JPH0447543B2 - - Google Patents

Description

[Detailed description of the invention] (b) Field of invention This invention relates to improvements in overcurrent protection devices.

(b) Prior art and its problems Conventionally, various sensors (detection devices) have a detection section for detecting a certain state and a drive circuit section for driving a display device or the like in response to the output of the detection section. It consists of: The detection section and the drive circuit section have been coupled by a contact such as a relay, or by an electronic circuit using a switching element such as a transistor.

However, in a device that connects the detection part and the drive circuit part through contacts, if an overcurrent flows through the drive circuit part, the contacts will weld and the contacts cannot be used unless they are replaced, causing the overcurrent to flow. There was a problem that it had to be replaced every time. On the other hand, those connected by electronic circuits have the problem that they malfunction due to various noises, and that when an overcurrent flows, the electronic switching elements are destroyed, resulting in subsequent malfunctions.

(C) Purpose of the Invention This invention was made to solve the problems of the conventional ones as described above, and even if an overcurrent flows, it does not transmit the overcurrent to the other circuit part, and prevents contact welding. It is an object of the present invention to provide an overcurrent protection device that can be used normally even after an overcurrent flows without causing destruction of electronic switching elements, and that does not malfunction due to noise or the like.

(d) Structure and effect of the invention The overcurrent protection device of the present invention includes a first circuit section including a detection section for detecting a certain state, and a first circuit section provided in association with the first circuit section and including a detection section of the detection section. a second circuit section that operates based on the output; a first optical coupling element for transmitting the output of the first circuit section to the second circuit section by optical coupling; a second optical coupling element for detecting that an overcurrent has flowed and transmitting an overcurrent detection output to the first circuit section by optical coupling; a thyristor that operates in response to overcurrent detection by the second photocoupler and disables the first photocoupler; The overcurrent is detected by the optical coupling element, and in response to this overcurrent detection, the thyristor operates to disable the first optical coupling element to prevent overcurrent from flowing.

According to the present invention, even if an overcurrent flows once, it can be used again after that, is highly safe, and can operate stably and reliably without malfunctioning due to noise or the like.

(E) Description of Embodiment FIG. 1 is a circuit diagram of an overcurrent protection device according to an embodiment of the present invention. In the figure, the overcurrent protection device of this embodiment includes a first circuit section 10, a second circuit section 20, a first optical coupling element 30, a second optical coupling element 40, and an example of a disabling means. thyristor 5
Consists of 1.

Next, a more specific circuit configuration and its operation will be explained. First, in the normal case, that is, in the second
The operation when no overcurrent flows through the circuit section 20 will be explained.

The first circuit section 10 includes a detection (sensor) 11. This detection unit 11 is a proximity switch if the detection target to which the present invention is applied is metal or the like. In this case, the detection unit 11 detects the coil 11a.
and proximity switch main circuit (hereinafter referred to as main circuit) 11b
including. The coil 11a changes its inductance in response to the proximity of metal or the like, and provides the changed output to the main circuit 11b. Power is supplied from the power supply circuit 12 to the main circuit 11b. Main circuit 11b
includes an oscillation circuit that changes its oscillation state in response to changes in the inductance of the coil 11a, and a level discrimination circuit that derives a metal detection output when the output of the oscillation circuit reaches a predetermined state. This main circuit 11
The detection output b (for example, high level) is applied via a diode 13 to the base end of a transistor 14, which is an example of a switching element. The emitter of transistor 14 is grounded. transistor 1
A resistor 1 is connected between the collector of 4 and the power supply circuit 12.
5 and a photocoupler 30 as an example of the first optical coupling element.
A light emitting element (e.g. light emitting diode) 3 included in
A series circuit with 1 is connected. Then, the transistor 14 becomes conductive in response to the detection output of the main circuit 11b, and the light emitting diode (hereinafter abbreviated as LED)
31 (ie, supplies current). depending on
The LED 31 emits light and transmits the output of the detection section 11 to a phototransistor 32, which is an example of a light receiving element.
In response, the phototransistor 32 becomes conductive, so that the current from the battery 21 included in the second circuit section 20 flows from the relay coil 22 to the light receiving element 32 to the resistor 2.
It flows along the route 3-21. Therefore, the relay coil 22 is excited and its contacts (not shown) are operated to perform a predetermined operation in response to the output of the detection section 11.

Here, the noteworthy feature is that the first circuit section 10
Since the and second circuit section 20 are optically coupled by the photocoupler 30, it is possible to prevent malfunctions due to noise etc. and to operate stably, compared to a switch using an electronic switch.

By the way, if no overcurrent flows in the closed circuit of the second circuit section 20, the terminal voltage of the resistor 23 is relatively low and the light emitting element (for example, LED) included in the photocoupler, which is an example of the second optical coupling element 40, is The voltage does not reach the voltage that causes 41 to emit light.

Next, the operation when an overcurrent flows through the second circuit section 20 will be explained. In this case, the terminal voltage of the resistor 23 increases in proportion to the overcurrent. When the terminal voltage of the resistor 23 reaches a predetermined voltage that correlates with the flow of an overcurrent that may destroy the phototransistor 32 or burn out the relay coil 22, for example,
The LED 41 emits light and provides a light signal indicating that an overcurrent has flowed through the second circuit section 20 to the phototransistor 42, which is an example of a light receiving element. In response, phototransistor 42 becomes conductive. Therefore, the output current of the power supply circuit 12 flows through the resistor 16, the phototransistor 42, and the resistor 17, and a predetermined voltage is generated at the emitter terminal of the phototransistor 42. Since this voltage is applied as a gate signal to the thyristor 51, the thyristor 51 becomes conductive.

Therefore, if an overcurrent flows through the second circuit 20, the detected output current of the main circuit 11b is grounded via the thyristor 51, so even if a nearby object is detected, the transistor 14 will not be rendered conductive. The light emitting display of the LED 31 is disabled. As a result, once an overcurrent flows through the second circuit section 20, the conductive state of the thyristor 51 is maintained, and this state is maintained unless the output of the power supply circuit 12 is stopped. In this case, a staff member or the like turns off a switch (not shown) that stops power supply to the power supply circuit 12 to restore the power supply.

With the configuration of this embodiment, even if an overcurrent flows through the second circuit section 20, the overcurrent detection output is optically coupled to the first circuit section using the photocoupler 40, and the transistor 14 and ED3 Since the circuit is disabled, it is possible to prevent overcurrent from directly flowing into the first circuit 10, and it is possible to prevent damage to the elements of each part of the first circuit section 10 and prevent electric leakage, thereby increasing safety. It has the advantage of being

FIG. 2 is a circuit diagram of another embodiment of the overcurrent protection device of the present invention. This embodiment differs from the circuit shown in FIG. 1 in that it is constructed as follows. That is, the power supply circuit 12 is configured as a constant voltage circuit, and the disabling means is configured to include the transistor 52 for disabling the power supply circuit 12. More specifically, the power supply circuit 12 includes a control transistor 12a, a Zener diode 12b, a resistor 12c, and a capacitor 12d. Then, if it is normal, the capacitor 12a
is charged by a battery (external power source) E, and the Zener diode 12b turns on or off the control transistor 12a to keep the output voltage constant.
In this state, transistor 52 remains turned off.

However, when an overcurrent flows through the second circuit section 20, the phototransistor 42 becomes conductive in the same manner as in the operation shown in FIG. 1 described above. At this time, the emitter terminal of the phototransistor 42 and the resistors 18 and 17
Since the potential at the connection point of transistor 5 becomes high,
2 and thyristor 51 become conductive. In response, the transistor 14 is turned off regardless of the presence or absence of the output from the main circuit 11b, disabling the light emitting display of the LED 31. Also, a. Since the capacitor 12d is discharged in response to the conduction of the transistor 52,
The base potential of transistor 12a decreases, and control transistor 12a is turned off.

Since the LED 31 does not emit light, the phototransistor 32 remains turned off. Therefore, overcurrent does not flow to the second circuit section 20. After that, when the phototransistor 42 is turned off because the LED does not emit light,
Thyristor 51 is turned off, and transistor 52 is also turned off. Then, the power supply circuit 12
Power is supplied to the first circuit 10 from. In this state, when the main circuit 11b outputs a detection output to a nearby object, the transistor 14 becomes conductive and the LED
31 displays light emission. However, when an overcurrent is detected after a certain period of time after the phototransistor 32 has been turned on, the power supply circuit 12 is turned on again in the same way as in the above-described invention.
becomes immobilized.

In other words, in this embodiment, even if an overcurrent flows through the second circuit section 20, the output of the detection section 11 is intermittently transmitted to the second circuit 20, and the output is intermittently transmitted unless the cause of the overcurrent flow is resolved. The optical coupling state or cutoff state of both circuits is repeated repeatedly. Therefore, this embodiment has the advantage that even if an overcurrent once flows through the second circuit section 20, normal operation can be automatically restored once the cause of the overcurrent flow is eliminated.

FIG. 3 is a circuit diagram of another embodiment of the overcurrent protection device of the present invention. This embodiment differs from FIG. 1 in that the second optical coupling element 40' is constructed of an LED 41, which is an example of a light emitting element, and a photothyristor 43, which is another example of a light receiving element. This photothyristor 43 functions as a light receiving element when there is an optical signal indicating an overcurrent detection output, and functions similarly to the disabling means, that is, the thyristor 51 shown in FIG.

Next, the operation of this embodiment will be briefly explained. The operation when no overcurrent flows through the second circuit section 20 is the same as that shown in FIG. 1. On the other hand, when an overcurrent flows, the LED 41 emits light. Since this optical signal is given as a gate signal to the photothyristor 43, the photothyristor 43 becomes conductive.
Therefore, when an overcurrent flows through the second circuit section 20, even if the main circuit 11b derives a nearby object detection output, the photothyristor 43 shunts its output current to the ground side, so that the transistor 14 and
LED31 can be disabled.

The configuration of this embodiment has the advantage that the number of parts can be reduced compared to the configuration shown in FIG. 1, and the circuit configuration can be greatly simplified.

FIG. 4 is a circuit diagram of still another embodiment of the overcurrent protection device of the present invention. This embodiment differs from FIG. 3 in that the anode of the photothyristor 43 is connected to the output end of the power supply circuit 12.
In this embodiment, when an overcurrent in the second circuit section 20 is detected, the photothyristor 43
By shunting the output current of 2 to the ground side,
The current supplied to the LED 31 is cut off.

Note that the optical coupling device is not limited to one in which a light-emitting element and a light-receiving element are housed in one case like a photocoupler, but can be structurally separate as long as they are optically coupled. It's okay to be.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram of an overcurrent protection device according to an embodiment of the present invention. 2, 3 and 4 are circuit diagrams of other embodiments of the overcurrent protection device. 10...first circuit section, 11...detection section, 12
...Power supply circuit, 13...Diode, 14...Transistor, 20...Second circuit section, 30...First photocoupler (photocoupler), 40, 40'...
...Second optical coupling element, 51, 52, 43...immobilization means.

Claims (1)

[Claims] 1. A first circuit section including a detection section that detects a certain state, and a second circuit that is provided in association with the first circuit section and operates based on the output of the detection section. and the output of the first circuit section is optically coupled to the second circuit section.
detecting that an overcurrent has flowed through the first optical coupling element for transmitting the signal to the circuit section and the second circuit section;
a second optical coupling element for transmitting an overcurrent detection output to the first circuit section by optical coupling; and overcurrent detection by the second optical coupling element provided in relation to the first circuit section. an overcurrent protection device, comprising: a thyristor that operates in response to and disables the first optical coupling element. 2. The first optical coupling element is a first photocoupler including a first light emitting element and a first light receiving element, and the first circuit section is configured to connect the first optical coupling element to the first photocoupler in response to the output of the detection section. The overcurrent protection device according to claim 1, comprising a first switching element that energizes one light emitting element. 3. The second optical coupling element is provided in association with a second light emitting element that emits light in response to an overcurrent flowing through the second circuit section, and a second light emitting element that emits light in response to an overcurrent flowing through the second circuit section. The light emitting state of the second light emitting element is detected and the first light emitting element is detected.
3. The overcurrent protection device according to claim 2, wherein the overcurrent protection device is a second photocoupler including a second photodetector that transmits the signal to the circuit section. 4 The first circuit section includes a power supply circuit for supplying power to the first light emitting element, and a power supply circuit for supplying power from the power supply circuit to the first light emitting element in response to an output of the second photocoupler. 4. The overcurrent protection device according to claim 3, further comprising a second switching element for disabling the supply of the overcurrent. 5 The first circuit section includes a power supply circuit for supplying power to the first light emitting element, and the thyristor disables supply of power from the power supply circuit to the first light emitting element. The overcurrent protection device according to claim 3, which is an element that causes 6. The second optical coupling element includes a third light emitting element that emits light in response to an overcurrent in the second circuit section, and a third light emitting element that is provided in association with the first circuit section. 2. The overcurrent protection device according to claim 2, wherein the thyristor that disables the first optical coupling element is shared by the photothyristor. . 7. The overcurrent protection device according to claim 6, wherein the photothyristor is connected to a path that bypasses the input current of the first switching element when the photothyristor is conductive. 8. The first circuit section includes a power supply circuit that supplies power to the first light emitting element, and the photothyristor is configured to conduct current supplied from the power supply circuit to the first light emitting element by conducting the photothyristor. The overcurrent protection device according to claim 6, which is connected to a bypass path.