JPH11243329A - Electronic switch device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To surely prevent the malfunction of an output circuit at the time of starting a stabilizing power supply, accompanying power feeding from an external power supply, by generating a reset signal by synthesizing currents which are respectively outputted from 1st and 2nd current sources as a source current and a sink current. SOLUTION: When power supply voltage Vcc is fed, a 1st current source 11 operates and start to output a constant current. At this time, a stabilizing power supply 5 is also operated by receiving the voltage Vcc, and its output voltage Vreg that has a prescribed characteristic is started up. A 2nd current source 12 driven by the supply 5 is operated at a timing when output voltage of the supply 5 is started up and the output voltage reaches the lowest drive voltage of a sensor circuit part 4. A resetting circuit 10 outputs a signal as a resetting signal to an output circuit 7, by synthesizing currents outputted by the sources 11 and 12 as a source current and a sink current.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electronic switch device which performs an on / off operation by detecting the proximity of an object to be detected, and more particularly to a reset circuit for preventing a malfunction when a built-in stabilized power supply is started. Electronic switch device.

[0002]

[Related Background Art] In a high-frequency oscillation type proximity switch (electronic switch device), the inductance and loss of a detection coil forming a part of a high-frequency oscillation circuit are reduced by electromagnetic induction between the detection coil and a detection target (magnetic material). It detects the proximity of the object to be detected by utilizing the fact that the oscillation amplitude and the oscillation frequency of the high-frequency oscillation circuit change with this, and has excellent features such as high detection sensitivity and fast response speed. Have.

An electronic switch device of this type is, for example, shown in FIG.
A high-frequency oscillation circuit 1 having an LC tank circuit including a detection coil 1a and a capacitor 1b, a detection circuit 2 for detecting (integrating) an output of the high-frequency oscillation circuit 1 and detecting an oscillation amplitude thereof, The sensor circuit unit 4 includes a comparison circuit 3 that detects the proximity of a detection target by comparing the detection output with a predetermined threshold. Such a sensor circuit section 4 receives a predetermined drive voltage Vreg from the stabilized power supply 5 and operates while being supplied with current by the current source 6. The output circuit 7 turns on and off in response to the output of the sensor circuit section 4. The output circuit 7 drives the output transistor 7a connected between the pair of power supply lines to change the impedance between the power supply lines. And outputs a signal.

The electronic switch device having the above configuration is supplied with power from an external power supply Vcc incorporated in the monitoring device, for example, via a load 8 such as a relay, and further via the pair of power lines. The monitoring device detects the operation state of the electronic switch device from a change in the state of the load 8 due to a change in the impedance of the output transistor 7a.

The reset circuit 9 incorporated in the electronic switch device prevents the output circuit 7 from malfunctioning when the stabilized power supply 5 rises due to the start of power supply from the external power supply Vcc via the power supply line. Take a role. That is, the reset circuit 9 monitors the output voltage Vreg of the stabilized power supply 5, and resets the output circuit 7 until the sensor circuit unit 4 stably operates normally after receiving the output of the stabilized power supply 5. Has a role in keeping the state.

The sensor circuit section 4 is configured to detect, for example, when the oscillation amplitude of the high-frequency oscillation circuit 1 that oscillates by receiving power supply from the stabilized power supply 5 decreases as the proximity of the detection target. You. Therefore, even when the stabilizing power supply 5 does not rise sufficiently in the output circuit 7 and the high-frequency oscillation circuit 1 does not oscillate, the sensor circuit unit 4 operates as if the proximity of the detection target is detected. Therefore, the monitoring device may erroneously determine this. The reset circuit 9 functions to keep the output circuit 7 in a reset state until the stabilized power supply 5 rises and the sensor circuit unit 4 operates normally in order to prevent such a malfunction.

[0007]

In the reset circuit 9 functioning as described above, the output voltage Vreg of the stabilized power supply 5 is compared with a predetermined judgment voltage Vrst to monitor the output voltage Vreg. The reset signal is generated when the output voltage Vreg does not reach the determination voltage Vrst. Therefore, the determination voltage Vrst for generating such a reset signal is equal to or higher than the minimum drive voltage Vact necessary for the sensor circuit section 4 to operate normally, and the stabilizing power supply 5 completely rises and the sensor circuit The output voltage Vreg needs to be lower than the output voltage Vreg when the unit 4 is driven stably.

However, each of the voltages Vreg, Vrst, Vac
Since t depends on the variation in the circuit configuration and element characteristics of each part constituting the electronic switch device and further on its temperature characteristics, the reset circuit 9 is designed in consideration of the variations in these voltages Vreg, Vrst and Vact. It is very difficult. Furthermore, when the voltage difference (potential difference) between the output voltage Vreg of the stabilized power supply 5 and the minimum drive voltage Vact of the sensor circuit unit 4 is small, the judgment voltage Vrst in the reset circuit 9
Is very difficult to set, and it is difficult to guarantee a stable operation of the reset circuit 9.

The present invention has been made in view of such circumstances, and has as its object to provide a reset circuit capable of reliably preventing an output circuit from malfunctioning when a stabilized power supply rises due to power supply from an external power supply. It is an object of the present invention to provide an electronic switch device having a simple configuration including:

[0010]

In order to achieve the above-mentioned object, an electronic switch device according to the present invention is provided with a stabilized power supply that is supplied with power from an external power supply and operates to drive a sensor circuit unit; And an output circuit that performs an on / off operation in response to the output of the stabilizing power supply. A first current source that is supplied with power from the external power supply to generate a constant current, and a second current source that is driven by the stabilized power supply and generates a current corresponding to an output voltage of the stabilized power supply. Means for combining one of the currents output from the first and second current sources as a source current and the other as a sink current to generate the reset signal. It is characterized.

In particular, the second current source is activated when the output voltage of the stabilized power supply reaches the minimum drive voltage of the sensor circuit section, and the output current of the second current source is controlled by the second current source. The current value from the first current source is gradually increased in accordance with the output voltage of the stabilized power supply. That is, a first current source that is driven by an external power supply and outputs a constant current, and a second current source that outputs a current corresponding to the output voltage of the stabilized power supply driven by the external power supply, By controlling the operation of the output circuit by synthesizing the currents output from the respective current sources, and configuring the reset circuit to operate the output circuit only at the time of current sink, the output circuit is activated when the stabilized power supply rises. The feature is that the operation is surely prohibited.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, an electronic switch device according to the present invention will be described with reference to the drawings. FIG. 1 is a schematic configuration diagram of an electronic switch device according to this embodiment, and the same parts as those of the conventional device shown in FIG. This device is characterized in particular by the configuration of a reset circuit 10, and as shown in FIG. 1, a first current source 11 which operates upon receiving power supply from an external power supply Vcc and outputs a constant current Iconst. And a second current source 12 which operates in response to the output of the stabilized power supply 5 and outputs a current Ilamp corresponding to the output voltage Vreg.
One of the lamps is synthesized as a source current and the other is synthesized as a sink current, and the synthesized current is added to the output circuit 7 as a reset signal.

In particular, the second current source 12 is activated when the output voltage of the stabilized power supply 5 reaches a predetermined voltage, specifically, a minimum drive voltage Vact at which the sensor circuit section 4 operates normally. Thus, a lamp current Ilamp that is a current that gradually increases in accordance with the output voltage of the stabilized power supply 5 and that eventually reaches a current value exceeding the constant current Iconst output from the first current source 11 is output. It is characterized by having been constituted.

[0014] Such first and second current sources 11,
According to the electronic switch device including the reset circuit 10 mainly including the reset circuit 12, as shown in a timing chart showing the operation state in FIG. When a power supply voltage Vcc is supplied via a power supply line, the first current source 11
Operates, and the first current source 11 starts outputting a constant current Iconst as shown in FIG. At this time, the stabilizing power supply 5 operates in response to the power supply voltage Vcc, and its output voltage Vreg rises with predetermined characteristics as shown in FIG. The rising characteristic of the output voltage of the stabilized power supply 5 is defined by, for example, the capacity of the smoothing capacitor C connected to the stabilized power supply 5.

In the second current source 12 driven by the stabilized power supply 5, for example, the output voltage of the stabilized power supply 5 which operates in response to the power supply voltage Vcc rises, and the output voltage is changed to the sensor circuit section 4. Is activated from the timing t1 when the minimum drive voltage Vact is reached. Then, the second current source 12 gradually increases its current value according to the output voltage of the stabilized power supply 5, and the output voltage of the stabilized power supply 5 drives a predetermined drive voltage for constantly driving the sensor circuit unit 4. V
When the current reaches reg, a current Ilamp having a ramp-hold waveform of a constant current exceeding the constant current Iconst output from the first current source 11 is output.

The reset circuit 10 synthesizes one of the current Iconst output from the first current source 11 and the current Ilamp output from the second current source 12 as a source current and the other as a sink current, as described above. In FIG. 2C, a combined current indicated by a broken line is obtained, and this is output as a reset signal to the output circuit 7. In particular, when the combined current is in a sink state with respect to the output circuit 7, it is output as a reset signal for holding the output circuit 7 in a reset state.

Thus, according to the electronic switch device having the reset circuit 10 configured as described above, the current Iconst output from the first current source 11 and the second current source 12
And the current Ilamp output from each other attracts each other, and the operation of the output circuit 7 is controlled by the combined current. In particular, since the second current source 12 starts operating when the output voltage of the stabilized power supply 5 reaches the minimum drive voltage Vact of the sensor circuit unit 4, the first current source 12 operates until the second current source 12 operates. The operation of the output circuit 7 is reliably inhibited by the current Iconst from the current source 11.

Thereafter, with the operation of the second current source 12, the output current Ilamp from the second current source 12 increases, and the output current Ilamp is changed to a constant current output from the first current source 11. At a timing t2 exceeding Iconst, the combined current acts as a source current for the output circuit 7 for the first time, thereby permitting the operation of the output circuit 7.

At this point in time, the output voltage of the stabilized power supply 5 has already become the minimum drive voltage Vact of the sensor circuit 4 described above, which is the condition for starting the operation of the second current source 12.
Is exceeded, and the sensor circuit section 4 is operating normally, so that the output circuit 7 receives the output of the sensor circuit section 4 and turns on and off. Therefore, only when the sensor circuit section 4 is functioning normally, the operation of the output circuit 7 is allowed and the output circuit 7 performs the on / off operation.

In other words, when the output voltage of the stabilized power supply 5 has not risen sufficiently, the operation of the output circuit 7 is prohibited, and the output voltage of the stabilized power supply 5 is reduced to the minimum drive voltage Vact of the sensor circuit section 4. After that, at the timing t2 when the output current Ilamp of the second current source 12 that operates upon receiving the output voltage exceeds the constant current Iconst output from the first current source 11, the operation of the output circuit 7 is prohibited. Will be released. Therefore, the output circuit 7 operates at the timing t1.
After the sensor circuit section 4 functions normally, the operation is prohibited until the timing t2 at which the combined current turns to the source current with the operation of the second current source 12, and the malfunction is reliably prevented. Will be done.

When the first and second current sources 11 and 12 are operated to control the operation of the output circuit 7 by the combined current as described above, for example, as shown in FIG. The output current from the first current source 11 which operates upon receipt is received by a first current mirror circuit 21 comprising a pair of npn transistors Q1 and Q2, and the output current is taken out. Also, the output current from the second current source 12 operating in response to the output voltage of the stabilized power supply 5 is supplied to a pair of npn
The output current is received by a second current mirror circuit 22 including transistors Q3 and Q4, and the mirror current is inverted through a third current mirror circuit 23 including a pair of pnp transistors Q5 and Q6. . The respective currents are commonly input to the base of a pnp transistor Q7 for synthesis, so that the first current source 1 extracted through the first current mirror circuit 21 is output.
The current from one is sink current, and the second and third
The current from the second current source 12 extracted through the current mirror circuits 22 and 23 in this order may be combined as a source current by the transistor Q7 and output as a reset signal. At this time, a current is output to the sensor circuit section 4 through, for example, a mirror transistor Q8 whose base is commonly connected to the second current mirror circuit 22, thereby driving the sensor circuit section 4. You should do it.

Thus, as described above, the first current source 11
According to the reset circuit 10 including the second current source 12, the output circuit 7 can be reset very easily and reliably when the stabilized power supply 5 starts up. In addition, the minimum drive voltage Vact of the sensor circuit unit 4 for operating the second current source 12 and the sensor circuit unit 4
, The reset circuit 10 can be designed in consideration of only the drive voltage Vreg constantly applied to the reset circuit. Accordingly, even in a two-wire proximity switch in which the driving voltage Vreg is low and the potential difference from the minimum driving voltage Vact is small, the output circuit 7 is not affected by the circuit configuration or element characteristics and does not depend on temperature characteristics. Can be surely reset, and the advantage thereof is great, for example, malfunction of the output circuit 7 can be prevented.

The present invention is not limited to the above embodiment. For example, the present invention is not limited to the high-frequency oscillation type proximity switch, and can be similarly applied to other types of proximity switches that operate by receiving an external power supply. Of course, the present invention can be applied to other than the two-wire proximity switch. Further, the second current source 12 is operated at the same time as the operation of the stabilized power supply 5, and when the output voltage of the stabilized power supply 5 exceeds the minimum drive voltage Vact of the sensor circuit unit 4, the output current becomes the first current. The circuit may be configured to exceed the current value from the source. However, in this case, the output current from the second current source 12 may be set to exceed the current from the first current source when the output voltage of the stabilized power supply 5 becomes sufficiently high. is necessary. Further, in the circuit shown in FIG. 3, it is needless to say that the timing t2 can be adjusted by appropriately inserting an emitter resistor between the transistors Q1, Q2, Q5, and Q6. In addition, the present invention can be variously modified and implemented without departing from the gist thereof.

[0024]

As described above, according to the present invention, the first current source driven by the external power source and the second current source operated by receiving the output of the stabilized power source driven by the external power source And equipped. Since the operation of the output circuit is controlled by synthesizing the output currents from these current sources, malfunction of the output circuit can be easily and reliably prevented.

In particular, the second current source is operated at a timing at which the stabilized power supply obtains a predetermined output voltage capable of driving the sensor circuit section, so that the output circuit can be very easily operated. Can be prevented, and even if the operating voltage is low, the reset operation can be reliably performed.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram of an electronic switch device according to an embodiment of the present invention.

FIG. 2 is a timing chart showing a reset operation of an output circuit in the electronic switch device according to the present invention.

FIG. 3 illustrates a configuration example of a reset circuit.

FIG. 4 is a schematic configuration diagram of a conventional electronic switch device.

[Explanation of symbols]

 Reference Signs List 4 Sensor circuit section 5 Stabilized power supply 7 Output circuit 10 Reset circuit 11 First current source 12 Second current source Q7 Current synthesis transistor

Claims (2)

[Claims] 1. A sensor circuit for detecting the proximity of a detection target, a stabilized power supply which is supplied with power from an external power supply and operates to drive the sensor circuit, and turns on upon receiving an output of the sensor circuit. An output circuit that performs an off operation, and a reset circuit that outputs a reset signal at the time of starting power supply to the stabilized power supply and keeps the output circuit in a reset state. A first current source that is supplied with power and generates a constant current, a second current source that is driven by the stabilized power source and generates a current corresponding to an output voltage of the stabilized power source, And a means for combining the one of the currents output from the second current source as a source current and the other as a sink current to generate the reset signal. 2. The method according to claim 1, wherein the second current source is activated when an output voltage of the stabilized power supply reaches a minimum drive voltage of the sensor circuit, and gradually increases in accordance with the output voltage. 2. The electronic switch device according to claim 1, wherein a current exceeding a current value from the first current source is output.