JP2000165218A - Load short circuit protective circuit for proximity switch - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a load short circuit protective circuit for a proximity switch where the rise of a residual voltage is small when a load current becomes large by protecting an output switching circuit by periodically turning it on and off when overcurrent is caused to flow to a proximity switch. SOLUTION: When a load current is increased due to short circuit, etc., both-terminal voltage of a resistance R1 increases, and a current is caused to flow to a diode D1, a resistance R4 and the base of a transistor Q2 to turn on the transistor Q2. When the transistor Q2 is turned on, a voltage is fed to the base of the transistor Q4 to turn on the transistor Q4 and to turn off a transistor Q3, and because the current is not supplied to the base of a transistor Q1, the transistor Q1 is turned off and the current is not caused to flow to load 5. That is, the transistor Q3 is turned off, and the current is supplied from a capacitor C1 to the base of the transistor Q2 to keep the transistor Q2 on.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a load short-circuit protection for a proximity switch that periodically turns on and off an output transistor of an output switching circuit when an overcurrent flows due to a load short circuit or the like in the proximity switch. Circuit.

[0002]

2. Description of the Related Art FIG. 3 is a diagram showing a conventional short-circuit protection circuit for a proximity switch, which is a DC three-wire type. In the drawing, 1 is a detection coil, 2 is an oscillation circuit, and 3 is a detection circuit for detecting that an object to be detected (not shown) has approached the coil 1 from the output of the oscillation circuit 2. Transistor Q4 to which output signal is supplied, transistor Q
Capacitor C connected between the emitter and collector
2. The base is connected to the collector of the transistor Q4,
A transistor Q3 having an emitter connected to the emitter of the transistor Q4; a resistor R7 connected between the base of the transistor Q4 and the positive electrode of the power supply E; a resistor R6 connected between the emitter of the transistor Q4 and the positive electrode of the power supply E; It comprises a resistor R12 connected between the collector of Q4 and the negative side of the power supply E.

Reference numeral 4 denotes an output switching circuit for turning on / off the current supply from the power supply E to the load 5 based on the output signal of the detection circuit 3, and is connected to the collector of the transistor Q3 of the detection circuit 3 via a resistor R5. Light emitting diode L
ED, output transistor Q whose base is connected to LED
1, a resistor R3 connected between the connection point of the LED and the output transistor Q1 and the negative electrode of the power supply, a terminal T3 connected between the positive electrode of the power supply E and the positive electrode of the load 5, a terminal T2 connected to the negative electrode of the load 5, A terminal T1 to which the negative electrode of the power supply E is connected, a resistor R10 connected between the positive electrode side of the detection circuit 3 and the terminal T3.
The emitter of the output transistor Q1 is connected to a load short-circuit protection circuit 6 described later.

A load short-circuit protection circuit 6 has resistors R1 and R2 connected in series between the emitter of the output transistor Q1 of the output switching circuit 4 and the terminal T3, and a collector connected to the base of the output transistor Q1. The transistor Q2 is connected to the connection point of the resistors R1 and R2, the input side is connected to the base of the output transistor Q1, and the output side is the base of the transistor Q2 via the resistor R4.
And a capacitor C1 connected between the connection point of the diode D1 and the resistor R4 and the negative electrode of the power supply E.

Next, the operation will be described. Oscillation circuit 2
Always oscillates and outputs a signal, and when the object to be detected is inserted into the detection coil 1, oscillation stops and no signal is output. In the detection circuit 2, the output signal from the oscillation circuit 2 is supplied to the base of the transistor Q4, and the transistor Q4 is turned on and the transistor Q3 is turned off.

When the object to be detected is inserted into the detecting coil 1, the oscillation stops and the output signal is not supplied to the base of the transistor Q4, so that the transistor Q4 is turned off.
Then, the voltage of the power supply E is applied to the capacitor C via the resistor R6.
2 to be charged. When the voltage of the capacitor C2 increases, the base-emitter voltage of the transistor Q3 increases, and the transistor Q3 turns on.

In the output switching circuit 4, when the object to be detected is inserted into the detection coil 1 and the detection signal of the detection circuit 3 is output, the detection signal is supplied to the base of the output transistor Q1, and the output transistor Q1 is turned on. Thus, current is supplied from the power supply E to the load 5. When the object to be detected is not inserted into the detection coil 1, the detection signal of the detection circuit 3 is not supplied, so that the output transistor Q1 is turned off.

In the load short-circuit protection circuit 6, when a normal current flows through the load 5, the sum e1 of the base-emitter voltage (hereinafter referred to as V _BE ) of the output transistor Q1 and the voltage across the resistor R1 is 2 · because it is set lower than V _bE value, V _bE and the diode D of e1 the transistor Q2
When the voltage becomes higher than the voltage sum e2 between both ends of the transistor 1, a current flows through the base of the transistor Q2.

When a normal current flows through the load 5, e1
<E2, the diode D1 and the transistor Q2
No current flows through the base of the transistor Q2, and the transistor Q2 is turned off.

When the load current increases due to a short circuit or the like, the voltage across the resistor R1 increases, and when e1 exceeds e2,
A current flows through the diode D1 and the base of the transistor Q2, turning on the transistor Q2 and charging the capacitor C1. Accordingly, the current flowing in the base of the transistor Q1 also flows in the base of the transistor Q2, the base current of the output transistor Q1 decreases, the current flowing in the collector / emitter of the transistor Q1 also decreases, and e1 also decreases. However, current is supplied from the capacitor C1 to the base of the transistor Q2,
2 is turned on, and the output transistor Q1 is turned off.

When the discharge of the capacitor C1 is completed, the potential of the capacitor C1 becomes low, and the transistor Q2
Is turned off again, and the output transistor Q1 is turned on. At this time, if the load current is in an overcurrent state, the transistor Q1 is turned off again. This is repeated to protect the output transistor Q1 when the load is short-circuited.

FIG. 4 is a diagram showing a conventional DC 2-wire proximity switch and its load short-circuit protection circuit. In the figure, the same components as those in FIG. Reference numeral 7 denotes a detection circuit for detecting that the object to be detected approaches the coil 1, and reference numeral 8 denotes an output switching circuit.

In the detection circuit 7, Q4 is a transistor whose base is supplied with the output signal of the oscillation circuit 2, C2 is a capacitor connected between the emitter and collector of the transistor Q4, and Q3 is a base whose collector is connected to the collector of the transistor Q4. , The emitter of which is connected to the emitter of the transistor Q4. R6 is transistor Q
, A resistor connected between the emitter of P.4 and the positive side of the power supply E, R
Reference numeral 12 denotes a resistor connected between the collector of the transistor Q4 and the negative side of the power supply E.

In the output switching circuit 8, Q5 is a resistor R5 having a base connected in series and a light emitting diode L.
The transistor Q1 connected to the collector of the transistor Q3 via the ED, the base of which is connected to the collector of the transistor Q5 via the resistor R11, the collector connected to the emitter of the transistor Q5, and the terminal T2
Are connected to the output transistor. The positive terminal of the load 5 connected in series with the power supply E is connected to the terminal T2.

T1 is a terminal connected to the negative side of the power supply E,
R3 is a resistor connected between the connection point between the resistor R11 and the light emitting diode LED and the terminal T1, and R9 is a resistor connected between the connection point between the base of the transistor Q5 and the light emitting diode LED and the emitter of the transistor Q5. .

In this configuration, the operations of the oscillation circuit 2 and the load short-circuit protection circuit 6 are the same as those of the load short-circuit protection circuit of the DC 3-wire proximity switch shown in FIG. 3, and the detection circuit 7 and the output switching circuit 8 are different. The detection circuit 7 and the switching output switching circuit 8 will be described.

In the detection circuit 7, an output signal from the oscillation circuit 2 is supplied to the base of the transistor Q4, the transistor Q4 is turned on, a current flows from the resistor R6 to the transistor Q4, and then to the resistor R12, and the transistor Q3 is turned off. When the oscillation circuit 2 is oscillating, the transistor Q4 is repeatedly turned on and off, so that the transistor Q4 is immediately turned off, and the voltage of the power supply E is applied to the capacitor C2 via the resistor R6 and starts to be charged. When Q4 is turned on from off, the capacitor C2 is discharged to the emitter of the transistor Q4. As described above, the base-emitter voltage of the transistor Q3 does not increase, the transistor Q3 does not turn on, and the transistor Q3 does not turn on, so that there is no output.

When the object to be detected is inserted into the detection coil 1, the oscillation stops and the output signal is not supplied to the base of the transistor Q4, so that the transistor Q4 is turned off. Then, the voltage of the power supply E is applied to the capacitor C2 via the resistor R6 to be charged. When the voltage of the capacitor C2 increases, the base-emitter voltage of the transistor Q3 increases, and the transistor Q3 turns on.

In the output switching circuit 8, when the object to be detected is inserted into the detection coil 1 and the detection signal of the detection circuit 3 is output, the current is changed from the resistance R5 to the light emitting diode LED.
→ The current flows through the resistor R9, and the light emitting diode LED is turned on.
At this time, current also flows through the base of the transistor Q5.
The transistor Q5 is turned on, the current flows from the transistor Q5 to the resistor R11, and the base voltage of the transistor Q1 is increased. The output transistor Q1 is turned on, and the current is changed from the power supply E to the load 5 to the terminal T2. → Output transistor Q1 → Resistor R1, R2 of load short-circuit protection circuit 6 → Terminal T1, and current is supplied to load 5. When the object to be detected is not inserted into the detection coil 1, the detection signal of the detection circuit 3 is not supplied, so that the output transistor Q 1 is turned off, and no current is supplied to the load 5.

When the load current increases due to a short circuit or the like, when the voltage across the resistor R1 increases in the load protection circuit 6, the current flows through the diode D1, the resistor R4, and the base of the transistor Q2. The output transistor Q1 is turned on, the output transistor Q1 is turned off, and no current flows through the load 5, thereby protecting the output transistor Q1.

[0021]

In the conventional short-circuit load protection circuit of the proximity switch as described above, when the load current of the resistor R1 increases, the voltage across the resistor R1 increases to turn on the transistor Q2. Thus, the output transistor Q1 is protected, and the resistor R2 connects the output transistor Q1 and the emitter of the transistor Q2 to form an emitter-coupled circuit of a Schmitt circuit. However, the resistances R1, R2
Is connected to the emitter of the output transistor Q1, there is a problem that when the load current increases, the remaining voltage generated by the resistors R1 and R2 increases, resulting in a loss of current flowing through the load 5.

The present invention has been made in order to solve the above problems, and when the load current is increased,
It is an object of the present invention to obtain a load short-circuit protection circuit for a proximity switch in which a rise in a remaining voltage is small.

[0023]

A load short-circuit protection circuit for a proximity switch according to the present invention comprises a first transistor having a base connected to an output terminal of an output signal from an oscillation circuit, and an emitter of the first transistor. A detection circuit having a second transistor having an emitter connected to the collector of the first transistor and a base connected to the collector of the first transistor; and an output for supplying a current from the power supply to the load 5 based on an output signal from the detection circuit. A load short-circuit protection circuit for a proximity switch that periodically turns on and off an output transistor of the output switching circuit to protect the output transistor when an overcurrent flows in the proximity switch including the switching circuit; A first resistor connected to the negative electrode side of the power supply; and a collector connected to the first resistor via a second resistor.
A third transistor having an emitter connected to the negative electrode side, an input side connected to the base of the output transistor, and an output side connected to the third transistor via a third resistor. And a capacitor connected between the connection point of the diode and the third resistor and the negative electrode.

Also, a first transistor whose base is connected to the output terminal side of the output signal from the oscillation circuit and the first transistor
A detection circuit having a second transistor having an emitter connected to the emitter of the first transistor and a base connected to the collector of the first transistor; and a current flowing from the power supply to the load 5 based on an output signal from the detection circuit. And a load short-circuit protection circuit for a proximity switch that periodically turns on and off an output transistor of the output switching circuit to protect the output transistor when an overcurrent flows in the proximity switch including an output switching circuit that supplies the output switching circuit. A first resistor connected to the emitter of the transistor and the negative electrode of the power supply; a third transistor having a collector connected to the base of the second transistor and an emitter connected to the emitter of the first transistor The input side is connected to the base of the output transistor, and the output side is connected to the third transistor via a third resistor. Base of transistor - comprises a de a capacitor connected between the anode of the third connecting point of the resistor and the power supply, a - and a diode connected to the scan, the diode.

[0025]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiment 1 FIG. 1 is a circuit diagram showing a proximity switch and a load short-circuit protection circuit thereof according to the present invention, which is a DC three-wire type. In the figure, 1 is a detection coil, 2 is an oscillation circuit, 3 is a detection circuit for detecting that the object to be detected has approached the coil 1 based on the output of the oscillation circuit 2, 4
Is an output switching circuit for turning on / off the current supply from the power supply E to the load 5 based on the output signal of the detection circuit 3;
Is a load short-circuit protection circuit that periodically turns on and off the output switching circuit 4 to protect it when an overcurrent flows through the proximity switch.

In the detection circuit 3, Q4 is a transistor which is a second transistor whose base is supplied with the output signal of the oscillation circuit 2, C2 is a capacitor connected between the emitter and collector of the transistor Q4, and Q3 is a transistor connected to the base. A transistor which is a second transistor connected to the collector of Q4 and having an emitter connected to the emitter of transistor Q4, R7 is a resistor connected between the base of transistor Q4 and the positive electrode of power supply E, and R6 is the emitter of transistor Q4. R12 is a resistor connected between the collector of the transistor Q4 and the negative electrode of the power supply E.

In the output switching circuit 4, the LED
Is a resistor R5 connected to the collector of the transistor Q3 of the detection circuit 3.
LED, Q1 is an output transistor whose base is connected to the LED, R3 is LE
A resistor connected between the connection point of D and the output transistor Q1 and the negative side of the power supply; T3 a terminal connecting the positive side of the power supply E and the positive side of the load 5; T2 a terminal connecting the negative side of the load 5; Is a terminal to which the negative electrode of the power supply E is connected, and R10 is a resistor connected between the positive electrode side of the detection circuit 3 and the terminal T3.

In the load short-circuit protection circuit 6, R1 is a resistor which is a first resistor connected between the emitter of the output transistor Q1 of the output switching circuit 4 and the terminal T1, Q2.
A transistor which is a third transistor having a collector connected to the base of a transistor Q4 also used as a detection circuit 7 via a resistor R8 which is a second resistor, and an emitter connected to the load side of the power supply E; Diode D1 has its input side connected to the base of output transistor Q1 and its output side connected to the base of transistor Q2 via resistor R4. Diodes D1 and C1 are diode D1 and resistor R4 which is a third resistor. And a capacitor connected between the connection point and the negative electrode of the power supply E.

Next, the operation will be described. Oscillation circuit 2
Always oscillates and outputs a signal, and when the object to be detected is inserted into the detection coil 1, oscillation stops and no signal is output. First, in the detection circuit 3, the output signal from the oscillation circuit 2 is supplied to the base of the transistor Q4 at the time of non-detection, the transistor Q4 is turned on, and the current is changed from the power supply E → the resistance R10 → the resistance R6 → the transistor Q4 → the resistance R12 → the power supply E and the flow,
The transistor Q3 is turned off. When the oscillation circuit 2 is oscillating, the transistor Q4 is repeatedly turned on and off, so that the transistor Q4 is immediately turned off, and the voltage of the power supply E is applied to the capacitor C2 via the resistor R6 and starts to be charged. When Q4 is turned on from off, the capacitor C2 is discharged to the emitter of the transistor Q4. As described above, the base-emitter voltage of the transistor Q3 does not increase, the transistor Q3 does not turn on, and the transistor Q3 does not turn on, so that there is no output.

When the object to be detected is inserted into the detection coil 1, the oscillation stops and the output signal is not supplied to the base of the transistor Q4, so that the transistor Q4 is turned off.
Then, the voltage of the power supply E is applied to the capacitor C via the resistor R6.
2 to be charged. When the voltage of the capacitor C2 increases, the base-emitter voltage of the transistor Q3 increases, and the transistor Q3 turns on.

In the output switching circuit 4, when an object to be detected is inserted into the detection coil 1 and the detection signal of the detection circuit 3 is output, the detection signal is supplied to the resistor R5 and the light emitting diode L.
The power is supplied to the base of the output transistor Q1 via the ED, the output transistor Q1 is turned on, and the current is supplied to the power supply E.
→ Load 5 → Output transistor Q1 → Load short circuit protection circuit 6
, And a current is supplied to the load 5. When the object to be detected is not inserted into the detection coil 1, the detection signal of the detection circuit 3 is not supplied, so that the output transistor Q 1 is turned off, and no current is supplied to the load 5.

In the load short-circuit protection circuit 6, when a normal current flows through the load 5, the voltage across the resistor R1 is set to a value lower than the base-emitter voltage (hereinafter referred to as V _BE ) of the output transistor Q1. The sum e1 of V _{BE of the} output transistor Q1 and the voltage across the resistor R1 is 2 ·
Set to a value lower than V _BE . Here, the collector-emitter voltage of the transistor Q2 is equal to e1, and in order for a current to flow through the base of the transistor Q2, e1 must be higher than the voltage sum e2 between V _{BE of the} transistor Q2 and both ends of the diode D1. Must.

When a normal current flows through the load 5, e1
<E2, the diode D1 and the transistor Q2
, No current flows, the transistor Q2 is turned off, and the capacitor C1 is not charged.

When the load current increases due to a short circuit or the like, the voltage across the resistor R1 increases, and when e1 exceeds e2,
A current flows through the diode D1, the resistor R4, and the base of the transistor Q2, and the transistor Q2 is turned on. At this time, the capacitor C1 is charged. Transistor Q
When the transistor 2 is turned on, a voltage is supplied to the base of the transistor Q4, the transistor Q4 is turned on and the transistor Q3 is turned off. Since no current is supplied to the base of the transistor Q1, the transistor Q1 is turned off and a current flows through the load 5. Absent.

Accordingly, the current flowing through the collector / emitter of the transistor Q1 also decreases, and e1 also decreases. But,
Transistor Q3 is off, current is supplied from the charged capacitor C1 to the base of transistor Q2, and transistor Q2 remains on.

When the discharging of the capacitor C1 is completed, the potential of the capacitor C1 becomes low, and the transistor Q2
Is turned off again, and the transistor Q4 is also turned off. When the transistor Q4 is turned off, a current is supplied from the charged capacitor C2 to the base of the transistor Q3, the transistor Q3 is turned on, and the transistor Q1 is turned on.
And the output transistor Q1 is turned on. At this time, if the load current is in an overcurrent state, the transistor Q1 is turned off again. Repeat this,
When the load is short-circuited, the output transistor Q1 is protected.

The time during which the output transistor Q1 is in the ON state is the time from when the charging current starts flowing to the capacitor C1 to when the current is supplied to the base of the transistor Q2. By setting the discharge time of the capacitor C1 to be sufficiently longer than the charge time, the off time of the output transistor Q1 and the on time of the output transistor Q1 during an overcurrent can be increased. The on / off ratio of the output transistor Q1 can be 1: 100 to 1: 200, and heat generation when the output transistor Q1 is on can be suppressed.

As described above, by configuring the load short-circuit protection circuit with the transistors Q2 and Q4, the resistance on the emitter side of the output transistor Q1 can be made only the resistance R1. Voltage rise can be reduced.

Embodiment 2 FIG. 2 is a circuit diagram showing a proximity switch and a load short-circuit protection circuit thereof according to a second embodiment of the present invention, which is a DC 2-wire type. In the figure,
4 which are the same as or equivalent to those in FIG. 4 of the conventional example are denoted by the same reference numerals and description thereof is omitted. The oscillation circuit 2, the detection circuit 7, and the output switching circuit 8 are the same as those of the conventional example shown in FIG. The load short-circuit protection circuit 9 is a resistor R of the conventional load short-circuit protection circuit 6.
2 is omitted, R12 of the detection circuit 7 is used in place of the resistor R2 of the conventional example, and the transistor Q3 of the detection circuit is also used.

In the load short-circuit protection circuit 9, R1 is a resistor connected between the emitter of the output transistor Q1 of the output switching circuit 4 and the terminal T1, and Q2 is the base of a transistor Q3 whose collector also serves as the detection circuit 7. The transistor D1 is connected, the emitter of which is connected to the emitter of the transistor Q4 of the detection circuit 7, the input of which is connected to the base of the output transistor Q1 and the output of which is connected to the base of the transistor Q2 via the resistor R4. The diodes D1 and C1 are capacitors connected between the connection point between the diode D1 and the resistor R4 and the negative electrode of the power supply E. Resistance R1
Reference numeral 2 also serves as the detection circuit 7 and corresponds to the resistor R2 in FIG. Note that a Schmitt circuit is configured by the transistors Q2 and Q3.

Next, the operation will be described. The operations of the oscillation circuit 2, the detection circuit 7, and the output switching circuit 8 are shown in FIG.
Is the same as the conventional example shown in FIG.
Will be described.

In the load short-circuit protection circuit 9, when a normal current flows through the load 5, the voltage across the resistor R1 is set to a value lower than the base-emitter voltage of the output transistor Q1. The sum e1 of V _BE and the voltage across the resistor R1 is set to a value lower than 2 · V _BE . Here, in order for a current to flow to the base of the transistor Q2, e1 is the sum of V _{BE of the} transistor Q2, the voltage across the diode D1, and the voltage e of the capacitor C1.
The voltage must be higher than 3.

When a normal current flows through the load 5, e1
<E3, the diode D1 and the transistor Q2
, No current flows, the transistor Q2 is turned off, and the capacitor C1 is not charged.

When the load current increases due to a short circuit or the like, the voltage across the resistor R1 increases, and when e1 exceeds e3,
A current flows from the diode D1 to the resistor R4 to the base of the transistor Q2, and the transistor Q2 is turned on. At this time, the capacitor C1 is charged. Transistor Q
When 2 is turned on, the voltage at the base of transistor Q3 drops, and transistor Q3 is turned off. Then, the base-emitter voltage of the transistor Q5 of the output switching circuit 8 decreases, and the transistor Q5 is turned off. Since no current is supplied to the base of the transistor Q1, the transistor Q1 is turned off and no current flows to the load 5.

Accordingly, the current flowing through the collector / emitter of the transistor Q1 also decreases, and e1 also decreases. But,
Transistor Q3 is off, current is discharged from charged capacitor C1 to the base of transistor Q2, and transistor Q2 remains on.

When the discharge of the capacitor C1 is completed, the potential of the capacitor C1 becomes low, and the transistor Q2
Is turned off again, the base voltage of the transistor Q3 increases, and the transistor Q3 is turned on. Then, a current is supplied from the charged capacitor C2 to the base of the transistor Q3, and the transistor Q3 is turned on.
The base-emitter voltage of the transistor Q5 rises, the transistor Q5 turns on, a current is supplied to the base of the output transistor Q1, and the output transistor Q1 turns on. At this time, if the load current is in an overcurrent state, the transistor Q1 is turned off again. This is repeated to protect the output transistor Q1 when the load is short-circuited.

By appropriately selecting the values of the resistor R4 and the capacitor C1, the off time of the output transistor Q1 at the time of overcurrent can be made longer and the on time can be made shorter. The on / off ratio of the output transistor Q1 can be 1: 100 to 1: 200, and heat generation when the output transistor Q1 is on can be suppressed.

As described above, by configuring the Schmitt circuit of the load short-circuit protection circuit with the transistors Q2 and Q3, the emitter-side resistance of the output transistor Q1 is reduced to the resistance R.
It can be only one, and when the load current increases, the rise in the remaining voltage can be reduced.

[0049]

As described above, according to the present invention, the load short-circuit protection circuit of the proximity switch according to the present invention comprises a first transistor having a base connected to an output terminal of an output signal from an oscillation circuit. And a detection circuit having a second transistor having an emitter connected to the emitter of the first transistor and a base connected to the collector of the first transistor, and a load from a power supply based on an output signal from the detection circuit. And an output switching circuit that supplies a current to the proximity switch having an output switching circuit that periodically turns on and off an output transistor of the output switching circuit to protect the output transistor of the output switching circuit when an overcurrent flows. A first resistor connected to the emitter of the output transistor and the negative electrode of the power supply, and a collector connected via a second resistor. A third transistor connected to the base of the first transistor and having an emitter connected to the negative electrode side; an input side connected to the base of the output transistor; and an output side connected to the base via a third resistor. Since a diode connected to the base of the third transistor and a capacitor connected between the connection point of the diode and the third resistor and the negative electrode are provided, the load current is increased. In this case, the rise of the remaining voltage can be reduced.

Also, a first transistor whose base is connected to the output terminal side of the output signal from the oscillation circuit and the first transistor
A detection circuit having a second transistor having an emitter connected to the emitter of the first transistor and a base connected to the collector of the first transistor, and detecting a current from a power supply to a load based on an output signal from the detection circuit. A load short-circuit protection circuit for a proximity switch for periodically turning on and off an output transistor of the output switching circuit to protect the output transistor when an overcurrent flows in the proximity switch including the supply output switching circuit. A first resistor connected to the negative electrode of the power supply and a third transistor having a collector connected to the base of the second transistor and having an emitter connected to the emitter of the first transistor; The input side is connected to the base of the output transistor, and the output side is connected to the third transistor via a third resistor. A diode connected to the base of the transistor, and a capacitor connected between the connection point of the diode and the third resistor and the negative electrode of the power supply. , The rise of the remaining voltage can be reduced.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating a proximity switch and a load short-circuit protection circuit thereof according to a first embodiment of the present invention.

FIG. 2 is a diagram illustrating a proximity switch and a load short-circuit protection circuit thereof according to a second embodiment of the present invention;

FIG. 3 is a conventional proximity switch and its load short-circuit protection circuit diagram.

FIG. 4 is a conventional proximity switch and its load short-circuit protection circuit diagram.

[Explanation of symbols]

 2 Oscillation circuit 3 Detection circuit 4 Output switching circuit 5 Load 6, 9 Load short circuit protection circuit C1 Capacitor D1 Diode E Power supply Q1 Output transistor Q2, Q3, Q4, Q5 Transistor R1, R4, R8 Resistance

Claims (2)

[Claims] A first transistor having a base connected to an output terminal side of an output signal from an oscillation circuit; an emitter connected to an emitter of the first transistor;
To a proximity switch including a detection circuit having a second transistor having a base connected to the collector of the transistor, and an output switching circuit for supplying a current from a power supply to a load based on an output signal from the detection circuit. In a load short-circuit protection circuit of a proximity switch for periodically turning on and off an output transistor of the output switching circuit to protect the output transistor when a current flows, a first terminal connected to an emitter of the output transistor and a negative electrode of a power supply. A third transistor having a collector connected to the base of the first transistor via a second resistor, an emitter connected to the negative electrode side, and an input side connected to the base of the output transistor. A diode having an output connected to the base of the third transistor via a third resistor, and a diode connected to the diode. A load short-circuit protection circuit for a proximity switch, comprising: a connection point between a node and the third resistor; and a capacitor connected between the negative electrode. 2. A first transistor having a base connected to an output terminal side of an output signal from an oscillation circuit, and an emitter connected to an emitter of the first transistor;
To a proximity switch including a detection circuit having a second transistor having a base connected to the collector of the transistor, and an output switching circuit for supplying a current from a power supply to a load based on an output signal from the detection circuit. In a load short-circuit protection circuit of a proximity switch for periodically turning on and off an output transistor of the output switching circuit to protect the output transistor when a current flows, a first terminal connected to an emitter of the output transistor and a negative electrode of a power supply. A third transistor having a collector connected to the base of the second transistor, an emitter connected to the emitter of the first transistor, and an input connected to the base of the output transistor. A diode whose output side is connected to the base of the third transistor via a third resistor; - de and the third load short-circuit protection circuit of the proximity switch and a capacitor connected between the negative pole of the connection point of the resistor and the power supply, comprising the to the.