JP2012198085A - Current sensor - Google Patents

Abstract

An object of the present invention is to provide a small-sized current sensor that can cope with a large current and has low power consumption.
A magnetic detection element 13 for detecting a magnetic field to be measured generated by a current flowing through a current line 11, a cancel coil 14 surrounding the magnetic detection element 13, and a cylindrical magnetic core 15 surrounding the cancel coil 14 are provided. And a current sensor arranged so that the opening 17 of the cylindrical magnetic core 15 comes in the magnetic field direction of the magnetic field to be measured generated by the current flowing through the current line 11.
[Selection] Figure 2

Description

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

  In recent years, a current sensor has become necessary to detect battery current of a hybrid car, EV car, etc., drive current of an electric motor, and the like. On the other hand, as shown in FIG. 6, a cancel coil 3 is wound around a ring-type magnetic core 2 with a gap surrounding the current line 1, and a Hall element 4 is disposed in the gap portion. 1 was measured.

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

JP 2006-38834 A

  According to the conventional configuration, the current line needs to be surrounded by the ring-type magnetic core with a gap, and the shape becomes large. In addition, the current line through which a large current of about 200 A flows increases in cross-sectional area, and it is necessary to increase the ring type magnetic core in order to prevent magnetic saturation. For this reason, the shape of the current sensor is further increased, and when it is attempted to detect this current, it is necessary to pass a large current through the cancel coil, resulting in large power consumption.

  An object of the present invention is to provide a small current sensor with low power consumption.

  In order to solve the above-described problems, the present invention is a current sensor that is disposed on one surface of a current line and detects a current flowing through the current line. The current sensor detects a magnetic field to be measured generated by a current flowing through the current line. A magnetic detection element for detection, a cancel coil surrounding the magnetic detection element, and a cylindrical magnetic core surrounding the cancel coil, and a cylindrical magnet in the direction of the magnetic field to be measured generated by the current flowing through the current line It is arranged so that the opening of the body core comes.

  With the above configuration, there is no need to provide a ring-type magnetic core that surrounds the current line, and it is only arranged on one surface of the current line, so that it is possible to achieve downsizing as a whole, and a large current flows to the current line. Even if a large magnetic flux is generated around the magnetic field, much of the magnetic flux is absorbed by the cylindrical magnetic core and only a part of the magnetic core reaches the magnetic detection element, so that current consumption can be reduced. Further, since the cancel coil is covered with the cylindrical magnetic core, the cancel magnetic field can be generated with a small current, and the current consumption can be further reduced. Furthermore, since the magnetic field core other than the direction of the magnetic field generated by the current flowing through the current line is covered with the cylindrical magnetic core, it is less susceptible to disturbance.

The perspective view of the current sensor in one embodiment of the present invention Sectional drawing of the current sensor in one embodiment of this invention Sectional drawing of the magnetic detection element in one embodiment of this invention The circuit diagram for demonstrating operation | movement of the current sensor in one embodiment of this invention Sectional drawing of another electric current sensor in one embodiment of this invention A perspective view of a conventional current sensor

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

  FIG. 1 is a perspective view of a current sensor according to an embodiment of the present invention, in which a current sensor 12 is installed on a current line 11 through which a current I flows, and FIG. 2 is a sectional view thereof. The current line 11 is made of copper and has a rectangular shape with a cross section of 20 mm × 5 mm. The current sensor 12 is disposed on the wider surface.

  The current sensor 12 includes a magnetic detection element 13, a cancellation coil 14 that surrounds the magnetic detection element 13, and a cylindrical magnetic core 15 that surrounds the cancellation coil 14. The shape is 5 mm × 5 mm and the height is 3 mm. The cancel coil 14 is formed by winding an insulation-coated copper wire around a bobbin 16 made of a nonmagnetic material, and the magnetic detection element 13 is fixed to the center of the bobbin 16. The cylindrical magnetic core 15 has a rectangular cylindrical shape made of an iron alloy, and a bobbin 16 around which a cancel coil 14 is wound is inserted therein. The opening 17 of the cylindrical magnetic core 15 is arranged in the direction of the winding axis of the cancel coil 14. The current sensor 12 is installed so that the opening 17 of the cylindrical magnetic core 15 is in the direction of the magnetic field to be measured generated by the current I flowing through the current line 11 (that is, the direction perpendicular to the direction in which the current I flows). Has been.

  3 is a cross-sectional view of the magnetic detection element 13, FIG. 3A is a cross-sectional view when the magnetic detection element 13 is cut horizontally, and FIG. 3B is a cross-sectional view taken along line A- of FIG. It is sectional drawing when cut by A line.

  As shown in FIG. 3, the magnetoresistive elements 20a, 20b, 20c, and 20d are formed on an insulating substrate 21 such as ceramic, and these are made of a ferromagnetic material such as Ni—Co and have a thickness of about 0.1 μm. It is a resistive thin film. The magnetoresistive elements 20a and 20b and the magnetoresistive elements 20c and 20d are connected in series, and the longitudinal directions of the patterns are orthogonal to each other. The input electrode 22a is formed on the insulating substrate 21, and is electrically connected to the magnetoresistive element 20a and the magnetoresistive element 20d. The first output electrode 22b is also formed on the insulating substrate 21, and is electrically connected to the magnetoresistive element 20a and the magnetoresistive element 20b. Similarly, the ground electrode 22c and the second output electrode 22d are also formed on the insulating substrate 21, and are electrically connected to the magnetoresistive element 20b and the magnetoresistive element 20c, and the magnetoresistive element 20c and the magnetoresistive element 20d, respectively. ing.

Reference numeral 23 denotes an insulating layer. The insulating layer 23 is made of a SiO ₂ thin film having a thickness of about 1 μm, and covers the magnetoresistive elements 20a, 20b, 20c, and 20d, thereby providing an electrical connection with a bias magnetic field generating means including a thin film magnet 24 described later. Insulation.

Reference numeral 24 denotes a thin film magnet. The thin film magnet 24 is made of CoPt or the like having a thickness of about 0.6 μm, and is formed on the insulating layer 23 by vapor deposition, sputtering, or the like, and then patterned by exposure and etching, thereby providing magnetoresistance. The elements 20a, 20b, 20c, and 20d are divided into a plurality of substantially rectangular parallelepipeds having a longitudinal direction in a direction that forms 45 degrees with the magnetic detection direction. Then, by applying a very large magnetic field in the width direction of the plurality of substantially rectangular thin films, the substantially rectangular thin film is magnetized in the width direction, and the thin film magnet 24 can be obtained. The bias magnetic field H _B is applied in a direction that forms 45 degrees with respect to the magnetic detection direction of the resistance elements 20a, 20b, 20c, and 20d. The magnetic detection element 13 is arranged so that the direction of the bias magnetic field H _B substantially coincides with the direction of the current I.

  FIG. 4 is a circuit diagram for explaining the operation of the current sensor 12 according to the embodiment of the present invention. A constant voltage is applied between the input electrode 22a and the ground electrode 22c of the magnetic detection element 13. A power supply 26 is connected. In FIG. 4, reference numeral 27 denotes a detection unit that detects a potential difference between the first output electrode 22 b and the second output electrode 22 d, and the current flowing through the cancel coil 14 by the current control unit 28 based on the output signal of the detection unit 27. Is controlling. Reference numeral 29 denotes an output conversion unit, which amplifies a voltage drop at the load resistor 30 due to a current flowing through the cancel coil 14 and outputs the amplified voltage drop to the output terminal 31.

When the current flowing through the current line 11 is zero, only the bias magnetic field H _B is applied so as to form a certain angle (45 degrees) with respect to the magnetoresistive elements 20a, 20b, 20c, and 20d. , 20b, 20c, and 20d have substantially the same resistance value. For this reason, the magnetoresistive element bridge is balanced, the first output electrode 22 b and the second output electrode 22 d have the same potential, and no signal is output from the detection unit 27. As a result, no current flows through the cancel coil 14 and the load resistor 30, so that no output voltage appears at the output terminal 31.

When the current I flows through the current line 11, the current I by the magnetic field H _I is applied to the magnetic field detecting element occurs, the magneto-resistive element 20a, with 20c of resistance decreases, the magnetoresistive element 20b, the 20d of the resistor growing. For this reason, the balance of the magnetoresistive element bridge is broken, and a potential difference is generated between the first output electrode 22b and the second output electrode 22d. This potential difference is detected by the detection unit 27 and input to the current control unit 28. The current control unit 28 causes a current to flow through the cancel coil 14 based on this potential difference, generates a magnetic field H _c due to this current, and applies the net magnetic field applied to the magnetoresistive elements 20a, 20b, 20c, 20d to the thin film magnet 24. By using only the bias magnetic field H _B generated from the magnetic field, the potential difference of the magnetoresistive element bridge is made zero. Thus, when the magnetoresistive element bridge is balanced again, if the voltage generated at both ends of the load resistor 30 is monitored and amplified appropriately, a signal corresponding to the current flowing through the current line 11 is output to the output terminal 31. Become.

  With the configuration described above, most of the magnetic field generated when the current I flows through the current line 11 toward the current sensor 12 flows toward the cylindrical magnetic core 15 and a part thereof. Flows toward the opening 17 and passes through the magnetic detection element 13. If a large current flows through the current line 11 too much, the generated magnetic field becomes too strong and the magnetic detection element 13 may be saturated, but the opening of the cylindrical magnetic core 15 as in the present embodiment. By disposing 17 so as to be in the direction of the magnetic field and disposing the magnetic detection element 13 therein, it is possible to sufficiently detect even a large current.

  Further, when a large current flows, it is necessary to flow a large current through the cancel coil 14 in order to cancel the magnetic field, which causes a problem that power consumption increases. On the other hand, as in the present embodiment, the inductance value of the cancel coil 14 can be increased by covering the periphery of the cancel coil 14 with the cylindrical magnetic core 15 except for the winding axis direction. As a result, the current flowing through the cancel coil 14 can be reduced.

  In order to reduce the current that flows through the cancel coil 14, the cancel coil 14 and the inner wall of the cylindrical magnetic core 15 do not sandwich anything between them, and the inner wall of the cylindrical magnetic core 15 as much as possible. It is desirable to be in a state along the line. By doing so, the inductance value of the cancel coil 14 can be increased, so that current consumption can be further reduced.

  Further, since the magnetic detection element 13 is covered with the cylindrical magnetic body core 15 except for the direction of the magnetic field generated by the current I flowing through the current line 11, it is less susceptible to disturbance and improves the detection accuracy of the current sensor. be able to.

  In addition, in the said embodiment, although the cylindrical magnetic body core 15 used the shape of the square cylinder shape which consists of iron alloys, it was made into the square cylinder shape by bending the flat magnetic body board, for example. Things can be used. A ferrite core may also be used. Furthermore, instead of inserting a bobbin having a cancel coil wound into the cylindrical core, a magnetic core 18 having a U-shaped cross section is fitted into the cancel coil 14 as shown in FIG. You may make it form. By doing in this way, manufacture of a magnetic body core and assembly of a current sensor become easy. When a U-shaped magnetic core is combined, a magnetic gap is generated at the butted surfaces. However, as shown in FIG. 5, no magnetic gap is generated in the direction of the winding axis of the cancel coil. Absent.

  In this embodiment, the current sensor is arranged on one surface of the current line, but a similar current sensor may be arranged on the opposite surface. By doing in this way, the influence of disturbances, such as geomagnetism, can be canceled, and a precision can be improved further.

  In the present embodiment, the current line having a rectangular cross section is used, but a current section having a circular cross section may be used. In this case, the same effect can be obtained by arranging the magnetic detection element in the radial direction of the current line.

  The current sensor according to the present invention can deal with a large current, can provide a small current sensor with low power consumption, and is industrially useful.

DESCRIPTION OF SYMBOLS 11 Current line 12 Current sensor 13 Magnetic detection element 14 Cancel coil 15 Cylindrical magnetic body 16 Bobbin 17 Opening 18 Magnetic body 20a, 20b, 20c, 20d Magnetoresistive element 21 Insulating substrate 22a Input electrode 22b 1st output Electrode 22c Ground electrode 22d Second output electrode 23 Insulating layer 24 Thin film magnet 26 Power supply 27 Detection unit 28 Current control unit 29 Output conversion unit 30 Load resistance 31 Output terminal

Claims (2)

A current sensor that is disposed on one surface of a current line and detects a current flowing through the current line, the current sensor detecting a magnetic field to be measured generated by a current flowing through the current line, and the magnetic sensor A cancel coil surrounding the detection element and a cylindrical magnetic core surrounding the cancel coil, and an opening of the cylindrical magnetic core is formed in a magnetic field direction of a magnetic field to be measured generated by a current flowing through the current line. A current sensor arranged like a coil. The current sensor according to claim 1, wherein the cancel coil is disposed substantially along an inner wall of the cylindrical magnetic core.

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