Protection circuit

Abstract

To provide a novel, improved protection circuit that can suppress a failure in a switching element even if the protection circuit is reversely connected to a power source and a ground by mistake, for example.SOLUTION: One example of the protection circuit includes a switching element formed using a field effect transistor that switches between electric connection and disconnection between a power source terminal and a load terminal in accordance with control voltage applied from a control circuit to a gate, and a first protection element that electrically disconnects between a ground terminal and the gate when a first potential difference between the potential of the ground terminal and the potential of the power source terminal is less than a threshold, and electrically connects between the ground terminal and the gate when the first potential difference is more than or equal to the threshold.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present invention relates to a protection circuit. [Background technology]

[0002] Conventionally, a protection circuit is known that includes a switching element that electrically cuts off a load and a power supply for the load in response to a detection signal or the like when an abnormality such as an overcurrent is detected (for example, Patent Document 1). In the patent document, the switching element is configured using a field effect transistor. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 6-129337 Summary of the Invention [Problem to be solved by the invention]

[0004] In this type of protection circuit, if the protection circuit is mistakenly connected to the power supply and ground in reverse, i.e., if the power supply terminal of the protection circuit is connected to the ground and the power supply is connected to the ground terminal of the protection circuit, there is a risk of the switching element failing.

[0005] Therefore, one of the objects of the present invention is to provide a new and improved protection circuit that can suppress failure of a switching element even in the case where, for example, the protection circuit is erroneously connected in reverse to a power supply and ground. [Means for solving the problem]

[0006] The protection circuit of the present invention includes, for example, a switching element configured using a field effect transistor that switches between electrical connection and disconnection between a power supply terminal and a load terminal in response to a control voltage applied to a gate from a control circuit, and a first protection element that electrically disconnects the ground terminal and the gate when a first potential difference between the potential of the ground terminal and the potential of the power supply terminal is less than a threshold value, and electrically connects the ground terminal and the gate when the first potential difference is equal to or greater than a threshold value.

[0007] The protection circuit may include a second protection element having a control electrode electrically connected to the ground terminal, electrically insulating between the gate and the load terminal when a second potential difference between the potential of the ground terminal and the potential of the load terminal is less than a threshold value, and electrically connecting between the gate and the load terminal when the second potential difference is equal to or greater than the threshold value.

[0008] The protection circuit may include a third protection element that electrically disconnects the control electrode and the power supply terminal when a third potential difference between the potential of the ground terminal and the potential of the power supply terminal is less than a threshold value, and electrically connects the control electrode and the power supply terminal when the third potential difference is equal to or greater than the threshold value.

[0009] In the protection circuit, the ground terminal and the control electrode may be electrically connected via a resistor.

[0010] The protection circuit may include a capacitor interposed between the load terminal and the ground terminal. Effect of the Invention

[0011] According to the present invention, it is possible to obtain a new and improved protection circuit that can suppress failure of a switching element even in the case where, for example, the protection circuit is erroneously connected in reverse to the power supply and ground. [Brief description of the drawings]

[0012] [Figure 1] FIG. 1 is an exemplary block diagram of a protection circuit according to a first embodiment. [Diagram 2] FIG. 2 is an exemplary circuit diagram of the protection circuit of the first embodiment. [Diagram 3] FIG. 3 is an exemplary block diagram of a protection circuit according to the second embodiment. [Figure 4] FIG. 4 is an exemplary circuit diagram of a protection circuit according to the second embodiment. [Diagram 5] FIG. 5 is an exemplary circuit diagram of a protection circuit according to a modified example of the second embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0013] Exemplary embodiments and modifications of the present invention are disclosed below. The configurations of the embodiments and modifications shown below, as well as the actions and results (effects) brought about by the configurations, are merely examples. The present invention can be realized by configurations other than those disclosed in the following embodiments and modifications. Furthermore, according to the present invention, it is possible to obtain at least one of the various effects (including derivative effects) obtained by the configurations.

[0014] In addition, in this specification, ordinal numbers are given for the sake of convenience to distinguish between parts, members, portions, etc., and do not indicate priority or order.

[0015] [First embodiment] FIG. 1 is a schematic configuration diagram of a protection circuit 100A according to an embodiment.

[0016] The protection circuit 100A is provided between a power supply 200 and a load 300. The protection circuit 100A has an overload protection element 110 that prevents an overload on the load 300. The protection circuit 100A is mounted on a circuit board (not shown) such as a printed wiring board.

[0017] The power supply 200 is, for example, a DC power supply, and the power supply voltage is, for example, 12 [V] or 48 [V]. The power supply 200 supplies power supply power to the load 300. G2 is the ground of the power supply 200.

[0018] The load 300 is, for example, an inductive load such as a motor. G3 is the ground of the load 300.

[0019] The protection circuit 100A has a power terminal ts, a load terminal tl, and a ground terminal tg, where G1 is the ground of the protection circuit 100A.

[0020] The power supply terminal ts is, for example, a terminal of a circuit board on which the protection circuit 100A is mounted, and is provided between the overload protection element 110 and the power supply 200.

[0021] The load terminal tl is, for example, a terminal of a circuit board on which the protection circuit 100A is mounted, and is provided between the overload protection element 110 and the load 300.

[0022] The ground terminal tg is, for example, a terminal of a circuit board on which the protection circuit 100A is mounted, and is provided between the protection circuit 100A and ground G1, specifically, between the control circuit 120 and the reverse connection protection circuit 140A, and ground G1. The ground terminal tg is a terminal that serves as a common ground between the protection circuit 100A, a circuit other than the protection circuit 100A mounted on the circuit board, an element other than the element included in the protection circuit 100A mounted on the circuit board, etc. The common ground may also be referred to as a single-point earth.

[0023] In this specification, the potential of the ground terminal tg in a normal state in which the ground terminal tg and the ground G1 are electrically connected via a ground line is referred to as a normal ground potential.

[0024] The protection circuit 100A also includes an overload protection element 110, a control circuit 120, and a surge protection element .

[0025] The overload protection element 110 is provided between a power supply terminal ts and a load terminal tl. The overload protection element 110 switches between electrical connection and disconnection between the power supply terminal ts and the load terminal tl in response to a control signal from the control circuit 120.

[0026] The overload protection element 110 is configured using a field effect transistor. Hereinafter, the overload protection element 110 will be referred to as a transistor T1 (see FIG. 2). The overload protection element 110, that is, the transistor T1, is an example of a switching element.

[0027] The control circuit 120 outputs a control signal that switches the transistor T1 between on and off in response to a detection signal obtained from a sensor, a detection circuit, or the like (not shown).

[0028] In a normal state where no abnormality is detected, the control circuit 120 applies a control voltage as a control signal to the gate T1g (see FIG. 2) of the transistor T1 to turn on the transistor T1. In this state, the power supply terminal ts and the load terminal tl are electrically connected, and power supply power is applied from the power supply 200 to the load 300. The control circuit 120 may also be referred to as a gate driver. The gate T1g is an example of a control electrode.

[0029] On the other hand, in an abnormal state where an abnormality such as overheating or overcurrent is detected, the control circuit 120 turns off the transistor T1 by stopping the application of the control voltage to the gate T1g. In this state, the power supply terminal ts and the load terminal tl are electrically disconnected.

[0030] Moreover, the surge protection element 130 prevents the transistor T1 from breaking down due to a surge voltage of the load 300. The surge protection element 130 is, for example, a Zener diode. Hereinafter, the surge protection element 130 will be referred to as a diode D1 (see FIG. 2).

[0031] [Reverse connection protection circuit] If the protection circuit 100A having the above-described configuration is mistakenly connected to the power supply 200 and the ground G1 in reverse, i.e., if the ground G1 is connected to the power supply terminal ts and the power supply 200 is connected to the ground terminal tg, there is a risk that the transistor T1 will fail.

[0032] Therefore, in order to prevent such a failure of the transistor T1, the protection circuit 100A of this embodiment has a reverse connection protection circuit 140A. In the following, the state in which the power supply 200 and the ground G1 are connected in reverse is referred to as a reverse connection state.

[0033] Fig. 2 is a circuit diagram of the protection circuit 100A. As shown in Fig. 2, the reverse connection protection circuit 140A includes a transistor T2, a diode D21, and a diode D22.

[0034] The transistor T2 is configured as a bipolar transistor. The emitter of the transistor T2 is electrically connected to the ground terminal tg. The collector of the transistor T2 is electrically connected to the gate T1g of the transistor T1, and the base of the transistor T2 is electrically connected to the power supply terminal ts. A bias resistor is provided corresponding to the transistor T2 to stabilize the operation of the transistor T2. The transistor T2 is an example of a first protection element.

[0035] The diode D21 is interposed between the transistor T2 and the power supply terminal ts. The forward direction of the diode D21 is from the transistor T2 to the power supply terminal ts. In other words, the diode D21 allows a current to flow from the transistor T2 to the power supply terminal ts and blocks a current to flow from the power supply terminal ts to the transistor T2.

[0036] The diode D22 is interposed between the transistor T2 and the gate T1g. The forward direction of the diode D22 is from the transistor T2 to the gate T1g. That is, the diode D22 allows a current to flow from the transistor T2 to the gate T1g and blocks a current to flow from the gate T1g to the transistor T2.

[0037] The resistors R11 and R12 are interposed between the control circuit 120 and the gate T1g of the transistor T1. The resistor R11 is interposed between the control circuit 120 and the collector of the transistor T2. The resistor R12 is interposed between the gate T1g and the collector of the transistor T2. The magnitudes of the resistors R11 and R12 are appropriately set so that the transistors T1 and T2 operate properly.

[0038] In the reverse connection protection circuit 140A configured as described above, when a first potential difference between the potential of the ground terminal tg and the potential of the power supply terminal ts is less than a first threshold voltage, the transistor T2 is turned off and electrically disconnects the ground terminal tg from the gate T1g. The first threshold voltage is determined based on the base-emitter voltage (junction unsaturation voltage) of the transistor T2. The first threshold voltage is a positive value.

[0039] On the other hand, when a first potential difference between the potential of the ground terminal tg and the potential of the power supply terminal ts is equal to or greater than a first threshold voltage, the transistor T2 is turned on and electrically connects the ground terminal tg and the gate T1g.

[0040] Therefore, for example, when the power supply terminal ts is connected to the ground G1 and the power supply 200 is connected to the ground terminal tg, that is, when the transistor T2 is in a reverse connection state, the first potential difference becomes equal to or greater than the first threshold voltage, and the transistor T2 is turned on, electrically connecting the ground terminal tg and the gate T1g. In other words, the base current I2b flows, and the collector current I2c flows accordingly. This allows a positive potential to be applied to the gate T1g, and the transistor T1 to be turned on. If the transistor T1 is in an off state in the reverse connection state, a forward current flows through a parasitic diode formed inside the transistor T1, which may cause the transistor T1 to overheat and break down. If the transistor T1 is in an on state, such a breakdown does not occur. In this regard, according to the configuration of this embodiment, when the transistor T1 is in a reverse connection state, the transistor T1 can be turned on, and therefore the breakdown of the transistor T1 due to the current flowing through the transistor T1 in the off state of the transistor T1 can be suppressed.

[0041] [Second embodiment] FIG. 3 is a schematic configuration diagram of a protection circuit 100B according to an embodiment.

[0042] [Countermeasure circuit] The protection circuit 100B of this embodiment has a measure in place for the case where the power supply terminal ts is electrically connected to the power supply 200, but the ground terminal tg is not properly electrically connected to the ground G1.

[0043] In the protection circuit 100B, if the countermeasure circuit 150 is not provided, when the ground line between the ground terminal tg and the ground G1 is broken or the ground terminal tg is disconnected from the ground line, the potential of the ground terminal tg rises above the normal ground potential. In this case, the potential of the ground terminal tg is determined by the configuration of the circuit including the circuits other than the protection circuit 100B mounted on the circuit board, the resistance value of each part, etc. When the ground potential rises, the control voltage applied to the gate T1g of the transistor T1 via the control circuit 120 also rises, which may cause the transistor T1 to be turned on unintentionally. In other words, there is a risk of the transistor T1 malfunctioning.

[0044] Therefore, the protection circuit 100B of this embodiment has a countermeasure circuit 150 to prevent such a malfunction of the transistor T1.

[0045] Fig. 4 is a circuit diagram of the protection circuit 100B. As shown in Fig. 4, the countermeasure circuit 150 includes a transistor T3, a diode D3, and a resistor R3.

[0046] The transistor T3 is configured as a bipolar transistor. The base T3b of the transistor T3 is electrically connected to the ground terminal tg. The collector of the transistor T3 is electrically connected to the gate T1g of the transistor T1, and the emitter of the transistor T3 is electrically connected to the load terminal tl. The transistor T3 is an example of a second protection element. The base T3b is an example of a control electrode.

[0047] The transistor T3 is configured as a resistor-integrated transistor 150a that incorporates the transistor T3 and a bias resistor that stabilizes the operation of the transistor T3. The resistor-integrated transistor 150a may also be referred to as a digital transistor.

[0048] The diode D3 is interposed between the transistor T3 and the load terminal tl. The forward direction of the diode D3 is from the transistor T3 to the load terminal tl. In other words, the diode D3 allows a current from the transistor T3 to the load terminal tl and blocks a current from the load terminal tl to the transistor T3.

[0049] The protection circuit 100B includes resistors R121 and R122 that function similarly to the resistor R12 in the first embodiment. The resistors R11, R121, and R3 are interposed between the control circuit 120 and the collector of the transistor T3. The resistors R122 and R3 are interposed between the gate T1g and the collector of the transistor T3. The magnitudes of the resistors R11, R121, R122, and R3 are appropriately set so that the transistors T1 and T2 operate appropriately.

[0050] In the countermeasure circuit 150 configured as above, when a second potential difference between the potential of the ground terminal tg and the potential of the load terminal tl is less than a second threshold voltage, the transistor T3 is turned off and electrically disconnects the gate T1g from the load terminal tl. The second threshold voltage is determined based on the base-emitter voltage (junction unsaturation voltage) of the transistor T3. The second threshold voltage is a positive value.

[0051] On the other hand, when a second potential difference between the potential of the ground terminal tg and the potential of the load terminal tl is equal to or greater than a second threshold voltage, the transistor T3 is turned on and electrically connects the gate T1g and the load terminal tl.

[0052] Therefore, when the potential of the ground terminal tg becomes higher than the normal ground potential, and the second potential difference of the potential of the ground terminal tg with respect to the potential of the load terminal tl becomes equal to or greater than the second threshold, the transistor T3 turns on and electrically connects the gate T1g and the load terminal tl. In other words, the base current I3b flows, and the collector current I3c flows. In this case, the charge of the gate T1g can be released to the load terminal tl via the transistor T3, and this can prevent the transistor T1 from being unintentionally turned on due to the positive second potential difference of the potential of the gate T1g with respect to the potential of the load terminal tl. That is, according to the countermeasure circuit 150, even if the ground line between the ground terminal tg and the ground G1 is broken or the ground terminal tg is disconnected from the ground line, the increase in the voltage of the gate T1g can be suppressed, and the transistor T1 can be prevented from being unintentionally turned on.

[0053] In addition, in the protection circuit 100B, for example, when the transistor T1 switches from on to off while the current value of the current flowing through the transistor T1 is high, the potential of the load terminal tl may become lower than the normal ground potential. This is called a negative surge at the load terminal tl. In this case, too, when the second potential difference between the potential of the ground terminal tg and the potential of the load terminal tl becomes equal to or greater than the second threshold, the transistor T3 turns on and electrically connects the gate T1g and the load terminal tl. In other words, the base current I3b flows, and thus the collector current I3c flows. In this case, too, the charge of the gate T1g can be released to the load terminal tl via the transistor T3, and this makes it possible to prevent the transistor T1 from being unintentionally turned on by the second potential difference between the potential of the gate T1g and the potential of the load terminal tl. As a result, it is possible to prevent a short circuit failure due to the desaturation operation of the transistor T1.

[0054] The countermeasure circuit 150 also includes a capacitor C3. The capacitor C3 is interposed between the load terminal tl and the ground terminal tg, and between the emitter of the transistor T3 and the ground terminal tg. If the capacitor C3 is not provided in a case where the load 300 is an inductive load such as a motor, the potential of the emitter of the transistor T3 may fluctuate in response to the fluctuation of the potential of the load terminal tl, and the operation of the transistor T3 may not be stabilized. In this respect, the capacitor C3 can release high-frequency components to the ground terminal tg and suppress the transmission of the high-frequency components from the load terminal tl to the emitter of the transistor T3. That is, the capacitor C3 constitutes a low-pass filter. The operation of the transistor T3 can be further stabilized by such a capacitor C3.

[0055] [Combining reverse polarity protection circuitry and countermeasure circuitry] Moreover, the reverse connection protection circuit 140B has a different configuration from the reverse connection protection circuit 140A of the first embodiment. Specifically, the reverse connection protection circuit 140B differs from the reverse connection protection circuit 140A in that the reverse connection protection circuit 140B includes a transistor T4, a diode D23, a resistor R21, and a resistor R22.

[0056] Here, if transistor T4, diode D23, and resistor R21 were not provided and the base T3b of transistor T3 was electrically connected to the ground terminal tg, in a reverse connection state, the potential of the base T3b, which is electrically connected to the ground terminal tg, would rise, turning on transistor T3 and, as a result, there is a risk that transistor T1 would be turned off.

[0057] In order to avoid such inconvenience, a protection circuit 100B having a countermeasure circuit 150 of this embodiment has a transistor T4, a diode D23, and a resistor R21 added to the reverse connection protection circuit 140A of the first embodiment.

[0058] The transistor T4 is configured as a bipolar transistor. The base of the transistor T4 is electrically connected to the ground terminal tg. The collector of the transistor T4 is electrically connected to the base T3b of the transistor T3, and the emitter of the transistor T4 is electrically connected to the load terminal tl. A bias resistor is provided corresponding to the transistor T4 to stabilize the operation of the transistor T4. The transistor T4 is an example of a third protection element.

[0059] The diode D23 is interposed between the transistor T4 and the power supply terminal ts. The forward direction of the diode D3 is from the transistor T4 to the power supply terminal ts. That is, the diode D3 allows a current to flow from the transistor T4 to the power supply terminal ts and blocks a current to flow from the power supply terminal ts to the transistor T4.

[0060] The resistor R21 is interposed between the collector of the transistor T4 and the ground terminal tg, and is also interposed between the base T3b of the transistor T3 and the ground terminal tg.

[0061] Furthermore, the size of resistor R22 is appropriately set so that transistors T1 and T2 operate properly.

[0062] In the reverse connection protection circuit 140B configured as above, when a third potential difference between the potential of the ground terminal tg and the potential of the power supply terminal ts is less than a third threshold voltage, the transistor T4 is turned off and electrically disconnects the base T3b of the transistor T3 from the power supply terminal ts. The third threshold voltage is determined based on the base-emitter voltage (junction unsaturation voltage) of the transistor T4. The third threshold voltage is a positive value.

[0063] On the other hand, when a third potential difference between the potential of the ground terminal tg and the potential of the power supply terminal ts is equal to or greater than a third threshold voltage, the transistor T4 is turned on and electrically connects the base T3b of the transistor T3 and the power supply terminal ts.

[0064] Therefore, in the case where the transistor T4 is in a reverse connection state, the third potential difference becomes equal to or greater than the third threshold voltage, and the transistor T4 is turned on, electrically connecting the base T3b of the transistor T3 to the power supply terminal ts. In other words, the base current I4b flows, and the collector current I4c flows accordingly. This allows charge to escape from the base T3b, turning the transistor T3 into an off state, and thus preventing the transistor T1 from turning off due to the transistor T3 being turned on, i.e. preventing the countermeasure circuit 150 from operating.

[0065] In addition, in the reverse connection state, the larger the resistance value of the resistor R21, the smaller the collector current I4c and the lower the potential of the base T3b of the transistor T3. That is, the resistance value of the resistor R21 is appropriately set so that the transistor T4 operates as intended. In other words, the resistor R21 allows the transistors T2 to T4, and in turn the transistor T1, to operate as intended more reliably.

[0066] In this embodiment, when the power supply terminal ts is electrically connected to the power supply 200 but the ground terminal tg is not electrically connected to the ground G1, the transistor T2 is deactivated by the diodes D21 and D22, the transistor T4 is also deactivated by the diode D23, and the electrical connection between the base T3b of the transistor T3 and the ground terminal tg is ensured. Therefore, in this case, the transistors T2 and T4 are not activated to prevent the operation of the transistor T3, i.e., the operation of the countermeasure circuit 150.

[0067] [First Modification] 5 is a circuit diagram of a first modified example of the second embodiment. As shown in FIG. 5, in the reverse connection protection circuit 140B1 of the protection circuit 100B1 of this modified example, the resistor R22 and the diode D22 interposed between the collector of the transistor T2 and the gate T1g of the transistor T1 are removed from the reverse connection protection circuit 140B of the protection circuit 100B of the second embodiment. In the reverse connection protection circuit 140B1, the point p1 between the control circuit 120 and the collector of the transistor T2 and the power supply terminal ts are electrically connected via the diode D24 and the resistor R23. Except for this change, the protection circuit 100B1 has the same configuration as the protection circuit 100B.

[0068] The forward direction of the diode D24 is from the transistor T2 to the power supply terminal ts, i.e., the diode D24 allows a current to flow from the transistor T2 to the power supply terminal ts and blocks a current to flow from the power supply terminal ts to the transistor T2.

[0069] In the reverse connection state, the potential of the point p1 depends on the resistance value of the resistor R23. The point p1 may also be called a voltage dividing point. According to this modification, when the transistor T1 is turned on by the operation of the transistor T2 in the reverse connection state, the potential of the gate T1g of the transistor T1 can be set to a potential at which the transistor T1 operates more reliably.

[0070] Although the embodiment of the present invention has been illustrated above, the above embodiment and modified examples are merely examples and are not intended to limit the scope of the invention. The above embodiment and modified examples can be implemented in various other forms, and various omissions, substitutions, combinations, and modifications can be made without departing from the gist of the invention. In addition, the specifications of each configuration, shape, and the like (structure, type, direction, model, size, length, width, thickness, height, number, arrangement, position, material, etc.) can be appropriately changed and implemented. [Explanation of symbols]

[0071] 100A,100B,100B1…Protection circuit 110...Overload protection element (switching element) 120...Control circuit 130...Surge protection element 140A, 140B, 140B1...Reverse connection protection circuit 150…Countermeasure circuit 150a…Resistor built-in transistor 200…Power supply 300…load C3…Capacitor D1…Diode D21, D22, D23, D24...Diodes D3…Diode G1…Ground G2…Ground G3…Ground I2b…Base current I2c…Collector current I3b…Base current I3c…Collector current I4b…Base current I4c…Collector current p1...point (voltage division point) R11…Resistance R12, R121, R122...Resistors R21,R22,R23…Resistance R3…Resistance T1: Transistor (switching element) T1g…gate T2: Transistor (first protection element) T3: Transistor (second protection element) T3b…Base (control electrode) T4: Transistor (third protection element) tg: Ground terminal tl…Load terminal ts…power terminal

Claims

1. a switching element configured using a field effect transistor that switches between electrical connection and disconnection between a power supply terminal and a load terminal in response to a control voltage applied to a gate from a control circuit; a first protection element that electrically disconnects the ground terminal and the gate when a first potential difference between a potential of a ground terminal and a potential of the power supply terminal is less than a first threshold voltage, and electrically connects the ground terminal and the gate when the first potential difference is equal to or greater than a first threshold voltage; a second protection element having a control electrode electrically connected to the ground terminal, electrically disconnecting the gate and the load terminal when a second potential difference between a potential of the ground terminal and a potential of the load terminal is less than a second threshold voltage, and electrically connecting the gate and the load terminal when the second potential difference is equal to or greater than a second threshold voltage; a third protection element that electrically disconnects the control electrode and the power supply terminal when a third potential difference between the potential of the ground terminal and the potential of the power supply terminal is less than a third threshold voltage, and electrically connects the control electrode and the power supply terminal when the third potential difference is equal to or greater than a third threshold voltage; A protection circuit.

2. 2. The protection circuit of claim 1, further comprising a capacitor interposed between the load terminal and the ground terminal.

3. a switching element configured using a field effect transistor that switches between electrical connection and disconnection between a power supply terminal and a load terminal in response to a control voltage applied to a gate from a control circuit; a first protection element that electrically disconnects the ground terminal and the gate when a first potential difference between a potential of a ground terminal and a potential of the power supply terminal is less than a first threshold voltage, and electrically connects the ground terminal and the gate when the first potential difference is equal to or greater than a first threshold voltage; a second protection element having a control electrode electrically connected to the ground terminal, electrically disconnecting the gate and the load terminal when a second potential difference between a potential of the ground terminal and a potential of the load terminal is less than a second threshold voltage, and electrically connecting the gate and the load terminal when the second potential difference is equal to or greater than a second threshold voltage; a capacitor interposed between the load terminal and the ground terminal; A protection circuit.

4. 3. The protection circuit according to claim 1, wherein the ground terminal and the control electrode are electrically connected via a resistor.

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