Relay circuit device

Abstract

To provide a relay circuit device capable of reducing an exchange frequency by suppressing occurrence of arc discharge between contact members of a mechanical relay.SOLUTION: A relay circuit device 10 comprises: mechanical relays 2A and 2B including normally open contacts 23 and 24; semiconductor relays 3A and 3B connected in series with the mechanical relays 2A and 2B; and a control section 5 which controls the mechanical relays 2A and 2B and the semiconductor relays 3A and 3B. The normally open contacts 23 and 24 of the mechanical relays 2A and 2B and the semiconductor relays 3A and 3B are brought into a conducted state together, load currents I1 and I2 flow. When electrifying the load currents I1 and I2, the control section 5 brigs the normally open contacts 23 and 24 of the mechanical relays 2A and 2B into the conducted state ahead of the semiconductor relays 3A and 3B and when cutting off the load currents I1 and I2, the control section brings the semiconductor relays 3A and 3B into a cut-off state ahead of the normally open contacts 23 and 24 of the mechanical relays 2A and 2B.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a relay circuit device having a plurality of relays and a control unit that controls these relays. [Background technology]

[0002] Conventionally, a programmable controller for controlling equipment such as a machine tool uses a relay circuit device for turning on (conducting) and off (interrupting) a load current for operating an actuator of the machine tool that is the object of control. Some such relay circuit devices have duplicated (redundant) relays so that the load current is interrupted reliably when it is necessary to interrupt the current.

[0003] Patent Document 1 describes a relay circuit in which two mechanical relays are connected in series, in which a common terminal (COM) and a normally open terminal (NO) are electrically connected when a current is passed through a coil, and the common terminal (COM) and a normally closed terminal (NC) are electrically connected when the coil is not energized, and a current is supplied to a load when the common terminals (COM) and the normally open terminals (NO) of both mechanical relays are in a conductive state. In addition, in this relay circuit, a readback circuit made of a photocoupler is provided corresponding to each of the two mechanical relays, and the operating state of each mechanical relay can be monitored in a control unit. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2020-47556 A Summary of the Invention [Problem to be solved by the invention]

[0005] A mechanical relay has a fixed contact member and a movable contact member, and switches between an on state and an off state when the movable contact member comes into contact with and separates from the fixed contact member in conjunction with an iron piece that is operated by the magnetic force generated by an electromagnet. In addition, a mechanical life of, for example, 10 million operations (the number of times the relay can be opened and closed without an electrical load) and an electrical life of, for example, 100,000 operations (the number of times the relay can be opened and closed with a rated load) are specified for a mechanical relay. However, if an arc discharge occurs between the contact members when the movable contact member comes into contact with the fixed contact member or when the movable contact member separates from the fixed contact member, the electrical characteristics of the contact member may deteriorate, or a malfunction or recovery failure may occur even if the number of times is less than the number of times the relay can be opened and closed.

[0006] Even if such a defect occurs, if the relay is duplicated as described above, it is possible to avoid a situation in which, for example, current continues to be supplied to the actuator when an emergency stop of the equipment should be performed, but there are problems such as the need to stop the equipment to replace the relay and the cost of replacing the relay.In particular, in the case of a programmable controller configured by combining various modules, in order to replace a defective relay, it is necessary to replace the entire output module having multiple relay circuits including the defective relay, which increases the cost of replacement.

[0007] The present invention has been made in consideration of the above circumstances, and an object of the present invention is to provide a relay circuit device that can suppress the occurrence of arc discharge between contact members of a mechanical relay and reduce the frequency of replacement. [Means for solving the problem]

[0009] In order to achieve the above object, the present invention provides a relay circuit device comprising first and second mechanical relays each having a mechanical contact that switches between a conductive state and a cut-off state in response to a relay control signal, a semiconductor relay connected in series with the first and second mechanical relays, and a control unit that controls the mechanical relay and the semiconductor relay of each of the first and second mechanical relays, wherein a load current flows when the mechanical contacts of each of the first and second mechanical relays and the semiconductor relay are all in a conductive state, and the load current is cut off when at least one of the mechanical contacts of each of the first and second mechanical relays and the semiconductor relay is in a cut-off state, and the control unit brings the mechanical contacts of each of the first and second mechanical relays into a conductive state before the semiconductor relay when passing a load current, and brings the semiconductor relay into a cut-off state before the mechanical contacts of each of the first and second mechanical relays when cutting off the load current. Effect of the Invention

[0010] According to the relay circuit device of the present invention, it is possible to suppress the occurrence of arc discharge between the contact members of the mechanical relay, thereby making it possible to reduce the frequency of replacement. [Brief description of the drawings]

[0011] [Figure 1] 1 is a circuit diagram showing a configuration example of a relay circuit device according to an embodiment of the present invention; [Diagram 2] 1A and 1B are schematic diagrams showing an example of the configuration of an input-side mechanical relay, in which (a) shows a state in which an electromagnet is not energized, and (b) shows a state in which the electromagnet is energized. [Diagram 3] FIG. 2 is a circuit diagram showing an example of a circuit configuration of a first semiconductor relay. [Figure 4] 4 is a timing chart showing an example of the operation of the relay circuit device. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0012] [Embodiment Mode] An embodiment of the present invention will be described with reference to Figures 1 to 4. Note that the embodiment described below is shown as a preferred specific example for carrying out the present invention, and while there are some parts that specifically exemplify various technical matters that are technically preferable, the technical scope of the present invention is not limited to this specific embodiment.

[0013] Fig. 1 is a circuit diagram showing an example of a circuit configuration of a relay circuit device according to an embodiment of the present invention. This relay circuit device 10 is used to pass and cut off load current to first and second loads 61, 62 in an output module 1 of a programmable controller that controls equipment such as a machine tool. The output module 1 has a plurality of relay circuit devices 10, and Fig. 1 shows one of these relay circuit devices 10.

[0014] The relay circuit device 10 includes two mechanical relays 2A, 2B, two semiconductor relays 3A, 3B, first to sixth photocouplers 41-46, and a control unit 5 that controls the mechanical relays 2A, 2B and the semiconductor relays 3A, 3B. The control unit 5 outputs first and second relay control signals 51, 52 to control the mechanical relays 2A, 2B, and outputs third and fourth relay control signals 53, 54 to control the semiconductor relays 3A, 3B.

[0015] The control unit 5 simultaneously asserts (activates) and simultaneously negates (deactivates) the first and second relay control signals 51, 52, but the first relay control signal 51 and the third relay control signal 53, and the second relay control signal 52 and the fourth relay control signal 54 are output by different control circuits within the control unit 5. That is, in the control unit 5, these control circuits are duplicated, and the control unit 5 is configured to be able to cut off the load current to the first and second loads 61, 62 if at least one of the control circuits is operating normally.

[0016] The first and second loads 61 and 62 are, for example, electric actuators that operate a magnet switch or a movable part of equipment. The first load 61 is connected to the positive pole of a first DC power supply 71, and the second load 62 is connected to the positive pole of a second DC power supply 72. The output module 1 has a first input terminal 11 connected to the first load 61, a second input terminal 12 connected to the second load 62, a first output terminal 13 connected to the negative pole of the first DC power supply 71, and a second output terminal 14 connected to the negative pole of the second DC power supply 72. The output module 1 also has a P terminal 15 and an N terminal 16 to which a control power supply 8 for operating the mechanical relays 2A and 2B is connected. The control power supply 8 generates, for example, a DC voltage of 24 V between the P terminal 15 and the N terminal 16.

[0017] Hereinafter, of the two mechanical relays 2A, 2B, the mechanical relay 2A on the side of the first and second input terminals 11, 12 may be referred to as the input-side mechanical relay 2A, and the mechanical relay 2B on the side of the first and second output terminals 13, 14 may be referred to as the output-side mechanical relay 2B. Also, of the semiconductor relays 3A, 3B, the semiconductor relay 3A for conducting and cutting off the load current of the first load 61 may be referred to as the first semiconductor relay 3A, and the semiconductor relay 3B for conducting and cutting off the load current of the second load 62 may be referred to as the second semiconductor relay 3B.

[0018] Each of the mechanical relays 2A and 2B is a forced guide relay having an electromagnet 21, one normally closed contact 22, and first and second normally open contacts 23 and 24. When the electromagnet 21 is not energized, the normally closed contact 22 is in an ON (conductive) state, and the first and second normally open contacts 23 and 24 are in an OFF (disconnected) state. When the electromagnet 21 is energized, the normally closed contact 22 is in an OFF state, and the first and second normally open contacts 23 and 24 are in an ON state. The normally closed contact 22 and the first and second normally open contacts 23 and 24 are mechanical contacts that are switched between an ON state and an OFF state by mechanical contact / non-contact between contact members.

[0019] 2 is a schematic diagram showing a configuration example of an input-side mechanical relay 2A, where (a) shows a state in which the electromagnet 21 is not energized, and (b) shows a state in which the electromagnet 21 is energized. The normally closed contact 22 is made up of a fixed contact member 221 attached to the fixed plate 201 and a movable contact member 222 attached to the movable plate 202. The first normally open contact 23 is made up of a fixed contact member 231 attached to the fixed plate 203 and a movable contact member 232 attached to the movable plate 204. The second normally open contact 24 is made up of a fixed contact member 241 attached to the fixed plate 205 and a movable contact member 242 attached to the movable plate 206.

[0020] The electromagnet 21, the normally closed contact 22, and the first and second normally open contacts 23, 24 are housed in a resin housing 28 together with an iron piece 25 arranged opposite the electromagnet 21, a return spring 26 for biasing the iron piece 25, and a guide plate 27 interlocking with the iron piece 25. When the electromagnet 21 is switched between a conductive state and a non-conductive state, the iron piece 25 rotates and swings about a support shaft 251, and the guide plate 27 moves forward and backward. The iron piece 25 is biased to one side in the rotational direction by the return spring 26. The guide plate 27 connects the iron piece 25 and the movable plates 202, 204, 206, and the movable plates 202, 204, 206 flex relative to the fixed plates 201, 203, 205 in conjunction with the movement of the iron piece 25.

[0021] When the electromagnet 21 is not energized, the fixed contact member 221 and the movable contact member 222 of the normally closed contact 22 are in contact with each other, and the fixed contact members 231, 241 and the movable contact members 232, 242 of the first and second normally open contacts 23, 24 are not in contact with each other. When the electromagnet 21 is energized, the fixed contact member 221 and the movable contact member 222 of the normally closed contact 22 are separated from each other, and the fixed contact members 231, 241 and the movable contact members 232, 242 of the first and second normally open contacts 23, 24 are in contact with each other. Although not shown in the figure, the mechanical relay 2B on the output side is also configured in a similar manner.

[0022] Fig. 3 is a circuit diagram showing an example of the circuit configuration of the first semiconductor relay 3A. The first semiconductor relay 3A is configured as an IC (Integrated Circuit) in which an IC chip is sealed in a sealing material made of resin or the like, and Fig. 3 shows the circuit configuration together with the pin numbers (1 to 6) of the first semiconductor relay 3A.

[0023] The first semiconductor relay 3A has a photodiode 31, first and second photoMOSFETs 32, 33, and first and second rectifier diodes 34, 35. When a current flows from pin 1 to pin 2 and the photodiode 31 emits light, the first and second photoMOSFETs 32, 33 are activated, and a current can flow from pin 6 to pin 4 by the first photoMOSFET 32 and the second rectifier diode 35, or from pin 4 to pin 6 by the second photoMOSFET 33 and the first rectifier diode 34. Although not shown, the second semiconductor relay 3B is configured in a similar manner.

[0024] A third relay control signal 53 is input from the control unit 5 to the first pin of the first semiconductor relay 3A. When the third relay control signal 53 is asserted, a current flows from the sixth pin to the fourth pin of the first semiconductor relay 3A. The sixth pin is a current input terminal of the first semiconductor relay 3A, and the fourth pin is a current output terminal of the first semiconductor relay 3A. In addition, a fourth relay control signal 54 is input to the first pin of the second semiconductor relay 3B. When the fourth relay control signal 54 is asserted, a current flows from the sixth pin to the fourth pin of the second semiconductor relay 3B. The sixth pin is a current input terminal of the second semiconductor relay 3B, and the fourth pin is a current output terminal of the second semiconductor relay 3B.

[0025] Hereinafter, a state in which a current can flow from pin 6 to pin 4 in the first semiconductor relay 3A is referred to as the on state of the first semiconductor relay 3A, and a state in which a current is interrupted between pins 6 and 4 of the first semiconductor relay 3A is referred to as the off state of the first semiconductor relay 3A. Also, a state in which a current can flow from pin 6 to pin 4 in the second semiconductor relay 3B is referred to as the on state of the second semiconductor relay 3B, and a state in which a current is interrupted between pins 6 and 4 of the second semiconductor relay 3B is referred to as the off state of the second semiconductor relay 3B.

[0026] The first semiconductor relay 3A is connected in series between the first normally open contact 23 of the input-side mechanical relay 2A and the first normally open contact 23 of the output-side mechanical relay 2B. The second semiconductor relay 3B is connected in series between the second normally open contact 24 of the input-side mechanical relay 2A and the second normally open contact 24 of the output-side mechanical relay 2B.

[0027] A load current I1 flows through the first load 61 when the first normally open contact 23 of the input side mechanical relay 2A, the first semiconductor relay 3A, and the first normally open contact 23 of the output side mechanical relay 2B are all in the ON state. When at least one of the first normally open contact 23 of the input side mechanical relay 2A, the first semiconductor relay 3A, and the first normally open contact 23 of the output side mechanical relay 2B is in the OFF state, the load current I1 is interrupted.

[0028] A load current I2 flows through the second load 62 when the second normally open contact 24 of the input side mechanical relay 2A, the second semiconductor relay 3B, and the second normally open contact 24 of the output side mechanical relay 2B are all in the ON state. When at least one of the second normally open contact 24 of the input side mechanical relay 2A, the second semiconductor relay 3B, and the second normally open contact 24 of the output side mechanical relay 2B is in the OFF state, the load current I2 is interrupted.

[0029] The first relay control signal 51 output by the control unit 5 is input to the anode terminal of the first photocoupler 41, and the second relay control signal 52 is input to the anode terminal of the second photocoupler 42. When both the first and second relay control signals 51, 52 are asserted, the phototransistors of the first and second photocouplers 41, 42 are both turned on, and a current supplied from the control power supply 8 flows through each of the electromagnets 21 of the mechanical relays 2A, 2B. As a result, the normally closed contacts 22 of each of the mechanical relays 2A, 2B are turned off, and the first and second normally open contacts 23, 24 are turned on.

[0030] An anode terminal of the third photocoupler 43 is supplied with current from the control power supply 8 via the normally closed contact 22 of the input side mechanical relay 2A. In addition, an anode terminal of the fourth photocoupler 44 is supplied with current from the control power supply 8 via the normally closed contact 22 of the output side mechanical relay 2B. The phototransistor of the third photocoupler 43 is turned on when the normally closed contact 22 of the input side mechanical relay 2A is turned on, and the phototransistor of the fourth photocoupler 44 is turned on when the normally closed contact 22 of the output side mechanical relay 2B is turned on.

[0031] The output signal of the third photocoupler 43 is input to the control unit 5 as a first readback signal 55, and the output signal of the fourth photocoupler 44 is input to the control unit 5 as a second readback signal 56. The first readback signal 55 and the second readback signal 56 are pulled up by pull-up resistors 91 and 92, respectively. The control unit 5 can check the operating state of the mechanical relay 2A on the input side by the first readback signal 55, and can check the operating state of the mechanical relay 2B on the output side by the second readback signal 56.

[0032] The first semiconductor relay 3A has a 6th pin connected to the first normally open contact 23 of the input-side mechanical relay 2A, and a 4th pin connected to the first normally open contact 23 of the output-side mechanical relay 2B. The 6th pin of the first semiconductor relay 3A is connected to the anode terminal of the fifth photocoupler 45 via a resistor 93. The cathode terminal of the fifth photocoupler 45 is connected to the 4th pin of the first semiconductor relay 3A.

[0033] Furthermore, the second semiconductor relay 3B has a 6th pin connected to the second normally open contact 24 of the input-side mechanical relay 2A, and a 4th pin connected to the second normally open contact 24 of the output-side mechanical relay 2B. Furthermore, the 6th pin of the second semiconductor relay 3B is connected to the anode terminal of the sixth photocoupler 46 via a resistor 94. The cathode terminal of the sixth photocoupler 46 is connected to the 4th pin of the second semiconductor relay 3B.

[0034] The output signal of the fifth photocoupler 45 is input to the control unit 5 as a first diagnostic signal 57, and the output signal of the sixth photocoupler 46 is input to the control unit 5 as a second diagnostic signal 58. The first diagnostic signal 57 and the second diagnostic signal 58 are pulled up by pull-up resistors 95 and 96, respectively. The first diagnostic signal 57 is asserted when a potential difference of a predetermined value or more occurs between the 4th pin and the 6th pin of the first semiconductor relay 3A, and is negated otherwise. The second diagnostic signal 58 is asserted when a potential difference of a predetermined value or more occurs between the 4th pin and the 6th pin of the second semiconductor relay 3B, and is negated otherwise.

[0035] The first output terminal 13 is connected to the movable contact member 232 of the first normally open contact 23 of the output-side mechanical relay 2B, and a load current I1 is output from the first output terminal 13. The second output terminal 14 is connected to the movable contact member 242 of the second normally open contact 24 of the output-side mechanical relay 2B, and a load current I2 is output from the second output terminal 14.

[0036] Fig. 4 is a timing chart showing an example of the operation of the relay circuit device 10. In Fig. 4, the voltage level of each signal is indicated by H (high) and L (low). In Fig. 4, the first external output signal indicates the voltage of the first input terminal 11. Moreover, the second external output signal indicates the voltage of the second input terminal 12.

[0037] When the control unit 5 applies the load currents I1 and I2 to the first and second loads 61 and 62, respectively, it simultaneously asserts (L→H) the first and second relay control signals 51 and 52. As a result, a current flows through the electromagnets 21 of the mechanical relays 2A and 2B, the normally closed contacts 22 of the mechanical relays 2A and 2B are turned off, and the signal states of the first and second readback signals 55 and 56 change from L to H. At the same time as the changes in the first and second readback signals 55 and 56, the first and second normally open contacts 23 and 24 of the input side mechanical relay 2A are turned on, and the signal states of the first and second diagnostic signals 57 and 58 change from H to L.

[0038] The control unit 5 can detect that the mechanical relays 2A, 2B have been operated, i.e., that the normally closed contact 22 has been turned off and the first and second normally open contacts 23, 24 have been turned on, from the change in the signal state of the first and second readback signals 55, 56. The control unit 5 can also directly detect that the first normally open contact 23 of the input side mechanical relay 2A has been turned on, from the change in the signal state of the first diagnostic signal 57, and can directly detect that the second normally open contact 24 of the input side mechanical relay 2A has been turned on, from the change in the signal state of the second diagnostic signal 58.

[0039] The control unit 5 detects that the first normally open contact 23 of the input side mechanical relay 2A has been turned on by at least any one of the input signals of the first readback signal 55 and the first diagnostic signal 57, and further detects that the first normally open contact 23 of the output side mechanical relay 2B has been turned on by the second readback signal 56, and then asserts the third relay control signal 53 to turn on the first semiconductor relay 3A. That is, when passing the load current I1 through the first load 61, the control unit 5 turns on the first normally open contacts 23 of the mechanical relays 2A and 2B before the first semiconductor relay 3A.

[0040] As a result, when the first normally open contacts 23 of each of the mechanical relays 2A, 2B are turned on, no load current I1 flows through these first normally open contacts 23, thereby preventing arc discharge from occurring at the first normally open contacts 23.

[0041] Furthermore, the control unit 5 detects that the second normally open contact 24 of the input side mechanical relay 2A has been turned on by at least any one of the input signals of the first readback signal 55 and the second diagnostic signal 58, and further detects that the second normally open contact 24 of the output side mechanical relay 2B has been turned on by the second readback signal 56, and then asserts the fourth relay control signal 54 to turn on the second semiconductor relay 3B. That is, when passing the load current I2 through the second load 62, the control unit 5 turns on the second normally open contacts 24 of the mechanical relays 2A and 2B before the second semiconductor relay 3B.

[0042] As a result, when the second normally open contacts 24 of each of the mechanical relays 2A, 2B are turned on, no load current I2 flows through these second normally open contacts 24, thereby preventing arc discharge from occurring at the second normally open contacts 24.

[0043] On the other hand, when the control unit 5 cuts off the load currents I1 and I2, it simultaneously negates (H→L) the first and second relay control signals 51 and 52 and the third and fourth relay control signals 53 and 54. Since the first and second semiconductor relays 3A and 3B have a faster response speed than the mechanical relays 2A and 2B, by simultaneously negating all of the first to fourth relay control signals 51-54, the first and second semiconductor relays 3A and 3B are turned off before the first and second normally open contacts 23 and 24 of the mechanical relays 2A and 2B, respectively.

[0044] As a result, the load currents I1, I2 are interrupted by the first and second semiconductor relays 3A, 3B before the first and second normally open contacts 23, 24 of the mechanical relays 2A, 2B are turned off, so that the movable contact members 232, 242 of the first and second normally open contacts 23, 24 are separated from the fixed contact members 231, 241 in a state in which no current flows through them. This makes it possible to suppress the occurrence of arc discharge at the first and second normally open contacts 23, 24.

[0045] When the signal state of one or both of the first and second read-back signals 55, 56 does not change from L to H even if the control unit 5 asserts the first and second relay control signals 51, 52, it determines that an abnormality has occurred in the circuit and negates all of the first to fourth relay control signals 51 to 54. Also, when the signal state of one or both of the first and second read-back signals 55, 56 remains H, the control unit 5 determines that an abnormality has occurred in the circuit and negates all of the first to fourth relay control signals 51 to 54.

[0046] In addition, when the control unit 5 asserts the first to fourth relay control signals 51 to 54 to pass the load currents I1 and I2, it instantaneously negates the third relay control signal 53 to generate a test pulse, and judges whether the signal state of the first diagnostic signal 57 changes at this timing. If the signal state of the first diagnostic signal 57 does not change in this judgment, it is diagnosed that the 6th pin and the 4th pin of the first semiconductor relay 3A are in a short-circuit state. However, even in this case, the mechanical relays 2A and 2B can pass and cut off the load currents I1 and I2, so it only issues an alarm and continues operation. The control unit 5 also generates a test pulse for the second semiconductor relay 3B in the same way, and diagnoses the operation state of the second semiconductor relay 3B based on the signal state of the second diagnostic signal 58.

[0047] (Effects of the embodiment) According to the embodiment of the present invention described above, it is possible to prevent arc discharge from occurring at the first and second normally open contacts 23, 24 of the mechanical relays 2A, 2B when the load currents I1, I2 are applied and cut off, and it is possible to reduce the frequency of replacing the output module 1.

[0048] (Additional Note) Although the present invention has been described above based on the embodiment, the invention according to the claims is not limited to the embodiment. It should be noted that not all of the combinations of features described in the embodiment are necessarily essential to the means for solving the problems of the invention.

[0049] In addition, the present invention can be modified as appropriate by omitting some of the configurations or adding or replacing some of the configurations without departing from the spirit of the present invention. For example, in the above embodiment, the load currents I1 and I2 of the first and second loads 61 and 62 are energized and cut off, but one of the first and second loads 61 and 62 may be omitted. In the above embodiment, the semiconductor relays 3A and 3B are connected in series between the input-side mechanical relay 2A and the output-side mechanical relay 2B, but one of the input-side and output-side mechanical relays 2A and 2B may be omitted. [Explanation of symbols]

[0050] 10... Relay circuit device 21... Electromagnet 22: normally closed contact; 23, 24: first and second normally open contacts 2A, 2B: Mechanical relay 3A, 3B: Semiconductor relay 5...Control unit 51...First relay control signal 52: Second relay control signal 53: Third relay control signal 54...fourth relay control signal 55...first readback signal 56...second readback signal 57...first diagnostic signal 58...Second diagnostic signal I1, I2...Load current

Claims

[Claim 1] A relay circuit device comprising: first and second mechanical relays each having a mechanical contact that switches between a conductive state and a cut-off state in response to a relay control signal; a semiconductor relay connected in series with the first and second mechanical relays; and a control unit that controls the first and second mechanical relays and the semiconductor relay, wherein a load current flows when the mechanical contacts of the first and second mechanical relays and the semiconductor relay are all in a conductive state, and the load current is cut off when at least one of the mechanical contacts of the first and second mechanical relays and the semiconductor relay is in a cut-off state, the control unit, when passing a load current, brings the mechanical contacts of the first and second mechanical relays into a conductive state before the semiconductor relay does, and, when interrupting the load current, brings the semiconductor relay into a cut-off state before the mechanical contacts of the first and second mechanical relays do. Relay circuit device.

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