JPS6156685B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a ground fault detection device equipped with an optimal current detection device.

Conventionally, ground fault detection devices (earth leakage circuit breakers) have been composed of mechanical elements, but due to their poor characteristics, electronic devices have been promoted for several years. Computerization has made the zero-phase current transformer, which converts ground fault current into voltage, smaller and has greater cost advantages. FIG. 1 shows a schematic configuration of an electronic circuit of a conventional ground fault detection device.

In FIG. 1, 1 is an electric circuit, 2 is a circuit breaker, 3 is a zero-phase current transformer, 4 is a differential amplifier, 5 is a time delay circuit, and 6
is a Schmitts circuit, 7 is a Zener diode for stabilizing the power supply voltage, 8 is a thyristor, 9 is a cutoff coil, 10 is a voltage drop that determines the potential of the power supply E6 applied to the differential amplifier 4, time delay circuit 5, and Schmitts circuit ₆ . 11 is a smoothing capacitor, 1
2 is a rectifier diode, and 13 is an AC power source. The outputs E ₁ and E ₂ of the zero-phase current transformer 3 are given to the inverting and non-inverting inputs of the differential amplifier 4, and the outputs of the differential amplifier 4 are
E ₃ is given to the input of the time delay circuit 5, and the time delay circuit 5
The output E ₄ of is given to the input of the Schmitt circuit 6, and the output E ₅ of the Schmitt circuit 6 is applied to the thyristor 8.
The structure is such that the circuit breaker 2 is activated by driving the circuit breaker 2. The zero-phase current transformer 3 is a type of transformer that generates a voltage on its secondary side when an imbalance occurs in the electric line 1. The shutoff operation in this configuration will be explained below.

When a ground fault occurs, the outputs E ₁ and E ₂ of zero-phase current transformer 3
A voltage is generated at , the outputs E ₁ and E ₂ are amplified by the differential amplifier 4, the output E ₃ is delayed by the delay circuit 5, and the output E ₄ of the delay circuit 5 is sent to the Schmitts circuit 6.
The waveform is shaped by the output _E5 , which drives the thyristor 8, and current flows through the cutoff coil 9 to cut off the electric path 1.

However, this method has a problem that makes it extremely difficult to use. That is when thyristor 8 is not operating,
When operating, the power supply current is approximately equal to the gate current of thyristor 8, that is, from power supply E ₆ to power supply E ₇
In other words, when the thyristor 8 is in operation, the voltage drop across the resistor 10 is larger as the gate current flows than when the thyristor 8 is not in operation. ,
Even when the gate current flows, it is necessary to keep the power supply E ₆ at a normal potential. Therefore, in the first case, when the thyristor 8 is not operating, the gate current of the thyristor 8 is transferred to the Zener diode 7.
is kept flowing at all times, so that even if the gate current flows during operation of the thyristor 8, the potential of the power source _E6 is maintained at a normal potential. Otherwise, when the Schmitts circuit 6 is operating, the voltage of the power supply E ₆ will drop due to the voltage drop across the resistor 10, and the desired power supply voltage will no longer be applied to the Schmitts circuit 6, so the voltage of its output E ₅ will drop. , thyristor 8
cannot be turned on. Therefore, it is necessary to allow a current as large as the gate current to flow through the voltage drop resistor 10, and in order to drop the voltage from an AC voltage of 100V or 200V, a resistor 10 that can withstand extremely large power is required. The size of the ground fault detection device is large, making it impossible to downsize the ground fault detection device.
In addition, when making a ground fault detection device (earth leakage breaker) that can be used for both 100V and 200V, the resistance value of resistor 10 depends on the 100V application, and since it allows a large amount of current to flow, it is used for the 200V application. In this case, the power consumption of the resistor 10 becomes large, so a resistor 10 that can withstand even higher power than a 100V-only resistor is required, and the shape becomes larger.

This invention has been made in consideration of the above points, and consists in using a Schmitt circuit as a waveform shaping circuit that operates as a latch circuit composed of, for example, an NPN transistor and a PNP transistor, thereby ensuring the operation of the thyristor 8. In addition to minimizing power consumption and miniaturization of electronic circuits,
The aim is to make it applicable to both 100V and 200V electronic circuits. An example is shown in FIG.

In Figure 2, E ₄ is the input, and 61 and 62 are
NPN transistor, 63, 64 are PNP transistors, 65, 66, 67 are resistors, E ₅ is output,
E ₆ and E ₇ are power supplies, and power supply E ₇ has the lowest potential.
In FIG. 2, NPN transistors 61, 62,
Configure a thyristor with PNP transistor 63,
It is amplified by the PNP transistor 64 to generate a high potential at the output _E5 . That is, when a potential equal to or higher than the base-emitter on-voltage threshold value of the NPN transistor 61 is applied to the input _E4 , the NPN transistor 61 turns on, pulling the base current of the PNP transistor 63, and the current becomes h in the PNP transistor 63. The current is multiplied by _FE and becomes the base current of the NPN transistor 62, and the current is multiplied by h _FE and becomes the base current of the NPN transistor 62.
This becomes the base current of the transistor 63. That is, positive feedback occurs between the NPN transistor 62 and the PNP transistor 63, and the operation is similar to that of a thyristor.

In the circuit shown in FIG. 2, the transistors 61, 62, The loop gain of the thyristor 63 can be appropriately controlled. By taking such considerations, it is possible to construct a thyristor that is resistant to surges and noise.

FIG. 3 shows an embodiment of a ground fault detection device in which the waveform shaping circuit 6' shown in FIG. 2 is used instead of the Schmitt circuit 6 shown in FIG. 1.

The embodiment of FIG. 3 differs from the embodiment of FIG. 1 in that there is no Zener diode 7 and that the Schmitt circuit 6 is
The difference is that the waveform shaping circuit 6' shown in the figure is used. Now, when no ground fault has occurred, no current flows through the waveform shaping circuit 6', and at that time, the voltage of the resistor 10 is adjusted so that the voltage of the power source _E6 is high enough to drive the differential amplifier 4 and the delay circuit 5. Choose a resistance value. When a ground fault occurs, a potential is generated at the outputs E ₁ and E ₂ of the zero-phase current transformer 3, and the outputs E ₁ and E ₂ are amplified by the differential amplifier 4, and the output E ₃ is sent to the time delay circuit. 5, and the output of the time delay circuit 5 is at a predetermined potential (V in the case of FIG.
_BE ), the waveform shaping circuit 6' operates, and since its output impedance is low (the resistance value of the resistor 66 in FIG. 2 is kept low), the voltage of the power supply E ₆ decreases, and the differential amplifier 4 , the current flowing through the time delay circuit 5 decreases, and that much current flows through the thyristor 8.
The gate current will be .

In addition, the power supply E ₆ of the waveform shaping circuit 6' is approximately 2V _BE +
Until Vsat (Vsat is the saturation voltage of about 1.6V),
In order to generate a potential at the output, the gate current of the thyristor 8 can continue to flow.

Therefore, in this device, when a ground fault occurs, that is, when controlling the thyristor 8, the decrease in the current flowing through the differential amplifier circuit 4 and the time delay circuit 5 is almost equal to the gate current of the thyristor 8. Therefore, when the thyristor 8 is not operating, as shown in FIG.
It is no longer necessary to keep the power supply current approximately equal to the gate current flowing, and the power consumption in the device can be reduced to a minimum, especially the power consumption in the resistor 10. 100V,
It can also be used for 200V.
Moreover, the waveform shaping circuit 6' has a power supply E ₆ of approximately 2V _BE +
A potential is generated at the output until it reaches Dsat, and even if the input signal to the amplifier 4 disappears, the gate current of the thyristor 8 continues to flow, so even if the current E ₆ is half-wave rectified by the AC power supply 13, Thyristor 8 can be operated reliably even if a ground fault occurs at any point during wave rectification (in order for the thyristor to maintain a conductive state,
It is necessary to flow a hold current between the anode and the cathode, and it is necessary to apply a predetermined potential between the anode and the cathode, and even if a trigger pulse is applied to the gate only when the potential is below the predetermined potential, the thyristor will not conduct. ), the number of parts can be reduced, and even if the power source E ₆ is a full-wave rectifier of the AC power source 13, even if a ground fault occurs when the power source E ₆ is below a predetermined potential, the thyristor can be used at least until the potential exceeds the predetermined potential. Since the gate current of 8 is flowing, the thyristor 8 can be operated reliably. As described above, the present invention, as a waveform shaping circuit, continues to maintain a conductive state even when the input signal of the amplifier disappears when it becomes conductive beyond a threshold value,
Furthermore, since we used a latch circuit that continues to maintain conduction even when the supply voltage of the waveform shaping circuit decreases, the current in the amplifier and delay circuit is reduced when the waveform shaping circuit is conductive, and this decreased current is transferred to the thyristor. Can be supplied as gate current. Therefore, it is possible to provide a ground fault detection device that reduces the power consumed by the electronic circuit of the ground fault detection device to a minimum, has good characteristics, and can operate the thyristor reliably. And, due to the reduction in power consumption,
Can be used for both 100V and 200V (AC power supply voltage range:
The electronic circuit section of the ground fault detection device (80 to 242V) can be easily configured and its size can be reduced, which is a huge benefit for both the manufacturer and the consumer. . Incidentally, with the ground fault detection device having the configuration shown in FIG. 3, we were able to complete an integrated circuit whose electronic circuit section consumed a current of 300 μA. In this case, a ground fault detection device that can be used for both 100V and 200V has been realized, and the power consumption of the voltage drop resistor has been significantly reduced compared to conventional methods.

[Brief explanation of the drawing]

Fig. 1 is a circuit diagram showing a conventional ground fault detection device, Fig. 2 is a circuit diagram showing an example of a waveform shaping circuit used in the present invention, and Fig. 3 is a circuit diagram showing an example of a waveform shaping circuit used in the present invention. FIG. 2 is a circuit diagram showing an example. In the figure, 1 is an electric circuit, 2 is a circuit breaker, 3 is a zero-phase current transformer, 4 is a differential amplifier, 5 is a time delay circuit, 6' is a waveform shaping circuit, 8 is a thyristor, 9 is a cutoff coil, 1
0 is a resistor, 11 is a smoothing capacitor, 12 is a rectifier diode, and 13 is an AC power source. Note that the same reference numerals in the figures indicate the same or corresponding parts.

Claims (1)

[Claims] 1. An amplifier that amplifies a signal according to the current to be detected;
A time delay circuit that delays the output, a waveform shaping circuit that receives the output, and a ground fault detection device that causes a current to flow through the gate of a thyristor by the output to turn on the thyristor and operate a circuit breaker. The waveform shaping circuit reduces the current of the amplifier and the time delay circuit when conductive, and supplies this reduced amount as the gate current of the thyristor, so that when conductive exceeds a threshold value, the input signal of the amplifier disappears. A ground fault detection device characterized by using a latch circuit which continues to maintain a conductive state even when the voltage supplied to the waveform shaping circuit decreases. 2 The waveform shaping circuit takes the base of the first NPN transistor as its input, connects its collector to the base of the first PNP transistor, and connects its collector to the base of the second PNP transistor.
Connect to the base of the NPN transistor and connect the second
The collector of the NPN transistor is the first NPN
a collector of the transistor, the emitter of which is commonly connected to the emitter of the first NPN transistor; the emitter of the first PNP transistor is connected to the base of a second PNP transistor; the collector of the second PNP transistor is connected to the collector of the transistor; The earth fault detection device according to claim 1, which is on the output side. 3 The waveform shaping circuit receives the base of the first NPN transistor as input, connects its collector to the base of the first PNP transistor, and connects its collector to the base of the first PNP transistor.
The emitter of the first PNP transistor is connected to the base of a second PNP transistor, and the collector of the second PNP transistor is the output side. Ground fault detection device.