JPS5944740A - Dc 2-wired proximity switch - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed description of the invention] The present invention relates to a DC two-wire proximity switch.

A conventional DC two-wire proximity switch includes one shown in FIG. 1, for example. To explain this, the drive current supplied to the proximity switch main circuit 1 consisting of an oscillation circuit including a detection coil L and a circuit that generates a detection signal according to the oscillation amplitude of this oscillation circuit is as follows. When the transistor Q1 is turned on by a detection signal generated by the proximity switch main circuit 1 detecting an object,
The voltage VON between the power supply terminal 10 and the circuit earth terminal 11 is
Since transistor Q2 of the output circuit is turned on, this ON
The voltage becomes the sum of the emitter and base voltage VBE at the time, the forward voltage sieve -FVI) of the operation display light emitting diode LID1), and the lefter and emitter voltage vcEs when the transistor Q+ (7) is ON. , which is usually a very small value of about 3 (V). Therefore, in this state, the voltage supplied to the proximity switch main circuit 1 via the constant current circuit CD is equal to the constant current Fjj! r
CI) voltage drop (it is difficult to make it less than 2cm in practice) makes the voltage equal to the terminal voltage VON minus the voltage drop of the constant current circuit CD, thus stably driving the circuit 1. However, it is difficult to obtain sufficient voltage for this purpose, and there is a drawback that it is impossible to obtain a proximity switch that operates reliably. Note 1 (, L is the load, V
is a circuit power supply, R1 is a resistor, ZD is a constant voltage diode, C7 is a capacitor, and Zl) and 01 constitute an external noise absorption circuit. In view of the above drawbacks of the prior art, the present invention provides a DC two-wire proximity switch that operates reliably and also has an overcurrent protection function in the output circuit (hereinafter referred to as the output circuit) for driving the load. be. An embodiment of the present invention will be described in detail below with reference to FIG. ■ is the proximity switch main circuit (hereinafter referred to as main circuit 1)
The oscillation circuit includes an oscillation circuit including a detection coil L, and an output circuit that detects changes in the oscillation amplitude of the oscillation circuit and generates ON and opF output signals from the output terminal OP. CI〕′
is a constant current element as a constant current circuit, one of which is connected to the load RL and the circuit power supply V via the power supply terminal 10, and the other of which is connected to the positive electrode side of the main circuit 1. Z1]
Reference numeral 3 denotes a constant voltage diode as a constant voltage means, which is connected between the positive circuit of the main circuit 1 and the ground lj1. 2 is a first switching circuit whose main component is a transistor Q, the emitter of which is connected to the output terminal OP of the main circuit 1, and the base of which is connected to the resistor 1-1. , which is connected to the power supply terminal 10 through resistor I (connected to circuit ground 1 through resistor I).
(, 4 can be replaced by a constant voltage diode, since any device that applies a predetermined voltage to the base of the transistor Q) can be used instead. Furthermore, its collector is a second switching circuit whose main component is a transistor (Q), which will be described later. resistance 1
1.4) Connected to one end.

3 is a second switching circuit whose main component is the above-mentioned transistor Q, and the base of the transistor Q4 is connected to the other end of the resistor 1, and connected to the emitter of the transistor Q4 through the resistor 1. It is connected. Moreover, this emitter is connected to the power supply terminal I via the resistor It6.
Connected to O. Furthermore, its collector is connected to the cathode of the voltage regulator diode Z3]. 4
is an output circuit mainly composed of a transistor Q5, the emitter of which is connected to the power supply terminal 10, and its base connected to the emitter of the transistor Q4. Furthermore, the collector is the base resistor 1t8 of the transistor Q6 that constitutes the overcurrent detection circuit 5.
It is connected to the connection point of the resistor I, which is connected between one end of the circuit ground 8 and the circuit ground 8. Here, the collector of the transistor Q6 constituting the overcurrent detection circuit 5 is the transistor Q constituting the first switching circuit 2.

, and the emitter is connected to circuit earth E. In addition, ■ is the circuit power supply, M is the object to be detected, Zl)2 is a constant voltage diode, which is connected to the power supply terminal 10 and the base resistance I% of the transistor Q6 of the overcurrent detection circuit 5,
It is meant to absorb foreign zurges. The operation of the second configuration will be explained below.

First, when the circuit power supply V is applied and the circuit is in an operating state, the detected object M is the detection coil ■.

, the main circuit 1 enters the object detection state, and the output terminal OP of the main circuit 1 becomes O" level.

The base current flows through the transistor (also known as a resistor) and turns on.As a result, the light emitting diode L
Current also flows through E I) and lights it up. Furthermore, when the l-run lefter Q3 (7) is turned ON, a base current flows through the transistor Q4, and this transistor (Q, 4 is turned on. Therefore, the base current also flows to the transistor Q, and the l-run lefter is also turned on. Therefore, the load 1 (The drive current of 1- flows through the emitter-collector of transistor Q5, resistor 1 (,,, circuit ground E path t+, and the load 1 (+L is driven, and its driving state is light emitting diode L)) I)
This is what is displayed. In addition, in the above state, on the cathode side of the constant voltage diode Z1)3, the transistor Q,
Since the current flowing from the circuit power supply V through the resistors 1 and 6 is applied through the transistor Q4, the main circuit 1 receives a stable voltage due to the action of the constant voltage diode ZD3. Voltage (constant voltage diode Z[),
Since the main circuit 1 is supplied with a voltage defined by a constant voltage value of , the main circuit 1 operates stably. In this state, the voltage VON between terminals 10 and 11 (hereinafter referred to as residual voltage VON) is the voltage defined by the constant voltage diode Z1)3, and the base and emitter voltages when the transistor Q is (-)N. The main circuit 1 includes a constant voltage diode Z.
Since the configuration is such that a voltage defined by D3 is applied, it is possible to configure a proximity switch with a low residual voltage VON that does not require consideration of the voltage drop of the constant current element C1. Next, when the object to be detected moves away from the detection coil and the main circuit 1 is not detecting the object, the output terminal OP of the main circuit 1 becomes °゛]' level, so it is On the other hand, the transistor Q3 of the first switching circuit 2 is OF
F, so the transistor Q4 of the second switching circuit 3 also becomes OI"F, Jz. Therefore, the transistor Q5 of the output circuit 4 also becomes OFF. Therefore, the load It, +
Since no load drive current flows through , load 1(], is not driven.The circuit power supply V is applied to main circuit 1 via constant current element CI)' through load IL+. Since a predetermined current flows through the constant voltage diodes Z1) and l, the main circuit I maintains the detection timing state. In addition, here, the light emitting diode L for operation display
g: l), as mentioned above, transistor Q3 is 01”F.
Since the drive current is not flowing, the light is on, indicating that the proximity switch is not detecting an object. Furthermore, in the present invention, the overcurrent protection circuit 5
When the proximity switch detects an object, the output circuit 4 is in an operating state.For example, if the load circuit is damaged and a short circuit occurs, the output circuit 4 is connected to the output circuit 4.
A resistor 1 is also connected to the base of the transistor C>,n of the overcurrent protection circuit 5 through the emitter-collector of the transistor Q5. Since the voltage is applied to the terminal, the base potential of the transistor Q6 rises, and the transistor Q6 turns on. Therefore, the current applied to the base of the transistor Q6 flows to the circuit earth L, l through the collector and emitter of the transistor Q6, so the transistor Q23 shifts to the OJ, "li" state. Therefore, the transistor Q4 Since the base current no longer flows to the transistor Q of the output circuit 4, the base current also stops flowing to the transistor Q of the output circuit 4.
This effectively protects the transistor Q from the inflow of a large current caused by a short circuit in the load or the like.

Since the present invention is configured and operates as described above, it is possible to reliably drive a small load by keeping the remaining voltage of the proximity switch circuit low, and furthermore, it is possible to suppress the remaining voltage of the proximity switch circuit to a low level. Since it has an overcurrent protection circuit that works without any problem, even if an excessive current flows through the output circuit due to a load short circuit, etc., it can effectively protect the output circuit from damage. It is something to play.

[Brief explanation of the drawing]

FIG. 1 is a block circuit diagram of a conventional two-wire DC proximity switch. FIG. 2 is a block circuit diagram of an embodiment of the DC two-wire proximity switch of the present invention. 1 Proximity switch main circuit, 4 Output circuit, 5 Overcurrent protection circuit, Zl)2, Zl), ... Constant voltage diode, L
1 Bow 1) Light emitting diode, 1 (1L/Load, ■ Circuit voltage, M Object to be detected. Patent applicant: Yuyo Electronics Industry Co., Ltd.

Claims (1)

[Claims] (1) A constant current circuit is connected to the proximity switch main circuit, which consists of an oscillation circuit including the detection coil L and a circuit that detects changes in the oscillation amplitude of the oscillation circuit and generates an ON, 01"F output signal. In a proximity switch that applies power, a constant voltage element is connected between the positive side of the proximity switch main circuit and the circuit ground, and a constant voltage element is connected between the canard of the constant voltage element and the output circuit that drives the load. O
A second switching circuit is provided that operates in conjunction with the operating state of the first switching circuit that operates based on the state of the N, OFF output signal, and when an object is detected, the drive current to the proximity switch main circuit is transferred to the output circuit. , is applied to the constant voltage element through the path of the second Sinotig circuit, and the voltage defined by this constant voltage element is applied to the proximity switch main circuit, and a current is applied to the output circuit. 1. A direct current two-wire proximity switch characterized by being provided with an overcurrent protection circuit that operates to limit the current flowing through the output circuit when the current is detected and exceeds a predetermined value. (2. The proximity switch according to claim 1, characterized in that a light emitting element for displaying operation is provided between the positive power supply terminal and the connection point of the first and second switching circuits. Wire proximity switch.