JPS5946134B2 - AC 2-wire electronic switch - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to electronic switches such as proximity switches and photoelectric switches, and particularly to an AC two-wire electronic switch.

This type of electronic switch has separate normally open power terminals and normally closed power terminals, and the current flowing through each power terminal is guided to the input part of the photocoupler to control the input current of the photocoupler. If the output section of the photocoupler is used to switch the signal depending on the presence or absence of the signal, and the operation mode is to be switched, a circuit configuration as shown in FIG. 1 can be considered.

In this figure, 1 is a detection circuit such as a proximity switch circuit or a photoelectric detection circuit. In the case of a proximity switch circuit, there is an oscillation circuit including a detection coil, a detection circuit that detects the output of this oscillation circuit, and a detection circuit that detects the detection output. It is composed of a level discrimination circuit for level discrimination, and in the case of a photoelectric detection circuit, it is composed of a light projecting circuit and a light receiving circuit.

This detection circuit has output terminals 1a and ib that output normal-by and normal-low detection signals, respectively, and these output terminals 1a and lb are output parts (light receiving side) of a photocoupler. 1 s, and is connected to the input terminal 1c of the output circuit 2.

The output circuit 2 has a switching element such as an SCR or a transistor as shown in the figure, and this switching element opens and closes in response to a detection signal.

Reference numeral 3 denotes a constant voltage circuit, which supplies power to the detection circuit 1, output circuit 2, and the like.

Diode bridges 4 and 5 for full-wave rectification are connected to power terminals A and B for normally open and power terminals C and D for normally closed, respectively, and the output and ends of these diode bridges 4 and 5 are connected to photocouplers. The constant voltage circuit 3 is connected to the output circuit 2 through the input section (light emitting side) 10p and 11p.
connected to the switching element.

Therefore, if the AC power supply 13 and the load 12 are connected in series to the terminals A and B, current flows only to the input part 10p of the photocoupler, so a normal-by detection signal is sent to the output circuit 2, and the output circuit 2 is opened/closed. The device operates in a normally open operating mode.

If the load 12 and AC power supply 13 are connected to terminals C and D,
Since current flows through the photocoupler input section 11p, a normally low detection signal is sent to the output circuit 2, resulting in a normally closed operation mode.

By the way, when the switching element of the output circuit 2 is off, the current flowing through the input section 10p and lip of the photocoupler is only the current required by the circuit, so it is about several mA, but when the switching element is turned on, A current of several hundred mA or more, which is determined by the load 12, flows through.

Therefore, to prevent excessive current from flowing, the current limiting resistor 8,
9 are connected in series and Zener diodes 6.7 are connected in parallel to prevent excessive voltage from being applied across the input section 10p*11p of the photocoupler.

11p needs to be protected.

However, when doing this, it is necessary to apply a voltage of about 2 to 3 cm across the input part of the photocoupler, so the resistor 8
, 9 are added, and a somewhat large voltage is always generated across the series circuit of the photocoupler input parts 10p, 11p and the resistors 8, 9.

Therefore, when the switching element is on, this voltage remains as a residual voltage, and the voltage applied to the load 12 becomes lower by this residual voltage, causing a problem.

Furthermore, when the switching element is on, most of the current passes through the Zener diode 6.7, so a large current capacity is required, and it also generates a lot of heat, which is disadvantageous in terms of space and cost. .

In view of the above, the present invention reduces the residual voltage when the switching element is on, does not use parts with large current capacity, and
Moreover, it is an object of the present invention to provide an AC two-wire electronic switch that generates less heat and is improved in terms of space and manufacturing cost.

An embodiment of the present invention will be described below with reference to FIG.

According to the present invention, as shown in FIG. 2, a diode 14 is connected between the output ends of the diode bridges 4 and 5 and the switching element.
．． 15, and also connect this output terminal to the constant voltage circuit 3.
Diodes 16 and 17 are connected between them via photocoupler input parts 10p and 11p.

Since the other configurations are the same as those in FIG. 1, the same reference numerals are given and the explanation will be omitted.

In this way, the current flowing through the diode bridges 4 and 5 is
Diode 14.16 and diode 15.1 respectively
7, the current required by the circuit and the current flowing to the switching element are divided so as to prevent reverse flow.

Therefore, the input parts 10p and 11p of the photocoupler have several meters.
Only a current of about A flows, so no protection circuit is required.

Furthermore, since the residual voltage when the switching element is on is only the forward voltage drop across the diodes 14 and 15, it can be made extremely small.

As described above in Embodiment 5), according to the present invention, a Zener diode with a large current capacity is not required, resulting in low cost.

In addition, since there is little voltage drop, less heat is generated and it is possible to make the device more compact.

Furthermore, the residual voltage when the switching element is turned on can be reduced.

[Brief explanation of the drawing]

FIG. 1 is a conventional circuit diagram, and FIG. 2 is a circuit diagram of an embodiment of the present invention. 1...detection circuit, 2...output circuit, 3
... Constant voltage circuit, 4, 5 ... Diode bridge, 6, 7 ... Zener diode for voltage limitation, 8, 9 ... Resistor for current limitation , 10p,
11p...One-person photocoupler section, 10s,
11s...Output section of photocoupler, 12...
...Load, 13...AC power supply, 14-17.
...Diode for shunting.

Claims (1)

[Claims] 1 A detection circuit, an output circuit that opens and closes a switching element according to the detection signal of this detection circuit, a switching circuit consisting of the output section of two photocouplers, and a power supply circuit for supplying power to these circuits. , normally open power terminal,
a normally closed power supply terminal, two rectifier circuits respectively connected to both of these power supply terminals, and a diode connected between each DC output terminal of these rectifier circuits and the switching element; diodes are respectively connected between the DC output end of each of the rectifier circuits and the power supply circuit via the input section of each of the photocouplers, and a current flows through the input section of any of the photocouplers. The AC two-wire electronic switch is configured to switch the detection signal by the switching circuit accordingly, and operate the output circuit in a normally open or normally closed operation mode.