JPH0416507Y2 - - Google Patents

Description

[Detailed Description of the Invention] [Field of the Invention] The present invention relates to two-wire photoelectric switches, proximity switches, etc. 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. This is related to the detection switch.

[Summary of the idea]

The detection switch according to the present invention not only indicates that the power is turned on at the power input terminal of the detection circuit in an electronic switch such as a photoelectric switch or a proximity switch, but also detects the period between the power reset time and the discharge time of the power supply smoothing capacitor when the load is short-circuited. A display device is provided which blinks to indicate the short circuit state, thereby reducing the number of display devices and reducing the increase in current consumption of the detection 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 the switching element is driven based on the detection output to control the load. The device is configured to control the supply of power to the device. However, if the load becomes internally short-circuited due to an accident, or by mistake, the power source may be connected directly to the detection 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 detection switch. If the short circuit protection circuit is operating at the time of such a load short circuit, it is necessary to notify the short circuit state. Therefore, the detection switch requires an indicator to indicate the short circuit state in addition to a power indicator and an operation indicator. When the number of indicators increases in this manner, it becomes difficult to understand what the lights on the indicators indicate, and there is a problem in that it becomes difficult to understand at first glance that it is a short-circuit protection warning.

[Purpose of invention]

The present invention solves the problems of conventional detection switches, and provides a detection switch that can clearly indicate the short-circuit condition of the load by using the power supply display as is and making the display blink. It provides:

[Structure and effect of the idea]

The present invention is a detection switch that includes a detection 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 detection circuit. An overcurrent detection circuit that detects overcurrent flowing through the switching element, a self-holding switching element that is driven by the detection output of the overcurrent detection circuit and conducts in the event of a short circuit to cut off the overcurrent, and a storage device that supplies power to the detection circuit. Trigger an output switching element based on the output of the element and the detection circuit, and
A trigger circuit that has a constant current element and charges a power storage element is connected to a reset capacitor, and the output of the detection circuit is prohibited for a predetermined prohibition period during the voltage reset time after the power is turned on and when the supply voltage to the detection circuit decreases. A power supply reset circuit is connected in series between the trigger circuit and the detection circuit, and lights up when power is supplied to the detection circuit. The present invention is characterized by comprising an indicator that blinks to notify the short circuit state.

According to the present invention having such characteristics, when a short circuit occurs, the display is made to blink according to the cycle of the charging time of the reset capacitor and the prohibition time. Therefore, it is possible to display a short circuit using the power supply display as is. Furthermore, since the power indicator light is used as it is to indicate a short circuit, it is possible to reduce the current consumption of the detection switch by the power indicator light.

[Explanation of Examples]

(Configuration of Embodiment) FIG. 1 is a block diagram schematically showing an embodiment of an AC two-wire proximity switch according to the present invention, and FIG. 2 is a circuit diagram showing its detailed configuration. In this figure, a diode bridge 3 is connected between terminals 1 and 2, and between the positive and negative terminals of the diode bridge 3 are a thyristor 4, which is an output switching element that opens and closes a load L, and a current limiting transistor 5, which operates in the event of a short circuit. are connected in series. The current limiting transistor 5 is, for example, a power field effect transistor (power transistor) that can be driven by voltage.
MOSFET) is used. A thyristor 6, which is a self-holding switch, is connected between the gate and source of the FET 5 and operates to cut off the FET 5 when short-circuited. A constant voltage circuit comprising a Zener diode 7 and a transistor 8 is also connected between the positive and negative terminals of the diode bridge 3. Constant voltage circuit is IC
A trigger circuit 1 is connected to a detection circuit 9 formed as
0 to supply a constant voltage. The trigger circuit 10 is provided with a transistor 11 for current amplifying the object detection output of the detection circuit 9 and providing a gate signal to the thyristor 4, and a transistor 12 for charging a power supply capacitor. The emitter of transistor 8 is a light emitting diode 1 for indicating operation.
3 to the emitter of transistor 12. The base of transistor 12 is connected to the collector of transistor 11 via Zener diode 14 . The collector of the transistor 12 is connected to the power input terminal of the detection circuit 9 via a diode 15 and a light emitting diode 16 for power supply and short circuit indication.
Connected to Vcc. A smoothing and power supply capacitor C17 is connected between the anode of the light emitting diode 16 and the ground. Between the anode of the light emitting diode 13 and the collector of the transistor 12,
A constant current diode 18 is connected to prevent rush current from flowing into the capacitor C17 when the transistor 12 is off, to charge the capacitor C17 with a constant current, and to supply a power supply voltage to the detection circuit 9. A resonant circuit including a detection coil 19 and a capacitor C20 is connected to the detection circuit 9, and an oscillation circuit and a comparison circuit section for detecting an object based on a decrease in the output of the oscillation circuit are provided. The output section of the detection circuit 9 is provided with a series connection of output transistors Q1 and Q2 between the power supplies, and a transistor Q0 that drives these transistors based on an object detection signal. Q1 is turned on when an object is detected. An output circuit is formed that turns on Q2 when not detected. In addition, a power supply reset circuit 21 is provided which turns off both of these output transistors Q1 and Q2 during the power reset time after power-on and the prohibition time after short-circuit detection to prevent erroneous output from being output when the output voltage rises after power-on. is provided. The power supply reset circuit 21 is externally provided with a power supply reset time, which is the charging time from 0V to the power supply reset release voltage Vre, and an inhibition time, which is the charging time from the reset initial voltage Vs, which starts the reset operation, to the power supply reset release voltage Vre. A reset capacitor C22 is connected to define the voltage. Then, the operation of the constant current circuit 23 is stopped for the power supply reset time and prohibition time until the terminal voltage reaches the power supply reset release voltage Vre, and both transistors Q1 and Q2 are turned off. The midpoint of the transistors Q1 and Q2 is the NL output terminal of the detection circuit 9, which outputs an "L" level when the detection circuit 9 does not detect an object and an "H" level output when an object is detected. transistor 1
1 and the diode 25
The anode of the thyristor 6 is connected to the anode of the thyristor 6 via the thyristor 6. Furthermore, a resistor 26 for detecting overcurrent is connected between the cathode of the thyristor 4 and the negative terminal of the diode bridge.
27 voltage dividing circuits are connected, and the gate terminal of the thyristor 6 is connected to the common connection end of these resistors.

(Operation of this embodiment) 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 3, converted to a DC voltage of a predetermined voltage by the constant voltage circuit, and then sent to the detection circuit via the constant current diode 18 and the light emitting diode 16. 9 is supplied with power and the capacitor C
17 is charged. At this time, the light emitting diode 16
lights up continuously to indicate that power is being supplied. The oscillator of the detection circuit 9 oscillates due to the resonance circuit formed by the detection coil 19 and the capacitor C20 connected to the detection circuit 9, and is in a standby state waiting for the approach of an object. In this state, the thyristor 4 is off and the FET 5 is also off.

Now, suppose that the oscillation output of the detection circuit 9 decreases due to the proximity of an object, the detection output causes the transistor Q
0 is off, the output transistor Q1 is on, and the output terminal NL of the detection circuit 9 becomes "H" level.
Make FET5 conductive. At the same time, a base current is applied to transistor 11, turning on transistor 11 and triggering thyristor 4. Therefore, the thyristor 4 is turned on and current is supplied to the load L via the diode bridge 3, thereby driving the load L. In each subsequent cycle, when the zero crossing point is passed, the thyristor 4 is once turned off, but the transistors 11 and 12 are immediately turned on, the capacitor C17 is rapidly charged, and when the Zener voltage of the Zener diode 14 is reached, the transistor 12 is turned off. Thyristor 4 is turned on. In this way, power is supplied to the detection circuit 9 and the phase of the thyristor 4 is controlled. Therefore, the light emitting diode 16 is lit continuously, indicating that power is being supplied. At this time, each time the capacitor C17 is rapidly charged, the light emitting diode 13 for operation indication lights up. Therefore, the light emitting diode 13 repeatedly blinks at a frequency of 100 or 120 Hz, which is twice the frequency of commercial AC, but it appears to be continuously lit, indicating that the proximity switch is in a detection state in which it has detected an object.

(Operation when short-circuited) Now, the operation when an overcurrent flows through the load L or when the load L is short-circuited will be explained with reference to the waveform diagram in FIG. 3. If the load L is short-circuited at time t1 when an object to be detected is near the sensor section of the proximity switch, an overcurrent momentarily flows through the thyristor 4 and the FET 5. Therefore, the cathode voltage of the thyristor 4 rises, and the gate voltage of the thyristor 6 rises due to the voltage dividing circuit of the resistors 26 and 27, and the thyristor 6 turns on, lowering the gate of the FET 5 to near zero volts. Then, the emitter current of the transistor Q1 inside the detection circuit 9 flows out through the diode 25 and the thyristor 6 between the negative terminal of the power supply. Therefore, transistor 11 is cut off and thyristor 4 is also turned off. At this time, if the voltage at the power input terminal Vcc of the detection circuit 9 is Vf, then
The voltage Vf is the sum of the collector-emitter voltage Vce of the transistor Q1, the forward drop voltage of the diode 25, and the drain-source voltage of the thyristor 6. Therefore, the voltage at the power supply input terminal Vcc of the detection circuit 9 becomes low due to the short circuit of the load, and the capacitor C17 is discharged through the light emitting diode 16 and the transistors Q1 and Q2 inside the detection circuit 9. At this time, since the capacitor C22 forming the power supply reset circuit 21 is also discharged, the voltage at the input terminal of the power supply reset circuit 21 of the detection circuit 9 also decreases as shown in FIG. 3b. After time t1, the detection circuit 9
The current flowing through the light emitting diode 16 increases as the voltage of the power supply input terminal Vcc decreases.
Continue to light as shown. As shown in FIG. 3b, after the time t2 when the reset initial voltage Vs of the detection circuit 9 is reached, the reset operation of the power supply reset circuit 21 causes the transistors Q1 and Q1 of the detection circuit 9 to be reset.
Both Q2 are turned off, and no current flows out from the output terminal NL. Therefore, the voltage at the power input terminal Vcc of the detection circuit 9 returns to the state before the short circuit of the load L, as shown in FIG. 3a, and the voltage applied to the reset input terminal R also rises, as shown in FIG. 3b. do. At this time, the power supply reset circuit 21 inhibits the output of the detection circuit 9, and the two transistors Q1 and Q2
is turned off. Therefore, the current consumption of the detection circuit 9 is reduced, and the light emitting diode 16 is turned off. Then, as shown in FIG. 3b, the capacitor C22 connected to the power supply reset circuit 21 is charged again. And the power supply reset release voltage Vre
Output is prohibited for a prohibition time T1 until reaching t3, and the prohibition of output is canceled at time t3. Therefore, the transistor 15 and the thyristor 4 are momentarily turned on, and an overcurrent is detected. After this, as in the case described above, current flows out from the transistor Q1 of the detection circuit 9 and flows through the diode 25 and the thyristor 6.
The capacitor C17 is discharged through the detection circuit 9.
The voltage input terminal of will drop to Vf again. Therefore, as shown in FIG. 3a, the power supply voltage of the detection circuit 9 repeatedly rises and falls in a predetermined cycle, and accordingly, the light emitting diode 16 blinks as shown in FIG. 3c. This cycle is the reset capacitor C
It is possible to adjust the charging/discharging time of C22, that is, the capacitance of the capacitor C22 and the resistance value connected to the charging circuit or the discharging circuit. If the short-circuit condition is resolved here, even if a load current flows through the thyristor 4 and FET 5 next time, the thyristor 6 will not be triggered, and the normal state can be automatically restored.

In this embodiment, the output of the detection circuit is the NL output, which is at the "L" level when no object is detected, but the same configuration can be made by using the NH output, which is at the "H" level when no object is detected. It is possible. Furthermore, although the AC two-wire proximity switch has been described, it goes without saying that the present invention can be applied to other two-wire detection switches such as photoelectric switches. Further, although this embodiment uses an AC power source as the power source, it is also possible to apply the present invention to a detection switch using a DC power source.

[Brief explanation of drawings]

Fig. 1 is a block diagram showing an overview of an embodiment of the AC two-wire proximity switch according to the present invention, Fig. 2 is a circuit diagram showing its detailed configuration, and Fig. 3 shows waveforms of various parts in a load short-circuit state. FIG. 1, 2... terminal, 3... diode bridge,
4, 6...Thyristor, 5...FET, 9...Detection circuit, 10...Trigger circuit, 11, 12, Q
0, Q1, Q2...Transistor, 13,16...
...Light emitting diode, C17, C20, C22...
Capacitor, 21...Power reset circuit, 24,
26, 27...Resistance.

Claims (1)

[Claims for Utility Model Registration] (1) A detection switch having a detection 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 detection circuit. an overcurrent detection circuit that detects an overcurrent flowing through the output switching element; a self-holding switching element that is driven by the detection output of the overcurrent detection circuit and conducts in the event of a short circuit to cut off the overcurrent; a power storage element that supplies power to a detection circuit; a trigger circuit that triggers the output switching element based on the output of the detection circuit and that has a constant current element to charge the power storage element; and a reset capacitor. is connected in series between the trigger circuit and the detection circuit; An indicator is provided that lights up when power is supplied to the detection circuit and blinks at a cycle based on a discharging time and a prohibition time of a reset capacitor of the power reset circuit when a short circuit is detected to notify the short circuit state. A detection switch characterized by: (2) The detection switch according to claim 1, wherein the indicator is a light emitting diode. (3) Claim 1 or 2 of the utility model registration claim, characterized in that the electricity storage element is a capacitor.
Detection switch described in section.