JP2013047610A - Magnetic balance type current sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a magnetic balance type current sensor with improved sensitivity capable of accurately sensing a target current even if the value of the current is close to zero.SOLUTION: A magnetic balance type current sensor includes: a magnetic sensor element 21 formed in a sensor chip 12 and arranged such that the output thereof changes in proportion to a target magnetic field Ha induced by a target current Ia flowing through a bus bar 11; an electromagnet 14 which generates a counter magnetic field Hb; a supply means 40, formed in a circuit chip 15, for supplying a counter current to the electromagnet 14; and a bias magnet 13 which generates a bias magnetic field Hc having a magnetic field component of constant magnitude and direction that is in parallel with the direction of the target magnetic field Ha acting on the magnetic sensor element 21. The magnetic sensor element 21 is a magnetoresistive effect element having a magnetic film thereon. The electromagnet 14 cancels out a composite magnetic field Hd, comprising the target magnetic field Ha and the bias magnetic field Hc, with the counter magnetic field Hb.

Description

  The present invention relates to a magnetic balance type current sensor.

  Conventionally, what is shown by patent document 1 is known as a magnetic balance type current sensor. This current sensor is fixed to the bus bar so that a first magnetic field (hereinafter referred to as a detected magnetic field) generated by the bus bar and a current flowing through the bus bar (hereinafter referred to as a detected current) is applied to the magnetic sensitive surface. And a second magnetic field (hereinafter referred to as a cancellation magnetic field) that is fixed to the bus bar so as to be close to the magnetic detection element and cancels the detected magnetic field applied to the magnetic sensing surface of the magnetic detection element. A coil (hereinafter referred to as an electromagnet). The detected current flowing in the bus bar is detected based on the current flowing in the electromagnet (hereinafter referred to as the canceling current) to generate the canceling magnetic field.

  Such a magnetic balance type current sensor can detect the current to be measured with higher accuracy than other general current sensors (shunt resistance method, current transformer method, magnetic proportional method).

JP 2008-215970 A

  By the way, although a Hall element and a magnetoresistive effect element can be considered as the magnetic detection elements constituting the magnetic balance type current sensor, the magnetoresistive effect element is more preferable in consideration of sensitivity. Of the magnetoresistive effect elements, the magnetoresistive effect element having a magnetic film formed using a magnetic metal is more preferable than the semiconductor magnetoresistive effect element.

  However, when a magnetoresistive effect element having a magnetic film is used as the magnetic detection element, although the sensitivity is high, magnetic hysteresis due to residual magnetization becomes a problem. Specifically, even if the current to be detected flows to the bus bar and the magnetic field to be detected acts on the magnetic sensing element, and then the current to be detected becomes zero, the magnetic field to be detected (external magnetic field) becomes zero. Magnetization remains in the magnetic film of the detection element. The magnetic hysteresis due to the residual magnetization is increased as the external magnetic field acting on the magnetic detection element is generated in a predetermined range from zero, and the magnitude of the external magnetic field is closer to zero.

  In the configuration of Patent Document 1, when the detected current becomes zero, the detected magnetic field, that is, the external magnetic field acting on the magnetic detection element becomes zero. However, a magnetic field is generated due to the residual magnetization of the magnetic film. For this reason, in order to cancel the magnetic field due to residual magnetization, a canceling current flows through the electromagnet. Therefore, an error occurs when the value of the detected current is near zero, the proportional relationship between the detected current and the cancellation current is shifted, and the detection accuracy of the detected current is lowered.

  The detected current takes a value of zero for a predetermined period in the measurement environment. For this reason, the external magnetic field is also zero for a predetermined period, and the canceling current also has an error for a predetermined period. As described above, the error occurs in the cancellation current for a predetermined period as compared to the case where the external magnetic field continuously changes and takes an instantaneous value of zero, thereby causing an instantaneous error in the cancellation current. This is not preferable in terms of detection accuracy of the detection current.

  In view of the above problems, an object of the present invention is to provide a magnetic balance type current sensor capable of detecting a detected current with high accuracy when the value of the detected current is near zero while improving sensitivity.

In order to achieve the above object, a magnetic balanced current sensor according to claim 1,
Magnetic detection elements (21) provided on one surface (11a) of the bus bar (11) so that the output changes according to the detected magnetic field (Ha) formed by the detected current (Ia) flowing through the bus bar (11). , 50) and
An electromagnet (14) which is provided on one surface (11a) of the bus bar (11) and generates a canceling magnetic field (Hb) for canceling the detected magnetic field (Ha) acting on the magnetic detection elements (21, 50);
Supply means (40) for supplying a canceling current for forming a canceling magnetic field (Hb) to the electromagnet (14),
The detected current (Ia) flowing through the bus bar (11) is detected based on the canceling current.

The magnetic detection elements (21, 50) are magnetoresistive elements having a magnetic film formed using a magnetic metal,
There is a magnetic field component provided on one surface (11a) of the bus bar (11) and parallel to the direction of the detected magnetic field (Ha) acting on the magnetic detection elements (21, 50), and the direction and size of the magnetic field component. Comprises a bias magnet (13) that generates a constant bias magnetic field (Hc),
The electromagnet (14) generates a magnetic field that cancels a combined magnetic field (Hd) of a detected magnetic field (Ha) and a bias magnetic field (Hc) as a canceling magnetic field (Hb).

  In the present invention, a magnetoresistive effect element having a magnetic film is used as the magnetic detection element (21, 50). For this reason, the sensitivity of the sensor can be improved as compared with a configuration using a Hall element or a semiconductor magnetoresistive effect element.

  Further, a bias magnet (13) is provided separately from the electromagnet (14), and the bias magnet (13) generates a bias magnetic field (Hc) having a magnetic field component parallel to the direction of the detected magnetic field (Ha). Therefore, even if the value of the detected current (Ia) becomes zero and the detected magnetic field (Ha) becomes zero accordingly, the combined magnetic field (Hd) as an external magnetic field acting on the magnetic detection elements (21, 50). ) Is not zero.

  Thus, when the value of the detected current (Ia) is zero, the bias magnetic field (Hc) acts on the magnetic detection elements (21, 50) as the combined magnetic field (Hd), so that the sensitivity is improved while improving the sensitivity. The detected current (Ia) can be accurately detected when the value of the detected current (Ia) is near zero. Therefore, even if the detected current (Ia) takes a non-zero value and then takes a value of zero for a predetermined period, the detected current (Ia) can be detected with high accuracy.

  In the above-described invention, the detected magnetic current (Ia) is zero because of the bias magnetic field (Hc), because the combined magnetic field (Hd) when the value of the detected current (Ia) is zero is offset from zero. It is also conceivable that the composite magnetic field (Hd) becomes zero when the value is not.

Therefore, as described in claim 2,
The bias magnet (13) preferably generates a bias magnetic field (Hc) in which the combined magnetic field (Hd) does not become zero and changes within the same polarity.

  According to this, the combined magnetic field (Hd) does not become zero in the measurement range of the detected current (Ia). Therefore, the detected current (Ia) can be accurately detected regardless of the value of the detected current (Ia).

When the detected current (Ia) varies within the same polarity, as described in claim 3,
When the absolute value of the magnetic flux density of the bias magnetic field (Hc) acting on the magnetic detection element (21, 50) is larger than the absolute value of the residual magnetic flux density of the magnetic film constituting the magnetic detection element (21, 50). good.

  As described above, the magnetic hysteresis due to the remanent magnetization is increased when the external magnetic field acting on the magnetic detection elements (21, 50) is generated within a predetermined range from 0, and the magnitude of the external magnetic field is close to zero. On the other hand, in the present invention, with the above configuration, the range of change of the composite magnetic field (Hd), which is an external magnetic field, becomes a region where hysteresis due to residual magnetization does not occur regardless of the detected current (Ia). Therefore, the detected current (Ia) can be detected with higher accuracy. Further, since the offset amount by the bias magnet (13) can be smaller than that of claim 4 described later, an inexpensive bias magnet (13) having a weak magnetic force can be employed.

Further, when the polarity of the detected current (Ia) changes between plus and minus, as described in claim 4,
The absolute value of the magnetic flux density of the bias magnetic field (Hc) acting on the magnetic detection element (21, 50) is the absolute value of the residual magnetic flux density of the magnetic film constituting the magnetic detection element (21, 50) and the detected current ( It is preferable that the configuration be larger than the sum of the absolute value of the magnetic flux density corresponding to the lower limit that Ia) can take.

  According to this, as in the third aspect, the range of change of the composite magnetic field (Hd), which is an external magnetic field, is a region where hysteresis due to residual magnetization does not occur regardless of the detected current (Ia). Therefore, the detected current (Ia) can be detected with higher accuracy.

On the other hand, when the polarity of the detected current (Ia) changes between plus and minus, as described in claim 5,
Even if the absolute value of the magnetic flux density of the bias magnetic field (Hc) acting on the magnetic detection element (21, 50) is larger than the absolute value of the residual magnetic flux density of the magnetic film constituting the magnetic detection element (21, 50). good.

  According to this, even if the detected current (Ia) takes a value of zero for a predetermined period, the composite magnetic field (Hd), which is an external magnetic field, is generated by the bias magnetic field (Hc) so that hysteresis due to residual magnetization does not occur. Since it is offset, the detected current (Ia) can be detected with high accuracy. Note that since the combined magnetic field (Hd) when the value of the detected current (Ia) is zero is offset from zero, the combined magnetic field (Hd) is zero when the detected current (Ia) is a predetermined value that is not zero. It can be. However, the detected current (Ia) continuously changes at a value other than zero, and is instantaneous even when the combined magnetic field (Hd) becomes zero. That is, the period in which the combined magnetic field (Hd) is zero is shorter than the predetermined period in which the value of the detected current (Ia) is zero. For this reason, the error of the cancellation current due to the residual magnetization can be suppressed as compared with the conventional case.

  As described in claim 6, a configuration in which the magnetic detection element has an anisotropic magnetoresistive element (21) can be adopted.

Above all, as described in claim 7,
The magnetic detection element (21) has four anisotropic magnetoresistive elements (21a to 21d),
Of the four anisotropic magnetoresistive elements (21a to 21d), the first anisotropic magnetoresistive element (21a) is on the high potential side, and the second anisotropic magnetoresistive element (21b) is on the low potential side. The first half bridge is formed, and the second half bridge is formed with the third anisotropic magnetoresistive element (21c) on the high potential side and the fourth anisotropic magnetoresistive element (21d) on the low potential side. These half bridges form a full bridge circuit,
Of the four anisotropic magnetoresistive elements (21a to 21d), the first anisotropic magnetoresistive element (21a) and the fourth anisotropic magnetoresistive element (21d) are the elements (21, 21d). ) Is provided so that the direction of the current flowing in parallel to the detected magnetic field (Ha), the second anisotropic magnetoresistive element (21b) and the third anisotropic magnetoresistive element (21c) The direction of the current flowing through the element (21b, 21c) is provided to be perpendicular to the detected magnetic field (Ha),
The supply means (40) preferably employs a configuration for supplying a canceling current based on the difference between the midpoint potentials (V1, V2) of each half bridge to the electromagnet (14).

  According to this, since the midpoint potentials (V1, V2) of the first half bridge and the second half bridge swing in reverse due to the action of the combined magnetic field (Hd), the midpoint potentials (V1, V2) of the half bridges are reversed. The difference in V2), that is, the amount of change in the output of the magnetic detection element (21) can be increased. Thereby, the accuracy of the offset current, that is, the detection accuracy of the detected current (Ia) can be improved as compared with the configuration in which the amount of change in the output of the magnetic detection element (21) is small.

  As described in claim 8, the four anisotropic magnetoresistive elements (21a to 21d) are preferably formed on the same surface (12a) of the same chip (12). According to this, since the influence of the temperature which four anisotropic magnetoresistive elements (21a-21d) receive becomes substantially equal mutually, the influence of a temperature characteristic can be canceled. Moreover, since it forms in the same chip | tip (12), the manufacturing dispersion | variation of each anisotropic magnetoresistive effect element (21a-21d) can be suppressed. Moreover, it can also be reduced in size.

  As described in claim 9, the chip (12) has a surface (12a) on which the anisotropic magnetoresistive element (21) is formed in parallel with a surface (11a) of the bus bar (11). It may be arranged. In addition, as defined in claim 10, the surface (12a) on which the anisotropic magnetoresistive element (21) is formed is perpendicular to the surface (11a) of the bus bar (11), and the detected magnetic field ( You may arrange | position so that it may become parallel to Ha). In any arrangement, the direction of the current flowing through the first anisotropic magnetoresistive element (21a) and the fourth anisotropic magnetoresistive element (21d) depends on the detected magnetic field (21a, 21d). The second anisotropic magnetoresistive element (21b) and the third anisotropic magnetoresistive element (21c) are provided so as to be parallel to Ha), and the direction of the current flowing through the elements (21b, 21c) is It can be provided perpendicular to the detected magnetic field (Ha).

Further, as described in claim 11,
In the magnetic detection element, a free layer (54) whose magnetization direction varies with respect to the combined magnetic field (Hd) is provided on one surface of the fixed layer (52) whose magnetization direction is fixed via the nonmagnetic layer (53). It is also possible to employ a configuration having a magnetoresistive effect element (50) that exhibits a spin valve type giant magnetoresistive effect or tunnel magnetoresistive effect. In the case of the magnetoresistive effect element (50) exhibiting the giant magnetoresistive effect, the nonmagnetic layer (53) has conductivity, and in the case of the magnetoresistive effect element (50) exhibiting the tunnel magnetoresistive effect, the nonmagnetic layer. (53) has electrical insulation.

Again, as described in claim 12,
The magnetic detection element (50) includes four magnetoresistive elements (50a to 50d),
Of the four magnetoresistive elements (50a to 50d), the first half bridge is formed with the first magnetoresistive element (50a) as the high potential side and the second magnetoresistive element (50b) as the low potential side, A second half bridge is formed with the third magnetoresistive element (50c) on the high potential side and the fourth magnetoresistive element (50d) on the low potential side, and these half bridges form a full bridge circuit,
In the four magnetoresistive elements (50a to 50d), the magnetization direction of each fixed layer (52) is parallel to the detected magnetic field (Ha), and the first magnetoresistive element (50a) and the fourth magnetoresistive effect The magnetization direction of the fixed layer (52) in the element (50d) is opposite to the magnetization direction of the fixed layer (52) in the second magnetoresistive element (50b) and the third magnetoresistive element (50c). Provided in
The supply means (40) preferably employs a configuration for supplying a canceling current based on the difference between the midpoint potentials (V1, V2) of each half bridge to the electromagnet (14).

  Since the function and effect are the same as the function and effect of the invention described in claim 7, the description is omitted.

  According to a thirteenth aspect of the present invention, the bias magnet (13) may have a cylindrical shape, and the magnetic detection elements (21, 50) may be disposed inside the cylindrical shape. Further, as described in claim 14, the bias magnet (13) may have a cylindrical shape, and the electromagnet (14) may be disposed inside the cylindrical shape. Furthermore, as described in claim 15, the electromagnet (14) may have a coil (30), and the magnetic detection elements (21, 50) may be arranged in the coil (30). In any case, the size of the sensor can be reduced.

It is a perspective view which shows schematic structure of the magnetic balance type current sensor which concerns on 1st Embodiment. In order to illustrate a sensor chip or the like located in the case, the case is shown through for convenience. It is sectional drawing which follows the II-II line | wire of FIG. For convenience, the illustration of the case is omitted. It is a perspective view which shows schematic structure of the magnetic detection element formed in the sensor chip. It is a figure which shows schematic structure of the external magnetic field detection circuit by a magnetic detection element. (A) is a figure which shows the relationship between magnetic field intensity and resistance value change rate in the magnetic detection element based on 1st Embodiment, (b) is a figure which shows the magnetic hysteresis by residual magnetization. It is a circuit diagram of a magnetic balance type current sensor for obtaining a current output. It is a figure which shows the relationship of the to-be-detected current in the conventional magnetic balance type current sensor shown as a comparative example, the to-be-detected magnetic field as an external magnetic field, the cancellation magnetic field, and the cancellation current. (A) shows the change over time of the current values of the detected current (solid line) and the canceling current (broken line), and (b) shows the time lapse of the magnetic field strength of the detected magnetic field (solid line) and the canceling magnetic field (broken line). It shows a change. In a magnetic balance type current sensor concerning a 1st embodiment, it is a figure showing relation between current to be detected, a synthetic magnetic field as an external magnetic field, a cancellation magnetic field, and a cancellation current. (A) shows the change over time of the current values of the detected current (solid line) and the cancellation current (dashed line), and (b) shows the change over time of the magnetic field strength of the combined magnetic field (solid line) and the cancellation magnetic field (dashed line). Is shown. It is a circuit diagram of the magnetic balance type current sensor for obtaining a voltage output. (A)-(c) is a figure which shows the modification of an external magnetic field detection circuit. It is sectional drawing which shows schematic structure of the magnetic balance type current sensor which concerns on 2nd Embodiment, and respond | corresponds to FIG. It is a figure which shows the relationship between the to-be-detected current, the to-be-detected magnetic field as an external magnetic field, the cancellation magnetic field, and the cancellation current in the conventional magnetic balance type current sensor when the to-be-detected current takes a positive and negative value. (A) shows the change over time of the current values of the detected current (solid line) and the canceling current (broken line), and (b) shows the time lapse of the magnetic field strength of the detected magnetic field (solid line) and the canceling magnetic field (broken line). It shows a change. In a magnetic balance type current sensor concerning a 3rd embodiment, it is a figure showing the relation of detected current, synthetic magnetic field as an external magnetic field, cancellation magnetic field, and cancellation current. (A) shows the change over time of the current values of the detected current (solid line) and the cancellation current (dashed line), and (b) shows the change over time of the magnetic field strength of the combined magnetic field (solid line) and the cancellation magnetic field (dashed line). Is shown. In a magnetic balance type current sensor concerning a 4th embodiment, it is a figure showing the relation of detected current, synthetic magnetic field as an external magnetic field, cancellation magnetic field, and cancellation current. (A) shows the change over time of the current values of the detected current (solid line) and the cancellation current (dashed line), and (b) shows the change over time of the magnetic field strength of the combined magnetic field (solid line) and the cancellation magnetic field (dashed line). Is shown. It is sectional drawing to which the magnetic detection element periphery was expanded among the magnetic balance type current sensors which concern on 5th Embodiment, and respond | corresponds to FIG. It is a figure which shows the relationship between magnetic field intensity and resistance value change rate in the magnetic detection element which concerns on 5th Embodiment. It is a figure which shows schematic structure of the external magnetic field detection circuit by a magnetic detection element. (A), (b) is sectional drawing which shows the other modification of a magnetic balance type current sensor. (A), (b), (c) is sectional drawing which shows the other modification of a magnetic balance type current sensor. (A), (b) is sectional drawing which shows the other modification of a magnetic balance type current sensor.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. In the following embodiments, common or related elements are given the same reference numerals. The direction along the one surface 11a of the bus bar 11 and along the detected current Ia is in the x direction, the direction along the one surface 11a and perpendicular to the x direction is perpendicular to both the y direction, the x direction, and the y direction. This direction is indicated as the z direction. In the following embodiment, the longitudinal direction of the bus bar 11 is the x direction, the width direction of the bus bar 11 is the y direction, and the thickness direction of the bus bar 11 is the z direction.

(First embodiment)
As shown in FIG. 1, a magnetic balanced current sensor 10 (hereinafter simply referred to as a current sensor 10) according to this embodiment includes a bus bar 11, a sensor chip 12 on which a magnetic detection element is formed, a bias magnet 13, , A feedback electromagnet 14 and a circuit chip 15 formed with a control circuit and the like. The main feature of the present embodiment is that the bias magnet 13 is provided.

  The sensor chip 12, the bias magnet 13, the electromagnet 14, and the circuit chip 15 are fixed to one surface 11a of the bus bar 11 through a base 16 made of an electrically insulating material such as a synthetic resin. In this embodiment, a flat base 16 made of PPS is bonded and fixed to one surface 11 a of the bus bar 11. The sensor chip 12, the bias magnet 13, the electromagnet 14, and the circuit chip 15 are bonded and fixed to the surface of the base 16 opposite to the bonding surface, for example. A case 17 made of an electrically insulating material such as synthetic resin is assembled to the base 16, and the sensor chip 12, the bias magnet 13, the electromagnet 14, and the circuit chip 15 are protected by the base 16 and the case 17. .

  The bus bar 11 is formed using a metal material having excellent conductivity such as copper, and is a member that forms a path of the detected current Ia in a state of being attached to an attachment target. In this embodiment, the bus bar 11 is formed in a flat plate shape, and the planar shape along the xy plane of the bus bar 11 is a rectangle long in the x direction. Attachment holes (not shown) are formed in the vicinity of both ends in the longitudinal direction of the bus bar 11, and the bus bar 11 forms a path of the detected current Ia in a state of being attached to the attachment object via the attachment holes. Thus, the detected current Ia flows along the longitudinal direction of the bus bar 11, that is, the x direction. In the present embodiment, the detected current Ia flows only in the x direction, as shown in FIG. For this reason, in FIG. 2, the detected magnetic field Ha is generated so as to make a round in the counterclockwise direction around the bus bar 11. A detected magnetic field Ha is applied.

  The sensor chip 12 has a magnetic detection element for detecting the detected current Ia flowing through the bus bar 11. In the present embodiment, an anisotropic magnetoresistive element 21 (hereinafter referred to as an AMR element 21) is provided as a magnetic detection element. Further, as shown in FIG. 3, the AMR element 21 includes four AMR elements 21a to 21d formed on the same surface on one surface 12a of the same substrate 20 (hereinafter referred to as one surface 12a of the sensor chip 12). doing.

  In the present embodiment, the sensor chip 12 is placed flat on the one surface 11 a of the bus bar 11 so that the one surface 12 a on which the AMR elements 21 a to 21 d are formed is parallel to the one surface 11 a of the bus bar 11. Specifically, the sensor chip 12 is arranged on the one surface 11 a of the bus bar 11 so that the surface opposite to the one surface 12 a of the sensor chip 12 faces the base 16. Thereby, as shown in FIG. 2, the detected magnetic field Ha formed by the detected current Ia acts substantially parallel to the one surface 12 a of the sensor chip 12. In order to cause the detected magnetic field Ha to act substantially parallel to the one surface 12a of the sensor chip 12, as shown in FIGS. 1 and 2, the sensor chip 12 is arranged at the approximate center in the width direction of the bus bar 11. Is preferred.

  In the present embodiment, not only the detected magnetic field Ha, but also a canceling magnetic field Hb and a bias magnetic field Hc, which will be described later, are made of spacers made of an electrically insulating material so as to act along the one surface 12a of the sensor chip 12 (reference numeral in the figure). The position of the sensor chip 12 in the z direction with respect to the one surface 11a of the bus bar 11 is adjusted.

  The AMR elements 21a to 21d are formed by depositing Ni-Co-based or Ni-Fe-based ferromagnetic material on the substrate 20 by sputtering or vapor deposition and patterning. In FIG. 3, the planar shape of each of the AMR elements 21 a to 21 d is a rectangular shape whose longitudinal direction is the direction of current flow, but may be a meander shape. These AMR elements 21a to 21d have substantially the same material, shape, size, and film thickness, and have substantially the same resistance value when no magnetic field acts.

  Of the four AMR elements 21a to 21d, the first AMR element 21a and the second AMR element 21b are connected in series to form a first half bridge. In the first half bridge, the first AMR element 21a is on the power supply pad 22a side, and the second AMR element 21b is on the ground pad 22b side. On the other hand, the third AMR element 21c and the fourth AMR element 21d are connected in series to form a second half bridge. In the second half bridge, the third AMR element 21c is on the power supply pad 22a side, and the fourth AMR element 21d is on the ground pad 22b side. These two half bridges constitute an external magnetic field detection circuit having a full bridge configuration.

  3 is an output pad connected to a connection point between the first AMR element 21a and the second AMR element 21b, and a reference numeral 22d is a connection point between the third AMR element 21c and the fourth AMR element 21d. Connected output pads. As shown in FIG. 4, with the predetermined voltage Vcc applied between the power supply pad 22a and the ground pad 22d, the midpoint potential V1 of the AMR elements 21a, 21b is taken out from the output pad 22c, and the output pad 22d Thus, the midpoint potential V2 of the AMR elements 21c and 21d is taken out. In the present embodiment, as shown in FIG. 1, bonding wires 18 are connected to the pads 22 a to 22 d, and the sensor chip 12 and the circuit chip 15 are electrically connected via the bonding wires 18. .

  The first AMR element 21a and the fourth AMR element 21d are formed so that their longitudinal directions are substantially parallel to each other. That is, the direction of the current flowing through the AMR elements 21a and 21d (the direction of the broken line arrow in FIG. 4) is formed to be substantially parallel to each other. The second AMR element 21b and the third AMR element 21c are also formed so that their longitudinal directions are substantially parallel to each other. That is, the direction of the current flowing through the AMR elements 21b and 21c (the direction of the broken line arrow in FIG. 4) is formed to be substantially parallel to each other. Further, the direction of the current flowing through the first AMR element 21a and the fourth AMR element 21d and the direction of the current flowing through the second AMR element 21b and the third AMR element 21c are formed so as to be substantially perpendicular to each other.

  As shown in FIG. 4, the sensor chip 12 is configured so that the direction of the current flowing through the first AMR element 21a and the fourth AMR element 21d is substantially parallel to the direction of the detected magnetic field Ha acting on the AMR elements 21a and 21d. It is arranged with respect to the bus bar 11. In other words, the current flowing in the second AMR element 21b and the third AMR element 21c is arranged with respect to the bus bar 11 so that the direction of the detected magnetic field Ha acting on the AMR elements 21b and 21c is substantially perpendicular. . Specifically, the direction of current flowing through the first AMR element 21a and the fourth AMR element 21d is substantially parallel to the y direction, and the direction of current flowing through the second AMR element 21b and the third AMR element 21c is substantially parallel to the z direction. Thus, the sensor chip 12 is arranged on the bus bar 11.

  A combined magnetic field Hd described later is a combined magnetic field of the detected magnetic field Ha and a component parallel to the detected magnetic field Ha in the bias magnetic field Hc. Therefore, the direction of the current flowing through the first AMR element 21a and the fourth AMR element 21d is substantially parallel to the direction of the combined magnetic field Hd, and the direction of the current flowing through the second AMR element 21b and the third AMR element 21c is the direction of the combined magnetic field Hd. It can be said that the sensor chip 12 is arranged with respect to the bus bar 11 so as to be substantially vertical.

  Here, when the combined magnetic field Hd acts parallel to the one surface 12 a of the sensor chip 12, the angle formed by the combined magnetic field Hd with respect to the direction of the current flowing through the AMR element 21 and the resistance value of the AMR element 21 are calculated. The relationship shows a sine curve characteristic as is well known. The resistance value is maximized when the angle formed between the current direction and the combined magnetic field Hd is 0 degrees (180 degrees), and the resistance value is minimized when the angle formed is 90 degrees (270 degrees). Also, the resistance value becomes zero when the angle θ is around 30 degrees (150 degrees). Further, the rate of change in resistance value is as shown by a solid line in FIG. 5A when the direction of current flowing through itself and the direction of the combined magnetic field Hd are parallel. On the other hand, when the direction of the current flowing through itself and the direction of the combined magnetic field Hd are perpendicular, the broken line shown in FIG.

  As shown by the solid line in FIG. 5A, the first AMR element 21a and the fourth AMR element 21d in the present embodiment have a positive resistance value change rate according to the strength (magnetic field strength) of the acting combined magnetic field Hd. In the range (including zero). In particular, from zero to a predetermined magnetic field strength (absolute value of about 20 mT), the absolute value increases in proportion to the absolute value of the magnetic field strength. On the other hand, in the second AMR element 21b and the third AMR element 21c, as shown by a broken line in FIG. 5A, the resistance value change rate is in a negative value range according to the strength (magnetic field strength) of the acting combined magnetic field Hd. (Including zero). In particular, from zero to a predetermined magnetic field strength (absolute value of about 20 mT), the absolute value increases in proportion to the absolute value of the magnetic field strength. The resistance value change rate is a change rate of the resistance value based on the resistance value when the combined magnetic field Hd is zero.

  For this reason, in FIG. 4, the first AMR element 21a and the fourth AMR element 21d are given arrows pointing upward to the right. On the other hand, arrows pointing downward to the right are given to the second AMR element 21b and the third AMR element 21c.

  The bias magnet 13 has a magnetic field component parallel to the direction of the detected magnetic field Ha acting on the AMR element 21, and constantly generates a bias magnetic field Hc having a constant direction and magnitude during measurement of the detected current Ia. It is. In other words, the external magnetic field acting on the AMR element 21 is offset as compared with the case of only the detected magnetic field Ha. In the present embodiment, the bias magnet 13 is set so that the external magnetic field (synthetic magnetic field Hd) does not become zero. In addition, the bias magnet is configured so that the absolute value of the magnetic flux density of the magnetic field component in the y direction acting on the AMR element 21 of the bias magnetic field Hc is larger than the absolute value of the residual magnetic flux density of the magnetic film constituting the AMR element 21. 13 is set.

  As such a bias magnet 13, either a permanent magnet or an electromagnet can be employed. In this embodiment, a columnar permanent magnet is employed as the bias magnet 13, and one of the side surfaces perpendicular to both end surfaces forming the magnetic pole is bonded and fixed to the base 16. Further, the bias magnet 13 is magnetized with an N pole at the end surface facing the side surface of the sensor chip 12 and an S pole at the other end surface. Further, in the z-axis direction, the center of the end face (N pole) of the bias magnet 13 and the formation position of the AMR element 21 in the sensor chip 12 are substantially coincident. That is, as shown in FIG. 2, on the one surface 12a of the sensor chip 12, the bias magnetic field Hc from the right to the left in the drawing is applied to the AMR element 21 like the detected magnetic field Ha. Thus, the combined magnetic field Hd of the detected magnetic field Ha and the magnetic field component parallel to the detected magnetic field Ha out of the bias magnetic field Hc acts on the sensor chip 12 (AMR element 21) as an external magnetic field.

  The electromagnet 14 generates a canceling magnetic field Hb for canceling an external magnetic field acting on the AMR element 21 by energization, and has at least a coil 30. In the present embodiment, a canceling magnetic field Hb for canceling the combined magnetic field Hd as an external magnetic field is generated.

  In the present embodiment, the coil 30 is formed by winding a conductive wire. The electromagnet 14 has not only the coil 30 but also a soft magnetic core 31 around which the coil 30 is wound. The electromagnet 14 is disposed with respect to the bus bar 11 so that the axial direction of the coil 30 is substantially perpendicular to the longitudinal direction of the bus bar 11 and substantially parallel to the width direction. That is, the axial direction of the coil 30 and the extending direction of the core 31 are substantially parallel to the y direction and are also substantially parallel to the one surface 12a of the sensor chip 12. Further, in the z direction and the x direction, the axial center of the coil 30 substantially coincides with the center of the end face (N pole) of the bias magnet 13, and substantially the same as the formation position of the AMR element 21 in the sensor chip 12 in the z direction. I'm doing it. That is, the sensor chip 12 is located in a region where the end face on the N pole side of the bias magnet 13 and the electromagnet 14 are opposed to each other.

  Then, as shown in FIG. 2, the canceling magnetic field Hb in the direction opposite to the direction of the combined magnetic field Hd (from the left to the right in the drawing) so as to cancel the combined magnetic field Hd acting on one surface 12 a of the sensor chip 12, that is, the AMR element 21. Is applied to one surface 12 a of the sensor chip 12, that is, the AMR element 21. Due to the canceling magnetic field Hb, the magnetic field applied to the AMR element 21 becomes zero.

  In such an electromagnet 14, the coil 30 is electrically connected to the circuit chip 15. That is, a canceling current for generating the canceling magnetic field Hb is supplied from the circuit chip 15 to the electromagnet 14 (coil 30).

  The circuit chip 15 includes a circuit that supplies a canceling current for generating the canceling magnetic field Hb. This embodiment includes an operational amplifier 40 as supply means for supplying a cancellation current and a constant current source 41 for supplying a constant current to an external magnetic field detection circuit shown in FIG. Further, as shown in FIG. 1, the circuit chip 15 is connected to a lead 19 as an external connection terminal, and the current sensor 10 is electrically connected to an external device via the lead 19. .

  Here, the circuit configuration of the current sensor 10 will be described. In the present embodiment, as shown in FIG. 6, a canceling current proportional to the detected current Ia is detected as a current value.

  As shown in FIG. 6, a constant current source 41 provides a constant current between the power supply pad 22a and the ground pad 22b, that is, in an external magnetic field detection circuit in which four AMR elements 21a to 21d are connected in a full bridge. Is supplied. Then, with the current supplied to each of the AMR elements 21a to 21d, the midpoint potential V1 of the first AMR element 21a and the second AMR element 21b is taken out from the output pad 22c. The midpoint potential V1 is the power supply pad 22a. When the power supply voltage between the first AMR element 21a and the ground pad 22b is Vcc, the resistance value of the first AMR element 21a is R1, and the resistance value of the second AMR element 21b is R2.

(Expression 1) V1 = Vcc × R2 / (R1 + R2)
Similarly, the midpoint potential V2 of the third AMR element 21c and the fourth AMR element 21d is taken out from the output pad 22d. The midpoint potential V2 is the resistance value of the third AMR element 21c as R3 and the resistance value of the fourth AMR element 21d. Is represented by the following equation.

(Expression 2) V2 = Vcc × R4 / (R3 + R4)
An output pad 22c is connected to the inverting input terminal (−) of the operational amplifier 40, and an output pad 22d is connected to the non-inverting input terminal (+). The output terminal of the operational amplifier 40 is connected to the coil 30 constituting the electromagnet 14. The operational amplifier 40 supplies a canceling current to the coil 30 of the electromagnet 14 so that the potential difference (V1−V2) between the output pads 22c and 22d is always zero by sucking or discharging current from its output terminal. That is, on the one surface 12a of the sensor chip 12, a canceling current is supplied to the coil 30 of the electromagnet 14 so that the combined magnetic field Hd acting on the AMR element 21 is canceled by the canceling magnetic field Hb. At this time, the canceling current supplied to the coil 30 can be detected by an external ammeter 100 connected via the lead 19. Since the direction and magnitude of the bias magnetic field Hc are always constant, the detected current Ia can be detected from the canceling current. 6 indicates that the AMR elements 21a to 21d as the magnetic detection elements and the coil 30 are magnetically coupled.

  Next, the effect of the characteristic part of the current sensor 10 according to the present embodiment will be described.

  In the present embodiment, an AMR element 21 having a magnetic film is used as the magnetic detection element. The AMR element 21 has higher sensitivity than a Hall element or a semiconductor magnetoresistive effect element. Therefore, according to the present embodiment, the sensitivity of the current sensor 10 can be improved as compared with a configuration using a conventional Hall element or semiconductor magnetoresistive element.

  By the way, when the AMR element 21 having a magnetic film is used, sensitivity can be increased, but magnetic hysteresis due to residual magnetization becomes a problem. When an external magnetic field (≠ zero) acts on the AMR element 21 and then the external magnetic field becomes zero, magnetization remains in the magnetic film of the AMR element 21. For this reason, as shown in FIG. 5B, for example, when the magnetic field strength is changed from zero to a predetermined positive value (solid line in the figure), and when changed from a positive predetermined value to zero (the broken line in the figure). Thus, hysteresis occurs. As shown in FIG. 5B, the magnetic hysteresis due to the remanent magnetization is generated when the external magnetic field acting on the AMR element 21 is zero to a predetermined range (the magnetic field strength is zero to A in the figure). The closer the size of is to zero, the larger.

  Here, as in the present embodiment, a case is considered where the detected current Ia changes only within the same polarity, that is, the polarity of the detected current Ia does not change. As shown in FIG. 7A, it is assumed that the detected current Ia flowing through the bus bar 11 changes in the range of 0 [A] to + X [A].

  In the conventional configuration that does not have the bias magnet 13, when the detected current Ia indicated by the solid line in FIG. 7A becomes zero from a positive value, for example, the external magnetic field indicated by the solid line in FIG. The detected magnetic field Ha also becomes zero according to the detected current Ia. However, since a magnetic field is generated in the AMR element 21 due to the residual magnetization of the magnetic film, the state is as if the detected magnetic field Ha is acting on the AMR element 21. For this reason, the canceling magnetic field Hb indicated by a broken line in FIG. 7B does not become zero in order to cancel the magnetic field due to the residual magnetization, and the canceling current Ib flowing through the coil 30 of the electromagnet 14 is also shown in FIG. It does not become zero as shown by the broken line. Thus, if there is an influence of residual magnetization, an error occurs in the canceling current Ib when the value of the detected current Ia is near zero, so that the proportional relationship between the detected current Ia and the canceling current Ib shifts, and the detected current The detection accuracy of Ia is lowered.

  Note that, at time zero shown in FIG. 7A, there is no influence of residual magnetization, so the value of the canceling current Ib corresponding to zero of the detected current Ia is zero. On the other hand, in the predetermined period T1 having the influence of the residual magnetization, the value of the canceling current Ib corresponding to the value zero of the detected current Ia is not zero but shows a positive value. Thus, even if the value of the detected current Ia is the same zero, the value of the canceling current Ib varies depending on whether there is an influence of residual magnetization, and this difference is the error of the canceling current Ib.

  The detected current Ia continuously changes in the measurement environment, but takes a value of zero for a predetermined period T1, as shown in FIG. 7A. For this reason, the cancellation current Ib also has an error during the predetermined period T1. Thus, the occurrence of an error for a predetermined period in the canceling current Ib is not preferable in terms of the detection accuracy of the detected current Ia. In FIG. 7A, for the sake of convenience, the detected current Ia is shown as if it is constant for a predetermined period at the upper limit + X [A], but in actuality, the detected current Ia is zero. It is continuously changing at other values.

  On the other hand, in this embodiment, a bias magnet 13 that generates a bias magnetic field Hc is provided separately from the electromagnet 14. The bias magnet 13 always generates a bias magnetic field Hc having a magnetic field component parallel to the direction of the detected magnetic field Ha during measurement of the detected current Ia. Thus, the external magnetic field acting on the AMR element 21 is offset by the bias magnetic field Hc. Therefore, even if the value of the detected current Ia indicated by the solid line in FIG. 8A changes from, for example, a positive value and becomes zero during the predetermined period T1, the solid line in FIG. 8B. As shown, the combined magnetic field Hd acting on the AMR element 21 as an external magnetic field does not become zero. As described above, according to the current sensor 10 according to the present embodiment, it is possible to suppress the composite magnetic field Hd from becoming zero in the predetermined period T1 in which the value of the detected current Ia that greatly affects the measurement accuracy is zero. In addition, the detection accuracy of the detected current Ia can be improved as compared with the conventional case.

  By the way, in order to offset the combined magnetic field Hd when the value of the detected current Ia is zero by the amount of the bias magnetic field Hc, depending on the offset direction, when the detected current Ia is a non-zero value, the combined magnetic field Hd is It may be zero. On the other hand, in the present embodiment, as shown in FIG. 8B, the bias magnet 13 is set so that the value of the composite magnetic field Hd, which is an external magnetic field, is not zero as well as the predetermined period T1. ing. Specifically, the detected current Ia changes in the range of 0 [A] to + X [A], and the direction of the detected magnetic field Ha acting on the AMR element 21 is also constant. A bias magnetic field Hc having the same direction as the magnetic field Ha acts. For this reason, the composite magnetic field Hd does not become zero in the measurement range of the detected current Ia. Therefore, the detected current Ia can be accurately detected regardless of the value of the detected current Ia.

  As described above, the magnetic hysteresis due to the remanent magnetization is increased when the external magnetic field acting on the AMR element 21 is generated within a predetermined range from 0 (see FIG. 5B). . On the other hand, in this embodiment, the absolute value of the magnetic flux density of the magnetic field component in the y direction of the bias magnetic field Hc on the AMR element 21 is larger than the absolute value of the residual magnetic flux density of the magnetic film constituting the AMR element 21. The bias magnet 13 is set so that it becomes. Thus, even if the detected current Ia indicated by the solid line in FIG. 8A becomes zero for a predetermined period T1, for example, from a positive value, the combined magnetic field as an external magnetic field indicated by the solid line in FIG. 8B Hd takes a value that is not affected by magnetic hysteresis in the predetermined period T1. Thus, since the influence of the magnetic hysteresis is eliminated during the predetermined period T1, the detected current Ia can be detected with high accuracy. Note that the alternate long and short dash line shown in FIG. 8B is the upper limit of the magnetic field that generates magnetic hysteresis, and magnetic hysteresis due to residual magnetization occurs in the region from the alternate long and short dash line to the magnetic field of zero.

  In particular, in the case of the present embodiment, since the detected current Ia changes only within the same polarity, the value of the combined magnetic field Hd that is an external magnetic field does not become zero, and a region in which magnetic hysteresis due to residual magnetization occurs is not used. Therefore, the offset amount by the bias magnetic field Hc can be small. Therefore, an inexpensive bias magnet 13 having a weak magnetic force can be employed.

  Further, in the present embodiment, as described above, the four AMR elements 21a to 21d are arranged so that the midpoint potentials V1 and V2 of the first half bridge and the second half bridge swing reversely by the action of the combined magnetic field Hd. Thus, an external magnetic detection circuit having a full bridge configuration is formed. Therefore, the difference between the midpoint potentials V1 and V2 of each half bridge, that is, the amount of change in the output of the AMR element 21 (external magnetic detection circuit) can be increased. Thereby, the accuracy of the cancellation current, that is, the detection accuracy of the detected current Ia can be improved as compared with the configuration in which the change amount of the output of the AMR element 21 is small.

  In the present embodiment, all the AMR elements 21a to 21d constituting the external magnetic detection circuit are formed on the same surface 12a of the same sensor chip 12. For this reason, the influences of the temperatures on the four AMR elements 21a to 21d are almost equal to each other, and the influence of the temperature characteristics can be canceled. Further, since the same sensor chip 12 is used, manufacturing variations of the AMR elements 21a to 21d can be suppressed. Moreover, it can also be reduced in size.

(Modification)
In the above embodiment, a current output type circuit configuration is shown as the current sensor 10. However, a voltage output type circuit configuration can be adopted. FIG. 9 shows an example of the voltage output type current sensor 10. 6 differs from the current output type in FIG. 6 in that a detection resistor 42 and a differential amplifier circuit 43 are provided instead of the ammeter 100, and the output voltage of the differential amplifier circuit 43 is used as a sensor output. The detection resistor 42 and the differential amplifier circuit 43 are formed on the circuit chip 15, and the output voltage of the differential amplifier circuit 43 is output to the outside via the lead 19.

  The detection resistor 42 is a very small resistance for converting a canceling current to the coil 30 constituting the electromagnet 14 into a voltage, and its resistance value is sufficiently smaller than the input impedance of the differential amplifier circuit 43. The differential amplifier circuit 43 amplifies the voltage across the detection resistor 42 and outputs the voltage. The differential amplifier circuit 43 includes an operational amplifier 44, four fixed resistors 45 to 48, and a constant voltage source 49. The voltage of the constant voltage source 49 is, for example, 1/2 of the power supply voltage Vcc. The resistance values R1 to R4 of the fixed resistors 45 to 48 are R1 = R3 and R2 = R4, and the amplification degree of the differential amplifier circuit 43 is R2 / R1. The amplification degree is about 1, for example.

  In the above embodiment, an example of the external magnetic detection circuit including the four AMR elements 21a to 21d has been described. However, the configuration of the external magnetic detection circuit is not limited to the above example. For example, in FIG. 10A, as in the above embodiment, the first AMR element 21a and the second AMR element 21b are connected in series to form a first half bridge. On the other hand, the second half bridge is composed of fixed resistors 23a and 23b whose resistance value is not changed by an external magnetic field. In FIG. 10A, the first AMR element 21a is on the power supply pad 22a side and the second AMR element 21b is on the ground pad 22b side, as in the above embodiment. Further, the direction of the current flowing through the first AMR element 21a and the direction of the current flowing through the second AMR element 21b are formed so as to be substantially perpendicular to each other. In this case, since one of the half bridges is composed of the fixed resistors 23a and 23b, the amount of change in the output of the external magnetic detection circuit is smaller than in the above embodiment, but the influence of the temperature of the first AMR element 21a and the second AMR element 21b is mutually It is almost equal, and the influence of temperature characteristics can be canceled.

  Also, only one of the four resistors constituting the full bridge circuit may be the AMR element 21 and the remaining may be a fixed resistor. For example, in FIG. 10B, only the first AMR element 21a is used as the AMR element 21, and the rest are fixed resistors 23a to 23c. In the first half bridge, the first AMR element 21a is on the power supply pad 22a side, and the fixed resistor 23c is on the ground pad 22b side.

  Further, the AMR element 21 having substantially the same resistance value in the state where no external magnetic field acts and having the same direction of current flowing through itself forms a half bridge circuit, and one AMR element 21 is covered with a magnetic shield. good. For example, in FIG. 10C, the direction of the current flowing through the first AMR element 21a and the second AMR element 21b constituting the first half bridge is substantially perpendicular to the direction of the combined magnetic field Hd. The second AMR element 21b is covered with a magnetic shield 24 so that an external magnetic field does not act. According to this, since the influences of the temperatures of the first AMR element 21a and the second AMR element 21b are almost equal to each other, the influence of the temperature characteristic can be canceled compared to the configuration of FIG.

(Second Embodiment)
In the present embodiment, description of portions common to the current sensor 10 shown in the above embodiment is omitted. In the first embodiment, an example is shown in which the sensor chip 12 is placed flat on the bus bar 11 so that the one surface 12 a on which the AMR element 21 is formed in the sensor chip 12 is substantially parallel to the one surface 11 a of the bus bar 11.

  In contrast, in the present embodiment, as shown in FIG. 11, one surface 12a of the sensor chip 12, that is, the surface on which the AMR element 21 is formed is substantially perpendicular to the one surface 11a of the bus bar 11, and the detected magnetic field Ha. The sensor chip 12 is vertically placed on the bus bar 11 so as to be substantially parallel to the (synthetic magnetic field Hd).

  Even in such an arrangement, as shown in FIG. 4 of the first embodiment, the first AMR element 21a and the fourth AMR element 21d are arranged such that the direction of the current flowing through the AMR elements 21a and 21d is parallel to the combined magnetic field Hd. Provide as follows. The second AMR element 21b and the third AMR element 21c can be provided so that the direction of the current flowing through the AMR elements 21b and 21c is perpendicular to the combined magnetic field Hd. In other words, the amount of change in the output of the AMR element 21 (external magnetic detection circuit) can be increased to improve the accuracy of the cancellation current, that is, the detection accuracy of the detected current Ia. In addition, it can also be set as the structure shown to FIG. 10 (a)-(c) of 1st Embodiment.

  Also in this embodiment, the configuration shown in FIGS. 10A to 10C can be employed as a modification of the first embodiment.

(Third embodiment)
In the present embodiment, description of portions common to the current sensor 10 shown in the above embodiment is omitted. In the first embodiment, when the measurement range of the detected current Ia flowing through the bus bar 11 is 0 [A] to + X [A], the bias magnet 13 does not have a combined magnetic field Hd of zero and is the same. An example of generating a bias magnetic field Hc that varies within the polarity has been shown.

  In contrast, in the present embodiment, when the polarity of the detected current Ia changes between plus and minus, that is, when the measurement range of the detected current Ia is -Y [A] to + X [A], The bias magnet 13 is characterized in that the combined magnetic field Hd does not become zero and generates a bias magnetic field Hc that varies within the same polarity. For this reason, the current sensor 10 according to the present embodiment is suitable for measuring, for example, a battery current and a motor driving current of a hybrid car or an electric vehicle.

  In the conventional current sensor 10 that does not have the bias magnet 13, the measurement range is 0 [A] to + X [A] even when the measurement range of the detected current Ia is −Y [A] to + X [A]. As in the case of, residual magnetization becomes a problem. Specifically, when the detected current Ia indicated by the solid line in FIG. 12A becomes zero from a positive value, for example, the detected magnetic field Ha indicated by the solid line in FIG. 12B is also zero according to the detected current Ia. It becomes. However, since a magnetic field is generated in the AMR element 21 due to the residual magnetization of the magnetic film, the state is as if the detected magnetic field Ha is acting on the AMR element 21. For this reason, the canceling magnetic field Hb indicated by the broken line in FIG. 12B does not become zero in order to cancel the magnetic field due to the residual magnetization, and the canceling current Ib flowing through the coil 30 of the electromagnet 14 is also shown in FIG. It does not become zero as shown by the broken line. Thus, if there is an influence of residual magnetization, an error occurs in the canceling current Ib when the value of the detected current Ia is near zero, so that the proportional relationship between the detected current Ia and the canceling current Ib shifts, and the detected current The detection accuracy of Ia is lowered.

  In FIG. 12A, when the time is zero, −Y [A] is obtained, and the current value continuously changes from −Y [A] to + X [A]. During the predetermined period T1, the current value instantaneously takes a value of zero. In the process of continuously changing the current value, when the current value instantaneously becomes zero and the detected magnetic field Ha also instantaneously becomes zero, the influence of the residual magnetization hardly occurs. However, as shown in FIG. 12A, if the value is zero during the predetermined period T1, an error also occurs in the canceling current Ib during the predetermined period T1, so that the detection of the detected current Ia is detected. This is not preferable in terms of accuracy.

  In contrast, in the present embodiment, a bias magnet 13 that generates a bias magnetic field Hc is provided separately from the electromagnet 14 as in the first embodiment. The bias magnet 13 always generates a bias magnetic field Hc having a magnetic field component parallel to the direction of the detected magnetic field Ha during measurement of the detected current Ia. Thus, the external magnetic field acting on the AMR element 21 is offset by the amount of the bias magnetic field Hc. Therefore, even if the value of the detected current Ia indicated by the solid line in FIG. 13A changes from, for example, a positive value and becomes zero during the predetermined period T1, the solid line in FIG. As shown, the combined magnetic field Hd acting on the AMR element 21 as an external magnetic field does not become zero. As described above, according to the current sensor 10 according to the present embodiment, it is possible to suppress the composite magnetic field Hd from becoming zero in the predetermined period T1 in which the value of the detected current Ia that greatly affects the measurement accuracy is zero. In addition, the detection accuracy of the detected current Ia can be improved as compared with the conventional case.

  In the present embodiment, as shown in FIG. 13B, the bias magnet 13 is set so that the value of the combined magnetic field Hd, which is an external magnetic field, is not limited to the predetermined period T1, as described above. . Specifically, since the detected current Ia changes in the range of −Y [A] to + X [A], the detected current Ia can take the absolute value of the magnetic flux density of the bias magnetic field Hc acting on the AMR element 21. The bias magnet 13 is set so as to be larger than the absolute value of the magnetic flux density corresponding to the lower limit value (−Y [A]). For this reason, in the measurement range of the detected current Ia, the composite magnetic field Hd does not become zero but changes only within one polarity. Therefore, the detected current Ia can be accurately detected regardless of the value of the detected current Ia.

  Further, in this embodiment, the absolute value of the magnetic flux density of the magnetic field component in the y direction of the bias magnetic field Hc on the AMR element 21 is the absolute value of the residual magnetic flux density of the magnetic film constituting the AMR element 21 and the detected current. The bias magnet 13 is set so as to be larger than the sum of the absolute value of the magnetic flux density corresponding to the lower limit value (−Y [A]) that Ia can take. Thereby, even if the detected current Ia indicated by the solid line in FIG. 13A becomes zero for a predetermined period T1, for example, from a positive value, the combined magnetic field as the external magnetic field indicated by the solid line in FIG. Hd takes a value that is not affected by magnetic hysteresis in the predetermined period T1. Thus, since the influence of the magnetic hysteresis is eliminated during the predetermined period T1, the detected current Ia can be detected with high accuracy. Note that the alternate long and short dash line shown in FIG. 13B is the upper limit of the magnetic field that generates magnetic hysteresis, and magnetic hysteresis due to residual magnetization occurs in the region from the alternate long and short dash line to the magnetic field of zero.

(Fourth embodiment)
In the present embodiment, description of portions common to the current sensor 10 shown in the above embodiment is omitted. In the third embodiment, when the measurement range of the detected current Ia is −Y [A] to + X [A], the bias magnet 13 does not have a composite magnetic field Hd of zero and is within the same polarity. An example of generating a bias magnetic field Hc that changes is shown. On the other hand, in the present embodiment, the bias magnet 13 is set so that the combined magnetic field Hd instantaneously takes a zero value.

  As described above, when the bias magnet 13 is provided separately from the electromagnet 14, the external magnetic field acting on the AMR element 21 is offset by the bias magnetic field Hc. Therefore, it is possible to suppress the composite magnetic field Hd from becoming zero in the predetermined period T1 in which the value of the detected current Ia that greatly affects the measurement accuracy is zero. That is, the detection accuracy of the detected current Ia can be improved as compared with the conventional case.

  In the present embodiment, the absolute value of the magnetic flux density of the magnetic field component in the y direction of the bias magnetic field Hc on the AMR element 21 is made larger than the absolute value of the residual magnetic flux density of the magnetic film constituting the AMR element 21. In addition, a bias magnet 13 is set. Thereby, even if the detected current Ia indicated by the solid line in FIG. 14A becomes zero for a predetermined period T1, for example, from a positive value, the combined magnetic field as an external magnetic field indicated by the solid line in FIG. Hd takes a value that is not affected by magnetic hysteresis in the predetermined period T1. Thus, since the influence of the magnetic hysteresis is eliminated during the predetermined period T1, the detected current Ia can be detected with high accuracy. Note that the alternate long and short dash line shown in FIG. 14B is the upper limit of the magnetic field that generates magnetic hysteresis, and magnetic hysteresis due to residual magnetization occurs in the region from the alternate long and short dash line to the magnetic field of zero.

  Further, in this embodiment, since the offset amount by the bias magnet 13 is smaller than that in the third embodiment, the composite magnetic field Hd instantaneously becomes zero as shown in FIG. However, the detected current Ia continuously changes at a value other than zero, and is instantaneous even when the combined magnetic field Hd becomes zero. That is, the period in which the combined magnetic field (Hd) is zero is shorter than the predetermined period in which the value of the detected current Ia is zero. For this reason, the error of the cancellation current due to the residual magnetization can be suppressed as compared with the conventional case.

(Fifth embodiment)
In the present embodiment, description of portions common to the current sensor 10 shown in the above embodiment is omitted. In the above embodiment, an example in which the AMR element 21 is used as the magnetic detection element has been described. In contrast, in the present embodiment, a spin valve type giant magnetoresistive element (hereinafter simply referred to as a GMR element) or a tunnel magnetoresistive element (hereinafter simply referred to as a TMR element) is used as the magnetic detection element. It is characterized in that it is used.

  FIG. 15 is an enlarged cross-sectional view around the sensor chip 12 in the current sensor 10. The configuration is the same as that of the first embodiment (see FIGS. 1 and 2) except that the magnetic detection elements formed on the sensor chip 12 are different.

  In the example shown in FIG. 15, the GMR element 50 is provided on the sensor chip 12. As shown in FIG. 15, the GMR element 50 is formed by laminating an antiferromagnetic layer 51, a fixed layer 52, a nonmagnetic layer 53, a free layer 54, and a protective layer 55 in this order from the bus bar 11 (base 16) side.

  The antiferromagnetic layer 51 is formed using, for example, IrMn, and is formed on a base layer (not shown) in order to improve the crystal orientation. The fixed layer 52 (also referred to as a pinned layer) has a laminated ferrimagnetic structure in which a nonmagnetic intermediate layer made of, for example, Ru is disposed between fixed magnetic layers made of, for example, CoFe. The nonmagnetic layer 53 is formed using, for example, Cu having conductivity, and the free layer 54 is formed of, for example, a laminate of CoFe and NiFe. The protective layer 55 is formed using Ta. The configuration of the GMR element 50 is not limited to the above example. It is only necessary to have the fixed layer 52, the nonmagnetic layer 53, and the free layer 54. The fixed layer 52 is not limited to the laminated ferrimagnetic structure.

When the nonmagnetic layer 53 is formed using an insulating material such as Al ₂ O ₃ , a TMR element is obtained. In the case of a TMR element, it is necessary to form an electrode so that a current flows in a direction perpendicular to the laminated film, but the magnetoresistive element is basically the same as the GMR element 50.

  As is well known, the magnetization direction of the fixed layer 52 is fixed in a predetermined direction. On the other hand, the magnetization direction of the free layer 54 is not fixed, and the magnetization can be changed by the external magnetic field Hd. As the magnetization direction of the free layer 54 varies with respect to the external magnetic field Hd, the electric resistance value varies with the magnetization direction of the fixed layer 52.

  When the magnetization direction of the fixed layer 52 and the magnetization direction of the free layer 54 are antiparallel, the electric resistance value is maximized. On the other hand, when the magnetization direction of the fixed layer 52 and the magnetization direction of the free layer 54 are parallel, the electric resistance value is minimized. FIG. 16 shows the relationship between the magnetic field strength and the resistance value change rate. In the figure, the solid line indicates the GMR element 50 and the broken line indicates the TMR element. In both the GMR element 50 and the TMR element, when the magnetization direction of the fixed layer 52 and the magnetization direction of the free layer 54 are parallel, the resistance value change rate becomes a positive value, and the magnetization direction of the fixed layer 52 and the magnetization direction of the free layer 54 Is antiparallel, the resistance value change rate is a negative value. Although not shown, magnetic hysteresis due to residual magnetization occurs as in the AMR element 21 shown in the first embodiment.

  In the present embodiment, a GMR element 50 as a magnetic detection element has four GMR elements 50a to 50d as shown in FIG. These GMR elements 50a to 50d may be formed on separate sensor chips 12, or may be integrated on one chip.

  Of the four GMR elements 50a to 50d, a first half bridge is formed with the first GMR element 50a on the high potential side and the second GMR element 50b on the low potential side. A second half bridge is formed with the third GMR element 50c as the high potential side and the fourth GMR element 50d as the low potential side. These half bridges form an external magnetic field detection circuit having a full bridge configuration.

  In the four GMR elements 50a to 50d, the magnetization direction of each fixed layer 52 is parallel to the detected magnetic field Ha (synthetic magnetic field Hd), and the magnetization direction of the fixed layer 52 in the first GMR element 50a and the fourth GMR element 50d In addition, the magnetization direction of the fixed layer 52 in the second GMR element 50b and the third GMR element 50c is provided in the opposite direction.

  In the present embodiment, as shown in FIG. 17, all the GMR elements 50a to 50d have a rectangular planar shape along the xy plane. In addition to the rectangle (rectangle), for example, a meander shape may be used. The planar rectangular GMR elements 50a to 50d are formed so that their longitudinal directions are parallel to each other, and the longitudinal direction, that is, the current flow direction of the sensor chip is substantially parallel to the y direction. 12 is arranged on the bus bar 11. For this reason, the combined magnetic field Hd acting on the GMR elements 50 a to 50 d of the sensor chip 12 is parallel or antiparallel to the magnetization direction of the fixed layer 52.

  The magnetization direction of the fixed layer 52 and the magnetization direction F of the free layer 54 of the first GMR element 50a and the fourth GMR element 50d are antiparallel, and the resistance value is maximized. Further, the magnetization direction of the fixed layer 52 of the second GMR element 50b and the third GMR element 50c is parallel to the magnetization direction of the free layer 54, and the resistance value is minimized. As a result, a difference occurs in the midpoint potentials V1 and V2 of the external magnetic field detection circuit shown in FIG. Therefore, the canceling current and thus the detected current Ia can be detected by the current detection type circuit configuration (see FIG. 6) and the voltage detection type circuit configuration (see FIG. 9) shown in the first embodiment.

  Thus, the present embodiment can achieve the same effects as those of the first embodiment. Moreover, the structure shown in the modification of 1st Embodiment, 3rd Embodiment, and 4th Embodiment is also applicable.

  The preferred embodiments of the present invention have been described above. However, the present invention is not limited to the above-described embodiments, and various modifications can be made without departing from the spirit of the present invention.

  In the above embodiment, the resin base 16 is bonded and fixed to the bus bar 11, and the components of the current sensor 10 other than the bus bar 11, specifically, the sensor chip 12, the bias magnet 13, the electromagnet 14, and the circuit are fixed to the base 16. The chip 15 is bonded and fixed. And the example protected by case 17 was shown. However, the arrangement of the sensor chip 12, the bias magnet 13, the electromagnet 14, and the circuit chip 15 on the bus bar 11 is not limited to the above example. For example, in the example shown in FIG. 18A, the bus bar 11, the sensor chip 12, the bias magnet 13, and the electromagnet 14 with the sensor chip 12, the bias magnet 13, the electromagnet 14, and the circuit chip 15 being bonded and fixed to the base 16. The circuit chip 15 is covered with the mold resin 60. On the other hand, in the example shown in FIG. 18B, the base 16 is connected to the bus bar 11 by fastening with the screw 61 in a state where the sensor chip 12, the bias magnet 13, the electromagnet 14, and the circuit chip 15 are bonded and fixed to the base 16. It is fixed to.

  In the said embodiment, the electromagnet 14 showed the example which has the coil 30 formed by winding conducting wire, and the soft-magnetic core 31. FIG. However, an air core coil or a thin film coil may be adopted as the coil 30. In the case of an air-core coil, for example, as shown in FIG. 19A, the sensor chip 12 may be arranged in the coil 30. Thereby, the physique of the current sensor 10 can be reduced in size.

  In the above embodiment, an example of the columnar bias magnet 13 has been shown. However, a cylindrical bias magnet 13 can also be employed. For example, as shown in FIG. 19B, the sensor chip 12 may be arranged inside the cylindrical shape of the bias magnet 13. Further, the electromagnet 14 may be disposed inside the cylindrical shape of the bias magnet 13. In any case, the size of the current sensor 10 can be reduced.

  In the above embodiment, the side surface perpendicular to the magnetized end surface of the columnar bias magnet 13 so that the detected magnetic field Ha and the bias magnetic field Hc are substantially parallel on the one surface 12a of the sensor chip 12. One of these is shown as an example of being bonded and fixed to the base 16. However, the arrangement of the bias magnet 13 is not limited to the above example. The bias magnetic field Hc only needs to have a component substantially parallel (including antiparallel) to the detected magnetic field Ha on the one surface 12a of the sensor chip 12. For example, as shown in FIG. 19C, the bus bar 11 may be disposed obliquely with respect to the one surface 11a.

  In the above embodiment, an example in which only one bias magnet 13 is provided has been described. However, the number of bias magnets 13 is not particularly limited. For example, as shown in FIG. 20A, two bias magnets 13 a and 13 b may be provided so as to sandwich the sensor chip 12 and the electromagnet 14. In the example shown in FIG. 20, the end face on the sensor chip 12 side of the bias magnet 13a is magnetized to the N pole, and the end face on the sensor chip 12 side of the bias magnet 13b is magnetized to the S pole. Thereby, the magnetic field (bias magnetic field) generated by the bias magnet 13 can be made stronger.

  Further, the number of electromagnets 14 (coils 30) is not limited to one. For example, as shown in FIG. 20B, two electromagnets 14a and 14b may be provided so as to sandwich the sensor chip 12. Thereby, the magnetic field generated by the electromagnet 14 can be made stronger. When the cores 31 of the two electromagnets 14a and 14b are arranged on a straight line, a substantially perpendicular canceling magnetic field can be applied to the magnetic detection element.

  In the above embodiment, an example in which the circuit chip 15 is provided separately from the sensor chip 12 having the magnetic detection element has been described. However, the magnetic detection element formed on the sensor chip 12 and the processing circuit of the circuit chip 15 may be integrated on one chip.

  In the above embodiment, the sensor chip 12, the bias magnet 13, the electromagnet 14, and the circuit chip 15 are fixed to the bus bar 11, and the example in which the bus bar 11 is a constituent element of the current sensor 10 has been shown. However, the current sensor 10 may include the sensor chip 12, the bias magnet 13, the electromagnet 14, and the circuit chip 15.

  In the said embodiment, although the bus-bar 11 was made into flat form, the shape of the bus-bar 11 is not limited to the said example. For example, it may be a round bar or other shapes.

10 ... Current sensor device (magnetically balanced current sensor)
DESCRIPTION OF SYMBOLS 11 ... Bus bar 11a ... One side 12 ... Sensor chip 12a ... Element formation surface 13, 13a, 13b ... Bias magnet 14, 14a, 14b ... Electromagnet 15 ... Circuit chip 116- .... Base 17 ... Case 18 ... Bonding wire 19 ... Lead 20 ... Substrate 21, 21a-21d ... AMR element (anisotropic magnetoresistive element)
22a ... power supply pad 22b ... ground pads 22c, 22d ... output pads 23a-23c ... fixed resistor 24 ... magnetic shield 30 ... coil 31 ... bobbin 40 ... operational amplifier ( Supply means)
41 ... constant current source 42 ... detection resistor 43 ... differential amplifier circuit 44 ... operational amplifier 45-48 ... resistor 49 ... constant voltage source 50, 50a-50d ... magnetic detection Element (spin valve type GMR element, TMR element)
51 ... Antiferromagnetic layer 52 ... Fixed layer 53 ... Nonmagnetic layer 54 ... Free layer 55 ... Protective layer 60 ... Mold resin 61 ... Screw 100 ... Ammeter Ia: Detected current Ha ... Detected magnetic field Hb ... Canceling magnetic field Hc ... Bias magnetic field Hd ... Synthetic magnetic field

Claims (15)

Magnetic detecting elements (on the one surface (11a) of the bus bar (11) so that the output changes according to the detected magnetic field (Ha) formed by the detected current (Ia) flowing through the bus bar (11). 21, 50)
An electromagnet (14) which is provided on one surface (11a) of the bus bar (11) and generates a canceling magnetic field (Hb) for canceling the detected magnetic field (Ha) acting on the magnetic detection elements (21, 50). When,
Supply means (40) for supplying a canceling current for forming the canceling magnetic field (Hb) to the electromagnet (14),
A magnetic balance type current sensor for detecting a detected current (Ia) flowing through the bus bar (11) based on the offset current;
The magnetic detection element (21, 50) is a magnetoresistive effect element having a magnetic film formed using a magnetic metal,
A magnetic field component provided on one surface (11a) of the bus bar (11) and parallel to the direction of the detected magnetic field (Ha) acting on the magnetic detection elements (21, 50); A bias magnet (13) for generating a bias magnetic field (Hc) having a constant magnitude;
The electromagnet (14) generates a magnetic field that cancels a combined magnetic field (Hd) of the detected magnetic field (Ha) and the bias magnetic field (Hc) as the canceling magnetic field (Hb). Current sensor.   The magnetism according to claim 1, wherein the bias magnet (13) generates a bias magnetic field (Hc) in which the combined magnetic field (Hd) does not become zero and changes within the same polarity. Balanced current sensor. The detected current (Ia) varies within the same polarity,
The absolute value of the magnetic flux density of the bias magnetic field (Hc) acting on the magnetic detection element (21, 50) is larger than the absolute value of the residual magnetic flux density of the magnetic film constituting the magnetic detection element (21, 50). The magnetic balanced current sensor according to claim 2. The polarity of the detected current (Ia) changes between plus and minus,
The absolute value of the magnetic flux density of the bias magnetic field (Hc) acting on the magnetic detection element (21, 50) is the absolute value of the residual magnetic flux density of the magnetic film constituting the magnetic detection element (21, 50), The magnetic balance type current sensor according to claim 2, wherein the detected current (Ia) is larger than a sum of absolute values of magnetic flux densities corresponding to a lower limit value that can be taken. The polarity of the detected current (Ia) changes between plus and minus,
The absolute value of the magnetic flux density of the bias magnetic field (Hc) acting on the magnetic detection element (21, 50) is larger than the absolute value of the residual magnetic flux density of the magnetic film constituting the magnetic detection element (21, 50). The magnetic balanced current sensor according to claim 1.   The magnetic balance type current sensor according to claim 1, wherein the magnetic detection element includes an anisotropic magnetoresistive element (21). The magnetic detection element (21) has four anisotropic magnetoresistive elements (21a to 21d),
Of the four anisotropic magnetoresistive elements (21a to 21d), the first anisotropic magnetoresistive element (21a) is on the high potential side and the second anisotropic magnetoresistive element (21b) is on the low potential side. A first half bridge is formed on the side, and a second half bridge is formed with the third anisotropic magnetoresistive element (21c) on the high potential side and the fourth anisotropic magnetoresistive element (21d) on the low potential side. Then, a full bridge circuit is configured by these half bridges,
Of the four anisotropic magnetoresistive elements (21a to 21d), the first anisotropic magnetoresistive element (21a) and the fourth anisotropic magnetoresistive element (21d) are the elements ( 21, 24) and the second anisotropic magnetoresistive effect element (21 b) and the third anisotropic magnetoresistive effect element are provided so that the direction of the current flowing through the detected magnetic field (Ha) is parallel to the detected magnetic field (Ha). (21c) is provided such that the direction of the current flowing through the element (22, 23) is perpendicular to the detected magnetic field (Ha),
The magnetic balance according to claim 6, wherein the supply means (40) supplies the canceling current based on a difference between the midpoint potentials (V1, V2) of the half bridges to the electromagnet (14). Current sensor.   The magnetic balanced current sensor according to claim 7, wherein the four anisotropic magnetoresistive elements (21a to 21d) are formed on the same surface (12a) of the same chip (12). .   The chip (12) is arranged such that one surface (12a) on which the anisotropic magnetoresistive element (21) is formed is parallel to one surface (11a) of the bus bar (11). The magnetic balance type current sensor according to claim 8.   In the chip (12), one surface (12a) on which the anisotropic magnetoresistive element (21) is formed is perpendicular to one surface (11a) of the bus bar (11), and the detected magnetic field (Ha) The magnetic balance type current sensor according to claim 8, wherein the magnetic balance type current sensor is arranged in parallel with the current sensor.   The magnetic detection element has a free layer (54) whose magnetization direction varies with respect to the combined magnetic field (Hd) on one surface of a fixed layer (52) whose magnetization direction is fixed via a nonmagnetic layer (53). 6) a magnetoresistive effect element (50) having a spin valve type giant magnetoresistive effect or a tunnel magnetoresistive effect disposed therein. Balanced current sensor. The magnetic detection element (50) has four magnetoresistive elements (50a to 50d),
Of the four magnetoresistive elements (50a to 50d), the first half bridge is formed with the first magnetoresistive element (50a) as the high potential side and the second magnetoresistive element (50b) as the low potential side. A second half bridge is formed with the third magnetoresistive element (50c) on the high potential side and the fourth magnetoresistive element (50d) on the low potential side, and these half bridges form a full bridge circuit,
In the four magnetoresistive elements (50a to 50d), the magnetization direction of each fixed layer (52) is parallel to the detected magnetic field (Ha), and the first magnetoresistive element (50a) and the first magnetoresistive element (50a) The magnetization direction of the fixed layer (52) in the four magnetoresistive effect element (50d), and the magnetization direction of the fixed layer (52) in the second magnetoresistive effect element (50b) and the third magnetoresistive effect element (50c) Is provided in the opposite direction,
The magnetic balance according to claim 11, wherein the supply means (40) supplies the electromagnet (14) with the canceling current based on a difference between the midpoint potentials (V1, V2) of the half bridges. Current sensor.   The magnetic balance type according to any one of claims 1 to 12, wherein the bias magnet (13) has a cylindrical shape, and the magnetic detection element (21, 50) is disposed inside the cylindrical shape. Current sensor.   The magnetic balance type current sensor according to any one of claims 1 to 13, wherein the bias magnet (13) has a cylindrical shape, and the electromagnet (14) is disposed inside the cylindrical shape. The electromagnet (14) has a coil (30);
The magnetic balance type current sensor according to any one of claims 1 to 12, wherein the magnetic detection element (21, 50) is disposed in the coil (30).

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