, if the AC power supply is replaced with a DC power supply, where the DC signal provided by the DC power supply does not have a natural zero crossing (because the DC signal is constant) and / or the DC voltage of the DC signal is insufficient to reset the voltage clamp circuit (for example, if the DC power supply is a high-voltage DC power supply), then this existing surge protection device topology cannot be directly applied. More specifically, after the voltage clamp circuit is triggered (and even after the surge has ended), the power provided by the DC power supply can provide an electrical parameter greater than the recovery threshold, i.e., such that the conductive component G1 does not exit the low-voltage conductive state. In this way, the voltage clamp circuit can continue to "freeze" and conduct current. For example, in an LED driver, the normal DC output voltage is typically several hundred volts, and the corresponding potential between the DC positive terminal and the protective ground is also several hundred volts, making it impossible to reset the voltage clamp circuit.

[0073] The present disclosure proposes a technique for overcoming this problem.

[0074] More specifically, the present disclosure provides a technique for establishing an effective "near zero crossing" of a DC signal to effectively interrupt the freewheeling of a voltage clamp circuit.

[0075] Figure 2 A first embodiment of a surge protection circuit 200 is illustrated for use between a DC power source (not shown, but potentially located to the left of the surge protection circuit) and a load (not shown, but could be located to the right of the surge protection circuit).

[0076] In the example shown, the DC power supply provides a first supply voltage V+ at the positive terminal 201 and a second supply voltage V- at the negative terminal 202. The first supply voltage is greater than the second supply voltage.

[0077] The surge protection circuit again includes a power terminal 211 and a protective ground terminal 215. The power terminal 211 is configured to be connected between a DC power source and a load. For example, the power terminal 211 may be the positive terminal 201. The protective ground terminal is configured to be connected to a protective ground GND.

[0078] The surge protection circuit 200 includes a voltage clamping circuit VDR, G1 connected between the power supply terminal 211 and the protection ground terminal 215. The voltage clamping circuit VDR, G1 may be similar to Figure 1 Voltage clamping circuit for AC.

[0079] The voltage clamp circuit VDR, G1 is configured to reduce its impedance to a low impedance and clamp the voltage across the voltage clamp circuit in response to the voltage across the voltage clamp circuit exceeding a surge threshold voltage (ie, when a surge voltage occurs).

[0080] The voltage clamp circuit is further configured to restore to high impedance in response to an electrical parameter across the voltage clamp circuit falling below a restoration threshold. The electrical parameter may be a voltage across the voltage clamp circuit or a current through the voltage clamp circuit. Thus, the voltage clamp circuit may restore if the voltage across the voltage clamp circuit falls below a second threshold voltage, falls below a surge threshold voltage, and / or if the current through the voltage clamp circuit falls below a first threshold current.

[0081] The method for forming such a voltage clamping circuit has been described above. In particular, the voltage clamping circuit may include a voltage clamping component VDR and / or a conductive component G1. If both components are present, these components are connected in series.

[0082] If present, the voltage clamping component VDR is configured to clamp the voltage across the voltage clamping component, optionally to a non-zero clamping voltage, when the voltage across the voltage clamping circuit exceeds a surge threshold voltage (i.e., when a surge voltage occurs). This effectively reduces the impedance of the voltage clamping component at high voltage levels.

[0083] If present, the conductive component G1 is configured to become conductive in response to a surge voltage across the voltage clamp circuit exceeding a surge threshold voltage. In particular, the conductive component may be switched to have a low impedance.

[0084] In this way, the impedance of the voltage clamp circuit is significantly reduced, causing current to flow through the voltage clamp circuit.

[0085] The surge protection circuit further comprises a control circuit 250 comprising an active switch M1. In the example shown, the active switch is a MOSFET, but may be replaced by any other form of switch or switching circuit arrangement, such as a BJT or even a triac.

[0086] The active switch M1 is configured to clamp the electrical parameter across the voltage clamp circuit below a recovery threshold when operated. This effectively forces the voltage clamp circuit to reset to a higher impedance.

[0087] In the example shown, this is achieved by the active switch M1 (when operated) redirecting current from the power supply terminal 211 to the negative terminal 202 (i.e., effectively shorting the DC power supply or lowering the potential of the positive power supply terminal). The active switch diverts current from the voltage clamp circuit, and thereby the freewheeling current in the voltage clamp circuit is interrupted, causing the voltage clamp circuit to reset.

[0088] In other examples, the active switch M1 is configured to redirect current from the power supply terminal 211 to the protective ground terminal 215 (when operated). This effectively pulls the potential of the positive power supply terminal toward the protective ground. As a result, the voltage across the voltage clamp circuit is greatly reduced and reset.

[0089] The control circuit is adapted to operate the active switch for at least a period of time after the voltage exceeding the surge threshold voltage (e.g., the surge voltage) ends. Thereafter, it does not operate the active switch, which causes the voltage clamp circuit to return to high impedance as the electrical parameter decreases to or remains at the recovery threshold.

[0090] In order to know when to operate the voltage clamp circuit and when not to operate the voltage clamp circuit, in the illustrated embodiment, the control circuit 250 further includes detection components L1 , L2 configured to sense the current through the voltage clamp circuit.

[0091] The control circuit is configured to operate the active switch M1 in response to the sensed current. Specifically, the control circuit 250 can operate or activate the active switch in response to the sensed current rising above a second threshold current. This means that the active switch is operated when current flows through the voltage clamp circuit.

[0092] In the illustrated example, the detection assembly includes a first winding L1 connected in series with a voltage clamp circuit and a second winding L2 magnetically coupled to the first winding. Current flowing through the first winding L1 induces a current in the second winding L2. The current flowing through the second winding L2 charges a capacitor CL. When the voltage across the capacitor reaches a specific voltage, this indicates that the sensed current has risen to a second threshold current. Then, for example, a suitable voltage is supplied to the gate of the active switch, via capacitor C1, activating the active switch M1.

[0093] like Figure 2 As shown, the control circuit 250 may include additional control circuitry D1, D2, D3, D4, D5, D6, R1, R2, R3 for controlling the operation of the active switches. Nevertheless, the general principles of the control circuit remain unchanged.

[0094] For example, the control circuit arrangement may include a rectifying arrangement D1, D2, D3, D4 (e.g., in the form of a bridge rectifier) between the second winding L2 and the capacitor C1. The rectifier may detect surges across V+ and GND of positive or negative polarity. The capacitor C1 is used to convert the current through the second winding L2 into a voltage.

[0095] The control circuit arrangement may comprise a resistor arrangement R1, R2, R3. One or more of the resistor arrangements may be omitted. The resistor arrangement may be used as a biasing arrangement for appropriately biasing the gate voltage to the active switch via the capacitor C1.

[0096] The control circuit may further include a delay circuit capacitor C1 / C2 configured to delay the sensed current through the voltage clamp circuit.The control circuit may be configured to operate the active switch and optionally cease operating the active switch in response to the delayed sensed current.

[0097] More specifically, the control circuit 250 can operate the active switch in response to the delayed sensed current rising above a first value, and stop operating the active switch in response to the delayed sensed current falling below a second value. For hysteresis control, the first value and the second value can be the same or different.

[0098] In the control circuit 250 shown, this delay function is provided by the use of capacitor C1. Specifically, if the current through the first winding L1 suddenly rises (thereby increasing the current through the second winding L2), the voltage across the capacitor will remain low for a period of time, and then the active switch M1 is operated, effectively delaying the change in the active switch M1, which allows the voltage clamp circuit to begin to release the surge. The delay can be set according to the normal duration of the surge, which means that after the surge, the control circuit begins to operate the active switch M1.

[0099] Other methods or techniques for performing such a delay will be apparent to those skilled in the art.

[0100] It should be understood that, typically, a DC power supply is configured to operate in an operating mode in which it generates a rated power at the power supply terminals. The rated power produces (one or more) electrical parameters above a recovery threshold across the voltage clamp circuit. The DC power supply can provide this rated power when the terminals are not short-circuited, for example, when the active switch is not activated. Figure 2 Embodiments of the invention offer another advantage because the active switch pulls the DC power supply's output terminal. In many applications, a DC power supply is configured to enter a protection mode if both the positive and negative terminals are shorted together, reducing the power output at the positive terminal. In some embodiments, the active switch, when operated, shorts the DC power supply to force it into protection mode. In this protection mode, the DC power supply's output is significantly reduced, and the voltage on the positive output V+ can drop so low that it can reset the voltage clamp circuit. Thus, the DC power supply can be controlled to help suppress electrical parameters that cause the voltage clamp circuit to freewheel and ultimately stop freewheeling.

[0101] The protection mode of the DC power supply can also be designed to provide power below the recovery threshold. This can therefore restore the voltage clamp circuit to a high impedance.

[0102] Figure 3 An alternative surge protection circuit 300 is illustrated.

[0103] The overall structure of the alternative surge protection circuit 300 is similar to that of the previously described surge protection circuit 200. For the sake of simplicity, only the differences between the two circuits will be described. Figure 3 The difference is that the active switch is implemented at a different position.

[0104] The control circuit 350 also includes a recoverable component DIAC, VDR3, and GDT1 connected in series with the voltage clamp circuit. The recoverable component is configured to become conductive and / or reduce its impedance after a breakdown voltage across the recoverable component is exceeded. When an electrical parameter (e.g., voltage or current) across / through the recoverable component drops below a certain recovery threshold, the recoverable component can return to a high impedance.

[0105] Examples of recoverable components include DIACs, SiDACs, varistors, or gas discharge tubes. Other examples will be clear to those skilled in the art. Figure 3 Three alternatives for the resettable component are shown. It will be appreciated that only a single resettable component is required. The resettable component has a rating less than that of the voltage clamp circuit, for example, a rating of 20-40V compared to the 470V rating of the voltage clamp circuit.

[0106] The active switch M1 is positioned in parallel with the restorable component. The optional diode is positioned to enable current to flow from the voltage clamping circuit VDR1, G1 to the active switch, but not vice versa.

[0107] The DC power supply again provides a supply voltage V+ at the power terminal 201. The surge protection circuit again includes a protective ground terminal 215. The power terminal 211 is configured to be connected between the DC power supply and the load. For example, the power terminal 211 can be the positive terminal 201. The protective ground terminal is configured to be connected to a protective ground GND.

[0108] The surge protection circuit 200 includes a voltage clamp circuit VDR1 , G1 connected between a power supply terminal 211 and a protective ground terminal 215 .

[0109] The voltage clamp circuit VDR1 , G1 is configured to reduce its impedance to a low impedance and clamp the voltage across the voltage clamp circuit in response to the voltage across the voltage clamp circuit exceeding a surge threshold voltage (ie, when a surge voltage occurs).

[0110] In use, when a surge voltage occurs at the power supply terminal 211, the voltage between the power supply terminal and the protective ground terminal causes the voltage clamping circuit and the restorative component to activate, and the impedance of the voltage clamping circuit and the restorative component to decrease. This allows current to flow through the voltage clamping circuit, causing current to flow through winding L1. This current is sensed by the second winding L2 and causes the active switch M1 to be operated (first turned on) with a selectable time delay (e.g., caused by the charging of capacitor C1). This creates an alternative current path for the current that bypasses the restorative component, causing it to turn off. As the voltage between the power supply terminal and the protective ground terminal decreases, the active switch will further operate to turn off (as the current flowing through the first winding L1 decreases). This cuts off any path for current to pass through the voltage clamping circuit (because the restorative component will not turn on due to insufficient voltage and the active switch does not provide a current path). This, therefore, turns off the voltage clamping circuit.

[0111] In this manner, the control circuit is configured to operate the active switch M1 to restore the voltage clamping circuit to high impedance by first closing the active switch M1 to bypass the restorable component and restore the restorable component to a high impedance state; and then opening the active switch M1 to thereby cut off current through the voltage clamping circuit GDT.

[0112] Note that in this embodiment, the active switch is operated in a sequence of on and off to reset the voltage clamp circuit. Figure 2 In the embodiment, to reset the voltage clamp circuit, it is sufficient to simply turn on the active switch. Depending on the implementation of the active switch, the method for operating the active switch to reset the voltage clamp circuit may also vary, but all fall within the scope of "operation."

[0113] Figure 4 The lighting arrangement 40 employing an embodiment of the present invention is illustrated. Specifically, the lighting arrangement 40 includes a lighting module 400 and a DC power supply 450.

[0114] The DC power supply 450 is configured to provide a first supply voltage V+ at the positive terminal 211 and a second supply voltage V- at the negative terminal 212. The first supply voltage is greater than the second supply voltage. A protective ground GND is also defined.

[0115] The lighting module 400 (which itself represents one embodiment) includes any of the surge protection circuits 200, 300 disclosed herein.

[0116] The lighting module 400 further includes a load 410 (for a surge protection circuit), wherein the load includes an LED lighting load 411. In particular, the LED lighting load may include one or more LEDs (LED1, LED2, LED3). In the example shown, the LED lighting load includes an LED string.

[0117] The lighting module 400 also includes a housing 412 for the LED lighting load, wherein the housing is configured by default to be connected to a protective ground. Figure 4 Shown schematically.

[0118] Because LED lighting load 411 is typically placed on a conductive substrate close to the housing, a parasitic leakage path 415 exists between LED lighting load 411 and housing 412. When the voltage supplied to the LED lighting load relative to the protective ground (e.g., a surge voltage) exceeds the breakdown voltage, current is conducted along this parasitic leakage path. If a fault occurs, severe damage may occur, such as the LED being damaged by the large breakdown voltage.

[0119] To prevent breakdown, the surge threshold voltage (at which the voltage clamping circuit effectively reduces its impedance) is preferably less than the breakdown voltage. Thus, the surge protection circuit effectively clamps the voltage across the lighting module to below the breakdown voltage, ensuring that the voltage supplied to the LED lighting load never reaches the breakdown voltage and the lighting load never breaks down.

[0120] The surge protection circuit is coupled between one of the positive and negative terminals (serving as a power supply terminal) and the other of the positive and negative terminals or the protective ground terminal 215 .

[0121] The DC power supply 450 can be configured to operate in an operating mode in which it provides a rated power at the power terminal 211. The rated power can be capable of producing electrical parameters above the recovery threshold across the voltage clamp circuit, for example, having a sufficiently high voltage and / or current greater than the recovery threshold. This approach makes the advantages of the proposed active switch clear.

[0122] Example configurations of a DC power supply are well known to those skilled in the art and may include one or more cells or batteries and / or an AC-DC converter. The DC power supply may include additional circuitry, such as for performing power factor correction, DC-DC conversion (e.g., a voltage regulator), etc. The precise configuration or design of the DC power supply is not critical to the basic inventive concept, but certain design features may be used to advantage.

[0123] For example, some DC power supplies can be configured to enter a protection mode when their output is short-circuited. In the protection mode, the DC power supply is configured to reduce the power on the positive output to a power lower than the rated power ("protection power"). This configuration can be utilized by a control circuit that can be configured to short-circuit the DC power supply (e.g., only) when an active switch is operated or activated, such as Figure 2 The voltage clamp circuit can be designed so that the protection power is below the recovery threshold. This causes the voltage clamp circuit to revert to high impedance. Thus, this technique utilizes the operation of the DC power supply to control the recovery of the voltage clamp circuit.

[0124] Regardless of whether the DC power supply has such a protection mode, Figure 3 The illustrated embodiment may also be used to actively cut off any power to the voltage clamp circuit and reset the voltage clamp circuit.

[0125] Figure 4 A lighting arrangement utilizing the proposed surge protection circuit is illustrated. The lighting arrangement comprises an LED lighting module as described above and a DC power supply 450, wherein a positive output of the DC power supply is connected to a positive input of a load via a positive terminal of the surge protection circuit, and a negative output of the DC power supply is connected to a negative input of the load via a negative terminal of the surge protection circuit, wherein the DC power supply is configured to operate in an operating mode after a voltage exceeding a surge threshold voltage has ceased, without the active switch being operated, in which operating mode the DC power supply is adapted to generate a rated power at the power supply terminals that is capable of producing an electrical parameter above a recovery threshold across the voltage clamping component.

[0126] The DC power supply is configured to provide a first supply voltage at a positive terminal and a second supply voltage at a negative terminal, the first supply voltage being greater than the second supply voltage; and the control circuit is configured to short-circuit the DC power supply, wherein the DC power supply is adapted to switch from an operating mode to a protection mode upon short-circuit and reduce power on the positive output to a power lower than a rated power, wherein the lower power is adapted to generate an electrical parameter across the voltage clamping component that is lower than a recovery threshold so as to restore the voltage clamping component to a high impedance.

[0127] Variations to the disclosed embodiments may be understood and effected by those skilled in the art in practicing the claimed invention by studying 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.

[0128] 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.

[0129] If the term "adapted to" is used in the claims or description, it should be noted that the term "adapted to" is intended to be equivalent to "configured to". If the term "arranged" is used in the claims or description, it should be noted that the term "arranged" is intended to be equivalent to the term "system", and vice versa.

[0130] Any reference signs in the claims should not be construed as limiting the scope.

Claims

1. A surge protection circuit (200, 300) for use between a DC power supply (450) and a load (410), the surge protection circuit comprising: A power terminal (211) configured to be connected between the DC power source and the load, wherein the power terminal is one of the following: The positive power supply terminal of the surge protection circuit (200, 300) is configured to be connected between the positive output of the DC power supply and the positive input of the load, and The negative power supply terminal of the surge protection circuit (200, 300) is configured to be connected between the negative output of the DC power supply and the negative input of the load; a protective ground terminal (215) different from the positive terminal and the negative terminal and configured to be connected to a protective ground (GND); A voltage clamping circuit (VDR1, G1) is connected between the power supply terminal and the protective ground terminal and is adapted to: in response to a surge voltage across the voltage clamping circuit exceeding a surge threshold voltage, reducing an impedance of the voltage clamping circuit to a low impedance and clamping the voltage across the voltage clamping circuit; as well as reverting to high impedance in response to an electrical parameter across the voltage clamp circuit falling below a recovery threshold; as well as The control circuit (250, 350) includes: an active switch (M1) connected between the positive power terminal and the negative power terminal and configured to, when operated, limit the electrical parameter across the voltage clamp circuit to below the recovery threshold, wherein the control circuit is adapted to operate the active switch to short-circuit the DC power supply after the surge voltage ends, thereby causing the voltage clamp circuit to return to the high impedance, or A recoverable component (DIAC, VDR3, G2) is connected in series with the voltage clamping circuit (VDR1, G1); and an active switch (M1) is connected in parallel with the recoverable component, wherein the recoverable component has a rated voltage less than the rated voltage of the voltage clamping circuit, and the control circuit is configured to operate the active switch (M1) to restore the voltage clamping circuit to the high impedance by: closing the active switch (M1) to bypass the recoverable component and restore the recoverable component to a high impedance state; and then opening the active switch (M1) to thereby cut off current through the voltage clamping circuit (VDR1, G1).

2. The surge protection circuit of claim 1 , wherein the electrical parameter across the voltage clamp circuit falls below a recovery threshold when either or both of the following are met: The voltage across the voltage clamp circuit as the electrical parameter is below a second threshold voltage and below the surge threshold voltage, and The electrical parameter, a current through the voltage clamping circuit, is below a first threshold current.

3. The surge protection circuit according to claim 1 or 2, wherein the voltage clamping circuit comprises at least one of the following: a voltage clamping component (MOV) configured to clamp a voltage across the voltage clamping component in response to the voltage across the voltage clamping circuit exceeding the surge threshold voltage, optionally clamping the voltage across the voltage clamping component to a non-zero clamping voltage; and A conductive component (GDT) is configured to become conductive in response to the voltage across the voltage clamping circuit exceeding the surge threshold voltage.

4. The surge protection circuit according to any one of claims 1 to 3, wherein: The control circuit further includes a detection component configured to sense current through the voltage clamp circuit; and The control circuit is configured to operate the active switch in response to the sensed current, optionally in response to the sensed current rising above a second threshold current. 5 . The surge protection circuit of claim 4 , wherein the control circuit is configured to cease operating the active switch in response to the sensed current falling below the second threshold current, optionally to zero.

6. The surge protection circuit according to claim 4 or 5, wherein: The control circuit further includes a delay circuit configured to delay the sensed current through the voltage clamp circuit; and The control circuit is configured to operate the active switch in response to the delayed sensed current, and optionally to cease operating the active switch.

7. The surge protection circuit according to claim 6, wherein the control circuit is configured to: operating the active switch in response to the delayed sensed current rising above a first value; and Operating the active switch is ceased in response to the delayed sensed current falling below a second value.

8. The surge protection circuit according to any one of claims 4 to 7, wherein the detection component comprises: a first winding connected in series with the voltage clamping circuit; as well as a second winding magnetically coupled to the first winding to generate a current in response to the current flowing through the voltage clamp circuit, wherein the control circuit is adapted to operate the active switch in response to the generated current. 9 . The surge protection circuit according to claim 1 , wherein the power terminal is the positive power terminal configured to be connected between a positive output of the DC power source and a positive input of the load. 10 . The surge protection circuit of claim 9 , wherein the power terminal is the negative power terminal configured to be connected between the negative output of the DC power source and the negative input of the load.

11. A lighting module (400), comprising: The surge protection circuit (200, 300) according to any one of claims 1 to 10; The load (410), wherein the load comprises an LED lighting load (411); and a housing (412) for the LED lighting load, wherein the housing is configured to be connected to the protective ground, The LED lighting load and the housing have a parasitic leakage path (415), and when a voltage, optionally a surge voltage, supplied to the LED lighting load relative to the protective ground exceeds a breakdown voltage, the lighting load breaks down along the parasitic leakage path.

12. The lighting module of claim 11, wherein the surge threshold voltage is lower than the breakdown voltage, such that the surge protection circuit is adapted to prevent the voltage provided to the LED lighting load from reaching the breakdown voltage.

13. A lighting arrangement (40) comprising: The lighting module (400) according to any one of claims 11 or 12; as well as The DC power supply (450), wherein a positive output of the DC power supply is connected to the positive input of the load via the positive terminal of the surge protection circuit, and a negative output of the DC power supply is connected to the negative input of the load via the negative terminal of the surge protection circuit, wherein the DC power supply is configured to operate in an operating mode after the voltage exceeding the surge threshold voltage ends, without the active switch being operated, in which operating mode the DC power supply is adapted to generate a rated power at the power terminals, the rated power being capable of producing the electrical parameter above the recovery threshold across the voltage clamping component.

14. A lighting arrangement according to claim 13, wherein The DC power supply is configured to provide a first supply voltage at the positive terminal and a second supply voltage at the negative terminal, the first supply voltage being greater than the second supply voltage; and The control circuit is configured to short-circuit the DC power supply, wherein the DC power supply is adapted to switch from the operating mode to a protection mode upon the short-circuit and reduce power on the positive output to a power lower than the rated power, wherein the lower power is adapted to generate the electrical parameter across the voltage clamping component lower than the recovery threshold so as to restore the voltage clamping component to high impedance.

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