WO2012053296A1

WO2012053296A1 - Current sensor

Info

Publication number: WO2012053296A1
Application number: PCT/JP2011/070886
Authority: WO
Inventors: 斎藤　正路; 高橋　彰; 俊彦西田; 雅博飯塚
Original assignee: アルプス・グリーンデバイス株式会社
Priority date: 2010-10-20
Filing date: 2011-09-13
Publication date: 2012-04-26
Also published as: JPWO2012053296A1

Abstract

The objective of the present invention is to provide a current sensor that has both a wide range of measurement and a high resolution. This current sensor (1) is characterized by being provided with: a first current sensor (11A) that is equipped with a first magnetic sensor and that has a first measurable range; a second current sensor (11B) that is equipped with a second magnetic sensor and that has a second measurable range that has a higher upper limit value than the first measurable range; and a sensor selection means (12) that, in accordance with the magnitude of the current to be measured that is conducting through a current line, selects the output of the first current sensor or the output of the second current sensor.

Description

Current sensor

The present invention relates to a current sensor that measures current without contact. In particular, the present invention relates to a current sensor having a wide measurement range and high resolution.

In the field of motor drive technology in electric vehicles and hybrid cars, a relatively large current is handled, and a current sensor capable of measuring a large current without contact is required for such an application. And, as such a current sensor, one of a method of detecting a change of a magnetic field generated by a current to be measured by a magnetic sensor has been put to practical use. There are various such magnetic sensors. For example, Patent Document 1 discloses a current sensor using a magnetoresistive element as an element for the magnetic sensor.

Japanese Patent Laid-Open No. 2002-156390

By the way, it is known that various electric circuits, electronic devices and the like mounted on the above-mentioned electric car and the like consume a power by supplying a minute current (called a dark current) even in the off state. . Although the energy that can be supplied by the battery fluctuates greatly depending on the power consumption due to dark current, accurate measurement of dark current enables appropriate management of the remaining battery capacity. It is possible to operate the battery efficiently.

However, while the current sensor for measuring the high current described above has a wide measurement range, the resolution (also referred to as sensitivity) is low. In other words, current sensors for high current measurement are not suitable for applications that measure minute current such as dark current. Therefore, if such a current sensor for measuring a large current is used to measure the dark current, it is difficult to properly manage the remaining battery capacity, and it is necessary to operate the battery with a sufficient remaining capacity. Absent.

The present invention has been made in view of the foregoing, and it is an object of the present invention to provide a current sensor having a wide measurement range and high resolution.

The current sensor of the present invention comprises a first magnetic sensor, and comprises a first current sensor having a first measurable range and a second magnetic sensor, wherein the upper limit value is higher than the first measurable range. And the output of the first current sensor or the output of the second current sensor, depending on the magnitude of the measured current flowing through the current line. And sensor selection means for selecting In the above, the “measurable range” is a range defined by the lower limit value and the upper limit value of the current, and is a range in which the current value can be measured with appropriate accuracy.

According to this configuration, by selecting and using one of the outputs of the two current sensors having different measurable ranges, it is possible to measure a minute current with high accuracy while measuring a large current.

In the current sensor of the present invention, the first current sensor may have a first resolution, and the second current sensor may have a second resolution lower than the first resolution. In the above, “resolution” is an index that represents sensitivity, and refers to an index that is represented by the smallest measurable current value.

According to this configuration, it is possible to measure a minute current with high accuracy while measuring a large current by selecting and using one of the outputs of two current sensors having different measurable ranges and different resolutions. become.

In the current sensor of the present invention, the upper limit value of the second measurable range may be ten times or more of the upper limit value of the first measurable range. The first resolution may be ten times or more of the second resolution. Note that resolution of "a-fold or more" (a is an arbitrary number) is synonymous with sensitivity of "a-fold or more", and the minimum measurable current value is "1 / a or less". It says that there is.

According to this configuration, by selecting and using the output of the current sensor whose upper limit value of the measurable range is sufficiently high and the output of the current sensor whose resolution is sufficiently high, a minute current can be measured while measuring a large current. It becomes possible to measure with high accuracy.

In the current sensor of the present invention, the second magnetic sensor may include an element shield that covers the magnetic sensor element.

According to this configuration, since the influence of the induced magnetic field due to the current to be measured is mitigated by the element shield, the upper limit value of the measurable range of the second current sensor provided with the second magnetic sensor can be sufficiently increased. it can.

In the current sensor of the present invention, the first current sensor and the second current sensor may be provided in the same chip.

According to this configuration, by providing the first current sensor and the second current sensor in the same chip, compared to the case where the first current sensor and the second current sensor are separate chips, It is possible to improve the alignment accuracy of the position and angle. This improves the current measurement accuracy. In addition, the number of chips can be increased and the package cost can be reduced, as compared to the case where the first current sensor and the second current sensor are separate chips. Thereby, the cost of the current sensor can be reduced.

In the current sensor of the present invention, each of the first magnetic sensor and the second magnetic sensor may be a magnetic balance type sensor using a feedback coil.

According to this configuration, a highly sensitive current sensor can be easily realized. Further, the characteristics of the magnetic sensor can be easily changed by adjusting the number of turns of the feedback coil.

In the current sensor according to the present invention, the first current sensor includes a pair of the first magnetic sensors, is connected to the pair of first magnetic sensors, and calculates an output signal of the first magnetic sensor differentially; May be provided. The second current sensor may include a pair of the second magnetic sensors, may be connected to the pair of the second magnetic sensors, and may include an arithmetic device that differentially calculates output signals thereof. .

According to this configuration, since the influence of the external magnetic field can be canceled by the differential operation, the measurement accuracy of the current can be sufficiently improved. In particular, in a current sensor for fine current measurement which is greatly affected by an external magnetic field, the effect is large.

The current sensor of the present invention can measure a minute current with high accuracy while measuring a large current by selecting and using the outputs of two current sensors having different measurable ranges and different resolutions.

It is a schematic diagram which shows the circuit structure of a current sensor. It is a cross-sectional schematic diagram which shows the laminated constitution of the magnetic sensor used for an electric current sensor. It is a flowchart explaining a current measurement algorithm. It is a figure which shows the relationship between the output voltage of each current sensor, and a to-be-measured electric current.

Current sensors for large current measurement are not suitable for applications to measure minute current such as dark current. If dark current is managed using this, the battery can be operated with enough remaining capacity. I can not but do. The reason that the current sensor for high current measurement is not suitable for fine current measurement is that the resolution, which is in a trade-off relationship with the measurement range, is low in order to widen the measurement range.

Focusing on this point, the inventors have found that it is possible to cope with high current measurement and fine current measurement by selecting and using the outputs of two current sensors having different measurable ranges and different resolutions. The

That is, the gist of the present invention is measured by including at least two or more current sensors having different measurable ranges and resolutions, and a sensor selection unit which selects these outputs according to the magnitude of the measured current. The measurement range is changed according to the magnitude of the current to realize appropriate current measurement. Hereinafter, the embodiments will be described in detail with reference to the drawings.

FIG. 1 is a block diagram showing an example of a circuit configuration of a current sensor 1 according to the present embodiment. FIG. 1 is a view for explaining the features of the present invention in an easy-to-understand manner, and does not strictly represent the configuration of the current sensor 1. That is, in FIG. 1, a part of the configuration of the current sensor 1 may be omitted. In addition, another configuration may be added to the configuration shown in FIG.

As shown in FIG. 1, the current sensor 1 is a sensor selection circuit to which the outputs of the first current sensor 11A and the second current sensor 11B, and the first current sensor 11A and the second current sensor 11B are input. And 12). Here, the first current sensor 11A and the second current sensor 11B have different measurable ranges and resolutions, and each output a voltage corresponding to the current to be measured. The sensor selection circuit 12 determines which of the output of the first current sensor 11A and the output of the second current sensor 11B is to be adopted according to the output voltage of the first current sensor 11A or the second current sensor 11B. The output of the adopted sensor is output as the output of the current sensor 1. That is, the sensor selection circuit 12 selects the output of the first current sensor 11A and the output of the second current sensor 11B according to the current to be measured.

The first current sensor 11A and the second current sensor 11B have different measurable ranges and resolutions, but one has high resolution and the other has wide measurable range (or the upper limit of the measurable range is high) It is desirable to be configured to be For example, the first current sensor 11A has a narrow measurable range (hereinafter referred to as the first measurable range) so as to be able to measure a minute current, but sufficient resolution (hereinafter referred to as the first resolution) It is configured to be high. Also, for example, the resolution (hereinafter referred to as the second resolution) is low so that the second current sensor 11B can measure a large current, but the measurable range (hereinafter referred to as the second measurable range) is sufficiently It is configured to be broad.

More specifically, the first resolution is 10 times or more of the second resolution, and the upper limit value of the second measurable range is 10 times or more of the upper limit value of the first measurable range. For example, the first resolution is about 0.001 to 0.1 A, typically about 0.01 A, and the second resolution is about 0.1 A to 1 A, typically about 0.1 A. The upper limit of the first measurable range is about 1 A to 100 A, typically about 10 A, and the upper limit of the second measurable range is about 10 A to 1000 A, typically about 100 A.

By adopting the configuration as described above, a minute current can be measured with high accuracy while measuring a large current.

For example, a magnetic balance type magnetic sensor is used for the first current sensor 11A and the second current sensor 11B. A magnetic balance type magnetic sensor is arranged so as to be able to generate a magnetic field in the direction to cancel the magnetic field generated by the current to be measured, and a bridge circuit consisting of two magnetoresistive elements and two fixed resistance elements as magnetic sensor elements. It comprises a feedback coil.

The feedback coil is disposed in the vicinity of the magnetoresistive element of the bridge circuit, and generates a cancellation magnetic field that cancels out the induced magnetic field generated by the current to be measured. A GMR (Giant Magneto Resistance) element, a TMR (Tunnel Magneto Resistance) element, or the like can be used as the magnetoresistive effect element of the bridge circuit. The magnetoresistance effect element has a characteristic that the resistance value is changed by the induced magnetic field from the current to be measured. A high sensitivity current sensor can be realized by configuring a bridge circuit using a magnetoresistance effect element having such characteristics. Further, by using the magnetoresistive effect element, the sensitivity axis can be easily arranged in the direction parallel to the substrate surface on which the current sensor is installed, and it becomes possible to use a planar coil.

The magnetic sensors that can be used for the first current sensor 11A and the second current sensor 11B are not limited to the magnetic balance type. It is also possible to use a magnetic proportional sensor or the like which does not have a feedback coil. The first current sensor 11A or the second current sensor 11B may have a pair of magnetic sensors and a computing device, and may be a current sensor of a type that differentially calculates output signals of the pair of magnetic sensors. By adopting such a configuration, it is possible to cancel the influence of the external magnetic field by differential operation, so it is possible to sufficiently improve the measurement accuracy of the current. In particular, in the first current sensor 11A for fine current measurement which is greatly affected by the external magnetic field, the effect is large.

In the current sensor 1, the first current sensor 11A and the second current sensor 11B may be provided in the same chip. In this case, the mounting positions of the first current sensor 11A and the second current sensor 11B, and the mounting angles of the first current sensor 11A and the second current sensor 11B can be accurately adjusted. This can enhance the accuracy of current measurement. Further, by providing the first current sensor 11A and the second current sensor 11B in the same chip, the number of chips can be increased and the package cost can be reduced. Thereby, cost reduction of the current sensor 1 can be achieved.

Although the configuration in which the current sensor 1 includes two current sensors (the first current sensor 11A and the second current sensor 11B) having different measurable ranges and resolutions has been described here, the current sensor included in the current sensor 1 Is not limited to two. For example, in addition to the current sensor (first current sensor 11A) for fine current measurement and the current sensor (second current sensor 11B) for large current measurement, for accurately measuring the vicinity of a high frequency current value A current sensor (third current sensor, not shown) may be provided, and these outputs may be input to the sensor selection circuit. In this case, while measuring a large current and a minute current, it is possible to measure a high frequency current value with high accuracy. The current sensor 1 may include four or more current sensors having different measurable ranges and resolutions.

Next, an example of the layer configuration of the magnetic sensor used for the first current sensor 11A and the second current sensor 11B will be described. Here, when the magnetic sensor used for the first current sensor 11A and the magnetic sensor used for the second current sensor 11B are built on the same substrate, that is, the first current sensor 11A and the second current sensor 11A The case where the current sensor 11B is provided on the same chip will be described. FIG. 2 shows the layer configuration (left in FIG. 2) of the magnetic sensor (hereinafter referred to as the first magnetic sensor 201A) used for the first current sensor 11A, and the magnetic sensor (hereinafter referred to as the second sensor) used for the second current sensor 11B. It is a cross-sectional schematic diagram which shows the layer structure (FIG. 2 right) of 2nd magnetic sensor 201 B). FIG. 2 mainly shows the layer configuration of the bridge circuit and the feedback coil in the first magnetic sensor 201A and the second magnetic sensor 201B. Further, FIG. 2 also shows a current line 13 through which the current to be measured flows in the back direction of the drawing.

In the first magnetic sensor 201A and the second magnetic sensor 201B shown in FIG. 2, the insulating layer 212 is formed on the substrate 211. As the substrate 211, a silicon substrate or the like is used, and as the insulating layer 212, a silicon oxide film, an aluminum oxide film, or the like is used. The silicon oxide film can be formed by a method such as thermal oxidation of a silicon substrate, sputtering, plasma CVD or the like. The aluminum oxide film can be formed using a method such as sputtering or plasma CVD.

On the insulating layer 212,

magnetoresistive effect elements

213A and 213B which are magnetic sensor elements are formed. The

magnetoresistive effect elements

213A and 213B may form a bridge circuit. When, for example, a GMR element is used as the

magnetoresistive effect elements

213A and 213B, a GMR element having a layer configuration including an antiferromagnetic layer, a pinned magnetic layer, a nonmagnetic layer, and a free magnetic layer can be employed.

In addition to the

magnetoresistance effect elements

213A and 213B and the fixed resistance element, an electrode (not shown) may be formed on the insulating layer 212. The electrodes are formed, for example, by forming an electrode material layer and then patterning the electrode material layer by photolithography and etching.

An insulating layer 214 is formed on the

magnetoresistive effect elements

213A and 213B, the fixed resistance element, the electrodes, and the like so as to cover them. As the insulating layer 214, a polyimide film, a silicon oxide film, or the like is used. The polyimide film can be formed by applying and curing a polyimide material. The silicon oxide film can be formed using a method such as sputtering or plasma CVD.

Feedback coils 215A and 215B are formed on the insulating layer 214. The feedback coils 215A and 215B can be formed by forming a coil material layer and then patterning the coil material layer by photolithography and etching. Alternatively, the feedback coils 215A and 215B can be formed by photolithography and plating after forming the base material layer.

On the insulating layer 214, coil electrodes (not shown) are formed in the vicinity of the feedback coils 215A and 215B. The coil electrode can be formed by forming an electrode material layer and then patterning the electrode material layer by photolithography and etching.

An insulating layer 216 is formed on the feedback coils 215A and 215B, the coil electrode, and the like so as to cover them. As the insulating layer 216, a polyimide film, a silicon oxide film, or the like is used. The polyimide film can be formed by applying and curing a polyimide material. The silicon oxide film can be formed using a method such as sputtering or plasma CVD.

A magnetic shield 217 is formed on the insulating layer 216 and in a region overlapping the magnetoresistive effect element 213B. As a material for forming the magnetic shield 217, a high magnetic permeability material such as an amorphous magnetic material, a permalloy magnetic material, or an iron-based microcrystalline material can be used. Note that the magnetic shield 217 is not formed on the insulating layer 216 and in a region overlapping the magnetoresistive effect element 213A.

An insulating layer 218 is formed on the insulating layer 216, the magnetic shield 217, and the like. As the insulating layer 218, a polyimide film, a silicon oxide film, or the like is used. The polyimide film can be formed by applying and curing a polyimide material. The silicon oxide film can be formed using a method such as sputtering or plasma CVD. A contact hole is formed in a predetermined region such as the insulating layer 216 or the insulating layer 218, and an electrode connected to a coil electrode or the like is formed (not shown). The electrodes can be formed by forming an electrode material layer and then patterning the electrode material layer by photolithography and etching.

By adopting the configuration as shown in FIG. 2, on the same substrate 211, the first magnetic sensor 201A used for the first current sensor 11A and the second magnet used for the second current sensor 11B. The sensor 201B can be built into one chip. In this case, the mounting positions of the first current sensor 11A and the second current sensor 11B and the mounting angles of the first current sensor 11A and the second current sensor 11B can be improved in accuracy. As a result, since it is possible to suppress a decrease in current measurement accuracy due to positional deviation, angular deviation or the like of the first current sensor 11A and the second current sensor 11B, the current measurement accuracy is enhanced.

Further, by providing the first current sensor 11A and the second current sensor 11B in the same chip, the number of chips can be increased and the package cost can be reduced. Thereby, cost reduction of the current sensor 1 can be achieved. Further, the current sensor can be miniaturized as compared to the case where the first current sensor 11A and the second current sensor 11B are separate chips. In addition, since the first current sensor 11A and the second current sensor 11B can be disposed equidistantly from the current line, the measurement accuracy of the current can be enhanced. Here, the first magnetic sensor 201A used for the first current sensor 11A and the second magnetic sensor 201B used for the second current sensor 11B are built on the same substrate 211 to form a single chip. However, the present invention is not limited to this, and the first current sensor 11A and the second current sensor 11B may be separate chips.

In the magnetic sensor having such a configuration, when the

magnetoresistance effect elements

213A and 213B receive the induced magnetic fields A and B by the measured current flowing through the current wire 13, the feedback coils 215A and 215B generate the induced magnetic fields A and B. A canceling magnetic field that cancels out is generated, and adjustment is made so that the magnetic fields received by the

magnetoresistive elements

213A and 213B become zero.

Here, while the first magnetic sensor 201A in the first current sensor 11A does not have the magnetic shield 217 in a region overlapping with the magnetoresistive effect element 213A, the second magnetic sensor 201B in the second current sensor 11B The magnetic sensor 201B has a magnetic shield 217 in a region overlapping with the magnetoresistive effect element 213B. Since the magnetic shield 217 attenuates the induction magnetic field generated from the current to be measured, the induction magnetic field A received by the magnetoresistive effect element 213A not overlapping the magnetic shield 217 is received by the magnetoresistive effect element 213B overlapping the magnetic shield 217 It becomes larger than B. Further, since the cancellation magnetic field from the feedback coil 215B is enhanced by the magnetic shield 217, the effect of the cancellation magnetic field by the feedback coil 215B is greater than the effect of the cancellation magnetic field by the feedback coil 215A.

Therefore, in the first current sensor 11A, the measurable range is narrow but the resolution is high, and in the second current sensor 11B, the resolution is low but the measurable range is wide. The number of turns (or number of turns) of feedback coil 215A may be smaller than the number of turns (or number of turns) of feedback coil 215B in order to further increase the resolution of first current sensor 11A.

Next, a current measurement flow of the current sensor 1 that performs current measurement by selecting the output of the first current sensor 11A and the output of the second current sensor 11B will be described. FIG. 3 is a flowchart illustrating the current measurement algorithm.

When the current measurement is started, the first current sensor 11A and the second current sensor 11B measure the current to be measured (step 301). Thus, from the first current sensor 11A, it is output the output voltages V ₁ corresponding to the current to be measured, from the second current sensor 11A, the output voltage V ₂ corresponding to the current to be measured is output.

Next, it is determined which output of the first current sensor 11A or the second current sensor 11B is to be adopted (step 302).

Here, in FIG. 4, the relationship between the output voltage V1 of the _first current sensor 11A and the current to be measured (line A), and the relationship between the output voltage V2 of the _second current sensor 11B and the current to be measured (Line B) is schematically shown. As can be seen from FIG. 4, the first current sensor 11A has a steep output characteristic, which makes it possible to measure a small amount of current accurately. That is, the resolution of the measurement is enhanced. On the other hand, the second current sensor 11B has a moderate output characteristic, which makes it possible to measure a wide range of measured current. That is, the upper limit of the measurable range is raised.

For this reason, the determination as to which output of the first current sensor 11A or the second current sensor 11B is adopted depends on the output voltage V1 of the _first current sensor 11A and the threshold value V _th1 determined in advance. This may be done by comparing the sizes (step 302). For the threshold value V _th1 , for example, a voltage corresponding to the upper limit of the measurable range of the first current sensor 11A can be adopted (see FIG. 4). If V ₁ is greater than V _th1, that is, the measured current, if it exceeds the upper limit of the measurement range of the first current sensor 11A executes step 303. Otherwise, step 304 is performed.

In step 303, the current value of the current to be measured is calculated from the output voltage V2 of the _second current sensor 11B. If V ₁ is greater than V _th1, that is, the measured current, if it exceeds the upper limit of the measurement range of the first current sensor 11A, the upper limit of the measurable range of the high second current sensor 11B This is because it is appropriate to adopt the output and calculate the current value of the current to be measured.

In step 304, the current value of the current to be measured is calculated from the output voltage V1 of the _first current sensor 11A. When V ₁ is equal to or less than V _th1 , that is, when the measured current does not exceed the upper limit of the measurable range of the first current sensor 11A, the output of the first current sensor 11A with high resolution is adopted. It is appropriate to calculate the current value of the current to be measured.

As described above, when the current value of the current to be measured is calculated in step 303 or step 304, the measurement ends.

Here, although the magnitude of the output voltage V1 of the _first current sensor 11A and the threshold V _th1 are compared, the magnitude of the output voltage V2 of the _second current sensor 11B and the threshold V _th2 You may compare In this case, for example, the output voltage of the second current sensor 11A corresponding to the upper limit of the measurable range of the first current sensor 11A can be adopted as the threshold value V _th2 (see FIG. 4). Then, V ₂ is greater than V _th2, the output of the second current sensor 11A employed, in other cases employing the output of the first current sensor 11B. That is, if V ₂ is greater than V _th2 in the (current to be measured is, if it exceeds the lower limit of the measurable range of the second current sensor 11B), and executes step 303, otherwise, Step 304 is performed.

As described above, by selecting and using the outputs of two current sensors having different measurable ranges and different resolutions, it is possible to measure a minute current with high accuracy while measuring a large current.

The present invention is not limited to the above embodiment, and can be implemented with various modifications. For example, the connection relation, size, and the like of each element in the above-described embodiment can be appropriately changed and implemented. In addition, the structures described in the above embodiments can be implemented in combination as appropriate. In addition, the present invention can be implemented with appropriate modifications without departing from the scope of the present invention.

The current sensor of the present invention can be used, for example, to detect the magnitude of the current for driving a motor of an electric car or a hybrid car. Moreover, it is possible to use for measuring the dark current of the battery mounted in an electric vehicle etc.

This application is based on Japanese Patent Application No. 2010-235047 filed on October 20, 2010. All this content is included here.

Claims

A first current sensor comprising a first magnetic sensor and having a first measurable range;
A second current sensor having a second magnetic sensor and having a second measurable range whose upper limit is higher than the first measurable range;
A sensor selection means for selecting an output of the first current sensor or an output of the second current sensor in accordance with the magnitude of the measured current flowing through the current line. Sensor.
The first current sensor has a first resolution,
The current sensor according to claim 1, wherein the second current sensor has a second resolution lower than the first resolution.
The current sensor according to claim 2, wherein the first resolution is ten times or more of the second resolution.
The current sensor according to any one of claims 1 to 3, wherein an upper limit value of the second measurable range is ten times or more of an upper limit value of the first measurable range.
The current sensor according to any one of claims 1 to 4, wherein the second magnetic sensor includes an element shield that covers a magnetic sensor element.
The current sensor according to any one of claims 1 to 5, wherein the first current sensor and the second current sensor are provided in the same chip.
The current according to any one of claims 1 to 6, wherein each of the first magnetic sensor and the second magnetic sensor is a magnetic balance type sensor using a feedback coil. Sensor.
The first current sensor comprises a pair of the first magnetic sensors,
The current sensor according to any one of claims 1 to 7, further comprising: an arithmetic device connected to the pair of first magnetic sensors and performing a differential operation on the output signals thereof.