JP2015188124A - Semiconductor device and semiconductor relay - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a semiconductor device and a semiconductor relay using the same capable of preventing heat generation when an excess voltage is applied.SOLUTION: A semiconductor device 1 includes: a light-emitting part 2; a light relieving part 3; a light receiving part 5; an impedance circuit 6; and an invalidation circuit 7. The light-emitting part 2 converts an electric signal into light. The light receiving part 3 converts the light output from the light-emitting part 2 into a drive signal. The light receiving part 5 opens/closes an electric circuit L1 across a pair of output terminals 11 and 12 responding to the light output from the light-emitting part 2. The impedance circuit 6 outputs a voltage according to the voltage applied across the pair of output terminal 11 and 12 when the electric circuit L1 is opened/closed. When the output voltage from the impedance circuit 6 exceeds a predetermined voltage, the invalidation circuit 7 invalids the drive signal to a third output terminal 13.

Description

  The present invention generally relates to a semiconductor device, a semiconductor relay, and more particularly to a semiconductor device that protects a circuit from an excessive voltage and a semiconductor relay using the semiconductor device.

  2. Description of the Related Art Conventionally, there is known a semiconductor switch device that switches between output terminals between a conductive state and a non-conductive state by a semiconductor switching element that is turned on / off according to a control input. In such a semiconductor switch device, a protection circuit for preventing thermal destruction of the semiconductor switching element is provided, which is disclosed in Patent Document 1, for example.

  The conventional example described in Patent Document 1 includes a current detection resistor and a gate control transistor. The current detection resistor is a resistor having a positive temperature coefficient, and is connected between one end of the semiconductor switching element (power MOSFET) and one output end. The gate control transistor controls the gate potential of the semiconductor switching element according to the voltage drop generated in the current detection resistor.

  In this conventional example, when an excessive voltage is applied between the drain and source of the semiconductor switching element due to a short circuit of the load or the like, the voltage across the current detection resistor rises and the gate control transistor is turned on. As a result, the gate current of the semiconductor switching element is lowered to suppress the drain current, so that the semiconductor switching element is protected.

JP 2000-307398 A

  However, in the above conventional example, the semiconductor switching element is kept on even while the protection circuit is operating. For this reason, in the conventional example, if an excessive voltage is continuously applied between the output terminals while the semiconductor switching element is kept on, the semiconductor switching element may generate heat.

  The present invention has been made in view of the above points, and an object thereof is to provide a semiconductor device capable of suppressing heat generation when an excessive voltage is applied, and a semiconductor relay using the semiconductor device.

  The semiconductor device according to the present invention is electrically connected between a light emitting unit that converts an electrical signal into light, a light receiving unit that converts light output from the light emitting unit into a drive signal, and a first output terminal and a second output terminal. And a switching circuit that opens and closes an electric circuit between the first output terminal and the second output terminal according to light output from the light emitting unit, and the first output terminal and the second output terminal. And an invalidation circuit electrically connected to a third output terminal to which the drive signal is input, wherein the impedance circuit includes the first output terminal and the first output terminal. A voltage corresponding to a voltage applied between the first output terminal and the second output terminal in a state where the switching circuit is connected in series between the two output terminals and the electric circuit is closed. And the invalidation circuit is configured to output the impedance. When the output voltage of the road is above a predetermined voltage, characterized in that it is configured to disable the drive signal to the third output terminal.

  In this semiconductor device, it is preferable that the switching circuit includes a photodiode that generates a photovoltaic power according to light output from the light emitting unit, and a switching element that switches on / off according to the photovoltaic power. .

  In this semiconductor device, it is preferable that the switching circuit includes a phototransistor that switches on / off in accordance with light output from the light emitting unit.

  In this semiconductor device, the impedance circuit preferably includes at least one of a resistor, a capacitor, and a coil.

  The semiconductor relay of the present invention is a semiconductor switch that is electrically connected between any one of the semiconductor devices described above, and the first output terminal and the second output terminal, and that switches on / off according to the drive signal. It is characterized by providing.

  In the present invention, when an excessive voltage is applied between the first output terminal and the second output terminal, the invalidation circuit operates to invalidate the drive signal for the third output terminal. For this reason, the present invention can prevent an excessive voltage from being applied to the semiconductor switch while the semiconductor switch is kept on when the semiconductor switch that is turned on / off by the drive signal is used. Therefore, the present invention can suppress heat generation when an excessive voltage is applied.

It is the schematic which shows the semiconductor device and semiconductor relay of this embodiment. It is a circuit diagram showing an example of a semiconductor device of this embodiment. It is explanatory drawing of operation | movement of the semiconductor relay of this embodiment. It is a circuit diagram which shows an example of the switching circuit in the semiconductor device of this embodiment. It is the schematic which shows the conventional semiconductor device.

  As shown in FIG. 1, the semiconductor device 1 according to the embodiment of the present invention includes a light emitting unit 2, a light receiving unit 3, a switching circuit 5, an impedance circuit 6, and a disabling circuit 7. The light emitting unit 2 converts an electrical signal into light. The light receiving unit 3 converts the light output from the light emitting unit 2 into a drive signal. The switching circuit 5 is electrically connected between the first output end 11 and the second output end 12, and between the first output end 11 and the second output end 12 according to the light output from the light emitting unit 2. The electric circuit L1 is opened and closed. The impedance circuit 6 is electrically connected between the first output terminal 11 and the second output terminal 12. The invalidation circuit 7 is electrically connected to the third output terminal 13 to which a drive signal is input.

  The impedance circuit 6 is connected in series with the switching circuit 5 between the first output terminal 11 and the second output terminal 12. And the impedance circuit 6 is comprised so that the voltage according to the voltage applied between the 1st output terminal 11 and the 2nd output terminal 12 may be output in the state where the electric circuit L1 is closed. The invalidation circuit 7 is configured to invalidate the drive signal for the third output terminal 13 when the output voltage of the impedance circuit 6 exceeds a predetermined voltage.

  The semiconductor relay 100 according to the embodiment of the present invention includes a semiconductor device 1 and a semiconductor switch 8 as shown in FIG. The semiconductor switch 8 is electrically connected between the first output end 11 and the second output end 12, and is switched on / off according to a drive signal.

  Hereinafter, the semiconductor device 1 of this embodiment and the semiconductor relay 100 using the same will be described in detail. However, the configuration described below is only an example of the present invention, and the present invention is not limited to the following embodiment, and the technical idea according to the present invention is not deviated from this embodiment. Various changes can be made in accordance with the design or the like as long as they are not.

  The semiconductor relay 100 of this embodiment is a contactless relay that does not have a movable contact, such as a mechanical relay. The semiconductor relay 100 of this embodiment has various uses such as control of security devices, amusement devices, medical devices, storage battery systems, heaters, DC motors, and the like.

  As shown in FIG. 1, the semiconductor relay 100 of this embodiment includes the semiconductor device 1 of this embodiment and a semiconductor switch 8. Further, the semiconductor relay 100 of the present embodiment includes a pair of input terminals 101 and 102 (first input terminal 101 and second input terminal 102) and a pair of output terminals 103 and 104 (first output terminal 103 and second output). Terminal 104). The pair of input terminals 101 and 102 is also a pair of input terminals of the semiconductor device 1 of the present embodiment. In addition, the semiconductor device 1 of this embodiment includes a pair of output ends 11 and 12 (first output end 11 and second output end 12) and a third output end 13.

  For example, a microcomputer (microcomputer) is electrically connected to the pair of input terminals 101 and 102. An electric signal output from the microcomputer is input to the pair of input terminals 101 and 102. The pair of output terminals 103 and 104 are electrically connected to a load (not shown) and a power supply (DC power supply or AC power supply, not shown) for supplying power to the load. When the pair of output terminals 103 and 104 are conductive, a current flows between the pair of output terminals 103 and 104. Hereinafter, the current flowing between the pair of output terminals 103 and 104 is referred to as “inter-terminal current”. A voltage applied between the pair of output terminals 103 and 104 (or between the pair of output terminals 11 and 12) is referred to as “inter-terminal voltage”.

  As shown in FIG. 1, the semiconductor device 1 of the present embodiment includes a light emitting unit 2, a light receiving unit 3, a drive circuit 4, a switching circuit 5, an impedance circuit 6, and an invalidation circuit 7. .

  The light emitting unit 2 is electrically connected to the pair of input terminals 101 and 102, and is configured to convert an electrical signal input to the pair of input terminals 101 and 102 into light. In the semiconductor device 1 of the present embodiment, the light emitting unit 2 includes a light emitting diode 21 as shown in FIG. The light emitting diode 21 is provided in such a direction that the anode is connected to the first input terminal 101 and the cathode is connected to the second input terminal 102. Therefore, when a voltage (forward voltage) having the first input terminal 101 as the positive electrode and the second input terminal 102 as the negative electrode is applied between the pair of input terminals 101 and 102, the light emitting diode 21 emits light.

  The light receiving unit 3 is configured to convert light output from the light emitting unit 2 into a drive signal. In the semiconductor device 1 of the present embodiment, as shown in FIG. 2, the light receiving unit 3 includes a photodiode array formed by connecting a plurality of photodiodes 31 in series. The light receiving unit 3 is arranged in a direction in which the light receiving surface (not shown) faces the light emitting surface (not shown) of the light emitting unit 2. Specifically, the light receiving unit 3 is disposed to face the light emitting unit 2 through an optical coupling member (not shown) having electrical insulation and translucency. For this reason, since the light emitting unit 2 and the light receiving unit 3 are optically coupled to each other, the light output from the light emitting surface of the light emitting unit 2 enters the light receiving surface of the light receiving unit 3. And the light-receiving part 3 will generate a photovoltaic power, if the light output from the light emission part 2 is received.

  The anode of the photodiode array is electrically connected to the positive input terminal of the drive circuit 4. The cathode of the photodiode array is electrically connected to the negative input terminal of the drive circuit 4. For this reason, a photocurrent flows into the positive input terminal of the drive circuit 4 due to the photovoltaic force generated by the light receiving unit 3.

  As shown in FIG. 2, the drive circuit 4 includes a variable impedance element 41 and a resistor 42 that are electrically connected between the output terminals of the light receiving unit 3. The variable impedance element 41 and the resistor 42 are connected in series between the output ends of the light receiving unit 3. In the semiconductor device 1 of the present embodiment, the variable impedance element 41 is an n-channel depletion type MOSFET (Metal-Oxide-Semiconductor Field-Effect Transistor).

  The drain of the variable impedance element 41 is electrically connected to the positive output terminal of the light receiving unit 3. The source of the variable impedance element 41 is electrically connected to the output terminal of the negative electrode of the light receiving unit 3 through the resistor 42. The gate of the variable impedance element 41 is electrically connected to the negative output terminal of the light receiving unit 3. In other words, the resistor 42 is electrically connected between the gate and the source of the variable impedance element 41. The drain of the variable impedance element 41 is electrically connected to the third output end 13 and the source is electrically connected to the second output end 12.

  Hereinafter, the operation of the drive circuit 4 will be briefly described. When photocurrent flows through the variable impedance element 41 and the resistor 42 due to the photovoltaic force generated by the light receiving unit 3, a potential difference is generated between both ends of the resistor 42. Due to this potential difference, the variable impedance element 41 is switched off. Then, the drain-source region of the variable impedance element 41 is in a high impedance state. Therefore, when the photocurrent flows, the drive circuit 4 outputs the photovoltaic force generated by the light receiving unit 3 as a drive signal. A drive signal output from the drive circuit 4 (in other words, output from the light receiving unit 3) is input to the third output terminal 13.

  When the light receiving unit 3 does not generate a photoelectromotive force, a photocurrent does not flow and a potential difference does not occur between both ends of the resistor 42, so that the variable impedance element 41 is turned on. Then, the drain-source region of the variable impedance element 41 is in a low impedance state. Therefore, when the photocurrent from the light receiving unit 3 stops flowing, the drive circuit 4 does not output a drive signal.

  The switching circuit 5 is electrically connected between the pair of output terminals 11 and 12. The switching circuit 5 is configured to open and close the electric circuit L1 between the pair of output ends 11 and 12 according to the light output from the light emitting unit 2. In the semiconductor device 1 of this embodiment, as shown in FIG. 2, the switching circuit 5 includes an NPN type phototransistor 51. The phototransistor 51 is arranged in a direction in which the light receiving surface (not shown) faces the light emitting surface (not shown) of the light emitting unit 2. Specifically, the base of the phototransistor 51 is disposed facing the light emitting unit 2. For this reason, since the light emitting unit 2 and the base of the phototransistor 51 are optically coupled to each other, the light output from the light emitting surface of the light emitting unit 2 is incident on the base of the phototransistor 51. Then, when the phototransistor 51 receives the light output from the light emitting unit 2, the collector-emitter conducts and is turned on. In addition, when the phototransistor 51 does not receive light (that is, the light emitting unit 2 does not output light), the collector-emitter becomes non-conductive and is turned off.

  The collector of the phototransistor 51 is electrically connected to the first output terminal 11. The emitter of the phototransistor 51 is electrically connected to the second output terminal 12 via the impedance circuit 6. Therefore, the phototransistor 51 opens and closes the electric circuit L1 between the pair of output terminals 11 and 12 by switching on / off according to the light output from the light emitting unit 2.

  The impedance circuit 6 is electrically connected between the pair of output terminals 11 and 12. The impedance circuit 6 is connected in series with the switching circuit 5 between the pair of output terminals 11 and 12. And the impedance circuit 6 is comprised so that the voltage according to the voltage between terminals may be output in the state by which the electric circuit L1 is closed. In the semiconductor device 1 of the present embodiment, the impedance circuit 6 includes a resistor 61 as shown in FIG. One end of the resistor 61 is electrically connected to the emitter of the phototransistor 51, and the other end of the resistor 61 is electrically connected to the second output terminal 12. Therefore, the inter-terminal voltage is applied to the impedance circuit 6 when the phototransistor 51 is on, and the inter-terminal voltage is not applied to the impedance circuit 6 when the phototransistor 51 is off. Then, the voltage across the resistor 61 is output to the invalidation circuit 7.

  The invalidation circuit 7 is electrically connected to the third output terminal 13. The invalidation circuit 7 is configured to invalidate the drive signal for the third output terminal 13 when the output voltage of the impedance circuit 6 exceeds a predetermined voltage. In the semiconductor device 1 of the present embodiment, as shown in FIG. 2, the invalidation circuit 7 includes a switching element 71 that is an n-channel enhancement type MOSFET. The drain of the switching element 71 is electrically connected to the positive output terminal of the drive circuit 4. The source of the switching element 71 is electrically connected to the negative output terminal of the drive circuit 4 and the second output terminal 12. Further, the gate of the switching element 71 is electrically connected to the emitter of the phototransistor 51 and one end on the positive electrode side of the resistor 61.

  That is, the output voltage of the impedance circuit 6 (here, the voltage across the resistor 61) is applied between the gate and source of the switching element 71. The switching element 71 is turned on when the voltage across the resistor 61 (that is, the gate-source voltage) exceeds the first threshold voltage, and turned off when the voltage across the resistor 61 falls below the first threshold voltage. When the switching element 71 is turned on, the drain-source state of the switching element 71 is in a low impedance state, and the drive signal is not input to the third output end 13.

  In the semiconductor device 1 according to the present embodiment, a terminal voltage is applied across the resistor 61 when the resistance component of the switching circuit 5 is ignored. Therefore, the switching element 71 is turned on when the inter-terminal voltage exceeds the first threshold voltage (predetermined voltage).

  The semiconductor switch 8 is electrically connected between the pair of output terminals 11 and 12, and is configured to be switched on / off according to a drive signal. In the semiconductor relay 100 of the present embodiment, as shown in FIG. 2, the semiconductor switch 8 includes a switching element 81 that is an n-channel enhancement type MOSFET. The drain of the switching element 81 is electrically connected to the first output end 11. The source of the switching element 81 is electrically connected to the second output end 12. Further, the gate of the switching element 81 is electrically connected to the third output end 13.

  The switching element 81 switches on / off according to a drive signal input via the third output end 13. That is, the switching element 81 is turned on when the gate-source voltage exceeds the second threshold voltage due to the input of the drive signal. At this time, the pair of output terminals 103 and 104 are electrically connected. On the other hand, the switching element 81 is turned off when the drive signal is not input and the gate-source voltage falls below the second threshold voltage. At this time, the pair of output terminals 103 and 104 are not conductive.

  Hereinafter, the operation of the semiconductor relay 100 of the present embodiment will be described. When the forward voltage of the light emitting diode 21 is applied between the pair of input terminals 101 and 102, the light emitting unit 2 emits light. And the light-receiving part 3 receives the light which the light emission part 2 outputs, and generate | occur | produces a photovoltaic power. Due to this photoelectromotive force, a photocurrent flows into the drive circuit 4, and a voltage drop occurs between both ends of the resistor 42. Due to this voltage drop, the variable impedance element 41 is switched off, so that the drain-source between the variable impedance element 41 is in a high impedance state. Then, since the drive signal is input to the third output terminal 13, the gate capacitance of the switching element 81 is charged, and the switching element 81 is turned on. That is, the semiconductor switch 8 is turned on, and the pair of output terminals 103 and 104 are electrically connected.

  On the other hand, the light emitting unit 2 does not emit light when no voltage is applied between the pair of input terminals 101 and 102 or when a voltage lower than the forward voltage of the light emitting diode 21 is applied. For this reason, no photoelectromotive force is generated in the light receiving unit 3, and no photocurrent flows through the drive circuit 4. In this state, there is no voltage drop across the resistor 42, so the variable impedance element 41 is switched on. Then, the drain-source region of the variable impedance element 41 is in a low impedance state. At this time, the drive signal is not input to the third output end 13, the gate capacitance of the switching element 81 is discharged through the variable impedance element 41, and the switching element 81 is switched off. That is, the semiconductor switch 8 is switched off, and the pair of output terminals 103 and 104 are not connected.

  Next, the operation of the semiconductor device 1 of this embodiment will be described. In the following description, it is assumed that a load and a power source are electrically connected to the pair of output terminals 103 and 104. Therefore, a voltage supplied by the power source is applied between the pair of output terminals 103 and 104 (between the pair of output terminals 11 and 12). When the light emitting unit 2 emits light, the phototransistor 51 is turned on in response to the light output from the light emitting unit 2. Then, the electric circuit L <b> 1 is closed, and the inter-terminal voltage is applied to the impedance circuit 6. Here, when the voltage between terminals increases due to a load short circuit or the like, the current between terminals also increases (see FIG. 3). When the voltage between the terminals exceeds a predetermined voltage (“V1” in FIG. 3), the gate-source voltage of the switching element 71 exceeds the first threshold voltage, and the switching element 71 is turned on. Then, the driving signal is not input to the third output terminal 13 (that is, the driving signal for the third output terminal 13 becomes invalid), and the gate capacitance of the switching element 81 is discharged through the path through the switching element 71. For this reason, the switching element 81 is switched off. And since a pair of output terminals 103 and 104 become non-conductive, the electric current between terminals does not flow.

  That is, the semiconductor device 1 according to this embodiment functions as an overcurrent protection circuit that prevents an excessive inter-terminal current from flowing through the semiconductor switch 8. In addition, the semiconductor device 1 of this embodiment also functions as an overvoltage protection circuit that prevents an excessive inter-terminal voltage from being applied to the semiconductor switch 8 while the semiconductor switch 8 is kept on.

  As described above, in the semiconductor device 1 according to the present embodiment, when an excessive voltage is applied between the first output terminal 11 and the second output terminal 12, the invalidation circuit 7 operates to operate the third output. The drive signal for end 13 is disabled. For this reason, in the semiconductor device 1 of the present embodiment, an excessive voltage is applied between the first output terminal 11 and the second output terminal 12 when the semiconductor switch 8 that is turned on / off by the drive signal is used. The semiconductor switch 8 can be switched off. That is, the semiconductor device 1 of this embodiment can prevent an excessive voltage from being applied to the semiconductor switch 8 while the semiconductor switch 8 is kept on. Therefore, the semiconductor device 1 of this embodiment can suppress heat generation when an excessive voltage is applied.

  In the semiconductor device 1 of the present embodiment, the switching circuit 5 is configured by the phototransistor 51, but the present invention is not limited to this configuration. That is, for example, as shown in FIG. 4, the switching circuit 5 may include a plurality of photodiodes 52 and a switching element 53 that is an n-channel enhanced MOSFET. The plurality of photodiodes 52 generate photovoltaic power in accordance with the light output from the light emitting unit 2. The plurality of photodiodes 52 are connected in series to form a photodiode array. The anode of the photodiode array is electrically connected to the gate of the switching element 53. Further, the cathode of the photodiode array is connected to the source of the switching element 53. Accordingly, the switching element 53 is turned on when the photovoltaic power generated by the plurality of photodiodes 52 exceeds the third threshold voltage, and is turned off when the photovoltaic element is lower than the third threshold voltage.

  The drain of the switching element 53 is electrically connected to the first output end 11. The source of the switching element 53 is electrically connected to the second output end 12 via the impedance circuit 6. Therefore, the switching element 53 opens and closes the electric circuit L1 between the pair of output ends 11 and 12 by switching on / off according to the light output from the light emitting unit 2.

  Further, in the semiconductor device 1 of the present embodiment, the impedance circuit 6 is configured by the resistor 61. This has the following advantages. That is, the impedance circuit 61 can be easily created by using the resistor 61 as the impedance circuit 6. The resistor 61 can be formed by a semiconductor process similar to the semiconductor process for forming the light receiving unit 3 (photodiode array), the semiconductor switch 8 (switching element 81), and the like. Therefore, the resistor 61 can be formed on the same semiconductor chip together with components such as the light receiving unit 3 and the semiconductor switch 8, and the size can be reduced.

  Of course, the configuration of the impedance circuit 6 described above is merely an example, and can be changed as appropriate. That is, the impedance circuit 6 may be configured by a circuit in which a plurality of resistors are connected in series, for example. In this configuration, for example, when the inter-terminal voltage exceeds the rated voltage of the invalidation circuit 7, a voltage obtained by dividing the inter-terminal voltage by a plurality of resistors can be applied to the invalidation circuit 7. Therefore, with this configuration, it is possible to prevent an excessive voltage exceeding the rated voltage from being applied to the invalidation circuit 7.

  In addition, the impedance circuit 6 may be configured by an impedance element such as a coil or a capacitor. That is, the impedance circuit 6 may be configured to include at least one of a resistor, a capacitor, and a coil.

  In addition, the structure of the light-emitting part 2 and the light-receiving part 3 mentioned above is only an example, and can be changed suitably. That is, the light emitting unit 2 may be configured using a light emitting element other than the light emitting diode, such as an organic EL (Electro-Luminescence) element. In addition, the light receiving unit 3 may be configured using, for example, a single-shot photodiode, a phototransistor, a solar cell, or the like.

  The circuit configurations of the drive circuit 4 and the semiconductor switch 8 described above are merely examples, and can be changed as appropriate. For example, the semiconductor switch 8 is not limited to the configuration using the enhancement type MOSFET, but may be configured using an IGBT (Insulated Gate Bipolar Transistor) or the like.

  Furthermore, in the semiconductor device 1 of the present embodiment, the invalidation circuit 7 is configured by a single switching element 71 (enhancement type MOSFET), but the present invention is not limited to this configuration. That is, the invalidation circuit 7 may be configured by a plurality of switching elements, for example. If the invalidation circuit 7 is configured by a single switching element 71, the mounting area can be reduced and the cost can be reduced. Further, the switching element 71 may be constituted by, for example, an NPN bipolar transistor.

  In addition, when the semiconductor device 1 of this embodiment and the semiconductor switch 8 are separate bodies, the 1st output terminal 11, the 2nd output terminal 12, and the 3rd output terminal 13 are terminals. On the other hand, in the case where the semiconductor device 1 and the semiconductor switch 8 of the present embodiment are integrally formed (that is, the semiconductor relay 100), the first output terminal 11, the second output terminal 12, and the third output terminal 13 are not terminals. .

(Comparative example)
Here, as a comparative example with the semiconductor device 1 of the above-described embodiment, a semiconductor device (switching device 200) described in JP-A-8-162931 will be described. As shown in FIG. 5, the switching device 200 includes an n-channel FET (Field Effect Transistor) 201, a resistor 202, a photodiode array 203, and a light emitting diode 204. A power supply 300 is electrically connected between the pair of output terminals of the switching device 200. A load 400 is electrically connected to the negative electrode of the power supply 300.

  The drain of the FET 201 is electrically connected to the positive electrode of the power supply 300 via the output terminal. The source of the FET 201 is electrically connected to the negative electrode of the power supply 300 via the output terminal and the load 400. The resistor 202 is electrically connected between the gate and source of the FET 201. The photodiode array 203 is electrically connected in parallel with the resistor 202. The photodiode array 203 generates an electromotive force by light emission of the light emitting diode 204.

  The switching device 200 includes an NPN transistor 205, resistors 206 and 207, and a capacitor 208. The collector of the transistor 205 is electrically connected to the gate of the FET 201. The emitter of the transistor 205 is electrically connected to the negative electrode of the power supply 300 via the output terminal and the load 400. The resistors 206 and 207 are connected in series, and the connection point is electrically connected to the base of the transistor 205. One end of the resistor 207 opposite to the connection point is electrically connected to the negative electrode of the power supply 300 via the output end and the load 400. The capacitor 208 is electrically connected between one end opposite to the connection point of the resistor 206 and the collector of the FET 201.

  Hereinafter, the operation of the switching device 200 will be briefly described. When the light emitting diode 204 emits light according to the input signal, the photodiode array 203 generates an electromotive force. This electromotive force causes a potential difference between the gate and source of the FET 201, and the FET 201 is turned on. Then, since a pair of output terminals are conducted, a current flows from the power supply 300 to the load 400.

  Here, when the power supply 300 and the load 400 are connected to the switching device 200 with the power supply 300 turned on, or when the power supply 300 is turned on with the power supply 300 connected, a voltage that rises sharply is applied between the drain and source of the FET 201. . At this time, a current flows through a differential circuit composed of resistors 206 and 207 and a capacitor 208, and the transistor 205 is turned on. As a result, no potential difference occurs between the gate and source of the FET 201. With the above configuration, the switching device 200 prevents a phenomenon in which the FET 201 is turned on instantaneously.

  The switching device 200 has a function of protecting the FET 201 from an excessive voltage for a certain time after the power supply 300 is turned on, but a function for protecting the FET 201 from an instantaneous voltage when the power supply 300 is turned on. Only it is. That is, the switching device 200 functions as a protection circuit from when the power supply 300 is turned on until charging of the capacitor 208 is completed, but does not function as a protection circuit when charging of the capacitor 208 is completed.

  On the other hand, in the semiconductor device 1 of the above-described embodiment, the switching circuit 5 functions while the light emitting unit 2 emits light. Therefore, the semiconductor device 1 always functions as a protection circuit for the semiconductor switch 8 while the power is turned on. . Furthermore, in the semiconductor device 1 of the above embodiment, when the power is turned off, the switching circuit 5 is turned off to open the electric circuit L1. For this reason, in the semiconductor device 1 of the said embodiment, the voltage between terminals is not applied to the impedance circuit 6 in the state which turned off. Therefore, the semiconductor device 1 of the above embodiment can reduce power consumption when the power is turned off.

DESCRIPTION OF SYMBOLS 1 Semiconductor device 2 Light emission part 3 Light reception part 5 Switching circuit 51 Phototransistor 52 Photodiode 53 Switching element 6 Impedance circuit 7 Invalidation circuit 8 Semiconductor switch 11 1st output terminal 12 2nd output terminal 13 3rd output terminal 100 Semiconductor relay L1 Electric circuit

Claims (5)

A light emitting unit for converting an electrical signal into light;
A light receiving unit that converts light output from the light emitting unit into a drive signal;
A switching circuit that is electrically connected between the first output terminal and the second output terminal, and opens and closes an electric circuit between the first output terminal and the second output terminal in accordance with light output from the light emitting unit. When,
An impedance circuit electrically connected between the first output terminal and the second output terminal;
A disabling circuit electrically connected to a third output terminal to which the drive signal is input,
The impedance circuit is connected in series with the switching circuit between the first output end and the second output end, and the first output end and the second output end in a state where the electric circuit is closed. Is configured to output a voltage according to the voltage applied between
The invalidation circuit is configured to invalidate the drive signal for the third output terminal when an output voltage of the impedance circuit exceeds a predetermined voltage.   2. The switching circuit includes a photodiode that generates a photovoltaic power according to light output from the light emitting unit, and a switching element that switches on / off according to the photovoltaic power. The semiconductor device described.   The semiconductor device according to claim 1, wherein the switching circuit includes a phototransistor that switches on / off in accordance with light output from the light emitting unit.   The semiconductor device according to claim 1, wherein the impedance circuit includes at least one of a resistor, a capacitor, and a coil. The semiconductor device according to any one of claims 1 to 4,
A semiconductor relay, comprising: a semiconductor switch that is electrically connected between the first output terminal and the second output terminal, and that switches on / off according to the drive signal.

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