Connection failure detection circuit

Abstract

To provide a poor connection detection circuit that can satisfactorily detect poor connection even with a small electrical circuit current.SOLUTION: A poor connection detection circuit 1 detects poor connection of an electric circuit connection part 2 provided on an electric circuit L connected with an AC power supply 10. The electrical circuit connection part 2 is formed by connecting a power supply-side terminal 2a connected with a power supply-side electrical circuit and a load-side terminal 2b connected with a load-side electrical circuit. The poor connection detection circuit has: a potential difference detection circuit 4 that detects a potential difference between the power supply-side terminal 2a and the load-side terminal 2b upon generation thereof; a sensitivity setting circuit 3 that causes a voltage for determining the occurrence of poor connection to fluctuate according to an electrical circuit current; and an output circuit 5 that outputs a poor connection occurrence signal when the potential difference detected by the potential difference detection circuit 4 exceeds the voltage set by the sensitivity setting circuit 3.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a connection failure detection circuit that detects connection failure in an electric path connection portion such as a terminal portion. [Background technology]

[0002] In terminals that connect electric wires, conductor bars, etc., connection failures can occur due to loose screws, loose plugs, etc. If such connection failures occur in electrical circuits that carry relatively large currents, such as power distribution equipment and electric power equipment, the increased contact resistance can cause heat generation and deterioration of the equipment, and even arc discharge can occur, which can lead to a fire in the worst case scenario. Therefore, in order to avoid this, a technique for detecting the occurrence of a connection failure is disclosed in, for example, Patent Document 1. In Patent Document 1, a photocoupler is arranged so as to be turned on by a potential difference between terminals, and a connection failure is detected by the turning on of this photocoupler. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2009-145083 A Summary of the Invention [Problem to be solved by the invention]

[0004] However, the technology of the above-mentioned Patent Document 1 is configured to detect a connection failure by the potential difference generated between the terminals, and the potential difference generated varies depending on the magnitude of the electric circuit current, leading to inconsistent judgments. That is, if the electric circuit current is small, the photocoupler does not turn on unless the contact resistance becomes relatively large, whereas if the electric circuit current is large, the photocoupler turns on at a stage when the contact resistance is small, and it is determined that a connection failure has occurred. As a result, the sensitivity was set so that malfunctions would not occur even when a large current was passed through it, making it difficult to increase the detection sensitivity while preventing malfunctions.

[0005] SUMMARY OF THE PRESENT DISCLOSURE In view of the above problems, an object of the present invention is to provide a connection failure detection circuit that can effectively detect a connection failure even when the circuit current is small. [Means for solving the problem]

[0006] In order to solve the above problem, the invention of claim 1 is a poor connection detection circuit that detects a poor connection at an electric circuit connection part provided in an electric circuit, the electric circuit connection part 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 is characterized in having a potential difference detection circuit that detects a potential difference that occurs between the power supply side terminal and the load side terminal, a sensitivity setting circuit that varies a voltage that determines the occurrence of a poor connection in accordance with the electric circuit current, and an output circuit that outputs a poor connection occurrence signal when the potential difference detected by the potential difference detection circuit exceeds the voltage set by the sensitivity setting circuit. With this configuration, the voltage at which the output circuit determines that a poor connection has occurred changes depending on the circuit current, so there is no need to set a fixed high threshold voltage to prevent malfunction. Regardless of whether the circuit current is large or small, poor connection can be detected effectively and malfunction can be prevented. Furthermore, since the determination voltage is not set using an element that requires a constant voltage, such as a diode, even if the potential difference generated in 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.

[0008] Claim 2 The invention is characterized in that, in the configuration described in claim 1, 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 sources of the potential difference detection circuit, sensitivity setting circuit, and output circuit that detect a poor connection at the electric circuit connection portion of any one of the electric wires are AC power sources obtained from all the other electric wires. According to this configuration, the power supply for driving the potential difference detection circuit, the sensitivity setting circuit, and the output circuit does not require a DC power supply, so there is no need to provide a separate power supply circuit.

[0009] Claim3 The invention of claim 1 or 2 In the configuration described above, the sensitivity setting circuit has a resistor for detecting the path current provided in the power supply side electric path of the electric path connection portion, and two transistors, a first transistor and a second transistor of NPN type whose bases are connected to each other, the emitter of the second transistor is connected to the power supply side terminal and the collector outputs voltage information for determining the occurrence of a connection failure, the emitter of the first transistor is connected to the power supply side of the resistor and the collector is open, and when the voltage drop amount of the resistor changes, the collector voltage of the second transistor changes. According to this configuration, the sensitivity setting circuit is configured by two transistors and a resistor, so that the voltage for determining a poor connection can be changed according to the circuit current with a simple circuit configuration.

[0010] Claim 4 The invention is as follows: 3 In the configuration described above, the sensitivity setting circuit is characterized in that a first diode is used instead of the first transistor, the anode of the first diode is connected to the base of the second transistor, and the cathode is connected to the power supply side of the resistor. According to this configuration, the sensitivity setting circuit can be configured with a simple circuit.

[0011] Claim 5 The invention is as follows: 3 or 4 In the configuration described above, the potential difference detection circuit is composed of a current mirror circuit using a third transistor and a fourth transistor of an NPN type, the emitter of the fourth transistor is connected to the load side terminal, and the emitter of the third transistor is connected to the collector of the second transistor of the sensitivity setting circuit. According to this configuration, the potential difference detection circuit is made up of a current mirror circuit, and therefore can be made up of a simple circuit.

[0012] Claim 6 The invention is as follows: 5In the configuration described in the above, the current mirror circuit is characterized in that a second diode is used instead of the fourth transistor, and the cathode of the second diode is connected to the load side terminal. According to this configuration, the potential difference detection circuit can be configured more simply.

[0013] Claim 7 The invention is as follows: 5 or 6 In the configuration described above, the output circuit has a PNP transistor, the base of which is connected to the collector of the third 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. Effect of the Invention

[0014] According to the present invention, the voltage at which the output circuit determines that a poor connection has occurred changes depending on the circuit current, so there is no need to set a fixed high threshold voltage to prevent malfunction. Whether the circuit current is large or small, poor connection can be detected effectively and malfunction can be prevented. Furthermore, since the determination voltage is not set using an element that requires a constant voltage, such as a diode, even if the potential difference generated in 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. [Brief description of the drawings]

[0015] [Figure 1] 1 is a circuit diagram showing an example of a connection failure detection circuit according to the present invention; [Diagram 2] FIG. 13 is a circuit diagram showing another example of the connection failure detection circuit. [Diagram 3] 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

[0016] Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings. Fig. 1 is a circuit diagram showing an example of a connection failure detection circuit for an electric circuit connection portion according to the present invention, and shows a configuration in which a single-phase electric circuit is provided. 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 100V AC commercial power 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.

[0017] The electric path connection portion 2 has a power source side terminal 2a and a load side terminal 2b, and the power source side terminal 2a and the load side terminal 2b are provided on each of the electric wires L1, L2 of the electric path L consisting of two wires. 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 circuit current. The r in Figure 1 indicates this contact resistance. A resistor 7 for detecting a circuit current is attached to the power supply side of the power supply side terminal 2a of the second electric wire L2. Incidentally, the multiple arrows A shown in FIG. 1 indicate the flow of current when the connection failure detection circuit 1 operates, and operates during a half wave in which the power source 10, which is an AC power source, has one polarity.

[0018] The connection failure detection circuit 1 includes a sensitivity setting circuit 3, 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. R2 to R11 are resistor elements that set the current and voltage flowing through each circuit. The electrical path connection portion 2 is specifically a screw-fastened terminal portion, a quick-connect terminal, a plug and outlet connection portion, or the like.

[0019] The sensitivity setting circuit 3 is a circuit that varies the threshold (voltage) for determining a poor connection according to the magnitude of the circuit current supplied to the load 11, and has a first terminal portion 3a to which the voltage of the power supply side terminal 2a of the circuit connection portion 2 is input as a reference voltage, a second terminal portion 3b for varying the threshold value, a third terminal portion 3c for outputting the threshold value, and a fourth terminal portion 3d connected to the power source 10.

[0020] 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 fifth terminal 4a connected to the third terminal 3c and to which a threshold value is input, a sixth terminal 4b to which the voltage of the load side terminal 2b is input, a seventh terminal 4c that outputs a signal (potential difference detection signal), and an eighth terminal 4d connected to the power source 10. When the detected potential difference exceeds the voltage set by the sensitivity setting circuit 3, a signal is output to the output circuit 5.

[0021] The output circuit 5 has a 9th terminal 5a (connected to the 7th terminal 4c) to which the signal output by the potential difference detection circuit 4 is input, a 10th terminal 5b to which a reference voltage is input, an 11th terminal 5c which is an output section that outputs a signal (a poor connection occurrence signal), and a 12th terminal 5d connected to a power source 10.

[0022] The power supply line L4 of this connection failure detection circuit 1 is connected to the first electric wire L1 on the opposite side of the pair with the second electric wire L2 for detecting a connection failure, and is configured to supply AC power to the sensitivity setting circuit 3, the potential difference detection circuit 4, and the output circuit 5. A diode D1 provided in the power supply line L4 is for preventing backflow.

[0023] Each circuit will be described in detail below. The sensitivity setting circuit 3 has two NPN transistors, a first transistor T1 and a second transistor T2, whose bases are connected to each other to form a circuit like a current mirror circuit, and whose bases are connected to a power supply 10 via a resistor element R6. The second transistor T2 has an emitter connected to the power supply side terminal 2a and acts as a reference potential. The collector is connected to the power supply 10 via a resistor element R5 and is also connected to the third terminal 3c. The first transistor T1 has an emitter connected to the power supply side of a resistor 7 having a lower potential than the power supply side terminal 2a, and a voltage adjusted by a resistive element R3 is applied to the first transistor T1, while the collector is open.

[0024] As a result, the second transistor T2 is always on, and a constant current flows between the collector and emitter even in a normal state without a connection failure. The resistor element R2 is connected to the power supply 10, and a current i1 flows through it. When the current in the electric path L increases, the voltage drop in the resistor 7 increases, so that the potential of the second terminal 3b decreases, and the base potential of the second transistor T2 decreases. Thus, the collector current of the second transistor T2 decreases, while the current i1 of the resistor element R2 increases, and the collector voltage of the second transistor T2 rises. That is, the potential of the third terminal 3c rises. In this way, the potential of the third terminal 3c, i.e., the potential of the fifth terminal 4a, fluctuates with the change in the path current. Incidentally, the resistive elements R3 and R4 are for adjusting the sensitivity (threshold value) and are set in advance together with the resistor 7.

[0025] The potential difference detection circuit 4 specifically includes a current mirror circuit composed of a third transistor T3 and a fourth transistor T4. Both transistors T3 and T4 are NPN transistors, for example, monolithic dual type transistors, and are configured to have the same characteristics. The emitter of the third transistor T3 is connected to the fifth terminal 4a, and the collector is connected to the seventh terminal 4c. The emitter of the fourth transistor T4 is connected to the sixth terminal 4b. The collectors of both transistors T3 and T4 are connected to the eighth terminal 4d via resistor elements R7 and R8. It is preferable that the pair of the first transistor T1 and the second transistor T2 is also of a monolithic dual type.

[0026] The output circuit 5 is configured to include a fifth transistor T5 made of a PNP transistor, the base of which is connected to the ninth terminal 5a, the collector of which is connected to the tenth terminal 5b, the emitter of which is connected to the twelfth terminal 5d and the power supply 10. The collector of the fifth transistor T5 is connected to the eleventh terminal 5c. The ninth terminal 5a is connected to the seventh terminal 4c. A resistive element R11 disposed between the tenth terminal 5b and the eleventh terminal 5c acts as a load resistor.

[0027] The operation of the connection failure detection circuit 1 configured in this manner is as follows. In a normal connection state where the contact resistance r in the electric path connection part 2 is zero or very small, the potentials of the power supply side terminal 2a and the load side terminal 2b are approximately equal. At this time, the fourth transistor T4 is in the on state, but due to the presence of the resistive element R2 through which the current i1 flows, the emitter potential of the third transistor T3 is high and the third transistor T3 is in the off state. Therefore, the fifth transistor T5 linked to the third transistor T3 is also in an off state, and no abnormality occurrence signal is output.

[0028] However, when a poor connection occurs in the electric path connection portion 2 and the contact resistance r increases, a voltage drop occurs between the power supply side terminal 2a and the load side terminal 2b. As a result, the potential of the load side terminal 2b rises relative to the power supply side terminal 2a, and the emitter potential of the fourth transistor T4 rises. As a result, the base potential of the third transistor T3 rises, turning the third transistor T3 on. In response to this on action, the fifth transistor T5 also turns on, and a poor connection occurrence signal is output from the eleventh terminal 5c.

[0029] Next, a case where the current in the electric circuit L increases will be described. When the current supplied to the load 11 increases, the voltage drop in the resistor 7 increases, and the potential of the second terminal 3b decreases when the power supply terminal 2a is used as the reference. As a result, the collector current decreases, and the voltage drop in the resistor R5 decreases, so the current i1 in the resistor R2 increases and the voltage drop increases. Thus, the potential of the third terminal 3c increases. This increases the threshold voltage at which the first transistor T1 turns on.

[0030] Conversely, when the current in the electric path L decreases, the voltage drop in the resistor 7 decreases, and the potential of the second terminal 3b increases with respect to the power supply terminal 2a. As a result, the base potential of the second transistor T2 increases, the collector current increases, and the current i1 of the resistor R2 decreases. As a result, the voltage drop in the resistor R2 decreases, and the potential of the third terminal 3c decreases. Thus, the threshold voltage is lowered.

[0031] In this way, the voltage at which the output circuit 5 determines that a poor connection has occurred changes depending on the current in the electrical path L, so there is no need to set a fixed high threshold voltage to prevent malfunction. Whether the current in the electrical path L is large or small, a poor connection can be detected effectively and malfunction can be prevented. And because the judgment voltage is not set using an element that requires a constant voltage, such as a diode, even if the potential difference generated 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, thereby enabling detection of connection failure with high sensitivity. Furthermore, the power supply for driving the potential difference detection circuit 4, the sensitivity setting circuit 3, and the output circuit 5 does not require a DC power supply, so there is no need to provide a separate power supply circuit. Furthermore, since the sensitivity setting circuit 3 is configured by the first transistor T1, the second transistor T2, and the resistor 7, the voltage for determining a poor connection can be changed according to the path current with a simple circuit configuration. In addition, since the potential difference detection circuit 4 is configured with a current mirror circuit, it can be configured with a simple circuit, and since the output circuit is also configured with only the fifth transistor T5, it can be configured with a simple circuit.

[0032] 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 electric wire opposite the electric wire for detecting the connection failure as described above. However, in the case of a single-phase three-wire system, since there are three electric wires, the power supply for the connection failure detection circuit 1 is supplied with AC power via diodes from both of the other two wires other than the electric wire for detecting the connection failure.

[0033] Fig. 2 shows a modified example of the connection failure detection circuit 1. In Fig. 1, the sensitivity setting circuit 3 and the potential difference detection circuit 4 are configured using pairs of two transistors T1, T2 and T3, T4 whose bases are connected to each other, but in Fig. 2, one of the pair of transistors is changed to a diode. Specifically, a first diode D11 is arranged in place of the first transistor T1, and a second diode D12 is arranged in place of the fourth transistor T4. The first diode D11 has an anode connected to the base of the second transistor T2 and a cathode connected to the power supply side of the resistor 7. The second diode D12 has a cathode connected to the load side terminal 2b. In this way, the second transistor T2 and the fourth transistor T4 may both be changed to diodes, and connection failures can be detected with high sensitivity in the same manner as in the above embodiment.The resistor element R12 is an element that replaces the resistor element R7.

[0034] In the above embodiment, a configuration is described in which the poor connection detection circuit 1 is provided in the electrical path connection portion 2 of the second electric wire L2, but a poor connection detection circuit may also be provided in the electrical path connection portion 2 of the first electric wire L1 on the opposite side, in which case the resistor 7 is also installed in the first electric wire L1. 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.

[0035] 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 above-mentioned 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. FIG. 3 shows a circuit diagram of a connection failure detection circuit 1 provided in a three-phase three-wire electric circuit to which a three-phase power source 20 is connected. Since the electric circuit L is composed of three electric wires L1 to L3, the driving power of the connection failure detection circuit 1 is obtained through diodes D1 and D2 from two electric wires (here, the first electric wire L1 and the third electric wire L3) other than the electric wire for detecting a 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 system, 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 a connection failure. [Explanation of symbols]

[0036] 1·· Connection failure detection circuit, 2·· Circuit connection part, 2a·· Power supply side terminal, 2b·· Load side terminal, 3·· Sensitivity setting circuit, 4·· Potential difference detection circuit, 5·· Output circuit, 7·· Resistor, 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, T4·· Fourth transistor, L·· Circuit, L1·· First wire (wire), L2·· Second wire (wire), L3·· Third wire (wire).

Claims

1. 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; A sensitivity setting circuit that varies the voltage for determining whether a connection failure has occurred in accordance with the circuit current; an output circuit that outputs a connection failure occurrence signal when the potential difference detected by the potential difference detection circuit exceeds the voltage set by the sensitivity setting circuit.

2. 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; 2. The connection failure detection circuit according to claim 1, wherein the power source of the potential difference detection circuit, the sensitivity setting circuit, and the output circuit which detect a connection failure of the electric path connection portion of any one of the electric wires is an AC power source obtained from all other electric wires.

3. the sensitivity setting circuit includes a resistor for detecting a path current provided in the power supply side path of the path connection portion, and two transistors, a first transistor and a second transistor, which are NPN type transistors having bases connected to each other; an emitter of the second transistor is connected to the power supply side terminal, and a collector of the second transistor outputs voltage information for determining the occurrence of a connection failure; the emitter of the first transistor is connected to the power supply side of the resistor, and the collector is open; 3. The connection failure detection circuit according to claim 1, wherein a collector voltage of said second transistor changes when a voltage drop amount of said resistor changes.

4. 4. The connection failure detection circuit according to claim 3, wherein the sensitivity setting circuit uses a first diode instead of the first transistor, the anode of the first diode is connected to the base of the second transistor, and the cathode of the first diode is connected to the power supply side of the resistor.

5. 5. The connection failure detection circuit according to claim 3, wherein the potential difference detection circuit is composed of a current mirror circuit using a third transistor and a fourth transistor of an NPN type, the emitter of the fourth transistor being connected to the load side terminal, and the emitter of the third transistor being connected to the collector of the second transistor of the sensitivity setting circuit.

6. 6. The connection failure detection circuit according to claim 5, wherein the current mirror circuit includes a second diode instead of the fourth transistor, and the cathode of the second diode is connected to the load side terminal.

7. 7. The connection failure detection circuit according to claim 5, wherein the output circuit has a PNP transistor, the base of which is connected to the collector of the third 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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