JP2012026966A - Current sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a current sensor capable of suppressing influences of electromagnetic noise and suppressing noise from being mixed into an output signal from a magnetic detection element.SOLUTION: A current sensor includes: a conductor 102 for causing a current to flow; a magnetic detection element 101 of which resistance value is changed by applying an induction magnetic field from the current flowing to the conductor 102; a sensor substrate 100 on which a driver circuit is formed for driving the magnetic detection element 101; output wiring electrically connected to the driver circuit; and metal shields 103a and 103b provided between the conductor 102 and the sensor substrate 100 and formed from a non-magnetic and metal material. The output wiring is formed from a shield line 104 having a signal line 104a and a wiring shield 104b surrounding the signal line 104a, and the wiring shield 104b is electrically insulated from the metal shields 103a and 103b and a ground of the sensor substrate 100.

Description

  The present invention relates to a current sensor for measuring the magnitude of a current in a conductor, and more particularly to a current sensor using a magnetic detection element.

  In an electric vehicle, a motor is driven using electricity stored in a secondary battery such as lithium ion, and the magnitude of the current for driving the motor is detected by, for example, a current sensor. As this current sensor, there has been proposed one in which a magnetic core having a notch (core gap) is arranged around a conductor and a magnetic detection element is arranged in the core gap (for example, a patent) Reference 1). In this current sensor, a magnetic field proportional to the current to be measured passes through the core gap due to the lines of magnetic force generated in the magnetic core. The magnetic detection element converts this magnetic field into a voltage signal, and an output voltage from the magnetic detection element is amplified by an amplifier circuit to generate an output voltage proportional to the current to be measured.

  By the way, in recent years, with the increase in output and performance of electric vehicles, the current value handled has increased, and it is necessary to avoid magnetic saturation at the time of a large current in the current sensor. In order to avoid magnetic saturation, it is necessary to enlarge the magnetic core, but if the magnetic core is enlarged, there is a problem that the current sensor itself is enlarged. In order to solve the problem of such a current sensor using a magnetic core, a current sensor not using a magnetic core has been proposed (see, for example, Patent Document 2 and Patent Document 3).

JP 2007-212306 A JP 2000-258464 A JP 2006-112968 A

  As disclosed in Patent Document 2, in the current sensor, a magnetic shield made of a magnetic material is provided in order to suppress the influence of an external magnetic field on the magnetic detection element. By providing a magnetic shield, it is possible to suppress magnetic interference from outside and stably detect a magnetic field generated by a current flowing in a conductor (also referred to as a bus bar).

  However, as a result of further studies by the present inventor, when a high-voltage, large-current power supply line is provided in the circuit or when circuit elements are integrated at a high density, the static electricity between the conductor and other wirings, etc. It has been found that electromagnetic noise that cannot be suppressed by the magnetic shield occurs due to electrical coupling or the like, and noise is mixed in a signal (output voltage signal) output from the magnetic detection element. In particular, when electromagnetic noise is generated in the conductor through which the current to be measured flows, there is a problem that the electric circuit including the magnetic detection element provided in the vicinity is greatly affected.

  The present invention has been made in view of the above points, and an object of the present invention is to provide a current sensor capable of suppressing the influence of electromagnetic noise and suppressing the mixing of noise into an output signal from a magnetic detection element. .

  According to one aspect of the current sensor of the present invention, a conductor for passing a current, a magnetic detection element whose characteristics are changed by application of an induced magnetic field from the current flowing through the conductor, and a drive circuit for driving the magnetic detection element are formed. A sensor board; an output wiring electrically connected to the drive circuit; and a metal shield provided between the conductor and the sensor board and made of a nonmagnetic material and made of a metal material, and outputs The wiring is a shield line having a signal line and a wiring shield surrounding the signal line, and the wiring shield is electrically insulated from the metal shield and the ground of the sensor substrate. According to this configuration, the influence of electromagnetic noise generated in the conductor or the like can be suppressed by the metal shield, and the influence of noise generated in the wiring shield on the sensor substrate can be suppressed. As a result, it is possible to prevent noise from being mixed into the signal output from the sensor substrate.

  In the current sensor of the present invention, it is preferable that the metal shield is grounded to the ground of the sensor substrate, and the wiring shield is grounded to the ground provided outside the sensor substrate.

  In the current sensor of the present invention, it is preferable that the metal shield is provided so as to include the sensor substrate.

  In the current sensor of the present invention, the metal shield is preferably formed of at least one metal selected from aluminum, copper and silver.

  In the current sensor of the present invention, the magnetic detection element is preferably a magnetoresistance effect element.

  According to one embodiment of the present invention, it is possible to suppress the influence of electromagnetic noise and to prevent noise from being mixed into the output signal from the magnetic detection element.

It is a figure which shows an example of the current sensor which concerns on embodiment of this invention. It is a figure which shows another example of the current sensor which concerns on embodiment of this invention. It is a figure which shows the measurement result of the output voltage of the current sensor which concerns on the Example and comparative example of this invention.

  In the current sensor using the magnetic detection element, the present inventor has found that electromagnetic noise is generated by electrostatic coupling formed between the conductor and other wirings, even when no current flows through the conductor (bus bar). Has been found to affect the magnetic sensing element provided in the vicinity. In order to suppress the influence of electromagnetic noise generated by electrostatic coupling, the inventors conceived of providing a metal shield between the conductor through which the current to be measured flows and the sensor substrate on which the magnetic detection element is formed. In addition, when the present inventor has studied in more detail, when a shield wire is used as the output wiring of the sensor substrate, if the shield wire is grounded to the ground of the sensor substrate in the same manner as the metal shield, noise will be applied to the sensor substrate. Faced with problems that would have an impact. As a result of diligent examination of this problem, it was determined that the noise generated in the shield part (wiring shield) of the shield wire had an effect on the sensor board, and when using the shield wire as the output wiring of the magnetic detection element, the shield wire and metal The present invention has been completed with the idea of separating the shield and controlling the grounding location of the shield wire.

  Hereinafter, an embodiment of the present invention will be described in detail with reference to FIG. In FIG. 1, FIG. 1A is a schematic diagram of a top view of a current sensor, and FIG. 1B is a schematic diagram of a cross section between A and B in FIG.

  The current sensor shown in FIG. 1 includes a conductor 102 for passing a current, a sensor substrate 100 on which a magnetic detection element 101 and a drive circuit for driving the magnetic detection element 101 are formed, and a drive circuit formed on the sensor substrate 100. An electrically connected shield wire 104 and a metal shield 103 a provided between the conductor 102 and the sensor substrate 100 are provided. The shield line 104 is formed of a signal line 104a electrically connected to the drive circuit of the sensor substrate 100 and a wiring shield 104b surrounding the signal line 104a. The wiring shield 104b is formed of the metal shield 103a and the sensor. The substrate 100 is provided separately from the ground and electrically insulated.

  The conductor 102 is a portion through which a current to be measured measured by a current sensor flows, and is sometimes called a bus bar. The conductor 102 can be formed using aluminum, copper, a copper alloy, or the like.

  The magnetic detection element 101 is an element (magnetic sensor) whose characteristics are changed by application of an induced magnetic field from a current flowing through the conductor 102, and is formed on the sensor substrate 100. In the current sensor, the magnitude of the current can be measured based on the characteristic change of the magnetic detection element 101. The magnetic detection element 101 is driven by a drive circuit formed on the sensor substrate 100, and a signal output from the magnetic detection element 101 is output via an output wiring (shield line 104) electrically connected to the drive circuit. Can be output externally.

  Further, the magnetic detection element 101 has a magnetic field sensitivity selectively in at least one direction and does not have a magnetic field sensitivity in another direction different from the one direction or has a very low magnetic field sensitivity. Is preferably used. In this case, the positions where the conductor 102 and the magnetic detection element 101 are provided are controlled so that the direction of the magnetic field generated when a current flows through the conductor 102 matches the sensitivity direction (one direction) in the magnetic detection element 101. . As the magnetic detection element 101, a magnetoresistive effect element such as a TMR element (tunnel type magnetoresistive effect element) or a GMR element (giant effect element) whose resistance value is changed by application of an induced magnetic field from a current flowing in the conductor 102, a hole Magnetic sensors such as elements and Hall ICs can be used. The magnetic detection element 101 shown in FIG. 1 includes a magnetic sensor and a peripheral circuit for driving the magnetic sensor.

  The metal shield 103a is an electromagnetic shield that reduces the influence of externally generated electromagnetic noise on the magnetic detection element 101, and is formed using a metal material. Further, in order for the magnetic detection element 101 to detect a change in the magnetic field generated when a current flows through the conductor 102, the metal shield 103a is formed of a nonmagnetic material. For example, the metal shield 103a is preferably formed using aluminum, copper, silver, or the like.

  Further, the metal shield is provided not only between the conductor 102 and the sensor substrate 100 but also on the surface opposite to the surface on which the conductor 102 is provided, and includes the sensor substrate 100 with the metal shields 103a and 103b. It is preferable to adopt a configuration to do so. Thereby, the influence of electromagnetic noise on the sensor substrate 100 can be effectively suppressed.

  When the metal shield 103b is provided, the metal shields 103a and 103b may be electrically connected to be equipotential. For example, the sensor substrate 100 can be disposed on the metal shield 103a, and the metal shield 103b can be formed in a housing that covers the sensor substrate 100. In this case, the metal shield 103b may be formed of the same material as the metal shield 103a or may be formed of a different material. The metal shields 103a and 103b may be configured to be grounded to the ground of the sensor substrate 100, or may be in a floating state.

  The shield line 104 functions as an output wiring for outputting a signal from the sensor substrate 100, and is connected between the signal line 104a electrically connected to the drive circuit formed on the sensor substrate 100 and the signal line 104a. And a wiring shield 104b surrounding the signal line 104a with a dielectric or the like interposed therebetween.

  In this embodiment, the wiring shield 104b and the metal shields 103a and 103b are not grounded to the ground at the same place (for example, the sensor substrate 100), but the wiring shield 104b and the metal shields 103a and 103b are separated and electrically connected. Insulate. Preferably, the wiring shield 104b is grounded to a ground provided outside the sensor substrate 100, and the metal shields 103a and 103b are grounded to the ground of the sensor substrate 100. Thereby, the influence of electromagnetic noise generated in the conductor 102 and the like can be suppressed, and the influence of noise generated in the wiring shield 104b on the sensor substrate 100 can be suppressed. As a result, it is possible to prevent noise from being mixed into the signal output from the sensor substrate 100.

  In the current sensor shown in FIG. 1, a magnetic shield made of a magnetic material may be provided. In this case, as shown in FIG. 2, the magnetic shield 200 is provided outside so as to include the metal shields 103 a and 103 b and the conductor 102. As a result, the magnetic detection element 101 formed on the sensor substrate 100 using the magnetic shield 200 and the external magnetic interference acting on the drive circuit are suppressed, and the influence of electromagnetic noise is suppressed using the metal shields 103a and 103b. can do.

  Examples of the present invention will be described below, but the present invention is not limited to these examples.

  As shown in FIG. 1, a sensor substrate 100 provided with a magnetic detection element 101 and a drive circuit was formed on a conductor 102 via a metal shield 103a. In addition, a metal shield 103b is also provided on the upper surface (the surface opposite to the surface on which the conductor 102 is provided) of the sensor substrate 100, and the sensor substrate 100 is covered with the metal shield. Further, the wiring shield 104 b of the shield wire 104 that is electrically connected to the drive circuit of the sensor substrate 100 is grounded to a ground provided outside the sensor substrate 100. For each configuration, the following materials were specifically used.

Conductor 102: Copper with 5 μm tin plating on the surface Magnetic sensing element 101: Magnetoresistive element (GMR)
Metal shields 103a and 103b: 0.3 mm thick copper plate Wiring shield 104b: Copper

(Comparative example)
Similar to the above embodiment, the sensor substrate 100 having the magnetic detection element 101 formed on the conductor 102 via the metal shield 103a is provided, and the metal shield 103b is also provided on the upper side of the sensor substrate 100 to make the sensor substrate 100 a metal. The structure is covered with a shield. In the comparative example, the shield of the shield wire and the metal shield were grounded to the ground of the sensor substrate 100. That is, the grounding place of the wiring shield of the shield wire is different between the example and the comparative example.

(Evaluation)
Next, in the current sensors of the example and the comparative example, the output voltage (output voltage of the signal line 104a) output from the magnetic detection element 101 when current was passed through the conductor 102 was measured. The measurement results are shown in FIG.

  3 is a comparative example, in which the wiring shield 104b of the shield wire 104 and the metal shields 103a and 103b are grounded to the GND of the sensor substrate 100. FIG. b and a are embodiments of the present invention, b is a metal shield 103a, 103b is grounded to the GND of the sensor substrate 100. a shows the result when the metal shields 103a and 103b are floated. In FIG. 3, the voltage values of the respective output signals are displayed by being shifted by 0.2 V in order to make the drawing easier to see.

  Under any condition, noise generated in the wiring is generated in a periodic spike shape and is about 0.3-0.4 Vp-p. The major difference between the comparative example and the embodiment of the present invention is that there is a difference in the fluctuation of the baseline, which is the output of the sensor itself. In the output of the comparative example in FIG. 3, particularly large fluctuations are observed in the portion surrounded by the dotted line. On the other hand, in the embodiment, the baseline fluctuation as described above is not observed.

  This baseline fluctuation is caused by the influence of electromagnetic noise on the sensor substrate 100 including the magnetic detection element 101. In the comparative example, since the wiring shield 104b of the shield wire 104 and the metal shields 103a and 103b have the same potential, electromagnetic noise received by the shield wire 104 affects the sensor substrate 100 including the magnetic detection element 101. . On the other hand, in the embodiment, since the wiring shield 104 b of the shield wire 104 and the metal shields 103 a and 103 b are electrically separated, the electromagnetic noise received by the shield wire 104 causes the sensor substrate 100 including the magnetic detection element 101. It is possible to suppress the influence on

  The present invention is not limited to the above embodiment, and can be implemented with various modifications. In addition, the material, the arrangement position of the current sensor, the thickness, the size, the manufacturing method, and the like in the above embodiment can be changed as appropriate. In addition, the present invention can be implemented with appropriate modifications without departing from the scope of the present invention.

  The present invention can be applied to a current sensor that detects the magnitude of current in an electric vehicle or the like.

DESCRIPTION OF SYMBOLS 100 Sensor board 101 Magnetic detection element 102 Conductor 103a Metal shield 103b Metal shield 104 Shield wire 104a Signal line 104b Wiring shield 200 Magnetic shield

Claims (5)

A conductor for passing current;
A magnetic sensing element whose characteristics are changed by application of an induced magnetic field from a current flowing through the conductor, and a sensor substrate on which a driving circuit for driving the magnetic sensing element is formed;
An output wiring electrically connected to the drive circuit;
A metal shield provided between the conductor and the sensor substrate and made of a nonmagnetic material and a metal material;
The output wiring is a shield line having a signal line and a wiring shield surrounding the signal line, and the wiring shield is electrically insulated from the metal shield and the ground of the sensor board. .   The current sensor according to claim 1, wherein the metal shield is grounded to a ground of the sensor substrate, and the wiring shield is grounded to a ground provided outside the sensor substrate.   The current sensor according to claim 1, wherein the metal shield is provided so as to include the sensor substrate.   The current sensor according to any one of claims 1 to 3, wherein the metal shield is made of at least one metal selected from aluminum, copper, and silver.   The current sensor according to claim 1, wherein the magnetic detection element is a magnetoresistive effect element.