JPS5854448B2 - AC photoelectric switch - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an AC photoelectric switch equipped with a power reset circuit for preventing malfunctions when the power is turned on.

In general, in a photoelectric switch, the time required for each block of the photoelectric switch, such as the light emitting circuit, light receiving circuit, signal processing circuit, and output circuit, to start operating stably after the power is turned on differs; for example, when an output signal should not be output. E. Problems such as an erroneous output signal being output for a certain period of time when the power is turned on may occur.

SUMMARY OF THE INVENTION An object of the present invention is to provide an AC photoelectric switch that prevents malfunctions when the power is turned on and has improved resistance to noise during steady operation.

The AC photoelectric switch according to the present invention includes a light projector, a light receiving circuit that generates a detection signal by receiving light from the light projector, a cutoff circuit that is triggered by the output of the light receiving circuit, and an operation of the cutoff circuit. a smoothing circuit that performs a charging/discharging operation according to the charging/discharging operation; and a power supply reset circuit that receives a voltage that changes with the charging/discharging operation of the smoothing circuit and cuts off the input voltage from the smoothing circuit until the projector stably operates. and a load switching circuit that receives the output of the power supply reset circuit and controls switching on and off of energization to the load.

Therefore, according to the present invention, the trigger circuit is kept in a non-operating state by the power supply reset circuit for a certain period of time immediately after the power is turned on, thereby preventing malfunctions when the power is turned on. Charge/discharge operations are carried out by the operating cutoff circuit, and the output of this smoothing circuit controls the load switching circuit via the power supply reset circuit, so even if the light receiving circuit malfunctions due to noise etc. during normal operation, This prevents the load switching circuit from being erroneously triggered and improves noise resistance.

Examples of the present invention will be described below.

Examples of the present invention will be described below.

FIG. 1 shows a transmission type AC photoelectric switch in which light is blocked by an object to be detected, according to a first embodiment.

This transmission type AC photoelectric switch consists of a transmitter 1 and a receiver 3.
and are connected to an AC power source.

Further, a load is connected between the load switching terminal of the light receiver 3 and one power supply terminal, and the transmitted light is detected depending on the presence or absence of the object to be detected 2, thereby opening and closing the load.

In the floodlight 1, a light emitting diode (hereinafter referred to as LED) 1
1 is a predetermined phase at each falling edge of the full-wave rectified waveform in synchronization with the AC power supply, and is driven once per half-wave.

The light receiver 3 includes a half-wave rectifier diode 31 and a constant voltage circuit 4.
, a light receiving circuit 5 , a cutoff circuit 6 , a smoothing circuit 7 , a power supply reset circuit 8 , a trigger circuit 9 , a load switching circuit 10 , and a surge absorption circuit 30 .

The constant voltage circuit 4 includes a resistor 41, a constant voltage diode 42, and a capacitor 43, and supplies a constant voltage to the light receiving circuit 5.

The light receiving circuit 5 includes a light receiving element 51 such as a photodiode, and transistors 52 and 53 for amplifying the output thereof.

The cutoff circuit 6 includes a 5CR 61 that is triggered by a detection signal from the light receiving circuit 5 and a resistor 62.

Note that a resistor 54 and a capacitor 55 are connected in series between the gate and cathode of 5CR61;
This is to add sufficient hysteresis characteristics to R61.

The smoothing circuit 7 includes a resistor 71 and a smoothing capacitor 72, and smoothes the half-wave rectified output from the rectifier diode 31.

The power supply reset circuit 8 receives voltage supply from the constant voltage circuit 4 via a resistor 81, a capacitor 82, and a resistor 83, 84.
．． 85 connects the transistor 86 for a certain period of time after the power is turned on (
The transistor 86 is kept in a cut-off state (hereinafter referred to as a power supply reset time), and then the transistor 86 is turned on.

The trigger circuit 9 includes an operation display LED 91, a PUT 92, and the like.

The AC switching circuit 10 is a full-wave rectifier circuit 101, 5CR102
and an avalanche diode 103, and this 5CR 102 is triggered by the output of the trigger circuit 9.

The surge absorption circuit 30 includes a varistor 301 and a coil 302.
, a capacitor 303, and the internal circuits of the light receiver 3, such as the light receiving circuit 5, are affected by surges generated when electrical equipment is opened and closed, for example, when relays, solenoids, or similar inductive loads are opened and closed. It works to prevent it from spreading.

Next, the operation of the photodetector 3 is controlled by the power supply reset circuit 8.
This will be explained with reference to the figures.

First, when the pulsed light emitted from the LED 11 of the emitter 1 is blocked by the object 2 to be detected and does not reach the light receiving element 51 (hereinafter referred to as a light-blocking state), a power supply voltage is applied to the power terminals of the emitter 1 and the receiver 3. When, 5CR61
is not triggered, the capacitor 72 of the smoothing circuit 7 immediately starts charging, and the voltage across the capacitor 72 gradually rises as shown in the second diagram.

When the circuit 9 is in the light-shielded state, the gate voltage of the PUT 92 is always set to be lower than the anode voltage, but the transistor 86 of the power supply reset circuit 8 is in the cut-off state for the power supply reset time t. Therefore (see FIG. 2F), the anode voltage of PUT 92 remains lower than the gate voltage and PUT 92 remains off.

After the power supply reset time t has elapsed, the transistor 86 changes to a conductive state, turning off the PUT 92, and as a result, a gate current flows through the 5CR12 (see FIG. 2G).
CR102 turns on and current is supplied to the load (see Figure 2, H and I).

Note that the power supply reset time t is determined when the voltage across the capacitor 43 of the photoreceiver 3, especially the constant voltage circuit 4 is zener diode, -
The power supply reset time t is set with a sufficient margin until the breakover voltage of the power source 42 is sufficiently reached and the light receiving circuit 5 etc. performs a sufficient detection function (see FIG. 2 C and F). .83 to 85, it is possible to set it freely by selecting the constant of the capacitor 82.

Even when the detected object 2 has left and the transmitted light enters the light receiving element 51 (hereinafter referred to as the light receiving state), when the power supply voltage is applied to the power terminals of the emitter 1 and the light receiver 3, the power supply reset time Since the transistor 86 is in the cutoff state during the period t, the PUT 92 of the trigger circuit 9 is not turned on and the 5CR
Since no trigger signal is applied to the load switching circuit 102, the load switching circuit 10 is turned off and the supply of alternating current to the load is stopped (see FIGS. 2F, G, H, and I).

Then, after the power supply reset time t has elapsed, the light receiving circuit 5 is in a state where it can sufficiently detect transmitted light, so the 5CR61 is triggered at the timing of the detection signal from the light receiving circuit 5, and both ends of the smoothing capacitor 72 are connected to the resistor. 62, and the voltage at the white point of the smoothing circuit 7 becomes a triangular wave as shown at the right end of the second diagram.

In the light receiving state where pulsed light is incident, the gate voltage is always set to be higher than the anode voltage (the peak of the triangular wave voltage is lower than the gate voltage), so PUT92 remains off. The state of the load switching circuit 10 and the load is off as in the power supply reset time.

In this way, during steady state, the capacitor 72 of the smoothing circuit 7 is
Since the cutoff circuit 6 is short-circuited in response to the detection signal from the light receiving circuit 5, the zero point potential is low as shown on the right end of the second diagram, and the light receiving circuit 5 is short-circuited.
Even if the cutoff circuit 6 does not operate for one cycle (or several cycles) due to malfunction or noise, the voltage across the mouth will only rise slowly and the PUT
92 remains off and the load switching circuit 10 is not triggered.

As a result, strength against noise is improved.

The circuit in Figure 1 uses an AC power supply of 100 volts or 200 volts.
The above operation remains the same even with volts, and the power reset time t
can be made almost the same at 100 volts and 200 volts depending on how each constant is set.

FIG. 3 shows a reflective AC photoelectric switch according to the second embodiment, which generates reflected light from an object to be detected. As in the first embodiment, when the load is switched on and off when no pulsed light is incident, SCR 102 of circuit 10 turns on and current is supplied to the load.

This embodiment is characterized in that a field effect transistor (FET) 87 is used in the power supply reset circuit 8 to reduce current consumption.

Since the other operations are almost the same as those in the first embodiment, the same parts are given the same numbers and further detailed explanation will be omitted.

Although the above embodiments relate to AC 3-wire photoelectric switches, the present invention is not limited to AC 3-wire photoelectric switches, but is applicable to other transformer-less type AC photoelectric switches, such as AC 2-wire type photoelectric switches. It is also fully applicable to photoelectric switches.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram showing a first embodiment of the present invention, FIG. 2 is a waveform diagram for explaining the operation of FIG. 1, and FIG.
FIG. 2 is a circuit diagram showing an embodiment of the present invention. L...Load, 1...Floodlight, 2...
...Object to be detected, 3...Receiver, 4...
... Constant voltage circuit, 5 ... Light receiving circuit, 6 ...
...Cut-off circuit, 7...Smoothing circuit, 8.
...Power supply reset circuit, 9...Trigger circuit, 10...Load switching circuit, 30...
Surge absorption circuit, 11... LED for light projection, 51
......Light receiving element, 61°91...LED for operation display.

Claims (1)

[Claims] 1. A light projector, a light receiving circuit that generates a detection signal by receiving light from the light projector, a cutoff circuit that is triggered by the output of this light receiving circuit, and a charging/discharging operation according to the operation of this cutoff circuit. smoothing circuit,
A power supply reset circuit that cuts off the input voltage from the smoothing circuit until a voltage that changes with the charging/discharging operation of the smoothing circuit is input and the projector operates stably; An AC photoelectric switch equipped with a load switching circuit that controls switching on and off of current.