JP3516644B2 - Magnetic sensor device and current sensor device - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetic sensor device for measuring a relatively large magnetic field and a current sensor device for non-contact measurement of a large current using the magnetic sensor device.

[0002]

2. Description of the Related Art In recent years, electric hybrid vehicles, fuel cells, solar power generation, etc. have been put into practical use due to social demands concerning environmental problems and resource energy problems. These techniques are common in that they handle a large DC current, and thus require a current sensor device for measuring a large DC current. Therefore, the development of an inexpensive and highly reliable DC high current sensor device has become a social demand.

Generally, as a method for measuring a large DC current in a non-contact manner, a method in which a magnetic sensor element detects a magnetic field generated by the current is adopted. Conventionally, Hall elements have been often used as magnetic sensor elements for this purpose.

Further, the present inventors have proposed a magnetic sensor device and a current sensor device using an inductance change type magnetic sensor element having excellent stability, that is, a fluxgate element. Here, the principle of magnetic field detection using the fluxgate element will be briefly described.
The flux gate element has a coil with a magnetic core. In the coil with a magnetic core, when the coil current exceeds a certain value, the magnetic core is saturated, so that the inductance thereof decreases. Here, when a bias current such that the inductance is halved, for example, is applied to the coil and a magnetic field is externally applied to the magnetic core, the inductance changes in accordance with the direction and magnitude of the applied magnetic field. Therefore, it is possible to detect the magnetic field given from this change in inductance. As the magnetic core, a rod-shaped magnetic core or a drum-shaped magnetic core is used.

However, the above-mentioned inductance change of the coil with a magnetic core is not very linear with respect to an external magnetic field, and is quite steep. This deteriorates the linearity of the magnetic sensor device and the current sensor device and narrows the measurement range.

As a technique for avoiding this drawback, there is a negative feedback method. In the negative feedback method, a feedback magnetic field whose absolute value is equal to the magnetic field to be measured and whose polarity is opposite to that of the magnetic field to be measured is added to the magnetic sensor element so that the magnetic sensor element always operates in a magnetic field close to zero. It is a thing. The feedback magnetic field can be easily obtained by converting the output of the magnetic field sensor element into a current and applying this current to the feedback magnetic field generating coil as a feedback current.

The potential difference across the resistor inserted in the path of the feedback current is proportional to the feedback current. Since the feedback current produces a magnetic field whose absolute value is equal to that of the magnetic field to be measured, the potential difference is completely proportional to the magnetic field to be measured. Therefore, the magnetic field to be measured can be detected by detecting this potential difference. In this way the linearity is good,
It is possible to realize a magnetic sensor device or a current sensor device without gain fluctuation.

[0008]

However, when the negative feedback method is applied to a magnetic sensor device or a current sensor device using an inductance change type magnetic sensor element, there are the following problems.

In order for the negative feedback method to be fully established, the feedback magnetic field must be completely proportional to the feedback current. Here, according to a detailed analysis, the measured magnetic field h and the feedback current i have a relationship represented by the following equation (1).

[0010]   h = -Ai {1 + Ne (μs-1)} / {1 + Nc (μs-1)} (1)

Where A is a constant, Ne is the demagnetizing factor of the sensor magnetic core as seen from the magnetic field to be measured, Nc is the demagnetizing factor of the sensor magnetic core as seen from the sensor coil, and μs is the relative permeability of the sensor magnetic core. is there. Here, when Ne = Nc or Ne (μ
When s−1) and Nc (μs−1) are sufficiently larger than 1, the term of relative permeability μs, which greatly varies depending on the temperature, is deleted in the formula (1), and the formula (1) is expressed by h = − Ai or h = -A'i, and the measured magnetic field h is proportional to the feedback current i. However, A'is approximately equal to Ne / Nc,
It is a constant that does not depend on the relative permeability μs.

However, Ne = Nc, or Ne (μs-
If there is no relationship such that 1) and Nc (μs−1) are sufficiently larger than 1, when the relative permeability μs changes depending on the temperature, the proportional constant relating the measured magnetic field h and the feedback current i changes. Here, i / h corresponds to the gain of the magnetic sensor device. Therefore, if the relative permeability μs changes depending on the temperature, the gain i / h also changes depending on the temperature. When the gain i / h fluctuates, an error occurs in the measurement result of the magnetic sensor device or the current sensor device. Since such a variation of the gain i / h is a principle,
In an actual magnetic sensor device or current sensor device, some kind of gain correction is necessary.

By the way, in the formula (1), the relative permeability μ
When s is changed from 1 to infinity, the gain i / h is −
It changes from 1 / A to -1 / A (Ne / Nc). Ne
If Nc, the gain increases as the relative permeability μs increases. On the other hand, if Ne> Nc, the gain decreases as the relative permeability μs increases.

As a magnetic sensor device or a current sensor device, Ne> Nc is more convenient because a large magnetic field to be measured can be measured with a small feedback current, resulting in less power consumption. In this case, the gain decreases as the relative permeability μs increases. In the case of a ferrite core, the relative permeability μs increases with an increase in temperature. The usable temperature range required for automotive sensor devices is
Since it is as wide as −40 to + 105 ° C., the gain variation due to the temperature variation of the relative permeability μs may reach several percent.

As a countermeasure when the gain increases as the temperature rises, a negative temperature coefficient thermistor (hereinafter simply referred to as the thermistor) circuit may be connected in parallel with the current detection resistor inserted in the feedback current path. So the measures are simple.

On the other hand, when the gain decreases as the temperature rises, in order to perform temperature compensation at the current detection resistor, an element having a positive temperature coefficient must be used. However, since the positive temperature coefficient resistor is not only expensive but also has a small temperature coefficient itself, it is not suitable for a large correction. Further, the positive temperature coefficient thermistor cannot be actually used because of its large non-linearity of resistance change.

Now, with reference to FIG. 6, an example of the configuration of the magnetic sensor device will be described in which the gain that decreases as the temperature rises is compensated. This magnetic sensor device includes a power supply input terminal 101, a resistor 102 having one end connected to the power supply input terminal 101, a cathode connected to the other end of the resistor 102, and an anode grounded Zener diode 1
03, and an operational amplifier 104 having a non-inverting input terminal connected to a connection point between the resistor 102 and the Zener diode 103. The inverting input terminal of the operational amplifier 104 is connected to the output terminal. The power supply voltage Vd is applied to the power input terminal 101.
Is applied.

The magnetic sensor device further includes a magnetic sensor unit 105 having a reference voltage input terminal connected to the output terminal of the operational amplifier 104, a feedback coil 106 having one end connected to the output terminal of the operational amplifier 104, and a non-inverting input terminal. Is the magnetic sensor unit 1
A feedback amplifier 107 formed of an operational amplifier connected to the output terminal of 05, a resistor 108 having one end connected to the output terminal of the operational amplifier 104 and the other end connected to the non-inverting input terminal of the feedback amplifier 107, and one end of the operational amplifier 104. Of the resistor 109, the other end of which is connected to the inverting input end of the feedback amplifier 107, the other end of which is connected to the inverting input end of the feedback amplifier 107, and the other end of which is connected to the output end of the feedback amplifier 107. And a current detecting resistor 111 having one end connected to the output end of the feedback amplifier 107 and the other end connected to the other end of the feedback coil 106. The magnetic sensor unit 105 includes a magnetic sensor element and a circuit that drives the magnetic sensor element.

The magnetic sensor device further has a resistor 11 at one end.
1 is connected to one end of the thermistor 121, one end is connected to the other end of the thermistor 121, a resistor 112, one end is connected to the other end of the resistor 111, a thermistor 122, and one end is connected to the other end of the thermistor 122. Resistance 113
And an inverting input terminal connected to the other end of the resistor 112 and a non-inverting input terminal connected to the other end of the resistor 113, a differential amplifier 114 including an operational amplifier, and one end connected to the inverting input terminal of the differential amplifier 114. And a resistor 115 having the other end connected to the output end of the differential amplifier 114 and a measurement signal output end 116 connected to the output end of the differential amplifier 114.

The magnetic sensor device further includes an operational amplifier 11 having a reference voltage input terminal 117, a non-inverting input terminal connected to the reference voltage input terminal 117, and an inverting input terminal connected to the output terminal.
8 and a resistor 119 having one end connected to the output end of the operational amplifier 118 and the other end connected to the non-inverting input end of the differential amplifier 114.

The power supply input terminals of the operational amplifier 104, the feedback amplifier 107, the differential amplifier 114, and the operational amplifier 118 are connected to the power supply input terminal 101, and the ground terminals thereof are grounded.

Next, the operation of the magnetic sensor device shown in FIG. 6 will be described. In this magnetic sensor device, the power supply voltage Vd is applied to the power supply input terminal 101, and the power supply voltage Vd
Each circuit part is operating by.

Resistor 102 and Zener diode 103
Generates a reference voltage Vp at the connection point between the two using the power supply voltage Vd. The operational amplifier 104 constitutes a voltage follower, and the potential at the output end of the operational amplifier 104 is equal to the reference voltage Vp. The reference voltage Vp is the reference voltage input terminal of the magnetic sensor unit 105, the feedback coil 106,
It is applied to one end of each of the resistors 108 and 109.

A reference voltage Vref is applied to the reference voltage input terminal 117. The operational amplifier 118 constitutes a voltage follower, and the potential at the output end of the operational amplifier 118 is equal to the reference voltage Vref. The reference voltage Vref is the resistance 1
It is applied to the non-inverting input terminal of the differential amplifier 114 via 19.

The magnetic sensor section 105 is
A signal according to the magnetic field to be measured is output to the non-inverting input terminal of the feedback amplifier 107. The feedback amplifier 107 generates an output voltage that changes according to the magnetic field to be measured with the reference voltage Vp as a reference. When the measured magnetic field is zero, the output voltage of the feedback amplifier 107 is equal to the reference voltage Vp.

A feedback current path is formed from the feedback amplifier 107 to the feedback coil 106 via the resistor 111. In this feedback current path, a feedback current is generated according to the difference between the output voltage of the feedback amplifier 107 and the reference voltage Vp, and this feedback current is supplied to the feedback coil 106. This feedback current flows in both forward and reverse directions depending on whether the output voltage of the feedback amplifier 107 is higher or lower than the reference voltage Vp. The voltage (potential difference) generated between both ends of the resistor 111 inserted in the feedback current path is the reference voltage V as the common mode voltage.
It is superimposed on p and input to the differential amplifier 114. The differential amplifier 114 outputs a signal corresponding to the magnetic field to be measured and having the common mode voltage Vp removed. The reference voltage Vref is applied to the non-inverting input terminal of the differential amplifier 114 via the resistor 119. Therefore, the differential amplifier 11
The output signal of No. 4, that is, the measurement signal output from the measurement signal output terminal 116 is a unipolar signal that changes according to the magnetic field to be measured with the reference voltage Vref as a reference.

In the magnetic sensor device shown in FIG. 6, the thermistor 12 is connected to the input resistors 112 and 113 of the differential amplifier 114 in order to compensate for the gain that decreases as the temperature rises.
1, 122 are connected in series. However, in the case of this method, unless the thermistor is inserted into both the non-inverting input side and the inverting input side of the differential amplifier 114, the differential balance of the differential amplifier 114 is lost, so two thermistors are required. . Further, since the thermistor generally has a poor resistance value, the above method has a problem that the differential balance of the differential amplifier 114 is easily destroyed. When the differential balance is lost, the common mode voltage leaks and an offset voltage is generated.

FIG. 7 is a circuit diagram showing a main part of a magnetic sensor device adapted to compensate a gain that decreases with an increase in temperature by using another method. In this magnetic sensor device,
No thermistor is inserted on the input side of the differential amplifier 114. Instead, a resistor 1 inserted in the feedback current path
A circuit for extracting the voltage between both ends of 11 and using it as an output voltage is configured by using a two-stage amplifier, so that the amplification degree of the second-stage amplifier increases as the temperature rises. A thermistor is used as at least a part of the input resistance. More specifically, the magnetic sensor device shown in FIG. 7 has a thermistor 131 having one end connected to the output end of the differential amplifier 114, one end connected to the other end of the thermistor 131, and the other end grounded. The resistor 132 and the operational amplifier 133 whose non-inverting input terminal is connected to the other end of the thermistor 131 and whose output terminal is connected to the measurement signal output terminal 116 are provided. The inverting input terminal of the operational amplifier 133 is the operational amplifier 1
It is connected to the output terminal of 33. However, the method shown in FIG. 7 has a problem that two amplifiers are required.

The present invention has been made in view of the above problems, and an object thereof is a magnetic sensor device and a current sensor having a simple structure and capable of correcting the gain when the gain decreases with an increase in temperature. To provide a device.

[0030]

A magnetic sensor device according to the present invention comprises a magnetic sensor section for outputting a signal which changes according to the value of a magnetic field to be measured, and a conversion means for converting an output signal of the magnetic sensor section into an output current. A feedback means for generating a feedback magnetic field having an absolute value equal to that of the magnetic field to be measured and having a polarity opposite to that of the magnetic field to be measured by using the output current obtained by the converting means,
A measurement signal output means for converting the output current into a voltage and outputting it as a measurement signal, and a shunt circuit connected in parallel to the load in the current path of the output current and shunting a part of the output current via the thermistor. Be prepared.

The current sensor device of the present invention comprises a magnetic sensor section for outputting a signal that changes according to the value of the magnetic field under measurement generated by the measured current, and a conversion means for converting the output signal of the magnetic sensor section into an output current. Using the output current obtained by the conversion means, a feedback means for generating a feedback magnetic field whose absolute value is equal to that of the magnetic field to be measured and has a polarity opposite to that of the measured magnetic field, and the output current is converted into a voltage for measurement. The measurement signal output means for outputting as a signal, and a shunt circuit connected in parallel to the load in the current path of the output current and shunting a part of the output current via the thermistor are provided.

In the magnetic sensor device or the current sensor device of the present invention, the magnetic sensor unit outputs a signal that changes according to the value of the magnetic field to be measured. This output signal is converted into an output current by the conversion means. Then, the feedback means generates a feedback magnetic field using the output current. Also,
The measurement signal output means converts the output current into a voltage and outputs it as a measurement signal. A part of the output current is divided by the shunt circuit through the thermistor. As a result, the resistance value of the shunt circuit decreases as the temperature rises, the output current increases, and the gain that decreases as the temperature rises is compensated.

In the magnetic sensor device or the current sensor device of the present invention, the feedback means may generate a feedback magnetic field using the output current, and may include a feedback coil which serves as a load in the current path.

In the magnetic sensor device or the current sensor device of the present invention, the magnetic sensor portion may include a fluxgate element.

[0035]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. [First Embodiment] FIG. 1 is a circuit diagram showing a configuration of a magnetic sensor device according to a first embodiment of the present invention. The magnetic sensor device 1 includes a power supply input terminal 2, a reference voltage input terminal 17, a non-inverting input terminal connected to the reference voltage input terminal 17, and an operational amplifier 18 having an inverting input terminal connected to an output terminal. There is. A power supply voltage Vd is applied to the power supply input terminal 2. A reference voltage is externally applied to the reference voltage input terminal 17.

The magnetic sensor device 1 further includes an operational amplifier 21 whose non-inverting input terminal is connected to the output terminal of the operational amplifier 18.
And a resistor 22 having one end connected to the inverting input end of the operational amplifier 21 and the other end connected to the output end, and a resistor 2 having one end connected to the inverting input end of the operational amplifier 21 and the other end grounded.
3 and 3. The operational amplifier 21 is adapted to generate the reference voltage Vp.

The magnetic sensor device 1 is further provided with a magnetic sensor section 5 whose reference voltage input terminal is connected to the output terminal of the operational amplifier 21, and in the vicinity of this magnetic sensor section 5.
A feedback coil 6 having one end connected to the output end of the operational amplifier 21, a feedback amplifier 7 including an operational amplifier having a non-inverting input end connected to the output end of the magnetic sensor unit 5, and one end connected to the output end of the operational amplifier 21. , The other end of which is connected to the non-inverting input end of the feedback amplifier 7, and the other end of which is the operational amplifier 2.
1 is connected to the output end of the feedback amplifier 7 and the other end is connected to the inverting input end of the feedback amplifier 7, and one end is connected to the inverting input end of the feedback amplifier 7 and the other end is connected to the output end of the feedback amplifier 7. And a current detection resistor 11 having one end connected to the output end of the feedback amplifier 7 and the other end connected to the other end of the feedback coil 6.

The magnetic sensor device 1 further has a resistor 1 at one end.
1 has a resistor 12 connected to one end, a resistor 13 having one end connected to the other end of the resistor 11, an inverting input end connected to the other end of the resistor 12, and a non-inverting input end connected to the other end of the resistor 13. A differential amplifier 14 made up of connected operational amplifiers, a resistor 15 having one end connected to the inverting input end of the differential amplifier 14 and the other end connected to the output end of the differential amplifier 14, and one end output from the operational amplifier 18. It has a resistor 19 connected to the end and the other end connected to the non-inverting input end of the differential amplifier 14, and a measurement signal output end 16 connected to the output end of the differential amplifier 14.

The magnetic sensor device 1 further includes a feedback coil 6
And a shunt circuit 24 connected in parallel with.
The shunt circuit 24 has a thermistor 25 and a resistor 26 connected in series. In the shunt circuit 24, the resistor 26 is provided to adjust the resistance change rate of the entire shunt circuit 24 with respect to the temperature change. The positional relationship between the thermistor 25 and the resistor 26 may be opposite to the state shown in FIG.

The configuration of the shunt circuit 24 is not limited to the configuration in which the thermistor 25 and the resistor 26 are connected in series as shown in FIG. 1, but, for example, the thermistor 25 and the resistor 27 are connected as shown in FIG. A configuration in which they are connected in parallel may be used, or in FIG.
As shown in FIG. 5, the thermistor 25 and the resistor 28 may be connected in series, and the resistor 29 may be connected in parallel to the thermistor 25. Resistance 2 in FIG. 2 or FIG.
7, 28 and 29 are provided to adjust the resistance change rate of the entire shunt circuit 24 with respect to temperature change.

The power supply input terminals of the operational amplifier 21, the feedback amplifier 7, the differential amplifier 14, and the operational amplifier 18 are connected to the power supply input terminal 2, and the ground terminals thereof are grounded.

The measurement signal output from the measurement signal output terminal 16 of the magnetic sensor device 1 is input to the A / D converter 31 which performs analog-digital conversion (hereinafter referred to as A / D conversion) of this measurement signal. It has become so. The digital measurement signal output from the A / D converter 31 is input to, for example, a CPU (central processing unit) 33 that processes the digital measurement signal. A reference voltage source 32 supplies a reference voltage with high accuracy and stability to the A / D converter 31. The reference voltage source 32 may be built in the A / D converter 31 or may be provided outside the A / D converter 31. As the reference voltage source 32, for example, a bandgap type reference voltage generating circuit is used.

A reference voltage for the A / D converter 31 generated from a reference voltage source 32 is applied to the reference voltage input terminal 17 of the magnetic sensor device 1 as the reference voltage Vref.

In this embodiment, the feedback amplifier 7 corresponds to the conversion means in the present invention, the resistor 11 and the feedback coil 6 correspond to the feedback means in the present invention, and the resistor 11 and the differential amplifier 14 are the measurement in the present invention. It corresponds to the signal output means.

FIG. 4 is a circuit diagram showing an example of the configuration of the magnetic sensor section 5 in FIG. The magnetic sensor unit 5 in this example has an inductance change type magnetic sensor element, that is, a fluxgate element, as a magnetic sensor element. This fluxgate element has a magnetic core 51.
And a sensor coil 52 wound around the magnetic core 51. The magnetic sensor unit 5 further includes a capacitor 53 having one end connected to one end of the sensor coil 52, an excitation circuit 54 connected to the other end of the capacitor 53, one end connected to the other end of the sensor coil 52, and the like. Magnetic sensor part 5 at the end
Inductance element 55 connected to the reference voltage input terminal of
And have. The inductance element 55 is for detecting a change in the inductance value of the sensor coil 52, and is made of, for example, a coil. In addition, in FIG. 4, the power supply and the ground terminal of the excitation circuit 54 are not shown.

The magnetic sensor unit 5 further has a capacitor 56 having one end connected to the connection point between the sensor coil 52 and the inductance element 55, one end connected to the other end of the capacitor 56, and the other end connected to the magnetic sensor unit 5. And a resistor 57 connected to the reference voltage input terminal of. The capacitor 56 and the resistor 57 form a differentiating circuit that differentiates the voltage generated across the inductance element 55.

The magnetic sensor unit 5 further has a positive peak hold circuit 58 whose input end is connected to the connection point of the capacitor 56 and the resistor 57, and an input end of which is the capacitor 56 and the resistor 57.
A negative peak hold circuit 59 connected to the connection point with
Each input terminal has an output terminal of the positive peak hold circuit 58 and an adder circuit 60 connected to the output terminal of the negative peak hold circuit 59. Positive peak hold circuit 58
Holds the positive peak value of the output signal of the differentiating circuit,
The negative peak hold circuit 59 holds the negative peak value of the output signal of the differentiating circuit. The adder circuit 60 outputs the output signal of the positive peak hold circuit 58 and the negative peak hold circuit 5
The output signal of 9 is added and output from the output end of the magnetic sensor unit 5.

In the magnetic sensor section 5 shown in FIG. 4, the exciting circuit 54 generates an exciting current based on the power supply voltage Vd applied to the magnetic sensor section 5. This excitation current flows through the sensor coil 52 and the inductance element 55. The excitation current is an alternating current so that the magnetic core 51 enters the saturation region at the peak. In this application,
The saturation region of the magnetic core is a region in which the absolute value of the magnetic field is larger than the absolute value of the magnetic field when the magnetic permeability of the magnetic core reaches the maximum magnetic permeability. When the magnetic core 51 reaches the saturation region near the peak value of the exciting current, the inductance value of the sensor coil 52 sharply decreases, and the exciting current rapidly increases. By differentiating the waveform of the excitation current twice, it is possible to detect the output of the opposite phase, which is similar to the current waveform of the sharply increased portion.

The exciting current is differentiated twice by the inductance element 55 and the differentiating circuit, and the differentiating circuit outputs spike-like voltage signals having mutually opposite polarities, which represent positive and negative peak values of the exciting current. Each peak value of the positive and negative spike-shaped voltage signals is held by the positive peak hold circuit 58 and the negative peak hold circuit 59, and the adder circuit 60.
Are added and output as an output signal corresponding to the magnetic field to be measured from the output end of the magnetic sensor unit 5.

Next, the operation of the magnetic sensor device 1 according to this embodiment will be described. In this magnetic sensor device,
A power supply voltage Vd is applied to the power supply input terminal 2, and each circuit portion operates by the power supply voltage Vd. That is, each circuit portion is driven by the unipolar power supply.

A reference voltage for the A / D converter 31 generated by the reference voltage source 32 is applied to the reference voltage input terminal 17 as the reference voltage Vref. The operational amplifier 18 constitutes a voltage follower, and the potential at the output end of the operational amplifier 18 is equal to the reference voltage Vref. Operational amplifier 1
The reference voltage Vref output from the output terminal of
It is applied to the non-inverting input terminal of the differential amplifier 14 via the, and is also applied to the non-inverting input terminal of the operational amplifier 21.

The operational amplifier 21 amplifies the reference voltage Vref with a predetermined amplification degree G to generate a reference voltage Vp. Resistance 2
When the resistance value of 2 is R1 and the resistance value of the resistor 23 is R2, the amplification degree G of the operational amplifier 21 is 1 + R1 / R2. Reference voltage V output from the output terminal of the operational amplifier 21
p is applied to the reference voltage input terminal of the magnetic sensor unit 5, each end of the feedback coil 6, and the resistors 8 and 9.

The magnetic sensor section 5 outputs a signal corresponding to the magnetic field to be measured from its output terminal to the non-inverting input terminal of the feedback amplifier 7. The feedback amplifier 7 generates an output voltage that changes according to the magnetic field to be measured with the reference voltage Vp as a reference. When the measured magnetic field is zero, the output voltage of the feedback amplifier 7 is equal to the reference voltage Vp.

A feedback current path is formed from the feedback amplifier 7 through the resistor 11 to the feedback coil 6. In this feedback current path, the output voltage of the feedback amplifier 7 and the reference voltage V
An output current is generated according to the difference with p. Therefore, it can be said that the feedback amplifier 7 converts the output signal of the magnetic sensor unit 5 into an output current. The output current flows in both forward and reverse directions depending on whether the output voltage of the feedback amplifier 7 is higher or lower than the reference voltage Vp. A part of the output current is supplied to the feedback coil 6 as a feedback current. The feedback coil 6 generates a feedback magnetic field having an absolute value equal to that of the magnetic field to be measured and a polarity opposite to that of the magnetic field to be measured according to the feedback current.

The voltage (potential difference) generated across the resistor 11 inserted in the feedback current path is superimposed on the reference voltage Vp as the common mode voltage and input to the differential amplifier 14. The differential amplifier 14 outputs a signal corresponding to the magnetic field to be measured and having the common mode voltage Vp removed. The reference voltage Vref is applied to the non-inverting input terminal of the differential amplifier 14 via the resistor 19. Therefore, the output signal of the differential amplifier 14, that is, the measurement signal output from the signal output terminal 16 is a unipolar signal that changes according to the magnetic field to be measured with the reference voltage Vref as a reference.

In the magnetic sensor device 1 according to the present embodiment, the gain decreases as the temperature rises when the shunt circuit 24 is omitted.

In the present embodiment, the shunt circuit 24 is provided in parallel with the feedback coil 6 that generates a feedback magnetic field and serves as a load in the feedback current path. The shunt circuit 24 shunts a part of the output current via the thermistor 25. In order to divide a part of the output current by the shunt circuit 24, the resistance value of the feedback coil 6 needs to be large to some extent, but the resistance value of the feedback coil 6 is
Usually several tens of ohms is sufficient.

In the present embodiment, as the temperature rises, the resistance value of the shunt circuit 24 decreases, and as a result, the output current flowing through the resistor 11 increases and the voltage across the resistor 11 increases. This compensates for the gain that decreases with increasing temperature.

Further, in this embodiment, the operational amplifier 21 is used.
Thus, the reference voltage Vp is generated based on the reference voltage Vref given from the outside regardless of the power supply voltage Vd. The reference voltage for the A / D converter 31 generated by the reference voltage source 32 is used as the reference voltage Vref. Generally, the accuracy and stability of the reference voltage used in the A / D converter are very high. Therefore, the reference voltage Vref in the present embodiment is the power supply voltage Vref supplied to the magnetic sensor device 1.
This voltage is independent of d and has high accuracy and stability, and is not affected by fluctuations in the power supply voltage Vd at all. As a result, the reference voltage Vp generated based on the reference voltage Vref is also a voltage with high accuracy and stability that is not affected by the fluctuation of the power supply voltage Vd. Therefore, in the present embodiment, the differential amplifier 1
Resistors 12, 13, 1 that determine the common mode suppression ratio of 4
Even if the resistance values of 5 and 19 are not perfectly balanced, the measurement signal output from the differential amplifier 14 does not fluctuate with the fluctuation of the power supply voltage Vd.

By the way, in the present embodiment, the operational amplifier 21 sets the ratio of the reference voltage Vref to the standard voltage Vp to 1.
Alternatively, the reference voltage Vp may be equal to the reference voltage Vref.

The reference voltage Vp determines the zero point of the operation of the feedback amplifier 7. Generally, the reference voltage Vref is 2.5
In many cases, the minimum value of the power supply voltage Vd is about 8V. Therefore, when the reference voltage Vref is 2.5V and the power supply voltage Vd is 8V, the zero point of the operation of the feedback amplifier 7 becomes 2.5V when the reference voltage Vp is equal to the reference voltage Vref. The operating range on the low voltage side is reduced. Therefore, the reference voltage Vp is 1 of the power supply voltage Vd.
It is better to set about / 2, that is, about 4V. In the present embodiment, as an example, by the operational amplifier 21,
Amplify the 2.5V reference voltage Vref 1.6 times to 4V
To generate the reference voltage Vp. In this case, compared with the magnetic sensor device shown in FIG. 6, newly added resistors 22 and 2 are
3, the price of the magnetic sensor device 1 hardly increases.

When the reference voltage Vp is made equal to the reference voltage Vref, it is sufficient to set R1 = 0 and R2 = ∞, so that the resistors 22 and 23 are also unnecessary, and compared with the magnetic sensor device shown in FIG. The price increase of the magnetic sensor device 1 is completely eliminated. In this case, the operational amplifier 21 constitutes a voltage follower.

As described above, according to the magnetic sensor device 1 of the present embodiment, the shunt circuit 24 for shunting a part of the output current via the thermistor 25 is provided in parallel with the feedback coil 6. Therefore, with a simple configuration, it is possible to correct the gain when the gain decreases as the temperature rises. That is, in this embodiment, the resistance 1
1 circuit that takes the voltage between both ends of 1 and uses it as the output voltage
The thermistor 25 can be configured by the differential amplifier 14 in stages, and only one thermistor 25 may be used. Therefore, the gain can be corrected while suppressing the price increase. Further, in the present embodiment, the differential balance of the differential amplifier 14 is not lost by inserting the thermistor 25.

Further, according to the magnetic sensor device 1 according to the present embodiment, it is possible to operate with a unipolar power source to output a unipolar measurement signal, and to use a simple configuration to measure the measurement signal accompanying the fluctuation of the power supply voltage. Fluctuations can be suppressed.

In this embodiment, the reference voltage V
When the ratio between ref and the reference voltage Vp is set to a constant value other than 1, the zero point of the operation of the feedback amplifier 7 can be set to an appropriate potential.

In this embodiment, the reference voltage V
When p is made equal to the reference voltage Vref, the configuration of the magnetic sensor device 1 can be simplified.

[Second Embodiment] FIG. 5 is a circuit diagram showing a structure of a current sensor device according to a second embodiment of the present invention. The current sensor device according to the present embodiment is the first
The magnetic sensor device according to the embodiment is used.

Current sensor device 41 according to the present embodiment
Is the conductive portion 4 through which the measured current as the measured object passes.
The magnetic yoke 43 is provided so as to surround 2 and partially has a gap. The magnetic sensor unit 5 of the magnetic sensor device according to the first embodiment is arranged in the gap of the magnetic yoke 43.

In the current sensor device of the present embodiment, the magnetic flux generated by the current to be measured flowing through the conductive portion 42 in the direction perpendicular to the paper surface of FIG. 5 is converged by the magnetic yoke 43 and passes through the magnetic yoke 43. As a result, a magnetic field to be measured is generated in the gap of the magnetic yoke 43. Magnetic sensor unit 5 arranged in the gap of the magnetic yoke 43
Outputs a signal that changes according to the value of the measured magnetic field generated by the measured current. As a result, the current to be measured is measured without contact.

Other configurations, operations and effects in this embodiment are the same as those in the first embodiment.

The present invention is not limited to the above-mentioned embodiments, and various modifications can be made. For example, the magnetic sensor unit is not limited to one including a fluxgate element, but may include another magnetic sensor element such as a Hall element.

[0072]

As described above, according to the magnetic sensor device or the current sensor device of the present invention, a part of the output current is shunted through the thermistor in parallel with the load in the current path of the output current. Since the shunt circuit is provided, it is possible to correct the gain when the gain decreases as the temperature rises with a simple configuration.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing a configuration of a magnetic sensor device according to a first embodiment of the present invention.

FIG. 2 is a circuit diagram showing an example of another configuration of the shunt circuit in FIG.

FIG. 3 is a circuit diagram showing an example of still another configuration of the shunt circuit in FIG.

4 is a circuit diagram showing an example of a configuration of a magnetic sensor unit in FIG.

FIG. 5 is a circuit diagram showing a configuration of a current sensor device according to a second embodiment of the invention.

FIG. 6 is a circuit diagram showing an example of a configuration of a magnetic sensor device that compensates a gain that decreases with an increase in temperature.

FIG. 7 is a circuit diagram showing a main part of a magnetic sensor device configured to compensate for a gain that decreases as the temperature rises by using another method.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Magnetic sensor device, 2 ... Power supply input terminal, 5 ... Magnetic sensor part, 6 ... Feedback coil, 7 ... Feedback amplifier, 11 ... Current detection resistance, 14 ... Differential amplifier, 16 ... Measurement signal output end, 17
... reference voltage input terminal, 18 ... operational amplifier, 21 ... operational amplifier, 24 ... shunt circuit, 25 ... thermistor, 26 ... resistance.

─────────────────────────────────────────────────── ─── Continuation of front page (58) Fields surveyed (Int.Cl. ⁷ , DB name) G01R 33/02-33/10 G01R 15/18-15/26

Claims (6)

(57) [Claims] 1. A magnetic sensor unit that outputs a signal that changes according to the value of a magnetic field to be measured, a conversion unit that converts an output signal of the magnetic sensor unit into an output current, and an output current obtained by the conversion unit. Feedback means for generating a feedback magnetic field having an absolute value equal to that of the magnetic field to be measured and having a polarity opposite to that of the magnetic field to be measured, and a measuring signal output means for converting the output current into a voltage and outputting it as a measurement signal. A magnetic sensor device, comprising: a shunt circuit that is connected in parallel to a load in a current path of the output current and that diverts a part of the output current via a thermistor. 2. The magnetic sensor device according to claim 1, wherein the feedback means includes a feedback coil that generates the feedback magnetic field using the output current and serves as a load in the current path. 3. The magnetic sensor device according to claim 1, wherein the magnetic sensor unit includes a fluxgate element. 4. A magnetic sensor section that outputs a signal that changes according to the value of a magnetic field to be measured generated by a current to be measured, a conversion unit that converts an output signal of the magnetic sensor unit into an output current, and the conversion unit. A feedback means for generating a feedback magnetic field having an absolute value equal to that of the magnetic field to be measured and having a polarity opposite to that of the magnetic field to be measured by using the output current obtained by the above; and converting the output current into a voltage and outputting it as a measurement signal. A current sensor device, comprising: a measurement signal output means for connecting the output current and a shunt circuit that is connected in parallel to a load in a current path of the output current and shunts a part of the output current via a thermistor. . 5. The current sensor device according to claim 4, wherein the feedback means includes a feedback coil that generates the feedback magnetic field using the output current and serves as a load in the current path. 6. The current sensor device according to claim 4, wherein the magnetic sensor unit includes a fluxgate element.