JPH0311579B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an improvement of a semiconductor device for a high frequency oscillation type proximity switch, and more specifically, it aims to reduce the residual voltage, stabilize the detection operation, and moreover, improves the semiconductor device for a high frequency oscillation type proximity switch. We propose an integrated circuit that achieves these functions without increasing the number of terminals.

FIG. 1 is a circuit diagram showing the configuration of a conventional proximity switch. The area surrounded by a dashed line shows a proximity switch integrated circuit (hereinafter referred to as IC) 18, to which external components are connected to operate the proximity switch. 17 (encircled by a two-dot chain line). When the test object M approaches the detection coil L, the switch transistor _Q2 , which is an external component, is turned on, and power is supplied from the power supply V to the load RL. This circuit will be explained below.

The IC 18 includes an oscillation circuit 11, a detection circuit 12, a voltage comparison circuit 13, an output circuit 14, an initial reset circuit 15, a power supply circuit 16, and the like. The oscillation circuit 11 is connected to a parallel circuit of a detection coil L and a tuning capacitor C, and a series circuit of a resistance R for adjusting sensitivity (operating distance). In some cases, it oscillates with a predetermined amplitude, and this output is given to the detection circuit 12. An integrating capacitor is connected to the output terminal of the detection circuit 12.
_C1 is externally connected, and this terminal is connected to the input terminal of the voltage comparator circuit 13. The input voltage of the voltage comparison circuit 13 is a voltage corresponding to the amplitude of the output of the oscillation circuit 11, but if this voltage exceeds a predetermined comparison reference value, the output of the voltage comparison circuit 13 turns off the output circuit 14, and then When the voltage becomes low, the output circuit 14 is turned on.

When the test object M approaches the detection range of the detection coil L, the amplitude of the oscillation output of the oscillation circuit 11 is attenuated or the oscillation stops, and as a result, the voltage comparison circuit 1
The third input becomes a low level, and the output circuit 14 is turned on. Conversely, when the object M moves away, the output circuit 14 is turned off.

The output circuit 14 has one end connected to the terminal l ^- of the proximity switch 17 via the terminal E, and this l ^- terminal is connected to the negative pole of the power supply V. The other end of the output circuit 14 is connected to the output terminal OUT of the IC 18.
Power supply circuit 1 that supplies power to the internal circuit of IC18
6 is connected to an external circuit via a power supply terminal VT. The positive terminal of the power supply V is connected to another terminal l ⁺ of the proximity switch 17 via the switch 19 and the load RL. The transistor is connected between terminals l ⁺ and l ^-.
A switch circuit including Q ₂ is connected, and IC18
A circuit for power supply is connected. That is, the emitter of the PNP transistor Q ₂ is connected to the terminal l ⁺ , and the collector is also connected to the terminal l ^- .
Its base is connected to the emitter of PNP transistor _Q1 . The collector of the transistor _Q1 is connected to the terminal VT, and the base is connected to the terminal OUT via the resistor _R1 . Also transistor
A resistor _R2 is interposed between the emitter and base of _Q2 . A constant current element CD is interposed between the terminal l ⁺ and the terminal VT, and a constant voltage element ZD is interposed between the terminals VT and E.

As described above, when the object M is far away, the output circuit 14 is turned off, and when the object M is close, the output circuit 14 is turned on, and the switch circuit is also turned off and on accordingly. That is, when the output circuit 14 is off, the transistor _Q1 is off, and therefore the transistor _Q2 is also off. On the other hand, when the output circuit 14 is turned on, a current flows to the base of the transistor _Q1 , conducts between the collector and the emitter, and short-circuits the constant current element CD via the base of the transistor _Q2 . Therefore, a base current flows through the transistor _Q2 , and a drive current can be supplied to the power supply terminal VT of the IC 18 via the transistor _Q1 . and transistor Q ₂
is turned on, current flows through the load RL, and the proximity of the test object M is detected.

The voltage between l ^- and l ⁺ in such a test object detection state, the so-called residual voltage, is the constant voltage of constant voltage element ZD, the collector-emitter saturation voltage of transistor Q ₁ , and the base-emitter voltage of transistor Q ₂ . As a summation, the smaller the remaining voltage and the larger the difference from the power supply V, the more reliable and stable the operation of the load RL becomes.

On the other hand, when the test object M moves away and the output circuit 14 turns off, and the transistors Q ₁ and Q ₂ turn off, the load RL
No drive current flows through. At this time IC18
A voltage determined by a constant voltage element ZD is supplied to the power supply terminal VT of the power supply terminal VT via a constant current element CD. The current consumption of IC18 in this condition, that is, the load
Constant current element CD is selected so that the leakage current that also flows through RL is reduced.

Next, the initial reset circuit 15 inside the IC 18 has an initial reset capacitor _C2 connected to the terminal I for determining its time constant.
Contains a timer circuit using _C2 . This timer circuit starts counting when the switch 19 is closed and power supply to the IC 18 is started. The initial reset circuit 15 inhibits the operation of the output circuit 14 and restricts it to the OFF state until the timer circuit reaches its limit. When the time limit is reached, this restriction is released and the switch is turned on or off in accordance with the proximity or separation of the object M. Immediately after the switch 19 is closed, the amplitude of the output of the oscillation circuit 11 is small, and returns to normal amplitude after a short delay. Therefore, if there is no initial reset circuit 15 that operates as described above, there is a risk that the output circuit 14 will be turned on immediately after the switch 19 is closed, similar to when the object M approaches, resulting in an erroneous output. The initial reset circuit 15 prevents this.

Now, in such a conventional circuit, it is necessary to select a constant voltage element ZD whose rated voltage value is slightly higher than the minimum operating voltage of the IC 18. Therefore, the minimum operating voltage of IC18 is, for example, 4.75V.
In this case, it is difficult to reduce the remaining voltage to 5 to 6 V or less.

The present invention was made in view of the problems of the conventional circuit, and is designed to reduce the residual voltage to ensure stable and reliable operation of the load, and to reduce the remaining voltage to the same number of pins as the conventional circuit. The purpose of the present invention is to provide a semiconductor device.

The semiconductor device for a proximity switch of the present invention includes an oscillation circuit to which a parallel circuit of a detection coil and a tuning coil is connected as external components, a detection circuit that detects the output of the oscillation circuit, and a detection circuit that detects the output of the detection circuit and a predetermined value. A voltage comparison circuit to be compared, an output circuit that changes its output according to the comparison result output of the voltage comparison circuit, and an initial reset capacitor are externally connected, and at the time of initial reset, the output circuit is closed for a time determined by the capacity of the initial reset capacitor. an initial reset circuit that turns off the power supply, and a power supply circuit connected to one pole of the external DC power supply via the same external load and outputting a voltage for driving the internal circuit; A first transistor is interposed between the load and the first transistor, and the first transistor is interposed between the first transistor and a constant voltage circuit for on/off control of the first transistor, and the first transistor is interposed between the first transistor and a constant voltage circuit, and is turned on and off by the output of the output circuit. A semiconductor device for a proximity switch is configured to connect a switch circuit including a second transistor that is turned off, and includes the constant voltage circuit, the output of the constant voltage circuit is connected, and the initial reset capacitor and It is characterized by comprising a common terminal to which one terminal of the second transistor is connected, and a backflow prevention diode connected between the voltage output terminal of the power supply circuit and the common terminal.

In addition to these, a discharge circuit is provided which is connected to the output terminal of the power supply circuit and the common terminal and which discharges the charge of the initial reset capacitor when the output voltage of the power supply circuit becomes less than a predetermined value. Features.

The present invention will be described in detail below based on drawings showing embodiments thereof.

FIG. 2 is a circuit diagram showing the structure of a proximity switch including a proximity switch IC according to the present invention.

The number of terminals of the proximity switch IC 28 is the same as that of the conventional IC 18 shown in FIG. The terminals are connected. Further, the detection circuit 22 is connected to a terminal for connecting an integrating capacitor _C1 . The output circuit 24 has the output terminal OUT of IC28.
are connected, and the initial reset circuit 25 has a terminal I for connecting the initial reset capacitor _C2 .
are connected, and the power supply circuit 26 has a power terminal VT.
are connected. The ground side line of the internal circuit described above is connected to the ground terminal E. Power circuit 2
The configuration of power supply circuit 6 is similar to the conventional power supply circuit 16, and is configured to supply a required voltage to the internal circuit. The structures of the oscillation circuit 21, the detection circuit 22, the voltage comparison circuit 23, and the output circuit 24 are similar to the conventional device shown in FIG. The amplitude of the output of 21 decreases and increases, and the output circuit 24 is turned on and off.

This IC 28 is provided with a constant voltage generating circuit 30, the positive side line of which is connected to the terminal I and to the anode of a diode D for preventing backflow. The cathode of diode D is connected to the output terminal of power supply circuit 26.

The initial reset circuit 25 is constructed similarly to the initial reset circuit 15 shown in FIG. 1, and operates to turn off the output circuit 24 immediately after the switch 19 is closed.
is connected. This discharge circuit 29 monitors the output of the power supply circuit 6, and when the output falls below a predetermined value, discharges the charge in the reset capacitor _C2 connected to the terminal I.

The negative terminal of the power supply V is the terminal of the proximity switch 27
l ^- or connected to the ground line of the proximity switch 27. Transistors that make up the switch circuit
Of Q ₁ and Q ₂ , the transistor Q ₂ (which is responsible for the first transistor) has its emitter and collector connected to the terminals l ⁺ and ^{l -} , respectively, as in the case of the one in FIG. A resistor _R2 is interposed between the direct connection line to the power supply terminal VT, that is, the emitter and base of the transistor _Q2 . The base of the transistor _Q2 is connected to the emitter of the transistor _Q1 , and the collector of the transistor _Q1 (responsible for the second transistor) is connected to the terminal I. The base of the transistor _Q1 is connected to the output terminal OUT via a resistor _R1 . A series circuit including a load RL, a switch 19, and a power supply V is connected between the terminals l ⁺ and l ^- .

Comparing this type of external circuit with the circuit shown in Figure 1, the constant current element CD is not used, and the collector of transistor _Q1 is connected to terminal I, through which constant voltage generation inside the IC28 occurs. It can be seen that the difference is that they are connected to the circuit.

Next, the circuit operation of the device of the present invention as described above will be explained.

When switch 19 is closed, current is supplied to power supply terminal VT via load RL. This supplies power to the power supply circuit 26, and a voltage for driving the internal circuit is generated from its output terminal.

The initial reset circuit 25 starts charging the initial reset capacitor _C2 and turns off the output circuit 24 until that time limit. Since the output of the power supply circuit 26 is connected to the terminal I via the reverse current prevention diode D, the capacitor _C2 is charged only from the initial reset circuit 25. The discharge circuit 9 also includes a power supply circuit 26.
Since the output voltage is given, the capacitor
_C2 is not discharged, and in short, the initial reset circuit 25 works to prevent erroneous output when the power supply V is turned on, regardless of the presence of the diode D and the discharge circuit 9. Of course, while the output circuit 24 is off due to the function of the initial reset circuit 25, the transistors Q ₁ and Q ₂ are off.
Only the leakage current consumed by IC28 flows through the load RL.

Next, when the object M is separated from the detection coil L, the amplitude of the oscillation output of the oscillation circuit 21 is large;
For this reason, the output circuit 24 is turned off.

Now, when the object M approaches the detection coil L, the amplitude of the output of the oscillation circuit 21 is attenuated or oscillation is stopped, and the output circuit 24 is turned on. As a result, current flows to the base of transistor Q ₁ via resistor R ₁ and conduction occurs between its collector and emitter, which turns on transistor Q ₂ and causes a drive current to flow to load RL. It operates as if the specimen M had been detected. At this time, the load RL→
Current flows through the route from the emitter and base of transistor Q ₂ to the emitter and collector of transistor Q ₁ to terminal I. The current flowing into the terminal I causes the constant voltage generating circuit 30 to generate a constant voltage, and this constant voltage can be applied to the internal circuit via the diode D. Therefore, the remaining voltage between the terminals l ⁺ and l ^- of the proximity switch 27 is the sum of the constant voltage value of the constant voltage generating circuit 30, the collector-emitter saturation voltage of the transistor Q ₁ , and the emitter-base voltage of the transistor Q ₂ , By keeping the internal voltage of the IC 28 low, this remaining voltage can be lowered.

Note that even if the voltage at the power supply terminal VT becomes lower than the minimum operating voltage of the power supply circuit 6, power can be supplied to the internal circuit from the terminal I, that is, from the constant voltage generation circuit 30 side. In this case, the constant voltage generation circuit 30
It is preferable to set the output voltage of the power supply circuit 26 higher than the normal output voltage of the power supply circuit 26 by the forward voltage of the diode D in order to stabilize the operation of the internal circuit.

The discharge circuit 29 discharges the charge in the capacitor _C2 when the switch 19 is opened. That is, when the voltage at the output terminal of the power supply circuit 26 decreases due to the switch 19 being opened, even if this is detected, the charge in the capacitor _C2 is discharged. Therefore, even if the switch 19 is repeatedly turned off, charging of the capacitor _C2 starts from a state where the residual charge is zero, so that the time for restraining the output circuit 24 or the time limit of the timer circuit of the initial reset circuit 25 is stabilized, and the time when the power is turned on is stabilized. Malfunctions at times are reliably avoided.

FIG. 3 is a circuit diagram showing an example of a specific configuration of the essential parts of the device of the present invention. The output circuit 24 includes transistors 115 and 116 that constitute a current mirror circuit that operates in response to a signal from the initial reset circuit 25;
It consists of transistors 117 and 118 that perform a switching operation in response to a signal from the voltage comparison circuit 23. Transistor 11 of current mirror circuit
When no current is supplied from 6,
Transistor 118 is off regardless of the signal from voltage comparison circuit 23. On the other hand, when current is supplied from the transistor 116, the transistor 111 responds to the signal from the voltage comparison circuit 23.
8 turns on and off. That is, when the amplitude of the output of the oscillation circuit 21 is large and the output of the voltage comparison circuit 23 is at a high level, the transistor 117 is turned on and the transistor 118 is turned off. When the output of the voltage comparator circuit 23 becomes low level (near the specimen M), the transistor 117 is turned off and the transistor 118 is turned on.

The initial reset circuit 25 includes a transistor 109,
110, a low resistor 121 that determines the current value, a resistor 122 inserted in the line that supplies the mirror current to the initial reset capacitor _C2 , and a charging voltage of the capacitor _C2 that is detected and output. and a charging current detection circuit portion that supplies current to the current mirror circuit of the circuit 24.

The charging current detection circuit part is a diode 103,1
04, transistors 111 and 112 forming a current mirror circuit, and a resistor 123 interposed between the transistor 112 and the output circuit 24,
The charging voltage of the initial reset capacitor _C2 is connected to the diodes 103 and 104 and the transistors 111 and 11.
2, the current from the collector of transistor 110 becomes a mirror current of the current mirror circuit of transistors 111 and 112, and the mirror current is generated from the collector of transistor 112, thereby causing an output. The inhibition of the output of the circuit 24 is canceled.

In other words, after the switch 19 is turned on, while the voltage of the capacitor C ₂ is below the threshold value, no mirror current is generated in the transistors 111 and 112, and the transistor 116 is kept off and the transistor 118 is kept off. I'll keep it.

The initial reset capacitor discharge circuit 29 includes diodes 101 and 102 and a resistor 1 for circuit voltage detection.
19, a transistor 108 serving as a discharge circuit, and a discharge resistor 120. diode 1
01 and 102 are connected in series, the anode side is connected to the output terminal of the power supply circuit 26, and the cathode side is connected to the resistor 1.
It is connected to the ground side line via 19. The base of the transistor 108 is connected to the connection point between this cathode side and the resistor 119, its collector is connected to the ground side line, and the emitter is connected to the resistor 129.
It is connected to terminal I via. transistor 1
The base of 08 is the voltage for driving the internal circuit, that is, the voltage of the diodes 101 and 102 is higher than the output of the power supply circuit 26.
The emitter of transistor 108 is higher than the forward voltage drop by the base-emitter voltage. Assuming that the forward voltage of one diode is equal to the base-emitter voltage, the emitter voltage of transistor 108 is lower than the internal circuit driving voltage by the forward voltage drop of one diode. Therefore, under normal conditions, the transistor 108 is on, but if the output of the power supply circuit 26 decreases by more than the forward voltage drop of one diode due to an open circuit of the switch 19, etc., the emitter-collector current increases to match the drop. is flowing and resistance 12
The discharge of capacitor C ₂ through 0 will take place.

The constant voltage generating circuit 30 includes diodes 105, 106, and 107 connected in series, and a resistor 1 interposed between the cathode side of this group of diodes and the ground line.
24, a transistor 113 whose base is connected to the connection point of these, and a transistor 114 which is connected to this by Darlington, the collector of the transistor 114 is connected to the anode side of the diode group, and the emitter is connected to the ground line. There is. The anode of the diode group is connected to the terminal I, and is also connected to the output of the power supply circuit 26 via a diode D for preventing backflow. When a current is applied to terminal I from an external circuit, diode 105,1
This becomes a constant voltage circuit that can obtain a constant voltage value equal to the sum of the forward voltage drops of transistors 06 and 107 and the base-emitter voltage of transistors 113 and 114. If the forward voltage drop of one diode in this IC28 is equal to the base-emitter voltage of one transistor, let this be V _D.
The constant voltage value of this circuit is 5V _D. The output voltage of the power supply circuit 26 is set to be equivalent to 4V _D.

When the switch 19 is closed and voltage is applied to the power supply circuit 26 via the terminal VT, its output becomes the above-mentioned 4V _D. At this time, the base of the transistor 108 of the discharge circuit 29 is lower by the forward voltage drop of two diodes, and when a voltage higher than that by one diode is applied to the emitter, a current flows to the emitter. In other words, when the emitter of the transistor 108 exceeds [4V _D -2V _D +V _D ], a current flows through the emitter. However, as will be described later, until the timer circuit of the initial reset circuit 25 reaches its expiration date, the emitter potential of the transistor 108 does not exceed 3V _D , so no current flows therein.

Similarly, in the constant voltage generating circuit 30, since the terminal voltage of the terminal I does not exceed 5V _D , no circuit current flows therein, and since the voltage at the anode is lower than the cathode of the backflow prevention diode D, No current flows either.

Now, in the initial reset circuit 25, when the switch 19 is closed, a mirror current flows and charges the capacitor _C2 . This charging voltage will be applied to the charging current detection circuit section, resulting in a forward voltage drop of two diodes and a base voltage drop of the transistor 112.
The sum of the emitter voltages, 3V _D , is the threshold. As long as the charging voltage of the capacitor _C2 is below 3V _D , the output circuit 24 or the transistor 118 is off as described above.

When the charging voltage of the capacitor _C2 becomes 3V _D or more, normal detection operation becomes possible, and when the object M approaches, the amplitude of the oscillation circuit output becomes small, or oscillation stops and the output circuit 24 turns on, and the transistor _Q1 ,
Q ₂ turns on and drive current is supplied to the load. On the other hand, current flows into terminal I. Then, the constant voltage generation circuit 30 generates a voltage of 5V _D , and the power supply circuit 26 no longer supplies voltage to the internal circuits. Therefore, voltage is supplied to the internal circuit through the reverse current prevention diode D, but if the forward voltage of this diode D is set to V _D , the voltage supplied from the constant voltage generation circuit 30 to the internal circuit is also
The voltage becomes 4V _D , and the internal circuit operation becomes stable.

At the time of detecting such a test object, the emitter of the transistor 108 of the discharge circuit 29 is at 3V _D , and a voltage of 2V _D is applied to the resistor 120 between this emitter and the terminal I. The resistance value of this resistor 120 is selected to be several tens of kΩ, and the current flowing through it is suppressed to several tens of μA.
This is to prevent excessive current from flowing to the emitter of 08.

Regarding the initial reset circuit 25, _the difference of 2V D between the voltage 5V _D on the terminal I side and the threshold value 3V _D is the resistance 12.
It will be added to 2, but it will also cost several tens of k.
Ω, and the current flowing through the resistor 122 is several tens of μA.
to be suppressed. This current defines the current flowing through the collector of the transistor 112 as a mirror current, but by appropriately selecting the value of the resistor 123, the internal current consumption can be suppressed.

Note that the charging current to the capacitor _C2 flows from the collector of the transistor 110 through the resistor 122, but in order to increase the time limit of the timer circuit, the charging current is often set to 10 to 20 μA, and as described above, the charging current is set to 10 to 20 μA. When determining the resistance value, the voltage drop is
It is about 0.1 to 0.3V and has no effect on timer operation.

Next, when the test object M is separated, voltage is supplied to the power supply circuit 6 from the terminal VT, and current is no longer supplied from the transistor _Q1 .
A current flows from the collector of the transistor 110 of the current mirror circuit of the initial reset circuit 25 to the capacitor C ₂ and the current mirror circuit of the transistors 111 and 112, and the output circuit 24 is caused by the mirror current flowing from the collector of the transistor 112 of the current mirror circuit. It is maintained in a state where it can be turned on and off.

While the detection operation is being performed as described above, when the switch 19 is opened, the transistor 108 of the discharge circuit 9 is turned on and the charge in the capacitor _C2 is discharged. Even if the resistance is set to several tens of kilohms, the discharge current will be sufficiently large and the discharge will occur quickly.

As described in detail above, in the case of the semiconductor device for a proximity switch according to the present invention, the remaining voltage between the terminals l ⁺ and l ^- of the proximity switch 27 is divided into the 5V _D of the constant voltage generation circuit and the emitter-collector saturation of the transistor _Q1. The sum of the voltage and the base-emitter voltage of transistor _Q2 is approximately 4V, which is extremely low, and is extremely effective in ensuring stable and reliable operation of the load. Furthermore, since this reduction in residual voltage was achieved without increasing the number of terminals, there is no need to increase the size of the product compared to conventional products.

Furthermore, when an initial reset capacitor discharge circuit is provided, the initial reset capacitor is immediately discharged each time the switch is opened or the power is turned off, so the output circuit off period immediately after the switch is closed or the power is turned on is stabilized. There will be no erroneous output.

[Brief explanation of the drawing]

FIG. 1 is a schematic circuit diagram of a conventional device, FIG. 2 is a schematic circuit diagram of the device of the present invention, and FIG. 3 is a circuit diagram of essential parts of the device of the present invention. 21... Oscillation circuit, 24... Output circuit, 25... Initial reset circuit, 26... Power supply circuit, 29... Discharge circuit, 30... Constant voltage generation circuit, D... Backflow prevention diode, V... Power supply, RL... Load, Q ₁ , Q ₂ ...transistor.

Claims (1)

[Claims] 1. An oscillation circuit to which a parallel circuit of a detection coil and a tuning coil is connected as an external component, a detection circuit that detects the output of the oscillation circuit, and a voltage that compares the output of the detection circuit with a predetermined value. A comparison circuit, an output circuit that changes its output according to the comparison result output of the voltage comparison circuit, and an initial reset capacitor are externally connected, and at the time of initial reset, the output circuit is turned off for a time determined by the capacity of the initial reset capacitor. It is equipped with an initial reset circuit, and a power supply circuit that is connected to one pole of the external DC power supply via the same external load and outputs a voltage for driving the internal circuit, and connects the other pole of the DC power supply with the load. a first transistor interposed therebetween; and a first transistor interposed between the first transistor and a constant voltage circuit for on/off control of the first transistor, and controlled on/off by the output of the output circuit. A semiconductor device for a proximity switch is configured to be connected to a switch circuit including a second transistor, which includes the constant voltage circuit, the output of the constant voltage circuit is connected, and the initial reset capacitor and the second transistor are connected to each other. 1. A semiconductor device for a proximity switch, comprising: a common terminal to which one terminal of the power supply circuit is connected; and a backflow prevention diode connected between the voltage output terminal of the power supply circuit and the common terminal. 2. An oscillation circuit to which a parallel circuit of a detection coil and a tuning coil is connected as an external component, a detection circuit that detects the output of the oscillation circuit, a voltage comparison circuit that compares the output of the detection circuit with a predetermined value, and the voltage comparison. An output circuit that changes its output depending on the comparison result output of the circuit, an initial reset circuit to which an initial reset capacitor is externally connected and turns off the output circuit for a time determined by the capacitance of the initial reset capacitor at the time of initial reset; A power supply circuit connected to one pole of the DC power supply connected via an external load and outputting a voltage for driving the internal circuit, and interposed between the other pole of the DC power supply and the load. a first transistor; and a second transistor interposed between the first transistor and a constant voltage circuit for on/off control of the first transistor, and controlled on/off by the output of the output circuit. A semiconductor device for a proximity switch, which is designed to connect a switch circuit, includes the constant voltage circuit, an output of the constant voltage circuit is connected, and one terminal of the initial reset capacitor and the second transistor is connected. a common terminal connected to the voltage output terminal of the power supply circuit and the common terminal; 1. A semiconductor device for a proximity switch, comprising: a discharge circuit for discharging the charge in an initial reset capacitor when the initial reset capacitor becomes less than a predetermined value.