JPH066199A - Three-wire type electronic switch - Google Patents

Abstract

PURPOSE:To reduce consumption current of a power supply circuit by avoiding to supply a holding current of a thyristor from a sensor circuit in the 3-wire electronic switch employing the thyristor as an output switching element. CONSTITUTION:A diode bridge 8 is connected between terminals 2, 3 and a power supply circuit 6 is connected between its negative terminal and a terminal 1. Power is supplied from the power supply circuit 6 to a sensor circuit 7. Furthermore, a thyristor 9 short-circuiting the diode bridge 8 is provided and a switching transistor(TR) 11 is connected between the anode and the gate. Then an object detection signal from the sensor circuit 7 is given to a base of the TR 11. When the TR 11 is turned on at the detection of an object, a gate current is supplied to the thyristor 9 through the diode bridge 8 and the TR 11.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a three-wire type electronic switch, and more particularly to an electronic switch using a thyristor as an output switching element.

[0002]

2. Description of the Related Art An example of a conventional three-wire type electronic switch is shown in FIG.
Shown in. This electronic switch has three terminals 1 to 3, an AC power source 4 outside the terminals 1 and 3, and a load 5 outside the terminals 1 and 2. A power supply circuit 6 is connected to the terminal 1 to rectify and smooth the input voltage to a constant DC voltage. Then, a constant voltage is supplied from the power supply circuit 6 to the sensor circuit 7. If this electronic switch is a reflection type photoelectric switch, the sensor circuit 7 has a light projecting portion and a light receiving portion, and detects an object based on the presence or absence of reflected light from the detection area. The section is provided with a discrimination circuit and a signal processing circuit for discriminating the light reception output. A diode bridge 8 is connected between the terminals 2 and 3, and a thyristor 9 which is an output switching element for opening and closing the outputs 2 and 3 is connected between the positive and negative ends of the diode bridge 8. A resistor R1 and a capacitor C1 are connected in parallel between the gate of the thyristor 9 and the negative terminal, and an object detection signal is output from the sensor circuit 7.

In such a conventional photoelectric switch, the AC power supply 4 is rectified by the power supply circuit 6 and supplied to the sensor circuit 7. When an object is detected, the sensor circuit 7 triggers the thyristor 9 to short-circuit the terminals 2 and 3, so that power is supplied to the load 5.

[0004]

However, in such a conventional electronic switch using a thyristor as an output switching element, the holding current of the thyristor is supplied from the sensor circuit 7. In such a gate current supply method, the sensor circuit 7 of the electronic switch needs to be supplied with the gate current of the thyristor from the power supply circuit 6 in addition to the consumption current of the sensor circuit itself. Therefore, there is a drawback in that it is necessary to increase the supply capacity of the power supply circuit and heat dissipation processing is required. Further, there is a drawback that the current consumption of the electronic switch itself increases.

The present invention has been made in view of such conventional problems, and it is a technical object to make it possible to reduce the current consumption of a power source that is stabilized in an electronic switch.

[0006]

The present invention is a three-wire type electronic switch in which a power source is connected between first and third terminals and a load is connected between first and second terminals. A thyristor that opens and closes between the three terminals, a power supply circuit that is connected to the first terminal to generate a constant voltage, a sensor circuit to which a constant voltage is supplied from the power supply circuit, and a second terminal and the gate end of the thyristor. And a switching transistor connected to the sensor circuit to which a control signal is applied from the sensor circuit, and the gate current is supplied to the thyristor by energizing the switching transistor.

[0007]

According to the present invention having such a feature, the DC power supply of a constant voltage is supplied to the sensor circuit by the power supply circuit connected to the terminal 1. When the sensor circuit detects an object, an object detection signal is given to the transistor, the emitter current of this transistor is added to the thyristor as a gate current, and the thyristor is triggered.
Therefore, the terminals 2 and 3 are short-circuited, and power is supplied to the load. At this time, the collector current is supplied to the transistor from the terminal 2, and this current is supplied to the gate of the thyristor as the emitter current, so that it is not necessary to supply the gate current from the power supply circuit.

[0008]

1 is a circuit diagram showing the configuration of a three-wire type electronic switch according to an embodiment of the present invention. In this figure, the same parts as those of the conventional example described above are designated by the same reference numerals, and detailed description thereof will be omitted. Also in this embodiment, the AC power source 4 is connected between the terminals 1 and 3, the load 5 is connected between the terminals 1 and 2, and the diode bridge 8 is connected between the terminals 2 and 3 for switching between the positive and negative ends thereof. The connection of the thyristor 9 is similar to the conventional example. A power supply circuit 6 is connected between the terminal 1 and the negative terminal of the diode bridge 8. Power circuit 6
Generates a constant voltage, and the voltage is supplied to the sensor circuit 7. In this embodiment, the transistor 1 is connected to the positive terminal of the diode bridge 8 via the resistor R2.
One collector is connected. The emitter of the transistor 11 is connected to the gate of the thyristor 9, and the resistor R1,
It is connected to the negative terminal of the diode bridge 8 via the capacitor C1. Further, the object detection output of the sensor circuit 7 is given to the base of the transistor 11 via the voltage dividing circuit composed of the resistors 3 and R4. Other configurations are the same as those of the conventional example described above.

Next, the operation of this embodiment will be described. A constant voltage is supplied to the sensor circuit 7 by the power supply circuit 6 connected to the terminal 1 and the negative terminal of the diode bridge 8. When the sensor circuit 7 detects the object, the object detection signal is transmitted to the transistor 11 via the voltage dividing circuit of the resistors R3 and R4. When the transistor 11 is turned on, the gate current is also supplied to the thyristor 9 and the thyristor 9 is triggered. Therefore, the terminals 2 and 3 are short-circuited, and the AC voltage is supplied to the load 5. Then, the collector current and the emitter current continue to flow through the transistor 11 via the diode bridge 8, and this current is added as the gate current of the thyristor 9.
Therefore, it is not necessary to directly supply the gate current from the power supply circuit 6. Since only the base current of the transistor 11 needs to be supplied from the sensor circuit 7, the thyristor 9 can be held in the ON state only by supplying a current of approximately 1 / h _FE in addition to the conventional example. Therefore, the current supplied from the sensor circuit 7 is significantly reduced, and the current consumption of the power supply circuit 6 is also reduced. Therefore, the power supply circuit 6 can be downsized.

Although the present embodiment has been described with respect to a three-wire type photoelectric switch, it is needless to say that the present invention can be applied to various other electronic switches such as a proximity switch. Further, the present invention can be applied not only to an AC power source but also to an electronic switch using a DC power source.

[0011]

As described in detail above, according to the present invention, the current consumption of the power supply circuit is small, so that the power supply circuit can be significantly downsized. Further, it is possible to reduce the price of the electronic switch.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing a configuration of an electronic switch according to an embodiment of the present invention.

FIG. 2 is a circuit diagram showing a configuration of a conventional electronic switch.

[Explanation of symbols]

 1 to 3 terminals 4 AC power supply 5 Load 6 Power supply circuit 7 Sensor circuit 8 Diode bridge 9 Thyristor 11 Transistor

Claims (1)

[Claims] 1. A power supply between the first and third terminals, and the first and second terminals.
A three-wire type electronic switch in which a load is connected between the terminals of, a thyristor that opens and closes between the second and third terminals, and a power supply circuit that is connected to the first terminal and generates a constant voltage. A switching circuit connected between the second terminal and a gate end of the thyristor, to which a control signal is applied from the sensor circuit; A three-wire electronic switch, wherein a gate current is supplied to the thyristor by energizing a transistor.