A Schmitt trigger circuit for a thyristor magnetization system

Abstract

This application relates to the technical field of thyristor drive circuits, and in particular to a Schmitt trigger circuit for a thyristor magnetization system. It includes an isolated power supply unit, an energy storage unit, a trigger pulse receiving unit, and a Schmitt strong pulse forming unit. The isolated power supply unit includes an isolation transformer and a filter capacitor. The energy storage unit consists of a charging resistor and an energy storage capacitor connected in series. The trigger pulse receiving unit receives external trigger commands. The Schmitt strong pulse forming unit includes an NPN transistor, a MOSFET switch, etc. These units cooperate with each other. The application also covers parameter limitations and electrical isolation settings for each component. This circuit can be applied to high-power, high-voltage, strong magnetic pulse magnetization equipment. This application achieves electrical isolation and equivalent Schmitt trigger characteristics, providing nanosecond-level steep-front strong trigger pulses to the thyristor, thereby reducing turn-on losses, improving di / dt tolerance, and enhancing electromagnetic interference immunity.

Description

Technical Field

[0001] This application relates to the technical field of thyristor drive circuits, and in particular to a Schmitt trigger circuit for a thyristor magnetization system. Background Technology

[0002] In the industrial-scale mass magnetization of high-coercivity permanent magnet materials such as NdFeB and SmCo, a common approach is to use high-power capacitors for energy storage followed by pulsed discharge of the magnetization coil via thyristors. A typical system consists of a three-phase rectified charging power supply, a pulse capacitor bank, high-power thyristors, and a toroidal or solenoid magnetization coil. The magnetization process requires the pulsed magnetic field strength to be 3-5 times the material's coercivity, corresponding to a discharge current di / dt (rate of rise) exceeding 30 A / μs, and a pulse width of 1-5 ms. As the core switching device, the thyristor's triggering characteristics directly determine the system's reliability, efficiency, and magnetization consistency.

[0003] Traditional technical solutions primarily employ isolation pulse transformers to achieve electrical isolation between the control circuit and the high-voltage main circuit, as well as to transmit trigger pulses. The PLC outputs a weak 5-24V trigger signal to drive the primary winding of the pulse transformer, inducing a 10-30V high-voltage pulse which is then applied to the thyristor gate via a current-limiting resistor. However, pulse transformers suffer from leakage inductance and distributed capacitance defects. Leakage inductance prolongs the rise time of the trigger pulse, failing to meet the requirements of high di / dt applications. A gentle pulse leading edge limits the expansion speed of the thyristor chip's conduction area, leading to localized overheating and increased turn-on losses. Furthermore, a gentle pulse leading edge reduces the device's tolerance to di / dt, making it prone to latch-up effects or secondary breakdown failures under long-term operation.

[0004] Furthermore, high-power magnetization systems generate strong electromagnetic interference during operation. Pulse currents with di / dt as high as 50-100 A / μs can intrude into the trigger control circuit through spatial radiation and ground coupling. The coupling capacitance between the primary and secondary windings of the pulse transformer provides a path for common-mode interference. When the interference voltage exceeds the thyristor gate trigger voltage threshold, it will cause false triggering, resulting in the main circuit conducting before charging is complete or due to timing errors. Although this can be improved by adding shielding layers and optimizing the winding process, it cannot fundamentally solve the problem and will significantly increase the size and cost of the transformer. Summary of the Invention

[0005] In order to provide a nanosecond-level steep-front strong trigger pulse for the thyristor while avoiding the limitations of leakage inductance and distributed capacitance, so as to reduce turn-on loss, improve di / dt tolerance and enhance electromagnetic interference resistance, this application provides a Schmitt strong trigger circuit for a thyristor magnetization system.

[0006] This application provides a Schmitt trigger circuit for a thyristor magnetization system, employing the following technical solution: A Schmitt trigger circuit for a thyristor magnetization system includes: An isolated power supply unit includes an isolation transformer and a filter capacitor C1, wherein the filter capacitor C1 is connected in parallel to the output side of the isolation transformer; The energy storage unit includes a charging resistor R4 and an energy storage capacitor C2 connected in series. The negative terminal of the energy storage capacitor C2 is connected to the output side of the isolation transformer. One end of the charging resistor R4 is connected to the output side of the isolation transformer, and the other end is connected to the positive terminal of the energy storage capacitor C2. A trigger pulse receiving unit is used to receive external trigger pulses. It includes a current-limiting resistor R1, a pull-up resistor R3, and a high-voltage optocoupler U. The current-limiting resistor R1 is connected in series with the input terminal of the high-voltage optocoupler U, and the emitter of the high-voltage optocoupler U is connected to the output side of the isolation transformer via the pull-up resistor R3. The Schmitt pulse forming unit includes an NPN transistor Q2, a MOSFET switch Q3, a gate current limiting resistor R6, and a pull-down resistor R7. The source of the MOSFET switch Q3 is connected to the gate G of the thyristor via the gate current limiting resistor R6. The pull-down resistor R7 is connected in parallel between the gate G and the cathode K of the thyristor. The positive terminal of the energy storage capacitor C2 is connected to the drain of the MOSFET switch Q3. The collector of the high-voltage optocoupler U is connected to the base of the NPN driving transistor Q2.

[0007] By adopting the above technical solutions, the isolated power supply and high-voltage optocoupler achieve dual electrical isolation, ensuring the safety of the high-voltage main circuit and the control circuit. The energy storage unit stores energy in advance, providing an energy basis for generating large-current trigger pulses. The Schmitt strong pulse forming unit shapes the slow input signal into a drive pulse with extremely steep edges, and the cascaded switch quickly releases the stored energy, ultimately outputting a trigger pulse with a steep leading edge and strong driving capability. This significantly shortens the thyristor's turn-on time, reduces turn-on losses, and enhances its ability to withstand high di / dt. At the same time, the Schmitt characteristic itself effectively suppresses false triggering caused by electromagnetic interference.

[0008] Optionally, the primary winding of the isolation transformer is connected to 220V AC power, and the secondary winding outputs 15-25V AC power, and the secondary winding generates an isolated 25V DC bus and a 0V ground wire. The negative terminal of the energy storage capacitor C2 is connected to the 0V ground wire, and the other end of the charging resistor R4 is connected to the 25V DC bus. The emitter of the high-voltage optocoupler U is connected to the 25V DC bus via a pull-up resistor R3.

[0009] By adopting the above technical solution, the safety isolation between the trigger circuit and the mains power grid is ensured, and a stable and isolated DC power supply is provided for the other units, laying the energy foundation for the stable operation of the entire circuit.

[0010] Optionally, the resistance of the charging resistor R4 is in the range of 90-110Ω, and the capacitance of the energy storage capacitor C2 is in the range of 900-1100μF.

[0011] By adopting the above technical solution, the resistance and capacitance values ​​of the charging resistor R4 and the energy storage capacitor C2 are limited, thereby determining the pre-charge time constant. This ensures that the energy storage capacitor C2 can be fully charged to the operating voltage within a reasonable time and store sufficient energy to ensure that a strong trigger pulse with sufficient energy and consistent intensity is released each time it is triggered, while avoiding excessive charging current from impacting the power supply.

[0012] Optionally, a current-limiting resistor R8 is connected between the collector of the high-voltage optocoupler U and the base of the NPN transistor Q2, and the resistance value of the current-limiting resistor R8 is not less than 6.2kΩ.

[0013] By adopting the above technical solution, the current-limiting resistor R8 protects the NPN transistor Q2 in the subsequent stage, limiting the base current of the NPN transistor Q2 within a safe range, preventing overcurrent damage, and improving the reliability of the circuit.

[0014] Optionally, the MOSFET switch Q3 is an N-channel MOSFET, and a pull-down resistor R5 with a value of 4.7kΩ is connected between the gate of the MOSFET switch Q3 and the 0V ground line.

[0015] By adopting the above technical solution and adding a pull-down resistor R5 connected between the MOSFET gate and the 0V ground line, reliable turn-off of the MOSFET switch Q3 is ensured when there is no effective drive signal. The pull-down resistor R5 provides a fast discharge path for the gate charge of Q3, which can effectively eliminate gate voltage fluctuations or coupling interference caused by parasitic parameters, prevent Q3 from being mistakenly turned on due to gate floating, and further enhance the static stability of the circuit.

[0016] Optionally, the resistance value of the gate current limiting resistor R6 is in the range of 1-10Ω, and the power rating is not less than 5W.

[0017] By employing the above technical solution, the resistance range and power rating of the gate current limiting resistor R6 are limited, thus precisely controlling the magnitude of the peak trigger current applied to the thyristor gate. This not only generates a current that meets the strong triggering requirements but also avoids potential damage to the thyristor gate caused by excessive current.

[0018] Optionally, the pull-down resistor R7 is a non-inductive wire-wound resistor with a resistance range of 10-51Ω and a power rating of not less than 2W.

[0019] By adopting the above technical solution, the non-inductive characteristic of the pull-down resistor R7 avoids the induced electromotive force generated by the resistor's own inductance under high-speed pulses, which would affect the purity of the trigger pulse waveform. Appropriate resistance and power ensure that it can effectively pull down the gate potential and dissipate interference energy that may couple to the gate, further strengthening the circuit's resistance to false triggering.

[0020] Optionally, the filter capacitor C1 is a 2200μF electrolytic capacitor, and the equivalent series resistance of capacitor C1 is less than 0.5Ω.

[0021] By adopting the above technical solution, the 2200μF electrolytic capacitor ensures the energy storage and filtering effect of the isolated power supply unit, providing a stable DC voltage for the circuit. The equivalent series resistance of capacitor C1 is less than 0.5Ω, enabling it to quickly provide transient current compensation when the MOSFET switch Q3 is turned on and the energy storage capacitor C2 discharges instantaneously, maintaining the voltage stability of the isolated power supply unit and preventing the normal operation of other parts from being affected by instantaneous voltage drops.

[0022] Optionally, the current-limiting resistor R1 has a resistance of 1kΩ.

[0023] By adopting the above technical solution, the current limiting resistor R1 has a resistance of 1kΩ, which ensures that the current flowing into the input terminal of the high-voltage optocoupler U is within its safe operating range, ensuring that the high-voltage optocoupler U can be reliably driven, and preventing excessive input current from damaging the high-voltage optocoupler U or other control equipment such as the front-end stage.

[0024] Optionally, a bias resistor R2 is connected in parallel between the collector of the high-voltage optocoupler U and the 0V ground line, and the resistance value of the bias resistor R2 is in the range of 4.7kΩ-10kΩ.

[0025] By adopting the above technical solution, a bias resistor R2 is added and its resistance value is limited, providing a definite pull-up bias for the collector of the high-voltage optocoupler U. Together with the pull-up resistor R3 and the current-limiting resistor R8, it forms the stable operating point of the output stage of the high-voltage optocoupler U, ensuring the voltage swing and load-carrying capacity of the output signal of the high-voltage optocoupler U, making the signal transmission more stable and reliable.

[0026] In summary, this application includes at least one of the following beneficial effects: 1. It avoids the limitations of leakage inductance and distributed capacitance, providing nanosecond-level steep leading edge strong trigger pulses for thyristors, reducing turn-on losses and improving di / dt tolerance; 2. A first layer of electrical isolation is achieved by using a high-voltage optocoupler, and a second layer of electrical isolation is achieved by using the isolation transformer secondary to generate an isolated DC bus and ground wire, thereby enhancing the electromagnetic interference resistance. 3. Q2 and Q3 form a cascaded switch structure to achieve equivalent Schmitt triggering characteristics, with an on-time of <50ns, which improves the timeliness and reliability of triggering. Attached Figure Description

[0027] Figure 1 This is a schematic diagram of the circuit structure of the Schmitt trigger circuit used in the thyristor magnetization system in the embodiments of this application; Detailed Implementation

[0028] The following is in conjunction with the appendix Figure 1 This application will be described in further detail.

[0029] The technical solutions in the embodiments of the present invention will be further described in detail below with reference to the accompanying drawings.

[0030] This application mainly adopts a Schmitt trigger circuit design to avoid the defects of pulse transformers, thereby providing nanosecond-level steep leading edge strong trigger pulses for thyristors and improving system performance. The following is a further detailed description of this application.

[0031] The Schmitt strong trigger circuit for a thyristor magnetization system provided in this application includes an isolated power supply unit, an energy storage unit, a trigger pulse receiving unit, and a Schmitt strong pulse forming unit. The isolated power supply unit provides isolated power to the entire circuit, the energy storage unit stores energy, the trigger pulse receiving unit receives external trigger pulses, and the Schmitt strong pulse forming unit forms strong trigger pulses according to instructions. This achieves the effect of providing nanosecond-level steep leading edge strong trigger pulses to the thyristor while avoiding the limitations of leakage inductance and distributed capacitance, thereby reducing turn-on losses, improving di / dt tolerance, and enhancing electromagnetic interference resistance.

[0032] Reference Figure 1 The isolated power supply unit includes an isolation transformer (not shown in the figure) and a filter capacitor C1. The primary winding of the isolation transformer is connected to 220V AC, and the secondary winding outputs 15V-25V AC. After passing through a rectifier bridge and the filter capacitor, the secondary winding generates a +25V DC bus and a 0V ground wire. An EI-type transformer or a toroidal transformer can be used as the isolation transformer. The filter capacitor C1 is a 2200μF electrolytic capacitor with an equivalent series resistance of less than 0.5Ω, used to suppress power supply ripple and provide transient current compensation during pulse discharge. The filter capacitor C1 is connected in parallel between the +25V DC bus and the 0V ground wire.

[0033] Reference Figure 1The energy storage unit includes a charging resistor R4 and an energy storage capacitor C2 connected in series. The charging resistor R4 can be a wire-wound resistor or a metal film resistor, with a resistance range of 90-110Ω. The energy storage capacitor C2 has a capacitance range of 900-1100μF and can be an aluminum electrolytic capacitor, etc. The negative terminal of the energy storage capacitor C2 is connected to the 0V ground line on the output side of the isolation transformer. One end of the charging resistor R4 is connected to the 25V DC bus on the output side of the isolation transformer, and the other end of the charging resistor R4 is connected to the positive terminal of the energy storage capacitor C2. In this embodiment, the charging resistor R4 is selected as 100Ω, and the energy storage capacitor C2 is selected as 1000μF. After the charging resistor R4 and the energy storage capacitor C2 are connected in series, the time constant τ formed by them is 100ms, ensuring that the energy storage capacitor is charged to no less than 24V within 100ms. This combination allows the energy storage capacitor to effectively store energy, providing energy support for subsequent trigger pulses.

[0034] Reference Figure 1 The trigger pulse receiving unit receives external trigger pulses and includes a current-limiting resistor R1, a pull-up resistor R3, and a high-voltage optocoupler U. The current-limiting resistor R1 has a resistance of 1kΩ and its function is to limit the current flowing into the high-voltage optocoupler U. The pull-up resistor R3 can be a metal film resistor, and the high-voltage optocoupler U can be a CNY65A type optocoupler. The current-limiting resistor R1 is connected in series to the positive terminal of the input of the high-voltage optocoupler U, and the emitter of the high-voltage optocoupler U is connected to the 25V DC bus on the output side of the isolation transformer via the pull-up resistor R3. When there is an external trigger pulse, the high-voltage optocoupler U can isolate and transmit the weak signal, avoiding the influence of electromagnetic interference on the trigger signal. A bias resistor R2 is connected in parallel between the collector of the high-voltage optocoupler U and the 0V ground line. The resistance of the bias resistor R2 ranges from 4.7kΩ to 10kΩ. The addition of the bias resistor R2 can further stabilize the operating state of the high-voltage optocoupler and optimize the transmission of the trigger signal. In this embodiment, the bias resistor R2 is 4.7kΩ.

[0035] Reference Figure 1The Schmitt trigger pulse forming unit includes an NPN transistor Q2, a MOSFET switch Q3, a gate current limiting resistor R6, and a pull-down resistor R7. The NPN transistor Q2 is an SS8050 model, and the MOSFET switch Q3 is an N-channel MOSFET, specifically an IRF540. The gate current limiting resistor R6 has a resistance range of 1-10Ω and a power rating of not less than 5W, used to limit the peak trigger current to the range of 4-10A; in this embodiment, a 1Ω gate current limiting resistor R6 is used. The pull-down resistor R7 is a non-inductive wire-wound resistor with a resistance range of 10-51Ω and a power rating of not less than 2W; in this embodiment, a 51Ω pull-down resistor R7 is used. The source of the MOSFET switch Q3 is connected to the gate G of the thyristor via the gate current limiting resistor R6, and the pull-down resistor R7 is connected in parallel between the thyristor gate G and cathode K. The positive terminal of the energy storage capacitor C2 is connected to the drain of the MOSFET switch Q3. The collector of the high-voltage optocoupler U is connected to the base of the NPN driver transistor Q2, and a current-limiting resistor R8 is connected between the collector of the high-voltage optocoupler U and the base of the NPN driver transistor Q2. The resistance value of the current-limiting resistor R8 is not less than 6.2kΩ, which is used to limit the base current of the NPN transistor Q2 to no more than 20mA. In this embodiment, the current-limiting resistor R8 is 6.2kΩ. The NPN transistor Q2 and the MOSFET switch Q3 form a cascaded switch structure. Its fast turn-on and turn-off characteristics are similar to the toggling behavior of a Schmitt trigger, which can shape slowly changing input signals into pulses with steep edges and has a certain anti-interference capability and a short turn-on time. When a trigger signal is received, the cascaded switch structure can respond quickly, forming a nanosecond-level steep-edge strong trigger pulse, providing reliable triggering for the thyristor.

[0036] The implementation principle of this embodiment is as follows: The Schmitt trigger circuit achieves electrical isolation from 220V AC power through an isolated power supply unit, avoiding power supply interference. The energy storage unit can store sufficient energy to provide power for the trigger pulse. The trigger pulse receiving unit achieves electrical isolation through a high-voltage optocoupler to prevent electromagnetic interference from entering. The cascaded switching structure composed of NPN transistor Q2 and MOSFET switch Q3 can respond quickly, forming a strong trigger pulse with a steep leading edge, avoiding the problems caused by leakage inductance and distributed capacitance of traditional pulse transformers, reducing the turn-on loss of thyristors, improving its tolerance to di / dt, and enhancing its anti-electromagnetic interference performance, making it suitable for high-power, high-voltage, strong magnetic pulse magnetization equipment.

[0037] The above are all preferred embodiments of this application, and are not intended to limit the scope of protection of this application. Therefore, all equivalent changes made in accordance with the structure, shape and principle of this application should be covered within the scope of protection of this application.

Claims

1. A Schmitt trigger circuit for a thyristor magnetization system, characterized in that, include: An isolated power supply unit includes an isolation transformer and a filter capacitor C1, wherein the filter capacitor C1 is connected in parallel to the output side of the isolation transformer; The energy storage unit includes a charging resistor R4 and an energy storage capacitor C2 connected in series. The negative terminal of the energy storage capacitor C2 is connected to the output side of the isolation transformer. One end of the charging resistor R4 is connected to the output side of the isolation transformer, and the other end is connected to the positive terminal of the energy storage capacitor C2. A trigger pulse receiving unit is used to receive external trigger pulses. It includes a current-limiting resistor R1, a pull-up resistor R3, and a high-voltage optocoupler U. The current-limiting resistor R1 is connected in series with the input terminal of the high-voltage optocoupler U, and the emitter of the high-voltage optocoupler U is connected to the output side of the isolation transformer via the pull-up resistor R3. The Schmitt pulse forming unit includes an NPN transistor Q2, a MOSFET switch Q3, a gate current limiting resistor R6, and a pull-down resistor R7. The source of the MOSFET switch Q3 is connected to the gate G of the thyristor via the gate current limiting resistor R6. The pull-down resistor R7 is connected in parallel between the gate G and the cathode K of the thyristor. The positive terminal of the energy storage capacitor C2 is connected to the drain of the MOSFET switch Q3. The collector of the high-voltage optocoupler U is connected to the base of the NPN driving transistor Q2.

2. The Schmitt trigger circuit for a thyristor magnetization system according to claim 1, characterized in that: The primary winding of the isolation transformer is connected to 220V AC power, and the secondary winding outputs 15-25V AC power. The secondary winding also generates an isolated 25V DC bus and a 0V ground wire. The negative terminal of the energy storage capacitor C2 is connected to the 0V ground wire, and the other end of the charging resistor R4 is connected to the 25V DC bus. The emitter of the high-voltage optocoupler U is connected to the 25V DC bus via a pull-up resistor R3.

3. The Schmitt trigger circuit for a thyristor magnetization system according to claim 1, characterized in that: The resistance value of the charging resistor R4 is in the range of 90-110Ω, and the capacitance value of the energy storage capacitor C2 is in the range of 900-1100μF.

4. The Schmitt trigger circuit for a thyristor magnetization system according to claim 2, characterized in that: A current-limiting resistor R8 is connected between the collector of the high-voltage optocoupler U and the base of the NPN transistor Q2. The resistance value of the current-limiting resistor R8 is not less than 6.2kΩ.

5. The Schmitt trigger circuit for a thyristor magnetization system according to claim 2, characterized in that: The MOSFET switch Q3 is an N-channel MOSFET, and a pull-down resistor R5 with a value of 4.7kΩ is connected between the gate of the MOSFET switch Q3 and the 0V ground line.

6. The Schmitt trigger circuit for a thyristor magnetization system according to claim 1, characterized in that: The gate current limiting resistor R6 has a resistance range of 1-10Ω and a power rating of not less than 5W.

7. The Schmitt trigger circuit for a thyristor magnetization system according to claim 1, characterized in that: The pull-down resistor R7 is a non-inductive wire-wound resistor with a resistance range of 10-51Ω and a power rating of not less than 2W.

8. The Schmitt trigger circuit for a thyristor magnetization system according to claim 1, characterized in that: The filter capacitor C1 is a 2200μF electrolytic capacitor, and the equivalent series resistance of capacitor C1 is less than 0.5Ω.

9. The Schmitt trigger circuit for a thyristor magnetization system according to claim 1, characterized in that: The current-limiting resistor R1 has a resistance of 1kΩ.

10. The Schmitt trigger circuit for a thyristor magnetization system according to claim 4, characterized in that: A bias resistor R2 is connected in parallel between the collector of the high-voltage optocoupler U and the 0V ground line. The resistance value of the bias resistor R2 is in the range of 4.7kΩ-10kΩ.

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