JPH0354902B2 - - 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 display indicating the short-circuit protection operation, it is difficult for the user to know whether the electronic switch itself is malfunctioning or whether it is not operating due to the load short-circuit. There is a point. For this reason, there are electronic switches equipped with display elements such as light emitting diodes that light up when short circuit protection is activated.
Since it is necessary to provide an indicator for short-circuit protection in addition to an indicator for displaying operation, the structure of the electronic switch becomes complicated, which requires time and effort during assembly, resulting in an increase in price. Another problem is that when there are a large number of indicators, it becomes difficult to understand what the lights on the indicators indicate, and it becomes difficult to understand at first glance that it is a short-circuit protection warning.

Furthermore, in conventional electronic switches with short-circuit protection, when the short-circuit protection circuit is activated, the short-circuit condition cannot be resolved and the normal state cannot be restored unless the power is cut off or the object to be detected is removed. Another problem was that it took time and effort to restore operation in the event of a short circuit or the like.

Purpose of the Invention The present invention is to solve the problems of the conventional electronic switch, and to clearly indicate the short-circuit condition of the load by using the operating display as it is and making the display blink. The present invention provides an electronic switch that can automatically recover from a short circuit.

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 connected in series to the output switching element, and a current limiting transistor provided between the control terminal of the current limiting transistor and the power input terminal, which conducts in the event of a short circuit to cut off the current limiting transistor, and also a thyristor to which a holding current is applied;
Charging includes a storage element that supplies power to the sensor circuit, a switching element for output switching based on the sensor circuit output, and a constant current element that supplies a current below the holding current of the thyristor to the storage element as a charging current. a trigger circuit including a circuit and a quick charging circuit for quickly charging a power storage element; and a trigger circuit provided in the quick charging circuit of the trigger circuit, which lights up when an object is detected and maintains the charging current of the charging circuit and the thyristor when a short circuit occurs. The present invention is characterized by comprising an indicator that blinks at a period based on the difference between the current and the current to notify the short circuit state.

According to the present invention having such characteristics, the holding current of the thyristor that conducts during a short circuit is made smaller than the charging current to the storage element that serves as the power source of the sensor circuit, and the operation of the sensor circuit is stopped at a predetermined cycle. This causes the operation display to blink. Therefore, it is possible to use the operation indicator as is to indicate a short circuit.
In addition, when a short circuit occurs, there is no need to cut off the power supply or remove the object to be detected to cancel the protection state, and the protection state is automatically canceled when the short circuit is no longer present. Therefore, once the short-circuit condition, such as an instantaneous short-circuit, is resolved, it can be restored as is, making it possible to provide an extremely 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. The output terminal of the constant voltage circuit 9 is connected to the emitter of the transistor 13 via a light emitting diode 14 for power display and a light emitting diode 15 for operation display, and its base is connected to the collector of the transistor 12 via a Zener diode 16. Ru. 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 C18 is connected between the power supply terminals of the sensor circuit 10.
is connected. A constant current diode 19 is provided between the cathode of the light emitting diode 14 and the collector of the transistor 13 to prevent rush current from flowing into the capacitor C18 when the transistor 13 is off, charge it with a constant current, and provide a power supply voltage to the sensor circuit 10. It is connected. Furthermore, a resonant circuit including a detection coil 20 and a capacitor C21 is connected to the sensor circuit 10. The sensor circuit 10 outputs an "L" level when the sensor circuit 10 does not detect an object, and outputs an "H" level when an object is detected.
The NL output terminal of the thyristor 8 is connected to the base of the transistor 12, and the NL output terminal of the
connected to the anode of the A voltage dividing circuit including resistors R23 and R24 is connected between the cathode of the thyristor 6 and the negative terminal of the diode bridge 4, and the gate terminal of the thyristor 8 is connected to the common connection end of these resistors.

FIGS. 2a and 2b are a front view and a side view showing the appearance of the proximity switch according to this embodiment. As shown in this figure, this proximity switch has a sensing surface on the front and an indicator on the side. As described above, the display device includes a light emitting diode 14 for indicating power supply and a light emitting diode 15 for indicating operation, which are provided at a position easily visible to the user as shown in the figure.

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 source 30, which is rectified by the diode bridge 4, and converted into a DC voltage of a predetermined voltage by the constant voltage circuit 9. Power is supplied to the sensor circuit 10 via the capacitor C18, and the capacitor C18 is charged. Therefore, the power supply display light emitting diode 14 lights up to indicate that the power supply is connected. At this time, the sensor circuit 10
Detection coil 19 and capacitor C connected to
The oscillator of the sensor circuit 10 oscillates due to the resonance circuit 21, 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. and the time
Assuming that an object approaches at time t1 and the oscillation state of the sensor circuit 10 changes, the sensor circuit 10 outputs an "H" level output from the output terminal NL, making the FET 7 conductive, as shown in FIG. 3c. At the same time, transistor 12 turns on and triggers thyristor 6. Therefore, the thyristor 6 is turned on and current is supplied to the load L via the diode bridge 4, thereby driving the load L. 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 C18 is rapidly charged, and when the Zener voltage of the Zener diode 16 is reached, the transistor 13 is turned off. Thyristor 6 is turned on. During this time, FET7 continues to be on, but since FET7 has an extremely high input impedance, the current flowing through resistor R22 is extremely small. In this way, sensor circuit 1
0 and also controls the phase of the thyristor 6. At this time, each time the capacitor C18 is rapidly charged, the light emitting diode 15 for indicating operation lights up. Therefore, the light emitting diode 15 repeatedly flashes at 100 or 120 Hz, which is twice the frequency of commercial AC, but as shown in Figure 3b, it appears to be lit continuously, indicating that the proximity switch has detected an object. This will be displayed.

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
Assume that an object approaches the proximity switch at time t3 as shown in FIG. 4 while the switch is in a short-circuited state. Then, the sensor circuit 10 outputs an NL output, and a large current flows through the thyristor 6 and FET 7.
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, low anti-R23,
A voltage is applied to the gate of the thyristor by the voltage dividing circuit of R24, 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 C18 to the thyristor 8 via the sensor circuit 10 and the resistor R22, keeping the thyristor 8 in the on state. Here, the resistance value of the resistor R22 is selected so that the holding means of the thyristor 8 is larger than the charging current flowing through the light emitting diode 14 and the constant current diode 19. Then thyristor C1
The power supply voltage applied to the sensor circuit 10 at both ends of the sensor circuit 8 gradually decreases as shown in FIG. 4a, and reaches the IC reset voltage Vr of the sensor circuit 10 at time t4. When the reset voltage Vr is reached, the NL output of the sensor circuit 10 becomes "L" level,
Thyristor 8 loses its holding current and turns off. Then, the current consumption of the capacitor C18 decreases, the capacitor C18 is charged via the constant current diode 19, and the power supply voltage applied to the sensor circuit 10 increases again. If this voltage exceeds the reset voltage Vr, the sensor circuit 10
The NL output outputs an "H" level output again, transistor 12 is turned on, and capacitor C18 is rapidly charged via transistor 13, and at the same time, light emitting diode 15 lights up momentarily as shown in FIG. 4b. When an object is close to the proximity switch, the transistor 13 is turned off and the thyristor 6 and FET 7 are triggered and turn on for a moment, but the thyristor 8 turns on and the FET
7 is turned off to stop the short circuit current. Thereafter, a protection current flows from the capacitor C18 to the thyristor 8 via the sensor circuit 10 and the resistor R22. At this time, the capacitor C18 is charged via the power supply display light emitting diode 14 and the constant current diode 19, and the above-described operation is repeated. Therefore, as shown in FIG.
As shown in Figure b, a light emitting diode 15 for operation display
flashes. This cycle is set to be about 1.5 seconds, for example, by adjusting the resistance value of the resistor R22. This makes it possible to notify the user that the short-circuit protection circuit is operating. If the short-circuit condition is resolved here, even if a load current flows through the thyristor 6 and FET 7 next time, the thyristor 8 will not be triggered. Therefore, the normal operation shown in FIG. 3 can be restored as is.

In this embodiment, a light emitting diode 14 for indicating power is provided in series with the power input terminal of the trigger circuit 11, but it is not necessary to provide a light emitting diode for indicating power, and a light emitting diode 15 for indicating operation is provided.
It can also be done only.

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, Fig. 2a and Fig. 2b
3 is a waveform diagram showing the waveform of each part during normal operation, and FIG. 4 is a waveform diagram showing the waveform of each part in a load short-circuit state. It is a diagram. 1, 2... terminal, 4... diode bridge,
6, 8... Thyristor, 7... FET, 9... Constant voltage circuit, 10... Sensor circuit, 11... Trigger circuit, 12, 13... Transistor, 14, 15
...Light emitting diode, 16 ... Zena diode, C18, C21 ... Capacitor, 19 ... Constant current diode, 20 ... Detection coil, R22,
R23, R24...Resistance.

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 comprising: a current limiting transistor connected in series to the output switching element; and a current limiting transistor provided between a control terminal and a power supply input terminal of the current limiting transistor and conductive when short-circuited to close the current limiting transistor. a thyristor that interrupts the output and is supplied with a holding current from the sensor circuit; a power storage element that supplies power to the sensor circuit; a constant current element that triggers the output switching element based on the sensor circuit output; a trigger circuit comprising: a charging circuit that supplies a current equal to or less than the holding current of the thyristor to the electricity storage element as a charging current; and a quick charging circuit that rapidly charges the electricity storage element; and a quick charging circuit of the trigger circuit. and an indicator that lights up when an object is detected and blinks at a cycle based on the difference between the charging current of the charging circuit and the holding current of the thyristor when a short circuit occurs to notify the short circuit state. An electronic switch featuring 2. The electronic switch according to claim 1, wherein the charging circuit for the storage element of the sensor circuit is provided with a display for displaying the power supply to notify the state of charge. 3. The electronic switch according to claim 1 or 2, wherein the indicator is a light emitting diode. 4. The electronic switch according to claim 1, 2, or 3, wherein the electricity storage element is a capacitor.