JP2005012923A - Protective device against overcurrent - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To materialize a protective device against overcurrents which compulsively switches off a switching element without affected by the heat generation of an overcurrent breaking element. <P>SOLUTION: This protective device against overcurrents for an output circuit for switching on or switching off the power supply to load via the switching element has the above overcurrent breaking element connected in series to the above switching element, and an overcurrent detecting circuit connected in series to the above switching element. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention is applied to external devices (hereinafter referred to as loads) such as lamps and motors via switching elements that are binary-controlled by an arithmetic processing unit of a programmable controller (hereinafter referred to as PLC) used for controlling machine tools and production lines. The present invention relates to an overcurrent protection device in an output circuit that performs on / off control of the power supply connection.
[0002]
[Prior art]
An overcurrent protection device using an overcurrent cutoff element connected in series to a switching element is disclosed in Patent Literature.
[0003]
[Patent Literature]
Japanese Patent Application Laid-Open No. 6-244414 “Semiconductor Device Protection Circuit and Semiconductor Device Having the Same”
[0004]
FIG. 3 is a basic configuration diagram of on / off power source connection control to a load by a PLC processing unit and a switching element. Reference numeral 1 denotes an arithmetic processing unit that forms the main part of the PLC. Reference numeral 2 denotes a switching element realized by a transistor or FET, which is binary-controlled by a signal S from the arithmetic processing unit 1 program.
[0005]
Reference numerals 3 and 4 denote output terminals of the PLC, to which the output electrodes (collector, emitter) of the switching element 2 are connected. Reference numeral 5 denotes a load exemplified by a lamp, and 6 a power source exemplified by a battery. These are connected in series and connected to the output terminals 3 and 4. A region (A) on the side of the arithmetic processing unit 1 and the switching element 2 with the output terminals 3 and 4 as a boundary is inside the PLC, and a region (B) on the side of the load 5 and the power source 6 is an external device.
[0006]
In such a basic configuration, when the switching element 2 in the PLC is turned on when the terminal of the load 5 is short-circuited due to a connection error, a large current flows through the switching element 2 and the switching element 2 or It is conceivable that the output terminals 3 and 4 burn out. In that case, repair work is required, which takes time and effort.
[0007]
FIG. 4 is a basic configuration diagram of on / off power source connection control to a load by a switching element having such a protection device against overcurrent in the PLC. A protection circuit 7 is inserted in the middle of the switching element 2 circuit. Specifically, the following circuit or electronic component can be used for this protection circuit.
[0008]
(I) Use a fuse. It cuts off when a large current flows, preventing damage to other parts. If it blows, replace the fuse.
(Ii) An overcurrent cutoff element that cuts off a current exceeding a certain level is used. This element has a characteristic that when a large current flows, the resistance value increases and the current does not flow.
(Iii) Using an overcurrent detection circuit that detects that a current exceeding a certain level flows, the processor 1 is notified of the overcurrent by the abnormal signal AR. When the arithmetic processing unit 1 receives this notification, it forcibly controls the switching element 2 to be turned off. Further, the occurrence of abnormality is recorded in the record through the arithmetic processing unit 1 or notified to other devices.
[0009]
[Problems to be solved by the invention]
(1) The use of the fuse in the above item (i) requires manual replacement after operation, which makes maintenance extremely complicated.
(2) In the use of the overcurrent cutoff element of (ii), heat is generated when the element resistance value increases. Since the device continues to generate heat while voltage is applied to it, peripheral components and printed circuit boards may be damaged by high heat when operating for a long time.
(3) In the use of the overcurrent detection circuit of (iii), since it passes through the arithmetic processing unit 1 from when the increase in the current value is detected until the switching element 2 is turned off and the output current is cut off, generally time is required. Take it. During this time, the switching element 2 may be destroyed.
[0010]
The object of the present invention is to force the switching element without being affected by the heat generated by the overcurrent cutoff element by combining the use of the overcurrent cutoff element of (ii) and the use of the overcurrent detection circuit of (iii). It is to realize an overcurrent protection device that is controlled to be turned off.
[0011]
[Means for Solving the Problems]
The configuration of the present invention for achieving such an object is as follows.
(1) In an overcurrent protection device for an output circuit that controls on / off of power supply to a load via a switching element,
An overcurrent interrupting element connected in series to the switching element;
An overcurrent detection circuit connected in series to the switching element;
An overcurrent protection device comprising:
[0012]
(2) When the breakdown current of the switching element is Ia, the cutoff current of the overcurrent cutoff element is Ib, and the operating current of the overcurrent detection circuit is Ic,
The overcurrent protection device according to (1), wherein Ia>Ib> Ic is selected.
[0013]
(3) The overcurrent according to (1) or (2), wherein the overcurrent detection circuit notifies an abnormal signal to an arithmetic processing unit that controls the switching element when the operating current Ic is detected. Protective device.
[0014]
(4) The overcurrent protection device according to any one of (1) to (3), wherein the arithmetic processing unit forcibly controls the switching element to be turned off when the abnormal signal is received. .
[0015]
(5) The overcurrent interrupting element is a thermistor element having a characteristic that its resistance value suddenly changes when the element temperature due to overcurrent exceeds a predetermined value. An overcurrent protection device according to claim 1.
[0016]
(6) A plurality of switching elements (breakdown current: Ia) selectively binary-controlled by the arithmetic processing unit at the other ends of a plurality of loads having the same rating (rated current: Id) and having one end connected in common ) Are connected to each other, and the other ends of these switching elements are connected in common via an overcurrent cutoff element (cutoff current: Ib), and this common connection point serves as an overcurrent detection circuit (operation current: Ic) and a power source Connected to the common connection point of the load via
The overcurrent protection device according to any one of (1) to (5), wherein Ia> Ib and Ic> Id are selected.
[0017]
(7) The overcurrent protection device according to any one of (1) to (6), wherein the arithmetic processing unit is a programmable controller.
[0018]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a circuit configuration diagram showing an example of an overcurrent protection device to which the present invention is applied. The same components as those described in the conventional device in FIG.
[0019]
A feature of the present invention resides in a configuration in which an overcurrent cutoff element and an overcurrent detection circuit are connected in series to a switching element in an output circuit that controls on / off of power supply to a load via the switching element.
[0020]
In FIG. 1, 10 is an overcurrent interruption element, 11 is an overcurrent detection circuit, and these are connected in series to the switching element 2 inside the PLC. When the breakdown current of the switching element 2 is Ia, the cutoff current of the overcurrent cutoff element 10 is Ib, and the operating current of the overcurrent detection circuit 11 is Ic,
Ia>Ib> Ic is selected.
[0021]
The operation when an overcurrent occurs will be described. The overcurrent detection circuit 11 notifies the arithmetic processing device 1 that controls the switching element 2 when the operating current Ic is detected, and the arithmetic processing device 1 receives the abnormal signal AR. Force off control.
[0022]
In the time until the switching device 2 is forcibly turned off after the arithmetic processing device 1 detects the abnormal signal AR, if the current is going to increase more than the cut-off current Ib of the overcurrent cut-off device 10, Due to the characteristics of the current interrupting element 10, the current to the switching element 2 is suppressed to the interrupting current Ib.
[0023]
The operation time of the overcurrent interruption element 10 is a short period until the arithmetic processing device 1 receives the abnormal signal AR and forcibly controls the switching element 2 to be turned off, and there is almost no influence of heat generation on the surroundings.
[0024]
The overcurrent interrupting element 10 is realized by a polymer PTC (Positive Temperature Coefficient) thermistor element having a characteristic that its resistance value changes suddenly when the element temperature due to overcurrent exceeds a predetermined value. Such a thermistor element is commercially available as a polyswitch (trade name of Raychem), and its electrical characteristics are Internet URL (http://www.raychem.co.jp/polyswitch/product/). It has been published.
[0025]
FIG. 5 is an element temperature and element resistance characteristic diagram of the polymer PTC thermistor element. The temperature increases rapidly from 1 Ω to 10 kΩ between 125 degrees and 150 degrees. If the temperature rise due to overcurrent disappears, the element resistance has a reversible characteristic that returns to the original low resistance state, so that replacement such as food is unnecessary.
[0026]
FIG. 2 is a circuit configuration diagram showing another embodiment of the present invention. In a PLC, when a plurality of loads are on / off controlled, the negative voltage side is often shared to reduce the number of connectors. In this example, four loads are controlled on and off by four minus output terminals with one minus output terminal.
[0027]
Reference numerals 51 to 55 denote a plurality of loads having the same rating, one end of which is commonly connected (P point). The other ends of these loads are connected to one ends of a plurality of switching elements 21 to 24 that are selectively binary-controlled by signals S1 to S4 of the arithmetic processing unit 1.
[0028]
The other ends of these switching elements 21 to 24 are connected in common (point Q) via overcurrent cutoff elements 101 to 104, respectively, and this common connection point is connected to the negative output terminal via the common overcurrent detection circuit 11. 4 is connected. A power source 6 is connected between the output terminal 4 and a common connection point P of the load.
[0029]
In such a connection relationship, the breakdown current of the switching elements 21 to 24 is Ia, and the cutoff current of the overcurrent cutoff elements 101 to 104 is Ib. When the operating current of the overcurrent detection circuit 11 is Ic and the rated currents of the switching elements 21 to 24 are Id,
Select Ia> Ib and Ic> Id.
[0030]
According to such selection of the current level, if the current of any of the switching elements 21 to 24 that are selected and turned on exceeds the rated value Id and the operating current of the overcurrent detection circuit 11 becomes equal to or greater than Ic, The abnormal signal AR is notified to the arithmetic processing unit 1, and the switching elements 21 to 24 are forcibly turned off.
[0031]
That is, in the circuit shown in FIG. 2, the overcurrent detection circuit 11 does not determine which of the loads 51 to 54 is abnormal, and even if an abnormality occurs only in the overcurrent cutoff element 101, The switching elements 21 to 24 included in the blocking elements 101 to 104 are forcibly turned off.
[0032]
In addition, if the current further increases after the processing device 1 detects the abnormal signal AR and until the switching elements 21 to 24 are forcibly turned off, the overcurrent inserted in series in each switching element 21 to 24 The interrupting elements 101 to 104 limit the current to an interrupting current Ib that is smaller than the breakdown current Ia.
[0033]
The feature of this embodiment is that a single overcurrent detection circuit 11 is provided in common with the resource saving of the output terminal. In general, it is relatively easy to individually incorporate an overcurrent interrupting element into a switching element such as an output transistor or FET, but the overcurrent detection circuit has a complicated and expensive mechanism compared to other fuses or current interrupting elements. There are many cases. Therefore, the configuration in which one overcurrent detection circuit 11 is provided in common can reduce the number of overcurrent detection circuits, thereby simplifying the overall configuration and reducing the cost.
[0034]
【The invention's effect】
As is clear from the above description, the following effects can be expected according to the present invention.
(1) There is no need to bother manual operations like fuse replacement.
(2) There is little possibility of causing secondary destruction due to heat generation as in the case where the overcurrent interrupting element is used alone.
(3) By using the overcurrent detection circuit, it is possible to easily record the occurrence of abnormality in the record or notify other devices.
(4) Since a thermistor element can be used as an overcurrent interrupting element, it can be made maintenance-free, so that it can be easily incorporated into the PLC, and can contribute to improving the reliability and cost of the PLC.
[Brief description of the drawings]
FIG. 1 is a circuit configuration diagram showing an example of an overcurrent protection device to which the present invention is applied.
FIG. 2 is a circuit configuration diagram showing another embodiment of an overcurrent protection device to which the present invention is applied.
FIG. 3 is a basic configuration diagram of on / off power source connection control to a load by a PLC processing unit and a switching element;
FIG. 4 is a basic configuration diagram of on / off power source connection control to a load by a conventional switching element having a protection device against overcurrent in a PLC.
FIG. 5 shows element temperature and element resistance characteristics of a polymer-based PTC thermistor element.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Arithmetic processing apparatus 2 Switching element 3, 4 Output terminal 5 Load 6 Power supply 10 Overcurrent interruption element 11 Overcurrent detection circuit

Claims (7)

In an overcurrent protection device for an output circuit that controls on / off of power supply to a load via a switching element,
An overcurrent interrupting element connected in series to the switching element;
An overcurrent detection circuit connected in series to the switching element;
An overcurrent protection device comprising: When the breakdown current of the switching element is Ia, the cutoff current of the overcurrent cutoff element is Ib, and the operating current of the overcurrent detection circuit is Ic,
2. The overcurrent protection device according to claim 1, wherein Ia>Ib> Ic is selected. 3. The overcurrent protection device according to claim 1, wherein the overcurrent detection circuit notifies an abnormal signal to an arithmetic processing unit that controls the switching element when the operating current Ic is detected. The overcurrent protection device according to any one of claims 1 to 3, wherein the arithmetic processing unit forcibly controls the switching element to be turned off when the abnormal signal is received. 5. The overcurrent interrupting element according to claim 1, wherein the overcurrent interrupting element is a thermistor element having a characteristic that a resistance value thereof changes suddenly when an element temperature due to overcurrent exceeds a predetermined value. Current protection device. One end of a plurality of switching elements (breakdown current: Ia) selectively binary controlled by the arithmetic processing unit at the other end of each of a plurality of loads having the same rating (rated current: Id) and having one end connected in common The other ends of these switching elements are connected in common via an overcurrent cutoff element (cutoff current: Ib), and this common connection point is connected to the above-mentioned via an overcurrent detection circuit (operating current: Ic) and a power source. Connected to the common connection point of the load,
6. The overcurrent protection device according to claim 1, wherein Ia> Ib and Ic> Id are selected. The overcurrent protection device according to claim 1, wherein the arithmetic processing device is a programmable controller.

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