JP2008270128A - Electronic switch - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain normal output even when an operation indicating lamp 9 causes an open failure while restraining current consumption. <P>SOLUTION: The operation indicating lamp 9 is arranged on a current path for on/off-controlling an output transistor 10 to use the current of the current path for driving the operation indicating lamp 9 at the same time, a constant-voltage diode 18 is connected in parallel to the operation indicating lamp 9 as a bypass circuit, and the current is carried to the output transistor 10 through the constant-voltage diode 18 when the operation indicating lamp 9 causes an open failure and the current does not flow. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an electronic switch such as a proximity switch or a photoelectric switch used for applications such as object detection.

  Such an electronic switch detects the position of an object and the presence / absence of an object in a non-contact manner using a magnetic field, an electric field, light, etc. Has been used.

  In general, an electronic switch is provided with a dedicated integrated circuit for miniaturization. In such an integrated circuit, power consumption is limited in order to prevent malfunction of the circuit and destruction of the circuit due to heat generation. Yes.

  In addition, the integrated circuit of the electronic switch is connected with an operation indicator lamp that lights it when an object is detected so that the operating state can be visually confirmed. If the power dedicated to driving the operation indicator lamp is secured, the power that can be consumed by other circuits in the integrated circuit is reduced accordingly.

In view of this, the present applicant has proposed a configuration in Japanese Patent Application Laid-Open No. 2004-151405 that drives an operation indicator that displays an operation state using electric power that controls on / off of an output transistor that outputs a detection result.
Japanese Patent No. 3451346

  In the said patent document 1, since the operation indicator lamp is provided in the electric current path | route of an output transistor, there exist the following subjects.

  In general, light emitting diodes (LEDs) that can obtain sufficient luminance with low current consumption are used as operation indicator lamps. Such light emitting diodes are molded by a transparent resin having a larger thermal expansion coefficient than that of black resin. For this reason, in a high temperature use environment, the mechanical life due to thermal stress is shortened compared to other circuit elements molded with black resin.For example, the joint is peeled off or the bonding wire is disconnected. May cause an open failure.

  When such an open failure occurs, a current for controlling on / off of the output transistor cannot be supplied to the output transistor provided in the same current path, resulting in an output failure. There is a problem that there is a case where it is necessary to stop the equipment that is operated based on.

  The present invention has been made in view of the above-described points, and an object of the present invention is to provide an electronic switch capable of obtaining a normal output even when an operation indicator lamp is open.

 (1) An electronic switch according to the present invention includes an output unit that provides an on / off output according to a detection result of a detection target, and a display unit that displays an output state of the output unit, and performs on / off control of the output unit. An electronic switch for providing the display unit in a current path and sharing the current in the current path for driving the display unit, wherein a bypass circuit is provided in parallel with the display unit, and the current in the current path is When the current does not flow through the display unit, a current is passed through the output unit via the bypass circuit.

  For example, the current consumption of the electronic switch is preferably several tens mA or less, and more preferably about 30 mA or less.

  Moreover, it is preferable that the consumption current of a display part is below several mA, for example.

  According to the electronic switch of the present invention, the on / off control of the output unit and the driving of the display unit are performed by the current in the same current path, so that current consumption can be reduced.

  In addition, since a bypass circuit is provided in parallel with the display unit, even if the display unit is open failure and current does not flow, it is possible to perform on / off control by flowing current to the output unit via the bypass circuit. There is no output failure.

  (2) In one embodiment of the electronic switch of the present invention, the output unit is constituted by a transistor, while the display unit is constituted by a light emitting diode.

  According to this embodiment, since the light emitting diode is used, sufficient luminance can be obtained with a small current consumption.

  (3) In the embodiment of the above (2), the bypass circuit is composed of a constant voltage diode connected to the light emitting diode in reverse polarity parallel.

  According to this embodiment, when the light emitting diode is normal, no current flows through the constant voltage diode, so that no wasteful current is consumed, and when the light emitting diode does not flow due to an open failure, It is possible to perform on / off control by supplying a current to the output section via the constant voltage diode, and no output failure occurs.

  (4) In the embodiment of (2), the bypass circuit is configured by a series circuit of a plurality of diodes connected in parallel to the light emitting diodes with the same polarity.

  According to this embodiment, when the light emitting diode is normal, no current flows in the series circuit of the plurality of diodes, so that no unnecessary current is consumed, and the current does not flow due to an open failure of the light emitting diode. In this case, it is possible to perform on / off control by supplying a current to the output section through a series circuit of a plurality of diodes, so that no output failure occurs.

  (5) In the embodiment of (2) above, the bypass circuit is configured by a resistor connected in parallel to the light emitting diode.

  According to this embodiment, when the light-emitting diode fails to open and current does not flow, it is possible to control the on / off by supplying current to the output section via the resistor, so that no output failure occurs.

  (6) In another embodiment of the electronic switch of the present invention, the electronic switch includes an integrated circuit that performs on / off control of the output unit and performs display control of the display unit.

  According to this embodiment, in an integrated circuit in which power consumption is limited, it is effective for suppressing current consumption.

 (7) In still another embodiment of the electronic switch of the present invention, a magnetic field is generated in a detection region of the detection object.

  According to this embodiment, it is suitable as an inductive proximity switch.

  According to the present invention, since the on / off control of the output unit and the display unit are driven by the current in the same current path, the current consumption can be reduced. In addition, since a bypass circuit is provided in parallel with the display unit, even if the display unit is open failure and current does not flow, it is possible to perform on / off control by flowing current to the output unit via the bypass circuit. There is no output failure.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

(Embodiment 1)
FIG. 1 is a block diagram of a proximity switch as an electronic switch according to an embodiment of the present invention.

  The proximity switch 1 of this embodiment includes a detection element 2 including a detection coil, a detection circuit unit 3 including an oscillation circuit connected to the detection element 2, an integration circuit unit 4 that detects and integrates an oscillation signal, Based on the output of the integration circuit unit 4, a discrimination circuit unit 5 that discriminates the presence / absence of the detection target object, an output control circuit unit 6 that controls the output based on the discrimination result, and power supply to the circuit units 3 to 6 The circuit units 3 to 7 are constituted by an integrated circuit (IC) 8.

  The integrated circuit 8 is connected with an operation indicator lamp 9 made of an LED (light emitting diode) and an output transistor 10 as external components.

  That is, the anode of the operation indicator lamp 9 is connected to the power supply line between the power supply terminal T1 of the proximity switch 1 and the power supply terminal T4 of the integrated circuit 8, and the cathode of the operation indicator lamp 9 is connected to the connection terminal T5 of the integrated circuit 8. Connected. A constant voltage diode 18 (to be described later) is connected in reverse polarity in parallel with the operation indicator lamp 9, and the constant voltage diode 18 has a Zener voltage larger than the voltage drop of the operation indicator lamp 9.

  Further, the collector of the output transistor 10 is connected to the output terminal T2 of the proximity switch 1, the base of the output transistor 10 is connected to the output terminal T6 of the integrated circuit 8, and the emitter of the output transistor 10 is connected to the proximity switch 1. Are connected to a ground line between the power supply terminal T3 of the integrated circuit 8 and the power supply terminal T7 of the integrated circuit 8.

  The connection terminal T5 and the output terminal T6 of the integrated circuit 8 are connected to the internal output control circuit unit 6.

  FIG. 2 is a path diagram showing the main parts of the output transistor 10, the operation indicator lamp 9 and the output control circuit unit 6 of FIG. 1, and the same reference numerals are given to the portions corresponding to FIG.

  The output control circuit unit 6 includes a transistor 12 to which a detection output S corresponding to the detection state from the discrimination circuit 5 is applied to the base, and a constant current circuit 11, and the collector of the transistor 12 is connected to the connection terminal T5. On the other hand, the emitter is connected to the constant current circuit 11, and this constant current circuit 11 is connected to the output terminal T6.

  In this embodiment, when an object to be detected is detected, a high-level detection output S is given from the discrimination circuit unit 5 to the base of the transistor 12 of the output control circuit unit 6, and the transistor 12 is turned on. The constant current I flows through the operation indicator lamp 9 through the constant current circuit 11 and the operation indicator lamp 9 is turned on, and the constant current I flows through the base of the output transistor 10 and the output transistor 10 is turned on.

  In the state where the detection target object is not detected, a low level detection output S is given from the discrimination circuit unit 5 to the base of the transistor 12 of the output control circuit unit 6 to turn off the transistor 12, and the operation indicator lamp 9 Current does not flow, the operation indicator lamp 9 is not lit, current does not flow to the base of the output transistor 10, and the output transistor 10 is turned off.

  Thus, since the operation indicator lamp 9 is provided in the current path for controlling the on / off of the output transistor 10, it is not necessary to secure power dedicated to driving the operation indicator lamp 9, and the current consumption is reduced accordingly. Can do.

  The operation indicator lamp 9 uses an LED (light emitting diode) because high luminance can be obtained with a low current consumption of about 5 mA. This LED is another type of LED molded with a black resin in a high temperature use environment. Compared to circuit elements, the mechanical life due to thermal stress is shortened, and an open failure may occur.

  Therefore, in this embodiment, as described above, the constant voltage diode 18 constituting the bypass circuit is connected in reverse polarity to the operation indicator lamp 9 in parallel.

  Since the constant voltage diode 18 is provided in parallel with the operation indicator lamp 9 in this way, when the operation indicator lamp has an open failure, when the detection target object is detected and the transistor 12 of the output circuit controller 6 is turned on. The voltage across the constant voltage diode 18 becomes equal to or higher than the zener voltage, and the constant voltage diode 18 becomes conductive. As a result, a current flows through the base of the output transistor 10 and the output transistor 10 is turned on. Will be obtained.

  Therefore, according to this embodiment, when the operation indicator lamp 9 has an open failure as in the prior art, the output of the output transistor becomes defective and the facility has to be stopped.

  Further, when the operation indicator lamp 9 is operating normally, no current flows through the constant voltage diode 18 and there is no unnecessary current consumption.

(Embodiment 2)
FIG. 3 is a circuit diagram of a main part corresponding to FIG. 2 of another embodiment of the present invention.

  In this embodiment, the bypass circuit is a series circuit of two diodes 19 and 20 having a voltage characteristic larger than the voltage drop of the operation indicator lamp 9 instead of the constant voltage diode 18.

  Also in this embodiment, when the operation indicator lamp 9 has an open failure and the detection target object is detected, the diodes 19 and 20 are turned on, whereby a current flows to the base of the output transistor 10 and the output transistor 10 is turned on, and a normal output is obtained.

  Further, when the operation indicator lamp 9 is operating normally, no current flows through the diodes 19 and 20 and there is no unnecessary current consumption.

(Embodiment 3)
FIG. 4 is a circuit diagram of a main part of still another embodiment of the present invention.

  In this embodiment, the bypass circuit is configured by the resistor 21.

  Also in this embodiment, even if the operation indicator lamp 9 is open-failed and current stops flowing through the operation indicator lamp 9, the drive current can be supplied to the base of the output transistor 10 via the resistor 21.

(Other embodiments)
As another embodiment of the present invention, as shown in FIGS. 5 to 7, the operation indicator lamp 9 and the bypass circuit may be provided between the output terminal T <b> 6 of the integrated circuit 8 and the output transistor 10.

  In each of the above-described embodiments, an example using an NPN transistor has been described. However, as another embodiment of the present invention, a PNP transistor may be used.

  Although the above embodiment has been described as applied to a proximity switch, it may be applied to a photoelectric switch as another embodiment of the present invention.

  The present invention is useful for proximity switches, photoelectric switches, and the like.

It is a block diagram which shows the structure of the proximity switch which concerns on one embodiment of this invention. It is a circuit diagram of the principal part of FIG. It is a block diagram corresponding to FIG. 2 of other embodiment of this invention. It is a block diagram corresponding to FIG. 2 of further another embodiment of this invention. It is a block diagram corresponding to FIG. 1 of other embodiment of this invention. It is a block diagram corresponding to FIG. 5 of other embodiment of this invention. It is a block diagram corresponding to FIG. 5 of further another embodiment of this invention.

Explanation of symbols

1 Proximity Switch 9 Operation Indicator Light 10 Output Transistor 18 Constant Voltage Diodes 19, 20 Diode 21 Resistance

Claims (7)

An output unit that provides an on / off output according to a detection result of the detection target; and a display unit that displays an output state of the output unit; and the display unit is provided in a current path that controls on / off of the output unit, An electronic switch that uses the current in the current path to drive the display unit,
An electronic switch, wherein a bypass circuit is provided in parallel with the display unit, and a current flows through the output unit via the bypass circuit when a current in the current path does not flow through the display unit.   The electronic switch according to claim 1, wherein the output unit is configured by a transistor, and the display unit is configured by a light emitting diode.   The electronic switch according to claim 2, wherein the bypass circuit includes a constant voltage diode connected in parallel with the light emitting diode in reverse polarity.   The electronic switch according to claim 2, wherein the bypass circuit includes a series circuit of a plurality of diodes connected to the light emitting diodes in parallel with the same polarity.   The electronic switch according to claim 2, wherein the bypass circuit includes a resistor connected in parallel to the light emitting diode.   The electronic switch according to claim 1, further comprising an integrated circuit that performs on / off control of the output unit and performs display control of the display unit.   The electronic switch according to any one of claims 1 to 6, wherein a magnetic field is generated in a detection region of the detection object.

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