JPH0775311B2 - AC 2-wire solid state switch - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an AC two-wire non-contact switch that is turned on and off by a sensor circuit that operates with DC power, such as a proximity switch and a photoelectric switch.

[Conventional technology]

This type of AC 2-wire non-contact switch must supply DC power to a sensor circuit that controls the non-contact switch, regardless of the on / off state of the non-contact switch. An example of such a conventional AC 2-wire non-contact switch is shown in FIG.

In FIG. 2, the AC 2-wire non-contact switch includes a switch circuit 1, a constant voltage circuit 2, an operation display light emitting diode 3, a capacitor 4, a shunt circuit 5, a trigger circuit 6, a sensor circuit 7, and a detection transistor 8. The switch circuit 1 comprises a single-phase bridge rectifier circuit 9, a thyristor 10 connected between the DC output terminals of the rectifier circuit 9, and a resistor 11 connected between the gate and cathode of the thyristor 10, A series circuit of an AC power supply 12, a switch 13, and a load 14 is connected between the AC input terminals. The constant voltage circuit 2 comprises a charging transistor 15, a resistor 16 connected between the collector and the base of the charging transistor 15, and a zener diode 17 connected to the base of the charging transistor 15 in a series control type constant voltage. It is composed of a circuit and is connected between the DC output terminals of the rectifier circuit 9 via a backflow prevention diode 18, and the anode of the Zener diode 17 is connected to a detection transistor 8 driven by a signal from the sensor circuit 7. The output of the constant voltage circuit 2 is connected via a light emitting diode 3 so as to charge a capacitor 4, and a sensor circuit 7 is connected to both ends of this capacitor 4.

The shunt circuit 5 includes resistors 19 and 20 for dividing the constant voltage output of the constant voltage circuit 2, a series circuit of an emitter / collector of a transistor 21 and a resistor 22 connected to both ends of the light emitting diode 3, and a base / emitter of the resistor 22. Is connected to both ends of the transistor 23, the collector of which is connected to the base of the charging transistor 15, and the connecting point of the voltage dividing resistors 19 and 20 is the transistor 2.
Connected to the base of 1. When the transistor 21 is turned on, a series circuit of the emitter / collector of the transistor 21 and the resistor 22 is formed to shunt the current flowing to the light emitting diode 3, and when the transistor 23 is turned on, a charging transistor.
15 base currents are shunted. The trigger circuit 6 includes a resistor 24 and a Zener diode 25 connected in parallel with the capacitor 4.
It is composed of a transistor 26 whose base is connected to the connection point of this resistor 24 and Zener diode 25. The emitter of this transistor 26 is connected to the + end of the capacitor 4, and the collector is connected to the gate of the thyristor 10. There is. The constant voltage output of the constant voltage circuit 2 is the trigger circuit 6
Is set lower than the Zener voltage of the Zener diode 25 of, and the series circuit of the resistor 24 of the trigger circuit 6 and the Zener diode 25 is prevented from conducting during the period when the constant voltage function of the constant voltage circuit 2 is operating. There is.

In the AC 2-wire non-contact switch shown in FIG. 2, when the switch 13 is turned on while the sensor circuit 7 is not detecting a predetermined phenomenon and is outputting a high level signal, the DC of the rectifier circuit 9 is changed. An attempt is made to charge the capacitor 4 via the backflow prevention diode 18, the charging transistor 15 and the light emitting diode 3 with the rectified voltage between the output terminals. At this time, the detection transistor 8 is driven by the high level signal from the sensor circuit 7.
Is turned on and the Zener diode 17 of the constant voltage circuit 2 is conducting, so that the constant voltage function of the constant voltage circuit 2 is working, which turns on the transistor 21 and then the transistor 21.
Since 23 turns on, the base current of the charging transistor 15 is shunted by the transistor 23, the emitter current of the charging transistor 15, that is, the charging current of the capacitor 4 is limited, and the charging current that flows even though the thyristor 10 does not turn on. This prevents the load 14 from malfunctioning. When the constant voltage function of the constant voltage circuit 2 is working, the transistor 21 of the shunt circuit 5 is turned on.
The emitter current of charging transistor 15 is transistor 21
Flows into the capacitor 4 through the emitter / collector and the resistor 22 to charge the capacitor 4. At this time, the voltage applied to both ends of the light emitting diode 3 is the sum of the base-emitter voltage of the transistor 23 and the voltage drop of the transistor 21, and since the sum voltage is lower than the forward voltage of the light emitting diode 3, the light emitting diode 3 emits light. The diode 3 does not emit light.
In the trigger circuit 6, the zener diode 25 is prevented from conducting at the constant voltage output of the constant voltage circuit 5, so that the transistor 26 is in the off state, and the thyristor 10 is thereby turned off. In such an operation standby state of the contactless switch, when the sensor circuit 7 detects a predetermined phenomenon and the high level signal constantly shifts to the low level, the detection transistor 8 is turned off and the constant voltage circuit 2 has the constant voltage function. Lose. When the constant voltage circuit 2 loses the constant voltage function, the capacitor 4 is charged by the rectified voltage of the rectifier circuit 9 via the charging transistor 15 of the constant voltage circuit 2 and the light emitting diode 3, and the voltage across the capacitor 4 is an AC power source. Increase to 12 peak voltage. When the capacitor 4 is charged with the rectified voltage of the rectifier circuit 9, a large current flows through the light emitting diode 3 to emit light, which indicates that the contactless switch is turned on. When the voltage of the capacitor 4 rises to the peak voltage of the AC power supply 12,
The Zener diode 25 of the trigger circuit 6 is turned on to turn on the transistor 26, which turns on the thyristor 10.
When the thyristor 10 is turned on, an operating current flows through the load 14 and the load 14 operates.

When the thyristor 10 is turned on, the voltage across the thyristor 10 drops to almost 0V, so that the charging current from the rectifier circuit 9 to the capacitor 4 is cut off, but the sensor circuit 7 consumes the charge of the capacitor 4. Continue the detection operation.
Since the voltage applied to the thyristor 10 becomes 0 V for each cycle of the power supply frequency of the AC power supply 12, the thyristor 10
Although it is turned off once every 0V, the transistor 26 is turned on and the gate signal is continuously applied to the thyristor 10 while the charge of the capacitor 4 is not lower than the zener voltage of the zener diode 25 of the trigger circuit 6, and the thyristor 10 is rectified by the rectifier circuit. It turns on again when the rectified voltage of 9 rises, so the load
It does not affect the operation of 14. Since the capacitor 4 is discharged by the power supply to the sensor circuit 7, its charge gradually decreases, and the voltage of the capacitor 4 changes to the Zener diode 25.
When the zener voltage falls below the zener voltage, the zener diode 25 turns off, the transistor 26 turns off, and the thyristor 10 turns off when the rectified voltage of the rectifier circuit 9 becomes 0V. At this time, since the zener diode 17 of the constant voltage circuit 2 is non-conductive, the constant voltage function of the constant voltage circuit 2 is lost.
Since the transistors 21 and 23 are off, the capacitor 4 is quickly charged to the peak voltage of the AC power source 12 via the charging transistor 15 and the light emitting diode 3. A charging current to the capacitor 4 flows through the light emitting diode 3 to continue the light emitting state, and the non-contact switch indicates the on state. When the sensor circuit 7 no longer detects a predetermined phenomenon, a high level signal is applied to the base of the detection transistor 8 to turn on the detection transistor 8 and the constant voltage function of the constant voltage circuit 2 is restored. Since the transistor 21 of the circuit 5 is turned on and the charging path to the capacitor 4 is switched to the emitter / collector path of the transistor 21 and the path of the resistor 22, the light emitting diode 3 stops emitting light. In this way, the contactless switch turns on / off the load 14 in accordance with the detection operation of the sensor circuit 7.

[Problems to be Solved by the Invention]

Since the contactless switch shown in FIG. 2 supplies the electric charge of the capacitor 4 to the sensor circuit 7 as described above, when the sensor circuit 7 detects a predetermined phenomenon and the thyristor 10 is turned on. The electric charge of the capacitor 4 gradually decreases. However, if the rectified voltage of the rectifier circuit 9 rises in the next cycle after the rectified voltage of the rectifier circuit 9 exceeds 0V,
Since the constant voltage function of the constant voltage circuit 2 is lost and the shunt circuit 5 does not function, the capacitor 4 is quickly charged to the peak voltage of the AC power supply 12. In this way capacitor 4
Is charged to the peak voltage of the AC power supply 12, the load 14
If the impedance of is low, charging transistor 15
Since a large pulsed current flows through the light emitting diode 3, there is a disadvantage that a large capacity element must be used for the charging transistor 15 and the light emitting diode 3.

Therefore, an object of the present invention is to eliminate the drawbacks of the conventional device described above and to charge a capacitor without using a large capacity charging transistor or light emitting diode even when the load impedance is low. To provide a contact switch.

[Means for Solving the Problems]

In order to achieve the above-mentioned object, the present invention provides a switch circuit including a rectifier circuit in which a series circuit of an AC power source and a load is connected between AC input terminals, and a thyristor connected between DC output terminals of the rectifier circuit, A capacitor that is charged by a rectified output of a rectifier circuit through a series circuit of a charging transistor and a light emitting diode for operation display, a sensor circuit connected to both ends of the capacitor to detect a predetermined phenomenon and output a detection signal, A series control type constant voltage circuit having a charging transistor and a Zener diode connected to the base of the charging transistor, the base current of the charging transistor and the operation display light emitting diode with the voltage of the constant voltage circuit as an input. A shunt circuit for shunting a current, a detection transistor that is controlled by the detection signal of the sensor circuit and invalidates the constant voltage circuit. A trigger circuit that gives a trigger signal to the thyristor when the charging voltage of the capacitor and the capacitor reaches a predetermined value, and the constant voltage output of the constant voltage circuit is set to an alternating current lower than the voltage at which the trigger circuit outputs the trigger signal. In the two-wire type contactless switch, the shunt circuit has a resistor connected between the operation display light emitting diode and the capacitor to detect a charging current of the capacitor, and the voltage generated in the resistor and the constant voltage. It is characterized in that the base current of the charging transistor and the current of the operation display light emitting diode are shunted by using the voltage of the circuit as an input.

[Action]

In the AC two-wire type contactless switch configured as described above, when the sensor circuit detects a predetermined phenomenon, the thyristor turns on and the constant voltage function of the constant voltage circuit is lost by turning on the detection transistor. It is about to be charged to the peak voltage of the AC power supply through the charging transistor and the light emitting diode. At this time, when the impedance of the load is low and the charging current, that is, the current flowing through the light emitting diode, becomes large, the magnitude of the charging current is detected by the voltage drop of the resistor inserted between the light emitting diode and the capacitor, and the resistance The shunt circuit that receives the voltage generated at the input functions to shunt the charging current flowing through the light emitting diode, thereby suppressing the current flowing through the charging transistor and the light emitting diode.

〔Example〕

An embodiment of an AC two-wire non-contact switch according to the present invention is shown in FIG. In FIG. 1, components having the same functions as those of the conventional device shown in FIG. 2 are designated by the same reference numerals.

The AC two-wire type contactless switch shown in FIG. 1 has a switch circuit 1, a constant voltage circuit 2, an operation display light emitting diode 3, a capacitor 4, a shunt circuit 5, a trigger circuit 6, and a sensor circuit, as in the conventional device. 7 and a detection transistor 8 and is the same as the conventional device shown in FIG. 2 except for the shunt circuit 5. In the shunt circuit 5, the connection point of the resistors 19 and 20 for dividing the constant voltage output of the constant voltage circuit 2 is connected to the base of the transistor 21, and the emitter / collector of the transistor 21 and the resistor are connected.
A series circuit of 22 is connected to both ends of the light emitting diode 3, the collector of the transistor 23 is connected to the base of the charging transistor 15 of the constant voltage circuit 2, and the transistor
The base of 23 is connected to the connection point of the collector of the transistor 21 and the resistor 22, and a resistor 27 for detecting the charging current of the capacitor 4 is provided between the connection point of the other end of the light emitting diode 3 and the resistor 22 and the capacitor 4. The voltage drop across the resistor 27 is connected between the base and emitter of the transistor 23. The shunt circuit 5 differs from the shunt circuit of the conventional device shown in FIG. 2 in that a resistor 27 is connected in series between the light emitting diode 3 and the capacitor 4, and the emitter of the transistor 23 is the resistor 27 and the capacitor. It is connected to the connection point with 4 and the voltage drop of the resistor 27 is applied between the base and emitter of the transistor 23.

The AC two-wire type contactless switch in the embodiment shown in FIG. 1 has a constant voltage when the sensor circuit 7 does not detect a predetermined phenomenon and outputs a high level signal to turn on the detection transistor 8. Since the constant voltage function of the voltage circuit 2 is active, the capacitor 4 is almost the same as the conventional device of FIG.
Is a constant voltage output of the constant voltage circuit 2, a transistor 21, a resistor 2
2. It is charged by the route of resistor 27. Here, when the sum of the voltage drop of the resistor 22 and the voltage drop of the resistor 27 exceeds a predetermined voltage (base-emitter voltage V _BE of the transistor 23), the transistor 23 is turned on and the base current of the charging transistor 15 is shunted. Since the charging current to the capacitor 4 is suppressed, the load 14 is prevented from malfunctioning due to the charging current. When the sensor circuit 7 detects a predetermined phenomenon and the output of the sensor circuit 7 becomes a low level signal, the detection transistor 8 is turned off and the constant voltage function of the constant voltage circuit 2 is lost. The transistors 21 and 23 are also turned off. Therefore, the capacitor 4 is charged via the charging transistor 15, the light emitting diode 3 and the resistor 27. At this time, if the charging current of the capacitor 4 is large, the voltage drop of the resistor 27 exceeds the base-emitter voltage V _BE of the transistor 23, so that the transistor 23 is turned on. As a result, the base current of the charging transistor 15 is shunted, and the charging transistor 15
The charging current flowing through 15 and the light emitting diode 3 is suppressed.

As described above, in the AC two-wire type contactless switch according to this embodiment, when the sensor circuit 7 does not detect a predetermined phenomenon, the constant voltage output of the constant voltage circuit 2 is used as an input to the transistor 21 of the shunt circuit 5. , 23 are turned on, the base current of the charging transistor 15 is shunted by the transistor 23, the current flowing in the light emitting diode is shunted by the transistor 21, and the constant voltage circuit is turned on when the sensor circuit 7 detects a predetermined phenomenon. Even when the constant voltage function of 2 is lost, the transistor 23 is turned on by inputting the charging current of the capacitor 4 with the voltage drop of the resistor 27, so that the charging transistor
The base current of 15 is shunted to suppress the charging current to the capacitor 4.

〔The invention's effect〕

As described above, according to the present invention, a switch circuit including a rectifier circuit in which a series circuit of an AC power source and a load is connected between AC input terminals and a thyristor connected between DC output terminals of the rectifier circuit, A capacitor charged by a rectified output of the rectifier circuit via a series circuit of a charging transistor and an operation display light emitting diode, a sensor circuit connected to both ends of the capacitor to detect a predetermined phenomenon and output a detection signal, A series control type constant voltage circuit having the charging transistor and a Zener diode connected to the base of the charging transistor, the base current of the charging transistor and the operation display light emitting diode using the voltage of the constant voltage circuit as an input Shunt circuit for shunting the current of the detection circuit, a detection transistor for controlling the constant voltage circuit which is controlled by the detection signal of the sensor circuit. A trigger circuit that gives a trigger signal to the thyristor when the charging voltage of the capacitor and the capacitor reaches a predetermined value, and the constant voltage output of the constant voltage circuit is set to an alternating current lower than the voltage at which the trigger circuit outputs the trigger signal. In the two-wire type contactless switch, the shunt circuit has a resistor connected between the operation display light emitting diode and the capacitor to detect a charging current of the capacitor, and the voltage generated in the resistor and the constant voltage. Since the base current of the charging transistor and the current of the light emitting diode for operation display are shunted by using the voltage of the circuit as an input, the charging current of the capacitor flowing when the AC two-wire non-contact switch is turned on. The base current of the charging transistor is shunted by detecting the voltage drop of the resistor provided in the shunt circuit, Since it is possible to suppress the charging current, the charging current of the capacitor even when the impedance of the load is low without increasing,
This has an advantage that it is not necessary to use a large-capacity charging transistor and an operation display light emitting diode.

[Brief description of drawings]

FIG. 1 is a connection diagram showing an embodiment of an AC two-wire type contactless switch according to the present invention, and FIG. 2 is a connection diagram showing an example of a conventional AC two-wire type contactless switch. 1: switch circuit, 2: constant voltage circuit, 3: light emitting diode for operation display, 4: capacitor, 5: shunt circuit, 6: trigger circuit,
7: Sensor circuit, 8: Detection transistor, 9: Rectifier circuit, 10:
Thyristor, 12: AC power supply, 13: Switch, 14: Load, 15: Charging transistor, 17,25: Zener diode, 21,23,2
6: Transistor, 27: Resistor.

Claims (1)

[Claims] 1. A switch circuit comprising a rectifier circuit in which a series circuit of an AC power source and a load is connected between AC input terminals and a thyristor connected between DC output terminals of the rectifier circuit, and a rectified output of the rectifier circuit. A capacitor charged through a series circuit of a charging transistor and an operation display light emitting diode, a sensor circuit connected to both ends of the capacitor to detect a predetermined phenomenon and output a detection signal, the charging transistor and the charging Series control type constant voltage circuit having a Zener diode connected to the base of the operating transistor, and a shunt for shunting the base current of the charging transistor and the current of the operation display light emitting diode with the voltage of the constant voltage circuit as an input Circuit, a detection transistor controlled by a detection signal of the sensor circuit to invalidate the constant voltage circuit, and the capacitor Charging voltage comprises a trigger circuit providing a trigger signal to said thyristor reaches a predetermined value,
A constant voltage output of the constant voltage circuit is set to be lower than a voltage at which the trigger circuit outputs a trigger signal. In the AC 2-wire non-contact switch, the shunt circuit is provided between the operation display light emitting diode and a capacitor. Has a resistor for detecting the charging current of the capacitor connected to, and shunting the base current of the charging transistor and the current of the light emitting diode for operation display by inputting the voltage generated in this resistor and the voltage of the constant voltage circuit. AC two-wire non-contact switch characterized by.