JPH0226823B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an AC two-wire non-contact switch that is equipped with a sensor circuit such as a proximity sensor circuit or a photoelectric sensor circuit, and in which a transistor for switching the load opens and closes according to the detection operation of the sensor circuit. .

The AC 2-wire non-contact switch has only two terminals, and by simply connecting the AC power source and the load in series to these two terminals, the load switching transistor turns on and off in response to the detection operation of the sensor circuit. Since the load is opened and closed by turning off, 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, when the load is short-circuited, an excessive current flows through the load switching transistor and there is a risk that it may be destroyed. Also, regardless of whether the load switching transistor is on or off, at least the power needed to operate the sensor circuit must be given to the sensor circuit, but this power tends to be insufficient when the load switching transistor is on. .

In view of the above, the present invention has been developed to protect the internal circuit from destruction when excessive current flows, and to efficiently supply power to the sensor circuit when the load switching transistor is turned on, thereby preventing a power shortage. The purpose is to provide a wire type non-contact switch.

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. Further, a voltage detection circuit consisting of a series circuit of a resistor 18, a voltage regulator diode 12, and a resistor 32 is connected between the output terminals of the diode bridge 24.
The base of the transistor 30 is connected to the connection point with the transistor 2. A detection signal from the sensor circuit 25 is sent to the base of this transistor 29, but the voltage between the output terminals of the diode bridge 24 is higher than the threshold voltage Vz ₁₂ of the constant voltage diode 12, and this constant voltage When the base current is supplied through the diode 12 and the transistor 30 is turned on, no matter what the detection signal is, the base of the transistor 29 becomes "L" and the transistor 29 is turned off. 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 its power terminal is connected to the diode bridge 24, the transistor 10,
It is connected to the output side of a constant voltage circuit consisting of a constant voltage diode 13, resistors 20 and 22, and a capacitor 14. Between the output side of the constant voltage circuit and the cathode of the constant voltage diode 11, a series circuit consisting of a diode for preventing backflow and a resistor 35 forming a low-pass filter together with the capacitor 14 is connected.

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, e, f, and h are shown in Figure 1 a, b,
The voltage waveforms at points d, f, and h and the current waveforms at points c and e 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 ₁₂ , current e flows through the constant voltage diode 12. In other words, this current e
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 A, the transistor 30 is turned on because this current e is flowing, 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 constant voltage 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 constant voltage diode 11, the voltage generated across the resistor 16, and the transistor 6. The value is determined by the voltage between the base and emitter of the voltage regulator diode 11, and is generally limited to a value approximately equal to the threshold voltage _Vz11 of the voltage regulator diode 11. And this Vz ₁₁
Since it is set lower than Vz ₁₂ , the current e 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 power supply voltage h applied to the sensor circuit 25 is a full-wave rectified output that is made constant by a constant voltage circuit when the transistor 6 is off. When the transistor 6 is on, the voltage appearing at the cathode of the constant voltage diode 11 is applied to the diode 34 and the resistor 3.
5 to one end of the capacitor 14.
In this manner, when the transistor 6 is turned on, power is supplied to the sensor circuit 25 without going through the constant voltage circuit, which is efficient. That is, if power is supplied via the constant voltage circuit even when the transistor 6 is on, the potential at point a is suppressed to Vz ₁₁ as described above, so the constant voltage diode 13 of the constant voltage circuit
Since only a small current flows through , sufficient zener voltage is not generated, and the base
Since a lower voltage is applied to the capacitor 14 by the forward voltage drop across the emitters, the potential at point H becomes lower, and there is a possibility that sufficient power cannot be applied to the sensor circuit 25, but this can be resolved. Note that the diode 34 is provided to prevent the output of the constant voltage circuit from flowing into the base of the transistor 6 when the transistor 6 is off.

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 the transistor 6 is limited and a constant current operation is performed, but at this time, the impedance between the collector and emitter of the transistor 6 increases, so the voltage at point a increases. As a result, the threshold voltage Vz ₁₂ is exceeded, so a current e flows through the constant voltage diode 12, turning on the transistor 30, turning off the transistor 29, and turning off the transistors 28 and 6. That is, after time t from point c, transistor 7 operates to perform constant current operation and the voltage at point a begins to rise, a kind of positive feedback operation occurs and transistor 6 is immediately turned off, causing the voltage at point a to rise. Voltage increases rapidly.
In this manner, when an excessive current attempts to flow through the transistor 6 during an abnormality, the transistor 6 is turned off when the current reaches a constant level, so that it can be protected from destruction.

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 the resistors 17, 31 and the transistor 29. Therefore, the leakage current can be limited to only the current required by the sensor circuit 25, and the leakage current can be reduced. can.

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 attempts to flow to 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 this embodiment, a transistor 33 and a diode 41 are added to the constant voltage circuit of the circuit in FIG. 1 to form a Darlington configuration to increase h _FE and further reduce the current g. In order to reduce the leakage current (the current flowing to the load 3 when the transistor 6 is off), the resistor 20 of the constant voltage circuit and the constant voltage diode 13 are also used for voltage detection, and the resistor shown in FIG. 18 and the constant voltage diode 12 are omitted to simplify the circuit. That is, instead of using the current e in Figure 1, a
The point potential is the threshold voltage of the constant voltage diode 13
The transistor 30 is turned on using the current g that flows when Vz ₁₃ is exceeded. In other respects, it is the first
The waveforms at each point are shown in FIG. 5 (normal state) and FIG. 6 (abnormal state), respectively, since they are similar to those shown in the figure and the operation is substantially the same, and further 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 operation of the constant current circuit are
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. Furthermore, by efficiently supplying power to the sensor circuit 25 when the transistor 6 is turned on, the sensor circuit 2
5 can be reliably operated regardless of whether the transistor 6 is on or off.

[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 series circuit of a third transistor and a constant voltage diode forming a path for supplying a base current to the first transistor, a constant voltage circuit connected between the rectified output terminals of the rectifier circuit, and the constant voltage a series circuit of a diode and a resistor for applying the voltage appearing at one end of the diode to the output side of the constant voltage circuit; a sensor circuit that applies a base current to a transistor and as a result turns on the first transistor; and when the first transistor is on, the second transistor operates to perform constant current operation and rectify the rectifier circuit. An AC two-wire contactless point comprising a voltage detection circuit that detects the voltage increase when the voltage between the output terminals increases, cuts off the base current of the third transistor, and turns off the first transistor as a result. Switch.