JPS626530A - Ac 2-wire proximity switch - Google Patents

Abstract

PURPOSE:To make a leakage current at off-state to a very small value and to lower the residual voltage by using a different path for a drive power fed to a proximity detecting circuit depending on/off state of the proximity detecting circuit. CONSTITUTION:When the detection circuit 2 is turned on, a power supply from a rectifier bridge 3 is fed to the detection circuit 2 through the path of a light emitting diode LED, a resistor R3, a transistor (TR) 2, a TR 3 and a diode D2 not via a DC stabilizing circuit 6. When the detection circuit 2 is turned off, a power supply from the rectifier bridge 3 is regulated by the DC stabilizing circuit 6 and fed to the detection circuit 2 via a resistor 4 and a diode D1 to decrease the current consumption. In this case, even when the value of the resistor 4 is selected sufficiently large to decrease the leakage current, or the conduction angle of a thyristor SCR is increased, the drive current to the detection circuit 2 is ensured sufficiently.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a so-called AC two-wire proximity switch in which a signal line and an AC power line share a hole.

(Prior art) In an AC two-wire proximity switch, the signal line that operates the load and the AC power supply line are shared, and in order to operate the proximity switch, a driving current is required for the internal circuit even when the load is not being driven. As a result, some leakage current flows even when the switch is in the off state. Furthermore, in order to ensure the drive current for the internal circuit even when the proximity switch is in the on state, some residual voltage is required on the output side. If this leakage current and residual voltage are large, the load that can be connected is limited. Therefore, in an AC two-wire proximity switch, it is important that the leakage current is small and the residual voltage is small.

FIG. 4 is a circuit diagram showing a conventional AC two-wire proximity switch disclosed in, for example, Japanese Unexamined Patent Publication No. 56-83814.
In the figure, (1) is the detection coil, (2) is the detection circuit, (
3) is a rectifier bridge, (4) is a load, (5) is an AC power supply, (6) d is a DC stabilization circuit, and (7) Ir! It is the object to be detected. (1, C2 is a capacitor, SCR is a thyristor,
ZD2 fl Zener diode as a constant voltage element,
D3H light emitting diode, R10 to R12 are resistors, Tr4
is a transistor.

Next, the operation will be explained.

When the detected object (7) approaches the detection coil (1), the oscillation of the detection circuit (2) stops and the output of this detection circuit (2) is turned on. Then, the current flowing through the resistor a11ft and the base current of the transistor Tr flow through the resistor R10 to the light emitting diode D6, causing it to light up, thereby indicating that the switch is turned on. Therefore, the transistor Tr16 is turned on, and the capacitor 02 is charged via the resistor R12. And this capacitor C2
The potential of Zener diode ZD2 is Zener SCRV
The current flowing through the i-ion load (4) increases significantly and drives the load.

(Problems to be Solved by the Invention) In the conventional AC two-wire proximity switch as described above, since there is no current control means between the power supply and the detection circuit, a large amount of current flows into the capacitor C1 when the power is turned on. Therefore, if the load is light and the current is 10 to 20 mA, it may malfunction, and the VC
There was a problem in that the leakage current was also inevitably high.

In addition, in order to reduce the residual voltage and operate the thyristor SCR reliably, the VC requires a capacitor C2, which requires a relatively large capacitance, which is a problem. - (Means for Solving the Problems) The AC two-wire proximity switch according to the present invention controls the conduction of the thyristor connected to the DC output end of the rectifier bridge in accordance with the output of the proximity detection circuit. An AC two-wire proximity system in which a switch output is obtained at the AC input end of the rectifier bridge, and the driving power for the proximity detection circuit is obtained via a DC stabilizing circuit and a smoothing capacitor connected in parallel to the rectifier bridge. In the switch, a current limiting element connected between the DC stabilizing circuit and the smoothing capacitor, and opening/closing of the DC stabilizing circuit and the current limiting element are controlled by an output signal of the proximity detection circuit. The present invention is characterized by comprising a shunt circuit and a constant voltage element connected between the shunt circuit and the gate of the thyristor.

(Function) In the present invention, when the output of the proximity detection circuit is in an off state, driving power is supplied to the proximity detection circuit via the DC stabilizing circuit and the resistor.

When the output of the proximity detection circuit is in the on state, drive power is supplied to the proximity detection circuit via the shunt circuit, and the DC stabilization circuit and the resistor are short-circuited by the shunt circuit. Then, current flows through the constant voltage element K through the shunt circuit, turning on the thyristor and causing current to flow to the load.

(Example) Embodiments of the present invention will be described below based on the drawings.

FIG. 1 is a circuit diagram of an AC two-wire proximity switch according to an embodiment of the present invention.

In the figure, it includes (1) a detection coil, (2) an oscillation circuit, and a circuit for amplifying and detecting the output of the oscillation circuit.

This is a detection circuit that sends out a switching output. (3) is a rectifier bridge consisting of a diode, which is connected in series to the AC power supply (5) via a load (4). Furthermore, a DC stabilizing circuit (6) is provided which uses the voltage appearing at the output end of the rectifier bridge (3) as an input voltage, and its output is connected to a smoothing capacitor C1 via a resistor R4 and a diode D1. The signal is added to the detection circuit (2) via the sensor.

The output of the detection circuit (2) is connected to the base of the transistor Tr3 via a resistor R6, and the base thereof is connected to the emitter of the transistor Tr2 via a resistor R5.

Furthermore, this emitter is connected to the emitter of the transistor Try. Further, the collector of the transistor Tr2 is connected to the positive electrode side of the rectifying bridge (3) via the resistor R6 and the light emitting diode LED'i, and the collector of the transistor Tr2 is
The pace of r, is connected to the emitter of a transistor Tr, which constitutes a DC stabilizing circuit (6). transistor T
The collector of r, is connected to the detection circuit (2) via a diode D2', which is connected to the thyristor 5CRQ gate via a Zener diode ZD2. Further, its anode and cande are connected to the positive and negative sides of the rectifying bridge (3), respectively, and the gate is connected to the negative side via a resistor R1.

Further, the collector of the transistor Tri of the DC stabilizing circuit (6) is connected to the positive electrode side of the rectifying bridge (3), and the resistor R2 is connected between the collector and the pace.

Furthermore, the pace of this transistor TrI is connected to the negative electrode side of the rectifier bridge (3) via a Zener diode ZD1.

In this embodiment, it is assumed that when a detected object (7) such as a piece of iron approaches the detection coil (1), the detection circuit (2) stops oscillating and its output is turned on.

Next, the operation will be explained.

Assuming that the object to be detected (7) is now away from the detection coil (1), the detection circuit (2) is in an oscillating state and its output is off. Therefore, the transistor Tr is also off, and since no voltage is applied to the Zener diode zD2, the thyristor SCR is also off, and the output of the proximity switch is also off. At this time, the detection circuit (2) is further connected to the rectifier bridge (3) via the DC stabilization circuit (6).
A DC voltage is supplied as a driving power source through a resistor R4 and a diode D1 to operate the detection circuit (2).

Next, when the detected object (7) approaches the detection coil (1),
The detection circuit (2) becomes in an oscillation stopped state and its output is turned on. Therefore, the transistor Tr is also turned on, and thereby the transistor Tr is also turned on.

When the transistor Tr is turned on VC, the light emitting diode LED and the resistor R6 are
A current flows through the transistor Tr, and this current is further supplied to the detection circuit (2) K through the transistor Tr and the diode D2. This supplied current charges the smoothing capacitor C1! When the potential of the collector of the transistor Tr becomes higher than the Zener voltage of the Zener diode ZD2, the Zener diode ZD2 becomes conductive. As a result, a current VC1t flows through the gate of the thyristor SCH, which turns on the thyristor and causes a current to flow through the load (4). At this time, until the thyristor SCR is turned on, the smoothing capacitor C1 is charged as described above and a pulsating voltage is applied to the detection circuit (2).
At the same time as R turns on, charging to the smoothing capacitor C1 stops, and the current change is released [11! A drive current is supplied to the detection circuit (2) by the current.

In this case, the output voltage of the rectifier bridge (3) is
Since it is applied to CH, the thyristor SCRfl is turned off when the half wave of the rectified voltage ends. Then, the potential of the smoothing capacitor C1 rises again and the Zener diode Z
Thyristor SCRVi remains off until current begins to flow into D1. Also, during that time, capacitor C1 is connected to the detection circuit (
2) is charged for supplying drive current to K.

As mentioned above, when the detection circuit (2) is on, the power obtained from the rectifier bridge (3) is transferred to the DC stabilizing circuit (6).
The light is supplied to the detection circuit (2) through the path of the light emitting diode LED, the resistor R3, the transistors Tr, Tr, and the diode D2. Furthermore, when the detection circuit (2) is off, the power obtained from the rectifier bridge (3) is further stabilized by the DC stabilization circuit (6) l' (and further supplied to the detection circuit ( 2), and its current consumption can be reduced.At this time, even if the value of resistor R4 is set sufficiently large to make the leakage current value unreasonable, the detection circuit (2) when turned on can be Power is supplied to the light emitting diode IJD, resistor R5 (resistance value is small), transistor Try, Tr3.Diode D2.
Since the voltage drop is small, a sufficient drive current to the detection circuit (2) can be ensured even if the conduction angle of the thyristor SCR is increased.

Furthermore, since the pace of the transistor Tr2 is connected to the collector of the transistor Tr constituting the DC stabilization circuit (6), the potential of the emitter of the transistor Tr becomes higher than the output voltage of the DC stabilization circuit (6). Therefore, the transistor Tr, ij connected to the emitter of the transistor Trt, the DC stabilizing circuit (6
) may be used, and general small signal transistors can be used.

Furthermore, at a point in time when the output voltage of the DC stabilizing circuit (6) is low.

Since sufficient pace current can be secured for the transistor Tr, the transistor Tr2 is sufficiently turned on even if the conduction angle of the thyristor SCR is increased, so that the drive current can be supplied to the detection circuit (2) without any problems. Can be done.

Furthermore, in the actual example shown in FIG. 1, an example is shown in which a light emitting diode LED is connected in series to the resistor R6 to indicate that the object to be detected (7) is in a close state. It may be connected in series with the diode D2 as shown in FIG. Furthermore, in a circuit that exhibits so-called reverse operation, in which the detection circuit (2) turns off when the detected object (7) approaches the detection coil (1) and turns on when it moves away, the third
The light emitting diode LED is diode D1 as shown in the figure.
By connecting the detection target (7) in series, it is possible to display the proximity state of the detected object (7).

In addition, although the above embodiment shows an example of a high frequency oscillator,
Needless to say, it can be applied to capacitance type devices.

(Effect of invention) Ki-ni f! A is because, as explained above, the path of the drive power supplied to the proximity detection circuit is made different when the proximity detection circuit is on and off.

Leakage current during off-time can be made extremely small, which in turn makes it possible to increase residual voltage. Further, the capacitor (C2) as shown in the prior art is not required, and this operation at power-on can be prevented.

[Brief explanation of drawings]

Figure 1 is a circuit diagram of an AC two-wire proximity switch according to an embodiment of the present invention, and Figures 2 and 3 are circuit diagrams of an AC two-wire proximity switch according to another embodiment of the present invention. FIG. 4 is a circuit diagram of a conventional AC two-wire proximity switch. (1)...detection coil, (2)...detection circuit, (4
)...load, (5)...AC power supply, (6)...DC stabilization circuit, (7)...detected object.

Claims (1)

[Claims] By controlling the conduction of a thyristor connected to the DC output end of the rectifier bridge in accordance with the output of the proximity detection circuit, a switch output is obtained at the AC input end of the rectifier bridge, and In an AC two-wire proximity switch in which a driving power source for a detection circuit is obtained through a DC stabilizing circuit and a smoothing capacitor connected in parallel to a rectifier bridge, the DC stabilizing circuit is connected between the DC stabilizing circuit and the smoothing capacitor. a current limiting element, a shunt circuit whose opening/closing is controlled by the output signal of the proximity detection circuit for the DC stabilizing circuit and the current control element, and a shunt circuit connected between the shunt circuit and the gate of the thyristor. An AC two-wire proximity switch characterized by comprising a constant voltage element and.