JPH11122088A - Dc input circuit and programmable controller - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a DC input circuit, capable of making the external input equipment of different polarities to coexist and simultaneously using them, even without the use of a changeover switch or the like. SOLUTION: This DC input circuit 3 is provided with a terminal part 5, composed of plural input terminals 8a-8c and a pair of common terminals 6 and 7 connected to both poles of a DC power source 4 and plural current detection circuits. The current detection circuits are provided with current limiting elements 31a-31c and current detection elements 34a-34c, detect a current on the side of the external input equipment 11 and 21 inputted through the terminal part 5 and output in to the side of a controller 2. Between the terminal part 5 and the respective current detection circuits, a push-pull power source circuit 26 is provided. The power source circuit 26 generates a voltage which is equivalent to a value corresponding to almost the middle of the voltage values of a pair of the common terminals 6 and 7 and respectively supplies the intermediate voltage power source output via the respective current limit elements 31a-31c to the respective current detection elements 34a-34c.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a DC input circuit including a DC power supply for external input devices, a terminal section, and a plurality of current detection circuits, and a programmable controller including the same.

[0002]

2. Description of the Related Art Conventionally, there has been known a programmable controller including an external input device, a control device, and a DC input circuit interposed between the external input device and the control device. The external input device is for detecting an operation state of an actuator or the like, and includes, for example, a proximity switch. There are two types of proximity switches of this type: those using an NPN transistor on the output side and those using a PNP transistor. FIG. 8A shows the former conventional example, and FIG. 8B shows the latter conventional example. For convenience, only one proximity switch is shown.

In a programmable controller 81 shown in FIG. 8A, a proximity switch 82 has an internal main circuit 83.
And an NPN transistor 84. The plus side of the DC power supply 85 constituting the DC input circuit is connected to the internal main circuit 8.
3 and a common terminal 87 of the terminal section 86. Therefore, the common terminal 87 is on the plus side. The reason why such a common terminal 87 is provided is to reduce the overall wiring. The negative side of the DC power supply 85 is connected to the second terminal of the internal main circuit 83 and the emitter terminal of the NPN transistor 84. The collector terminal of the NPN transistor 84 is connected to one of the plurality of input terminals 88a, 88b, 88c at the terminal 86. The anode terminal of the light emitting diode 90 constituting the unidirectional photocoupler 89 as a current detecting element is connected to the common terminal 87 side. On the other hand, a cathode terminal of the light emitting diode 90 is connected to an input terminal 88 a via a current limiting resistor 91. The unidirectional photocouplers 89 are provided by the number of input terminals 88a to 88c. In the thus configured programmable controller 81,
When the proximity switch 82 is turned on, a current flows from the common terminal 87 to the input terminal 88a via the light emitting diode 90, and the light emitting diode 90 emits light. Then, the phototransistor 9 paired with the light emitting diode 90
2 is short-circuited and turned on, and a current is output to the control device 93 side.

In a programmable controller 95 shown in FIG. 8B, a proximity switch 94 using a PNP transistor 96 instead of the NPN transistor 84 is used. The programmable controller 95 has the same configuration as the programmable controller 81, except that the connection method of the DC power supply 85 is different and the connection method of the unidirectional photocoupler 89 is different. Therefore, when the proximity switch 94 is turned on, a current flows from the input terminal 88a to the common terminal 87 via the light emitting diode 90, and the light emitting diode 90 emits light. Then, the phototransistor 92 paired with the light emitting diode 90 is short-circuited and turned on, so that a current is output to the control device 93 side. In this programmable controller 95, the common terminal 8
7 is on the minus side.

[0005]

FIG. 8 (a)
Since the programmable controller 81 is exclusively used for the NPN type proximity switch 82, the PNP type proximity switch 94 cannot be connected. Similarly, FIG.
Since the programmable controller 95 shown in FIG. 2B is dedicated to the PNP type proximity switch 94, the NPN type proximity switch 82 cannot be connected.

Therefore, as a configuration for solving the above-mentioned problem, for example, as shown in FIGS. 8C and 8D, a programmable controller 101 for both types is used.
Can be considered. This programmable controller 101
In this case, a bidirectional photocoupler 102 including a phototransistor 92 and a pair of light emitting diodes 90 is used instead of the unidirectional photocoupler 89. Therefore, in this configuration, the NPN type proximity switch 82 is used.
Not only can be connected (see FIG. 8 (c)), but also a PNP type proximity switch 94 can be connected (see FIG. 8 (d)).

[0007] A similar technique is disclosed, for example, in Japanese Utility Model Laid-Open No. 62-40602 and Japanese Utility Model Laid-Open No. 59-58804. However, in the above-described programmable controller 101 for both types, the common terminal 87 is fixed to one of the positive and negative polarities. Therefore, the proximity switches 84 and 92 having different polarities cannot be used simultaneously in the same unit in a mixed state.

Further, Japanese Patent Application Laid-Open No. 7-36368 discloses that
There is disclosed an apparatus having a bidirectional photocoupler and capable of switching the polarity of a common terminal by a changeover switch or the like. However, even with such a configuration,
Proximity switches with different polarities cannot be used simultaneously in a mixed state. Further, since a changeover switch is required, it has been difficult to say that the programmable controller structure is convenient for preventing an increase in size and improving reliability.

[0009] The present invention has been made in view of the above circumstances, and an object thereof is to provide a semiconductor device without using a changeover switch or the like.
An object of the present invention is to provide a DC input circuit and a programmable controller in which external input devices having different polarities can be mixed and used simultaneously.

[0010]

In order to solve the above-mentioned problems, the invention according to claim 1 comprises a plurality of input terminals and a pair of common terminals to which both poles of a DC power supply for an external input device are connected. A DC input including a terminal portion, and a plurality of current detection circuits including a current limiting element and a current detection element, and detecting a current input to the external input device through the terminal portion and outputting the detected current to the control device side. In the circuit, a push-pull power supply for generating a voltage corresponding to a substantially intermediate value between the voltage values of the pair of common terminals and supplying the intermediate voltage power supply output to each of the current detection elements via each of the current limiting elements The gist is a DC input circuit characterized by including a circuit.

According to a second aspect of the present invention, in the first aspect, the push-pull power supply circuit comprises: a pair of reference voltage generating elements connected in series between the pair of common terminals; An operational amplifier connected to a connection intermediate point of the voltage generating element and having an output side connected to each of the current limiting elements is provided.

According to a third aspect of the present invention, in the second aspect, the push-pull power supply circuit further includes a push-pull type current buffer circuit on the output side of the operational amplifier.

According to a fourth aspect of the present invention, in the first aspect, the push-pull power supply circuit includes a pair of reference voltage generating elements connected in series between the pair of common terminals, and a first transistor. A first emitter-follower circuit, a second emitter-follower circuit including a second transistor having a different polarity from the first transistor, and base terminals of the two transistors are connected to a connection intermediate point of the two reference voltage generating elements. Connected,
The emitter terminals of the two transistors are both connected to the respective current detection elements via the respective current limiting elements, and the collector terminals of the two transistors are connected to the pair of common terminals. I decided to prepare.

According to a fifth aspect of the present invention, in any one of the first to fourth aspects, the push-pull power supply circuit includes a rectifier circuit connected to the pair of common terminals.

[0015] The invention according to claim 6 is the invention according to claims 1 to 5.
The gist is a programmable controller including the DC input circuit according to any one of the above. Hereinafter, the “action” of the present invention will be described.

The operation of the first aspect of the present invention is as follows. External input device having a specific polarity (for convenience,
External input device. ) Is connected to any common terminal and any input terminal. In addition, an external input device having a polarity different from that of the external input device (for convenience, a second external input device) is also connected to any one of the common terminals and any one of the input terminals. However, the connection to the DC power supply is reversed.

For example, it is assumed that the first and second external input devices are connected simultaneously with the first common terminal side as a positive pole and the second common terminal side as a negative pole.
In this case, when only the first external input device is turned on, the positive pole of the DC power supply, the first common terminal, the push-pull power supply circuit, the current limiting element, the input side of the current detection element,
DC current flows through a path of the input terminal, the first external input device, and the negative pole of the DC power supply. Then, the current detection element operates and a current flows to the output side, so that the control device detects that the first external input device is in the ON state. When the first external input device is turned off,
No DC current flows through the path. Therefore, no current flows to the output side of the current detection element, and the control device detects that the first external input device is in the off state.

In the above case, when only the second external input device is turned on, the plus pole of the DC power supply, the second external input device, the input terminal, the input side of the current detection element, the current limiting element, the push-pull power supply DC current flows through the circuit, the second common terminal, and the negative pole of the DC power supply. Then, the current detection element operates to cause a current to flow to the output side, so that the control device detects that the second external input device is in the ON state. When the second external input device is turned off, no DC current flows through the path. Therefore, no current flows to the output side of the current detection element, and the control device detects that the second external input device is in the off state.

In the case where the first and second external input devices are simultaneously turned on and substantially the same current flows in each of them, the positive pole of the DC power supply, the second external input device, the input terminal, the current detection DC current through the path of the input side of the element, the current limiting element, the output side of the push-pull power supply circuit, the current limiting element, the input side of the current detecting element, the input terminal, the first external input device and the negative pole of the DC power supply Flows. As a result, the control device detects that both the first and second external input devices are on. At this time, since the output side of the push-pull power supply circuit has a voltage corresponding to a substantially intermediate value between the voltage values of the pair of common terminals, the outflow / inflow of current to the push-pull power supply circuit hardly occurs. That is, at this time, the push-pull power supply circuit is maintained in a non-operating state.

That is, according to the configuration of the present invention, external input devices having different polarities can be mixed and used simultaneously. Also, in this case, since there is no need to use a changeover switch, it is possible to prevent an increase in size and improve reliability.

According to the second aspect of the present invention, the connection intermediate point between the pair of reference voltage generating elements is a voltage corresponding to a substantially intermediate value of the voltage value between the pair of common terminals, that is, about half of the power supply voltage. Is a voltage corresponding to the value of The operational amplifier performs an arithmetic operation using the voltage value at the connection intermediate point as a reference voltage, thereby generating a push-pull output at the output side substantially equal to the voltage value at the connection intermediate point. Further, since the push-pull output obtained by the arithmetic operation is relatively accurate, the operation can be stabilized.

According to the third aspect of the invention, since the current of the output of the operational amplifier is amplified by the push-pull type current buffer circuit, the current supplied to each current limiting element also increases accordingly. . Therefore, a structure is possible in which a larger number of external input devices can be connected.

According to the fourth aspect of the present invention, the connection intermediate point of the pair of reference voltage generating elements is a voltage corresponding to a substantially intermediate value of the voltage value between the pair of common terminals, that is, about half of the power supply voltage. Is a voltage corresponding to the value of Therefore, a voltage corresponding to about a half of the power supply voltage is applied as an input voltage to each base terminal of the transistors constituting the pair of emitter follower circuits. In this case, both the emitter follower circuits output a push-pull output substantially equal to the voltage value at the connection intermediate point to the emitter terminal side. In such a case, the output voltage value on the emitter terminal side is suppressed within twice the potential difference between the base terminal and the emitter terminal. At that time, both emitter follower circuits are maintained in a non-operating state. Further, with such a push-pull power supply circuit, the structure can be simplified and the cost can be reduced.

According to the fifth aspect of the present invention, DC currents from the first and second external input devices are supplied to the push-pull power supply circuit after their polarities are made uniform by the rectifier circuit. Therefore, the push-pull power supply circuit can be made operable regardless of the polarity of the DC power supply.

According to the sixth aspect of the present invention, an extremely excellent programmable controller having the above-described effects can be provided.

[0026]

BEST MODE FOR CARRYING OUT THE INVENTION

[First Embodiment] Hereinafter, a programmable controller according to a first embodiment of the present invention will be described in detail with reference to FIG.

The programmable controller of the first embodiment is a dual-purpose type, and includes proximity switches 11 and 21 as external input devices, a control device 2, a DC input circuit 3 interposed therebetween, and a DC power supply 4. Consists of

A first proximity switch 11 as a first external connection device includes an internal main circuit 12 and an NPN transistor 1.
3 is provided. The proximity switch 11 has three terminals 14
a, 14b and 14c. The base terminal of the NPN transistor 13 is connected to the internal main circuit 12. Therefore, when the base current flows when the internal main circuit 12 operates, the NPN transistor 13 is turned on. That is, as a result of short-circuiting between the emitter terminal and the collector terminal of the NPN transistor 13, a current flows between the second and third terminals 14b and 14c to which they are connected.

A second proximity switch 21 as a second external connection device includes an internal main circuit 22 and a PNP transistor 2
3 is provided. The proximity switch 21 has three terminals 24
a, 24b and 24c. The base terminal of a PNP transistor 23 is connected to the internal main circuit 22. Therefore, the base current flows when the internal main circuit 22 operates, and the PNP transistor 23 is turned on. That is, as a result of short-circuiting between the emitter terminal and the collector terminal of the PNP transistor 23, a current flows between the second and third terminals 24b and 24c to which they are connected.

The terminal section 5 constituting the DC input circuit 3 includes a first common terminal 6, a second common terminal 7, and an input terminal 8
a, 8b, and 8c, which are installed on or outside the board on which the DC input circuit 3 is assembled. The first common terminal 6 is one, and is connected to the positive electrode which is one electrode of the DC power supply 4 (24 V in the present embodiment). There is also one second common terminal 7, which is connected to the other electrode of the DC power supply 4, which is the negative side. There are a plurality of input terminals 8a, 8b, 8c, and the number of input terminals 8a, 8b, 8c is greater than or equal to the number of proximity switches 11, 21 to be connected. In the present embodiment, the number is set to three for convenience of explanation. Of course, the number is three or more (4,
5, 6, 7, 8, 9, 10,...). The DC power supply 4 does not necessarily have to be a component of the DC input circuit 3 as shown in FIG. 1, and may be, for example, outside a board on which the DC input circuit 3 is assembled. Of course, the DC power supply 4 may be a component of the DC input circuit 3, and may be provided on a board on which the DC input circuit 3 is assembled.

The first common terminal 6 is connected to both terminals 14a and 24c of the proximity switches 11 and 21. The second common terminal 7 includes the proximity switches 11 and
One terminal 14c, 24a is connected together. The input terminal 8a is connected to the terminal 14b of the proximity switch 11, and the input terminal 8b is connected to the terminal 24b of the proximity switch 21. The remaining one input terminal 8c is in a free state in which nothing is connected.

The DC input circuit 3 of this embodiment has the same number (ie, three) of current detection circuits as the input terminals 8a, 8b, 8c. Each of the current detection circuits has the same configuration.

The current detecting circuit constituting the DC input circuit 3 includes photocouplers 34a and 34 as current detecting elements.
b, 34c. The photocouplers 34a, 3
4b and 34c are bidirectional, each comprising a phototransistor 35 and a pair of light emitting diodes 36 and 37. These light emitting diodes 36 and 37 are connected in opposite directions. The bidirectional photocoupler 3
In 4a, 34b and 34c, the input side has a pair of light emitting diodes 36 and 37, and the output side has the phototransistor 35.

When a current is supplied to the input side of the photocouplers 34a, 34b, 34c, one of the light emitting diodes 36, 37 regardless of the direction of the current.
, And the light emitting diodes 36, 37 emit light. Then, the collector terminal and the emitter terminal of the phototransistor 35 forming a pair with the light emitting diodes 36 and 37 are short-circuited and turned on. As a result, a current is output to the control device 2 side. Also, the photocoupler 34
When no current is supplied to the input sides of a, 34b and 34c, none of the light emitting diodes 36 and 37 emits light. Accordingly, the phototransistor 35 paired with the light emitting diodes 36 and 37 is turned off, and the control device 2
No current is output to the side. That is, the photocouplers 34 a, 34 b, and 34 c play a role of detecting the current of the proximity switches 11 and 21 that are input via the terminal unit 5 and outputting the current to the control device 2.

The current detecting circuit constituting the DC input circuit 3 includes current limiting resistors 31a and 31 as current limiting elements.
b, 31c and an operation stabilizing resistor 38. Current limiting resistors 31a, 31b, 31c and operation stabilizing resistor 38
Are connected in series with each other. The input side of the photocoupler 34a, that is, the cathode terminal and the anode terminal of the light emitting diodes 36 and 37 are connected between the input terminal 8a and the intermediate connection point of the pair of the current limiting resistor 31a and the operation stabilizing resistor 38. Have been. Similarly, the input side of the photocoupler 34b is connected between the intermediate connection point of another pair of resistors 31b and 38 and the input terminal 8b. The input side of the photocoupler 34c is connected to another pair of resistors 3
It is connected between the intermediate connection point of 1c and 38 and the input terminal 8c.

The operation stabilizing resistor 38 is connected to the light emitting diode 3.
6, 37 are connected in parallel between the cathode terminal and the anode terminal. Such a resistor 38 serves to bypass and flow an extra current that should not be supplied between the cathode terminal and the anode terminal. Therefore, when the proximity switches 11 and 21 are turned off, the transistor 1
The light-emitting diodes 36 and 37 are prevented from shining thinly due to the leakage currents of the light-emitting diodes 3 and 23, and the operation of the DC input circuit 3 is stabilized.

The current detection circuit constituting the DC input circuit 3 further includes a light emitting diode current limiting resistor 39, a pull-up resistor 40 and a light emitting diode 41 on the output side of the photocouplers 34a, 34b and 34c. Resistance 3
9 and 40 and the light emitting diode 41 constitute an input display unit. One terminal of the resistor 39 is a phototransistor 3
5, the other end is connected to the light emitting diode 4
1 cathode terminal. Light emitting diode 4
Reference numeral 1 denotes a display means, and each anode terminal is connected to the plus side 42 of an internal power supply (not shown). Also,
A pull-up resistor 40 is connected in parallel to the resistor 39 and the light emitting diode 41 connected in series.
The emitter terminal of each phototransistor 35 is connected to the negative side 43 of the internal power supply.

When the phototransistor 35 is not operating and is in the off state, no current flows from the plus side 42 to the minus side 43 of the internal power supply. Therefore, the light emitting diode 41 is also turned off. When the phototransistor 35 operates and is in the ON state, the collector terminal and the emitter terminal are short-circuited, and the positive side 4 of the internal power supply passes through the light emitting diode 41, the resistor 39 and the phototransistor 35.
Current flows from 2 to the minus side 43. At this time, the light emitting diode 41 emits light, and the operator can recognize that there is an input from the proximity switches 11 and 21.

In the DC input circuit 3, a push-pull power supply circuit 26 is provided between the terminal section 5 and each current detection circuit. The push-pull power supply circuit 26 of the present embodiment includes a first reference voltage generating resistor 27 as a first reference voltage generating element, a second reference voltage generating resistor 28 as a second reference voltage generating element, And an operational amplifier IC29 as an amplifier.

The first and second reference voltage generating resistors 27 and 2
8 is connected in series between the pair of common terminals 6 and 7, and forms one voltage dividing circuit. The resistance values of the two resistors 27 and 28 are set to the same value. First
The reference voltage generating resistor 27 is connected to the first common terminal 6 side, and the second reference voltage generating resistor 28 is connected to the second common terminal 7 side. The connection midpoint between the two resistors 27 and 28 is a voltage corresponding to a substantially intermediate value between the voltage values of the pair of common terminals 6 and 7, that is, a voltage corresponding to approximately half of the power supply voltage (12V in this case). . Hereinafter, this voltage is referred to as an intermediate voltage.

The operational amplifier IC 29 has a non-inverting input terminal,
It has an inverting input terminal, an output terminal, a positive power supply terminal and a negative power supply terminal. The operational amplifier IC 29 has a push-pull amplifier (not shown) therein. The positive power supply terminal of the operational amplifier IC 29 is the first common terminal 6
And the negative side power supply terminal is connected to the second common terminal 7.
It is connected to the. The non-inverting output terminal of the operational amplifier IC 29 is connected to a connection intermediate point between the resistors 27 and 28, and the inverting input terminal is connected to the output terminal. Therefore, a negative feedback circuit in which the voltage on the output terminal side is applied to the inverting input terminal is configured. The output terminal is connected to each current limiting resistor 31a,
The respective photocouplers 34a, 34 are connected via 31b, 31c.
b, 34c are connected to the input side.

The operational amplifier IC 29 uses the voltage value (ie, 12 V) at the connection intermediate point as a reference voltage, and compares the reference voltage and the output voltage input to the inverting input terminal so that the potential difference becomes zero. Perform arithmetic operation. The operational amplifier IC29 generates a push-pull output substantially equal to the value of the intermediate voltage at its output terminal side by a so-called negative feedback action.

Next, the operation of the programmable controller configured as described above will be described. When only the first proximity switch 11 is turned on, a short circuit occurs between the collector terminal and the emitter terminal of the NPN transistor 13.
As a result, the positive pole of the DC power supply 4, the first common terminal 6, the push-pull power supply circuit 26, the current limiting resistor 31a,
Light emitting diode 36 of photocoupler 34a, input terminal 8
a, a DC current flows through a path of the NPN transistor 13 and the negative pole of the DC power supply 4. The push-pull power supply circuit 26 enters an operating state, and applies an intermediate voltage of 12 V to a connection point between its output terminal and the current limiting resistor 31a.
At this time, the light-emitting diode 36 of the photocoupler 34a emits light, and the phototransistor 35 paired with the light-emitting diode 36 is short-circuited. As a result of the operation of the photocoupler 34a, a current flows to its output side, and the first proximity switch 11
Is detected on the control device 2 side. The input display light-emitting diode 41 corresponding to the photocoupler 34a also emits light, and the first proximity switch 11
The operator can visually recognize that there is an input from the side.

When the first proximity switch 11 is turned off, no DC current flows through the path. Therefore, no current flows to the output side of the photocoupler 34a, and the control device 2 detects that the first proximity switch 11 is in the off state. Of course, the light emitting diode 41 for input display does not emit light. Further, since a pair of reference voltage generating resistors 27 and 28 are connected in series between the common terminals 6 and 7, a very large current does not flow between the common terminals 6 and 7 at this time.

When only the second proximity switch 21 is turned on, the collector terminal and the emitter terminal of the PNP transistor 23 are short-circuited. As a result, the positive pole of the DC power supply 4, the PNP transistor 23, the input terminal 8b, the light emitting diode 37 of the photocoupler 34b, and the current limiting resistor 31
b, a DC current flows through a path of the push-pull power supply circuit 26, the second common terminal 7, and the negative pole of the DC power supply 4. The push-pull power supply circuit 26 is in an operating state, and one point is connected to the connection point between its output terminal and the current limiting resistor 31b.
Give an intermediate voltage of 2V. At this time, the photocoupler 34
The light emitting diode 37 of b emits light, and the phototransistor 35 paired with the light emitting diode 37 is short-circuited. As a result of the operation of the photocoupler 34b, a current flows to its output side,
The control device 2 detects that the second proximity switch 21 is on. Further, the light emitting diode 41 for input display corresponding to the photocoupler 34b also emits light,
The operator can visually recognize that there is an input from the second proximity switch 21 side.

When the second proximity switch 21 is turned off, no DC current flows through the path. Therefore, no current flows to the output side of the photocoupler 34b, and the control device 2 detects that the second proximity switch 21 is in the off state. Of course, the light emitting diode 41 for input display does not emit light. The point that a large current does not flow between the common terminals 6 and 7 at this time is as described above.

Also, the first and second proximity switches 11,
21 are turned on at the same time, and almost the same current flows in each, the following occurs. That is, the positive pole of the DC power supply 4, the PNP transistor 23, the input terminal 8
b, light emitting diode 37 of photocoupler 34b, current limiting resistor 31b, output terminal side of push-pull power supply circuit 26, current limiting resistor 31a, light emitting diode 36 of photocoupler 34a, input terminal 8a, NPN transistor 13
A DC current flows through a path of a negative pole of the DC power supply 4. As a result, the two photocouplers 34a, 3
4b operate together, resulting in both proximity switches 11, 21
Are detected on the control device 2 side. At this time, since the output side of the push-pull power supply circuit 26 has an intermediate voltage value, almost no outflow / inflow of current to the push-pull power supply circuit 26 occurs. That is, at this time, the push-pull power supply circuit 26 is maintained in a non-operating state.

Now, the characteristic effects of the present embodiment will be enumerated below. (A) According to the programmable controller of the present embodiment having the above configuration, as described above, proximity switches 11 and 21 having different polarities can be mixed and used simultaneously in the same unit. Therefore, versatility is reliably increased. Of course, this configuration of the programmable controller can be used exclusively for any type.

(B) The programmable controller of this embodiment has an advantage that a changeover switch for changing the polarities of both common terminals 6 and 7 is not necessarily required. Therefore, it is possible to surely prevent the device from being increased in size because the installation space for the device is not required. Further, since there is no need to worry about deterioration of the contact due to long-term use of the changeover switch, reliability can be improved as a result.

(C) In the DC input circuit 3 of the programmable controller, a pair of reference voltage generating resistors 27 and 2
A push-pull power supply circuit 26 comprising an operational amplifier 8 and an operational amplifier IC 29 is provided between the terminal unit 5 and each current detection circuit. Therefore, the intermediate voltage power supply output generated on the output side of the operational amplifier IC 29 is supplied to each of the photocouplers 34a to 34c via each of the current limiting resistors 31a to 31c.

The output of the intermediate voltage power supply, which is a push-pull output, is less affected by fluctuations in the power supply voltage of the DC power supply 4. Further, since such a push-pull output is obtained by an arithmetic operation, the intermediate voltage becomes a value very close to 12 V, and the accuracy is higher than when no arithmetic operation is performed. These two things contribute to stabilization of the operation of the push-pull power supply circuit 26. Second Embodiment Next, a programmable controller according to a second embodiment will be described with reference to FIG.

In the DC input circuit 46 of this programmable controller, the configuration of the current detection circuit is slightly different from that of the first embodiment. Therefore, only the differences will be mainly described here, and the common points will be assigned only the same member numbers.

In the DC input circuit 46 according to the second embodiment, an input of a diode bridge 48 as a rectifier circuit is provided between the input terminal 8a and the intermediate connection point of the pair of the current limiting resistor 31a and the operation stabilizing resistor 38. Side is connected. Another pair of intermediate connection points of the resistors 31b and 38 and the input terminal 8
Similarly, a diode bridge 48 is connected between the input terminal 8c and the intermediate connection point of another pair of resistors 31c and 38.

On the output side of each diode bridge 48,
Photocouplers 49a and 4 as current detecting elements, respectively
The input sides of 9b and 49c are connected. Unlike the first embodiment, these photocouplers 49a, 49b, and 49c are unidirectional, and all of them are phototransistors 35.
And one light emitting diode 37. The anode terminal of the light emitting diode 37 is connected to the positive output terminal of the diode bridge 48. Same light emitting diode 3
The cathode terminal 7 is connected to the negative output terminal of the diode bridge 48.

In the programmable controller configured as described above, the direct currents from the proximity switches 11 and 12 are unidirectional photocouplers 49 a and 49 after the polarities of the direct currents are previously adjusted by the diode bridge 48.
b, 49c. That is, the flow of the current output from the diode bridge 48 is in a fixed direction. Therefore, regardless of the polarity type of the proximity switches 11, 12, the unidirectional photocouplers 49a, 49b, 49
c operates reliably. As a result, a current flows to the output side of the unidirectional photocouplers 49a, 49b, 49c, and the control device 2 reliably detects that the proximity switches 11, 21 are in the ON state.

The characteristic effects of the present embodiment will be listed below. (A) Since the programmable controller of the present embodiment also has the same basic configuration as the programmable controller of the first embodiment, it goes without saying that the programmable controller of the first embodiment exhibits the operational effects of A, B, and C described in the first embodiment. .

(B) In the DC input circuit 46 of the programmable controller, the current is rectified by the diode bridge 48 as described above. As a result, the unidirectional photocouplers 49a, 49b, 49c having a simpler structure than the bidirectional photocouplers 34a, 34b, 34c.
Can be used, and cost reduction can be achieved. Third Embodiment Next, a programmable controller according to a third embodiment will be described with reference to FIG.

In the DC input circuit 51 of this programmable controller, the configuration of the push-pull power supply circuit 52 is slightly different from that of the first embodiment. Therefore, only the differences will be mainly described here, and the common points will be assigned only the same member numbers.

The push-pull power supply circuit 52 of the third embodiment
Is provided with a diode bridge 48 as a rectifier circuit on the input side. The pair of common terminals 6 and 7 are connected to respective input terminals of the diode bridge 48. The positive power supply terminal of the operational amplifier IC 29 and the first reference voltage generating resistor 27 are connected to the positive output terminal of the diode bridge 48. The negative power supply terminal of the operational amplifier IC 29 and the second reference voltage generating resistor 28 are connected to the negative output terminal of the diode bridge 48.

Now, the characteristic effects of this embodiment will be listed below. (A) Since the programmable controller of the present embodiment also has the same basic configuration as the programmable controller of the first embodiment, it goes without saying that the programmable controller of the first embodiment exhibits the operational effects of A, B, and C described in the first embodiment. .

(B) In the DC input circuit 51 of the programmable controller, the first and second proximity switches 1
The DC currents from 1, 21 are supplied to both power supply terminals of the operational amplifier IC 29 after their polarities are made uniform by the diode bridge 48. Therefore, regardless of the polarity of the DC power supply 4, the push-pull power supply circuit 52 can be made operable. Therefore, the push-pull power supply circuit 52 can be operated without separately providing a connection changeover switch and the like, and the enlargement and the like can be prevented. [Fourth Embodiment] Next, a programmable controller according to a fourth embodiment will be described with reference to FIG.

In the DC input circuit 54 of this programmable controller, the configuration of the push-pull power supply circuit 55 is slightly different from that of the first embodiment. Therefore, only the differences will be mainly described here, and the common points will be assigned only the same member numbers.

That is, the push-pull power supply circuit 55 in the DC input circuit 54 further includes a push-pull type buffer circuit 60 on the output side of the operational amplifier IC 29 as an operational amplifier.

The buffer circuit 60 of the present embodiment comprises an NPN transistor 56a as a first transistor, a second
A PNP transistor 56b, resistors 57a and 57b, a first diode 58a, a second diode 58b, and resistors 59a and 59b.

The collector terminal of the NPN transistor 56a and one end of the resistor 57a are connected to the first common terminal 6. The resistor 57a and the first diode 58a are connected in series. The cathode terminal of the first diode 58a is connected to the output terminal of the operational amplifier IC29 and the anode terminal of the second diode 58b. NP
The base terminal of the N transistor 56a is connected to the anode terminal of the first diode 58a. One end of a resistor 59a is connected to the emitter terminal of the NPN transistor 56a. The other end of the resistor 59a is connected to the resistor 59b, the inverting input terminal of the operational amplifier IC29, and the current limiting resistors 31a, 31b, 31c.

The collector terminal of the PNP transistor 56b and one end of the resistor 57b are connected to the second common terminal 7. The resistor 57b and the second diode 58b are connected in series. The anode terminal of the second diode 58b is connected to the output terminal of the operational amplifier IC29 and the cathode terminal of the second diode 58b. NP
The base terminal of the N transistor 56b is connected to the cathode terminal of the second diode 58b. One end of a resistor 59b is connected to the emitter terminal of the PNP transistor 56b. The other end of the resistor 59b is connected to the resistor 59a, the inverting input terminal of the operational amplifier IC29, and the current limiting resistors 31a, 31b, 31c. The output point of the current buffer circuit 60 (that is, the connection point between the two resistors 59a and 59b) has the value of the intermediate voltage.

Now, the characteristic effects of the present embodiment will be enumerated below. (A) Since the programmable controller of the present embodiment also has the same basic configuration as the programmable controller of the first embodiment, it goes without saying that the programmable controller of the first embodiment exhibits the operational effects of A, B, and C described in the first embodiment. .

(B) In the DC input circuit 54 of the programmable controller, the output of the operational amplifier IC 29 is amplified by the push-pull type current buffer circuit 60. From this, each current limiting resistor 3
The current supplied to 1a, 31b, 31c also increases accordingly. Therefore, as compared with the configuration of the first embodiment using the operational amplifier IC 29, a larger number of proximity switches 11 and
1 can be configured to be connectable regardless of its type. [Fifth Embodiment] Next, a programmable controller according to a fifth embodiment will be described with reference to FIG.

In the DC input circuit 61 of this programmable controller, the configuration of the push-pull power supply circuit 62 is different from that of the first embodiment. Therefore, only the differences will be mainly described here, and the common points will be assigned only the same member numbers. The push-pull power supply circuit 62 of the present embodiment does not include the operational amplifier IC 29 as an operational amplifier, but includes two emitter follower circuits instead. These emitter follower circuits are connected in series between a pair of common terminals 6 and 7. The first emitter follower circuit includes an NPN transistor 63a as a first transistor, and the second emitter follower circuit includes a PNP transistor 63b as a second transistor. Both transistors 63a, 63
The base terminal b is connected to a connection intermediate point between the reference voltage generating resistors 27 and 28. Both transistors 63
a and 63b are connected to the respective current limiting resistors 3
1a, 31b, and 31c, each photocoupler 34a,
34b, 34c are respectively connected to the input side. N
The collector terminal of the PN transistor 63a is connected to the first common terminal 6, and the collector terminal of the PNP transistor 63b is connected to the second common terminal 7.

Since the connection intermediate point between the resistors 27 and 28 has an intermediate voltage value, a voltage (approximately 12 V) corresponding to about a half of the power supply voltage is applied to each base terminal of the transistors 63a and 63b. Applied as input voltage. In this case, both emitter follower circuits output a push-pull output substantially equal to the intermediate voltage value to the emitter terminal side. In such a case, the output voltage value on the emitter terminal side is suppressed within a certain range. Normally, the potential difference between the base terminal and the emitter terminal is about 0.6 V, so a value twice as large (1.2 V) becomes the width of the dead zone. That is, specifically, the output voltage value is suppressed within the range of 12V ± 0.6V.

Next, the operation of the programmable controller configured as described above will be described. When only the first proximity switch 11 is turned on, a short circuit occurs between the collector terminal and the emitter terminal of the NPN transistor 13.
As a result, the positive pole of the DC power supply 4, the first common terminal 6, the first emitter follower circuit, the current limiting resistor 31
a, a DC current flows through a path of the light emitting diode 36 of the photocoupler 34a, the input terminal 8a, the NPN transistor 13, and the negative pole of the DC power supply 4. The push-pull power supply circuit 62 enters an operation state, and applies an intermediate voltage of about 12 V to a connection point between its output terminal and the current limiting resistor 31a. Then, as a result of the photocoupler 34a operating due to the short circuit of the phototransistor 35, the control device 2 detects that the first proximity switch 11 is in the ON state.

When the first proximity switch 11 is turned off, no DC current flows through the path. Therefore, no current flows to the output side of the photocoupler 34a, and the control device 2 detects that the first proximity switch 11 is in the off state. Further, since a pair of reference voltage generating resistors 27 and 28 are connected in series between the common terminals 6 and 7, a very large current does not flow between the common terminals 6 and 7 at this time.

When only the second proximity switch 21 is turned on, the collector terminal and the emitter terminal of the PNP transistor 23 are short-circuited. As a result, the positive pole of the DC power supply 4, the PNP transistor 23, the input terminal 8b, the light emitting diode 37 of the photocoupler 34b, and the current limiting resistor 31
b, a DC current flows through a path of the second emitter follower, the second common terminal 7 and the negative pole of the DC power supply 4. The push-pull power supply circuit 62 enters an operating state,
The connection point between the output terminal and the current limiting resistor 31b is approximately 12
Give an intermediate voltage of V. Then, the phototransistor 3
As a result of the photocoupler 34b operating due to the short circuit of No. 5, the control device 2 detects that the second proximity switch 21 is on. When the second proximity switch 21 is turned off, no DC current flows through the path. Therefore, no current flows to the output side of the photocoupler 34b, and the control device 2 detects that the second proximity switch 21 is in the off state. The point that a large current does not flow between the common terminals 6 and 7 at this time is as described above.

Further, the first and second proximity switches 11,
21 are turned on at the same time, and almost the same current flows in each, the following occurs. That is, the positive pole of the DC power supply 4, the NPN transistor 23, the input terminal 8
b, light emitting diode 37 of photocoupler 34b, current limiting resistor 31b, output side of both emitter follower circuits, current limiting resistor 31a, light emitting diode 36 of photocoupler 34a, input terminal 8a, NPN transistor 13, and negative pole of DC power supply 4. DC current flows through the path of. As a result, as a result of the two photocouplers 34a and 34b operating together, the control device 2 detects that both the proximity switches 11 and 21 are on. At this time, the output side of the push-pull power supply circuit 62, that is, the emitter terminal side of both transistors 63a and 63b has a substantially intermediate voltage value. Therefore, almost no outflow or inflow of current to the push-pull power supply circuit 62 occurs. That is, the voltage value on the emitter terminal side of both transistors 63a and 63b is 1
Within the range of 2V ± 0.6V, all the emitter follower circuits are maintained in the non-operating state.

Now, the characteristic effects of the present embodiment will be enumerated below. (A) Since the programmable controller of the present embodiment also has the same basic configuration as the programmable controller of the first embodiment, it goes without saying that the functions and advantages of the first and second embodiments described in the first embodiment can be obtained.

(B) In this DC input circuit 61, a push-pull power supply circuit 62 is constituted by four inexpensive elements such as a pair of reference voltage generating resistors 27 and 28 and two transistors 63a and 63b having different polarities. doing.
The push-pull power supply circuit 62 that obtains a push-pull output without performing an arithmetic operation is slightly inferior in accuracy to the first embodiment that performs the arithmetic operation. On the other hand, there is an advantage that the structure can be simplified and the cost can be reduced. [Sixth Embodiment] Next, a programmable controller according to a sixth embodiment will be described with reference to FIG.

In the DC input circuit 71 of this programmable controller, the configuration of the push-pull power supply circuit 72 is different from that of the first embodiment. Therefore, only the differences will be mainly described here, and the common points will be assigned only the same member numbers.

The push-pull power supply circuit 72 of this embodiment
Includes a three-terminal regulator 74a for a positive voltage as an intermediate voltage generation source (pull side) based on a positive electrode, and a three-terminal regulator 74b for a negative voltage as an intermediate voltage generation source (push side) based on a negative electrode. I have.

The three-terminal regulators 74a and 74b are a kind of constant voltage IC and have three terminals (input terminal,
Output terminal and ground terminal). These three
Between the output terminals of the terminal regulators 74a, 74b, there are first and second diodes 73a, 73b as backflow prevention elements.
73b are connected in series. Both diodes 73a,
Reference numeral 73b indicates a forward direction from the three-terminal regulator 74a for the positive voltage to the three-terminal regulator 74b for the negative voltage. Here, diodes 73a and 7 having the same standard are used.
3b are used.

The input terminal of the three-terminal regulator 74 a for positive voltage (for +12 V) is connected to the first common terminal 6, and the ground terminal is connected to the second common terminal 7. The anode terminal of the first diode 73a is connected to the output terminal of the three-terminal regulator 74a, and the cathode terminal of the first diode 73a is connected to each of the current limiting resistors 31a.
a, 31b, and 31c.

The input terminal of the three-terminal regulator 74 b for negative voltage (for -12 V) is connected to the second common terminal 7, and the ground terminal is connected to the first common terminal 6. The cathode terminal of the second diode 73b is connected to the output terminal of the three-terminal regulator 74b, and the anode terminal of the second diode 73b is connected to each of the current limiting resistors 31b.
a, 31b, and 31c. It should be noted that a push-pull output substantially equal to the intermediate voltage value is output at the connection midpoint between the diodes 73a and 73b. The accuracy obtained at this time is exactly intermediate between the case where the configuration of the first embodiment is adopted and the case where the configuration of the fifth embodiment is adopted.

The push-pull power supply circuit 72 has four transmission preventing capacitors 75a, 75b, 75c and 75d. The capacitor 75a is connected between the input terminal of the three-terminal regulator 74a for positive voltage and the ground terminal. The capacitor 75b is connected between the output terminal of the three-terminal regulator 74a for positive voltage and the ground terminal. The capacitor 75c is connected between the input terminal of the three-terminal regulator 74b for negative voltage and the ground terminal. The capacitor 75d has a 3
It is connected between the output terminal of the terminal regulator 74b and the ground terminal. A connection intermediate point between the capacitors 75a and 75b is connected to an input terminal of a three-terminal regulator 74b for negative voltage. The connection midpoint between the capacitors 75c and 75d is connected to the input terminal of the three-terminal regulator 74a for positive voltage.

The push-pull power supply circuit 72 further includes one voltage stabilizing capacitor 76. The capacitor 76 is connected between the input terminals of the three-terminal regulators 74a and 74b.

Next, the operation of the programmable controller configured as described above will be described. When only the first proximity switch 11 is turned on, a short circuit occurs between the collector terminal and the emitter terminal of the NPN transistor 13.
As a result, the positive pole of the DC power supply 4, the first common terminal 6, the three-terminal regulator 74a for positive voltage, the first diode 73a, the current limiting resistor 31a, the photocoupler 34
A DC current flows through the light emitting diode 36 a, the input terminal 8 a, the NPN transistor 13, and the negative pole of the DC power supply 4. The push-pull power supply circuit 72 operates and applies an intermediate voltage of about 12 V to a connection point between its output terminal and the current limiting resistor 31a. Then, as a result of the photocoupler 34a operating due to the short circuit of the phototransistor 35, the control device 2 detects that the first proximity switch 11 is in the ON state.

When the first proximity switch 11 is turned off, no DC current flows through the path. Therefore, no current flows to the output side of the photocoupler 34a, and the control device 2 detects that the first proximity switch 11 is in the off state.

When only the second proximity switch 21 is turned on, the collector terminal and the emitter terminal of the PNP transistor 23 are short-circuited. As a result, the positive pole of the DC power supply 4, the PNP transistor 23, the input terminal 8b, the light emitting diode 37 of the photocoupler 34b, and the current limiting resistor 31
b, second diode 73b, three-terminal regulator IC 74b for negative voltage, second common terminal 7, and DC power supply 4
DC current flows through the path of the negative pole of the. The push-pull power supply circuit 72 is activated, and applies an intermediate voltage of about 12 V to a connection point between its output terminal and the current limiting resistor 31b. Then, as a result of the photocoupler 34b operating due to the short circuit of the phototransistor 35, the control device 2 detects that the second proximity switch 21 is on. When the second proximity switch 21 is turned off,
No DC current flows through the path. Therefore, no current flows to the output side of the photocoupler 34b, and the control device 2 detects that the second proximity switch 21 is in the off state.

The first and second proximity switches 11,
21 are turned on at the same time, and almost the same current flows in each, the following occurs. That is, the positive pole of the DC power supply 4, the NPN transistor 23, the input terminal 8
b, light-emitting diode 37 of photocoupler 34b, current limiting resistor 31b, connection midpoint between diodes 73a, 73b, current limiting resistor 31a, light emitting diode 36 of photocoupler 34a, input terminal 8a, NPN transistor 13
A DC current flows through a path of a negative pole of the DC power supply 4. As a result, the two photocouplers 34a, 3
4b operate together, resulting in both proximity switches 11, 21
Are detected on the control device 2 side. At this time, the output side of the push-pull power supply circuit 72, that is, the connection intermediate point between the diodes 73a and 73b has a value of almost the intermediate voltage. Therefore, both diodes 73a, 73b
Within the range where the voltage difference equal to or larger than the forward voltage difference does not occur, almost no outflow / inflow of current to the three-terminal regulators 74a and 74b occurs. At this time, the push-pull power supply circuit 72 is maintained in a non-operating state.

Now, the characteristic effects of this embodiment will be listed below. (A) Since the programmable controller of the present embodiment also has the same basic configuration as the programmable controller of the first embodiment, it goes without saying that the functions and advantages of the first and second embodiments described in the first embodiment can be obtained.

(B) In this DC input circuit 71, two three-terminal regulators 74a and 74b, two diodes 73a and 73b, and a plurality of capacitors 75a to 75b
The push-pull power supply circuit 72 is composed of inexpensive elements such as d and 76. This push-pull power supply circuit 72 for obtaining a push-pull output without performing an arithmetic operation
The accuracy is slightly inferior to that of the first embodiment that performs the arithmetic operation.
On the other hand, there is an advantage that the structure can be simplified and the cost can be reduced. [Seventh Embodiment] Next, a programmable controller according to a seventh embodiment will be described with reference to FIG.

In the DC input circuit 77 of this programmable controller, the configuration of the push-pull power supply circuit 78 is different from that of the first embodiment. Therefore, only the differences will be mainly described here, and the common points will be assigned only the same member numbers.

In the push-pull power supply circuit 78 in the DC input circuit 77, a Zener diode 79 is used as a second reference voltage generating element in place of the second reference voltage generating resistor. There is no change in other configurations. The cathode terminal of the Zener diode 79 is connected to the non-inverting input terminal of the operational amplifier IC 29 and the resistor 27.
It is connected to the. The anode terminal of the Zener diode 79 is connected to the negative power supply terminal of the operational amplifier IC 29 and the second common terminal 7. The Zener diode 79 and the resistor 27 form one voltage dividing circuit. Also, the Zener diode 79
The intermediate point between the resistor and the resistor 27 is an intermediate voltage value of about 12 V
Becomes

Now, the characteristic effects of this embodiment will be enumerated below. (A) Since the programmable controller of the present embodiment also has the same basic configuration as the programmable controller of the first embodiment, it goes without saying that the programmable controller of the first embodiment exhibits the operational effects of A, B, and C described in the first embodiment. .

(B) With the configuration of the present embodiment using the Zener diode 79, the intermediate voltage is less affected by the fluctuation of the power supply voltage 4 than in the first embodiment. Therefore, there is an advantage that the operation of the push-pull power supply circuit 78 can be stabilized.

The present invention is not limited to the above embodiment, but can be modified to another form as follows. The diode bridge 48 as a rectifier circuit may be employed in embodiments other than the second and third embodiments.

A push-pull power supply circuit 26, 52, 5
5, 62, 72, 78 are DC input circuits 3, 46, 5
The present invention is not limited to the case where components are configured on a board on which the components 1, 54, 61, 71, and 77 are assembled. That is, the push-pull power supply circuits 26, 52, 55, 62, 72, 78 are formed on separate boards, and are connected to the DC input circuits 3, 46, 5
1, 54, 61, 71, and 77 may be externally attached to a board on which they are assembled.

In each embodiment, the resistors 39 and 40
The circuit configuration may be simplified by omitting some or all of the input display unit including the light emitting diodes 41. Further, other display means may be used in place of the light emitting diode 41.

The operation stabilizing resistor 38 used in each embodiment may be omitted when unnecessary. A rectifier circuit other than the diode bridge 48 exemplified in the second and third embodiments (for example, a single diode) may be used. As a current limiting element, a resistor 3
Other than 1 (for example, a constant current diode, an FET, a constant current circuit, etc.) may be used.

In place of the Zener diode 79 used in the seventh embodiment, for example, a varistor or the like may be used, or a drop in the forward voltage of a plurality of diodes may be used.

The external input devices are proximity switches 11 and
It is not limited to one, but may be another one (for example, a limit switch, a micro switch, a relay contact, an operation switch, etc.).

The current detection elements are photocouplers 34a to
34c, 49a to 49c, but may be other types (for example, a combination of a relay coil and a resistor and a logic circuit).

Here, in addition to the technical ideas described in the claims, the technical ideas grasped by the above-described embodiments are listed below together with their effects. (1) The DC input circuit according to any one of claims 2 to 5, wherein the first reference voltage generation element is a resistor, and the second reference voltage generation element is a Zener diode. With this configuration, the intermediate voltage is less likely to be affected by fluctuations in the power supply voltage, and the operation of the push-pull power supply circuit is stabilized.

(2) The DC input circuit according to any one of claims 2 to 5, wherein the first and second reference voltage generating elements are resistors having substantially equal resistance values.
With this configuration, the push-pull power supply circuit can be configured more easily and at lower cost.

(3) Claims 1 to 5, technical idea 1,
3. The DC input circuit according to claim 2, wherein a rectifier circuit is provided between each of the current limiting elements and each of the current detecting elements constituting each of the current detecting circuits.
With this configuration, it is possible to use a current detecting element having a simple structure such as a unidirectional photocoupler and the like, and cost can be reduced.

(4) A DC input circuit according to any one of claims 1 to 5, and a technical idea 1 to 3, wherein an operation stabilizing resistor is connected in parallel to an input side of the current detecting element. . With this configuration, the operation of the DC input circuit is stabilized because an excess current flows by bypass.

(5) In claim 1, a three-terminal regulator for positive voltage and a three-terminal regulator for negative voltage connected between the pair of common terminals and a series connection between output terminals of the two three-terminal regulators. A DC input circuit comprising: a pair of backflow prevention elements; and a connection midpoint between the two backflow prevention elements is connected to each of the current limiting elements.

(6) In any one of claims 1 to 5 and technical ideas 1 to 5, the push-pull power supply circuit is provided between the terminal section and each of the current detection circuits. Characteristic DC input circuit.

(7) Any one of the technical ideas 1 to 6
A programmable controller comprising the DC input circuit according to the item. According to this configuration, it is possible to provide a suitable programmable controller that can simultaneously use external input devices having different polarities without using a changeover switch or the like.

Note that the technical terms used in this specification are defined as follows. "Current detection element: Refers to a unidirectional photocoupler or a bidirectional photocoupler (including those configured by combining two unidirectional photocouplers) and an element having a function equivalent to these."

[0109]

As described in detail above, according to the first to fifth aspects of the present invention, external input devices having different polarities can be mixed and used simultaneously without using a changeover switch or the like. A DC input circuit can be provided.

According to the second aspect of the present invention, the operation can be stabilized by obtaining a push-pull output with relatively high accuracy. According to the invention described in claim 3,
A structure capable of connecting a larger number of external input devices can be provided.

According to the fourth aspect of the present invention, the structure is simplified and the cost can be reduced. According to the invention described in claim 5, the push-pull power supply circuit can be made operable regardless of the polarity of the DC power supply.

According to the sixth aspect of the present invention, it is possible to provide a programmable controller that can simultaneously use external input devices having different polarities without using a changeover switch or the like.

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing a programmable controller according to a first embodiment in which different types of proximity switches are simultaneously connected.

FIG. 2 is a circuit diagram showing a programmable controller according to a second embodiment in which different types of proximity switches are simultaneously connected.

FIG. 3 is a circuit diagram showing a programmable controller according to a third embodiment in which different types of proximity switches are simultaneously connected.

FIG. 4 is a circuit diagram showing a programmable controller according to a fourth embodiment in which different types of proximity switches are simultaneously connected.

FIG. 5 is a circuit diagram showing a programmable controller according to a fifth embodiment in which different types of proximity switches are simultaneously connected.

FIG. 6 is a circuit diagram showing a programmable controller according to a sixth embodiment in which different types of proximity switches are simultaneously connected.

FIG. 7 is a circuit diagram showing a programmable controller according to a seventh embodiment in which different types of proximity switches are simultaneously connected.

8A is a circuit diagram showing a conventional programmable controller in which only NPN type proximity switches are connected, and FIG. 8B is a conventional programmable controller in which only PNP type proximity switches are connected. FIG. 3C is a circuit diagram showing a controller, FIG. 4C is a circuit diagram showing a conventional dual-purpose programmable controller in which only NPN type proximity switches are connected, and FIG.
FIG. 9 is a circuit diagram showing a conventional dual-purpose programmable controller in which only a P-type proximity switch is connected.

[Explanation of symbols]

2. Control device, 3, 46, 51, 54, 61, 71, 7
7 DC input circuit, 4 DC power supply, 5 terminal part, 6 first common terminal, 7 second common terminal, 8a, 8b,
8c: input terminal, 11: first proximity switch as first external input device, 21: first proximity switch as second external input device, 26, 52, 55, 62, 72,
78: a push-pull power supply circuit; 27, a first reference voltage generating resistor as a first reference voltage generating element; 28, a first reference voltage generating resistor as a second reference voltage generating element;
9: operational amplifier ICs as operational amplifiers, 31a, 31
b, 31c... current limiting resistors as current limiting elements, 34
a, 34b, 34c: bidirectional photocoupler as current detecting element; 48, diode bridge as rectifying circuit; 49a, 49b, 49c, unidirectional photocoupler as current detecting element; 60, current buffer circuit; 63a
... NPN transistor forming an emitter follower circuit, 63b PNP transistor forming an emitter follower circuit, 79 ... Zener diode as a second reference voltage generating element.

Claims (6)

[Claims] An input terminal includes a pair of common terminals to which a plurality of input terminals and both poles of a DC power supply for an external input device are connected, and a current limiting element and a current detecting element. A plurality of current detection circuits for detecting a current on the external input device side and outputting the current to the control device side, wherein a voltage corresponding to a substantially intermediate value between the voltage values of the pair of common terminals is generated. And a push-pull power supply circuit for providing the intermediate voltage power supply output to each of the current detection elements via each of the current limiting elements. 2. The push-pull power supply circuit includes a pair of reference voltage generating elements connected in series between the pair of common terminals, and an input side thereof connected to a connection intermediate point between the two reference voltage generating elements. The DC input circuit according to claim 1, wherein an output side includes an operational amplifier connected to each of the current limiting elements. 3. The DC input circuit according to claim 2, wherein said push-pull power supply circuit further comprises a push-pull type current buffer circuit on the output side of said operational amplifier. 4. The push-pull power supply circuit includes: a pair of reference voltage generating elements connected in series between the pair of common terminals; a first emitter follower circuit including a first transistor; A second emitter follower circuit comprising a second transistor having a polarity different from that of the transistor; a base terminal of the both transistors being connected to a connection intermediate point of the two reference voltage generating elements; The terminals are both connected to the respective current detecting elements via the respective current limiting elements, and the collector terminals of the both transistors are connected to the pair of common terminals. The DC input circuit according to claim 1. 5. The DC input circuit according to claim 1, wherein said push-pull power supply circuit includes a rectifier circuit connected to said pair of common terminals. 6. A programmable controller comprising the DC input circuit according to claim 1.