JPH06174752A - Current sensor - Google Patents

Abstract

PURPOSE:To enhance accuracy in current detection by improving the linearity of a curve representative of relationship between the value of current to be detected within a measuring range and sensor output. CONSTITUTION:The current sensor comprises a coil 11, a core 12 having a magnetism collecting end part wounded by the coil, and a magnetoresistive element 13 arranged between the magnetism collecting end parts of the core 12 while having a bias field perpendicularly intersecting the field produced between the magnetism collecting end parts. The magnetoresistive element 13 or the core 12 itself of the current sensor for detecting a current value based on the strength of field produced between the magnetism collecting end parts upon application of a current to be detected to the coil 11 are arranged to allow inclination so that the directional perpendicularity between the bias field of the magnetoresistive element 13 and the field produced between the magnetism collecting end parts can be modified.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a configuration of a current sensor using a magnetoresistive element having a bias magnetic field (hereinafter referred to as MR element), and particularly to a test current value and a sensor output within a measured current value range. The present invention relates to a current sensor in which the linearity of a relation graph is improved to improve the current detection accuracy.

MR elements are used in various sensors such as position sensors and angle sensors because they are more sensitive to minute magnetic fields and superior in resolution than Hall elements or semiconductor type magnetoresistive elements, and they are used depending on the current value. It is also used in current sensors that detect fluctuating magnetic fields and conversely detect the original current value.

Since it is difficult to obtain a linear output with respect to an external magnetic field (detection magnetic field) with an ordinary ferromagnetic thin film magnetoresistive element, recently, in order to secure output linearity and improve detection accuracy, the back surface of the thin film magnetoresistive element is improved. M of the type that attaches a magnet plate to the side and applies a bias magnetic field to the element
The R element has been widely used.

[0004]

2. Description of the Related Art FIG. 7 is a diagram schematically illustrating the configuration of a conventional current sensor. (7-1) is a perspective view, (7-2) is a plan view of (7-1). is there.

FIG. 8 is a diagram for explaining a problem in the conventional current sensor. In FIG. 7, the current sensor 1 is a coil 11
An iron core 12 wound around and an MR element 13 arranged in a slit 12a portion of the iron core 12 are fixed on a circuit board 14.

The coil 11 has circuit boards 14 at both ends.
Since it is connected to the board-side ends of the external connection terminals 111a and 111b that are set up in the margins of the iron core 12, it is possible to connect the circuit-side signal line that detects the current value to the free-end side end of the iron core 12. An external magnetic field G having a strength corresponding to the current value is applied between the slits 12a.
Can be generated.

On the other hand, the MR element 13 arranged between the slits 12a has four resistors made of a ferromagnetic thin film connected to one surface in a bridge circuit shape as shown in the enlarged view (a) extracted. A substrate on which a magnetoresistive pattern 131 is formed, and a magnet plate 132 for applying a bias magnetic field G ₁ to the magnetoresistive pattern 131 is attached to the back surface side of the pattern formation region so that the magnetic field direction is the direction of arrow A. 133 is covered with resin 134, and is fixedly mounted on the circuit board 14 by four external connection terminals 135 connected to the magnetoresistive pattern 131.

On the circuit board 14, a signal processing IC 15 connected to the MR element 13 is mounted.
The external magnetic field G ₂ detected by is calculated and converted into a current value I, and the signal can be taken out from the external connection electrodes 15a and 15b.

Therefore, an external magnetic field generated between the slits 12a of the iron core 12 in proportion to the value of the verification current applied to the coil 11
The signal of the current value I corresponding to G ₂ can be taken out from the external connection electrodes 15a and 15b.

In the current sensor 1 having such a structure, the required current value signal can be taken out from the external connection electrodes 15a and 15b by connecting the test current value circuit between the external connection terminals 111a to 111b, so that the current value can be efficiently obtained. There is a merit that can be detected.

[0011]

However, the inherent characteristic of the magnetoresistive element is that the output of the magnetoresistive element does not follow it even when the external magnetic field changes linearly, that is, linearly. There is a weakness that the decrease in detection accuracy cannot be avoided.

Therefore, in order to improve such weak points, the above M
Although a bias magnetic field G ₁ is applied to the magnetoresistive element itself like the R element 13 to improve the followability as an output to the external magnetic field G ₂ , the two cannot be perfectly matched even in that case.

In FIG. 8 showing such a problem, (8-1) illustrates the output as the MR element and (8-2) illustrates the output as the current sensor. Horizontal magnetic field X is external magnetic field
In the figure (8-1) in which the vertical axis Y is taken as G ₂ and the output mV as the MR element is represented, the linear broken line (1) shows the ideal output as the MR element, and the curve ( 2) shows an actual output example.

In the figure, for easy understanding, the deviation of the broken line (1) and the curve (2) in the Y-axis direction (hatched area in the figure) is partially enlarged, but a bias magnetic field G ₁ is added. In the MR element 13, the deviation amount ΔV _{1 at} the point where the external magnetic field G ₂ is “0” is approximately 1% with respect to the potential difference V ₁ in the detected current value range.
This is a degree, and this deviation is unavoidable as the original of the magnetoresistive element.

On the other hand, the horizontal axis X is taken as the test current value I and the vertical axis Y is taken.
Is a voltage V obtained by amplifying the output of the MR element.
In (8-2), the linear broken line (3) shows the ideal output as a current sensor, and the curve (4) shows the actual output.In this case, the curve (4) shows (8 Curve in -1)
It is almost similar to (1).

In this case, the broken line (3) and the curve at the position of the current value "0", that is, at the position of the external magnetic field G ₂ "0"
(4) If the ratio “ΔV ₂ / V ₂ ” of the deviation “ΔV ₂ ” in the Y-axis direction to the potential difference V ₂ in the detected current value range is defined as the linearity L (unit:%) as a current sensor, In order to further improve the detection accuracy of the sensor, the linearity L and thus ΔV ₂ must be made as small as possible.

Therefore, the current sensor having the conventional structure cannot avoid the deterioration of the detection accuracy due to the original characteristics of the MR element, and must meet the demand for the current sensor with higher detection accuracy. There was a problem that I could not do it.

[0018]

Means for Solving the Problems The above problem is to provide a coil, an iron core having a magnetism collecting end around which the coil is wound, and a bias magnetic field in a direction orthogonal to a magnetic field generated between the magnetism collecting ends. A magnetic resistance element arranged at least between magnetic flux collecting ends of the iron core, and the test current value generated between the magnetic flux collecting ends of the iron core when a test current is applied to the coil. Is a current sensor for detecting the verification current value from a magnetic field having a strength corresponding to the magnetic resistance element arranged between the magnetic flux collecting ends of the iron core or the iron core itself between the magnetic flux collecting ends of the iron core. And a bias current direction of the magnetoresistive element can be tilted in a direction in which the orthogonal angle can be changed.

[0019]

When the strength of the bias magnetic field G ₁ applied to the MR element is set appropriately, the above-mentioned linearity L of the MR element can be improved.

On the other hand, the MR element located between the slits of the iron core is angled θ in a direction parallel to the external magnetic field G ₂ in the slits.
When it is rotated only by the bias magnetic field G ₁
A magnetic field corresponding to sin θ of the external magnetic field G ₂ can be superimposed in the same direction as.

Therefore, in the present invention, the current sensor is constructed so that the MR element located between the slits of the iron core can be rotated in the direction parallel to the external magnetic field G ₂ . This is
By rotating the MR element by the “angle at which the linearity L is minimized” obtained from the correlation diagram between the rotation angle of the MR element and the output curve of the current sensor, which is experimentally obtained in advance, a straight line is obtained. This means that it is possible to realize a current sensor that minimizes the property L.

Therefore, the linearity can be improved more than in the prior art, and the current sensor with high detection accuracy can be easily constructed.

[0023]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a diagram showing the principle of construction of a current sensor according to the present invention, FIG. 2 is a diagram for explaining the relationship between the MR element rotation angle and the current sensor output, and FIG. 3 is an MR element rotation angle and sensor. FIG. 4 is a diagram for explaining the relationship with the output linearity, FIG. 4 is a diagram showing a configuration example of a current sensor according to the present invention, FIG. 5 is a diagram showing another embodiment, and FIG. 6 is a diagram showing a third embodiment. is there.

In each of the figures, the case where the current sensor described in FIG. 7 is used as an example is shown. Therefore, the same reference numerals and symbols are given to the same target members and parts as in FIG. Omit it.

In FIG. 1 in which only the main part as the current sensor is extracted, the slit 12 of the iron core 12 around which the coil 11 is wound.
Although the MR element 13 described in FIG. 7 is arranged in a,
In particular, the MR element 13 in this case can rotate in the left and right directions of the paper with the magnetoresistive pattern forming region as the center.

Therefore, the MR initially located at the position indicated by the broken line B
When the element 13 is rotated clockwise by an angle θ, the state shown by the solid line in the drawing can be obtained. The said MR element 13 at this time, sin [theta content i.e. of the external magnetic field G ₂ are generated between the slits 12a to the bias magnetic field G ₁ described in FIG. 7 "G ₂ · sin
Since θ ”is superimposed, the bias magnetic field G ₁ of the MR element 13 can be set to“ G ₁ + G ₂ · sin θ ”.

Therefore, by freely changing the rotation angle θ in the ± directions, the bias magnetic field applied to the MR element 13 can be freely changed as a result. Horizontal axis X shows current value I
2 where the vertical axis Y is the output V of the MR element and FIG.
It shows the relationship between the verification current value and the output of the current sensor when is changed.

In a partially enlarged view, the alternate long and short dash line indicates the angle θ.
Is −7 °, the dotted line is the angle θ of 0 °, and the solid line is the angle θ +
7 °, the broken line represents each output V ₂ when the angle θ is + 20 °.

In this case, as is clear from the figure, the MR element 13
Output V as a current sensor by changing the rotation angle θ of
Can be changed, which means that the linearity L described in FIG. 8 can be changed by the rotation angle θ.

Therefore, by appropriately setting the rotation angle θ, it is possible to construct a current sensor which has a good followability with respect to the output V from the MR element 13, in other words, a linear output.

In FIG. 3 in which the horizontal axis X is taken as the test current value I and the vertical axis Y is taken as the linearity L in%, the shaded area corresponds to FIG. 2 and the rotation angle θ of the MR element 13 is -7. When the angle θ is 0 °, the following shows the angle θ = +
7 ° represents the case where the angle θ = + 20 °, respectively.

In this case, in order to improve the linearity L, it is desirable to set the angle of the region as close to the "0" line of the Y axis as possible. For example, in order to set the linearity within ± 0.5%, the MR element 13 described above is used. It can be seen that the rotation angle θ of is set within the range of 7 to 20 °.

FIG. 4 showing the configuration of the current sensor according to the present invention.
Here, (4-1) is an overall perspective view, and (4-2) is a side sectional view. In the figure, the current sensor 2 is a circuit board with the coil 11 wound.
It is composed of a U-shaped iron core 21 fixed to 14 and an MR element 22 arranged in a central region on a line connecting both ends of the iron core 21.

The coil 11 has external connection terminals 111 whose both ends are erected in the margin of the circuit board 14 as in FIG.
a, 111b, the external connection terminals 111a,
By connecting the signal line on the circuit side for detecting the current value to 111b, an external magnetic field having a strength corresponding to the current value is provided between both ends of the iron core 21.
Generation of G ₂ is the same as in FIG. 7.

In particular, the MR element 22 in this case is the same as the MR element 13 of FIG. 7, but the free end of the connection terminal 135 is so arranged that the mounting on the circuit board 14 can bend in the region of the external connection terminal 135. It is mounted on the substrate 14 only at the side tip.

Reference numeral 15 on the substrate 14 is the signal processing IC described in FIG. Therefore, for example, as shown by arrow C, the M
By pressing the R element 22 from its side, the MR element 22
Can be tilted with respect to the U-shaped iron core 21 like the MR element 13 in FIG.

Therefore, when the MR element 22 is rotated within its magnetoresistive pattern forming surface and within the appropriate angular range obtained in FIG. 3, the MR element 22 is biased by a bias magnetic field G ₁ and an external magnetic field G _2. Since the magnetic field “G ₂ · sin θ” related to the magnetic field is superposed, as a result, the current sensor 2 which can obtain the output V ₂ with good linearity by following the output V ₁ from the MR element 22 is realized. Can be made.

In this case, the U-shaped iron core of the MR element 22 in this case
The rotation with respect to 21 does not necessarily have to be performed centering on the magnetoresistive pattern forming region of the MR element 22, and even if it is bent in the external connection terminal region and inclined relative to the U-shaped iron core 21 as shown in FIG. The effect can be obtained.

FIG. 5 showing another example of the configuration is intended to facilitate rotation of the MR element. (5-1) is an overall perspective view, (5-)
2) is a side sectional view thereof. As shown in FIG. 4, the current sensor 3 includes a U-shaped iron core 21 fixed to a circuit board 31 in a state in which a coil 11 connected to the external connection terminals 111a and 111b is wound, and a central area on a line connecting both ends of the U-shaped iron core 21. The MR element 13 described in FIG. 7 is fixedly mounted on the circular circuit board 32 that is rotatably mounted on the circuit board 31.

In particular, the circular circuit board 32 on which the MR element 13 in this case is fixedly mounted is mounted on the circuit board 31 via a circular bush 33 made of, for example, resin or the like. The conductor patterns on the circular circuit board 32 connected to the external connection terminals 135 of
A reference numeral 32 is connected to a predetermined connection electrode of the circuit board 31 via a wiring member 34 having a sufficient extra length to rotate about the reference position in the horizontal direction by about 45 °.

Therefore, the circular circuit board 32 and thus the MR element 13 is arranged in the U-shaped iron core 21 within a range in which the extra length of the wiring member 34 can be consumed, that is, in the range of about 45 ° to the left and right around the reference position.
Can be rotated against.

Therefore, by rotating the MR element 13 together with the circular circuit board 32, a state similar to that shown in FIG. 1 can be obtained, and the output V ₁ from the MR element 13 can be followed to obtain an output V with good linearity. _The current sensor 3 that obtains ₂ can be realized.

In the figure, since the iron core 21 and the MR element 13 are mounted on the same circuit board 31, the element 13 is rotated in a direction parallel to the circuit board 31, but the element 13 is rotated by its magnetic field. If the condition of rotating along the resistance pattern forming surface is satisfied, the same effect can be obtained even if it is not parallel to the circuit board 31.

FIG. 6 showing the third embodiment illustrates the case where an iron core is rotated instead of the MR element.
1) is an overall perspective view, and (6-2) is a plan view of (6-1). That is, in the figure, the current sensor 4 can rotate with respect to the circuit board 41 in a state in which the coil 11 connected to the external connection terminals 111a and 111b by the wiring members 112a and 112b having a sufficient extra length is wound, as in FIG. The U-shaped iron core 21 fixed to the rotating plate 42 and the MR element 13 fixedly mounted on the circuit board 31 in the central region on the line connecting the both ends of the MR element 13 described with reference to FIG.

In particular, the rotary plate 42 to which the U-shaped iron core 21 in this case is fixed is mounted on the circuit board 41 via a circular bush made of, for example, resin as in FIG. The rotation of the U-shaped iron core 21 in the range of about 45 ° to the left and right with respect to the center can be ensured by consuming the extra length region of the wiring members 112a and 112b.

Therefore, by rotating the U-shaped iron core 21 together with the rotary plate 42, the same state as that shown in FIG. 1 can be obtained, and the output V ₁ from the MR element 13 can be followed to obtain an output with good linearity.
The current sensor 4 that can obtain V ₂ can be configured.

It is obvious that a current sensor capable of suppressing the disturbance magnetic field can be obtained by covering the circumference of each current sensor described in FIGS. 4 to 6 with a magnetic material such as permalloy.

[0048]

As described above, according to the present invention, it is possible to provide a current sensor in which the linearity of the relationship graph between the test current value and the sensor output within the measured current value range is improved to improve the current detection accuracy. You can

In the description of the present invention, the case where the U-shaped iron core is used is taken as an example, but the present invention is not necessarily limited to the U-shaped iron core, and the MR element can rotate in the external magnetic field generating region, that is, the magnetic flux collecting end region. It is obvious that the same effect can be obtained even if the iron core has another shape such as a "U" shape if the space can be secured.

[Brief description of drawings]

FIG. 1 is a diagram showing a configuration principle of a current sensor according to the present invention.

FIG. 2 is a diagram illustrating a relationship between an MR element rotation angle and a current sensor output.

FIG. 3 is a diagram illustrating a relationship between an MR element rotation angle and sensor output linearity.

FIG. 4 is a diagram showing a configuration example of a current sensor according to the present invention.

FIG. 5 is a diagram showing another embodiment.

FIG. 6 is a diagram showing a third embodiment.

FIG. 7 is a diagram schematically illustrating a configuration of a conventional current sensor.

FIG. 8 is a diagram illustrating a problem in a conventional current sensor.

[Explanation of symbols]

2,3,4 Current sensor 11 Coil 12,21 Iron core 12a Slit 13,22 Magnetoresistive element 14,31,41 Circuit board 15 Signal processing IC 15a, 15b External connection electrode 32 Circular circuit board 33 Circular bush 34,112a, 112b Wiring material 42 Rotating plate 111a, 111b, 135 External connection terminal

Continued Front Page (72) Inventor Narisei Tanji 1015 Kamiodanaka, Nakahara-ku, Kawasaki-shi, Kanagawa Fujitsu Limited

Claims (2)

[Claims] 1. An iron core having a coil and a magnetic flux collecting end portion around which the coil is wound, and a magnetic field generated between the magnetic flux collecting end portions and having a bias magnetic field perpendicular to the magnetic field between the magnetic flux collecting end portions of the iron core. And at least a magnetoresistive element arranged in
A current sensor for detecting a test current value from a magnetic field having a strength corresponding to the test current value generated between the magnetic flux collecting ends of the iron core when a test current is applied to the coil, The magnetoresistive element (13) or the iron core (12) arranged between the magnetism collecting ends of (12) has a magnetic field direction generated between the magnetism collecting ends of the iron core (12) and the magnetoresistive element (13). (3) A current sensor characterized by comprising means capable of tilting in a direction in which the angle orthogonal to the bias magnetic field direction of (1) can be changed. 2. A current sensor characterized in that an angle range in which the magnetoresistive element or the iron core according to claim 1 can be tilted is approximately 90 degrees when left and right are distributed around an orthogonal position.