JPS60150320A - Electronic switch - Google Patents

Abstract

PURPOSE:To attain an electronic switch with ease of use by enabling the short- circuit protection to be released by simply spacing away an object to be detected from a sensor circuit even if the short-circuit state is eliminated with a load short-circuited. CONSTITUTION:When an object approaches a proximity switch with the load L short-circuited, a sensor circuit 10 outputs an NL output, and a large current flows to a thyristor 6 and an FET7, but a power voltage given to the sensor circuit 10 is limited by a constant voltage circuit 9 and the short-circuit current is limited by the constant current characteristic of the FET7. Just thereafter, the thyristor 8 is turned on by a voltage division circuit comprising resistors R22, R23. Thus, the short-circuit current is cut off by the FET7. After the short-circuit state is finished, if the proximity switch detects no object, the NL output restores to L to stop the holding of the thyristor 8. Thus, the short-circuit state is eliminated, the state restores automatically to the stand-by state.

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 sensed output. It is related to switches.

Conventional technology 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 cyrisk, and switches based on the detection output. The device is configured so that the element is driven and the supply of power to the nine loads is controlled. By the way, if a load becomes internally short-circuited due to an accident, or by mistake, the power source may be connected directly 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, in a conventional electronic switch having short circuit protection, when the short circuit protection circuit is activated, the short circuit state is maintained until the power is cut off. Therefore, in the event of an instantaneous short circuit, such as when both ends of a load are accidentally shorted for a short period of time,
After a short circuit, the protection circuit is still working even though the load has returned to normal, so the problem is that operation cannot be restarted unless the power is shut off one by one and the operation of the short circuit protection circuit is stopped. there were.

Purpose of the Invention The present invention solves the problems of the conventional electronic switch, and is capable of canceling the protection operation of the short-circuit protection circuit during automatic fishing by stopping the sensor circuit from detecting an object in the event of a short circuit. The purpose is to provide an electronic switch that can be used.

Structure and Effects of the Invention The present invention provides an electronic switch having 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 terminal connected in series to the output switching element, and a current limiting terminal provided between the control terminal of the current limiting terminal and the power supply input terminal, which conducts in the event of a short circuit to limit the current. In addition to cutting off the transistor, the sensor circuit supplies a holding current to the power storage element, the power storage element that supplies power to the sensor circuit, and the ζ output switching element based on the sensor circuit output. The device is characterized by comprising a 1-rega circuit provided with a charging circuit that supplies charging current.

According to the present invention having such characteristics, even when a short circuit occurs, once the short circuit condition is resolved, the sensor circuit performs operations such as moving the object to be detected away so that the object is not detected. It is now possible to divide '+'Z,
It is possible to use an easy-to-use electronic switch.

DESCRIPTION OF EMBODIMENTS FIG. 1 shows an embodiment of an AC two-wire proximity switch according to the present invention. It is a δ diagram. In this diagram, terminal 1.2
A surge voltage absorbing ZNR3 and a diode bridge 4 are connected between the diode bridge 1. An avalanche diode 5 for absorbing surge voltage is connected between the positive and negative terminals of the diode 4. In parallel with the avalanche diode 5, a cyrisk 6 for opening and closing the load and a current limiting transistor that operates in the event of a short circuit are connected in series. The current limiting L-run transistor uses, for example, an electric field J-type transistor (power MO3FET) 7 for electric power that can be driven by a voltage. F F, T 7 Day 1-. A cyrisk 8 is connected between the sources to operate in the event of a short circuit and cut off the F)ET7. Furthermore, a constant voltage circuit 9 is connected in parallel between the positive and negative terminals v1)1 of the diode bridge 4.

Constant voltage circuit 9 &:l: A constant voltage is supplied via a trigger circuit 11 to a sensor circuit 10 which is a detection section formed as an IC. The trigger circuit 11 is provided with a 1-run resistor 12 for current amplifying the output of the sensor circuit 10 and providing a gate signal to the cyrisk 6, and a 1-run resistor 13 for charging a power supply capacitor. A light emitting diode 14 for Uu1 operation is connected between the emitter of I and the constant voltage circuit 9, and its base is connected to the two I rectors of the transistor I2 via a Zener diode 1''l5. It is also connected to the power supply input terminals Vc and c of the sensor circuit 10 through the collector of the L-range squirrel 13 and the J diode 16.The power supply +5i of the sensor circuit 10: between I-i'- and 17- ?
A 1 capacitor C17 for I' and power supply is connected. Between the output of the constant voltage circuit 9 and the collector of the transistor 13, there is a resistor R for charging the capacitor C7 in a standby state and for connecting the power supply to the sensor circuit 10.
1B is connected. Furthermore, a resonant circuit including a detection coil 19 and a sensor C20 is connected to the sensor circuit 10.

Then, when the sensor 1 and 10 do not detect an object,
'1, the output is at the "IT" level when an object is detected, and the NL output terminal of the sensor circuit 10 is connected to the terminal of the l-run risk 12, and the resistor R21
is connected to the anode of Cyrisk 8 via. Also, can-1 of thyristor 6 and diode dove 4)
(7) fj, 6i: f-/- Niha resistance b'122.
A voltage dividing circuit of R23 is connected, and the gate terminal of the thyristor 8 is connected to the common connection end of these resistors.

Now, connect the AC power supply 30 and the load I between terminals 1 and 2 as shown in the figure.
, and are connected in series. Then, a minute current flows through the load, and the AC voltage of the AC power source 30 is rectified by the diode bridge 4, converted to a DC voltage of a predetermined voltage by the constant voltage circuit 9, and is connected to the resistor R18 as shown in FIG.
Power is supplied to the sensor circuit 10 via the capacitor C17, and the capacitor C17 is charged. At this time, the oscillator of the sensor circuit 10 oscillates due to the resonance circuit formed by the detection coil 19 and the capacitor C20 connected to the sensor circuit 10, and the sensor circuit 10 is in a standby state waiting for the approach of an object.

In this state, the thyristor 6 is off and the FET 7 is also off. Then, if an object approaches at time L1 and the oscillation state of the sensor circuit 10 changes, the sensor circuit 10 outputs "" from the output terminal NL as shown in FIG.
■]” outputs the outputs of the relays and makes the FIET 7 conductive. At the same time, the 1-run risk 12 turns on and triggers the thyristor 6. Therefore, the thyristor 6 turns on and the diode Current is supplied to the load via the bridge 4 and the load is driven.J22
In each subsequent cycle, when the zero crossing point is passed, thyristor 6 turns off, but thyristor 1 turns off.
2 and 13 are immediately turned on, capacitor C17 is rapidly charged, and when the Zener voltage of Zener diode 1"15 is reached, transistor 13 is turned off and Cyrisk 6 is turned on. During this time, FET7 continues to be on, but FET7 Since the input impedance is extremely high, the current flowing through the resistor R21 is small.In this way, power is supplied to the sensor circuit 10 and the phase of the thyristor 6 is controlled.

Now, the operation when an overcurrent flows through the load or when the load (2) is short-circuited will be explained. Assume that an object approaches the proximity switch at time t3 as shown in FIG. 3 while the load I7 is in a short-circuited state.

Then, the sensor circuit 10 outputs an NL output as shown in FIG. 3(C), and a large current flows through the thyristor 6 and FET 7. However, since the power supply voltage given to the sensor circuit 10 is set to a constant voltage by the constant voltage circuit 9,
．． -, the gate voltage applied to FET 7 is also constant, and the short circuit current is limited to a constant value due to the constant current characteristics of FET 7. Immediately after that, a voltage of Day 1 is applied by the voltage divider circuit of resistors R22 and R23, turning on Cyrisk 8 and lowering the gate of FET 7 to near zero volts. Therefore, the short circuit current is FE as shown in Figure 3(b).
It is cut off by T7, and it becomes possible to protect the diode bridge 4 and the thyristor 6, which is a switching element, from a short circuit state. Thereafter, a holding current flows from the N L output of the sensor circuit 10 to the thyristor 8 via the resistor R21, keeping the thyristor 8 in the on state. And Figure 3 (C
As shown in 1, if the proximity switch no longer detects an object at time t4 after the short-circuit condition is resolved, the NL ratio output "
The proximity switch returns to the "L" level and stops holding the thyristor 8. Therefore, the proximity switch returns to the standby state shown in FIG. 6 and FET 7 are triggered, and it becomes possible to drive the load through the diode bridge 4.If the short-circuit condition is resolved in this way, it is possible to automatically return to the standby state without having to disconnect the power supply. can.

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 the drawing]

Fig. 1 is a circuit diagram showing an embodiment of the AC two-wire proximity switch according to the present invention, Fig. 2 is a waveform diagram showing the waveforms of each part under normal operating conditions, and Fig. 3 is a waveform diagram of each part during a short circuit. FIG. 1, 2-----One terminal 4-----Diode bridge 6.13--11--Thyristor 7-----F
ET 9-Constant voltage circuit 10----Sensor circuit 11--+-Riga circuit 12. 13------1-
Transistor 14- Light emitting diode 15 Middle-zener diode-1' C17, C20-con, 'nza 19-
-Detection coil R18, R21, R22゜R23-
1 Resistance patent applicant Tateishi Electric Co., Ltd. agent Patent attorney Yoshiki Okamoto (and 1 other person) Figure 2 1 1t2 Figure 3

Claims (2)

[Claims] (1) Connected in series to the sensor circuit, load and power supply,
An electronic switch comprising: an output switching element that controls power supply to a 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 connected in series to the output switching element. is provided between the control terminal of the transistor and the power supply input terminal, and conducts when short-circuited to cut off the current limiting I/Run risk, and also supplies power to the current limiting I/Run risk to which a holding current is applied from the sensor circuit, and to the sensor circuit. and a trigger circuit provided with a charging circuit that triggers the output switching element based on the output of the sensor circuit and supplies charging current to the storage element. switch 6 (2) The electronic switch according to claim 1, wherein the electricity storage element is a capacitor.