JP2010243232A - Current sensor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a miniaturizable current sensor whose detectable current-value range is wide. <P>SOLUTION: In this current sensor, first to fourth magnetoresistive elements 2a-2d are arranged so that a first and third magnetoresistive elements 2a and 2c and a signal magnetic field B are parallel to each other, and second and fourth magnetoresistive elements 2b and 2d and the signal field B are perpendicular to each other. First and second bias magnetic fields B1 and B2 are applied in a direction which forms an angle of 45° with respect to the first and second magnetoresistive elements 2a and 2b, and in a direction which forms the angle of 45° with respect to the third and fourth magnetoresistive elements 2c and 2d respectively. Moreover, the direction of the second bias field B2 is made to be a direction which forms an angle of 180° with respect to the direction of the first bias field B1, or a direction which forms an angle of 90° with respect to the first bias field B1 so that a component parallel to the signal field B becomes opposite in direction to the first bias field B1. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a current sensor for detecting a current flowing in a conductive wire of various electronic devices.

  A conventional current sensor of this type has two magnetoresistive elements whose extending directions are 90 ° to each other, and the extending directions of all the magnetoresistive elements are signal magnetic fields generated from the current flowing through the conductor. The magnet is arranged so as to form an angle of 45 ° with the direction, and the bias magnetic field forms an angle of 90 ° with the direction of the signal magnetic field. Then, the strength of the signal magnetic field is detected from the obtained output signal (voltage), and the value of the current flowing through the conductor is detected from the strength of the signal magnetic field.

As prior art document information relating to the invention of this application, for example, Patent Document 1 is known.
JP 2004-20371 A

  The conventional current sensor described above has a problem that the range of current values that can be detected is narrow and it is difficult to reduce the size.

  That is, the magnetoresistive element has a portion where the output with respect to the signal magnetic field becomes non-linear, so the range of the current value that can be detected is narrow, and the linear portion of the output should be widened to widen the range of the current value that can be detected. This is because it is necessary to increase the bias magnetic field, and for this purpose, it is necessary to use a large magnet.

  SUMMARY OF THE INVENTION The present invention solves the above-described conventional problems, and an object of the present invention is to provide a current sensor that has a wide range of detectable current values and can be miniaturized.

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

  According to a first aspect of the present invention, in a current sensor for detecting a signal magnetic field generated from a current flowing through a conductor and detecting a current flowing through the conductor, the extending directions are orthogonal and connected to each other at the end. A first detection unit composed of the first magnetoresistive element and the second magnetoresistive element, and a third magnetoresistive element and a fourth magnetoresistive element whose extending directions are orthogonal and connected to each other at the ends. A second detection unit, a first output unit formed at the connection between the first and second magnetoresistive elements, and a second output formed at the connection between the third and fourth magnetoresistive elements. The first and third magnetoresistive elements are connected to voltage terminals at the end of the first to fourth magnetoresistive elements that are not connected to the connecting section. The second and fourth magnetoresistive elements are connected to the ground, and the first and second magnetoresistive elements are connected to the ground. The first and third magnetoresistive elements are arranged so that the magnetoresistive element and the signal magnetic field are parallel to each other, and the second and fourth magnetoresistive elements and the signal magnetic field are perpendicular to each other. The second and fourth magnetoresistive elements are arranged so that the first detection unit has a first angle in a direction that forms an angle of 45 ° with the extending direction of the first and second magnetoresistive elements. A bias magnetic field is applied, and the second detector applies a second bias magnetic field in a direction that forms an angle of 45 ° with the extending direction of the third and fourth magnetoresistive elements. The first bias magnetic field so that the direction of the magnetic field is a direction that forms an angle of 180 ° with the direction of the first bias magnetic field, or a component parallel to the signal magnetic field is opposite to the first bias magnetic field. To be in a direction that makes an angle of 90 ° with the direction of According to this configuration, the output obtained by the first detection unit and the output obtained by the second detection unit can be symmetric with respect to the voltage (output) axis. The dynamic processing can cancel out the non-linear part of the characteristics of the magnetoresistive element, thereby improving the linearity of the output obtained by the differential processing with respect to the signal magnetic field, and can be detected without using a large magnet. The effect that the range of the current value can be widened can be obtained.

  According to the second aspect of the present invention, the magnetoresistive elements respectively constituting the first detection unit and the second detection unit are configured to be a full bridge circuit. According to this configuration, In each of the first and second detection units, the output of the first detection unit and the second detection unit are obtained because the output of the first detection unit and the second detection unit can be doubled by obtaining a differential output of the two output units. If the output is differentially processed, the change corresponding to the fluctuation in the signal magnetic field of the output obtained by this differential processing becomes large, and thereby the effect of enabling more accurate current value detection can be obtained. It is.

  In the invention according to claim 3 of the present invention, in particular, the strength of the first and second bias magnetic fields is 2.5 times or more than the strength of the signal magnetic field generated at the maximum current to be detected. According to this configuration, it is possible to obtain an operational effect that the linearity error can be less than 1%.

  In the invention according to claim 4 of the present invention, in particular, the first detection unit and the second detection unit are positioned on opposite sides of the conductor. According to this configuration, the first detection unit If the output obtained by the unit and the output obtained by the second detection unit are differentially processed, an effect of canceling the external magnetic field can be obtained.

  The invention according to claim 5 of the present invention is such that the first and second bias magnetic fields are applied by forming a CoPt magnet on the substrate as a thin film. According to this configuration, The effect that the current sensor can be reduced in thickness and size can be obtained.

  As described above, in the current sensor of the present invention, the first and third magnetoresistive elements are arranged so that the first and third magnetoresistive elements and the signal magnetic field are parallel to each other, and the second and second magnetoresistive elements are arranged. The second and fourth magnetoresistive elements are arranged so that the four magnetoresistive elements and the signal magnetic field are perpendicular to each other, and the first and second magnetoresistive elements are extended in the first detection unit. The first bias magnetic field is applied in a direction that forms an angle of 45 ° with the direction, and the second detection unit performs a second operation in a direction that forms an angle of 45 ° with the extending direction of the third and fourth magnetoresistive elements. The bias magnetic field is applied, and the direction of the second bias magnetic field is set to a direction that forms an angle of 180 ° with the direction of the first bias magnetic field, or a component parallel to the signal magnetic field is the first bias magnetic field. The direction of the first bias magnetic field and 90 Therefore, the output obtained by the first detection unit (first output unit) and the output obtained by the second detection unit (second output unit) are converted into voltages (outputs). ) The output can be made symmetrical with respect to the axis, and if the two are differentially processed, the nonlinear portion of the characteristics of the magnetoresistive element can be canceled out. As a result, it is possible to widen the range of current values that can be detected without using a large magnet.

  Hereinafter, a current sensor according to an embodiment of the present invention will be described with reference to the drawings.

  FIG. 1 is a top view of a main part of a current sensor according to an embodiment of the present invention, and FIG. 2 is a schematic view of the current sensor as viewed from the side.

  As shown in FIGS. 1 and 2, the current sensor according to the embodiment of the present invention has a first and a second magnetic field formed on an insulating substrate 1b provided on the upper surface of a base 1a and made of alumina or the like. Resistance elements 2a and 2b and third and fourth magnetoresistance elements 2c and 2d are provided. The first and second magnetoresistive elements 2a and 2b are connected so that the extending directions are orthogonal to each other, and the first and second magnetoresistive elements 2a and 2b are connected to the first and second magnetoresistive elements 2a and 2b. The first detection unit 5 is configured by the first output unit 4 formed at the connection unit 3 of the two magnetoresistive elements 2a and 2b. The third and fourth magnetoresistive elements 2c and 2d are also connected so that their extending directions are orthogonal to each other, and the third and fourth magnetoresistive elements 2c and 2d are connected to the third and fourth magnetoresistive elements 2c and 2d. The second detection unit 8 is configured by the second output unit 7 formed in the connection unit 6 of the four magnetoresistive elements 2c and 2d. At this time, at the end of the first to fourth magnetoresistive elements 2a to 2d that are not connected to the connecting parts 3 and 6, the first and third magnetoresistive elements 2a and 2c are used as voltage terminals. The second and fourth magnetoresistive elements 2b and 2d are connected to the ground while being connected.

  The first to fourth magnetoresistive elements 2a to 2d are formed on the substrate 1b by a method such as vapor deposition, and the shape thereof is shown as a rectangular shape in FIG. It is configured in a meandering manner so as to be folded back. And when the magnetic field is not applied, each resistance value of the 1st-4th magnetoresistive elements 2a-2d is substantially the same. Furthermore, the first to fourth magnetoresistive elements 2 a to 2 d (first and second detection units 5 and 8) are protected by the protective film 9. In FIG. 2, the first to fourth magnetoresistive elements 2 a to 2 d are not shown, but the first to fourth magnetoresistive elements 2 a to 2 d are located between the substrate 1 b and the protective film 9. is doing.

  In addition, a signal magnetic field B is generated from the current flowing through the conductor 10. Regarding the direction of the signal magnetic field B, the first and third magnetoresistive elements 2a and 2c and the signal magnetic field B are parallel to each other, and The first to fourth magnetoresistive elements 2a to 2d are arranged so that the second and fourth magnetoresistive elements 2b and 2d and the signal magnetic field B are perpendicular to each other. In FIG. 1, only the direction of the current flowing through the conductor 10 is shown. Further, the direction of current is not necessarily limited to the direction of FIG.

  Here, the conductor 10 is provided so as to be in contact with the current sensor or through a certain distance, and the signal magnetic field B is generated by the current flowing through the conductor 10. At this time, in the first to fourth magnetoresistive elements 2a to 2d, a voltage is applied between the voltage terminal and the ground, and the output (voltage V01) obtained from the first output unit 4 and the second output unit 7 are obtained. This signal magnetic field B is detected by the output obtained by differentially processing the output (voltage V02). Then, the current value flowing through the conductor 10 is calculated from the signal magnetic field B. In FIG. 1, the substrate 1b is omitted and the direction of the signal magnetic field B is also shown.

  Further, although not shown in FIG. 1, in order to apply the first bias magnetic field B1 to the first detector 5 and the second bias magnetic field B2 to the second detector 8, the lower surface of the base 1a is applied. A magnet 11 made of BaFe, SrFe or the like is provided. The magnet 11 only needs to be formed above or below the first to fourth magnetoresistive elements 2a to 2d. If the magnet 11 is made of CoPt and formed by thin film technology, the current sensor Thinning and miniaturization are possible. At this time, the magnet 11 may be provided on the substrate 1b, and the first to fourth magnetoresistive elements 2a to 2d may be formed thereon via an insulating film. Alternatively, the magnet 11 may be formed on the substrate 1b. The first to fourth magnetoresistive elements 2a to 2d may be provided, and the magnet 11 may be formed thereon via an insulating film.

  Next, the direction in which the first bias magnetic field B1 and the second bias magnetic field B2 are applied will be described.

  As shown in FIG. 3, the first bias magnetic field B1 is applied in a direction that forms an angle of 45 ° with the extending direction of the first and second magnetoresistive elements 2a and 2b.

  The second bias magnetic field B2 is in a direction that forms an angle of 45 ° with the extending direction of the third and fourth magnetoresistive elements 2c and 2d, and an angle of 180 ° with the direction of the first bias magnetic field B1. It is applied in the direction to make.

  In this case, as shown in FIG. 4, the direction of the second bias magnetic field B2 is such that the component parallel to the signal magnetic field B generated from the current flowing through the conductor 10 is opposite to the first bias magnetic field B1. As described above, the direction of the first bias magnetic field B1 may be 90 °.

  In the current sensor according to the embodiment of the present invention described above, the first detection unit 5 includes the first sensor in a direction that forms an angle of 45 ° with the extending direction of the first and second magnetoresistive elements 2a and 2b. A bias magnetic field B1 is applied, and the second detection unit 8 applies a second bias magnetic field B2 in a direction that forms an angle of 45 ° with the extending direction of the third and fourth magnetoresistive elements 2c and 2d. The direction of the second bias magnetic field B2 is set to a direction that forms an angle of 180 ° with the direction of the first bias magnetic field B1, or a component parallel to the signal magnetic field B is opposite to the first bias magnetic field B1. Since the direction of the first bias magnetic field B1 is 90 ° with respect to the voltage V01 obtained by the first detector 5 (first output unit 4) and the second Obtained by the detection unit 8 (first output unit 7) Since the voltage V02 can be symmetric with respect to the voltage (output) axis, and if both are differentially processed, the nonlinear portion of the characteristics of the magnetoresistive element can be canceled, so that the differential processing for the signal magnetic field B Thus, the linearity of the output obtained in (1) is improved. As a result, the range of current values that can be detected can be widened without using a large magnet.

  That is, when the first and second bias magnetic fields B 1 and B 2 are applied as described above, the signal generated from the voltage V 01 output from the first output unit 4 of the first detection unit 5 and the current flowing through the conductor 10. As shown by the solid line in FIG. 5, the relationship with the magnetic field B is a downwardly protruding non-linear portion, while the voltage V02 output from the second output unit 7 of the second detection unit 8 and the signal magnetic field B As shown by the broken line in FIG. 5, a non-linear part protruding downward is generated and is symmetrical with respect to the voltage (output) axis. Therefore, if the voltage V01 and the voltage V02 are differentially processed, The downwardly convex non-linear portion in the voltage V02 becomes the upward convex non-linear portion, and this is added to the downward convex non-linear portion in the voltage V01, and as a result, as shown in FIG. In the first detection unit 5 and the second detection unit 8, Relationship between the output obtained from the differential processing is to have a linearity.

  As a result, since the range of the linear portion of the output is widened, the range of current values that can be detected is widened. Further, at this time, it is not necessary to use a large magnet or a strong magnet, so that downsizing is possible and inexpensive. Can produce current sensors.

  Next, the relationship between the strength of the signal magnetic field B and the strength of the first and second bias magnetic fields B1 and B2, and the direction of the signal magnetic field B and the direction of the first and second bias magnetic fields B1 and B2 are made. The angle will be described.

  (Table 1) shows the strength of the first and second bias magnetic fields B1 and B2 when the strength of the signal magnetic field B generated from the current flowing through the conductor 10 is ± 100 gauss (± 0.01 T). 4 is a table showing a linearity error with respect to an angle formed between the direction of the first and second bias magnetic fields B1 and B2 and the direction of the signal magnetic field B.

  Here, the maximum value of the ratio of the difference between the output obtained from the differential processing of the first and second output units 4 and 7 and the actual straight line is represented as a linearity error.

  As is clear from Table 1, it can be seen that the linearity is improved by increasing the strength of the first and second bias magnetic fields B1 and B2. It can also be seen that the angle formed between the direction of the signal magnetic field B and the direction of the first and second bias magnetic fields B1 and B2 needs to be 45 ° instead of 90 °. Here, even when the angle is 90 °, the linearity is improved by increasing the strengths of the first and second bias magnetic fields B1 and B2, but if the bias magnetic fields B1 and B2 are increased, the magnet 11 is moved. It is not preferable because it is necessary to increase the size, which makes it difficult to reduce the size and disadvantages in terms of cost.

  FIG. 7 shows that the angle between the direction of the signal magnetic field B generated from the current flowing through the conductor 10 and the direction of the first and second bias magnetic fields B1 and B2 is 45 °, and the strength of the signal magnetic field B is ± It is a figure which shows the relationship between the ratio with respect to the intensity | strength of 1st, 2nd bias magnetic field B1, B2 of the intensity | strength of the signal magnetic field B when it is 100 gauss, and a linearity error. The signal magnetic field B at this time indicates a magnetic field generated at the maximum current among currents that can be detected by the current sensor.

  As is apparent from FIG. 7, if the strength of the first and second bias magnetic fields B1 and B2 is 2.5 times or more than the strength of the signal magnetic field B, the linearity error can be made less than 1%. . At this time, if the linearity error is less than 1%, it is possible to respond to a user's request for highly accurate current value detection.

  In the above-described current sensor according to the embodiment of the present invention, the magnetoresistive element constituting each of the first and second detection units 5 and 8 has been described as a half bridge circuit. You may comprise in a bridge circuit. According to this configuration, if the differential between the two output units 4 and 7 is obtained in each of the first and second detection units 5 and 8, a double output can be obtained. If the output obtained and the output obtained by the second detection unit 8 are further differentially processed, the change in the signal magnetic field B of the output obtained as a result of the differential processing becomes large, and thereby more accurate Current value can be detected.

  Further, the first and second detection units 5 and 8 are not arranged on the same plane, but the first detection unit 5 and the second detection unit 8 are opposite to each other on the conductor 10 as shown in FIG. You may make it locate in this.

  Normally, the external magnetic field Bex is applied to the first and second detection units 5 and 8 in the same direction. With this configuration, the first detection unit 5 (first output unit 4) uses this configuration. If the output obtained and the output obtained by the second detection unit 8 (second output unit 7) are differentially processed, the external magnetic field Bex can be canceled. Further, since the direction of the signal magnetic field B applied to the first detector 5 and the direction of the signal magnetic field B applied to the second detector 8 are opposite (180 °), the differential of the two outputs By performing the processing, the output component is amplified, thereby enabling more accurate current value detection. In FIG. 8, the base 1a and the magnet 11 are omitted.

  The current sensor according to the present invention has an effect that a range of current values that can be detected is wide and can be reduced in size, and in particular, a current sensor for detecting a current flowing in a conductor of various electronic devices, etc. It becomes useful by applying to.

The top view of the principal part of the current sensor in one embodiment of the present invention Schematic view when viewing the same current sensor from the side The figure which shows the direction of the 1st bias magnetic field in the same current sensor, and the 2nd bias magnetic field The figure which shows the direction of the 1st bias magnetic field in the same current sensor, and the 2nd bias magnetic field The figure which shows the relationship between the output and signal magnetic field which are each obtained in the 1st, 2nd output part in the same current sensor The figure which shows the relationship between the output and signal magnetic field which are obtained when the output obtained in the 1st, 2nd output part in the same current sensor is differentially processed The figure which shows the relationship between the ratio with respect to the intensity | strength of the 1st, 2nd bias magnetic field of the signal magnetic field intensity in the same current sensor, and a linearity error. Schematic diagram of the main part showing another example when the current sensor is viewed from the side.

DESCRIPTION OF SYMBOLS 1b Substrate 2a-2d 1st-4th magnetoresistive element 3 Connection part of 1st magnetoresistive element and 2nd magnetoresistive element 4 1st output part 5 1st detection part 6 3rd magnetoresistive element And 4th magnetoresistive element connection part 7 2nd output part 8 2nd detection part 10 Conductor 11 Magnet

Claims (5)

In the current sensor for detecting the signal magnetic field generated from the current flowing through the conductor and detecting the current flowing through the conductor,
A first detection unit composed of a first magnetoresistive element and a second magnetoresistive element whose extending directions are orthogonal to each other and connected to each other at an end;
A second detection unit composed of a third magnetoresistive element and a fourth magnetoresistive element whose extending directions are orthogonal to each other and connected to each other at an end;
A first output portion formed at a connection portion of the first and second magnetoresistive elements;
A second output portion formed at a connection portion of the third and fourth magnetoresistive elements,
At the end of the first to fourth magnetoresistive elements that are not connected to the connecting portion, the first and third magnetoresistive elements are connected to voltage terminals, and the second and fourth magnetoresistive elements are connected to voltage terminals. The magnetoresistive element is connected to ground,
The first and third magnetoresistive elements are arranged so that the first and third magnetoresistive elements and the signal magnetic field are parallel to each other, and the second and fourth magnetoresistive elements and the signal are arranged. The second and fourth magnetoresistive elements are arranged so that the magnetic field is perpendicular to each other,
In the first detection unit, a first bias magnetic field is applied in a direction that forms an angle of 45 ° with the extending direction of the first and second magnetoresistive elements,
In the second detection unit, a second bias magnetic field is applied in a direction that forms an angle of 45 ° with the extending direction of the third and fourth magnetoresistive elements,
The direction of the second bias magnetic field is set to a direction that forms an angle of 180 ° with the direction of the first bias magnetic field, or the component parallel to the signal magnetic field is opposite to the first bias magnetic field. A current sensor arranged to form a 90 ° angle with the direction of the first bias magnetic field. The current sensor according to claim 1, wherein the magnetoresistive elements respectively constituting the first detection unit and the second detection unit are configured as a full bridge circuit. 2. The current sensor according to claim 1, wherein the strength of the first and second bias magnetic fields is 2.5 times or more of the strength of the signal magnetic field generated at the maximum current to be detected. The current sensor according to claim 1, wherein the first detection unit and the second detection unit are positioned on opposite sides of the conductor. The current sensor according to claim 1, wherein the first and second bias magnetic fields are applied by forming a magnet made of CoPt as a thin film on the substrate.

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