JPH0693621B2 - Two-wire type electronic switch - Google Patents

Description

Description: FIELD OF THE INVENTION The present invention relates to a two-wire electronic switch to which both AC and DC power supplies can be connected.

[Outline of Invention]

In the two-wire electronic switch according to the present invention, a Zener diode and a field effect transistor for switching (hereinafter referred to as FET) are connected in series to a power supply terminal via a diode bridge, and the voltage across the Zener diode is applied to a detection circuit. The FET is operated based on the switching output to give a current to the load.

[Prior art and its problems]

A conventional two-wire type electronic switch capable of using both direct current and alternating current as a power source is, for example, as shown in FIG. 2, via a diode bridge 3 to input terminals 1 and 2 to which a power source and a load are connected in series. The zener diode D1 is connected to a switching element such as a power transistor Tr1 or a thyristor, and a constant voltage is supplied to the detection circuit 4 via a constant voltage circuit including a transistor Tr2 and a zener diode D2. ing. For such a two-wire type electronic switch, an electronic switch in which a power source connected to an input terminal is operated in a wide range of direct current and alternating voltage, for example, in a wide range of 10 to 200 tens of volts is required. Has been done. However, in order to operate from a low voltage in the conventional electronic switch, it is necessary to reduce the resistance value of the resistor R1 connected between the collector and base of the constant voltage transistor Tr2, and in that case a high voltage power supply is needed. There is a problem that the leakage current when connected becomes large and it is necessary to increase the allowable power of the Zener diode D2. In such a two-wire type electronic switch, it is necessary to minimize the residual voltage across the switch when it is on and to minimize the leakage current when it is off, which makes it difficult to handle a wide range of power supply voltages.

[Object of the Invention]

The present invention has been made in view of the above problems of the conventional electronic switch, and it is possible to reduce the residual voltage at the time of turning on and to use a power supply for both AC and DC, and to provide a wide range of power supplies. An object of the present invention is to provide an electronic switch that can be operated with respect to a voltage.

[Constitution and effect of the invention]

The present invention relates to a two-wire electronic switch connected in series to a load and a power supply to control power supply to the load, wherein a diode bridge connected to an input end of the electronic switch and a series connection between positive and negative ends of the diode bridge. A zener diode and a field effect transistor for switching, which are connected to the zener diode, and a detection circuit having power supply terminals connected to both ends of the zener diode and operating the field effect transistor by a detection output. Is.

According to the present invention having such characteristics, the zener diode and the switching FET are connected in series to the rectified output of the input terminal, and the constant voltage across the zener diode is supplied to the detection circuit as a power source. . Therefore, only the voltage necessary for the detection circuit remains, and the residual voltage can be reduced. Also, because FET is used as a switching element, current consumption other than the detection circuit is small,
It is possible to reduce the leakage current when the switch is turned off.
Further, when the switch is off, a constant current is supplied to the zener diode due to the constant current characteristic of the FET, and a constant voltage is supplied to the detection circuit from both ends of the zener diode, so that the configuration of the constant voltage circuit can be facilitated. Therefore, an AC or DC power supply can be used as a power supply, and a power supply having a wide range of voltages can be used, so that a versatile electronic switch can be obtained.

[Explanation of Examples]

FIG. 1 is a circuit diagram showing the configuration of a two-wire electronic switch for both direct current and alternating current according to an embodiment of the present invention. In this figure, a diode bridge 3 is connected between terminals 1 and 2, and a smoothing capacitor C1 and a Zener diode are connected between the positive and negative ends of the diode bridge 3.
A series connection body of D3 and a field effect transistor (FET) 5 is connected in parallel. The Zener diode D3 has a constant voltage characteristic of supplying a necessary voltage to the detection circuit 4, and both ends thereof are connected between the power supply terminals of the detection circuit 4 via the capacitor C2. The detection circuit 4 is various switch circuits such as a photoelectric switch, a proximity switch, and an ultrasonic switch, which detects a predetermined object, and gives its output to the transistor Tr3. The transistor Tr3 has an emitter connected to the positive terminal of the diode bridge 3 and a collector connected to the gate of the FET5. The emitter of the transistor Tr3 is connected to the diode bridge 3 via the series connection of resistors R2, R3 and R4.
Connected to the negative terminal of R3, R4, the common connection end of the resistors R3, R4 is the collector of the transistor Tr3 and the gate of the FET5, and the middle point of the resistors R2, R3 is the diode bridge 3 via the Zener diode D4.
Is connected to the negative electrode end of.

Now, the input terminal of the two-wire electronic switch configured in this way.
A DC or AC power source 6 and a load L are connected in series between 1 and 2. Then, when the detection circuit 4 is not detecting an object, the transistor Tr3 is in the off state, current flows through the series circuit of the resistors R2 and D4, and the voltage across the Zener diode D4 is divided by the resistors R3 and R4. It is given to the gate of FET5 through the circuit. Therefore, a constant voltage is supplied to the gate of the FET5, and a bias current flows through the drain / source of the FET5. Since the gate voltage of the FET5 is limited by the Zener diode D4, the drain current of the FET5 is constant regardless of the voltage of the power supply 6. Since the drain current flows through the Zener diode D3, the constant voltage across the Zener diode D3 is applied to the detection circuit 4. In this drain circuit, the resistance values of the resistors R3 and R4 are selected so that the current becomes a minute current so that the detection circuit 4 can be supplied with a necessary and sufficient current. Become. Since the FET 5 which is a voltage control type element is used as the switching element here, the leakage current can be reduced.

Now, when an object is detected by the detection circuit 4, a detection output is given to the transistor Tr3, the transistor Tr3 is turned on, and the gate voltage of the FET5 rises. Therefore, the drain current of the FET 5 increases significantly, and the load current of the load L flows through the diode bridge 3 to the Zener diode D3 and the FET 5. Also in this case, the voltage across the Zener diode D3 is applied to the detection circuit 4 as a residual voltage.
The voltage across it is very low and the residual voltage can be kept low.

Although the Zener diode D4 is used to fix the gate voltage of the FET5 in this embodiment, the collector of the transistor Tr3 may be directly connected to the gate of the FET5, or the FET5 may be directly connected by the detection output of the detection circuit 4. It can also be controlled.

[Brief description of drawings]

FIG. 1 is a circuit diagram of a two-wire electronic switch according to an embodiment of the present invention, and FIG. 2 is a circuit diagram showing an example of a conventional two-wire electronic switch. 1,2 …… Input terminal, 3 …… Diode bridge, 4 ……
Detection circuit, 5 ... FET, 6 ... Power supply, D1-D3 ... Zener diode, R1-R4 ... Resistor, Tr1-Tr3 ... Transistor

Claims (3)

[Claims] 1. A two-wire electronic switch connected in series to a load and a power supply to control power supply to the load, the diode bridge connected to an input end of the electronic switch, and a positive / negative of the diode bridge. A zener diode and a switching field effect transistor connected in series between both ends; and a detection circuit having a power supply terminal connected to both ends of the zener diode and operating the field effect transistor by a detection output. A two-wire electronic switch characterized in that 2. The two-wire electronic switch according to claim 1, wherein the detection circuit controls the field effect transistor through a switching transistor. 3. The two-wire electronic switch according to claim 1, wherein the field effect transistor is an enhancement field effect transistor.