A lightning surge protection circuit for a gallium nitride power device in a PFC circuit

Abstract

This invention discloses a surge protection circuit for gallium nitride (GaN) power devices in a power factor correction (PFC) circuit, aiming to solve the problems of insufficient surge resistance of GaN power devices and the high residual voltage of existing surge protection schemes, which easily leads to overvoltage breakdown of GaN power devices. A surge suppression unit is set between the rectifier circuit and the PFC main circuit. The surge suppression unit adopts a common-mode inductor containing a first coil L2A and a second coil L2B, coupled with a varistor VR4 in series, and is paired with capacitors C1 and C2 to form a π-type filter. Under normal operating conditions, it performs voltage filtering. During a lightning surge, VR4 breaks down, generating a surge current in L2A. The second coil L2B couples to generate a reverse electromotive force to offset the surge voltage, reducing the residual voltage at the input of the PFC main circuit. A primary protection unit assists in surge suppression. The PFC main circuit adopts a Boost topology and GaN power devices. This circuit has a simple structure, low cost, and high reliability, and is suitable for surge protection of outdoor GaN power supplies such as LED streetlights.

Description

Technical Field

[0001] This invention relates to the field of circuit design technology, and in particular to a lightning surge protection circuit for gallium nitride power devices in a PFC circuit. Background Technology

[0002] With the development of third-generation semiconductor technology, gallium nitride (GaN) power devices, with their advantages of low on-resistance, fast switching speed, and high high-frequency energy efficiency, are widely used in PFC+LLC topology power supplies, effectively reducing heat loss and improving energy conversion efficiency. However, when such power supplies (e.g., LED street light power supplies) are installed in outdoor high-altitude environments, they are susceptible to lightning surges. GaN power devices typically employ a high electron mobility transistor (HEMT) structure, lacking an internal body diode and the avalanche withstand capability of silicon-based MOSFETs, resulting in significantly weaker surge resistance. Once subjected to surge overvoltage, dielectric breakdown can easily occur, leading to complete power supply failure. This not only threatens road safety but also significantly increases the maintenance costs of outdoor equipment. Frequent device replacements and fault repairs reduce the reliability of the power system, severely restricting the large-scale application of GaN power devices in outdoor high-surge-risk scenarios.

[0003] The root of the problem lies in the fact that in a typical PFC+LLC topology, the PFC circuit, acting as the pre-amplifier of the power supply, is directly connected to the AC grid. The gallium nitride (GaN) power devices are positioned in front of the large electrolytic capacitor in the PFC circuit, making them susceptible to direct impact from lightning surges. Furthermore, existing lightning surge protection schemes have shortcomings: traditional solutions rely on hard-clamping devices such as varistors or transient voltage suppressor diodes (TVS), but these present inherent contradictions. If low varistor voltage parameters are used to control the surge residual voltage within the safe threshold of the GaN power devices, leakage current increases dramatically under normal operating conditions, leading to increased system losses, accelerated varistor aging, and a sharp reduction in lifespan. Conversely, if varistor voltage parameters are increased to reduce losses, the surge residual voltage easily exceeds the tolerance limit of the GaN power devices, resulting in an extremely high risk of protection failure. Another type of active protection scheme based on controller detection and feedback triggering typically has a response time in the microsecond range, which cannot match the protection requirements of gallium nitride power devices that need to respond within the nanosecond range, thus failing to achieve effective protection. At the same time, this type of scheme requires customized algorithms and hardware circuits for different power supply topologies, resulting in poor versatility, high engineering implementation complexity, and the introduction of additional control devices significantly increases system costs, making it difficult to meet the engineering requirements of outdoor power supplies for high reliability, low cost, and ease of maintenance.

[0004] In summary, existing lightning surge protection solutions fall short in terms of protection accuracy, response speed, system losses, device lifespan, and engineering applicability, and cannot provide reliable protection for gallium nitride power devices without avalanche capability. Summary of the Invention

[0005] To solve the above-mentioned technical problems, the present invention provides a lightning surge protection circuit for gallium nitride power devices in a PFC circuit. The PFC circuit includes a rectifier circuit and a PFC main circuit containing a gallium nitride power device Q1. The lightning surge protection circuit includes a surge suppression unit connected between the rectifier circuit and the PFC main circuit. The surge suppression unit includes a varistor VR4, a common-mode inductor L2, a first filter capacitor C1, and a second filter capacitor C2. The common-mode inductor L2 includes a first coil L2A and a second coil L2B that are coupled to each other. The first coil L2A is connected in series with the varistor VR4 to form a surge discharge branch, which is connected between the positive and negative output terminals of the rectifier circuit. The second coil L2B is connected in series between the positive output terminal of the rectifier circuit and the input terminal of the PFC main circuit. One end of the first filter capacitor C1 is connected to the common connection point between the second coil L2B and the positive output terminal of the rectifier circuit, and the other end is connected to the negative output terminal of the rectifier circuit. The second filter capacitor C2 is connected across the input terminal of the PFC main circuit and the negative output terminal of the rectifier circuit.

[0006] The surge protection circuit for gallium nitride power devices in the PFC circuit provided by this invention employs a series connection of a common-mode inductor and a varistor. It utilizes the reverse electromotive force induced in the common-mode inductor coil at the moment of varistor breakdown. This reverse electromotive force is superimposed on and cancels out the intruding surge voltage, thereby reducing the surge voltage and achieving precise and rapid protection for the gallium nitride power devices. Furthermore, it features a simple structure, easy engineering implementation, low cost, and significant residual voltage suppression effect.

[0007] Specifically, under normal operating conditions: when the AC input terminal is normally input at 220V, the varistor VR4 is in a high-resistance cutoff state, the first coil L2A is unloaded, and there is no current conduction in the surge discharge branch where it is located; the DC power output from the rectifier circuit is input to the PFC main circuit after passing through the second coil L2B. At this time, the second coil L2B and the filter capacitors C1 and C2 together form a π-type filter circuit to filter the rectified DC voltage, making the voltage input to the PFC main circuit more stable. In the case of lightning surge: when a lightning surge enters the surge suppression unit through the rectifier circuit, when the voltage reaches the breakdown threshold of the varistor VR4, the varistor VR4 conducts, causing the surge discharge branch to conduct, and a surge current is generated in the first coil L2A; with the help of the coil coupling effect of the common mode inductor L2, the second coil L2B will induce a reverse electromotive force opposite to the direction of the surge voltage; this reverse electromotive force is superimposed and canceled by the intruding surge voltage, which greatly reduces the surge residual voltage at the input of the PFC main circuit, ensuring that the voltage across the gallium nitride power device Q1 is within the safe threshold.

[0008] As an optional solution for the lightning surge protection circuit of the present invention, the common mode inductor L2 adopts a high coupling coefficient magnetic core, and the first coil L2A and the second coil L2B adopt a double-wire parallel winding process with the winding direction being consistent.

[0009] As a preferred option among the above-mentioned alternatives, the common-mode inductor L2 uses a magnetic core model of SQ1918CKA120.

[0010] As an optional solution for the lightning surge protection circuit of the present invention, the varistor VR4 has a varistor voltage between the normal output voltage of the rectifier circuit and the withstand voltage threshold of the gallium nitride power device in the PFC main circuit.

[0011] As a preferred option among the above-mentioned alternatives, the varistor VR4 is a zinc oxide varistor with a varistor voltage of less than or equal to 561V, model number 7D511K.

[0012] As an optional solution for the lightning surge protection circuit of the present invention, both the first filter capacitor C1 and the second filter capacitor C2 are CBB capacitors, and the capacitance of both the first filter capacitor C1 and the second filter capacitor C2 is 474J.

[0013] As an optional embodiment of the lightning surge protection circuit of the present invention, the lightning surge protection circuit further includes a primary protection unit connected in series between the AC input terminal and the rectifier circuit; the primary protection unit consists of a fuse MOV, a varistor VR1, a varistor VR2, a varistor VR3, a thermistor NTC, and a gas discharge tube G1; wherein, the fuse MOV is connected in series in the live wire L of the AC input terminal, the thermistor NTC is connected in series between the neutral wire N of the AC input terminal and the neutral input terminal of the rectifier circuit; the varistor VR1 is connected across the live wire L and the neutral wire N of the AC input terminal; one end of the varistor VR2 is connected to the live wire branch after the fuse MOV, one end of the varistor VR3 is connected to the neutral wire N of the AC input terminal, the other ends of the varistor VR2 and the varistor VR3 are connected to one end of the gas discharge tube G1, and the other end of the gas discharge tube G1 is connected to the protective ground.

[0014] As a preferred option among the above-mentioned alternatives, the varistor VR1, varistor VR2, and varistor VR3 are all of model 14D561K, the gas discharge tube G1 is of model 2R3000V, and the thermistor NTC is of model 2.5D-13.

[0015] As an optional solution for the lightning surge protection circuit of the present invention, the rectifier circuit includes a bridge rectifier DB1, model GBJ1510; the rated current of the bridge rectifier DB1 is greater than or equal to 15A and the reverse withstand voltage is greater than or equal to 1000V; the PFC main circuit adopts a Boost topology, the gallium nitride power device Q1 is a HEMT structure, and the withstand voltage of the gallium nitride power device Q1 is greater than or equal to 650V; the drain of the gallium nitride power device Q1 is connected to the output terminal of the second coil L2B through the inductor L3 in the PFC main circuit, and the source of the gallium nitride power device Q1 is connected to the circuit ground.

[0016] The present invention also provides a power supply device that includes a lightning surge protection circuit for the gallium nitride power device in the above-mentioned PFC circuit, and the power supply device is used for LED driving.

[0017] The power supply device provided by this invention is a low-cost, highly reliable, and easy-to-design LED power supply device. By incorporating a surge protection circuit consisting of a common-mode inductor and a varistor connected in series, it achieves precise and rapid protection for gallium nitride (GaN) power devices. This ensures the stable operation of the LED power system and promotes the large-scale application of GaN power devices in outdoor high-surge-risk scenarios.

[0018] Additional aspects and advantages of the invention will be set forth in part in the description which follows, some of which will become clear as the description proceeds, and others will be learned by practicing the invention. Attached Figure Description

[0019] To more clearly illustrate the technical solutions of the embodiments of this application, the accompanying drawings used in the embodiments of this application will be briefly introduced below. It should be understood that the following drawings only show some embodiments of this application and should not be regarded as a limitation of the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0020] Figure 1 This is a schematic diagram of the lightning surge protection circuit for gallium nitride power devices in the PFC circuit of this application embodiment.

[0021] Figure 2 This is a simulation diagram of the lightning surge protection circuit for gallium nitride power devices in the PFC circuit of this application embodiment.

[0022] Figure 3 This is a residual voltage waveform diagram of the lightning surge protection circuit of the gallium nitride power device in the PFC main circuit of this application when it is struck by lightning. Detailed Implementation

[0023] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application. Furthermore, in the description of this application, the terms "first," "second," etc., are used only for distinguishing descriptions and should not be construed as indicating or implying relative importance.

[0024] This application provides a lightning surge protection circuit for gallium nitride power devices in a PFC circuit. The PFC circuit includes a rectifier circuit and a PFC main circuit containing a gallium nitride power device Q1. The lightning surge protection circuit includes a surge suppression unit connected between the rectifier circuit and the PFC main circuit. The surge suppression unit includes a varistor VR4, a common-mode inductor L2, a first filter capacitor C1, and a second filter capacitor C2. The common-mode inductor L2 includes a first coil L2A and a second coil L2B that are coupled to each other. It should be noted that the first coil L2A and the second coil L2B are coupled to each other. If a surge current is generated in the first coil L2A, the second coil L2B will induce a reverse electromotive force that is opposite to the direction of the surge voltage. The first coil L2A is connected in series with the varistor VR4 to form a surge discharge branch, which is connected between the positive and negative output terminals of the rectifier circuit. It should be noted that when a lightning surge enters the surge suppression unit through the rectifier circuit, when the voltage reaches the breakdown threshold of the varistor VR4, the varistor VR4 conducts, causing the surge discharge branch to conduct, and a surge current will be generated in the first coil L2A. The second coil L2B is connected in series between the positive output terminal of the rectifier circuit and the input terminal of the PFC main circuit. It should be noted that the reverse electromotive force generated by the second coil L2B is superimposed and canceled by the intruding surge voltage, which greatly reduces the surge residual voltage at the input terminal of the PFC main circuit and ensures that the voltage across the gallium nitride power device Q1 is within the safe threshold. One end of the first filter capacitor C1 is connected to the common connection point between the second coil L2B and the positive output terminal of the rectifier circuit, and the other end is connected to the negative output terminal of the rectifier circuit. The second filter capacitor C2 is connected across the input terminal of the PFC main circuit and the negative output terminal of the rectifier circuit. It should be noted that the second coil L2B, together with the filter capacitors C1 and C2, forms a π-type filter circuit to filter the rectified DC voltage, making the voltage input to the PFC main circuit more stable.

[0025] In some embodiments, the common-mode inductor L2 employs a high-coupling-coefficient magnetic core, and the first coil L2A and the second coil L2B are wound in parallel using a double-wire winding process with the winding direction aligned. It should be noted that the high-coupling-coefficient magnetic core reduces magnetic leakage between coils, improves energy transfer efficiency, and prevents surge energy loss due to magnetic leakage from reducing the induction effect. This ensures that the magnetic field generated by the surge current in L2A is efficiently transferred to L2B, maximizing the amplitude of the back electromotive force (EMF) and precisely matching the patented "back EMF cancels surge voltage" protection mechanism. When the two coils are wound in the same direction, the direction of the magnetic field generated by the surge current in the first coil L2A and the direction of the induced magnetic field in the second coil L2B are synergistically superimposed, maximizing the amplitude of the back EMF induced by the second coil L2B. This further improves the surge residual voltage suppression accuracy and enhances the circuit's reliability in extreme surge environments. Furthermore, the double-wire winding process maximizes magnetic coupling and minimizes leakage inductance and parasitic parameters. This allows the common-mode inductor to generate a back EMF more quickly and efficiently in surge suppression scenarios, thereby accurately canceling surge voltage.

[0026] In some embodiments, the common-mode inductor L2 uses an SQ1918C KA120 magnetic core. It should be noted that the SQ1918C KA120 core has advantages such as a closed magnetic circuit structure, high permeability material properties, and optimized dimensions. These advantages collectively ensure that the common-mode inductor L2 can achieve a theoretically extremely high coupling coefficient. This is the physical basis for realizing the core mechanism of the patent, which is to "generate maximized back electromotive force through efficient magnetic coupling to accurately offset surge voltage." This selection directly determines the performance ceiling, suppression accuracy, and reliability of the surge protection circuit.

[0027] In some embodiments, the varistor VR4's varistor voltage is between the normal output voltage of the rectifier circuit and the withstand voltage threshold of the gallium nitride power device in the PFC main circuit. It should be noted that setting the varistor VR4's varistor voltage within this range ensures that under normal operating conditions (when the rectifier circuit outputs a normal voltage), the varistor VR4 remains in a high-resistance cutoff state. It only breaks down and conducts before the surge residual voltage exceeds the normal output voltage of the rectifier circuit and approaches the withstand voltage threshold of the gallium nitride power device. Activating protection before the surge residual voltage reaches the dangerous withstand voltage value of the gallium nitride power device avoids ineffective conduction during normal operation and precisely protects the gallium nitride power device from overvoltage damage.

[0028] In some embodiments, the varistor VR4 is a zinc oxide varistor with a varistor voltage of less than or equal to 561V, model number 7D511K. It should be noted that the nominal varistor voltage of 7D511K is 510V±10%, which is between the normal output voltage of the rectifier circuit (approximately 310V) and the withstand voltage threshold of the gallium nitride MOSFET (650V). This ensures that the varistor VR4 remains high-resistance cutoff under normal operating conditions, while also accurately breaking down and conducting before the surge residual voltage approaches the withstand voltage of the gallium nitride power device.

[0029] In some embodiments, both the first filter capacitor C1 and the second filter capacitor C2 are CBB capacitors, and the capacitance of both the first filter capacitor C1 and the second filter capacitor C2 is 474J. It should be noted that CBB capacitors have low high-frequency dielectric loss and high insulation resistance, which can effectively attenuate the 100Hz ripple after rectification and high-frequency EMI interference, avoiding the defects of poor high-frequency characteristics of conventional electrolytic capacitors. The capacitance of 474J can filter out voltage ripple under normal operating conditions.

[0030] In some embodiments, the lightning surge protection circuit further includes a primary protection unit connected in series between the AC input terminal and the rectifier circuit; the primary protection unit consists of a fuse MOV, a varistor VR1, a varistor VR2, a varistor VR3, a thermistor NTC, and a gas discharge tube G1; wherein, the fuse MOV is connected in series in the live wire L of the AC input terminal, the thermistor NTC is connected in series between the neutral wire N of the AC input terminal and the neutral input terminal of the rectifier circuit; the varistor VR1 is connected across the live wire L and the neutral wire N of the AC input terminal; one end of the varistor VR2 is connected to the live wire branch after the fuse MOV, one end of the varistor VR3 is connected to the neutral wire N of the AC input terminal, the other ends of the varistor VR2 and the varistor VR3 are connected to one end of the gas discharge tube G1, and the other end of the gas discharge tube G1 is connected to the protective ground. It should be noted that the MOV fuse provides overload and short-circuit protection; the VR1 varistor suppresses differential-mode surges; the VR2, VR3, and G1 varistors work together to suppress common-mode surges; and the NTC thermistor is used to limit the power-on inrush current.

[0031] In some embodiments, the varistor VR1, varistor VR2, and varistor VR3 are all of model 14D561K, the gas discharge tube G1 is of model 2R3000V, and the thermistor NTC is of model 2.5D-13. It should be noted that the varistor voltage of the 14D561K is 560V, which is lower than the peak voltage of lightning surges (usually above 2kV) and higher than the AC input voltage of 220V, making it suitable for 220V input scenarios. Under normal operating conditions, it exhibits high resistance and low power consumption, and breaks down quickly during surges, effectively suppressing differential-mode / common-mode surges. The 2R3000V gas discharge tube accurately responds to high common-mode voltages, precisely adapting to the high common-mode voltage between the L / N line and the protective ground during outdoor lightning strikes. Under normal operating conditions, it has no open-circuit current, only breaking down and conducting when the common-mode surge exceeds 3000V, ensuring reliable discharge. The 2.5D-13 NTC thermistor represents a resistance of approximately 2.5Ω at room temperature (25℃). Its low resistance at room temperature does not affect power supply and suppresses start-up surge current. The combined effect of these three components significantly reduces the pressure on subsequent protection stages by attenuating surge peaks, and is cost-effective and easy to implement in engineering.

[0032] In some embodiments, the rectifier circuit includes a bridge rectifier DB1, model GBJ1510; the rated current of the bridge rectifier DB1 is greater than or equal to 15A, and the reverse withstand voltage is greater than or equal to 1000V; the PFC main circuit adopts a Boost topology, the gallium nitride power device Q1 is a HEMT structure, and the withstand voltage of the gallium nitride power device Q1 is greater than or equal to 650V; the drain of the gallium nitride power device Q1 is connected to the output terminal of the second coil L2B through the inductor L3 in the PFC main circuit, and the source of the gallium nitride power device Q1 is connected to the circuit ground. It should be noted that the rectifier circuit is used to convert the AC input to DC, providing a stable DC input voltage for the subsequent surge suppression unit and the PFC main circuit. The 15A rated current provides sufficient overload redundancy; the 1000V reverse withstand voltage is much higher than the rectified 310V DC peak voltage, avoiding the risk of reverse breakdown. The source of the gallium nitride power device Q1 is connected to the circuit ground, and the gate of the gallium nitride power device Q1 is controlled by the driving circuit to control the conduction state. By taking advantage of the high frequency and high efficiency characteristics of the gallium nitride power device, the power conversion efficiency is improved and the heat generation is reduced.

[0033] This application embodiment also provides a power supply device that includes a lightning surge protection circuit for the gallium nitride power device in the above-mentioned PFC circuit, and the power supply device is used for LED driving.

[0034] The following are some embodiments of this application, which will further describe in detail the technical aspects, circuit structure design and parameters of the control circuit of this application. Example 1

[0035] To facilitate implementation of this invention, the following specific component parameter configurations are provided, adapted to a PFC circuit with 220V AC input and 150W output power: (e.g.)Figure 1 As shown, it includes an AC input terminal (L live wire, N neutral wire), a rectifier circuit, a lightning surge protection circuit, and a PFC main circuit. The lightning surge protection circuit consists of a primary protection unit and a surge suppression unit. The primary protection unit is connected in series between the AC input terminal and the rectifier circuit to initially suppress the peak current and voltage of lightning surges. The surge suppression unit is connected between the rectifier circuit and the PFC main circuit and is the core surge residual voltage suppression unit.

[0036] Specifically, the primary protection unit consists of a fuse MOV, varistors VR1, VR2, and VR3, a thermistor NTC, and a gas discharge tube G1. The connections are as follows: the fuse MOV is connected in series with the live wire L of the AC input terminal; the thermistor NTC is connected in series between the neutral wire N of the AC input terminal and the neutral input terminal of the rectifier circuit; varistors VR1 are connected across the live wire L and neutral wire N of the AC input terminal; one end of varistors VR2 is connected to the live wire branch after the fuse MOV; one end of varistors VR3 is connected to the neutral wire N of the AC input terminal; the other ends of varistors VR2 and VR3 are connected together to one end of the gas discharge tube G1; and the other end of the gas discharge tube G1 is connected to the protective ground.

[0037] The MOV fuse is a 5A, 250V square fuse with stable fusing characteristics due to its square structure, capable of quickly cutting off overload / short-circuit fault circuits. Varistors VR1, VR2, and VR3 are all model 14D561K, and the gas discharge tube G1 is model 2R3000V. Varistor VR1 is connected across the live wire (L) and neutral wire (N) of the AC input terminal to suppress differential-mode surges. Varistors VR2 and VR3, together with the gas discharge tube G1, suppress common-mode surges. The NTC thermistor is model 2.5D-13, used for rapid temperature rise and current limiting during surges, and has low resistance at room temperature, not affecting power supply.

[0038] Specifically, the rectifier circuit includes a bridge rectifier DB1, model GBJ1510, which converts the AC input voltage into a unidirectional pulsating DC voltage to provide the necessary DC input for the subsequent circuits.

[0039] Specifically, the surge suppression unit includes a varistor VR4, a common-mode inductor L2, a first filter capacitor C1, and a second filter capacitor C2, with the common-mode inductor L2 and the varistor VR4 connected in series. The specific connection is as follows: the common-mode inductor L2 includes a first coil L2A and a second coil L2B coupled together; the first coil L2A and the varistor VR4 are connected in series to form a surge discharge branch, which is connected between the positive and negative output terminals of the rectifier circuit; the second coil L2B is connected in series between the positive output terminal of the rectifier circuit and the input terminal of the PFC main circuit, forming the main power transmission path; one end of the first filter capacitor C1 is connected to the common connection point between the second coil L2B and the positive output terminal of the rectifier circuit, and the other end is connected to the negative output terminal of the rectifier circuit; the second filter capacitor C2 is connected between the input terminal of the PFC main circuit and the negative output terminal of the rectifier circuit.

[0040] The common-mode inductor L2 uses a high-coupling-coefficient magnetic core. The first coil L2A and the second coil L2B are wound in the same direction. The first filter capacitor C1 and the second filter capacitor C2 are CBB capacitors with a capacitance of 474J. The varistor VR4 is a zinc oxide varistor with a current carrying capacity of ≥1kA, model 7D511K. The varistor VR4 maintains high resistance and is cut off under normal operating conditions. It breaks down and conducts before the surge residual voltage approaches the withstand voltage of the gallium nitride power device.

[0041] Specifically, the PFC main circuit adopts a Boost topology, and the gallium nitride power device Q1 is a HEMT structure. The withstand voltage of the gallium nitride power device Q1 is greater than or equal to 650V. The drain of the gallium nitride power device Q1 is connected to the output terminal of the second coil L2B of the common mode inductor L2 in the surge suppression unit through the PFC inductor L3. The source of the gallium nitride power device Q1 is connected to the circuit ground and is the direct bearer of the surge residual voltage. The model of the gallium nitride power device Q1 is G1N65R150PB, with an on-resistance of 150mΩ, extremely low high-frequency switching loss, and is suitable for high-frequency operation scenarios of PFC circuits.

[0042] Under normal operating conditions, when the AC input terminal is normally input at 220V, varistors VR1, VR2, and VR3 are all in a high-impedance cutoff state. VR1 has no differential-mode current conduction, and varistors VR2 and VR3 have no common-mode current conduction. Gas discharge tube G1 remains open, with no current discharge and no additional system losses. Varistor VR4 is in a high-impedance cutoff state, the first coil L2A is idle, and its surge discharge branch has no current conduction. The DC power output from the rectifier circuit is input to the PFC main circuit after passing through the second coil L2B. At this time, the second coil L2B and filter capacitors C1 and C2 together form a π-type filter circuit to filter the rectified DC voltage, making the voltage input to the PFC main circuit more stable. In this embodiment, the PFC circuit operates under lightning surge conditions. When a lightning surge enters through the AC input terminal, the primary protection unit and the surge suppression unit work together to protect against the surge according to the logic of "first attenuating the peak value, then suppressing the residual voltage." The specific process is as follows: Differential-mode surge discharge: Varistor VR1 breaks down first, partially discharging the surge current between L and N, reducing the differential-mode surge peak value; Common-mode surge discharge: Varistors VR2 and VR3 break down simultaneously, forming common-mode current paths "VR2→G1→ground" and "VR3→G1→ground" with the gas discharge tube G1, discharging the common-mode surge current to the protective ground, reducing the peak value. Low common-mode surge peak; After being attenuated by the primary protection unit, the lightning surge enters the surge suppression unit through the rectifier circuit. When the voltage reaches the breakdown threshold of the varistor VR4, VR4 conducts, causing the branch containing the first coil L2A to conduct, generating a surge current in the first coil L2A. With the help of the coil coupling effect of the common-mode inductor L2, the second coil L2B will induce a reverse electromotive force opposite to the surge voltage. This reverse electromotive force is superimposed and canceled by the intruding surge voltage, significantly reducing the surge residual voltage at the input of the PFC main circuit, ensuring that the voltage across the gallium nitride power device Q1 is within the safe threshold. Example 2

[0043] To further illustrate the superiority of the gallium nitride power device lightning surge protection circuit in the PFC circuit of this invention, a simulation circuit was built based on the following parameters, as follows: Figure 2 As shown. Wherein: V1 is a 220V AC voltage source, V2 is a 2KV lightning surge generator, and V1 and V2 are connected in series to form an AC input source; D1-D4 are conventional fast recovery diodes, forming a rectifier bridge; L3 is the first coil of the common-mode inductor with an inductance of 7mH, and L2 is the second coil of the common-mode inductor with an inductance of 47mH, with a coupling coefficient of 0.7; U1 is a varistor, model 7D561K; the first filter capacitor C3 and the second filter capacitor C4 both have a capacitance of 220nF; inductor L4 is a PFC inductor with an inductance of 450uH; D9 is a freewheeling diode, which is a conventional fast recovery diode; M1 is a gallium nitride MOSFET with a drain-source withstand voltage of 650V; C1 is a filter capacitor with a capacitance of 120uH; R1 is the load with a resistance of 800Ω.

[0044] Figure 3The simulation results for the circuit are shown below. The green curve represents the voltage waveform at the AC input terminal, the red curve represents the surge residual voltage waveform at the PFC main circuit input terminal without the common-mode inductor L3, and the blue curve represents the surge residual voltage waveform at the PFC main circuit input terminal after the common-mode inductor L3 is added. The simulation results show that after adding the common-mode inductor L3, the surge residual voltage at the PFC main circuit input terminal drops from 1kV to 0.5kV, a reduction of 50%. Furthermore, this residual voltage value is lower than the withstand voltage threshold of the gallium nitride MOSFET, effectively protecting the gallium nitride MOSFET.

[0045] The above description is merely a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A surge protection circuit for gallium nitride power devices in a PFC circuit, the PFC circuit comprising a rectifier circuit and a PFC main circuit containing a gallium nitride power device Q1, characterized in that: The lightning surge protection circuit includes a surge suppression unit connected between the rectifier circuit and the PFC main circuit. The surge suppression unit includes a varistor VR4, a common mode inductor L2, a first filter capacitor C1, and a second filter capacitor C2. The common-mode inductor L2 includes a first coil L2A and a second coil L2B that are coupled to each other. The first coil L2A and the varistor VR4 are connected in series to form a surge discharge branch, which is connected between the positive output terminal and the negative output terminal of the rectifier circuit. The second coil L2B is connected in series between the positive output terminal of the rectifier circuit and the input terminal of the PFC main circuit; One end of the first filter capacitor C1 is connected to the common connection point between the second coil L2B and the positive output terminal of the rectifier circuit, and the other end is connected to the negative output terminal of the rectifier circuit. The second filter capacitor C2 is connected across the input terminal of the PFC main circuit and the negative output terminal of the rectifier circuit.

2. The lightning surge protection circuit for gallium nitride power devices in the PFC circuit according to claim 1, characterized in that: The common-mode inductor L2 uses a high-coupling-coefficient magnetic core, and the first coil L2A and the second coil L2B are wound in parallel with a double-wire winding process, with the winding direction being consistent.

3. The lightning surge protection circuit for gallium nitride power devices in the PFC circuit according to claim 2, characterized in that: The common-mode inductor L2 uses a magnetic core model of SQ1918C KA120.

4. The lightning surge protection circuit for gallium nitride power devices in the PFC circuit according to claim 1, characterized in that: The varistor VR4 has a varistor voltage between the normal output voltage of the rectifier circuit and the withstand voltage threshold of the gallium nitride power device in the PFC main circuit.

5. The lightning surge protection circuit for gallium nitride power devices in the PFC circuit according to claim 4, characterized in that: The varistor VR4 is a zinc oxide varistor with a varistor voltage of less than or equal to 561V, model number 7D511K.

6. The lightning surge protection circuit for gallium nitride power devices in the PFC circuit according to claim 1, characterized in that: Both the first filter capacitor C1 and the second filter capacitor C2 are CBB capacitors, and the capacitance of both the first filter capacitor C1 and the second filter capacitor C2 is 474J.

7. The lightning surge protection circuit for gallium nitride power devices in the PFC circuit according to claim 1, characterized in that: The lightning surge protection circuit also includes a primary protection unit connected in series between the AC input terminal and the rectifier circuit. The primary protection unit consists of a fuse MOV, a varistor VR1, a varistor VR2, a varistor VR3, a thermistor NTC, and a gas discharge tube G1. The fuse MOV is connected in series with the live wire L of the AC input terminal, and the thermistor NTC is connected in series between the neutral wire N of the AC input terminal and the neutral input terminal of the rectifier circuit. The varistor VR1 is connected across the live wire L and the neutral wire N of the AC input terminal. One end of the varistor VR2 is connected to the live wire branch after the fuse MOV, one end of the varistor VR3 is connected to the neutral wire N of the AC input terminal, and the other ends of the varistor VR2 and the varistor VR3 are connected to one end of the gas discharge tube G1. The other end of the gas discharge tube G1 is connected to the protective ground.

8. The lightning surge protection circuit for gallium nitride power devices in the PFC circuit according to claim 7, characterized in that: The varistors VR1, VR2, and VR3 are all of model 14D561K, the gas discharge tube G1 is of model 2R3000V, and the thermistor NTC is of model 2.5D-13.

9. The lightning surge protection circuit for gallium nitride power devices in the PFC circuit according to claim 1, characterized in that: The rectifier circuit includes a bridge rectifier DB1, model GBJ1510; the rated current of the bridge rectifier DB1 is greater than or equal to 15A and the reverse withstand voltage is greater than or equal to 1000V; the PFC main circuit adopts a Boost topology, the gallium nitride power device Q1 is a HEMT structure, and the withstand voltage of the gallium nitride power device Q1 is greater than or equal to 650V; the drain of the gallium nitride power device Q1 is connected to the output terminal of the second coil L2B through the inductor L3 in the PFC main circuit, and the source of the gallium nitride power device Q1 is connected to the circuit ground.

10. A power supply device, characterized in that, A lightning surge protection circuit comprising a gallium nitride power device in a PFC circuit according to any one of claims 1-9, wherein the power supply device is used for LED driving.

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