JPH0226822B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an AC two-wire type non-contact switch that includes a sensor circuit such as a proximity sensor circuit or a photoelectric sensor circuit, and performs a switching operation in response to a detection operation of the sensor circuit.

An AC 2-wire non-contact switch has only two terminals, and by simply connecting an AC power source and a load in series to these two terminals, the load is turned on and off according to the detection operation of the sensor circuit. Therefore, it can be used in the same way as a normal mechanical contact switch, making it extremely convenient. However, since the load and the AC power source are connected in series, there is a risk that an excessive current will flow and the device will be destroyed if the load is short-circuited or the like.

In view of the above, an object of the present invention is to provide an AC two-wire type non-contact switch which has a simple circuit configuration and is improved so as to protect the internal circuit from destruction when an excessive current flows.

An embodiment of the present invention will be described below with reference to the drawings. In FIG. 1, an AC two-wire type non-contact switch 1 has two terminals 4 and 5 to which an AC power source 2 and a load 3 are connected in series.
A full-wave rectifier diode bridge 24 is connected to these terminals 4 and 5. A load switching transistor 6 is connected to short-circuit the rectified output ends of the diode bridge 24, and a current detection resistor 15 is inserted in series in the collector-emitter path of the transistor 6. The transistor 7 bypasses the base current of the transistor 6 in accordance with the voltage generated across the resistor 15, thereby performing a constant current operation. The base current of the transistor 6 is connected to the constant voltage diode 11 and the PNP type transistor 2.
8 collector-emitter paths and a series circuit of 16 resistors. The base current of this transistor 28 is connected to the resistors 17 and 31 and the transistor 2
The power is supplied by a series circuit in which nine collector-emitter paths are connected in series. That is, this series circuit is connected between the rectified output terminals of the diode bridge 24, and one end of the resistor 17 on the collector-emitter path side of the transistor 29 is connected to the base of the transistor 28. When a negative base current is applied, the transistor 29 turns on.
When is off, this base current is not supplied, so it is off. Transistor 10, resistor 20, 2
2, 32, constant voltage diode 13, capacitor 1
The circuit consisting of 4 constitutes a constant voltage circuit of transistor series type, and of this circuit, the series circuit consisting of resistors 20, 32 and constant voltage diode 13 includes a transistor 30 which cuts off the base current of transistor 29. It also serves as a voltage detection circuit for control. A detection signal from the sensor circuit 25 is sent to the base of the transistor 29, but the voltage between the output terminals of the diode bridge 24 is equal to the threshold voltage of the constant voltage diode 13.
Vz ₁₃ , the base current is supplied through this voltage regulator diode 13, and the transistor 30
When the transistor 29 is on, the base of the transistor 29 becomes "L" and the transistor 29 is off, no matter what the detection signal is.
As a result, transistor 28 and transistor 6 are off. The sensor circuit 25 uses a high-frequency oscillation type proximity sensor circuit, a photoelectric sensor circuit that performs a detection operation according to the reflection or transmission of light, etc., and operates by being supplied with constant voltage power through a constant voltage circuit. do.

Next, the operation will be explained with reference to FIGS. 2 and 3. In these figures 2 and 3, a, b,
The waveforms c, d, f, g, and h are shown in Figure 1 a, b,
The voltage waveforms at points d, f, and h and the current waveforms at points e and g are shown, respectively. During normal operation, it will look like Figure 2. That is, the detection signal b is "L" from A to A in FIG. 2, and at this time, the transistor 29 is turned off because no base current is given to the transistor 29, and as a result, the transistors 28 and 6 are turned off. Become. Therefore, the voltage at point (a) is the same as the full-wave rectified alternating current, and when the voltage at point (a) is higher than the threshold voltage Vz ₁₃ , current g flows through the constant voltage diode 13. In other words, this current g
does not flow only near the AC zero point, but flows in most other phases. Therefore, even if the detection signal b becomes "H" in step A, the current g is flowing, so the transistor 30 is turned on and the base potential f of the transistor 29 is kept at "L". Transistor 29 does not turn on immediately, but remains off until the next AC zero point (c), and at this point, transistor 30 turns off, so the potential at point f becomes "H" and transistor 29 turns on. become. Therefore, the transistors 28 and 6 are turned on from the AC zero point. At this time, the transistor 6 receives the base current through the voltage regulator diode 11, the transistor 28, and the resistor 16, so the potential at point (a) is equal to the threshold voltage Vz ₁₁ of the voltage regulator diode 11, the voltage generated across the resistor 16, and the potential at point (a). The value is determined by the voltage between the base and emitter of the transistor 6, and is generally limited to a value approximately equal to the threshold voltage Vz ₁₁ of the voltage regulator diode 11. And this Vz ₁₁
Since it is set lower than Vz ₁₃ , the current g does not flow and the transistor 30 remains off, so the transistor 29 remains on as long as the detection signal b is "H". In this way, current flows through the load 3 from the AC zero point. When the detection signal b becomes "L" at point d, the transistor 29 is immediately turned off, so the transistors 28 and 6 are immediately turned off, and the current to the load 3 is also stopped. The potential at point h becomes somewhat low because the potential at point (a) is limited to approximately Vz ₁₁ when transistor 6 is on.

In the event of an abnormality in which load 3 has a short circuit failure,
It will look like Figure 3. The process up to point c is the same as in normal operation, but at point c, transistor 29 turns on, and as a result, transistors 28 and 6 turn on, and current c starts to flow, when load 3 is short-circuited. Therefore, this current c increases rapidly with the rise of the AC waveform. Therefore, the voltage developed across the resistor 15 also increases rapidly, and the transistor 7 tries to turn on, causing the base current of the transistor 6 to start flowing through the collector-emitter path of the transistor 7. In this way, the current c flowing through the collector-emitter of transistor 6 is limited and constant current operation is performed, but at this time, the impedance between the collector and emitter of transistor 6 increases, so the voltage at point (a) increases. . As a result, the threshold voltage Vz ₁₃ is exceeded, so a current g flows through the constant voltage diode 13, turning on the transistor 30, turning off the transistor 29, and turning off the transistors 28 and 6. That is, when the voltage at point (a) begins to rise after a time t from point c, transistor 7 operates and performs constant current operation, a type of positive feedback operation occurs and transistor 6 is immediately turned off, ( a) The voltage at point increases rapidly.
In this way, when an excessive current attempts to flow through the transistor 6 in an abnormal situation, the transistor 6 is turned off when the current reaches a constant level, so that protection from wave damage can be achieved.

Also, when the transistor 29 is off, the transistors 28 and 6 are off, and when the transistor 29 is on, the transistors 28 and 6 are on, and so on.
When transistor 6 is off, transistor 2
9 is off, and no current flows through the series circuit of resistors 17, 31 and transistor 29. Therefore, the leakage current when transistor 6 is off is limited to only the current required by sensor circuit 25, and the leakage current is reduced. Current can be reduced.

Note that the constant current circuit made up of the transistor 7 and the resistor 15 will not work even if the transistor 6 is normally turned on and off, and even if the load 3 is an inductance load and a rush current flows when it is on, even this rush current will not work. It is like that. For example, if the rated current is 200mA, and the rush current flows at 2A, which is 10 times that, the current value at which constant current operation starts is set to 3A, which is greater than this rush current.
and set. Therefore, when a current of 3 A or more attempts to flow into the load 3, the transistor 6 is turned off by the above operation.

In FIG. 1, a varistor 23 and an avalanche diode 27 are connected to protect the internal circuit of the AC two-wire non-contact switch 1 from surge voltage and the like.

FIG. 4 shows a second embodiment, in which a transistor 33 and a diode 41 are added to the constant voltage circuit of the circuit in _FIG . In addition, a series circuit of a diode 34 and a resistor 35 is connected between the cathode of the constant voltage diode 11 and the connection point of the resistor 22 and capacitor 14 to further reduce the voltage remaining at point (a) when the transistor 6 is turned on. We are trying to provide the capacitor 14 with efficiency. That is, when the transistor 6 is on, the potential at point (a) is limited to approximately Vz ₁₁ as described above, so only a small current flows through the voltage regulator diode 13 of the voltage regulator circuit, and a sufficient Zener voltage is not generated. In addition, since a lower voltage is applied to the capacitor 14 by the forward drop voltage between the base and emitter of the control transistors 10 and 33, the sensor circuit 2
There is also a possibility that sufficient power may not be given to 5. Therefore, the voltage appearing at the cathode of the constant voltage diode 11 is applied to the capacitor 14 more efficiently using a circuit including the diode 34 and the resistor 35. Here, the diode 34 is for preventing the output of the constant voltage circuit from flowing into the base of the transistor 6 when the transistor 6 is off, and the resistor 35 is for forming a low-pass filter together with the capacitor 14. Other points are the same as in FIG. 1 and the operation is also substantially the same, so the waveforms at each point are shown in FIG. 5 (normal time) and FIG. 6 (abnormal time), and the explanation will be omitted.

As described above for each of the embodiments, according to the present invention, the constant current circuit including the transistor 7 and the resistor 15 and the fact that the constant current circuit has worked are shown in (a).
Since a voltage detection circuit that detects a potential rise at a point is provided to turn off the transistor 6 immediately when constant current operation is started, it is possible to protect against excessive current. In addition, a part of the constant voltage circuit is also used as a voltage detection circuit used to detect excessive current flow, making it possible to simplify the circuit configuration and reduce the number of parts. can.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram of the first embodiment of the present invention;
3 and 3 are time charts for explaining the operation of the circuit in FIG. 1, FIG. 4 is a circuit diagram of the second embodiment, and FIGS. 5 and 6 illustrate the operation of the circuit in FIG. 4. This is a time chart for explanation. 1... AC 2-wire non-contact switch, 2... AC power supply, 3... Load, 24... Diode bridge, 25
...Sensor circuit.

Claims (1)

[Claims] 1 Two terminals to which an AC power source and a load are connected in series, a rectifier circuit connected to these two terminals, and a first terminal for load switching connected to short-circuit the rectified output terminals of this rectifier circuit. transistor and
a current detection resistor inserted in the collector-emitter path of the first transistor; and a second constant current transistor that reduces the base current of the first transistor in accordance with the voltage generated across the resistor. , a transistor series type constant voltage circuit comprising a third transistor and a constant voltage diode connected to the base of the transistor, and connected between the rectified output terminals of the rectifier circuit; and a detection operation powered by the constant voltage circuit. a sensor circuit that turns on the first transistor by applying a base current to the first transistor in response to the first transistor;
When the transistor is on, the second transistor operates to perform constant current operation, and when the voltage between the rectified output terminals of the rectifier circuit increases, the current flows through the constant voltage diode of the constant voltage circuit. An AC two-wire non-contact switch comprising a voltage detection circuit that detects this voltage rise and cuts off the base current of the first transistor to turn off the first transistor.