JP2015155796A - current sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a current sensor capable of precisely measuring a current flowing on a current path in a non-contact manner even when external magnetic field exists while reducing the size.

SOLUTION: The current sensor includes magnetic resistance elements 23 and 25 and magnets 24 and 26 which are disposed symmetrically with respect to a current path 22 and parallel to each other being interposed by the current path 22. The current sensor is arranged so that a direction of the magnet 24 from the N-pole to the S-pole and a direction of the magnet 26 from the S-pole to the N-pole coincide with a flowing direction of the detected current.

COPYRIGHT: (C)2015,JPO&INPIT

Description

  The present invention relates to a current sensor that measures a current to be measured by detecting a magnetic field generated around a current line through which the current to be measured flows.

  In recent years, there has been a demand for a current sensor for accurately measuring a large current on the order of several tens of A to several hundred A, such as a charge / discharge current of a battery of a hybrid car, an EV car, or the like, or a drive current of an electric motor. FIG. 7 is a plan view showing a schematic configuration of a conventional current sensor. When the XYZ coordinates are taken as shown in the figure, the current sensor 1 includes a substrate 2 placed parallel to the XY plane, and the substrate 2 has slits 3 penetrating the front surface 2a and the back surface 2b of the substrate 2. Is formed. A plate-like current path 4 through which the detected current I flows is inserted into the slit 3. The direction of the current I to be measured flowing through the current path 4 is the negative direction of the Z axis, that is, the direction penetrating perpendicularly from the front surface to the back surface of the paper. FIG. 8 is an explanatory diagram of the magnetic flux density vector acting on the current sensor.

  Magnetoresistive elements 5 a and 6 a are attached to the surface 2 a of the substrate 2. The magnetoresistive elements 5 a and 6 a are provided at symmetrical positions with respect to the current path 4. On the back surface 2b of the substrate 2, a bias magnet 5b for applying a bias magnetic field to the magnetoresistive element 5a and a bias magnet 6b for applying a bias magnetic field to the magnetoresistive element 6a are attached. The magnetoresistive element 5a is disposed directly above the bias magnet 5b with the substrate 2 interposed therebetween, and the magnetoresistive element 6a is disposed directly above the bias magnet 6b with the substrate 2 interposed therebetween. The area of the cross section of each bias magnet 5b, 6b is made larger than the area of the cross section of the magnetoresistive element arranged immediately above. In addition, the bias magnets 5b and 6b are arranged with the N poles facing each other.

  The magnetoresistive elements 5a and 6a are provided with magnetoresistors Ra and Rb constituting a half bridge circuit, respectively. Each magnetoresistor is formed on the same substrate surface. Further, the easy axis of magnetization (direction of current flow) of each magnetoresistance is the same as the direction of formation of each magnetoresistance, and each easy magnetization axis is parallel to the substrate surface. Further, each of the magnetic resistances Ra and Rb is arranged such that the easy axis of magnetization and the direction of the detected current I form 45 °. The magnetic resistance Ra and the magnetic resistance Rb in the magnetoresistive element 5a are connected at a connection point 7a, one end of the magnetic resistance Ra is connected to the ground, and one end of the magnetic resistance Rb is connected to the power source Vcc. Further, in the magnetoresistive element 6a, the magnetic resistance Ra and the magnetic resistance Rb are connected at a connection point 7b, one end of the magnetic resistance Ra is connected to the ground, and one end of the magnetic resistance Rb is connected to the power source Vcc. The connection points 7a and 7b are connected to input terminals of a differential amplifier (not shown).

In FIG. 8A, a magnetic flux density vector Bm1 from the bias magnet 5b is applied to the magnetoresistive element 5a in the positive direction of the Y axis, and a magnetic flux density vector Bm2 from the bias magnet 6b is applied to the magnetoresistive element 6a. It is applied in the negative direction of the Y axis. When the current I to be measured does not flow through the current path 4, the resistance values of the magnetic resistances Ra and Rb are uniformly reduced by the action of the magnetic flux density vectors Bm1 and Bm2. As a result, the full bridge circuit composed of the magnetoresistive elements 5a and 6a is balanced, so that the output V _{OUT of the} differential amplifier remains at a so-called zero point potential of Vcc / 2, for example.

  When the current I to be measured flows through the current path 4, a magnetic flux density vector Bc1 that is directed in the positive direction of the X axis is further applied to the magnetoresistive element 5a. Thereby, the magnetic flux density vector Bm1 of the magnetic flux density vector Bm1 from the bias magnet 5b and the magnetic flux density vector Bc1 by the measured current I is applied to the magnetoresistive element 5a. The resultant magnetic flux density vector B1 forms an angle θ with the magnetic flux density vector Bm1. Similarly, when the current I to be measured flows, the magnetic flux density vector Bc2 is further applied to the magnetoresistive element 6a in the negative direction of the X axis. Thereby, the combined magnetic flux density vector B2 of the magnetic flux density vectors Bm2 and Bc2 is applied to the magnetoresistive element 6a. The resultant magnetic flux density vector B2 forms an angle θ with the magnetic flux density vector Bm2. At this time, the magnitude of the magnetic flux density vector Bm1 is substantially uniform in the magnetoresistive element 5a, but the magnitudes of the magnetic flux density vectors Bc1 and Bc2 become smaller in inverse proportion to the distance from the current path 4.

  The magnetoresistive elements 5a and 6a have the same magnitude of the magnetic flux density vectors Bm1 and Bm2, and the magnitudes of the magnetic flux density vectors Bc1 and Bc2 at positions symmetrical to the current path 4 in the magnetoresistive elements 5a and 6a. It is comprised so that it may become the same. For this reason, the resultant magnetic flux density vectors B1 and B2 at positions symmetrical with respect to the current path 4 in the magnetoresistive elements 5a and 6a, for example, the centers of the magnetoresistive elements 5a and 6a, are the same in size and different in direction by 180 degrees. Therefore, the sum of both composite magnetic flux density vectors becomes zero.

When the detected current I increases, the magnetic flux density vectors Bc1 and Bc2 increase, so that the phase θ increases and the combined magnetic flux density vectors B1 and B2 increase. For this reason, the resistance value of the magnetic resistance Ra of the magnetoresistive element 5a increases, and the resistance value of the magnetic resistance Rb decreases. As a result, the potential at the connection point 7a increases. Further, the resistance value of the magnetoresistor Ra of the magnetoresistive element 6a decreases, and the resistance value of the magnetoresistor Rb increases. As a result, the potential at the connection point 7b decreases. As a result, the full bridge circuit composed of the magnetoresistive elements 5a and 6a is unbalanced, and the output V _{OUT of the} differential amplifier becomes V1, which is larger than the zero point potential of Vcc / 2, for example.

When the detected current I decreases, the magnetic flux density vectors Bc1 and Bc2 decrease, so that the phase θ decreases and the combined magnetic flux density vectors B1 and B2 decrease. As a result, the output V _{OUT of the} differential amplifier becomes V2 (V2 <V1) which is larger than the zero point potential of Vcc / 2, for example. Thus, the measured current I flowing in the current path 4 from the output V _{OUT of the} differential amplifier can be detected.

Next, consider a case where a uniform external density vector Bex is applied to the magnetoresistive elements 5a and 6a. For simplicity, it is assumed that the current I to be measured does not flow in the current path 4 and the external magnetic field density vector Bex is applied in the positive direction of the X axis as shown in FIG. 8B. At this time, although the magnitudes of the combined magnetic flux density vectors B1 and B2 are equal, the combined magnetic flux density vector B1 advances by a phase α with respect to the magnetic flux density vector Bm1, and the combined magnetic flux density vector B2 has a phase α with respect to the magnetic flux density vector Bm2. Will be delayed only. For this reason, the resistance value of the magnetic resistance Ra of the magnetoresistive element 5a increases, and the resistance value of the magnetic resistance Rb decreases. As a result, the potential at the connection point 7a increases. However, the resistance value of the magnetoresistor Ra of the magnetoresistive element 6a increases and the resistance value of the magnetoresistor Rb decreases. As a result, the potential at the connection point 7b increases. As a result, the full bridge circuit composed of the magnetoresistive elements 5a and 6a maintains a balanced state, so that the output V _{OUT of the} differential amplifier remains at a so-called zero point potential of Vcc / 2, for example.

  That is, this current sensor is capable of forming a current that flows in the current path without contact without causing an error in the current value of the current I to be measured even when an external magnetic field is present. .

  As prior art document information related to the invention of this application, for example, Patent Document 1 is known.

JP 2011-242270 A

  However, in the above-described conventional current sensor, the magnetic detection elements 5a and 6a are arranged in a plane (XY plane) perpendicular to the current I to be measured flowing through the current path 4, so that the Y axis direction of the current sensor is There was a problem that the size would increase. In addition, the magnetic detection elements 5a and 6a are arranged in a plane perpendicular to the current I to be measured flowing through the current path 4, and the magnetic resistances Ra to Rd have 45 axes of easy magnetization and directions of the current I to be detected. Since it is necessary to dispose the magnetic detecting elements 5a and 6a, there is a limit to disposing the magnetic detection elements 5a and 6a close to the current path 4. Therefore, it is difficult to effectively capture the magnetic field generated by the current I to be measured flowing in the current path 4, and there is a problem that the S / N of current measurement is lowered. Furthermore, since the magnetic flux density generated by the measured current I flowing in the current path 4 decreases in inverse proportion to the distance from the current path, the magnetic flux density in the magnetic detection elements 5a and 6a is not uniform. For this reason, if there is variation in the positions of the magnetic resistances Ra to Rd, an error occurs in the resistance change of the bridge circuit composed of the magnetic detection elements 5a and 6a, and an error occurs in the measured current value. .

  The present invention solves the above-mentioned conventional problems, can reduce the shape, and can effectively detect the magnetic field generated by the current I to be measured flowing in the current path to increase the S / N ratio. Furthermore, the restriction on the position in the plane of the magnetic detection element constituting the magnetoresistive element can be eliminated, and even when an external magnetic field exists, no error occurs in the current value of the current I to be measured. An object of the present invention is to provide a current sensor capable of accurately measuring a current flowing in a current path in a non-contact manner.

  In order to achieve the above object, the present invention has the following configuration.

  The invention according to claim 1 is characterized in that the first and second magnetoresistive elements arranged with a current path interposed therebetween, first magnetic field generating means for applying a bias magnetic field to the first magnetoresistive element, and the first A second magnetic field generating means for applying a bias magnetic field to the second magnetoresistive element, and configured to detect a current flowing through the current path from output signals of the first and second magnetoresistive elements. A direction from the center of the N pole of the first magnetic field generating means toward the center of the S pole coincides with the direction in which the current to be detected flows, and the center of the S pole of the second magnetic field generating means Are arranged so that the direction from the first to the center of the N pole coincides with the direction in which the current to be detected flows, and the plane including the magnetoresistance of the first magnetoresistance element and the magnetoresistance of the second magnetoresistance element The plane including the current path The distance between the plane including the magnetoresistance of the first magnetoresistive element and the current path is arranged in parallel, and the distance between the plane including the magnetoresistance of the second magnetoresistive element and the current path is With this configuration, the size of the current sensor in the Y-axis direction can be reduced, and the magnetoresistive element can be placed close to the current path, so that the device under test flowing in the current path The magnetic field generated by the current I can be effectively detected to increase the S / N ratio, and the magnetic flux density generated by the measured current I flowing in the current path is constant in the magnetoresistive element. The restriction on the position in the plane of the magnetic detection element that constitutes the resistance element can be eliminated, and even if an external magnetic field exists, no error occurs in the current value of the current I to be measured, and no contact is made. At And it has a effect that the current flowing through the road can be accurately measured.

  The invention according to claim 2 is the one in which the first and second magnetic field generating means are in particular thin film magnets, and according to this configuration, a more uniform and high magnetic flux density can be given to the magnetoresistive element. In addition, it can be integrally formed on the magnetic detection element, and has an effect that an extremely small current sensor can be realized.

  As described above, according to the present invention, the first and second magnetoresistive elements arranged with the current path interposed therebetween, the first magnetic field generating means for applying a bias magnetic field to the first magnetoresistive element, and the second And a second magnetic field generating means for applying a bias magnetic field to the magnetoresistive element, and configured to detect a current flowing through the current path from output signals of the first and second magnetoresistive elements. The direction from the center of the N pole to the center of the S pole of the first magnetic field generating means coincides with the direction in which the detected current flows, and from the center of the S pole of the second magnetic field generating means. The direction toward the center of the N pole is arranged so as to coincide with the direction in which the detected current flows, and the plane including the magnetoresistance of the first magnetoresistance element and the magnetoresistance of the second magnetoresistance element are The plane including the current path and And the distance between the current path and the plane including the magnetoresistance of the first magnetoresistive element is equal to the distance between the plane including the magnetoresistance of the second magnetoresistive element and the current path. With the same configuration, the shape can be reduced, the magnetic field generated by the current I to be measured flowing in the current path can be detected effectively, the S / N ratio can be increased, and the magnetoresistive element is further configured The restriction on the position of the magnetic detecting element in the plane can be eliminated, and even if an external magnetic field exists, the current value of the current I to be measured does not generate an error and flows in the current path without contact. This provides an excellent effect that a current sensor capable of accurately measuring current can be provided.

(A) Sectional drawing which shows the structure of the current sensor in Embodiment 1 of this invention, (b) Side view which shows the structure of the same current sensor (A) Plan view of the first magnetoresistive element, (b) Plan view of the second magnetoresistive element (A) Sectional view showing the configuration of an experimental apparatus for confirming the effect of the present invention, (b) Side view showing the configuration of the experimental apparatus (A) Top view of the first magnetoresistive element, (b) Cross section of the magnetoresistive element (A) The figure which shows the measurement data which show the output change rate of the adder when the magnetic flux density of the external magnetic field of X-axis direction is applied, (b) The adder when the magnetic flux density of the external magnetic field of Z-axis direction is applied Of measured data showing the rate of change in output (A) The top view of the magnetoresistive element in the current sensor in Embodiment 2 of this invention, (b) Sectional drawing of the same magnetoresistive element The top view which shows schematic structure of the conventional current sensor (A), (b) Explanatory drawing of the magnetic flux density vector which acts on the same current sensor

(Embodiment 1)
Hereinafter, the first aspect of the present invention will be described with reference to the drawings using the first embodiment. FIG. 1A is a cross-sectional view showing the configuration of the current sensor 21 according to Embodiment 1 of the present invention, and FIG. 1B is a side view showing the configuration of the current sensor 21. In FIGS. 1A and 1B, when XYZ coordinates are taken as shown in the figure, 22 is a current path extending in the Z-axis direction, and is made of a good conductor such as copper. A detected current I flows in the current path 22 in the negative direction of the Z axis. A first magnetoresistive element 23 and a first magnet 24 for applying a bias magnetic field to the first magnetoresistive element 23 are provided above the current path 22, that is, in the positive direction of the Y axis. It is arranged right above. A second magnetoresistive element 25 and a second magnet 26 for applying a bias magnetic field to the second magnetoresistive element 25 are provided below the current path 22, that is, in the negative direction of the Y axis. It is arranged immediately below. The direction from the center of the N pole of the first magnet 24 to the center of the S pole coincides with the direction in which the detected current I flows, and the direction from the center of the S pole of the second magnet to the center of the N pole It arrange | positions so that it may correspond with the direction through which to-be-detected current flows. A magnetic field 27 is generated around the current path 22 by the measured current I flowing in the current path 22. Further, 28 and 29 are magnetic fields generated around the first and second magnets 24 and 26, respectively.

  2A and 2B are plan views of the first and second magnetoresistive elements 23 and 25, respectively. The first and second magnetoresistive elements 23 and 25 include magnetic resistors 30a, 30b, 30c, and 30d that constitute a full bridge circuit, respectively. Reference numeral 31 denotes an insulating substrate such as ceramic, and the magnetic resistors 30a, 30b, 30c, and 30d are formed on the same substrate surface. The magnetic resistors 30a, 30b, 30c, and 30d are magnetoresistive thin films having a thickness of about 0.1 μm made of a ferromagnetic material such as Ni—Co. The magnetoresistors 30a and 30b and the magnetoresistors 30c and 30d are connected in series, and the longitudinal directions of the patterns, which are perpendicular to the magnetosensitive direction, are orthogonal to each other and 45 ° with respect to the direction of the detected current I. It is arranged to make. In the first magnetoresistive element 23, the magnetic resistance 30 a and the magnetic resistance 30 b are connected at a connection point 32, and the magnetic resistance 30 c and the magnetic resistance 30 d are connected at a connection point 33. The other ends of the magnetic resistance 30a and the magnetic resistance 30d are connected to the power supply Vcc, and the other ends of the magnetic resistance 30b and the magnetic resistance 30c are connected to the ground. Similarly, in the second magnetoresistive element 25, the magnetic resistance 30a and the magnetic resistance 30b are connected at the connection point 34, and the magnetic resistance 30c and the magnetic resistance 30d are connected at the connection point 35. The other ends of the magnetic resistance 30a and the magnetic resistance 30d are connected to the power supply Vcc, and the other ends of the magnetic resistance 30b and the magnetic resistance 30c are connected to the ground. The connection points 32 and 33 are connected to an input terminal of a first differential amplifier (not shown). Further, the connection points 34 and 35 are connected to an input terminal of a second differential amplifier (not shown). Further, the outputs of the first differential amplifier and the second differential amplifier are input to an adder (not shown).

  The plane including the magnetic resistances 30a, 30b, 30c, and 30d of the first magnetoresistance element 23, that is, the substrate surface, and the plane including the magnetic resistances 30a, 30b, 30c, and 30d of the second magnetoresistance element 25, that is, the substrate surface, are The distance between the current path 22 and the plane including the magnetic resistances 30 a, 30 b, 30 c, 30 d of the first magnetoresistive element 23 and the current path 22 is arranged in parallel to the current path 22. It arrange | positions so that it may become equal to the distance of the plane containing the magnetoresistors 30a, 30b, 30c, and 30d, and the electric current path 22. FIG.

  At this time, the center of the first magnetoresistive element 23 and the center of the first magnet 24 are arranged coaxially and close to each other, and the center of the second magnetoresistive element 25 and the first magnet It is desirable to arrange the two magnets 26 so that the centers of the two magnets 26 are coaxial and close to each other. By comprising in this way, the said 1st and 2nd magnetoresistive elements 23 and 25 can be given uniform and high magnetic flux density, and the electric current which flows into an electric current path can be measured with a further high precision.

  With reference to FIG. 2 (a) (b), operation | movement of the current sensor 21 in Embodiment 1 of this invention is demonstrated. In FIG. 2, the magnetic flux density vector Bm1 from the first magnet 24 is applied to the first magnetoresistive element 23 in the positive direction of the Z axis, and the second magnetoresistive element 25 is applied from the second magnet 26. A magnetic flux density vector Bm2 is applied in the negative direction of the Z axis.

When the current I to be measured is not flowing through the current path 22, the resistance values of the magnetic resistors 30a, 30b, 30c, and 30d are uniformly reduced by the action of the magnetic flux density vectors Bm1 and Bm2. At this time, if the product of the resistance values of the magnetic resistances 30a and 30c and the product of the resistance values of the magnetic resistances 30b and 30d are set to be equal to each other, the full configuration of the magnetic resistances 30a, 30b, 30c, and 30d is established. Since the bridge circuit is balanced, the outputs V _OUT1 and V _OUT2 of the first and second differential amplifiers are zero. The output of the adder that adds the outputs V _OUT1 and V _OUT2 of the first and second differential amplifiers remains at the so-called zero point potential of Vcc / 2, for example.

  When the current to be measured I flows through the current path 22, a magnetic flux density vector Bc1 that is directed in the positive direction of the X axis is further applied to the first magnetoresistive element. As a result, the magnetic flux density vector Bm1 from the first magnet 24 and the combined magnetic flux density vector B1 of the magnetic flux density vector Bc1 due to the measured current I are applied to the first magnetoresistive element 23. The resultant magnetic flux density vector B1 forms an angle θ1 with the magnetic flux density vector Bm1. Similarly, when the measured current I flows, the magnetic flux density vector Bc2 is further applied to the second magnetoresistive element 25 in the negative direction of the X axis. Thereby, the combined magnetic flux density vector B2 of the magnetic flux density vectors Bm2 and Bc2 is applied to the second magnetoresistive element 25. The resultant magnetic flux density vector B2 forms an angle θ2 with the magnetic flux density vector Bm2. Here, the strength of the first magnet 24, the strength of the second magnet 26, the first magnet 24 and the first magnet so that the magnitude of the magnetic flux density vector Bm1 matches the magnitude of the magnetic flux density vector Bm2. The distance between the resistance element 23 and the distance between the second magnet 26 and the second magnetoresistance element 25 are adjusted. Further, as described above, the plane including the magnetoresistances 30a, 30b, 30c, and 30d of the first magnetoresistance element 23 and the plane including the magnetoresistances 30a, 30b, 30c, and 30d of the second magnetoresistance element 25 are currents. The distance between the current path 22 and the plane including the magnetic resistances 30 a, 30 b, 30 c, 30 d of the first magnetoresistive element 23 and the current path 22 is arranged in parallel with the path 22. , 30b, 30c, and 30d are arranged so as to be equal to the distance between the current path 22 and the plane including the current path 22, the magnitudes of the magnetic flux density vectors Bc1 and Bc2 are respectively the first and second magnetoresistive elements 23, It is constant in the plane of 25 and is equal to each other. For this reason, the resultant magnetic flux density vectors B1 and B2 in the planes of the first and second magnetoresistive elements 23 and 25 have the same magnitude and different directions by 180 degrees.

When the detected current I increases, the magnetic flux density vectors Bc1 and Bc2 increase, so that the resistance values of the magnetic resistances 30a and 30c of the first magnetoresistive element 23 decrease and the resistance values of the magnetic resistances 30b and 30d increase. . As a result, the potential at the connection point 32 increases and the potential at the connection point 33 decreases. As a result, the balance of the full bridge circuit is lost, and the output V _OUT1 of the first differential amplifier is generated. Similarly, the resistance values of the magnetic resistors 30a and 30c of the second magnetoresistive element 25 are decreased, and the resistance values of the magnetic resistors 30b and 30d are increased. As a result, the potential at the connection point 34 increases and the potential at the connection point 35 decreases. As a result, the balance of the full bridge circuit is lost, and an output V _OUT2 having the same sign as the output V _OUT1 of the first differential amplifier is generated at the output of the second differential amplifier. The output of the adder that adds the outputs V _OUT1 and V _OUT2 of the first and second differential amplifiers becomes V1, which is larger than the so-called zero point potential of Vcc / 2, for example.

When the detected current I decreases, the magnetic flux density vectors Bc1 and Bc2 decrease, so that the combined magnetic flux density vectors B1 and B2 decrease. As a result, the output V _OUT1 of the first differential amplifier and the output V _OUT2 of the second differential amplifier are reduced. The output of the adder that adds the outputs V _OUT1 and V _OUT2 of the first and second differential amplifiers becomes V2 (V2 <V1), which is larger than the zero point potential of Vcc / 2, for example. Thus, the measured current I flowing in the current path 22 from the output of the adder can be detected.

Next, a case where a uniform external density vector Bex is applied to the first and second magnetoresistive elements 23 and 25 will be considered. At this time, due to the action of the external density vector Bex, the balance of the full bridge circuit of the first magnetoresistive element 23 is lost, and an increase of ΔV1 occurs in the output V _OUT1 of the first differential amplifier. Similarly, due to the action of the external density vector Bex, the balance of the full bridge circuit of the second magnetoresistive element 25 is lost, and an increment of ΔV2 occurs in the output V _OUT2 of the second differential amplifier. However, since the sign of the increment ΔV1 and the sign of the increment ΔV2 are different, the output of the adder remains at a so-called zero point potential of Vcc / 2, for example.

  That is, this current sensor is capable of forming a current that flows in the current path without contact without causing an error in the current value of the current I to be measured even when an external magnetic field is present. .

  FIG. 3A is a sectional view showing the configuration of an experimental apparatus for confirming the effect of the present invention, and FIG. 3B is a side view showing the configuration of the experimental apparatus.

  3A and 3B, when the XYZ coordinates are taken as shown in the figure, reference numeral 40 denotes a current path extending in the Z-axis direction, which is a copper round bar having a diameter of 3 mm. A detected current I flows in the current path 40 in the Z-axis direction. A first magnetoresistive element 41 and a first magnet 42 for applying a bias magnetic field to the first magnetoresistive element 41 are provided above the current path 40, that is, in the positive direction of the Y axis. It is arranged right above. A second magnetoresistive element 43 and a second magnet 44 for applying a bias magnetic field to the second magnetoresistive element 43 are provided below the current path 40, that is, in the negative direction of the Y axis. It is arranged immediately below. Reference numeral 45 denotes a magnetic field generated around the current path 40 by the measured current I flowing in the current path 40. Further, 46 and 47 are magnetic fields generated around the first and second magnets 42 and 44, respectively.

  The direction from the center of the N pole of the first magnet 42 to the center of the S pole coincides with the negative direction of the Z axis, and the direction from the center of the S pole of the second magnet to the center of the N pole is the Z axis. Arranged to match the negative direction. The first and second magnets 42 and 44 are so-called rubber magnets in which ferrite powder is kneaded and molded in rubber having a thickness of 3 mm □ and a thickness of 0.4 mm, and those having a surface magnetic flux density of 200 gauss are used.

The configuration of the first magnetoresistive element 41 used in this experiment will be described with reference to FIG. 4A is a top view of the first magnetoresistive element 41, and FIG. 4B is a longitudinal sectional view of FIG. 4A. Here, the lengths of the first magnetoresistive element 41 in the X-axis, Y-axis, and Z-axis directions are 3 mm, 0.8 mm, and 3 mm, respectively. In FIG. 4, four electrodes including a power application electrode 51, a first output electrode 52, a second output electrode 53, and a ground electrode 54 are formed on a ceramic insulating substrate 50. A meandering magnetoresistor 55 a made of a magnetoresistor is formed between the power application electrode 51 and the first output electrode 52. Similarly, between the first output electrode 52 and the ground electrode 54, between the power application electrode 51 and the second output electrode 53, and between the second output electrode 53 and the ground electrode 54, meandering shapes are respectively formed. Magnetic resistors 55b, 55c, and 55d are formed. By making such an electrical connection, the magnetic resistors 55a, 55b, 55c, and 55d constitute a bridge circuit. The magnetic resistors 55a, 55b, 55c, and 55d are magnetoresistive thin films having a thickness of about 0.1 μm made of a ferromagnetic material such as Ni—Co. In FIG. 4, the magnetoresistive 55a is located in the longitudinal direction of the meander pattern in the direction of 45 ° inclined obliquely to the right on the paper surface. The longitudinal direction of the meandering pattern is located in the direction of 45 ° inclined, and the angle between them is a right angle. The positional relationship between the magnetic resistance 55c and the magnetic resistance 55d is the same. Further, the positional relationship between the magnetic resistance 55a and the magnetic resistance 55c is the same. Here, the magnetosensitive directions of the magnetic resistors 55a, 55b, 55c, and 55d are directions perpendicular to the longitudinal direction of each meander pattern in the surface of the ceramic insulating substrate 50. Reference numeral 60 denotes an insulating layer made of a SiO ₂ thin film having a thickness of about 1 μm, and protects the magnetic resistances 55a, 55b, 55c, and 55d by covering the magnetic resistances 55a, 55b, 55c, and 55d. Since the configuration of the second magnetoresistive element 43 is the same as the configuration of the first magnetoresistive element 41, the description thereof is omitted. The first and second output electrodes 52 and 53 of the first magnetoresistive element 41 are connected to a first differential amplifier (not shown), and the first and second outputs of the second magnetoresistive element 43 are connected. The electrodes are connected to a second differential amplifier (not shown). The outputs of the first and second differential amplifiers are connected to an adder (not shown).

  The plane including the magnetic resistances 55 a, 55 b, 55 c and 55 d of the first magnetoresistive element 41, that is, the plane including the surface of the substrate 50 and the magnetic resistance of the second magnetoresistive element 43, that is, the substrate surface is parallel to the current path 40. In addition, the distance between the substrate surface of the first magnetoresistive element 41 and the current path 40 and the distance between the substrate surface of the second magnetoresistive element 43 and the current path 40 are both 1.76 mm.

  The entire experimental apparatus was placed at the axial center in the Helmholtz coil. Initially, when no current was applied to the Helmholtz coil and a 10 ampere current was passed through the current path 40, the output of the adder was 2.77 volts. At this time, the magnetic flux density of the current magnetic field applied to the first and second magnetoresistive elements 41 and 43 is about 0.2 mT. Next, the axial direction of the Helmholtz coil and the current direction of the current path 40 are orthogonal to each other, and a current of 10 amperes is passed through the current path 40, so that a current flows through the Helmholtz coil, that is, the X-axis direction of FIG. An external magnetic field directed in the same direction as the current magnetic field applied to the first and second magnetoresistive elements 41 and 43 was applied by the measured current I flowing in the current path 40.

  FIG. 5A shows the output change rate of the adder when the current flowing through the Helmholtz coil is adjusted to change the magnetic flux density of the external magnetic field facing the X-axis direction in FIG. 3 from 0 mT (Tesla) to 2 mT. Measurement data.

  Next, by making the axial direction of the Helmholtz coil coincide with the current direction of the current path 40 and flowing a current of 10 amperes through the current path 40, a current is passed through the Helmholtz coil, so that the Z-axis direction of FIG. An external magnetic field orthogonal to the current magnetic field 45 applied to the first and second magnetoresistive elements 41 and 43 was applied by the measured current I flowing in the current path 40.

  FIG. 5B shows the output change rate of the adder when the current flowing through the Helmholtz coil is adjusted to change the magnetic flux density of the external magnetic field facing the Z-axis direction in FIG. 3 from 0 mT (Tesla) to 2 mT. Measurement data.

  5A and 5B, the magnetic flux density of the current magnetic field 45 applied to the first and second magnetoresistive elements 41 and 43 by the measured current I = 10 amperes flowing in the current path 40 is about 0. The error voltage generated when an external magnetic field of 0.5 mT corresponding to 2.5 times 2 mT is applied is 0.05% or less, and an external magnetic field of 2 mT corresponding to 10 times the magnetic flux density of the current magnetic field is applied. Even when the measurement is performed, the error voltage generated is 0.15% or less, and even in the presence of an external magnetic field, the error generated in the current value of the current I to be measured is extremely small and non-contact. It was confirmed that the current flowing in the current path can be measured accurately.

  In the current sensor according to the first embodiment of the present invention, the plane including the magnetoresistance of the first magnetoresistance element 41 and the plane including the magnetoresistance of the second magnetoresistance element 43 are arranged in parallel with the current path 40. Therefore, the dimension in the Y-axis direction can be reduced. Further, since the magnetoresistive element can be disposed close to the current path 40, the S / N ratio can be increased by effectively detecting the magnetic field generated by the measured current I flowing in the current path. The first magnet 42 and the second magnet 44 are brought close to each other so that the north pole of the first magnet 42 and the south pole of the second magnet 44, and the south pole of the first magnet 42 and the second magnet 44. The first magnetoresistive element 41 and the second magnetoresistive element 43 can be easily attached to the current path 40 by utilizing the attractive force acting between the N poles. Furthermore, since the magnetic flux density generated by the current I to be measured flowing in the current path is constant in the magnetoresistive element, the effect of eliminating the restriction on the position of the magnetic sensing element constituting the magnetoresistive element in the plane is achieved. It is obtained. Furthermore, the distance between the plane including the magnetic resistance of the first magnetoresistive element 41 and the current path 40 is equal to the distance between the plane including the magnetic resistance of the second magnetoresistive element 43 and the current path 40. Even if an external magnetic field is present, the current value of the current I to be measured does not cause an error, and the current flowing in the current path can be accurately measured in a non-contact manner. The effect of being able to be obtained is obtained.

  In the current sensor of the first embodiment, the magnetic resistances 30a, 30b, 30c and 30d of the first and second magnetoresistive elements 23 and 25 are full-bridge connected. The same effect can be obtained by connecting the magnetic resistances of the magnetoresistive elements 23 and 25 to the half bridges.

(Embodiment 2)
Hereinafter, the second aspect of the present invention will be described with reference to the drawings. FIG. 6A is a plan view of a magnetoresistive element 71 used in the current sensor according to Embodiment 2 of the present invention. In addition, in this magnetoresistive element 71 in Embodiment 2 of this invention, what has the structure similar to the structure of the magnetoresistive element in Embodiment 1 of this invention mentioned above is attached | subjected the same code | symbol. The description is omitted. 6 (a) and 6 (b), the magnetoresistive element 71 in the second embodiment of the present invention is different from the magnetoresistive element 41 in the first embodiment of the present invention described above on the insulating layer 60 on the thin film magnet. This is the point where 61 is arranged. FIG. 6B is a cross-sectional view of the magnetoresistive element 71 used in the current sensor in the second embodiment.

In FIG. 6, the thin film magnet 61 is made of CoPt or the like having a thickness of about 0.6 μm. The thin film magnet 61 is formed on the insulating layer 60 by vapor deposition, sputtering, or the like, and then patterned by exposure and etching, thereby forming the magnetoresistive element. The elements 55a, 55b, 55c, and 55d are divided into a plurality of substantially rectangular parallelepipeds having a longitudinal direction in a direction that forms 45 degrees with the direction of magnetic sensing. Then, by applying a large magnetic field in the width direction of the plurality of substantially rectangular thin films, the substantially rectangular thin film is magnetized in the width direction, and the thin film magnet 61 can be obtained. Reference numeral 62 denotes a second insulating layer. The second insulating layer 62 is made of a SiO ₂ thin film having a thickness of about 1 μm, and protects the thin film magnet 61 by covering the thin film magnet 61. According to this configuration, the magnetoresistive element 71 can be given a more uniform and high magnetic flux density, and can be formed integrally on the magnetic detection element 71, so that an extremely small current sensor can be realized. It is.

  The current sensor according to the present invention can be reduced in size, can effectively detect the magnetic field generated by the current I to be measured flowing in the current path, and can increase the S / N ratio, and further configure the magnetoresistive element. In addition to eliminating restrictions on the position of the magnetic sensing element in the plane, there is no error in the current value of the current I to be measured even in the presence of an external magnetic field, and there is no contact with the current path. It has an effect that the flowing current can be accurately measured, and is particularly useful as a current detection device that detects a current in a vehicle, industrial equipment, or the like.

DESCRIPTION OF SYMBOLS 21 Current sensor 22 Current path 23 1st magnetoresistive element 24 1st magnet 25 2nd magnetoresistive element 26 2nd magnet 61 Thin film magnet

Claims (2)

First and second magnetoresistive elements arranged across the current path;
First magnetic field generating means for applying a bias magnetic field to the first magnetoresistive element;
Second magnetic field generating means for applying a bias magnetic field to the second magnetoresistive element,
A current sensor configured to detect a current flowing through the current path from output signals of the first and second magnetoresistive elements,
The direction from the center of the N pole to the center of the S pole of the first magnetic field generating means coincides with the direction in which the detected current flows;
The direction from the center of the S pole to the center of the N pole of the second magnetic field generating means is arranged so as to coincide with the flowing direction of the detected current.
The plane including the magnetoresistance of the first magnetoresistance element and the plane including the magnetoresistance of the second magnetoresistance element are arranged in parallel to the current path,
The distance between the plane including the magnetoresistance of the first magnetoresistive element and the current path is equal to the distance between the plane including the magnetoresistance of the second magnetoresistive element and the current path. Sensor. The current sensor according to claim 1, wherein the first and second magnetic field generating means are thin film magnets.

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