JP7645702B2 - Connection failure detection circuit - Google Patents

Description

The present invention relates to a connection failure detection circuit that detects connection failures in electrical circuit connections such as terminals.

In electrical circuit connections that connect electric wires and conductor bars that supply power, connection failures can occur due to loose screws, plugs, etc. If such connection failure occurs in electrical circuits that carry relatively large currents, such as in power distribution equipment and power equipment, the increased contact resistance can cause heat generation and deterioration of the connection, and even arc discharge can occur, which can lead to a fire in the worst case scenario.
Therefore, in order to avoid this, there are circuits that detect the occurrence of a connection failure. For example, the technology disclosed in Patent Document 1 arranges a photocoupler so that it turns on when there is a potential difference between terminals, and detects a connection failure by the turning on of this photocoupler.

JP 2009-145083 A

However, in the technology of Patent Document 1, the potential difference generated between the terminals depends on the forward voltage of a diode element such as a photocoupler, and therefore cannot be detected unless this forward voltage is reached.

In view of these problems, the present invention aims to provide a connection failure detection circuit that can detect connection failures in electrical circuit connections even when the generated voltage is small enough not to reach the forward voltage of the diode element.

In order to solve the above problem, the invention of claim 1 is a connection failure detection circuit that detects a connection failure at an electric circuit connection portion provided in an electric circuit, the electric circuit connection portion being formed by connecting a power supply side terminal to which a power supply side electric circuit is connected and a load side terminal to which a load side electric circuit is connected, and having a potential difference detection circuit that detects a potential difference when it occurs between the power supply side terminal and the load side terminal, and an output circuit that outputs a connection failure occurrence signal when the potential difference detection circuit detects the potential difference, characterized in that the power source connected to the electric circuit is a three-phase AC power source, the electric circuit is composed of three or four electric wires, and the power source of the potential difference detection circuit and the output circuit that detects a connection failure at the electric circuit connection portion of any one electric wire is an AC power source obtained from all the other electric wires .
According to this configuration, the threshold value at which the output circuit determines that a connection failure has occurred is not set using an element such as a diode that requires a certain drive voltage, so even if the potential difference occurring at the electric path connection portion is smaller than the forward voltage of the diode, it is possible to detect it and output a connection failure occurrence signal, thereby enabling detection of connection failure with high sensitivity.

In addition, the power supply for driving the potential difference detection circuit and the output circuit does not require a DC power supply, so there is no need to provide a separate power supply circuit.

The invention of claim 2 is characterized in that, in the configuration described in claim 1 , the potential difference detection circuit is composed of a current mirror circuit using two transistors, first and second NPN transistors, and the emitter of the second transistor is connected to the load side terminal and the emitter of the first transistor is connected to the power supply side terminal.
According to this configuration, since a connection failure is detected based on the emitter voltage difference between two transistors that constitute a current mirror circuit, it can be detected with high sensitivity using a simple circuit.

The present invention according to claim 3 is characterized in that in the configuration according to claim 2, the current mirror circuit uses a diode instead of the second transistor, and the cathode of the diode is connected to the load side terminal.

The invention of claim 4 is characterized in that, in the configuration of claim 2 or 3 , the output circuit has a PNP transistor, the base of which is connected to the collector of the first transistor of the current mirror circuit, and the collector of the PNP transistor is an output part for the connection failure occurrence signal.
According to this configuration, the output circuit is made up of a single transistor, and therefore can be made up of a simple circuit.

According to the present invention, the threshold value at which the output circuit determines that a connection failure has occurred is not set using an element that requires a constant drive voltage, such as a diode, so even if the potential difference occurring at the electrical path connection is smaller than the forward voltage of the diode, it is possible to detect it and output a connection failure occurrence signal. This allows for highly sensitive detection of connection failures.

1 is a circuit diagram showing an example of a connection failure detection circuit according to the present invention, illustrating a configuration in which the circuit is provided in a single-phase electric circuit. FIG. 13 is a circuit diagram showing another example of a connection failure detection circuit. FIG. 4 is a circuit diagram of a connection failure detection circuit provided in a three-phase electric circuit.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will now be described in detail with reference to the accompanying drawings, in which: FIG 1 is a circuit diagram showing an example of a circuit for detecting a connection failure in an electric circuit connection according to the present invention, and shows a configuration in which the circuit is provided in a single-phase electric circuit;
The electric circuit L to be detected is a single-phase two-wire wiring path consisting of two electric wires (a first electric wire L1 and a second electric wire L2) that supplies power from a power source 10 consisting of single-phase commercial power of, for example, 100V AC to a load 11, and is configured to detect any connection failure that occurs in an electric circuit connection part 2 provided on this electric circuit L.

The electrical circuit connection portion 2 has a power supply side terminal 2a connected to the power supply side electrical circuit and a load side terminal 2b connected to the load side electrical circuit, and the power supply side terminal 2a and the load side terminal 2b are provided on each of the electric wires L1, L2 of the two-wire electrical circuit L.
The power supply terminal 2a and the load terminal 2b are connected with little or no contact resistance under normal conditions, but if a connection failure occurs, the contact resistance between the terminals increases, causing a voltage drop proportional to the current in the circuit. The r in Figure 1 indicates this contact resistance.
1 indicate the flow of current when the connection failure detection circuit 1 operates, and operates during a half-wave of one polarity of the AC power source 10. R1 to R5 are resistive elements. The electrical path connection portion 2 is specifically a screw-fastened terminal portion, a quick-connect terminal, a connection portion between a plug and an outlet, or the like.

The connection failure detection circuit 1 is composed of a potential difference detection circuit 4 and an output circuit 5, and is configured to detect a connection failure in the electric path connection portion 2 of the second electric wire L2. Note that a connection failure detection circuit for detecting a connection failure in the electric path connection portion 2 of the first electric wire L1 is also provided separately, but is omitted here.
The potential difference detection circuit 4 is a circuit that detects a potential difference generated due to the contact resistance r of the electrical path connection portion 2, and has a first terminal portion 4a to which the voltage of the power supply side terminal 2a is input as a reference voltage, a second terminal portion 4b to which the voltage of the load side terminal 2b is input, a third terminal portion 4c that outputs a signal (potential difference detection signal), and a fourth terminal portion 4d that is connected to the power supply 10.

The output circuit 5 has a fifth terminal 5a (connected to the third terminal 4c) to which the potential difference detection signal output by the potential difference detection circuit 4 is input, a sixth terminal 5b to which a reference voltage is input, a seventh terminal 5c to which a signal (a connection failure occurrence signal) is output, and an eighth terminal 5d to which a power source 10 is connected.

The power supply for driving this connection failure detection circuit 1 is supplied from the opposite side, with the power supply line L4 connected to the first wire L1, which is the opposite side of the second wire L2 that detects connection failures. The diode D1 provided on the power supply line L4 is for preventing backflow.

Specifically, the potential difference detection circuit 4 includes a current mirror circuit composed of a first transistor T1 and a second transistor T2. Both transistors T1 and T2 are NPN transistors, and are, for example, monolithic dual type transistors, and are configured to have the same characteristics. The emitter of the first transistor T1 is connected to the first terminal 4a, and the collector is connected to the third terminal 4c. The emitter of the second transistor T2 is connected to the second terminal 4b. The collectors of both transistors T1 and T2 are connected to the fourth terminal 4d via resistor elements R1 and R2, respectively.
The collector of the second transistor T2 is connected to the common base.

The output circuit 5 is configured with a third transistor T3 made of a PNP transistor, the base of which is connected to the fifth terminal 5a, the collector of which is connected to the sixth terminal 5b, and the emitter of which is connected to the eighth terminal 5d. The seventh terminal 5c is provided at the collector. The resistive element R5 disposed between the sixth terminal 5b and the seventh terminal 5c acts as a load resistor.

The operation of the connection failure detection circuit 1 configured in this manner is as follows. In a normal connection state where the electrical path connection portion 2 has no or very small contact resistance r, the emitter potentials of the first transistor T1 and the second transistor T2 are approximately the same, so approximately the same current flows through both transistors T1 and T2 in the on state. In this state, the resistance elements R1 and R2 are set so that the third transistor T3 does not turn on. As a result, the third transistor T3 does not turn on, and no abnormality occurrence signal is output.

However, if a connection failure occurs in the electric path connection portion 2 and the contact resistance r increases, a voltage drop occurs between the power supply terminal 2a and the load terminal 2b. As a result, the emitter potential of the second transistor T2 rises relative to the emitter potential of the first transistor T1, taking the power supply terminal 2a as the reference. Then, the base potential of the second transistor T2 rises, so the base potential of the connected first transistor T1 rises, and the collector current of the first transistor T1 increases.
As a result of this increase in current, the voltage drop across the resistor R1 increases, the base potential of the third transistor T3 decreases, and the third transistor T3 turns on.
Thus, the potential of the seventh terminal 5c rises, and a connection failure occurrence signal is output.

In this way, the threshold value at which the output circuit 5 determines that a connection failure has occurred is not set using an element such as a diode that requires a constant drive voltage, so even if the potential difference occurring in the electric path connection part 2 is smaller than the forward voltage of the diode, it is possible to detect it and output a connection failure occurrence signal. Therefore, connection failure detection can be performed with high sensitivity.
Furthermore, the power source driving the potential difference detection circuit 4 and the output circuit 5 is an AC power source obtained from electric wires of opposite polarity, so that a DC power source is not required and there is no need to provide a separate power supply circuit.
Furthermore, since a connection failure is detected based on the emitter voltage difference between the two transistors T1 and T2 that form a current mirror circuit, it can be detected with high sensitivity using a simple circuit.
In addition, since the output circuit 5 is composed of one transistor T3, it can be composed of a simple circuit.

In the case of a single-phase two-wire system, the power supply for driving the connection failure detection circuit 1 is supplied from the wire opposite the wire that detects the connection failure as described above. However, in the case of a single-phase three-wire system, since there are three wires, the power supply for the connection failure detection circuit 1 is supplied via diodes from both of the other two wires other than the wire that detects the connection failure.

Fig. 2 shows a modified example of the connection failure detection circuit 1. In Fig. 1, the potential difference detection circuit 4 is configured as a current mirror circuit using two transistors T1 and T2, but Fig. 2 shows a circuit using a diode D2 instead of the second transistor T2. The cathode of the diode D2 is connected to the load side terminal 2b.
In this way, the second transistor T2 may be replaced with the diode D2, which simplifies the circuitry of the potential difference detection circuit 4. The resistor element R6 is an element that replaces the resistor element R2.

In the above embodiment, the first electric wire L1 is positive, but since the power source 10 is an AC power source, positive and negative poles are generated alternately. Therefore, when the first electric wire L1 is negative, a connection failure detection circuit (not shown) provided on the first electric wire L1 side is activated.
The connection failure detection circuit 1 can also be applied to detect connection failures in crimped terminals and electrical circuit connections welded with solder or the like.

In the above embodiment, the case where the electric circuit to be detected is an electric circuit L consisting of a single-phase two-wire has been described. However, the connection failure detection circuit 1 can also be applied to a multi-phase electric circuit. For example, the case of a three-phase electric circuit is shown in FIG. 3.
3 shows a circuit diagram of the connection failure detection circuit 1 provided in a three-wire circuit equipped with a three-phase three-wire power source 20. In this case, since the circuit L is composed of three electric wires L1 to L3, the drive power of the connection failure detection circuit 1 is obtained through diodes D1 and D3 from two electric wires (here, the first electric wire L1 and the third electric wire L3) other than the electric wire for detecting the connection failure (here, the second electric wire L2). By configuring in this way, the connection failure detection circuit 1 can be operated satisfactorily. Furthermore, in the case of a three-phase four-wire circuit, AC power is supplied to the connection failure detection circuit 1 through diodes from the three electric wires other than the electric wire for detecting the connection failure.

1: poor connection detection circuit, 2: electrical circuit connection part, 2a: power supply side terminal, 2b: load side terminal, 4: potential difference detection circuit, 5: output circuit, 10: power supply (single-phase AC power supply), 11: load, 20: three-phase power supply (three-phase AC power supply), T1: first transistor, T2: second transistor, T3: third transistor (PNP transistor), r: contact resistance, L: electrical circuit, L1: first wire (electric wire), L2: second wire (electric wire), L3: third wire (electric wire).

Claims (4)

A connection failure detection circuit for detecting a connection failure of an electric path connection portion provided in an electric path,
The electric circuit connection portion is configured by connecting a power supply side terminal to which a power supply side electric circuit is connected and a load side terminal to which a load side electric circuit is connected,
a potential difference detection circuit that detects a potential difference between the power supply terminal and the load terminal when the potential difference occurs;
an output circuit that outputs a connection failure occurrence signal when the potential difference detection circuit detects a potential difference ;
The power source connected to the electric circuit is a three-phase AC power source, and the electric circuit is composed of three or four electric wires;
A connection failure detection circuit, characterized in that the power source of the potential difference detection circuit and the output circuit, which detect a connection failure of the electrical path connection portion of any one of the electric wires, is an AC power source obtained from all other electric wires . 2. The connection failure detection circuit according to claim 1, wherein the potential difference detection circuit is configured as a current mirror circuit using two transistors, first and second NPN transistors, the emitter of the second transistor being connected to the load side terminal and the emitter of the first transistor being connected to the power supply side terminal. 3. The connection failure detection circuit according to claim 2, wherein the current mirror circuit uses a diode instead of the second transistor, and the cathode of the diode is connected to the load side terminal. 4. The connection failure detection circuit according to claim 2, wherein the output circuit has a PNP transistor, the base of which is connected to the collector of the first transistor of the current mirror circuit, and the collector of the PNP transistor is an output section for a connection failure occurrence signal.

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