Switching device, current determination method, and computer program

Abstract

The load (12) is detachably connected to the device connector (Ta) of the switch device (10). The resistance value of the switch circuit (26) when the auxiliary switch (40) is turned on is greater than the on-resistance value of the main switch (20). The microcomputer (23) obtains node voltage information representing the node voltage of the connection node on the downstream side of the main switch (20) and the auxiliary switch (40) from the voltage detection unit (31) when the main switch (20) is turned off and the auxiliary switch (40) is turned on. Based on the obtained node voltage information, the microcomputer (23) determines whether the switching current flowing through the main switch (20) when the main switch (20) is switched on is lower than the current threshold.

Description

Technical Field

[0001] The present disclosure relates to a switching device, a current determination method, and a computer program.

[0002] This application claims the benefit of priority based on Japanese Application No. 2019-225848, filed on December 13, 2019, and incorporates by reference all the contents described in the aforementioned Japanese Application. Background Art

[0003] Patent Document 1 discloses a vehicle switch device having a switch disposed in a current path from a DC power supply to a load. In this switch device, power supply from the DC power supply to the load is controlled by switching the switch on or off.

[0004] Prior art literature

[0005] Patent Literature

[0006] Patent Document 1: Japanese Patent Application Laid-Open No. 2019-146385 Summary of the Invention

[0007] A switching device according to one embodiment of the present disclosure includes a connector that is detachably connected to a load, a main switch provided in a first current path from a DC power supply to the connector, a switching circuit provided in a second current path from the DC power supply to the connector and having an auxiliary switch, and a processing unit that performs processing, wherein a resistance value of the switching circuit when the auxiliary switch is on is greater than an on-resistance value of the main switch, and the processing unit performs the following processing: when the main switch is off and the auxiliary switch is on, node voltage information indicating a node voltage of a connection node on a downstream side of the main switch and the auxiliary switch is obtained, and based on the obtained node voltage information, determining whether a switching current flowing through the main switch when the main switch is switched on is lower than a current threshold.

[0008] In a current determination method according to one embodiment of the present disclosure, a computer is caused to execute the following steps: when a main switch provided in a first current path from a DC power supply to a connector detachably connected to a load is disconnected, and an auxiliary switch included in a switching circuit provided in a second current path from the DC power supply to the connector is turned on, node voltage information indicating a node voltage of a connection node on a downstream side of the main switch and the auxiliary switch is obtained; and based on the obtained node voltage information, it is determined whether a switching current flowing through the main switch when the main switch is switched on is lower than a current threshold value, and the resistance value of the switching circuit when the auxiliary switch is turned on is greater than the on-resistance value of the main switch.

[0009] A computer program according to one embodiment of the present disclosure is used to cause a computer to execute the following steps: obtaining node voltage information indicating a node voltage of a connection node on a downstream side of the main switch and the sub-switch when a main switch provided in a first current path from a DC power supply to a connector detachably connected to a load is disconnected and a sub-switch provided in a switching circuit provided in a second current path from the DC power supply to the connector is connected; and determining, based on the obtained node voltage information, whether a switching current flowing through the main switch when the main switch is switched on is lower than a current threshold value, and a resistance value of the switching circuit when the sub-switch is on is greater than an on-resistance value of the main switch.

[0010] Furthermore, the present disclosure can be implemented not only as a switching device including such a characteristic processing unit, but also as a current determination method incorporating the aforementioned characteristic processing as steps, or as a computer program for causing a computer to execute the aforementioned steps. Furthermore, the present disclosure can be implemented as a semiconductor integrated circuit that implements part or all of the switching device, or as a power supply system including the switching device. BRIEF DESCRIPTION OF THE DRAWINGS

[0011] Figure 1 This is a block diagram showing a main configuration of a power supply system in the first embodiment.

[0012] Figure 2 It is a timing chart showing an operation example of the switching device.

[0013] Figure 3 It is a block diagram showing the main structure of a microcomputer.

[0014] Figure 4 : is a flowchart showing the procedure of connection detection processing.

[0015] Figure 5 : is a flowchart showing the procedure of the current determination process.

[0016] Figure 6 : is a flowchart showing the procedure of the power supply control process.

[0017] Figure 7 This is a block diagram showing the main configuration of a microcomputer in the second embodiment.

[0018] Figure 8 is a flowchart showing the procedure of the pause process.

[0019] Figure 9 This is a flowchart showing the procedure of the startup process.

[0020] Figure 10 This is a block diagram showing a main configuration of a switchgear according to a third embodiment. DETAILED DESCRIPTION

[0021] [Problems to be Solved by the Present Disclosure]

[0022] Conventional switch devices that include a switch in the current path from a DC power source to a load include those with a connector that is detachably connected to the load. In such switch devices, when the switch is on, the DC power source supplies power to the load via the switch and connector. The smaller the resistance component of the load connected to the connector, the greater the current flowing through the switch. At the connector, if a load with a low resistance component is connected to the connector, there is a risk of overcurrent flowing through the switch.

[0023] Therefore, an object of the present invention is to provide a switching device, a current determination method, and a computer program that can prevent the flow of an overcurrent.

[0024] [Effects of the Present Disclosure]

[0025] According to the present disclosure, it is possible to prevent the flow of an overcurrent.

[0026] [Description of Embodiments of the Present Disclosure]

[0027] First, the embodiments of the present disclosure will be described by way of example. At least some of the embodiments described below may be arbitrarily combined.

[0028] (1) A switching device according to one embodiment of the present disclosure comprises: a connector detachably connected to a load; a main switch provided in a first current path from a DC power supply to the connector; a switching circuit provided in a second current path from the DC power supply to the connector and having an auxiliary switch; and a processing unit that performs processing, wherein a resistance value of the switching circuit when the auxiliary switch is turned on is greater than an on-resistance value of the main switch, the processing unit performing the following processing: when the main switch is turned off and the auxiliary switch is turned on, obtaining node voltage information indicating a node voltage of a connection node on a downstream side of the main switch and the auxiliary switch, and determining, based on the obtained node voltage information, whether a switching current flowing through the main switch when the main switch is switched on is lower than a current threshold.

[0029] (2) In a switching device according to one embodiment of the present disclosure, the processing unit performs the following processing: based on the obtained node voltage information, the resistance component value of the load is calculated; based on the calculated resistance component value, the processing unit determines whether the switching current flowing when the main switch is switched on is lower than the current threshold.

[0030] (3) A switching device according to one embodiment of the present disclosure comprises: a resistor provided in a third current path from the DC power supply to the connector and having one end connected to the connection node; and a capacitor having one end connected to the connection node, wherein the processing unit performs the following processing: obtaining the node voltage information when the main switch and the sub-switch are disconnected, and determining whether the load is connected to the connector based on the node voltage information obtained when the main switch and the sub-switch are disconnected.

[0031] (4) In the switch device according to one aspect of the present disclosure, the processing unit executes processing for acquiring the node voltage information in a state where the main switch is off and the sub-switch is on when it is determined that the load is connected to the connector.

[0032] (5) In the switch device according to one aspect of the present disclosure, a resistance value of the resistor is larger than a resistance value of the switch circuit when the sub-switch is turned on.

[0033] (6) In the switch device according to one aspect of the present disclosure, the processing unit executes the following processing: when the main switch is turned on, the processing unit obtains current information indicating the switch current, and determines whether the load is connected to the connector based on the obtained current information.

[0034] (7) In the switch device according to one aspect of the present disclosure, the switch circuit includes a second resistor connected in series with the sub-switch.

[0035] (8) In the switch device according to one aspect of the present disclosure, the processing unit suspends operation, and when the operation is restarted, the processing unit performs the following processing: when the main switch is off and the sub-switch is on, the node voltage information is acquired.

[0036] (9) In the switch device of one embodiment of the present disclosure, when a load having a resistance component value of zero ohm is connected to the connector and the main switch and the sub-switch are respectively turned off and on, the current flowing is a normal value that does not cause smoke.

[0037] (10) In one embodiment of the current determination method disclosed herein, a computer executes the following steps: obtaining node voltage information indicating a node voltage of a connection node on a downstream side of the main switch and the sub-switch when a main switch provided in a first current path from a DC power supply to a connector detachably connected to a load is disconnected and a sub-switch provided in a switch circuit provided in a second current path from the DC power supply to the connector is turned on; and determining, based on the obtained node voltage information, whether a switching current flowing through the main switch when the main switch is switched on is lower than a current threshold value, and a resistance value of the switch circuit when the sub-switch is turned on is greater than an on-resistance value of the main switch.

[0038] (11) A computer program according to one embodiment of the present disclosure is used to cause a computer to execute the following steps: obtaining node voltage information indicating a node voltage of a connection node on a downstream side of the main switch and the sub-switch when a main switch provided in a first current path from a DC power supply to a connector detachably connected to a load is disconnected and a sub-switch provided in a switch circuit provided in a second current path from the DC power supply to the connector is turned on; and determining, based on the obtained node voltage information, whether a switching current flowing through the main switch when the main switch is switched on is lower than a current threshold value, and whether a resistance value of the switch circuit when the sub-switch is turned on is greater than an on-resistance value of the main switch.

[0039] In the switching device, current determination method, and computer program according to one embodiment described above, the sub-switch is switched on before the main switch is switched on, and node voltage information is acquired. When a load is connected to the connector, when the main switch is off and the sub-switch is on, the node voltage is the voltage obtained by dividing the DC power supply voltage by the switching circuit and the load. The greater the load resistance component, the greater the node voltage. The greater the load resistance component, the smaller the switching current flowing when the main switch is switched on. Therefore, the higher the node voltage, the smaller the switching current flowing when the main switch is switched on.

[0040] Based on the node voltage information, i.e., the node voltage, a determination is made as to whether the switch current flowing when the main switch is turned on is below a current threshold. If the switch current is determined to be below the current threshold, the main switch is turned on. This prevents the flow of overcurrent exceeding the current threshold.

[0041] In the switching device of the aforementioned embodiment, the load resistance component value is calculated based on the node voltage when the main switch is off and the sub-switch is on. Based on the calculated resistance component value, it is determined whether the switching current flowing when the main switch is switched on is lower than a current threshold.

[0042] In the switch device of the aforementioned embodiment, when a load is not connected to the connector, the capacitor is charged until the voltage across the capacitor reaches the voltage of the DC power supply when the main switch and auxiliary switch are off. Therefore, the voltage across the capacitor is high. On the other hand, when a load is connected to the connector, the capacitor is discharged until the voltage across the capacitor reaches the voltage obtained by dividing the DC power supply voltage by the resistor and the load when the main switch and auxiliary switch are off. Therefore, the voltage across the capacitor is low. Therefore, whether a load is connected to the connector can be determined based on the node voltage when the main switch and auxiliary switch are off, i.e., the voltage across the capacitor.

[0043] In the switch device of the aforementioned embodiment, when it is determined that a load is connected to the connector, the node voltage information is acquired with the main switch off and the sub-switch on. Thereafter, it is determined whether the switching current flowing when the main switch is on is less than a current threshold.

[0044] In the switching device of the above-described embodiment, since the resistance value of the resistor is large, when one of the main switch and the sub-switch is turned on, the current flowing through the resistor is substantially zero A.

[0045] In the switch device of the aforementioned embodiment, when the main switch is on, a switching current flows when a load is connected to the connector. On the other hand, when the main switch is on, a switching current does not flow when a load is not connected to the connector. Therefore, when the main switch is on, it is possible to determine whether a load is connected to the connector based on the switching current.

[0046] In the switch device of the aforementioned embodiment, when the auxiliary switch is switched on, it is necessary to prevent overcurrent from flowing through the switch circuit. Therefore, the resistance of the switch circuit when the auxiliary switch is on is preferably high. Since the second resistor is connected in series with the auxiliary switch, even when the on-resistance of the auxiliary switch is low, a switch circuit with a high resistance when the auxiliary switch is on can be realized.

[0047] In the switch device of the aforementioned embodiment, when the processing unit resumes operation, it determines whether the switching current flowing when the main switch is on is below the current threshold based on the node voltage information obtained when the main switch is off and the sub-switch is on. Therefore, while the processing unit is paused, the main switch 20 is not mistakenly turned on when the load connected to the connector is changed to a load with a lower resistance component.

[0048] In the switch device of the aforementioned embodiment, the resistance of the switch circuit is high when the auxiliary switch is on. Therefore, when a load with a zero-ohm resistance component is connected to the connector and the main switch and auxiliary switch are turned off and on, respectively, the current flowing is small, and smoke is not generated.

[0049] [Details of the embodiments of the present disclosure]

[0050] Specific examples of the power supply system according to the embodiment of the present disclosure will be described below with reference to the accompanying drawings. The present invention is not limited to these examples, but is defined by the claims and is intended to include all modifications within the meaning and scope of the claims.

[0051] (Implementation 1)

[0052] <Power supply system configuration>

[0053] Figure 1 This is a block diagram illustrating the main configuration of a power supply system 1 in Embodiment 1. The power supply system 1 is appropriately mounted on a vehicle and includes a switching device 10, a DC power supply 11, and a load 12. The switching device 10 includes a main switch 20 and a device connector Ta. The load 12 includes a load connector Tb. The switching device 10 is connected to the positive terminal of the DC power supply 11. The negative terminal of the DC power supply 11 is grounded. The device connector Ta is detachably connected to the load connector Tb. The load connector Tb is connected to the device connector Ta, thereby connecting the load 12 to the device connector Ta.

[0054] DC power supply 11 is, for example, a battery. Load 12 is, for example, an electrical device carried in a vehicle and has a resistive component. Load 12 operates when the power supplied to load 12 is above a certain level. The certain level is a value exceeding zero W. When the power supplied to load 12 falls below the certain level, load 12 ceases operation.

[0055] When the load 12 is connected to the device connector Ta and the main switch 20 is switched from off to on, the DC power supply 11 supplies power to the load 12 via the main switch 20 and the device connector Ta. At this time, the power supplied to the load 12 is above a certain level, and the load 12 operates. Similarly, when the main switch 20 is switched from on to off, the power supplied to the load 12 by the DC power supply 11 drops below the certain level, and the load 12 stops operating.

[0056] The switch device 10 receives an operation signal instructing the load 12 to operate and a stop signal instructing the load 12 to stop operating. When the operation signal is input, the switch device 10 switches the main switch 20 on to operate the load 12. When the stop signal is input, the switch device 10 switches the main switch 20 off to stop the load 12.

[0057] When a load 12 that could cause an overcurrent to flow through the switching device 10 is connected to the device connector Ta, the switching device 10 outputs a notification signal to a device (not shown) indicating that power cannot be supplied to the load 12. When an operation signal is input to the switching device 10 while the load 12 is not connected to the device connector Ta, the switching device 10 outputs a notification signal to a device (not shown) indicating that the load 12 is not connected.

[0058] <Structure of Switchgear 10>

[0059] In addition to the main switch 20 and the device connector Ta, the switching device 10 includes a current output circuit 21, a power supply detection unit 22, a microcomputer (hereinafter referred to as a microcomputer) 23, a drive circuit 24, a current resistor 25, a switching circuit 26, a selector switch 27, a switch resistor 28, a circuit resistor 29, a capacitor 30, and a voltage detection unit 31. The switching circuit 26 includes a sub-switch 40 and switch resistors 41 and 42. The main switch 20 is an N-channel FET (Field Effect Transistor). The selector switch 27 is an NPN bipolar transistor. The sub-switch 40 is a P-channel FET.

[0060] The drain of the main switch 20 is connected to the positive terminal of the DC power supply 11. The source of the main switch 20 is connected to the current output circuit 21. The current output circuit 21 is further connected to the device connector Ta. The device connector Ta is grounded. When the load 12 is connected to the device connector Ta, the load 12 is connected to the current output circuit 21 and is also grounded.

[0061] The drain of main switch 20 is further connected to power supply detection unit 22. Power supply detection unit 22 is connected to microcomputer 23. The gate of main switch 20 is connected to drive circuit 24. Drive circuit 24 is further connected to microcomputer 23. Current output circuit 21 is further connected to one end of current resistor 25. The other end of current resistor 25 is grounded. The connection node between current output circuit 21 and current resistor 25 is connected to microcomputer 23 and drive circuit 24.

[0062] The drain of the main switch 20 is further connected to the source of the sub-switch 40 in the switch circuit 26. The drain of the sub-switch 40 is connected to the connection node between the current output circuit 21 and the device connector Ta. Within the switch circuit 26, a switching resistor 41 is connected between the source and gate of the sub-switch 40. The gate of the sub-switch 40 is further connected to one end of a switching resistor 42. The other end of the switching resistor 42 is connected to the collector of the switch 27. The emitter of the switch 27 is grounded. The base of the switch 27 is connected to one end of a switching resistor 28. The other end of the switching resistor 28 is connected to the microcomputer 23.

[0063] The drain of main switch 20 is further connected to one end of circuit resistor 29. The other end of circuit resistor 29 is connected to a connection node between current output circuit 21 and device connector Ta. This connection node is further connected to one end of capacitor 30 and voltage detector 31. The other end of capacitor 30 is grounded. Voltage detector 31 is connected to microcomputer 23.

[0064] The power supply detection unit 22 detects the voltage of the DC power supply 11 with respect to the ground potential. Hereinafter, the voltage of the DC power supply 11 with respect to the ground potential will be described as the power supply voltage. The power supply detection unit 22 outputs power supply voltage information representing the detected power supply voltage to the microcomputer 23. The power supply voltage information is an analog value, for example, a voltage proportional to the detected power supply voltage. In addition to the load 12, the DC power supply 11 also supplies power to one or more second loads not shown. The positive pole of the DC power supply 11 is connected not only to the switching device 10, but also to one or more second loads. The power supply voltage of the DC power supply 11 varies depending on the current flowing out of the DC power supply 11. The greater the current flowing out of the DC power supply 11, the lower the power supply voltage.

[0065] In main switch 20, when the gate voltage relative to the source potential is above a certain voltage, the resistance between the drain and source is sufficiently low. In this case, main switch 20 is on, and current can flow through the drain and source. In main switch 20, when the gate voltage relative to the source potential is below a certain voltage, the resistance between the drain and source is sufficiently high. In this case, main switch 20 is off, and current does not flow through the drain and source.

[0066] An operating signal and a stop signal are input to the microcomputer 23. When the operating signal is input to the microcomputer 23, an on-state instruction is output to the drive circuit 24, instructing the main switch 20 to switch on. When the on-state instruction is input to the drive circuit 24, the drive circuit 24 increases the gate voltage of the main switch 20 relative to the ground potential. As a result, the gate voltage of the main switch 20 relative to the source reaches a certain voltage or higher, and the main switch 20 is switched on.

[0067] When a stop signal is input to the microcomputer 23, the microcomputer 23 outputs an OFF instruction to the drive circuit 24, instructing the main switch 20 to switch OFF. When the OFF instruction is input to the drive circuit 24, the gate voltage relative to the ground potential of the main switch 20 is reduced. As a result, the gate voltage relative to the source potential of the main switch 20 falls below a predetermined voltage, and the main switch 20 is switched OFF.

[0068] As described above, the drive circuit 24 switches the main switch 20 on or off.

[0069] When the load 12 is connected to the device connector Ta and the main switch 20 is turned on, current flows from the positive electrode of the DC power supply 11 through the main switch 20, the current output circuit 21, the device connector Ta, and the load 12 in this order. This causes the load 12 to operate. Hereinafter, the current that flows from the DC power supply 11 through the main switch 20 and the current output circuit 21 in this order and is output from one end of the current output circuit 21 on the device connector Ta side is referred to as the switching current.

[0070] The current path of the current flowing from the positive electrode of the DC power supply 11 through the main switch 20, the current output circuit 21, and the device connector Ta in this order corresponds to the first current path. The main switch 20 is provided in the first current path.

[0071] When the switching current flows, the current output circuit 21 outputs a current that is a predetermined fraction of the switching current to the current resistor 25. The current output circuit 21 includes, for example, a current mirror circuit. The predetermined fraction is, for example, 1000. The voltage across the ends of the current resistor 25 is input as current information to the microcomputer 23 and the drive circuit 24.

[0072] The switching current, the resistance value of current resistor 25, and the predetermined number are expressed as Is, rc, and N, respectively. The voltage across current resistor 25 is calculated as Is·rc / N. The "·" represents the product. The resistance value rc and the predetermined number N are constant. Therefore, the voltage across current resistor 25 is proportional to the switching current Is, and the current information represents the switching current Is.

[0073] When the DC power supply 11 supplies power to the load 12 via the main switch 20 , if the main switch 20 is switched off, the power supplied to the load 12 by the DC power supply 11 falls below a certain level, and the load 12 stops operating.

[0074] When the load 12 is not connected to the device connector Ta, no switching current flows, regardless of whether the main switch 20 is on. Furthermore, when the main switch 20 is off, no switching current flows. When no switching current flows, the current output circuit 21 does not output current to the current resistor 25 and inputs zero V as current information to the microcomputer 23 and the drive circuit 24.

[0075] When the switch current indicated by the input current information is equal to or greater than the cutoff threshold, the drive circuit 24 switches the main switch 20 off, regardless of the signal input from the microcomputer 23. After switching the main switch 20 off, the drive circuit 24 maintains the main switch 20 off, regardless of the input current information. The cutoff threshold is a constant value and is set in advance.

[0076] Regarding switch 27, when the base voltage relative to the emitter potential is above a certain voltage, the resistance between the collector and emitter is sufficiently low. In this case, switch 27 is closed, and current can flow through the collector and emitter. Regarding switch 27, when the base voltage relative to the emitter potential is below a certain voltage, the resistance between the collector and emitter is sufficiently high. In this case, switch 27 is open, and current does not flow through the collector and emitter.

[0077] The microcomputer 23 increases the voltage at the base of the selector switch 27, which is referenced to the ground potential. This causes the base voltage of the selector switch 27, which is referenced to the emitter potential, to exceed a certain voltage, and the selector switch 27 is switched on. The microcomputer 23 decreases the voltage at the base of the selector switch 27, which is referenced to the ground potential. This causes the base voltage of the selector switch 27, which is referenced to the emitter potential, to fall below a certain voltage, and the selector switch 27 is switched off. As described above, the microcomputer 23 switches the selector switch 27 on and off.

[0078] Regarding the sub-switch 40 of the switching circuit 26, when the gate voltage relative to the source potential is below a certain voltage, the resistance between the source and drain is sufficiently low. In this case, the sub-switch 40 is on, allowing current to flow through the source and drain. Regarding the sub-switch 40 of the switching circuit 26, when the gate voltage relative to the source potential is above a certain voltage, the resistance between the source and drain is sufficiently high. In this case, the sub-switch 40 is off, preventing current from flowing through the source and drain. The certain voltage associated with the sub-switch 40 is below zero V.

[0079] When the selector switch 27 is off, current does not flow sequentially through the switch resistors 41 and 42. At this time, the gate voltage of the sub-switch 40, which is referenced to the source potential, is zero V, exceeding a certain voltage. Consequently, the sub-switch 40 is off. When the microcomputer 23 switches the selector switch 27 on, current flows sequentially through the switch resistors 41 and 42. At this time, the gate voltage of the sub-switch 40, which is referenced to the source potential, falls below a certain voltage, and the sub-switch 40 is switched on.

[0080] When the microcomputer 23 switches the selector switch 27 off, the flow of current through the switch resistors 41 and 42 stops. Consequently, the gate voltage of the sub-switch 40, which is based on the source potential, rises to zero V and exceeds a certain voltage. Consequently, the sub-switch 40 switches off.

[0081] As described above, the microcomputer 23 switches the sub-switch 40 on by switching the changeover switch 27 on, and switches the sub-switch 40 off by switching the changeover switch 27 off.

[0082] The on-resistance of the sub-switch 40, i.e., the resistance of the switch circuit 26 when the sub-switch 40 is on, is sufficiently greater than the on-resistance of the main switch 20. The resistance of the circuit resistor 29 is sufficiently greater than the on-resistance of the sub-switch 40, i.e., the resistance of the switch circuit 26 when the sub-switch 40 is on. The on-resistance of the main switch 20 is, for example, several ohms. The on-resistance of the sub-switch 40 is, for example, in the range of several hundred ohms to several thousand ohms. The on-resistance of an N-channel FET is typically less than several ohms. Therefore, a P-channel FET with a large on-resistance is used as the sub-switch 40. The circuit resistance is, for example, several megohms. The on-resistance of a switch is the resistance of the switch when it is on.

[0083] The voltage detection unit 31 detects the voltage at the connection node between the current output circuit 21 and the device connector Ta. Hereinafter, the voltage at the connection node between the current output circuit 21 and the device connector Ta will be referred to as the node voltage. The node voltage is a voltage relative to the ground potential. Upon detecting the node voltage, the voltage detection unit 31 outputs node voltage information indicating the detected node voltage to the microcomputer 23. The node voltage information is an analog value, for example, representing a voltage proportional to the node voltage.

[0084] The microcomputer 23 determines whether the load 12 is connected to the device connector Ta based on the node voltage information obtained from the voltage detection unit 31 when the main switch 20 and the sub-switch 40 are off. If the microcomputer 23 determines that the load 12 is connected to the device connector Ta, it calculates the resistance component value of the load 12 based on the power supply voltage information and node voltage information obtained from the power supply detection unit 22 and the voltage detection unit 31 when the main switch 20 is off and the sub-switch 40 is on.

[0085] Based on the calculated resistance component value, the microcomputer 23 determines whether the switch current flowing when the main switch 20 is switched on is less than a current threshold. The current threshold is a constant, pre-set value. The current threshold is lower than the aforementioned cutoff threshold. If the microcomputer 23 determines that the switch current is less than the current threshold, it switches the main switch 20 on or off according to the input signal. If the microcomputer 23 determines that the switch current flowing when the main switch 20 is switched on is greater than the current threshold, or if an operation signal is input while the load 12 is not connected to the device connector Ta, the microcomputer 23 outputs a notification signal.

[0086] <Operation Example of Switch Device 10>

[0087] Figure 2 : is a timing chart showing an example of the operation of the switch device 10. Figure 2 In FIG, the transition of the state of the main switch 20 and the sub-switch 40 and the transition of the node voltage are shown. The horizontal axis shows time for these transitions. Figure 2 In FIG, Vb represents the power supply voltage. V1 represents the first divided voltage obtained by dividing the power supply voltage Vb by the switch circuit 26 and the load 12 when the auxiliary switch 40 is turned on. V2 represents the second divided voltage obtained by dividing the power supply voltage Vb by the circuit resistor 29 and the load 12. Figure 2 , an example of the operation of the switching device 10 when the power supply voltage Vb is stable is shown.

[0088] As described above, the resistance of circuit resistor 29 is sufficiently greater than the on-resistance of sub-switch 40. Therefore, second divided voltage V2 is sufficiently lower than first divided voltage V1. Vth is a voltage threshold used to determine whether load connector Tb is connected to device connector Ta. Voltage threshold Vth is lower than power supply voltage Vb and higher than second divided voltage V2.

[0089] The resistance component value of load 12 is sufficiently smaller than the resistance value of circuit resistor 29. Assuming load 12, a load with a resistance component value of, for example, several kilohms or less is assumed. As described above, the resistance value of circuit resistor 29 is, for example, several megohms. Therefore, second divided voltage V2 is a value close to zero V.

[0090] When the main switch 20 and the sub-switch 40 are off, and the load 12 is not connected to the device connector Ta, current flows from the positive electrode of the DC power supply 11 through the circuit resistor 29 and the capacitor 30 in that order. This causes the node voltage, i.e., the voltage across the capacitor 30, to be charged until it reaches the power supply voltage Vb. Therefore, when the load 12 is not connected to the device connector Ta, the node voltage detected by the voltage detection unit 31 is substantially consistent with the power supply voltage Vb and is above the voltage threshold Vth. When the main switch 20 and the sub-switch 40 are off, and the node voltage is above the voltage threshold Vth, the microcomputer 23 determines that the device connector Ta is not connected to the load connector Tb.

[0091] The electrostatic capacitance of the capacitor 30 is small. Therefore, when the capacitor 30 is charged, the node voltage rises quickly. When the capacitor 30 is discharged, the node voltage also drops quickly.

[0092] When the main switch 20 and the sub-switch 40 are disconnected and the load 12 is connected to the device connector Ta, the capacitor 30 discharges through the load 12 until the node voltage reaches the second divided voltage V2. When the load 12 is connected to the device connector Ta, the node voltage is lower than the voltage threshold Vth. When the main switch 20 and the sub-switch 40 are disconnected and the node voltage is lower than the voltage threshold Vth, the microcomputer 23 determines that the load 12 is connected to the device connector Ta.

[0093] When the main switch 20 and the sub-switch 40 are off and the load 12 is connected to the device connector Ta, current flows from the positive electrode of the DC power supply 11 through the circuit resistor 29, the device connector Ta, and the load 12 in this order. The current path of the current flowing through the circuit resistor 29 and the device connector Ta in this order corresponds to the third current path. The circuit resistor 29 is provided in the third current path.

[0094] As described above, the resistance value of the circuit resistor 29 is sufficiently large. Therefore, when the main switch 20 and the sub-switch 40 are off, the current flowing through the load 12 is small. As a result, the power supplied to the load 12 falls below a certain level, and the load 12 does not operate.

[0095] If the microcomputer 23 determines that the load 12 is connected to the device connector Ta, it switches the sub-switch 40 on. At this point, current flows from the positive electrode of the DC power supply 11 through the sub-switch 40, the device connector Ta, and the load 12 in this order. The current path of current flowing from the positive electrode of the DC power supply 11 through the sub-switch 40 and the device connector Ta in this order corresponds to the second current path. The sub-switch 40, or the switch circuit 26, is placed in the second current path. The connection node between the current output circuit 21 and the device connector Ta is the connection node on the downstream side of the main switch 20 and the sub-switch 40.

[0096] As described above, the resistance of circuit resistor 29 is sufficiently greater than the on-resistance of sub-switch 40. Therefore, when sub-switch 40 is on, the current flowing through circuit resistor 29 is substantially zero A. Furthermore, since the resistance of switching circuit 26, i.e., the on-resistance of sub-switch 40, is high when sub-switch 40 is on, the current flowing through load 12 is low. Consequently, the power supplied to load 12 falls below a certain level, and load 12 does not operate.

[0097] Furthermore, because the resistance of the switch circuit 26 is high when the sub-switch 40 is on, the current flowing when the load 12, with a zero-ohm resistance component, is connected to the device connector Ta and the main switch 20 and sub-switch 40 are respectively turned off and on is small. This current is a normal value that does not cause smoke in the connecting wires connecting the sub-switch 40, the DC power supply 11, and the sub-switch 40, or the connecting wires connecting the sub-switch 40 to the device connector Ta. The current flowing when the load 12, with a zero-ohm resistance component, is connected to the device connector Ta and the main switch 20 and sub-switch 40 are respectively turned off and on does not cause the temperature of the sub-switch 40 to rise to an abnormal level. Therefore, no malfunction occurs in the sub-switch 40. Here, zero ohm is not a strict value, but a substantial value.

[0098] When the sub-switch 40 is switched on while the main switch 20 is off and the load 12 is connected to the device connector Ta, the DC power supply 11 charges the capacitor 30 until the node voltage reaches the first divided voltage V1. The microcomputer 23 calculates the resistance component value of the load 12 based on the power supply voltage Vb detected by the power supply detection unit 22 and the first divided voltage V1, the node voltage detected by the voltage detection unit 31 when the main switch 20 is off and the sub-switch 40 is on.

[0099] The resistance value of the switch circuit 26 when the sub-switch 40 is turned on is represented by rs. The resistance component value of the load 12 is represented by rd. The first divided voltage V1 is represented by the following equation using the resistance value rs, the resistance component value rd, and the power supply voltage Vb.

[0100] V1=Vb·(rd / (rs+rd))

[0101] The resistance value rs of the switch circuit 26 is a known value measured in advance. The power supply voltage Vb and the first divided voltage V1 are detected by the power supply detection unit 22 and the voltage detection unit 31, respectively. Therefore, the resistance value rs of the switch circuit 26 can be calculated.

[0102] After acquiring the node voltage information indicating the first divided voltage V1, the microcomputer 23 switches off the sub-switch 40. As a result, the capacitor 30 is discharged until the node voltage reaches the second divided voltage V2.

[0103] Based on the calculated resistance value rs of the switch circuit 26, the microcomputer 23 determines whether the switch current (Vb / rs), which flows when the main switch 20 is switched on, is below a current threshold. If the microcomputer 23 determines that the switch current is above the current threshold, it outputs a notification signal indicating that power cannot be supplied to the load 12. If the microcomputer 23 determines that the switch current is below the current threshold, it executes a power supply control process to control the power supply to the load 12. During the power supply control process, the microcomputer 23 switches the main switch 20 on or off based on an input signal. During the power supply control process, the sub-switch 40 remains off.

[0104] As described above, when the main switch 20 is on, power is supplied to the load 12, causing the load 12 to operate. The on-resistance of the main switch 20 is sufficiently smaller than the resistance of the circuit resistor 29. Therefore, when the main switch 20 is on, the current flowing through the circuit resistor 29 is substantially zero A. When the main switch 20 is on, the capacitor 30 is charged until the node voltage reaches the power supply voltage Vb. When the main switch 20 is off, the capacitor 30 is discharged until the node voltage reaches the second divided voltage V2.

[0105] While executing the power supply control process, the microcomputer 23 periodically determines whether the load 12 is connected to the device connector Ta. When the main switch 20 is off and the load 12 is not connected, the node voltage is the power supply voltage Vb. Therefore, the microcomputer 23 determines whether the node voltage is greater than or equal to the voltage threshold Vth as described above.

[0106] When the sub-switch 40 is off and the main switch 20 is on, a switching current flows when the load 12 is connected to the device connector Ta. Similarly, when the load 12 is not connected to the device connector Ta, no switching current flows, and the switching current indicated by the current information input to the microcomputer 23 is zero A. When the main switch 20 is on, the microcomputer 23 determines whether the load 12 is connected to the device connector Ta based on the input current information.

[0107] <Structure of Microcomputer 23>

[0108] Figure 3This is a block diagram showing the main configuration of the microcomputer 23. The microcomputer 23 includes A / D converters 50, 51, and 52, output units 53 and 54, a switching unit 55, input units 56, 57, 58, and 59, a storage unit 60, and a control unit 61. The A / D converters 50, 51, and 52, the output units 53 and 54, the switching unit 55, the input unit 56, the storage unit 60, and the control unit 61 are connected to an internal bus 62. The A / D converters 50, 51, and 52 are further connected to input units 57, 58, and 59, respectively. The input units 57, 58, and 59 are respectively connected to the power supply detector 22, one end of the current resistor 25, and the voltage detector 31. The output unit 53 is further connected to the drive circuit 24. The switching unit 55 is connected to the base of the changeover switch 27 via the switch resistor 28.

[0109] Analog power supply voltage information is input from the power supply detection unit 22 to the input unit 57. Upon receiving the analog power supply voltage information, the input unit 57 outputs the analog power supply voltage information to the A / D converter 50. The A / D converter 50 converts the analog power supply voltage information input from the input unit 57 into digital power supply voltage information. The control unit 61 obtains the digital power supply voltage information from the A / D converter 50. The power supply voltage indicated by the power supply voltage information obtained by the control unit 61 substantially matches the power supply voltage detected by the power supply detection unit 22 at the time of the acquisition.

[0110] The output unit 53 outputs an on instruction and an off instruction to the drive circuit 24 according to the instruction of the control unit 61. As described above, the drive circuit 24 switches the main switch 20 on when the on instruction is input, and switches the main switch 20 off when the off instruction is input.

[0111] Analog current information is input from one end of the current resistor 25 to the input unit 58. Upon receiving the analog current information, the input unit 58 outputs the analog current information to the A / D converter 51. The A / D converter 51 converts the analog current information input from the input unit 58 into digital current information. The control unit 61 obtains the digital current information from the A / D converter 51. The switching current represented by the current information obtained by the control unit 61 substantially matches the switching current detected at the time of the acquisition.

[0112] The control unit 61 instructs the switching unit 55 to switch the sub-switch 40 on or off. When the control unit 61 instructs the sub-switch 40 to switch on, the switching unit 55 increases the voltage at the base of the switch 27 relative to the ground potential, switching the switch 27 on. As described above, when the switch 27 is switched on, the sub-switch 40 is switched on. When the control unit 61 instructs the sub-switch 40 to switch off, the switching unit 55 decreases the voltage at the base of the switch 27 relative to the ground potential, switching the switch 27 off. As described above, when the switch 27 is switched off, the sub-switch 40 is switched off.

[0113] Analog node voltage information is input from voltage detection unit 31 to input unit 59. Upon receiving the analog node voltage information, input unit 59 outputs the analog node voltage information to A / D conversion unit 52. A / D conversion unit 52 converts the analog node voltage information input from input unit 59 into digital node voltage information. Control unit 61 obtains the digital node voltage information from A / D conversion unit 52. The node voltage represented by the node voltage information obtained by control unit 61 substantially matches the node voltage detected by power supply detection unit 22 at the time of the acquisition.

[0114] The operation signal and the stop signal are input to the input unit 56. When a signal is input, the input unit 56 notifies the control unit 61 of the input signal.

[0115] The output unit 54 outputs a notification signal according to an instruction from the control unit 61 .

[0116] The storage unit 60 is a nonvolatile memory. A computer program P is stored in the storage unit 60. The control unit 61 includes a processing element, such as a CPU (Central Processing Unit), that performs processing and functions as a processing unit. The processing element (computer) of the control unit 61 executes the computer program P, thereby concurrently performing connection detection processing, current determination processing, and the aforementioned power supply control processing. The connection detection processing detects the connection of the load 12 to the device connector Ta. The current determination processing determines whether the switching current flowing when the main switch 20 is switched on is lower than a current threshold.

[0117] In addition, the computer program P can also be stored in the storage medium E in a manner that can be read by the processing element of the control unit 61. In this case, the computer program P read from the storage medium E by a reading device not shown in the figure is written to the storage unit 60. The storage medium E is an optical disc, a floppy disk, a magnetic disk, a magneto-optical disc or a semiconductor memory, etc. The optical disc is a CD (Compact Disc)-ROM (Read Only Memory), a DVD (Digital Versatile Disc)-ROM or a BD (Blu-ray (registered trademark) Disc), etc. The magnetic disk is, for example, a hard disk. In addition, the computer program P can also be downloaded from an external device not shown in the figure that is connected to a communication network not shown in the figure, and the downloaded computer program P can be written to the storage unit 60.

[0118] The number of processing elements included in the control unit 61 is not limited to one, and may be two or more. In this case, the plurality of processing elements may cooperatively execute the connection detection process, the current determination process, and the power supply control process according to the computer program P.

[0119] In addition to the computer program P, the storage unit 60 also stores the values of a connection flag and a permission flag. The values of the connection flag and the permission flag are each 0 or 1. A connection flag value of 0 indicates that the load 12 is not connected to the device connector Ta. A connection flag value of 1 indicates that the load 12 is connected to the device connector Ta. A permission flag value of 0 prohibits switching the main switch 20 to the on state. A permission flag value of 1 permits switching the main switch 20 to the on state.

[0120] <Connection detection processing>

[0121] Figure 4 This is a flowchart illustrating the sequence of the connection detection process. The control unit 61 periodically executes the connection detection process when the auxiliary switch 40 is off. During the connection detection process, the control unit 61 determines whether the main switch 20 is off (step S1). In step S1, if the most recent instruction output by the output unit 53 is an off instruction, the control unit 61 determines that the main switch 20 is off. If the most recent instruction output by the output unit 53 is an on instruction, the control unit 61 determines that the main switch 20 is on.

[0122] If the control unit 61 determines that the main switch 20 is open (S1: Yes), it obtains node voltage information from the A / D converter 52 (step S2). Next, based on the node voltage indicated by the node voltage information obtained in step S2, the control unit 61 determines whether the load 12 is connected to the device connector Ta (step S3). As described in the example operation of the switch device 10, in step S3, the control unit 61 determines that the load 12 is not connected if the node voltage is above the voltage threshold. If the node voltage is below the voltage threshold, the control unit 61 determines that the load 12 is connected.

[0123] If the control unit 61 determines that the load 12 is connected (S3: Yes), it sets the value of the connection flag to 1 (step S4), and ends the connection detection process. If the value of the connection flag is 1 at the time the control unit 61 determines that the load 12 is connected, it skips step S4 and ends the connection detection process.

[0124] If the control unit 61 determines that the load 12 is not connected (S3: No), it sets the value of the connection flag to zero (step S5), and ends the connection detection process. If the value of the connection flag is zero at the time the control unit 61 determines that the load 12 is not connected, the execution of step S5 is omitted and the connection detection process ends.

[0125] If the control unit 61 determines that the main switch 20 is not open, that is, the main switch 20 is on (S1: No), it obtains current information from the A / D converter 51 (step S6). Next, based on the switch current indicated by the current information obtained in step S6, the control unit 61 determines whether the load 12 is connected to the device connector Ta (step S7). As described in the operating example of the switch device 10, in step S7, if the switch current exceeds zero A, the control unit 61 determines that the load 12 is connected. If the switch current is zero A, the control unit 61 determines that the load 12 is not connected.

[0126] Unless the value of the connection flag is 1, the output unit 53 does not output the on instruction to the drive circuit 24. Therefore, the drive circuit 24 switches the main switch 20 on when the value of the connection flag is 1. When the main switch 20 is on, the value of the connection flag is 1. At the time of executing step S7, the value of the connection flag is 1.

[0127] If the control unit 61 determines that the load 12 is not connected (S7: No), it instructs the output unit 53 to switch the main switch 20 off (step S8). The output unit 53 switches the main switch 20 off by outputting the off instruction to the drive circuit 24. After executing step S8, the control unit 61 sets the value of the connection flag to zero (step S9). If the control unit 61 determines that the load 12 is connected (S7: Yes) or after executing step S9, the connection detection process ends.

[0128] As described above, during the connection detection process, the control unit 61 detects the connection of the load 12 based on the node voltage when the main switch 20 is off, and detects the connection of the load 12 based on the switch current when the main switch 20 is on. Even when the main switch 20 is on, if the load 12 is not connected, the drive circuit 24 switches the main switch 20 off, and the control unit 61 sets the value of the connection flag to zero. If the connection between the load 12 and the device connector Ta is lost while the load 12 is operating, the switch device 10 remains in a state where the load 12 is not connected, even when the main switch 20 is on.

[0129] <Current determination processing>

[0130] Figure 5 This is a flowchart illustrating the procedure for the current determination process. The control unit 61 periodically executes the current determination process when the main switch 20 is off. During the current determination process, the control unit 61 first determines whether the value of the connection flag has changed from zero to one, that is, whether the load 12 is connected to the device connector Ta (step S11). In step S11, if the value of the connection flag, which was zero at the start of the previous current determination process, has changed to one, the control unit 61 determines that the value of the connection flag has changed from zero to one.

[0131] If the control unit 61 determines that the value of the connection flag has not changed from zero to 1 (S11: No), it terminates the current determination process. When the next cycle arrives, the control unit 61 executes the current determination process again. Therefore, if the control unit 61 determines that the value of the connection flag has not changed from zero to 1, it waits until the value of the connection flag changes from zero to 1.

[0132] If the control unit 61 determines that the value of the connection flag has changed from zero to 1, that is, that the load 12 is connected to the device connector Ta (S11: Yes), it obtains power supply voltage information from the A / D converter 50 (step S12). Next, the control unit 61 instructs the switching unit 55 to switch the sub-switch 40 on (step S13). As described above, the switching unit 55 switches the sub-switch 40 on by switching the selector switch 27 on. When the sub-switch 40 is on, the capacitor 30 is charged until the node voltage reaches the first divided voltage.

[0133] After executing step S13, the control unit 61 obtains node voltage information from the A / D converter 52 (step S14). The period from the end of step S13 to the start of step S14 is longer than the period from the time the sub-switch 40 is turned on to the completion of charging of the capacitor 30. Therefore, the node voltage indicated by the node voltage information obtained by the control unit 61 in step S14 is the first divided voltage.

[0134] After executing step S14, the control unit 61 instructs the switching unit 55 to switch the auxiliary switch 40 off (step S15). As described above, the switching unit 55 switches the auxiliary switch 40 off by switching the selector switch 27 off. When the auxiliary switch 40 is switched off, the capacitor 30 discharges, and the node voltage drops to the second divided voltage.

[0135] After executing step S15, the control unit 61 calculates the resistance component value of the load 12 based on the node voltage indicated by the node voltage information obtained in step S14, i.e., the first divided voltage (step S16). Next, based on the resistance component value calculated in step S16, the control unit 61 determines whether the switching current flowing when the main switch 20 is turned on is less than a current threshold (step S17).

[0136] As a first example of step S17, the control unit 61 calculates the switching current based on the power supply voltage indicated by the power supply voltage information acquired in step S12 and the resistance component value calculated in step S16. The control unit 61 determines whether the calculated switching current is lower than the current threshold.

[0137] The larger the resistance component value of load 12, the smaller the switching current that flows when main switch 20 is turned on. Therefore, as a second example of step S17, control unit 61 determines that the switching current is below the current threshold when the resistance component value calculated in step S16 is above the resistance threshold. Control unit 61 determines that the switching current is above the current threshold when the resistance component value calculated in step S16 is below the resistance threshold. The resistance threshold is a fixed value that is set in advance.

[0138] If the control unit 61 determines that the switch current is lower than the current threshold (S17: Yes), it sets the value of the permission flag to 1 (step S18), terminating the current determination process. If the control unit 61 determines that the switch current is higher than the current threshold (S17: No), it instructs the output unit 54 to output a notification signal indicating that power cannot be supplied to the load 12 (step S19). Next, the control unit 61 sets the value of the permission flag to zero (step S20), terminating the current determination process.

[0139] As described above, in the current determination process, when load 12 is connected to device connector Ta, the resistance component value of load 12 is calculated. Based on the calculated resistance component value, it is determined whether the switch current is less than the current threshold. If the control unit 61 determines that the switch current is less than the current threshold, it sets the value of the permission flag to 1, thereby permitting the main switch 20 to be switched on.

[0140] Power supply control processing

[0141] Figure 6 It is a flowchart showing the order of the power supply control process. The control unit 61 periodically performs the power supply control process when the auxiliary switch 40 is disconnected. In the power supply control process, first, the control unit 61 determines whether the working signal is input to the input unit 56 (step S31). When the control unit 61 determines that the working signal is not input (S31: "No"), it determines whether the stop signal is input to the input unit 56 (step S32). When the control unit 61 determines that the stop signal is not input (S32: "No"), it ends the power supply control process. When the next cycle arrives, the control unit 61 performs the power supply control process again. Therefore, when the working signal or the stop signal is not input to the input unit 56, the control unit 61 waits until the working signal or the stop signal is input to the input unit 56.

[0142] If the control unit 61 determines that the operation signal has been input (S31: Yes), it determines whether the value of the connection flag is 1 (step S33). If the control unit 61 determines that the value of the connection flag is 1 (S33: Yes), it determines whether the value of the permission flag is 1 (step S34). If the control unit 61 determines that the value of the permission flag is 1 (S34: Yes), it instructs the output unit 53 to switch the main switch 20 on (step S35). The output unit 53 switches the main switch 20 on by outputting the on instruction to the drive circuit 24. As a result, the load 12 operates.

[0143] If the control unit 61 determines that the value of the connection flag is not 1 (S33: No) or if the value of the permission flag is not 1 (S34: No), it instructs the output unit 54 to output a notification signal (step S36). If the value of the connection flag is not 1, the output unit 54 outputs a notification signal indicating that the load 12 is not connected. If the value of the permission flag is not 1, the output unit 54 outputs a notification signal indicating that power cannot be supplied to the load 12. If the control unit 61 executes either step S35 or step S36, it terminates the power supply control process.

[0144] If the control unit 61 determines that a stop signal has been input (S32: Yes), it instructs the output unit 53 to switch the main switch 20 off (step S37). As described above, the output unit 53 switches the main switch 20 off by outputting the off instruction to the drive circuit 24. This stops the operation of the load 12. After executing step S37, the control unit 61 terminates the power supply control process.

[0145] As described above, during the power supply control process, when an operation signal is input and the value of the permission flag is 1, the control unit 61 instructs the output unit 53 to switch the main switch 20 on. If the value of the permission flag is zero, the control unit 61 does not instruct the output unit 53 to switch the main switch 20 on. This prevents the flow of overcurrent exceeding the current threshold. When a stop signal is input, the control unit 61 instructs the output unit 53 to switch the main switch 20 off.

[0146] (Implementation Method 2)

[0147] In the first embodiment, in order to realize the switching device 10 with low power consumption, a processing element that suspends operation may be used as the processing element included in the control unit 61 .

[0148] Next, Embodiment 2 will be described with respect to differences from Embodiment 1. Configurations other than those described below are common to Embodiment 1. Therefore, components common to Embodiment 1 are denoted by the same reference numerals as in Embodiment 1, and their descriptions are omitted.

[0149] <Structure of Microcomputer 23>

[0150] Figure 7 This is a block diagram showing the main configuration of microcomputer 23 in Embodiment 2. When comparing Embodiment 2 with Embodiment 1, the configuration of microcomputer 23 differs. In addition to the components of microcomputer 23 in Embodiment 1, microcomputer 23 in Embodiment 2 further includes a clock signal output unit 63. Clock signal output unit 63 is connected to internal bus 62 and directly connected to control unit 61.

[0151] Clock signal output unit 63 outputs a clock signal to control unit 61. The clock signal consists of a high-level voltage and a low-level voltage. The voltage represented by the clock signal periodically switches from a low-level voltage to a high-level voltage. Each time the voltage in the clock signal switches from a low-level voltage to a high-level voltage, the processing element of control unit 61 executes one process.

[0152] The control unit 61 causes the clock signal output unit 63 to stop outputting the clock signal via the internal bus 62. When the clock signal output unit 63 stops outputting the clock signal, the processing elements of the control unit 61 suspend their operations.

[0153] The operation signal and the stop signal are input not only to the input unit 56 but also to the clock signal output unit 63. When the operation signal or the stop signal is input while the clock signal output unit 63 is stopped from outputting the clock signal, the clock signal output unit 63 resumes outputting the clock signal to the control unit 61. As a result, the processing elements of the control unit 61 resume operation.

[0154] The processing elements of the control unit 61 execute computer program P, thereby performing not only connection detection processing, current determination processing, and power supply control processing, but also pause processing and startup processing. The pause processing is processing that stops the output of the clock signal. The startup processing is the first processing executed when the control unit 61 resumes operation.

[0155] <Suspended processing>

[0156] Figure 8 This is a flowchart illustrating the pause processing sequence. The control unit 61 periodically executes the pause processing. During the pause processing, the control unit 61 determines whether to pause the operation (step S41). In step S41, the control unit 61 determines to pause the operation if the main switch 20 and the sub-switch 40 are disconnected, that is, if the disconnection period is longer than the reference period. If the disconnection period is shorter than the reference period, the control unit 61 determines not to pause the operation.

[0157] If the control unit 61 determines that the operation is not to be suspended (S41: No), it ends the suspension process. When the next cycle arrives, the control unit 61 executes the suspension process again. Therefore, if the control unit 61 determines that the operation is not to be suspended, it waits until the off period becomes longer than the reference period.

[0158] If the control unit 61 determines that the operation is to be paused (S41: Yes), it instructs the clock signal output unit 63 to stop outputting the clock signal to the control unit 61 (step S42), thus terminating the pause process. As described above, when the output of the clock signal stops, the control unit 61 pauses its operation. After the control unit 61 stops its operation, if a start signal or a stop signal is input to the clock signal output unit 63, the clock signal output unit 63 resumes outputting the clock signal, and the control unit 61 resumes its operation.

[0159] <Startup Process>

[0160] Figure 9 This is a flowchart showing the sequence of the startup process. The control unit 61 executes the startup process when it resumes operation, that is, when it resumes outputting the clock signal. Since the control unit 61 suspends operation when the main switch 20 and the sub-switch 40 are off, the startup process is executed with the main switch 20 and the sub-switch 40 off. Part of the startup process is identical to part of the current determination process. Therefore, the description of steps S12 to S20, which are identical to the current determination process, will be omitted.

[0161] In the startup process, the control unit 61 first obtains node voltage information from the A / D converter 52 (step S51). Next, based on the node voltage indicated by the node voltage information obtained in step S51, the control unit 61 determines whether the load 12 is connected to the device connector Ta (step S52), similar to step S3 of the connection detection process.

[0162] If the control unit 61 determines that the load 12 is not connected (S52: No), it sets the value of the connection flag to zero (step S53) and terminates the startup process. If the control unit 61 determines that the load 12 is connected (S52: Yes), it sets the value of the connection flag to one (step S54). After executing step S54, the control unit 61 sequentially executes steps S12 to S16 to calculate the resistance component value of the load 12. Based on the calculated resistance component value, the control unit 61 determines whether the switching current flowing when the main switch 20 is turned on is lower than the current threshold. Depending on the determination result, the control unit 61 sets the value of the permission flag to zero or one.

[0163] After executing one of steps S18 and S20, the control unit 61 terminates the startup process. After completing the startup process, the control unit 61 executes a connection detection process, a current determination process, a power supply control process, and a pause process.

[0164] As described above, during the startup process, the control unit 61 determines whether the load 12 is connected to the device connector Ta. If the control unit 61 determines that the load 12 is connected, it calculates the resistance component value of the load 12 and, based on the calculated resistance component value, determines whether the switching current flowing when the main switch 20 is switched on is lower than the current threshold. Therefore, while the control unit 61 is suspended, if the electrical device connected to the device connector Ta as the load 12 is changed to one with a lower resistance component value, the control unit 61 will not erroneously instruct the output unit 53 to switch on the main switch 20.

[0165] The switch device 10 in the second embodiment also achieves the same effects as the switch device 10 in the first embodiment.

[0166] Postscript

[0167] When the power supply voltage of the DC power supply 11 hardly fluctuates, the control unit 61 may omit step S12 in the current determination process in Embodiments 1 and 2. In this case, the control unit 61 uses a preset value as the power supply voltage in step S16.

[0168] In step S17 of the current determination process in Embodiments 1 and 2, the control unit 61 determines whether the switch current is below the current threshold based on the resistance component value calculated in step S16. However, in step S17, the control unit 61 may also directly determine whether the switch current is below the current threshold based on the node voltage represented by the node voltage information obtained in step S14, i.e., the first divided voltage. As described above, the smaller the resistance component value of the load 12, the greater the switch current that flows when the main switch 20 is switched on. The lower the first divided voltage, the smaller the resistance component value of the load 12. Therefore, the lower the first divided voltage, the greater the switch current.

[0169] Therefore, in step S17, the control unit 61 determines that the switching current is greater than the current threshold when the node voltage indicated by the node voltage information obtained in step S14 is less than the reference voltage. The control unit 61 determines that the switching current is less than the current threshold when the node voltage indicated by the node voltage information obtained in step S14 is greater than the reference voltage. The first divided voltage is proportional to the power supply voltage of the DC power supply 11. Therefore, the reference voltage used in step S17 is changed according to the power supply voltage indicated by the power supply voltage information obtained in step S12.

[0170] The higher the power supply voltage, the higher the reference voltage. If the power supply voltage of the DC power supply 11 barely fluctuates, the control unit 61 does not need to change the reference voltage. In this case, the control unit 61 can also omit step S12 during the current determination process. Furthermore, the switch device 10 does not need to include the power supply detection unit 22, and the microcomputer 23 does not need to include the A / D converter 50 and the input unit 57.

[0171] If the power supply voltage of DC power supply 11 hardly fluctuates, control unit 61 may omit step S12 in the startup process of Embodiment 2, similarly to the current determination process. Furthermore, in step S17 of the startup process, control unit 61 may directly determine whether the switching current is below the current threshold based on the node voltage indicated by the node voltage information obtained in step S14, i.e., the first divided voltage, similarly to step S17 of the current determination process.

[0172] In Embodiment 2, the method by which the control unit 61 suspends operation is not limited to stopping the output of the clock signal. Typically, the period of the clock signal output by the clock signal output unit 63 to the control unit 61, that is, the interval between switching from a low-level voltage to a high-level voltage, is referred to as the first period. Alternatively, the control unit 61 can suspend operation by instructing the clock signal output unit 63 to change the period of the clock signal output to the control unit 61 from the first period to a second period that is longer than the first period.

[0173] In this configuration, the operation signal and the stop signal are not input to the clock signal output unit 63. The control unit 61 determines whether the operation signal or the stop signal has been input to the input unit 56 each time the voltage of the clock signal switches from a low-level voltage to a high-level voltage during the period when the clock signal cycle is the second cycle. If the control unit 61 determines that the operation signal or the stop signal has been input to the input unit 56, it instructs the clock signal output unit 63 to change the clock signal cycle to the first cycle and execute the startup process.

[0174] The clock signal is not limited to a signal whose voltage periodically switches from a low level voltage to a high level voltage, but may also be a signal whose voltage periodically switches from a high level voltage to a low level voltage. In this case, the processing element of the control unit 61 executes processing each time the voltage in the clock signal switches from a high level voltage to a low level voltage.

[0175] (Implementation 3)

[0176] In the first embodiment, the sub-switch 40 of the switch circuit 26 is not limited to a P-channel FET.

[0177] Next, Embodiment 3 will be described with respect to differences from Embodiment 1. Configurations other than those described below are common to Embodiment 1. Therefore, components common to Embodiment 1 are denoted by the same reference numerals as in Embodiment 1, and their descriptions are omitted.

[0178] <Structure of Switchgear 10>

[0179] Figure 10 This is a block diagram showing the main components of a switch device 10 according to a third embodiment. The switch device 10 according to the third embodiment includes the same components as the switch device 10 according to the first embodiment, excluding the selector switch 27 and the switch resistor 28. The switch device 10 according to the third embodiment further includes a drive circuit 32. The switch circuit 26 according to the third embodiment further includes a series resistor 43 in addition to the components of the switch circuit 26 according to the first embodiment. The sub-switch 40 according to the third embodiment is an N-channel FET.

[0180] The drain of the sub-switch 40 of the switching circuit 26 is connected to the drain of the main switch 20. The source of the sub-switch 40 is connected to one end of a series resistor 43. The series resistor 43 functions as a second resistor. The other end of the series resistor 43 is connected to the connection node between the current output circuit 21 and the device connector Ta. The switching resistor 41 is connected between the gate and source of the sub-switch 40. The gate of the sub-switch 40 is further connected to one end of a switching resistor 42. The other end of the switching resistor 42 is connected to the drive circuit 32. The drive circuit 32 is further connected to the switching unit 55 of the microcomputer 23.

[0181] In the sub-switch 40, when the gate voltage relative to the source potential is above a certain voltage, the resistance between the drain and source is sufficiently low. In this case, the sub-switch 40 is on, and current can flow through the drain and source. In the sub-switch 40, when the gate voltage relative to the source potential is below a certain voltage, the resistance between the drain and source is sufficiently high. In this case, the sub-switch 40 is off, and current does not flow through the drain and source.

[0182] In the microcomputer 23, when the control unit 61 instructs the switching unit 55 to switch the sub-switch 40 on, the switching unit 55 outputs a second on-instruction instructing the sub-switch 40 to switch on. Upon receiving the second on-instruction, the driver circuit 32 increases the voltage at the gate of the sub-switch 40 relative to the ground potential. As a result, the gate voltage relative to the source potential of the sub-switch 40 reaches a predetermined voltage or higher, and the sub-switch 40 switches on.

[0183] In the microcomputer 23, when the control unit 61 instructs the switching unit 55 to switch the sub-switch 40 off, the switching unit 55 outputs a second off instruction instructing the sub-switch 40 to switch off. Upon receiving the second off instruction, the drive circuit 32 reduces the voltage at the gate of the sub-switch 40 relative to the ground potential. As a result, the gate voltage of the sub-switch 40 relative to the source potential falls below a predetermined voltage, and the sub-switch 40 switches off.

[0184] As described in the first embodiment, the on-resistance of an N-channel FET is generally relatively low, at several ohms. In the third embodiment, a series resistor 43 is connected in series with the sub-switch 40 as the switch circuit 26 to achieve a circuit having a high resistance when the sub-switch 40 is on. For example, if the resistance of the series resistor 43 is several hundred ohms, the resistance of the switch circuit 26 when the sub-switch 40 is on will be several hundred ohms.

[0185] In the third embodiment, similar to the first embodiment, the resistance value of the switch circuit 26 when the sub-switch 40 is on is greater than the on-resistance value of the main switch 20. The resistance value of the circuit resistor is greater than the resistance value of the switch circuit 26 when the sub-switch 40 is on. Furthermore, when a load 12 having a zero-ohm resistance component is connected to the device connector Ta and the main switch 20 and sub-switch 40 are turned off and on, respectively, the current flowing therethrough is a normal value that does not cause smoke.

[0186] The switch device 10 in the third embodiment also achieves the same effects as the switch device 10 in the first embodiment.

[0187] Postscript

[0188] The on-resistance of relay contacts is lower than that of N-channel FETs. Therefore, relay contacts can also be used as the sub-switch 40 in Embodiment 3. In this case, a structure for switching the sub-switch 40 on and off is provided in the switch device 10. The sub-switch 40 is switched on and off by the switching unit 55. In Embodiment 3, if the on-resistance of the sub-switch 40 is large, the source of the sub-switch 40 can also be connected to the connection node between the current output circuit 21 and the device connector Ta.

[0189] In embodiments 1 and 2, when the on-resistance of the sub-switch 40 is small, one end of the series resistor 43 may be connected in series to the drain of the sub-switch 40. In this case, the other end of the series resistor 43 is connected to the connection node between the current output circuit 21 and the device connector Ta.

[0190] The switch device 10 in the second embodiment may also be configured similarly to the switch device 10 in the third embodiment.

[0191] In embodiments 1 to 3, the sub-switch 40 is not limited to a FET or relay contact, but may also be a switch such as a bipolar transistor or an IGBT (Insulated Gate Bipolar Transistor). The structure for detecting the switch current is not limited to outputting a current that is a predetermined fraction of the switch current to the current resistor 25, but may also be a structure using a shunt resistor or a current sensor. The shunt resistor is connected in series with the source of the main switch 20, and the switch current is detected based on the voltage across the shunt resistor. The current sensor detects the switch current based on the strength of the magnetic field generated when the switch current flows through the connection line connected to the source of the main switch 20.

[0192] The disclosed embodiments 1 to 3 are illustrative in all respects and are not restrictive. The scope of the present invention is indicated by the claims rather than the above meaning, and is intended to include all modifications within the meaning and scope equivalent to the claims.

[0193] Description of Reference Numerals

[0194] 1 Power System

[0195] 10 Switchgear

[0196] 11 DC power supply

[0197] 12 Load

[0198] 20 Main switch

[0199] 21 Current output circuit

[0200] 22 Power supply detection unit

[0201] 23 Microcomputer

[0202] 24, 32 drive circuit

[0203] 25 Current resistance

[0204] 26 Switching Circuit

[0205] 27 Toggle Switch

[0206] 28, 41, 42 switch resistors

[0207] 29 Circuit resistance

[0208] 30 capacitors

[0209] 31 Voltage detection unit

[0210] 40 auxiliary switches

[0211] 43 Series resistor (second resistor)

[0212] 50, 51, 52 A / D conversion unit

[0213] 53, 54 output section

[0214] 55 Switching Department

[0215] 56, 57, 58, 59 Input

[0216] 60 Storage

[0217] 61 Control Unit (Processing Unit)

[0218] 62 internal bus

[0219] 63 Clock signal output unit

[0220] E Storage Media

[0221] P Computer Program

[0222] Ta device connector

[0223] Tb load connector.

Claims

1. A switch device comprising: A connector, detachably connected to a load; a main switch provided in a first current path from the DC power source to the connector; a switch circuit provided in a second current path from the DC power supply to the connector and having a sub-switch; and Processing department, executes processing, When the auxiliary switch is turned on, the resistance value of the switch circuit is greater than the on-resistance value of the main switch. The processing unit obtains node voltage information indicating a node voltage of a connection node downstream of the main switch and the sub-switch when the main switch is off and the sub-switch is on, and determines, based on the obtained node voltage information, whether a switching current flowing through the main switch when the main switch is turned on is lower than a current threshold. The processing unit performs the following processing: Based on the obtained node voltage information, the resistance component value of the load is calculated. Based on the calculated resistance component value, it is determined whether the switching current flowing when the main switch is switched on is lower than the current threshold.

2. The switch device according to claim 1, wherein: The switch circuit includes a second resistor connected in series with the sub-switch.

3. The switch device according to claim 1, wherein: The processing unit suspends the action, The processing unit executes a process of acquiring the node voltage information in a state where the main switch is off and the sub-switch is on when the operation is resumed.

4. The switch device according to any one of claims 1 to 3, wherein: The current flowing when a load having a resistance component value of zero ohm is connected to the connector and the main switch and the sub-switch are respectively turned off and on is a normal value that does not cause smoke.

5. A switch device comprising: A connector, detachably connected to a load; a main switch provided in a first current path from the DC power source to the connector; a switch circuit provided in a second current path from the DC power supply to the connector and having a sub-switch; and Processing department, executes processing, When the auxiliary switch is turned on, the resistance value of the switch circuit is greater than the on-resistance value of the main switch. The processing unit obtains node voltage information indicating a node voltage of a connection node downstream of the main switch and the sub-switch when the main switch is off and the sub-switch is on, and determines, based on the obtained node voltage information, whether a switching current flowing through the main switch when the main switch is turned on is lower than a current threshold. The switch device comprises: a resistor provided in a third current path from the DC power supply to the connector, one end of the resistor being connected to the connection node; and A capacitor, one end of which is connected to the connection node, The processing unit performs the following processing: When the main switch and the auxiliary switch are in the off state, the node voltage information is obtained. Whether the load is connected to the connector is determined based on the node voltage information obtained when the main switch and the sub-switch are in an off state.

6. The switch device according to claim 5, wherein: The processing unit executes a process of acquiring the node voltage information in a state where the main switch is off and the sub-switch is on, when it is determined that the load is connected to the connector.

7. The switch device according to claim 5 or 6, wherein: The resistance value of the resistor is larger than the resistance value of the switch circuit when the sub-switch is turned on.

8. The switch device according to claim 5 or 6, wherein: The switch circuit includes a second resistor connected in series with the sub-switch.

9. The switch device according to claim 5 or 6, wherein: The processing unit suspends the action, The processing unit executes a process of acquiring the node voltage information in a state where the main switch is off and the sub-switch is on when the operation is resumed.

10. The switch device according to claim 5 or 6, wherein: The current flowing when a load having a resistance component value of zero ohm is connected to the connector and the main switch and the sub-switch are respectively turned off and on is a normal value that does not cause smoke.

11. A switch device comprising: A connector, detachably connected to a load; a main switch provided in a first current path from the DC power source to the connector; a switch circuit provided in a second current path from the DC power supply to the connector and having a sub-switch; and Processing department, executes processing, When the auxiliary switch is turned on, the resistance value of the switch circuit is greater than the on-resistance value of the main switch. The processing unit obtains node voltage information indicating a node voltage of a connection node downstream of the main switch and the sub-switch when the main switch is off and the sub-switch is on, and determines, based on the obtained node voltage information, whether a switching current flowing through the main switch when the main switch is turned on is lower than a current threshold. The processing unit performs the following processing: When the main switch is turned on, current information indicating the switch current is obtained. Based on the acquired current information, it is determined whether the load is connected to the connector.

12. The switch device according to claim 11, wherein: The switch circuit includes a second resistor connected in series with the sub-switch.

13. The switchgear according to claim 11 or 12, wherein: The processing unit suspends the action, The processing unit executes a process of acquiring the node voltage information in a state where the main switch is off and the sub-switch is on when the operation is resumed.

14. The switchgear according to claim 11 or 12, wherein: The current flowing when a load having a resistance component value of zero ohm is connected to the connector and the main switch and the sub-switch are respectively turned off and on is a normal value that does not cause smoke.

15. A current determination method, causing a computer to execute the following steps: Acquiring node voltage information indicating a node voltage at a connection node downstream of the main switch and the sub-switch, in a state where a main switch provided in a first current path from a DC power supply to a connector detachably connected to a load is off and a sub-switch included in a switching circuit provided in a second current path from the DC power supply to the connector is on; determining, based on the acquired node voltage information, whether a switching current flowing through the main switch when the main switch is switched on is lower than a current threshold; Calculating the resistance component value of the load based on the obtained node voltage information; and determining, based on the calculated resistance component value, whether the switching current flowing when the main switch is switched on is lower than the current threshold; The resistance value of the switch circuit when the sub-switch is turned on is greater than the on-resistance value of the main switch.

16. A current determination method, causing a computer to execute the following steps: Acquiring node voltage information indicating a node voltage at a connection node downstream of the main switch and the sub-switch, in a state where a main switch provided in a first current path from a DC power supply to a connector detachably connected to a load is off and a sub-switch included in a switching circuit provided in a second current path from the DC power supply to the connector is on; determining, based on the acquired node voltage information, whether a switching current flowing through the main switch when the main switch is switched on is lower than a current threshold; When the main switch and the auxiliary switch are disconnected, obtaining the node voltage information; and determining whether the load is connected to the connector based on the node voltage information obtained when the main switch and the sub-switch are in the off state; When the auxiliary switch is turned on, the resistance value of the switch circuit is greater than the on-resistance value of the main switch. One end of a resistor provided on a third current path from the DC power supply to the connector is connected to the connection node, and one end of a capacitor is connected to the connection node.

17. A current determination method, causing a computer to execute the following steps: Acquiring node voltage information indicating a node voltage at a connection node downstream of the main switch and the sub-switch, in a state where a main switch provided in a first current path from a DC power supply to a connector detachably connected to a load is off and a sub-switch included in a switching circuit provided in a second current path from the DC power supply to the connector is on; determining, based on the acquired node voltage information, whether a switching current flowing through the main switch when the main switch is switched on is lower than a current threshold; When the main switch is turned on, obtaining current information representing the switch current; and Based on the obtained current information, determining whether the load is connected to the connector, The resistance value of the switch circuit when the sub-switch is turned on is greater than the on-resistance value of the main switch.

18. A computer program product comprising a computer program configured to cause a computer to execute the following steps: Acquiring node voltage information indicating a node voltage of a connection node downstream of the main switch and the sub-switch in a state in which a main switch provided in a first current path from a DC power supply to a connector detachably connected to a load is off and a sub-switch included in a switching circuit provided in a second current path from the DC power supply to the connector is on; and determining, based on the acquired node voltage information, whether a switching current flowing through the main switch when the main switch is switched on is lower than a current threshold; Calculating the resistance component value of the load based on the obtained node voltage information; and determining, based on the calculated resistance component value, whether the switching current flowing when the main switch is switched on is lower than the current threshold; The resistance value of the switch circuit when the sub-switch is turned on is greater than the on-resistance value of the main switch.

19. A computer program product comprising a computer program configured to cause a computer to execute the following steps: Acquiring node voltage information indicating a node voltage at a connection node downstream of the main switch and the sub-switch, in a state where a main switch provided in a first current path from a DC power supply to a connector detachably connected to a load is off and a sub-switch included in a switching circuit provided in a second current path from the DC power supply to the connector is on; determining, based on the acquired node voltage information, whether a switching current flowing through the main switch when the main switch is switched on is lower than a current threshold; When the main switch and the auxiliary switch are disconnected, obtaining the node voltage information; and determining whether the load is connected to the connector based on the node voltage information obtained when the main switch and the sub-switch are in the off state; When the auxiliary switch is turned on, the resistance value of the switch circuit is greater than the on-resistance value of the main switch. One end of a resistor provided on a third current path from the DC power supply to the connector is connected to the connection node, and one end of a capacitor is connected to the connection node.

20. A computer program product comprising a computer program configured to cause a computer to execute the following steps: Acquiring node voltage information indicating a node voltage at a connection node downstream of the main switch and the sub-switch, in a state where a main switch provided in a first current path from a DC power supply to a connector detachably connected to a load is off and a sub-switch included in a switching circuit provided in a second current path from the DC power supply to the connector is on; determining, based on the acquired node voltage information, whether a switching current flowing through the main switch when the main switch is switched on is lower than a current threshold; When the main switch is turned on, obtaining current information representing the switch current; and Based on the obtained current information, determining whether the load is connected to the connector, The resistance value of the switch circuit when the sub-switch is turned on is greater than the on-resistance value of the main switch.

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