JPH0886813A - Detection circuit of non-contact type sensor - Google Patents

Abstract

PURPOSE: To obtain a detection circuit of non-contact type sensor which can detect a current or a voltage accurately while keeping the inside of a coil balanced magnetically by driving of a single power source. CONSTITUTION: A drive power source of a differential amplifier circuit 13 and a current buffer 15 employs a +12V power source and a transistor 15a or 15b of the current buffer 15 is turned on according to a voltage difference generated at an output terminal of a Hall element 3 provided in a gap of a magnetic core of a coil 1. Current proportional to a voltage from the differential amplifier circuit 13 runs in the direction opposite to the current of a primary winding 1b at this output terminal through a secondary winding 1c, a detection resistance RL and a voltage follower 24 to keep a magnetic flux in the coil 1 balanced. Here, the voltage follower 24 is so set to maintain an output voltage at a reference voltage.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a detection circuit for a non-contact type sensor, and more particularly to a detection circuit for a non-contact type sensor for non-contact measurement of voltage or current by driving with a single power source.

[0002]

2. Description of the Related Art In this example, a non-contact voltage sensor or current sensor used in an electric vehicle will be described as an example.

An electric vehicle is driven by a battery, and the driver determines the remaining capacity of the battery by looking at the remaining capacity of the displayed battery, so that the remaining capacity can be estimated. Very high precision is required.

For this reason, generally, there are CT type, servo type and the like for measuring voltage or current in a non-contact manner, but the servo type is generally used for high precision measurement.
Such a servo-type non-contact voltage sensor will be described below.

FIG. 5 is a schematic diagram of a conventional servo-type non-contact voltage sensor. In the figure, 1 is a coil. In the coil 1, a primary winding and a secondary winding are wound around a magnetic core, and a Hall element 3 is arranged in the gap. Hall element 3
Generates at the output terminal a voltage proportional to the magnetic flux density generated in the coil 1.

Further, one of the primary windings 1b of the coil 1 is connected between a resistor 5 having a large resistance value and the input terminal 7, and the resistor 7 is connected to one of the external batteries 9.
The other side of the primary winding 1b is connected to the other side of the battery 9. A load 11 is connected in parallel with the battery 9.

Reference numeral 13 is a differential amplifier circuit. The differential amplifier circuit 13 inputs the output of the Hall element, amplifies the error, and outputs it to the current buffer 15.

The current buffer 15 comprises an NPN transistor 15a and a PNP transistor 15b, the bases of which are connected to the output of the differential amplifier circuit 13,
Both emitters are connected to the other of the secondary side of coil 1. That is, the current buffer 15 constitutes a push-pull circuit.

Reference numeral 17 is a detection resistor. One of the detection resistors 17 is connected to one of the secondary windings 1c of the coil 1, and the other is connected to the ground.

Reference numeral 19 is a DC-DC converter. DC
The DC converter 19 is arranged outside the voltage sensor and converts the voltage from the sub-battery 10 into ± 12V,
It is supplied as a driving power source for the differential amplifier circuit 13 and the current buffer 15.

That is, the Hall element 3 is inserted into the gap in the magnetic core of the coil 1, the output of the Hall element 3 is input to the differential amplifier circuit 13, and the output of the differential amplifier circuit 13 is passed through the current buffer 15. A servo system that flows to the secondary side of the coil 1 is configured.

By constructing such a servo system, a current proportional to the battery voltage is passed through the detection resistor 17, and the voltage at the end of this resistor 17 is output as the terminal voltage of the main battery 9.

The operation of the conventional voltage sensor configured as described above will be described. A discharge current is supplied from the battery 9 as the load 11 changes.

This discharge current is also output to the voltage sensor side, and is output to the resistor 5 and the primary side 1b of the coil 1. As a result, the magnetic flux Φ ₁ is generated in the core of the coil 1.

At this time, the magnetic flux Φ appears at the output of the Hall element 3.
A voltage corresponding to ₁ is obtained, and this voltage is the differential amplifier circuit 1
The signal is amplified by 3 in the range of ± 12 V and output to the current buffer 15, and this current flows to the secondary winding 1c side of the coil 1 by the current buffer 15 and flows to the ground via the output resistor RL. At this time, the magnetic flux Φ is applied to the magnetic core of the coil 1.
Φ ₂ is generated in the magnetic flux in the direction in which ₁ is canceled. That is, since a magnetic flux in the direction opposite to the magnetic flux Φ ₁ due to the current I1 flowing in the primary winding is generated, the coil 1 and the Hall element are always in magnetic equilibrium.

The relation between the currents in the primary winding and the secondary winding of the coil 1 at this time is as follows: I1 × N1 = I2 × N2 N1: Number of turns of primary winding N2: Number of turns of secondary winding The voltage across RL is

## EQU1 ## E = R2 × (N1 / N2) × I1 = (R2N1
I1) / N2, and the output voltage E can be a voltage proportional to the measured current.

Then, for example, I1 flows in the primary winding (the measured voltage is positive) to create a magnetic flux Φ _1, and a current I 2 flows to create a magnetic flux Φ ₂ by the current buffer 15a so as to cancel it. Suppose Microscopically considering the relationship between Φ ₁ and Φ ₂ at this time, Φ ₂ = Φ ₁
At that moment, the output of the Hall element becomes zero, and the output I2 of the differential amplifier 13 and the current buffer 15a decreases, so that the magnetic flux Φ ₂ also decreases. However, at the moment when Φ ₂ <Φ ₁ , the Hall element detects the magnetic flux Φ ₁ −Φ ₂ , and Φ ₁ = Φ
_{Since the} current buffer 15a passes the current I2 so as to become ₂ , Φ ₂ = Φ ₁ again. Also, the current I1 of the primary winding
Is reversed (the measured voltage is negative), the current I2 flows through the current buffer 15b, and the same operation is performed. Thus, the magnetic flux Φ ₂ maintains a magnetic parallel state while constantly changing in the vicinity of Φ ₁ .

That is, even if the measured voltage or the measured current changes, if either of a and b is in the ON state in the current buffer 15 within the same polarity range, the measured value is Changes the current buffer that is turned on. That is, the output current of the same current buffer only increases or decreases.

Therefore, the voltage across the detection resistor 17 is ±
In the range of 12V, the voltage was proportional to the voltage across the main battery 9.

[0020]

The detection circuit of the non-contact type sensor described above supplies the drive power of ± 12 V to the differential amplifier circuit and the current buffer, and the Hall element inserted in the gap in the magnetic core of the coil. A coil 1 is maintained in a magnetic equilibrium state by constructing a servo system that amplifies the output difference of and the current buffer sends a current according to the output of the differential amplifier circuit to the secondary winding of the coil. At this time, a voltage corresponding to the current flowing through the secondary winding is obtained at both ends of the detection resistor.

The drive power source is set to ± 12 V because
This is because the operational amplifier normally uses a ± power source and measures ± current or voltage.

Particularly in an electric vehicle, it is necessary to reduce the power consumption of the battery by reducing the number of parts to be mounted as much as possible. However, since the sub battery of the electric vehicle is + 12V, the main battery is simply discharged. There is a problem that a battery for -12V or a converter for outputting -12V must be provided to detect the current or the terminal voltage.

The present invention has been made to solve the above problems, and a non-contact type sensor capable of accurately detecting a current or voltage while maintaining a magnetic equilibrium state in a coil by driving a single power source. Aim to get the circuit.

[0024]

A detection circuit of a non-contact type sensor according to the present invention is provided at least in a gap of a magnetic core of a coil having a secondary winding, and applies a voltage corresponding to a magnetic flux generated in the coil. One of the Hall element that is generated at the output terminal and the differential amplifier circuit that is connected to the output terminal of the Hall element and becomes the operating state with the supply of a single power source and that amplifies the voltage difference across the Hall element The single power supply, the other is connected to the ground, and the output end is connected to one of the secondary windings, and one of the transistors is turned on according to the voltage from the differential amplifier circuit. The output is connected to the other of the current buffer that flows a current proportional to the voltage from the dynamic amplification circuit and the other side of the secondary winding, and the other side is connected to the output, and the single power supply becomes the operating state with the supply, Maintain the output voltage at the reference voltage It is obtained by a constant voltage circuit.

In the constant voltage circuit, a first resistor and a second resistor are connected in series, one of which is connected to a single power source and the other of which is connected to ground, and a voltage at a voltage dividing point of the series circuit. It consists of a voltage follower that inputs and maintains the output at the voltage of its voltage dividing point.

Further, the first or second resistor is a variable resistor. Further, the primary winding of the coil is a coil which is insulated from the secondary winding and wound around a predetermined number of magnetic cores. Furthermore, the primary winding of the coil is a wire that passes through the magnetic core.

[0027]

In the present invention, at least the Hall element provided on the gap of the magnetic core of the coil having the secondary winding is
When a magnetic flux is generated in the coil, a voltage corresponding to the magnetic flux is generated at the output terminal.

Next, the differential amplifier circuit amplifies the voltage difference between both ends of the Hall element within the range of a single power supply, and one of the transistors of the current buffer is turned on according to the voltage from the differential amplifier circuit. Then, from the output end, a current proportional to the voltage from the differential amplifier circuit is passed through the secondary winding, the detection resistor, and the constant voltage circuit in the direction opposite to the current of the primary winding, and the magnetic flux is generated in the coil. To balance.

At this time, since the constant voltage circuit maintains the output voltage at the reference voltage, the voltage across the detection resistor is
A voltage in the range of ± (single power supply / 2) corresponding to the voltage from the differential amplifier circuit is generated.

In the constant voltage circuit, a first resistor and a second resistor are connected in series, one of which is connected to a single power source and the other of which is connected to ground, and a voltage at a voltage dividing point of the series circuit. When a voltage follower for inputting and maintaining the output at the voltage at the voltage dividing point is further configured, the voltage follower makes the voltage at the voltage dividing point at high speed even when the output changes.

When the first or second resistor is a variable resistor, it becomes a voltage at a voltage dividing point corresponding to the resistance value of the variable resistor, and the reference voltage output from the constant voltage circuit also becomes this voltage. Therefore, the measurement range is expanded according to the change of the variable resistance.

Further, when the primary winding of the coil is formed into a coil which is insulated from the secondary winding and wound around a predetermined number of magnetic cores, a magnetic flux is generated in the coil by the voltage, and the primary winding of the coil is also wound. When the wire is a wire that penetrates the magnetic core, a current produces a magnetic flux in the coil.

[0033]

【Example】

First Embodiment FIG. 1 is a schematic configuration diagram of the first embodiment. In the figure, R
L and 1 to 15 are the same as above, but as shown in the figure, the drive power source V for the differential amplifier circuit 13 and the current buffer 15 is only + 12V from the sub-battery 10.

Reference numeral 19 is a constant voltage circuit. Constant voltage circuit 19
One of the series circuits in which the resistors 20 and 22 are connected in series is connected to + 12V and the other is connected to the ground, and the input of the voltage follower 24 is at the voltage dividing point of the resistors 20 and 22.
The output is connected to the other side of the resistor RL, and one side of the resistor RL is connected to the other side of the secondary winding 1c of the coil 1.

The operation of the voltage sensor configured as described above will be described. Further, in this example, the resistor 20 and the resistor 2
The value of 2 is the same, and the voltage at the voltage dividing point is V / 2.

From the battery 9 as the load changes,
Discharge current is supplied.

This discharge current is also output to the voltage sensor side and output to the resistor 5 and the primary side 1b of the coil 1. As a result, the magnetic flux Φ1 is generated in the core of the coil 1.

At this time, the magnetic flux Φ is output to the Hall element 3.
A voltage corresponding to 1 is obtained, and this voltage is the differential amplifier circuit 1
3, the signal is amplified in the range of 0V to + 12V and output to the current buffer 15.

With this output, the transistor 15a of the current buffer 15 is turned on, and the magnetic flux Φ ₂ (Φ ₁ = Φ ₂ ) cancels the magnetic flux Φ ₁ on the side of the secondary winding 1c of the coil 1.
A current Iout that creates a current flows through the output resistance RL.

That is, since the magnetic flux Φ ₁ due to the current I1 flowing in the primary winding is generated in the direction opposite to the magnetic flux Φ ₁ , the inside of the coil 1 is always in a magnetic equilibrium state.

At this time, the output terminal VL of the voltage follower 24 is always V / 2, and the voltage VL across the resistor RL is VL = Iout × RL-V / 2.

For example, I1 flows in the primary winding (the measured voltage is positive) to create a magnetic flux Φ _1, and the current I 2 flows by the current buffer 15a so as to cancel it, and the magnetic flux Φ ₂
Are created and are in a magnetic parallel state. Φ at this time
Microscopically considering the relationship between ₁ and Φ ₂ , the output of the Hall element becomes zero at the moment when Φ ₂ = Φ ₁ , and the differential amplifier 1
3 and the output I2 of the current buffer 15a decrease, the magnetic flux Φ ₂ also decreases. However, at the moment when Φ ₂ <Φ ₁ ,
The magnetic flux [Phi ₁ - [Phi] ₂ detects Hall element, the current buffer 15a so that Φ ₁ = Φ ₂ since current flows I2, the Φ ₂ = Φ ₁ again. When the current I1 of the primary winding is in the opposite direction (the measured voltage is negative), the current buffer 15
A current I2 flows due to b and operates in the same manner. Like this
The magnetic flux Φ ₂ keeps the magnetic parallel state while constantly changing in the vicinity of Φ ₁ .

That is, even if the measured voltage or the measured current changes, if either of the a or b of the current buffer 15 is in the ON state within the range of the same polarity, the measured value The change does not change the current buffer that is turned on. That is, the output current of the same current buffer only increases or decreases.

Therefore, + 12V from the sub battery 19
Even if only by itself, the current in the opposite direction can be always flown to the primary side and the secondary side of the coil, so that the inside of the coil can be brought into a magnetic equilibrium state and the detection is performed within the range of ± 6V. Therefore, the detection voltage accuracy is the same as in the conventional case.

Further, since only + 12V from the sub-battery is required, the DC-DC converter is not required, so that the limited interior of the vehicle can be effectively used when mounted on the vehicle.

Second Embodiment FIG. 2 is a schematic configuration diagram of the second embodiment. As shown in the figure, the resistor 20 of the constant voltage circuit is a variable resistor. In the first embodiment, the resistors 20 and 22 are the same and the voltage at the voltage dividing point is 6 V. However, when the value of the resistor 5 on the primary side of the coil 1 is small, a large current is applied to the coil. 1 to the primary side and the secondary side. In such a case, if the voltage at the voltage dividing point remains 6 V, the magnetic equilibrium state cannot be maintained in the coil, and the measurement range is narrow even if measured.

Therefore, as shown in FIG. 2, the constant voltage circuit 21 is composed of a variable resistor 23 and a voltage follower 24 whose resistance value is changed by being operated, without setting the resistance 20 to a fixed value.

By doing so, the variable resistor 23
Is operated and its resistance value changes, the voltage at the voltage dividing point between the variable resistor 23 and the resistor 22 changes, and the voltage follower 24 of the constant voltage circuit 21 changes the voltage Vb at this voltage dividing point.
It operates so that x and the output are always the same.

Therefore, the voltage VL across the resistor RL is

[Formula 2] VL = Iout × RL + Vbx VL = −Iout × RL + Vbx However, (Vbx = 0 <Vbx <12V), and even if the value of the resistance 5 on the primary side of the coil 1 is small, The magnetic equilibrium can be maintained and the measurement range can be increased.

Embodiment 3 Embodiment 3 is an example in which the present invention is applied to a current sensor. The configuration of the constant voltage circuit may be the same as that of the first embodiment, but in this example, the constant voltage circuit 21 in which the resistor 20 is the variable resistor 23 is used in order to increase the measurement range.

Further, this embodiment will be described in detail by using the relationship between the direction of current and the voltage of the transistor.

For example, the variable range of the resistance value R1 of the variable resistor 23 is 0 <R1 ≦ R2. R2 is the resistance value of the resistor 22. That is, the resistance value R1 of the variable resistor 23 is 0 <R1 ≦
By setting R2, the measurement range of the current in the positive and negative directions is

## EQU3 ## Positive: Negative = {R2 / (R1 + R2)}: {R1 /
(R1 + R2)}.

Further, the current sensor uses the power line of the main battery and the load as the magnetic core of the coil.

Next, the operation will be described. For example, variable resistor 2
The resistance value R1 of 3 and the resistance value R2 of the resistor 22 are the same,
The voltage at the voltage dividing point = V / 2. (However, V = 12V) With the change of the load load, the discharge current flows from the battery 9 to the load side via the coil 1 of the current sensor. Due to this discharge current, a magnetic flux Φ ₁ is generated in the core of the coil 1, and a voltage corresponding to the magnetic flux Φ ₁ is obtained at the output of the Hall element 3, and this voltage is 0 V to 0V by the differential amplifier circuit 13.
It is amplified in the range of + 12V and output to the current buffer 15, the transistor 15a of the current buffer 15 is turned on, and the current Iou corresponding to the magnetic flux generated in the coil 1 is generated.
t flows toward the secondary winding, the resistor RL, and the voltage follower 24 side (hereinafter referred to as negative current).

[0055] This, by the current flowing through the secondary side, the magnetic flux [Phi ₁ and the magnetic flux [Phi ₂ in the reverse direction is generated, always in the coil 1 has a magnetic equilibrium state. At this time, the output of the voltage follower 24 is always the same as the voltage V / 2 at the voltage dividing point, and if this output voltage is used as the reference voltage, the current buffer 1
The maximum output voltage VE of the current buffer 15 when a negative current flows when the voltage between the collector and the emitter of the transistor 15a of No. 5 is VCE is VE = (V-VCE) -V / 2. .

Next, for example, when the voltage of the battery 9 decreases from time to time over time, the current I1 flowing through the primary side 1b of the coil 1 is smaller than before, and the magnetic flux Φ ₁ generated in the magnetic core of the coil ₁ also decreases. .

This magnetic flux is detected by the Hall element 3,
It is amplified by the differential amplifier circuit 13 and output to the current buffer 15, but the output voltage of the differential amplifier circuit 13 is lower than before, so the transistor 15a of the current buffer 15 is turned off and the transistor 15b is turned on. , A current flows through the voltage follower 24, the resistor RL, the secondary winding 1c, and the transistor 15b (hereinafter referred to as a positive direction current).

[0058] At this time, the magnetic core of the coil 1 [Phi ₂ in magnetic flux is generated in a direction to cancel the magnetic flux [Phi _1, the magnetic balance condition in the coil 1 is kept, the output VE of the current buffer 15, VE = ( V / 2) -VCE.

Therefore, when the resistance values of the variable resistors 23 and 22 are R1 = R2, the output VE of the current buffer 15 when the direction of the current is positive or negative has the following relationship.

In the negative direction,

VE = (V-VCE)-(V / 2) = (V /
2) -VCE In the positive direction, VE = (V / 2) -VCE, so the current measurement range in the negative and positive directions is 1: 1.
It has a relationship of.

Next, a case will be described in which the variable resistor 23 is changed to have its resistance value R1 = R2 / 2, and the reference voltage output from the voltage follower 24 is set to (2/3) V.

As described above, as the load changes,
In order to maintain the magnetic equilibrium state in the coil 1, a negative or positive current Iout flows from the current buffer 15 to the secondary winding, the detection resistor RL, the voltage follower, the voltage follower, the detection resistor RL, the secondary winding, It flows into the current buffer 15.

The output of the current buffer at this time is as follows:

VE = (V-VCE)-(2V / 3) = (V /
3) -VCE In the positive direction, VE = (2V / 3) -VCE. Therefore, the current measurement range in the positive and negative directions is 2: 1.
It has a relationship of.

Further, a case will be described in which the variable resistor 23 is changed to have its resistance value R1 = 0, and the reference voltage output from the voltage follower 24 is approximately V-1 (V).

The reason why the voltage is set to about V-1 (V) is that if R1≈0, the operational amplifier cannot pass a current in the direction of discharge, and the zero magnetic flux method may not work.

As described above, as the load changes,
In order to maintain the magnetic equilibrium state in the coil 1, a negative or positive current Iout flows from the current buffer 15 to the secondary winding, the detection resistor RL, the voltage follower 24, the voltage follower, the detection resistor RL, the secondary winding. , Current buffer 15
Flows to

In such a case, when the current is in the negative direction,
Although not measurable, in the positive direction, the output of the current buffer is VE = (V-VCE) -VCE = V, and the measurement range in the positive direction is wider than when R1 = R2.

That is, Io proportional to the magnitude of the measured current
ut flows, a voltage drop occurs on the secondary side and the detection resistor RL, and the output voltage VE of the current buffer 15 is the maximum (V−VC) when Iout flows from the current buffer 15.
E), the maximum (V-VCE) or maximum VCE can be changed in the direction of flow.

That is, if Iout flows into the current buffer when the current is positive at the power supply voltage V, Iout increases as the current increases, and VE decreases below the reference voltage.

When VE = VCE, Iou
t is saturated, and the measured current at that time becomes the maximum positive measured current. When the current is negative, Iout flows in the direction out of the current buffer, and when V = V-VCE, Iout is saturated, at which time the negative current becomes maximum.

Therefore, the more Iout can flow, the wider the current range becomes, and in terms of VE, the wider the range in which VE can change, the wider the measured current range.

For example, the range in which VE can change is positive (reference voltage-VCE) and negative ({V-VCE).
-Reference voltage}.

By varying R1 in this way, the ratio of the positive and negative measurement current ranges can be arbitrarily varied.

Further, as shown in FIG. 5, if the volume of the variable resistor 24 is attached to the exterior of the sensor and the scale is marked, the measuring range can be changed according to the current to be detected. The user can set it according to the detection accuracy of the directional current, and the accuracy of the measurement range can be changed according to the detected current.

In the above embodiment, the voltage follower is used for the constant voltage circuit, but any voltage follower having a fast rising speed may be used.

In the above embodiment, + 12V is used as the driving power source, but it may be -12V, and the power source voltage may be any voltage that can drive the circuit element.

[0077]

As described above, according to the present invention, the drive power supplies for the differential amplifier circuit and the current buffer are set to a single power supply, and the voltage difference generated at the output terminal of the Hall element provided in the gap of the magnetic core of the coil is reduced. Depending on the output, one of the transistors of the current buffer is turned on and the secondary winding,
A current proportional to the voltage from the differential amplifier circuit is passed through the detection resistor and constant voltage circuit in the direction opposite to the current of the primary winding to keep the magnetic flux in the coil in equilibrium. The voltage circuit maintains the output voltage at the reference voltage, so that the voltage across the detection resistor appears ± (single power supply / 2) according to the voltage from the differential amplifier circuit.
Since the voltage in the range is generated, the effect that another type of power supply is not required is obtained.

In the constant voltage circuit, the first resistor and the second resistor are connected in series, one of which is connected to a single power source and the other of which is connected to the ground, and the voltage at the voltage dividing point of the series circuit. When a voltage follower that inputs and maintains the output so as to maintain the voltage at the voltage dividing point is further configured, the voltage follower makes the voltage at the voltage dividing point at high speed even if the output changes. Even if the current direction of the coil changes abruptly, the reference voltage can always be kept constant.

When the first or second resistor is a variable resistor, it becomes a voltage at a voltage dividing point corresponding to the resistance value of the variable resistor, and the reference voltage output from the constant voltage circuit also becomes this voltage. Therefore, the effect that the measurement range is expanded according to the change of the variable resistance is obtained.

Further, when the primary winding of the coil is formed into a coil which is insulated from the secondary winding and wound around a predetermined number of magnetic cores, a magnetic flux is generated in the coil by the voltage, and the primary winding of the coil is also wound. When the wire is a wire that penetrates the magnetic core, a magnetic flux is generated in the coil due to the current, so that it can be used as a voltage or current sensor.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram of a first embodiment.

FIG. 2 is a schematic configuration diagram of a second embodiment.

FIG. 3 is a schematic configuration diagram of a third embodiment.

FIG. 4 is an external view of Example 3.

FIG. 5 is a schematic configuration diagram of a conventional voltage sensor.

[Explanation of symbols]

 1 coil 1a magnetic core 1b primary winding 1c secondary winding 3 hall element 13 differential amplifier circuit 15 current buffer 23 variable resistor 24 voltage follower

Claims (5)

[Claims] 1. A Hall element, which is provided at least in a gap of a magnetic core of a coil having a secondary winding and generates a voltage according to a magnetic flux generated in the coil at an output terminal, and an output terminal of the Hall element. A differential amplifier circuit that is connected and becomes an operating state with the supply of a single power supply, and that amplifies the voltage difference between both ends of the Hall element; one is connected to the single power supply and the other is connected to ground, and an output The end is connected to one of the secondary windings, and one of the transistors is turned on according to the voltage from the differential amplifier circuit, and is proportional to the voltage from the differential amplifier circuit from the output terminal. An output is connected to the other of the resistor, one of which is connected to the other of the secondary winding and a current buffer that allows a current to flow, and the single power supply is in an operating state with supply, and the voltage of the output is a reference voltage. Constant voltage times to maintain A detection circuit of a non-contact type sensor having a path. 2. The constant voltage circuit includes a series circuit in which a first resistor and a second resistor are connected in series, one of which is connected to the single power source and the other of which is connected to the ground, and a voltage divider of the series circuit. 2. A detection circuit for a non-contact type sensor according to claim 1, further comprising a voltage follower that inputs a voltage at a point and maintains an output at the voltage at the voltage dividing point. 3. The detection circuit for a non-contact type sensor according to claim 2, wherein the first or second resistor is a variable resistor. 4. The detection circuit for a non-contact type sensor according to claim 1, wherein the primary winding of the coil is a coil insulated from the secondary winding and wound around the magnetic core for a predetermined number of times. . 5. The detection circuit for a non-contact type sensor according to claim 1, wherein the primary winding of the coil is a wire penetrating the magnetic core.