JPH0354901B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to electronic devices such as two-wire photoelectric switches and proximity switches that are connected in series between a load and a power source and are configured to directly control the load based on a detection output. It's about the switch.

Prior art and its problems A two-wire electronic switch such as a photoelectric switch or a proximity switch that is configured to directly control a load has a detection section and a switching element such as a thyristor, and switches based on the detection output. The device is configured to drive and control the supply of power to the load. However, if the load becomes internally short-circuited due to an accident, or by mistake, the power source may be directly connected to the electronic switch without connecting the load. In order to protect the internal circuit from such a short-circuit condition, a protection circuit for short-circuit protection is provided inside the electronic switch. By the way, if the short-circuit protection circuit is operating when the load is short-circuited, if there is no indication that the short-circuit protection is operating, the user would have no way of knowing whether the electronic switch itself is malfunctioning or whether it is not operating due to the load short-circuit. . Particularly when a large number of electronic switches are used on a production line in a factory, etc., there is a problem in that if an electronic switch is not working during installation or operation, it is necessary to check both the load condition and the electronic switch. .

OBJECTS OF THE INVENTION The present invention solves the problems of the conventional electronic switches, and provides an electronic switch that can clearly indicate the short-circuit condition of the load.

Structure and Effects of the Invention The present invention is an electronic switch that includes a sensor circuit and an output switching element that is connected in series to a load and a power source and controls power supply to the load based on the output of the sensor circuit. A current limiting transistor is connected in series to the output switching element, a storage element supplies power to the sensor circuit, and a current limiting transistor is provided between the control terminal and power input terminal of the current limiting transistor and is conductive in the event of a short circuit. A thyristor that shuts off the current limiting transistor and is supplied with a holding current from a storage element, and a first display that triggers the output switching element based on the sensor circuit output and lights up when triggered to indicate the operating status. and a second indicator provided between the electricity storage element and the thyristor and lit by a holding current applied to the thyristor to notify the short circuit state. be.

According to the present invention having such features, when the short-circuit protection circuit is activated, it is possible to display it using a display other than the operation display. Therefore, if the electronic switch does not work, there is no need to remove it one by one and check its operation.
It is possible to create an easy-to-use electronic switch.

DESCRIPTION OF EMBODIMENTS FIG. 1 is a circuit diagram showing an embodiment of an AC two-wire proximity switch according to the present invention. In this figure, a ZNR 3 for absorbing surge voltage and a diode bridge 4 are connected between terminals 1 and 2, and an avalanche diode 5 for absorbing surge voltage is connected between the positive and negative terminals of diode bridge 4. A thyristor 6 that opens and closes the load L and a current limiting transistor that operates in the event of a short circuit are connected in series in parallel to the avalanche diode 5. As the current limiting transistor, for example, a power field effect transistor (power MOSFET) 7 that can be driven by voltage is used. Thyristor 8 is installed between the gate and source of FET7 and operates when short circuit occurs to cut off FET7.
is connected. Further, a constant voltage circuit 9 is connected in parallel between the positive and negative terminals of the diode bridge 4.
The constant voltage circuit 9 supplies a constant voltage via a trigger circuit 11 to a sensor circuit 10 which is a detection section formed as an IC. The trigger circuit 11 includes a transistor 12 that amplifies the output of the sensor circuit 10 and provides a gate signal to the thyristor 6;
A transistor 13 for charging a power supply capacitor is provided. A light emitting diode 14a for displaying operation is connected between the emitter of the transistor 13 and the constant voltage circuit 9, and its base is connected to the collector of the transistor 12 via a Zener diode 15. Further, the collector of the transistor 13 is connected to the power input terminal Vcc of the sensor circuit 10 via a diode 16. A smoothing and power supply capacitor C17 is connected between the power supply terminals of the sensor circuit 10. A resistor R18 is connected between the output of the constant voltage circuit 9 and the collector of the transistor 13 to charge the capacitor C17 in a standby state. Furthermore, a resonant circuit including a detection coil 19 and a capacitor C20 is connected to the sensor circuit 10.
The NL output terminal of the sensor circuit 10, which is at "L" level when the sensor circuit 10 does not detect an object and outputs an "H" level when an object is detected, is connected to the base of the transistor 12. Further, the positive end of the capacitor C17 is connected to the anode of the thyristor 8 via the light emitting diode 14b and the resistor R21. The light-emitting diode 14b is a short-circuit display light-emitting diode that lights up when the short-circuit protection circuit by the thyristor 8 is activated, and has a color different from that of the operation display light-emitting diode 14a. These light emitting diodes 14
It is preferable to use two-color light emitting diodes 14 housed in the same chip for a and 14b. Further, a voltage dividing circuit of resistors R22 and R23 is connected between the cathode of the thyristor 6 and the negative terminal of the diode bridge 4, and a thyristor 8 is connected to the common connection terminal of these resistors.
The gate terminal of is connected.

FIG. 2 is a sectional view of the proximity switch according to this embodiment. As shown in this figure, the proximity switch is provided with a detection coil 19 on the front surface and a detection circuit section 26 formed inside a case 25. The above-mentioned two-color light emitting diode 14 is placed in a position visible from the outside.
is arranged to guide display light to the outside via an optical fiber 27. By using the two-color light emitting diode 14 in this manner, the structure of the case can be simplified and the electronic switch can be made smaller.

Now, connect the AC power supply 30 between terminals 1 and 2 as shown in the figure.
and load L are connected in series. Then the load L
A minute current flows through the AC voltage of the AC power supply 30, which is rectified by the diode bridge 4, converted to a DC voltage of a predetermined voltage by the constant voltage circuit 9, and power is supplied to the sensor circuit 10 via the resistor R18. At the same time, the capacitor C17 is charged. At this time, the detection coil 1 connected to the sensor circuit 10
9 and a capacitor C20, the oscillator of the sensor circuit 10 oscillates, and is in a standby state awaiting the approach of an object. In this state, the thyristor 6 is off and the FET 7 is also off. If an object approaches and the oscillation state of the sensor circuit 10 changes, the sensor circuit 10 outputs an "H" level output from the output terminal NL and the FET 7
is in a conductive state. At the same time, transistor 12 turns on and triggers thyristor 6. Therefore, the thyristor 6 turns on and the diode bridge 4
A current is supplied to the load L via the current, and the load L is driven. In each subsequent cycle, when the zero crossing point is passed, the thyristor 6 is once turned off, but the transistors 12 and 13 are immediately turned on, and the capacitor C17 is rapidly charged, and when the Zener voltage of the Zener diode 15 is reached, the transistor 13 is turned off. Thyristor 6 is turned on. During this time, FET7 remains on, but
Since the input impedance of the FET 7 is extremely high, the current flowing through the light emitting diode 14b and the resistor R21 is extremely small, and the light emitting diode 14b does not light up. In this way, power is supplied to the sensor circuit 10 and the phase of the thyristor 6 is controlled. At this time, each time the capacitor C17 is rapidly charged, the light emitting diode 14a for operation display is activated.
lights up. Therefore, the light emitting diode 14a repeatedly blinks at 100 or 120 Hz, which is twice the frequency of commercial AC.
It appears to be lit continuously, indicating that the proximity switch is in a detection state when it detects an object.

Now, the operation when an overcurrent flows through the load L or when the load L is short-circuited will be explained. Current load L
Suppose that an object approaches the proximity switch while the switch is short-circuited. Then the sensor circuit 10
outputs NL output, and a large current flows through thyristor 6 and FET7. However, since the power supply voltage applied to the sensor circuit 10 is set to a constant voltage by the constant voltage circuit 9, the gate voltage applied to the FET 7 is also constant, and the short circuit current is kept at a constant value due to the constant current characteristics of the FET 7. limited. Immediately after that, a gate voltage is applied by the voltage divider circuit of low resistors R22 and R23, and the thyristor 8 is turned on.
Lower the gate of FET7 to near zero volts. Therefore, the short circuit current is cut off by the FET 7, and it becomes possible to protect the diode bridge 4 and the thyristor 6, which is a switching element, from the short circuit state. After that, a holding current flows from the power supply capacitor C17 to the thyristor 8 via the light emitting diode 14b and the resistor R21, lighting up the light emitting diode 14b for short circuit protection display and keeping the thyristor 8 in the on state. In this way, when the thyristor 8 operates due to the short circuit, no short circuit current flows through the thyristor 6 and the FET 7, so the diode bridge 4 and the switching thyristor 6
It becomes possible to protect the

In this embodiment, the light emitting diodes for operation display and short circuit protection display are two-color light emitting diodes formed in the same chip, but the two light emitting diodes can be configured for operation display and short circuit display, respectively. is also possible.

Furthermore, although this embodiment has been described with reference to an AC two-wire proximity switch, it goes without saying that the present invention can be applied to other two-wire electronic switches such as photoelectric switches. Further, although this embodiment uses an AC power source as a power source, it can be similarly applied to an electronic switch using a DC power source.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram showing an embodiment of an AC two-wire proximity switch according to the present invention, and FIG. 2 is a sectional view of the proximity switch according to the present invention. 1, 2... terminal, 4... diode bridge,
6, 8... Thyristor, 7... FET, 9... Constant voltage circuit, 10... Sensor circuit, 11... Trigger circuit, 12, 13... Transistor, 14a, 1
4b, 14...Light emitting diode, 15...Zena diode, C17, C20...Capacitor, R
18, R21, R22, R23...Resistance, 19...
...Detection coil.

Claims (1)

[Scope of Claims] 1. A sensor circuit, an output switching element connected in series to a load and a power source, and controlling power supply to the load based on the output of the sensor circuit;
An electronic switch having: a current-limiting transistor connected in series to the output switching element; a storage element supplying power to the sensor circuit; and a current-limiting transistor connected between a control terminal of the current-limiting transistor and a power input terminal. a thyristor that is provided and conducts when short-circuited to cut off the current limiting transistor and is supplied with a holding current from the storage element; and a thyristor that triggers the output switching element based on the sensor circuit output and lights up when triggered. a trigger circuit having a first indicator for displaying an operating state by a trigger circuit; and a second indicator provided between the electricity storage element and the thyristor and lit by a holding current applied to the thyristor to notify a short circuit state. An electronic switch comprising: 2. The electronic switch according to claim 1, wherein the first and second indicators are light emitting diodes. 3. The electronic switch according to claim 2, wherein the light emitting diodes are two-color light emitting diodes that emit light of different colors and are formed on the same chip.