JP2004312337A - Contactless type detection switch - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a contactless type detection switch for sharing the internal circuit and circuit board of 2-wire type and 3-wire type detection switches for which products are separately manufactured conventionally and reducing a product cost. <P>SOLUTION: The contactless type detection switch for detecting the presence / absence of an object, driving an output transistor and controlling a load is provided with a detection circuit 1, a constant voltage circuit 3, a constant current drive circuit 7 for driving the output transistor 3 by the output of the detection circuit, an output control circuit 6 for maintaining a voltage between power supply terminals (a) and b at a prescribed voltage required for the operation of the constant voltage circuit 2, and a switch 8 (selection means) switched corresponding to the specifications of a 2-wire type and a 3-wire type. In the case of using it as the 2-wire type (a), after the switch 8 is set to be ON, the load 4 is connected between the power supply terminals c and b serially to a power source 5. In the case of using it as the 3-wire type (b), after the switch 9 is set to be OFF, the load 4 is connected between the terminals (a) and c and the power source is connected between the terminals (a) and b. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a contactless detection switch for which an oscillation type proximity switch, a photoelectric switch, and the like are implemented.
[0002]
[Prior art]
The contactless detection switch described above has a three-wire system and a two-wire system as its output system, and switch circuits of each output system are shown in FIGS. In each of the drawings, reference numeral 1 denotes a detection circuit (for example, an oscillation coil and an oscillation circuit that constitute a detection unit of an oscillation type proximity switch), 2 denotes a constant voltage circuit that supplies a constant voltage to the detection circuit 1, 3 denotes an output transistor, Is a load (relay), and 5 is a power supply (DC power supply).
Here, the three-wire detection switch shown in FIG. 4 includes three terminals of power supply terminals a (positive side) and b (negative side) and a collector terminal c of the output transistor 3, and the power supply 5 has power supply terminals a and b. And the load 4 is connected between the positive terminal a of the power supply and the collector terminal c of the output transistor 3 (grounded emitter).
[0003]
On the other hand, the two-wire system shown in FIG. 5 has two terminals of a power supply terminal a (positive side) and b (negative side) as terminals of the detection switch, and has a connection between the collector of the output transistor 3 and the power supply terminal a. Is connected to a constant voltage circuit 6 (this constant voltage circuit 6 is for maintaining a voltage for operating the internal circuit when the output transistor 3 is turned on), and the load 4 is connected to the power terminal a. The power supply 5 is connected in series.
The detection operation of the contactless detection switch having the above configuration is well known. When the detection circuit 1 detects an object, the output signal turns on the output transistor 3 and the load (relay) 4 operates.
[0004]
[Problems to be solved by the invention]
Regarding the above-described three-wire type and two-wire type detection switches, the three-wire type detection switch does not decrease the voltage between the terminals a and b even when the output transistor 3 is turned on, so that a stable detection operation is performed. However, three external wirings for connecting the detection switch to the load 4 and the power supply 5 are required.
On the other hand, the two-wire detection switch requires only two external wirings and thus has the advantage of reducing the wiring cost, but has the following restrictions in use. That is, since the load 4 is connected in series with the power supply 5, a leakage current for operating the switch circuit flows to the load 3 when the output of the detection switch is OFF, and a residual current for operating the circuit when the output is ON. The presence of the voltage reduces the voltage applied to the load. For this reason, when the impedance of the load 4 used by connecting to the detection switch is large or when the return voltage is low, the detection operation may malfunction.
[0005]
Due to such a problem, manufacturers currently manufacture products having the same detection performance separately by changing the circuit for the model of the 3-wire detection switch and the model of the 2-wire detection switch. However, it is inefficient to manufacture with different circuit specifications for each model in terms of manufacturing cost and parts and product management, and it is a major challenge to improve this point.
The present invention has been made in view of the above points, and has as its object to reduce the production cost of products and the management cost for parts procurement by sharing the internal circuits and circuit boards of two-wire and three-wire detection switches. It is an object of the present invention to provide a contactless detection switch improved so as to be able to be used.
[0006]
[Means for Solving the Problems]
In order to achieve the above object, according to the present invention, in a contactless detection switch that detects the presence or absence of an object and controls a load by driving an output transistor,
In addition to the detection circuit and a constant voltage circuit that supplies a constant voltage to the detection circuit, a constant current drive circuit that drives an output transistor according to an output signal of the detection circuit, and a voltage between the power supply terminals of the detection switch in an actual use state. An output control circuit for reducing the current of the constant current drive circuit to maintain the voltage between the power supply terminals at a predetermined voltage when the voltage drops below the operating voltage of the constant voltage circuit; and a current input side terminal of the constant current drive circuit. And a selection means for switching the connection destination of the output side terminal according to the specification of the two-wire system or the three-wire system (claim 1), and is specifically configured in the following manner.
[0007]
(1) With the output transistor being an NPN transistor, the current input terminal of the constant current drive circuit is connected to the positive power supply terminal, and the output terminal is connected to the base of the output transistor. Is connected between the current input terminal and the collector of the output transistor (claim 2).
(2) With a PNP transistor as the output transistor, the current input terminal of the constant current drive circuit is connected to the base of the output transistor, and the output terminal is connected to the negative power supply terminal. Is connected between the current output side terminal and the collector of the output transistor (claim 3).
[0008]
(3) As the selection means in the above (1) and (2), a switch, a jumper wire for cutting a conductive path according to selection, or a conductor pattern of a circuit board is used (claim 4).
In the configuration of the above item (2), after closing the switch, which is a two-wire type or three-wire type selection means, or connecting a jumper wire, a switch is provided between the collector terminal of the output transistor and the negative power supply terminal. If a load and a power supply are connected in series, they function as a two-wire detection switch. In addition, if the switch is opened or the jumper wire is cut and the power supply is connected between the positive terminal and the negative terminal of the detection switch, and the load is connected between the power supply and the collector electrode of the output transistor, Functions as a three-wire detection switch.
[0009]
This makes it possible to easily cope with two-wire and three-wire detection switches simply by switching the selection means using the circuit board on which the circuit is mounted as a shared component. In addition, the function of the output control circuit can ensure a stable detection operation even when used as a two-wire system.
[0010]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described based on examples shown in FIGS. In the drawings of each embodiment, members corresponding to those in FIGS. 4 and 5 are denoted by the same reference numerals, and description thereof will be omitted.
[Example 1]
FIGS. 1A and 1B are circuit block diagrams of an embodiment corresponding to claim 2 of the present invention using an NPN transistor (common emitter) as the output transistor 3. FIG. This embodiment is different from the conventional circuits shown in FIGS. 4 and 5 in that, in addition to the detection circuit 1, the constant voltage circuit 2, and the output transistor 3, an output control circuit 6, a constant current drive circuit 7, and 2 A switch 8 for switching according to the selection of the wire system or the three-wire system is additionally provided, and a circuit board equipped with these circuits is used as a common component to correspond to a two-wire system or a three-wire detection switch as described later. Like that.
[0011]
Here, the output control circuit 6 is connected between the positive terminal a and the negative terminal b, and the voltage between the power terminals a and b in the actual use state of the detection switch as described later in detail. Is lower than the operating voltage of the constant voltage circuit 2, the current of the constant current drive circuit 7 is reduced to maintain the voltage between the power supply terminals a and b at a predetermined voltage. The constant current drive circuit 7 has a current input terminal d and an output terminal e, and the input terminal d is connected to the positive power supply terminal a of the detection switch, and the output terminal e is connected to the base of the output transistor 3. Connected to electrodes. The circuit configurations of the output control circuit 6 and the constant current drive circuit 7 will be described later with reference to FIG. Further, a switch 8 which is a two-wire type or three-wire type selection means is connected between the collector of the output transistor 3 and the current input terminal d of the constant current drive circuit 7.
[0012]
In the above circuit configuration, when the detection switch is used as a two-wire system, as shown in FIG. 1A, the switch 8 is set to ON, and the power supply terminal a on the positive side is opened. In this state, the load 4 and the DC power supply 5 are connected in series between the collector terminal c of the output transistor 3 and the negative power supply terminal b.
In this connection state, the output control circuit 6 has a threshold voltage set to a voltage slightly higher than the operating voltage of the constant voltage circuit 2 as described later, and the voltage between the power supply terminals a and b during the detection operation. Is lowered to the threshold voltage, the constant current drive circuit 7 is controlled to lower the base current of the output transistor 3 so that the voltage between the power supply terminals a and b does not drop below the operating voltage of the constant voltage circuit 2. . As a result, a stable detection operation can be ensured as a two-wire system.
[0013]
On the other hand, when using as a three-wire system, the switch 8 is set to OFF as shown in FIG. 1B, and in this state, the power supply 5 is connected between the power supply terminals a and b of the detection switch, and the load 4 Is connected between the power supply terminal a and the collector terminal c of the output transistor 3. In this three-wire connection state, even if the output transistor 3 is turned on by the output signal of the detection circuit 1, the voltage between the power supply terminals a and b does not decrease, so that a stable detection operation can be obtained.
Here, a specific circuit example of the output control circuit 6 and the constant current drive circuit 7 is shown in FIG. That is, the output control circuit 6 includes a bandgap circuit 9 set to conduct when the voltage between the power supply terminals a and b is higher than the operating voltage of the constant voltage circuit 2, and an output terminal f of the bandgap circuit 9. A transistor 10 connected between the power supply terminal a and the positive power supply terminal a, a transistor 11 connected between the terminal g of the bandgap circuit 9 and the negative power supply terminal b, and a base connected to the detection circuit 1, A current mirror circuit is formed with the transistor 10 and connected to the constant current driving circuit 7. When the voltage between the power supply terminals a and b becomes lower than the operating voltage of the constant voltage circuit 2, the constant current driving circuit 7 A transistor 12 that reduces the current to
[0014]
Further, the bandgap circuit 9 connects the transistors 9a, 9b, 9c with the collector resistors 9d, 9e of the transistors 9a, 9b and the emitter resistor 9f of the transistor 9b as shown in FIG. , G are adjusted.
On the other hand, the constant current drive circuit 7 includes a constant current circuit 13 connected between the collector of the transistor 12 and the negative power supply terminal, transistors 14, 15 and an emitter resistor 16 of the transistor 14, and the transistor 14 has a base connected to its base. Is connected to the collector of the transistor 12, the transistor 15 has the collector connected to the base of the transistor 14, and the base and the emitter are connected in parallel with the resistor 16. Here, the transistor 14 amplifies the current from the transistor 12 of the output control circuit 6 and supplies the base current to the output transistor 3 connected to the current output terminal e of the constant current drive circuit 7. Is smaller, the current flowing through the output transistor 3 is also smaller. The emitter current of the transistor 14 is limited by the transistor 15 and the resistor 16 so as not to become larger than a certain value.
[0015]
In order to use the circuit of FIG. 2 as a two-wire or three-wire detection switch, the switch 8 must be set to ON or OFF in accordance with the selection of the two-wire or three-wire specification, and then, as shown in FIG. The load 4 and the power source 5 are connected to the power terminals a and b and the collector terminal c of the output transistor 3 as described in 1 (a) and (b).
[Example 2]
Next, a circuit block according to a third embodiment of the present invention using a PNP transistor as the output transistor 3 is shown in FIGS. In this embodiment, the output control circuit 6 and the constant current drive circuit 7 are provided in the internal circuit of the detection switch as in the first embodiment, and the constant current drive circuit 7 outputs the current input terminal d. The current output terminal e is connected to the negative power terminal b on the base of the transistor 3, and the emitter of the output transistor 3 is connected to the positive power terminal a. The switch 8 is connected between the collector terminal c of the output transistor 3 and the current output terminal e of the constant current drive circuit 7.
[0016]
When used as a two-wire detection switch, as shown in FIG. 3A, the switch 8 is set to ON, and the negative power supply terminal b is opened (open). The load 5 and the DC power supply 5 are connected in series between the collector terminal c and the positive power supply terminal a.
When the switch is used as a three-wire detection switch, the switch 8 is set to OFF as shown in FIG. 3B, and in this state, the power supply 5 is connected between the power terminals a and b of the detection switch. The load 4 is connected between the power supply terminal b and the collector terminal c of the output transistor 3. The operations of the output control circuit 6 and the constant current drive circuit 7 in this embodiment are the same as those described with reference to FIG.
[0017]
In the illustrated embodiment, the switch 8 is used as a two-wire type or three-wire type selection means. Instead of the switch 8, a jumper wire or a circuit pattern is provided on a circuit board, and the three-wire type is used. When used, it is possible to cut a jumper wire or a circuit pattern by means such as laser irradiation, and the switch 8 is not required, thereby realizing low cost.
[0018]
【The invention's effect】
As described above, according to the present invention, in a contactless detection switch that detects the presence or absence of an object and controls a load by driving an output transistor, a detection circuit, and a constant voltage that supplies a constant voltage to the detection circuit. In addition to the circuit, a constant current drive circuit that drives an output transistor by an output signal of the detection circuit, and the voltage between the power supply terminals of the detection switch in an actual use state falls below the operating voltage of the constant voltage circuit. An output control circuit for reducing the current of the constant current drive circuit to maintain the voltage between the power supply terminals at a predetermined voltage; and connecting a current input terminal and an output terminal of the constant current drive circuit to a two-wire system and a three-wire system. By having a selection means that switches according to the specifications of the formula,
Conventionally, two-wire and three-wire detection switches, which were separately manufactured with different circuit specifications, can be easily changed by switching the selection means by using a circuit board manufactured by mounting the same circuit as a shared component. Compatible with 2-wire and 3-wire systems. As a result, the cost of the product can be significantly reduced, and the management cost for parts procurement can be reduced.
[Brief description of the drawings]
FIG. 1 is a block circuit diagram of a contactless detection switch according to a first embodiment of the present invention, wherein (a) and (b) show states of use as a two-wire detection switch and a three-wire detection switch, respectively; FIG. 2 is a diagram showing a detailed circuit configuration of an output control circuit and a constant current drive circuit in FIG. 1. FIG. 3 is a block circuit diagram of a contactless detection switch corresponding to a second embodiment of the present invention. (B) is a diagram showing a state of use as a two-wire type and three-wire type detection switch, respectively. [FIG. 4] A block circuit diagram of a conventional three-wire type non-contact type detection switch. [FIG. 5] Block circuit diagram of contactless detection switch [Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Detection circuit 2 Constant voltage circuit 3 Output transistor 4 Load 5 Power supply 6 Output control circuit 7 Constant current drive circuit 8 Switch (two-wire type, three-wire type selection means)
a Positive power supply terminal b Negative power supply terminal c Collector terminal of output transistor d Current input side terminal of constant current drive circuit e Current output side terminal of constant current drive circuit

Claims (4)

A contactless detection switch that detects the presence or absence of an object and controls a load by driving an output transistor.The detection circuit includes a detection circuit, a constant voltage circuit that supplies a constant voltage to the detection circuit, and an output signal output from the detection circuit. A constant current drive circuit for driving the transistor; and a power supply terminal for reducing the current of the constant current drive circuit when the voltage between the power supply terminals of the detection switch drops below the operating voltage of the constant voltage circuit in actual use of the detection switch. An output control circuit for maintaining the voltage between the output terminals at a predetermined voltage, and a selection means for switching a connection destination of a current input side or an output side terminal of the constant current drive circuit in accordance with a two-wire system or a three-wire system. Non-contact type detection switch characterized by the following. 2. The detection switch according to claim 1, wherein the output transistor is an NPN transistor, the current input terminal of the constant current drive circuit is connected to the positive power supply terminal, and the output terminal is connected to the base of the output transistor. A contactless detection switch, characterized in that selection means for switching according to the specification of the three-wire system is connected between the current input terminal and the collector of the output transistor. 2. The detection switch according to claim 1, wherein the output transistor is a PNP transistor, the current input terminal of the constant current drive circuit is connected to the base of the output transistor, and the output terminal is connected to the negative power supply terminal. A non-contact detection switch characterized in that selection means for switching according to the specification of the three-wire system is connected between the current output terminal and the collector of the output transistor. 4. The contactless detection switch according to claim 2, wherein the selection means is a switch, a jumper wire for disconnecting a conductive path in accordance with selection of a specification, or a conductor pattern of a circuit board.

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