semiconductor switch

Abstract

To provide a highly reliable semiconductor switch capable of reducing an operation voltage and reducing a cost compared to a thyratron switch.SOLUTION: Provided is a high-voltage, large-current semiconductor switch in which thyristors are connected in multiple stages. The semiconductor switch comprises: an avalanche circuit in which avalanche mode thyristors 1-1 to 1-N whose gates and cathodes are substantially short-circuited are connected in a multiple stages; gate trigger thyristors 2-1 to 2-M connected in multiple stages at a lower stage of the avalanche mode thyristors 1-1 to 1-N connected in multiple stages; and an optical trigger part 10 (a trigger circuit) provided for each stage of the gate trigger thyristors 2-1 to 2-M to supply a gate signal to the gate trigger thyristor of each stage.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a semiconductor switch capable of high-speed and high-current switching using a thyristor, which is a semiconductor switching device.

Background Art

[0002] A thyristor is a three-terminal semiconductor device that can conduct between the anode and the cathode mainly by flowing a gate current from the gate to the cathode. It can carry a large peak current, but the applied voltage is not as high as 1.5 kV. However, in the field of power system technology, controlling high voltage and high current is required. So far, a gas discharge tube called a cyclotron switch has been used. However, because it uses a discharge phenomenon, a peripheral circuit such as a heater power supply is required to operate stably. It is expensive and requires a large installation area. Therefore, the demand for switching circuits using semiconductors such as thyristors has been increasing. For example, to perform switching at a high voltage of 40 kV using a thyristor, about 30 thyristors need to be connected in series and in parallel in multiple stages. In addition, in a thyristor, a trigger signal is supplied to control the switching time. However, to supply a trigger signal to all thyristors constituting the switching circuit, a large number of components are required, which increases the cost and also increases the variation in switching performance.

[0003] The operating characteristics of a thyristor will be described with reference to FIG. 5. A thyristor has three terminals: an anode, a cathode, and a gate. When the potential of the anode is higher than the potential of the cathode and a current is passed through the gate, the thyristor conducts. Once it conducts, it continues to conduct even when the gate current becomes zero. FIG. 5 shows the V-I characteristics with the voltage V between the anode and the cathode on the horizontal axis and the current I flowing between the anode and the cathode on the vertical axis. The thyristor changes from the off state to the on state and the current increases rapidly by flowing a gate current (I G ) with a voltage (horizontal axis) applied. The gate current (I GIf the gate current (I) is large, the state will switch from off to on even if the voltage V between the anode and cathode is low, but the gate current (I) will be large. G If the gate current (I) is small, the voltage V between the anode and cathode must be increased to switch from off to on. G Even if the gate current (I) is zero, an overvoltage exceeding a certain voltage causes an electron avalanche to occur within the semiconductor, resulting in a gate current (I G The circuit turns on, just as when ) is applied. Gate current (I G The breakover voltage (V) is the voltage at which the state turns on even when the other voltage is zero. BO This is called an avalanche. When a voltage exceeding the breakover voltage is applied, it turns on, and the switching speed of the thyristor at this time depends on the characteristics of the individual thyristor, but it is known that the switching speed in an avalanche is faster than in normal operation.

[0004] Since avalanche mode (switching in an avalanche configuration) is not a typical use, the characteristics of thyristors in this mode are not specified or standardized. In avalanche mode, a higher voltage is applied compared to general operating modes, so the number of thyristor stages can be reduced when the switching voltage is the same, enabling faster switching speeds. Patent Document 1 describes a semiconductor switch that utilizes avalanche mode to enable high-speed, high-current switching, comprising an avalanche circuit that switches multiple thyristors connected in series in multiple stages with zero gate current, and a trigger circuit that supplies a trigger signal to the lowest stage of the avalanche circuit, applying a voltage close to the breakover voltage to each thyristor in the avalanche circuit and inputting a trigger signal to the trigger circuit. [Prior art documents] [Patent Documents]

[0005] [Patent Document 1] Japanese Patent Publication No. 2020-10417 [Overview of the Initiative] [Problems that the invention aims to solve]

[0006] In the conventional technology described above, multi-stage connected thyristors transition from off to on (avalanche mode) even without gate input by applying an overvoltage exceeding the breakover voltage between the anode and cathode. Furthermore, the switching speed becomes high by using avalanche mode, and gate inputs for each stage of the multi-stage connected thyristors become unnecessary.

[0007] However, the method described in Patent Document 1 has a constraint: in order to operate the thyristors in avalanche mode, the voltage applied to the multi-stage connected thyristors must be close to the breakover voltage. Due to this constraint, it is not possible to significantly reduce the operating voltage that starts the switching; for example, operation is difficult at less than half of the maximum operating voltage, limiting the range of application as a semiconductor switch. In addition, there are few types of thyristors that can be used at high voltages, limiting the choices and making it difficult to meet different requirements.

[0008] The object of the present invention is to solve the problems of the prior art described above and to provide a semiconductor switch that can lower the operating voltage, is highly reliable, and can achieve cost reduction compared to a thyratron switch. [Means for solving the problem]

[0009] To achieve the above objective, the present invention provides a high-voltage, high-current semiconductor switch comprising a multi-stage thyristor configuration, the switch comprising: an avalanche circuit in which avalanche mode thyristors, each having a substantially short-circuited gate and cathode, are connected in a multi-stage configuration; gate trigger thyristors connected in a multi-stage configuration below the multi-stage avalanche mode thyristors; and trigger circuits provided at each stage of the gate trigger thyristors to supply gate signals for each stage.

[0010] Furthermore, in the semiconductor switch described above, it is preferable that the cathode potential of the avalanche mode thyristor at the bottom of the avalanche circuit be set to a high voltage potential close to the breakover voltage.

[0011] Furthermore, in the semiconductor switch described above, it is desirable that the cathode potential of the avalanche mode thyristor at the bottom of the avalanche circuit be set to a potential of 80-90% of the breakover voltage.

[0012] Furthermore, it is desirable that the semiconductor switch described above includes a voltage divider resistor that divides the voltage of each stage of the avalanche mode thyristor and the gate trigger thyristor, and a Zener diode connected in parallel with the voltage divider resistor.

[0013] Furthermore, in the semiconductor switch described above, the trigger circuit is turned on by passing a trigger current through the gate of each thyristor in each stage of the gate trigger thyristor, and it is preferable to use an optical trigger that utilizes light as the trigger.

[0014] Furthermore, in the semiconductor switch described above, it is preferable that the trigger circuit uses a pulse transformer as its trigger to turn on the thyristor by passing a pulse current through its gate (hereinafter referred to as a pulse transformer trigger). [Effects of the Invention]

[0015] According to the present invention, an avalanche circuit is provided in which multiple avalanche mode thyristors, in which the gate and cathode of the thyristor are substantially short-circuited, are connected in multiple stages; gate trigger thyristors are connected in multiple stages below the multiple stages of connected avalanche mode thyristors; and trigger circuits are provided at each stage of the gate trigger thyristors to supply the gate signals for each stage. As a result, a semiconductor switch that operates at a lower voltage than conventional switches can be provided. Since a high-speed switch is possible, the present invention can be applied to technical fields that require high-voltage switches, such as high-voltage discharges, for example, electron gun power supplies, laser switch circuits, or power systems.

Brief Description of the Drawings

[0016] [Figure 1] It is a circuit of a semiconductor switch (a trigger circuit using an optical trigger) according to an embodiment of the present invention. [Figure 2] It is a diagram showing the difference in the connection of a gate trigger thyristor and an avalanche mode thyristor. [Figure 3] It is a circuit of a semiconductor switch (a trigger circuit using a pulse transformer) according to another embodiment of the present invention. [Figure 4] It is a diagram showing the characteristics of a semiconductor switch in one embodiment. [Figure 5] It is an explanatory diagram of the operating characteristics of a thyristor.

Modes for Carrying Out the Invention

[0017] Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 is a diagram showing a circuit of a semiconductor switch according to an embodiment of the present invention. Avalanche mode thyristors 1-1 to 1-N and gate trigger thyristors 2-1 to 2-M are thyristors capable of high-speed and high-current switching. As will be described later, in the avalanche mode thyristors 1-1 to 1-N and the gate trigger thyristors 2-1 to 2-M connected in multiple stages on the lower side thereof, the connection method of the gate and the cathode is different, and thereby, the behavior of the current with respect to the applied voltage is different.

[0018] First, the gate trigger thyristors 2-1 to 2-M will be described. A thyristor generally has the characteristic that when a gate current flows with a voltage applied between the anode and the cathode, it changes from the off state to the on state and the current increases rapidly. Therefore, usually, the current between the anode and the cathode is controlled by the gate current. The thyristor controlled in this way is also referred to as the "gate-triggered thyristor" hereinafter in this specification.

[0019] Next, the avalanche mode thyristors 1-1 to 1-N will be described. Figure 2 is a diagram showing the difference in the connection between a normal gate-triggered thyristor (Figure 2(a)) and an avalanche mode thyristor (Figure 2(b)). As already described, the gate-triggered thyristors 2-1 to 2-M are used by making the anode and the cathode conductive by flowing a gate current from the gate to the cathode. On the other hand, the avalanche mode thyristors 1-1 to 1-N have a connection in which the gate and the cathode are substantially short-circuited as shown in Figure 2(b). The thyristor configured in this way is referred to as the "avalanche mode thyristor (AMT: Avalanche mode Thyristor)" in this specification. For AMT, the gate and the cathode are set to the same potential, and when an excessive voltage exceeding the breakover voltage is applied between the anode and the cathode, a current flows and it shifts to the on state.

[0020] Although the avalanche mode thyristors 1-1 to 1-N and the gate trigger thyristors 2-1 to 2-M have different wiring configurations as described above, the elements themselves may be substantially identical or different. For substantially identical elements, a high switching speed and a large peak current in pulse mode are preferable. Furthermore, increasing the number of stages in the avalanche mode thyristors and gate trigger thyristors reduces the voltage applied to each thyristor, thus increasing the range of thyristor options. By appropriately selecting thyristors according to the required performance of the switching circuit, characteristics equivalent to or better than existing thyratrons can be achieved, and furthermore, they can operate at lower voltages than known semiconductor switches using avalanche circuits, such as those described in Patent Document 1.

[0021] The semiconductor switch in this embodiment operates when a high operating voltage HV is applied. Avalanche mode thyristors 1-1 to 1-N are connected in multiple stages (e.g., 17 stages) to form an avalanche circuit (a circuit that turns on when a voltage above the breakover voltage is applied). Below the lowest stage (bottom stage) of the multi-stage connection, gate trigger thyristors 2-1 to 2-M are connected in multiple stages (e.g., 10 stages). Note that the meaning of multi-stage connection is not necessarily a large number; it can be two or more stages, and depending on the required voltage and current performance, it may be a series-parallel connection rather than a series-parallel connection. Specifically, in the case of high voltage, they are connected in series, and in the case of high current, they are connected in parallel, and the multi-stage configuration is selected considering the performance of each thyristor used.

[0022] The operating voltage HV is adjusted by resistor R1, and the voltage is divided so that the voltage corresponding to the respective operating voltage is applied to each stage of the avalanche mode thyristors 1-1 to 1-N by voltage divider resistor R2, and to each stage of the gate trigger thyristors 2-1 to 2-M by voltage divider resistor R3. Using only voltage divider resistors R2 and R3 may cause an imbalance due to differences in leakage current, potentially damaging the thyristors with excessive voltage.

[0023] Therefore, the Zener diode Z1 connected in parallel to each stage is used in conjunction with the voltage divider resistors R2 and R3 to prevent excessive voltage from being applied to the avalanche mode thyristors 1-1 to 1-N and the gate trigger thyristors 2-1 to 2-M.

[0024] In the semiconductor switch shown in Figure 1, the charge stored in the capacitor 16 flows through the load resistor 17 by switching each thyristor. Therefore, even when each thyristor turns on and the anode voltage drops, there is a delay until the on-resistance drops sufficiently, making it impossible to pass a current exceeding 1kA in a short time.

[0025] A magnetic switch (MS) 15 is placed between resistor R1 and capacitor 16 to allow the load current to increase slowly and become large during the transient state when the on-resistance decreases. The magnetic switch (MS) 15 uses a core whose magnetization saturates rapidly, delaying the time from when the AMT is turned on until the load current reaches its peak. In other words, the magnetic switch (MS) 15 acts as a high inductance until the core saturates due to the current flowing through the coil of the magnetic switch (MS) 15.

[0026] Furthermore, the magnetic switch (MS) 15 acts as a low inductance when the core saturates, and the time until the core saturates prevents rapid current changes. The AMT is designed so that when the AMT in the lower stage switches, a voltage equal to or greater than the breakover voltage is applied to the AMT in the stage immediately above it, causing the AMT in that stage to switch spontaneously as well. Because this spontaneous switching propagates successively to the AMTs in the stages above, the switching speed hardly slows down even with multi-stage connection. In addition, the load current begins to flow with a delay after the anode voltage switches and the magnetic switch (MS) 15 saturates.

[0027] The optical trigger section 10 is a trigger circuit that uses light passing through optical fibers 13-1 to 13-M to activate switches such as photocouplers in the optical trigger receiving circuits 11-1 to 11-M, thereby supplying a trigger current to the gate of the thyristor. It is provided at each stage of the multi-stage connected gate trigger thyristors 2-1 to 2-M, and supplies the gate signal to each stage almost simultaneously.

[0028] In addition to the optical fibers 13-1 to 13-M and optical trigger receiving circuits 11-1 to 11-M mentioned above, the optical trigger unit 10 requires a DC-DC converter to generate a voltage for driving the optical trigger receiving circuits at a high voltage potential. The DC-DC converter circuit consists of an isolation transformer 12-1 to 12-M that isolates the DC voltage to AC voltage circuit 14 from the high-voltage optical trigger receiving circuits, and an AC-DC conversion circuit provided within the optical trigger receiving circuits 11-1 to 11-M.

[0029] At point A of the lowest stage of avalanche mode thyristors 1-1 to 1-N, a potential close to the breakover voltage of avalanche mode thyristor 1-1 is applied, for example, 80-90% of the breakover voltage. An even higher voltage is applied to the anode of avalanche mode thyristor 1-1. Similarly, the anodes of avalanche mode thyristors 1-2 to 1-N are also applied at a potential close to the breakover voltage, for example, 80-90% of the breakover voltage.

[0030] The potential at point A becomes low when the optical input is sent to the optical trigger unit 10 and each stage of the gate trigger thyristors 2-1 to 2-M conducts. As a result, the potential of the cathode of the avalanche mode thyristor 1-1 decreases, and the voltage between the anode and cathode of the avalanche mode thyristor 1-1 exceeds the breakover voltage, turning it ON.

[0031] The upper avalanche mode thyristors 1-2 turn on when a voltage exceeding the breakover voltage is applied, as avalanche mode thyristor 1-1 turns on. Subsequently, the avalanche mode thyristors turn on in a chain reaction up to the topmost avalanche mode thyristor 1-N. In this way, even when avalanche mode thyristors 1-1 to 1-N are connected in multiple stages, they form an avalanche circuit that switches even without a circuit to input current to the gate.

[0032] When all the gate trigger thyristors and avalanche mode thyristors that make up the semiconductor switch are turned on, current flows, but a differential waveform of the current is obtained by the differential circuit consisting of the capacitor 16 and load resistor 17 of the external circuit.

[0033] In this embodiment, the semiconductor switch allows the voltage at point A of the lowest stage of the avalanche mode thyristors 1-1 to 1-N to be arbitrarily set by selecting the thyristors and number of stages that constitute the gate trigger thyristors 2-1 to 2-M and the avalanche mode thyristors 1-1 to 1-N, thus resulting in a semiconductor switch that operates at a lower voltage than conventional switches. The operating voltage can also be set over a wide range by selecting the thyristors and number of stages that constitute the gate trigger thyristors 2-1 to 2-M and the avalanche mode thyristors 1-1 to 1-N.

[0034] For example, in a semiconductor switch consisting of 17 stages of avalanche mode thyristors 1-1 to 1-N and 10 stages of gate trigger thyristors 2-1 to 2-M, it has been confirmed that it operates from approximately 5kV, up to a maximum operating voltage of 40kV.

[0035] Figure 3 shows another embodiment in which the optical trigger section 10 of Figure 1, which is the trigger circuit, is replaced with a transformer trigger section 20. The other components are the same, so a detailed explanation is omitted. The transformer trigger section 20 is a circuit that generates a trigger signal using a pulse transformer. High-voltage isolated pulse transformers 19-1 to 19-M are provided corresponding to each stage of the multi-stage series-connected gate trigger thyristors 2-1 to 2-M, and by being connected in series, they serve to supply trigger current to each stage that is at a high voltage potential.

[0036] A DC power supply 21 is connected to the upper pulse transformer 19-M, and a gate trigger generation circuit 18, composed of MOS FETs (metal-oxide-semiconductor field-effect transistors), is connected to the lowest pulse transformer 19-1. When the gate trigger generation circuit 18 is triggered and switched, it supplies a gate signal to the gate trigger thyristors 2-1 to 2-M almost simultaneously.

[0037] The isolation function of the pulse transformers 19-1 to 19-M prevents the electricity from the input side of the gate trigger generation circuit 18 from flowing directly into the output side of the transformer trigger section 20, thus preventing accidental switching and protecting the output load. Furthermore, even if sudden voltage fluctuations occur in the gate trigger thyristors 2-1 to 2-M and the avalanche mode thyristors 1-1 to 1-N, the gate trigger generation circuit 18 can be protected. In addition, the pulse transformers 19-1 to 19-M reduce external noise, enabling safe and low-noise transmission of the trigger signal.

[0038] Figure 4 shows the characteristics of a semiconductor switch fabricated by connecting 17 stages of avalanche mode thyristors 1-1 to 1-N and 10 stages of gate trigger thyristors 2-1 to 2-M, with a maximum operating voltage of 40kV. The left vertical axis represents voltage (4kV / div), the right vertical axis represents load current (0.2kA / div), and the horizontal axis represents time (200ns / div). This example uses a voltage HV applied to the semiconductor switch circuit of 28kV, a load resistance 17 of 16Ω, and a capacitor 16 of 17nF.

[0039] The voltage switches in less than 50ns. In avalanche mode thyristors 1-1 to 1-N, when the lower stage turns on, the next stage also turns on in a chain reaction, so the switching speed hardly slows down even with multiple stages connected. The load current begins to flow approximately 300ns after the voltage switches. This delay is regulated by the magnetic switch (MS) 15.

[0040] The semiconductor switch circuit used in the experiment was designed for a maximum operating voltage of 40kV, but it can be seen that it can also operate at a lower voltage of 28kV.

[0041] By placing the multi-stage connected gate trigger thyristors below the avalanche mode thyristors, it is possible to obtain a semiconductor switch using avalanche mode with a wide operating range. Furthermore, reliability can be improved by making the trigger circuit of the gate trigger thyristor an isolated circuit.

[0042] Furthermore, by selecting the individual thyristors used and the number of stages of gate trigger thyristors and avalanche mode thyristors, the avalanche mode thyristor can be supplied with the necessary operating voltage and switch operation can be performed even at a voltage significantly lower than the rated voltage. The inventor's studies have confirmed that the semiconductor switch according to this embodiment can operate at a voltage of approximately 5kV, which is 1 / 8 of the maximum operating voltage of 40kV. According to the present invention, the operating voltage can be reduced compared to a semiconductor switch consisting of an avalanche mode thyristor and a single-stage trigger circuit for activating it. Furthermore, compared to a configuration using only a gate trigger thyristor, the number of trigger circuit stages can be omitted, thus increasing reliability and reducing costs. Moreover, by using a configuration that combines a gate trigger thyristor section consisting of multiple gate trigger thyristors and an avalanche mode thyristor section consisting of multiple avalanche mode thyristors, it becomes possible to use thyristors with lower rated voltages. As a result, the number of stages in the thyristor, gate trigger thyristor section, or avalanche mode thyristor section can be selected according to the required specifications such as operating voltage and switching characteristics, thus broadening the range of circuit configuration options. Furthermore, in the embodiments described above, we have described trigger circuits using an optical trigger and trigger circuits using a pulse transformer as gate trigger circuits that output a trigger signal to the gate trigger thyristor section, but the system is not limited to these two types of circuits. For example, a circuit using a capacitor to generate a trigger current can also be used, and multiple trigger circuits may be used in combination. [Explanation of symbols]

[0043] 1-1~1-N...Avalanche Mode Thyristor (AMT) 2-1~2-M...Gate Trigger Thyristor 10...Light trigger section 11-1~11-M…Optical trigger receiving circuit 12-1~12-M…Isolation Transformer 13-1~13-M…Optical Fiber 14…A circuit that converts DC voltage to AC voltage 15…Magnetic switch (MS) 16…Capacitor 17…Load resistance 18...Gate trigger generation circuit 19-1~19-M…Pulse transformer 20...Transtrigger section 21…Power supply HV...Operating voltage R2, R3... Voltage divider resistors Z1... Zener diode

Claims

1. A semiconductor switch in which a discharge path is formed by connecting multiple thyristors in stages, A capacitor for storing charge from a high-voltage power supply, A magnetic switch connected in series to the charging path from the high-voltage power supply to the capacitor, An avalanche circuit comprising multiple avalanche-mode thyristors, each having a connection point on the high-voltage power supply side of the magnetic switch in the charging path, and in which the gate and cathode of the thyristor are substantially short-circuited, connected adjacent to each other in a multi-stage configuration on the discharge path, A gate trigger thyristor connected in multiple stages adjacent to each other on the discharge path of the lower stage of the multi-stage connected avalanche mode thyristor, The gate trigger thyristor is provided with a trigger circuit that supplies a gate signal to each stage, In the off state, the potential of the lowest stage of the avalanche circuit is configured to be 80-90% of the breakover voltage of the lowest stage avalanche mode thyristor. A semiconductor switch configured such that, upon transitioning to the ON state, the conduction of the gate trigger thyristor reduces the cathode potential of the lowest stage avalanche mode thyristor based on the number of stages of the gate trigger thyristor, thereby reducing the potential of the lowest stage avalanche mode thyristor to a drop exceeding the breakover voltage, turning the lowest stage avalanche mode thyristor ON, and causing the upper stages avalanche mode thyristors to turn ON in a chain reaction.

2. A semiconductor switch according to claim 1, A voltage divider resistor that divides the voltage of each stage of the avalanche mode thyristor and the gate trigger thyristor, A Zener diode connected in parallel to the aforementioned voltage divider resistor, A semiconductor switch characterized by having the following features.

3. A semiconductor switch according to either claim 1 or 2, The aforementioned trigger circuit is a semiconductor switch characterized by being a circuit that uses light as a trigger.

4. A semiconductor switch according to claim 1 or 2, The semiconductor switch is characterized in that the trigger circuit is a circuit that uses a pulse transformer as a trigger.

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