JP7501187B2 - Ground fault detection circuit and ground fault detection device - Google Patents

Description

The present invention relates to a ground fault detection circuit and a ground fault detection device, and in particular to a technology for distinguishing between the positive and negative sides of a ground fault in a power supply line that supplies DC power to a load.

Conventionally, a ground fault detection circuit for individually detecting ground faults in two power supply lines connected between a DC power source and a load has been proposed in Patent Document 1. The ground fault detection circuit described in Patent Document 1 can also detect whether or not power is being supplied to the load.

JP 2009-270999 A

However, the inventor discovered that when there are multiple power supply sources with different voltages and loads connected to each of these sources, and the potential of one of the power supply lines is common, the ground fault detection circuits installed in each of the sources malfunction.

The present invention was made based on the inventor's findings, and aims to provide a ground fault detection circuit and a ground fault detection device that can suppress malfunction even when there are multiple power supply sources and loads that share one potential.

In order to achieve the above object, the present invention provides a ground fault detection circuit for individually detecting a ground fault in either a positive supply line or a negative supply line that connects a DC voltage device and a load, and includes a first current mirror circuit connected to the positive supply line and using the positive supply line as a reference potential, a second current mirror circuit connected to the negative supply line and using the negative supply line as a reference potential, a reference current line through which a reference current shared by the first current mirror circuit and the second current mirror circuit flows, a copy current line through which a copy current shared by the first current mirror circuit and the second current mirror circuit flows, a ground section provided on the copy current line, and a ground potential circuit connected to the reference current line and determining the ground potential of the ground section relative to the negative supply line based on the reference current.

In order to achieve the above object, another aspect of the present invention is a ground fault detection device, which is a ground fault detection circuit for individually detecting a ground fault in either a positive supply line or a negative supply line connecting a DC voltage device and a load, and includes a first current mirror circuit connected to the positive supply line and using the positive supply line as a reference potential, a second current mirror circuit connected to the negative supply line and using the negative supply line as a reference potential, a reference current line through which a reference current shared by the first current mirror circuit and the second current mirror circuit flows, and a reference current line between the first current mirror circuit and the second current mirror circuit. The device includes a copy current line through which a copy current shared by the first current mirror circuit and the second current mirror circuit flows, a ground section provided on the copy current line, a ground potential circuit interposedly connected to the reference current line and determining the ground potential of the ground section relative to the negative supply line based on the reference current, a first detection element that detects the current between the first current mirror circuit and the ground section, a second detection element that detects the current between the second current mirror circuit and the ground section, and a first notification means and a second notification means that respectively notify changes in the current detected by the first detection element and the second detection element.

This ground fault detection circuit allows the potential for detecting a ground fault to be set arbitrarily, which makes it possible to prevent the potential from other power sources and the potential for detecting a ground fault from becoming similar, thereby suppressing malfunctions of the ground fault detection circuit.

FIG. 1 is a diagram showing a ground fault detection device including a ground fault detection circuit according to an embodiment of the present invention. FIG. 2 is a diagram showing a ground fault detection device according to an embodiment when a ground fault occurs in a positive supply line. FIG. 3 is a diagram showing a ground fault detection device according to an embodiment when a ground fault occurs in a negative supply line. FIG. 4 shows variation 1 of the mounting position of the ground potential circuit. FIG. 5 shows variation 2 of the mounting position of the ground potential circuit.

Below, embodiments of the ground fault detection circuit and ground fault detection device according to the present invention will be described with reference to the drawings. Note that the numerical values, shapes, materials, components, positional relationships of the components, connection states, steps, and order of steps shown in the following embodiments are merely examples and are not intended to limit the present invention. In addition, although multiple inventions may be described as one embodiment below, components not described in the claims are described as optional components with respect to the invention related to that claim. In addition, the drawings are schematic diagrams in which emphasis, omission, and proportions have been appropriately adjusted in order to explain the present invention, and may differ from the actual shapes, positional relationships, and proportions.

Figure 1 shows a ground fault detection device equipped with a ground fault detection circuit according to an embodiment. In addition to the ground fault detection device 100, the figure also shows a DC voltage device 210 and a load 220.

The DC voltage device 210 is a power source that generates a DC voltage between the positive terminal 211 and the negative terminal 212. The DC voltage V generated by the DC voltage device 210 is not particularly limited, and examples include DC 12 V, DC 24 V, DC 48 V, and DC 280 V boosted by a DC/DC converter.

The load 220 is connected via a positive supply line 231 connected to the positive terminal 211 of the DC voltage device 210 and a negative supply line 232 connected to the negative terminal 212, and is, for example, a motor or an electric device. The negative supply line 232 is connected to the ground (GND). Connected to the ground means a potential that is a reference for the operation of the DC voltage device 210 and the load 220, and is a potential different from the earth potential or the frame ground. In this embodiment, the earth wire 162 is connected to the frame ground of the device, and the device is not connected to the earth (earth).

The ground fault detection device 100 is a device that distinguishes between a ground fault in either the positive supply line 231 or the negative supply line 232 and detects the ground fault and notifies a user or the like, and includes a ground fault detection circuit 110, a first detection element 101, a second detection element 102, a first notification means 103, and a second notification means 104.

The ground fault detection circuit 110 is a circuit for detecting ground faults individually by changing the current at different points corresponding to a ground fault in the positive supply line 231 and a ground fault in the negative supply line 232, and includes a first current mirror circuit 130, a second current mirror circuit 140, a reference current line 150, a copy current line 160, a ground section 161, and a ground potential circuit.

The current mirror circuit (hereinafter, the first current mirror circuit 130 and the second current mirror circuit 140 may be collectively referred to as the "current mirror circuit") is a circuit that uses active elements that perform operations such as amplification and rectification using supplied power, and can copy the reference current flowing through the reference current line 150 and pass a copy current of the same value as the reference current through the copy current line 160.

The current mirror circuit provided in the ground fault detection circuit 110 is not particularly limited, and examples include a current-voltage converter, a cascade-connected voltage-current converter, and a circuit using an operational amplifier. In the present embodiment, the current mirror circuit is configured using transistors. The type of transistor is not particularly limited, such as a FET (field effect transistor), but in this embodiment, a bipolar transistor will be used for explanation.

The first current mirror circuit 130 is connected to the positive supply line 231 and is a current mirror circuit that uses the positive supply line 231 as a reference potential. In this embodiment, the first current mirror circuit 130 includes a first transistor 131 and a second transistor 132 that are PNP type bipolar transistors and have the same specifications. The bases of the first transistor 131 and the second transistor 132 are connected to each other. Note that the same specifications means, for example, elements with the same model number, and include tolerances and errors between elements.

The emitter of the first transistor 131 is connected to the positive supply line 231, and the collector is connected to the negative supply line 232 (second current mirror circuit 140). The collector and base of the first transistor 131 are connected. A reference side current flows between the emitter and collector of the first transistor 131.

The emitter of the second transistor 132 is connected to the positive supply line 231, and the collector is connected to the negative supply line 232 (second current mirror circuit 140). The base of the second transistor 132 is connected to the collector of the first transistor 131. The collector and base of the second transistor 132 are not connected. A current of the copy side flows between the emitter and collector of the second transistor 132.

In addition, "connection" in the specification and claims means electrical connection, and "A is connected to B" and "A and B are connected" mean a connection so that a current flows from A to B or from B to A. A case where a single or multiple elements C are interposed between A and B, or a case where a current flows between A and B even if there is a point between A and B where the current branches or joins is included in "connection". In addition, "connection" also includes a connection where A and B are at the same potential in cases where no current flows. In addition, "connected between A and B through C" means a state where A and C are connected and C and B are connected, that is, a state where A and B are connected through C. "Connected between A and B through C in a branching manner" means a state where A and B are connected without C, and C is connected so that a current branches from the current flowing between A and B or joins the current flowing between A and B. "C is connected to the D line in a branching manner" means that the D line is not divided by C, but C is connected so that a current branches off from the current flowing on the D line, or flows to merge with the current flowing on the D line.

The second current mirror circuit 140 is connected to the negative supply line 232 and is a current mirror circuit that uses the negative supply line 232 as a reference potential. In this embodiment, the second current mirror circuit 140 includes a third transistor 141 and a fourth transistor 142, which are NPN-type bipolar transistors and have the same performance. The bases of the third transistor 141 and the fourth transistor 142 are connected to each other.

The emitter of the third transistor 141 is connected to the negative supply line 232, and the collector is connected to the positive supply line 231 (first current mirror circuit 130). The collector and base of the third transistor 141 are connected. A reference side current flows between the emitter and collector of the third transistor 141.

The emitter of the fourth transistor 142 is connected to the negative supply line 232, and the collector is connected to the positive supply line 231 (first current mirror circuit 130). The base of the fourth transistor 142 is connected to the collector of the third transistor 141. The collector and base of the fourth transistor 142 are not connected. A current of the copy side flows between the emitter and collector of the fourth transistor 142.

The current mirror circuit may include elements such as resistors that absorb the performance variations of each transistor. If FETs are used as transistors, the base can be read as the gate, the emitter as the source, and the collector as the drain.

The reference current line 150 is an electric wire, wiring pattern, etc. through which a reference current shared by the first current mirror circuit 130 and the second current mirror circuit 140 flows. In the present embodiment, the reference current line 150 connects the collector of the first transistor 131 of the first current mirror circuit 130 and the collector of the third transistor 141 of the second current mirror circuit 140.

The current value of the reference current flowing through the reference current line 150 is determined based on the DC voltage generated by the DC voltage device 210 and the combined resistance value of the first transistor 131, the third transistor 141, and other elements connected to the reference current line 150. Note that the reference current may be determined by interveningly connecting a constant current element or circuit to the reference current line 150. The constant current element is a circuit (including an element) that maintains the reference current at a constant value (e.g., 5 mA) when a voltage equal to or higher than a certain voltage is applied. An example of a constant current element is a constant current diode.

The copy current line 160 is an electric wire, wiring pattern, etc. through which a copy current shared by the first current mirror circuit 130 and the second current mirror circuit 140 flows. In the present embodiment, the copy current line 160 connects the collector of the second transistor 132 of the first current mirror circuit 130 and the collector of the fourth transistor 142 of the second current mirror circuit 140.

In a normal state where no ground fault occurs, the current value of the copy current flowing through the copy current line 160 is the same as that of the reference current line 150 due to the action of the first current mirror circuit 130 and the second current mirror circuit 140.

The ground section 161 is a terminal or the like provided on the copy current line 160 between the first current mirror circuit 130 and the second current mirror circuit 140. The ground section 161 is connected to a so-called earth line 162 so that the potential of the ground section 161 becomes the ground potential.

The ground potential circuit is a circuit that determines the ground potential of the ground section 161 relative to the negative supply line 232 connected to ground, based on the reference current flowing through the reference current line 150. In the present embodiment, the ground potential circuit is connected in a branched manner to the reference current line 150 between the first current mirror circuit 130 and the second current mirror circuit 140, and includes a potential determination transistor 171 that is interposedly connected to the copy current line 160 between the first current mirror circuit 130 and the second current mirror circuit 140.

In this embodiment, the potential determination transistor 171 is an NPN-type bipolar transistor, with a base connected to the reference current line 150, an emitter connected to the ground section 161 side of the copy current line 160, and a collector connected to the first current mirror circuit 130 side or the second current mirror circuit 140 side of the copy current line 160.

When using a FET as a transistor for determining the potential, the base can be read as the gate, the emitter as the source, and the collector as the drain.

The ground potential circuit also includes a constant voltage circuit 172 that is interposed between the base of the potential determination transistor 171 and the reference current line 150 between the second current mirror circuit 140. The constant voltage circuit 172 is not particularly limited as long as it is a circuit that supplies a constant voltage even if the temperature or the voltage supplied by the DC voltage device 210 changes, and examples of the constant voltage circuit 172 include a circuit that includes a Zener diode, a three-terminal regulator, etc. In the case of this embodiment, the constant voltage circuit 172 includes a Zener diode.

The constant voltage circuit 172 allows the ground potential, which is the potential of the ground part 161, to be set arbitrarily. Therefore, for example, by setting the potential of the ground part 161 in each fault detection device 100 to a potential lower than the potential generated by other DC voltage devices that share the potential of the negative supply line 232, it is possible to suppress malfunction of the ground fault detection device 100. Specifically, when multiple DC voltage devices 210 that generate voltages of DC 12V, DC 24V, and DC 48V are mixed and the negative supply line 232 is common, if a constant voltage circuit 172 is provided so that the ground potential of the ground part 161 of each fault detection device 100 in each DC voltage device 210 is about 4 to 8V and is the same potential in each fault detection device 100, malfunction of each fault detection device 100 can be suppressed.

In this embodiment, a reverse voltage prevention circuit 180 is provided. In the event of a ground fault, reverse power is applied to elements of the ground potential circuit, such as the potential determination transistor 171, and elements of the current mirror circuit, to suppress the occurrence of malfunctions such as breakdowns. For example, in this embodiment, a rectifier diode is connected to the copy current line 160 between the ground section 161 and the potential determination transistor 171 with its anode facing the potential determination transistor 171 side and its cathode facing the ground section 161 side, and functions as the reverse voltage prevention circuit 180.

The first detection element 101 is an element that detects the current flowing in the copy current line 160 between the first current mirror circuit 130 and the ground part 161. The second detection element 102 is an element that detects the current flowing in the copy current line 160 between the second current mirror circuit 140 and the ground part 161.

The detection element (hereinafter, the first detection element 101 and the second detection element 102 may be collectively referred to as the "detection element") is an element that detects the current flowing through the copy current line 160. The detection element is not particularly limited as long as it can detect changes in the current flowing through the copy current line 160, and may be a DC ammeter, a coil that acquires changes in the current flowing through the copy current line 160, or the like. In this embodiment, the detection element is a light-emitting element (light-emitting diode).

The first notification means 103 is a device that notifies the change in current detected by the first detection element 101. The second notification means 104 is a device that notifies the change in current detected by the second detection element 102.

The notification means (hereinafter, the first notification means 103 and the second notification means 104 may be collectively referred to as "notification means") is not particularly limited as long as it can notify a person or other devices of the change in current detected by the detection element as information. For example, if the detection element is a light-emitting element, the detection element also functions as a notification means, since it can notify a person of the presence or absence of current as information based on the presence or absence of light emission. In the case of this embodiment, the notification means is a photodiode. Also, the first detection element 101 and the first notification means 103 are packaged so-called photocouplers. Similarly, the second detection element 102 and the second notification means 104 are packaged so-called photocouplers.

The notification means may include a notification circuit or communication device (not shown) and may output information to other devices such as a computer.

Next, the operation of the ground fault detection circuit 110 and the ground fault detection device 100 in this embodiment configured as described above will be described.

(Normal operation)
The operation in a steady state where no ground fault occurs will be described. The steady state is when the DC voltage generated by the DC voltage device 210 is applied to the load 220 and no ground fault occurs in either the positive supply line 231 or the negative supply line 232. In the steady state, a constant reference current flows from the positive supply line 231 to the negative supply line 232 in the reference current line 150 of the ground fault detection circuit 110. The value of the reference current is not particularly limited, but it is sufficient to adjust the resistance values of multiple elements connected to the reference current line 150 so that the reference current value is, for example, 5 mA, and it is also possible to adjust the resistance value by interposing a resistor to the reference current line 150 to set the reference current to a predetermined value.

When a reference current of a predetermined value flows through the reference current line 150, a copy current flows through the copy current line 160 based on the first current mirror circuit 130 and the second current mirror circuit 140. The value of the copy current is the same as the reference current. The detection element detects the copy current of a predetermined value, and the notification means notifies the detection state of the detection element. Note that, in a steady state, the current value of the copy current is constant, so the detection element may not detect a change in the copy current. However, in this embodiment, the detection element is a light-emitting element that emits light based on a current, so the first detection element 101 and the second detection element 102 emit light based on the copy current. In addition, the first notification means and the second notification means notify information indicating that a copy current is flowing at a predetermined value. This makes it possible to know that the steady state is being reached.

In addition, in a steady state, the DC voltage device 210 can be considered to be in a floating state because the circuit impedance of the earth fault detection device 100 is high relative to the earth connected to the ground part 161 in terms of potential, so the copy current flowing through the copy current line 160 does not flow to the earth.

(When the positive supply line has a ground fault)
Next, a case where a ground fault occurs in the positive supply line 231 will be described with reference to FIG.

When a ground fault occurs in the positive supply line 231, the potential of the emitter side of the second transistor 132 of the first current mirror circuit 130 and the potential of the ground part 161 of the copy current line 160 become the same potential (ground potential). Therefore, no current flows between the first current mirror circuit 130 and the ground part 161 of the copy current line 160. As a result, the first detection element 101, which is a light-emitting element, stops emitting light, and the first notification means 103, which is a photodiode, notifies the user that no current has flowed, i.e., that the positive supply line 231 has been grounded.

Meanwhile, the ground potential of the ground part 161 with respect to the negative supply line 232 is maintained at the potential set by the constant voltage circuit 172 of the ground potential circuit, and is also different from the voltage generated by other DC voltage devices that share the negative supply line 232, so that a current flow is maintained in the copy current line 160 between the ground part 161 and the negative supply line 232. As a result, the second detection element 102, which is a light-emitting element, maintains its emission, and the second notification means 104, which is a photodiode, notifies the user that there is no change in the current, i.e., that no ground fault has occurred in the negative supply line 232.

(When the negative supply line has a ground fault)
Next, a case where a ground fault occurs in the negative supply line 232 will be described with reference to FIG.

When a ground fault occurs in the negative supply line 232, the potential of the emitter side of the fourth transistor 142 of the second current mirror circuit 140 and the potential of the ground part 161 of the copy current line 160 become the same potential (ground potential). Therefore, no current flows between the second current mirror circuit 140 and the ground part 161 of the copy current line 160. As a result, the second detection element 102, which is a light-emitting element, stops emitting light, and the second notification means 104, which is a photodiode, notifies the fact that the current has stopped flowing, that is, that the negative supply line 232 has a ground fault.

On the other hand, the ground potential of the ground part 161 relative to the positive supply line 231 is maintained at the potential set by the constant voltage circuit 172 of the ground potential circuit, so that a current flow is maintained in the copy current line 160 between the ground part 161 and the positive supply line 231. As a result, the first detection element 101, which is a light-emitting element, continues to emit light, and the first notification means 103, which is a photodiode, notifies the user that there is no change in the current, i.e., that no ground fault has occurred in the negative supply line 232.

As described above, according to the ground fault detection device 100 equipped with the ground fault detection circuit 110 of this embodiment, by providing the first current mirror circuit 130 and the second current mirror circuit 140 on either side of the grounding part 161, it is possible to distinguish and notify the occurrence of a ground fault in the positive supply line 231 from the occurrence of a ground fault with the negative supply line 232. Furthermore, even if there is another DC voltage device that shares the negative supply line 232, it is possible to distinguish and notify the location of the ground fault without causing a malfunction.

In addition, the ground potential circuit can set the ground potential to a constant level, so that even if the voltage generated by the DC voltage device 210 becomes unstable due to fluctuations in the load 220, the ground potential of the grounding section 161 remains stable, thereby preventing malfunction of the ground fault detection device 100.

The present invention is not limited to the above-described embodiment. For example, the components described in this specification may be combined in any way, or some of the components may be removed to create another embodiment of the present invention. The present invention also includes modifications that are made to the above-described embodiment by those skilled in the art without departing from the spirit of the present invention, i.e., the meaning of the words in the claims.

For example, in this embodiment, detection of a ground fault has been described, but by using a notification means to obtain information indicating that a current is flowing through the first detection element 101 and the second detection element 102, it is also possible to know that a ground fault has not occurred and that the DC voltage device 210 is operating normally.

In addition, after determining that the device is operating normally, it is possible to obtain information indicating that current has stopped flowing through the first detection element 101 and the second detection element 102 using a notification means, thereby determining that an abnormality has occurred in the DC voltage device 210.

The ground potential circuit may also be provided between the ground section 161 and the second current mirror circuit 140 as shown in FIG. 4.

In addition, the ground potential circuit may be provided both between the first current mirror circuit 130 and the ground section 161 and between the ground section 161 and the second current mirror circuit 140, as shown in FIG. 5.

The present invention can be used in a ground fault detection circuit and a ground fault detection device that detects ground faults in the positive supply line and negative supply line that connect a DC voltage device to a load, and in particular in a case where multiple DC voltage devices share a negative supply line and have different supply voltages.

100 Ground fault detection device 101 First detection element 102 Second detection element 103 First notification means 104 Second notification means 110 Ground fault detection circuit 130 First current mirror circuit 131 First transistor 132 Second transistor 140 Second current mirror circuit 141 Third transistor 142 Fourth transistor 150 Reference current line 160 Copy current line 161 Ground section 162 Earth line 171 Potential determination transistor 172 Constant voltage circuit 180 Reverse voltage prevention circuit 210 DC voltage device 211 Positive terminal 212 Negative terminal 220 Load 231 Positive supply line 232 Negative supply line

Claims (4)

A ground fault detection circuit for individually detecting a ground fault in either a positive supply line or a negative supply line connecting a DC voltage device and a load, comprising:
a first current mirror circuit connected to the positive supply line and using the positive supply line as a reference potential;
a second current mirror circuit connected to the negative supply line and using the negative supply line as a reference potential;
a reference current line through which a reference current shared by the first current mirror circuit and the second current mirror circuit flows;
a copy current line through which a copy current shared by the first current mirror circuit and the second current mirror circuit flows;
a ground portion provided on the copy current line;
a ground potential circuit that determines a ground potential of the ground section with respect to the negative supply line based on the reference current ;
The ground potential circuit includes:
a potential determining transistor connected in a branched manner to the reference current line and connected interposedly to the copy current line;
a constant voltage circuit connected to the reference current line between the base or gate of the potential determining transistor and the second current mirror circuit;
The base or gate of the potential determination transistor is connected to the reference current line, the emitter or source is connected to the ground side of the copy current line, and the collector or drain is connected to the first current mirror circuit side or the second current mirror circuit side of the copy current line.
A ground fault detection circuit. The ground fault detection circuit according to claim 1 , wherein the constant voltage circuit comprises a Zener diode. A ground fault detection circuit according to claim 1 or 2 ,
a first detection element that detects a current between the first current mirror circuit and the ground;
a second detection element that detects a current between the second current mirror circuit and the ground;
a first notification means and a second notification means for notifying a change in the current detected by the first detection element and the second detection element, respectively;
A ground fault detection device comprising: the first detection element and the second detection element are light-emitting elements that emit light based on a current,
4. The ground fault detection device according to claim 3 , wherein the first notification means and the second notification means include a first light detection element and a second light detection element which detect the light emitted by the first detection element and the second detection element, respectively.

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