JP2012058150A - Current sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a current sensor which is capable of measuring a current to be measured over a wide range and further can be small-sized.SOLUTION: A current sensor 1 includes: a magnetic field detection bridge circuit including magneto-resistance effect elements 122a-122d of which the resistance value is varied by an induction magnetic field from a current to be measured being applied; electromagnets 13a, 13b for applying a magnetic field H1 to the magneto-resistance effect elements 122a-122d; and a switching control circuit 221 for controlling a magnetic field strength to be applied from the electromagnets 13a, 13b to the magneto-resistance effect elements 122a-122d in accordance with an output signal outputted from the magnetic field detection bridge circuit.

Description

  The present invention relates to a current sensor that measures the magnitude of a current, and more particularly to a current sensor that detects a current flowing through a conductor via a magnetoelectric conversion element.

  In recent years, in the fields of electric vehicles and solar batteries, the current value handled has increased with the increase in output and performance of electric vehicles and solar battery devices. Sensors are widely used. As such a current sensor, a sensor having a magnetoelectric conversion element that detects a current flowing through a conductor to be detected through a change in a magnetic field around the conductor has been proposed. As a current sensor, a current sensor having a wide measurement range has been developed.

  As a current sensor having a wide measurement range, a current sensor has been proposed in which two magnetic sensors are arranged at positions where the distance from a conductor is changed (see, for example, Patent Document 1). In such a current sensor, two magnetic sensors are arranged at different magnetic field strengths of the induced magnetic field from the current to be measured flowing through the conductor, and the current to be measured is measured by the output signals of the two magnetic sensors.

JP 2004-132790 A

  However, in the current sensor described in Patent Document 1, it is necessary to increase the distance between the conductor and the magnetic sensor in order to obtain a wide measurement range. In addition, there is a problem that the measurement accuracy of the current sensor is lowered due to an error in the distance between the two magnetic sensors and the conductor, and particularly when the current sensor is downsized, there is a problem between the two magnetic sensors and the conductor. It is necessary to match the distance with high accuracy. As described above, it has been difficult for the conventional current sensor to realize both the downsizing of the current sensor and the expansion of the measurement range of the current to be measured.

  The present invention has been made in view of this point, and an object of the present invention is to provide a current sensor that can measure a wide range of currents to be measured and can be miniaturized.

  The current sensor of the present invention includes a magnetic field detection bridge circuit including at least one magnetoresistive effect element whose resistance value is changed by applying an induction magnetic field from a current to be measured, and at least one applying a magnetic field to the magnetoresistive effect element. An electromagnet and switching control means for controlling a magnetic field intensity applied from the electromagnet to the magnetoresistive element in accordance with an output signal output from the magnetic field detection bridge circuit.

  According to this configuration, by applying a magnetic field from the electromagnet to the magnetoresistive effect element, a magnetization vector composed of an induced magnetic field from the current to be measured and a magnetic field from the electromagnet and a sensitivity axis direction of the magnetoresistive effect element are formed. Since the angle increases, the detection sensitivity of the magnetoresistive effect element decreases. Therefore, by controlling the magnetic field strength applied from the electromagnet to the magnetoresistive effect element according to the output signal output from the magnetic field detection bridge circuit, the detection sensitivity of the magnetoresistive effect element is increased according to the magnitude of the current to be measured. It becomes possible to adjust. Thereby, even when the current to be measured is a large current, the magnetic saturation of the magnetoresistive element can be suppressed. Also, by adjusting the strength of the magnetic field applied from the electromagnet to the magnetoresistive effect element, the detection sensitivity of the magnetoresistive effect element is adjusted without changing the distance between the magnetoresistive effect element and the conductor through which the current to be measured flows. Therefore, the current sensor can be miniaturized. Therefore, it is possible to provide a current sensor that can measure a wide range of current under measurement and can be miniaturized.

  The current sensor according to the present invention further includes a feedback coil that is disposed in the vicinity of the magnetoresistive effect element and generates a canceling magnetic field that cancels the induced magnetic field, and the feedback based on a voltage difference obtained by the magnetic field detection bridge circuit. The current to be measured is preferably measured based on a current flowing through the feedback coil when the coil is energized to achieve an equilibrium state in which the induction magnetic field and the cancellation magnetic field cancel each other.

  In the current sensor of the present invention, the magnetoresistive effect element has a shape formed by folding a plurality of strip-like long patterns arranged so that the longitudinal directions thereof are parallel to each other, and the induction magnetic field and the cancellation It is preferable that the magnetic field is applied so as to be along a direction orthogonal to the longitudinal direction.

  In the current sensor of the present invention, it is preferable that the current to be measured is measured by the magnetic field detection bridge circuit based on outputs of the two magnetoresistive elements proportional to the induced magnetic field.

  According to the present invention, it is possible to provide a current sensor that can measure a wide range of currents to be measured and can be miniaturized.

It is a typical perspective view of the current sensor which concerns on embodiment of this invention. It is a plane schematic diagram of the current sensor according to the embodiment of the present invention. (A) is a figure which shows the magnetic field detection bridge circuit in the current sensor which concerns on embodiment of this invention, (b) is a schematic diagram of the AA arrow cross section of (a). (A), (b) is explanatory drawing of the detection principle of the magnetoresistive effect element of the current sensor which concerns on embodiment of this invention. It is a functional block diagram of the current sensor which concerns on embodiment of this invention. It is a figure which shows an example of the control flow at the time of the to-be-measured current measurement of the current sensor which concerns on embodiment of this invention. It is a figure which shows the other example of the control flow at the time of the to-be-measured current measurement of the current sensor which concerns on embodiment of this invention. It is a plane schematic diagram which shows the other example of the current sensor which concerns on embodiment of this invention.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. First, the case where the current sensor according to the present invention is a magnetic balance type current sensor will be described. In the following embodiment, an example in which a magnetic field detection bridge circuit is configured by four magnetoresistive effect elements will be described. However, the magnetic field detection bridge circuit may be configured by using at least one magnetoresistive effect element. For example, it may be configured using two magnetoresistive elements and two fixed resistance elements.

  FIG. 1 is a schematic perspective view of a current sensor 1 according to the present embodiment, and FIG. 2 is a schematic plan view of the current sensor 1 according to the present embodiment. As shown in FIGS. 1 and 2, the current sensor 1 according to the present embodiment is disposed in the vicinity of the conductor 11 through which the current I to be measured flows. The current sensor 1 includes a feedback circuit 12 that generates a magnetic field (cancellation magnetic field) that cancels the induced magnetic field H caused by the current I to be measured flowing through the conductor 11. The feedback circuit 12 includes a feedback coil 121 wound in a direction that cancels a magnetic field generated by the current I to be measured, and four magnetoresistive elements 122a to 122d. The current sensor 1 also includes a pair of electromagnets 13a and 13b that apply a magnetic field H1 (see FIG. 4) toward the magnetoresistive effect elements 122a to 122d. The detection sensitivity of 122a-122d is comprised so that adjustment is possible.

  The feedback coil 121 is a planar coil. In this configuration, since the magnetic core is not provided, the feedback coil 121 can be manufactured at a low cost. Further, as compared with the case of the toroidal coil, the cancel magnetic field generated from the feedback coil 121 can be prevented from spreading over a wide range, and the influence on the peripheral circuit can be avoided. Further, when the current I to be measured is an alternating current as compared with the case of the toroidal coil, the control of the cancellation magnetic field by the feedback coil 121 is easy, and the current flowing for the control is not so large. About these effects, it becomes so large that the to-be-measured current I becomes a high frequency by alternating current. When the feedback coil 121 is configured by a planar coil, the planar coil is preferably provided so that both the induction magnetic field H and the canceling magnetic field are generated in a plane parallel to the plane of formation of the planar coil.

  The resistance values of the magnetoresistive elements 122a to 122d change due to the application of the induced magnetic field H from the current I to be measured. The four magnetoresistive effect elements 122a to 122d constitute a magnetic field detection bridge circuit 123. By using the magnetic field detection bridge circuit 123 having the magnetoresistive effect elements 122a to 122d as described above, the highly sensitive current sensor 1 can be realized.

  The magnetic field detection bridge circuit 123 includes two outputs that generate a voltage difference corresponding to the induced magnetic field H generated by the current I to be measured. In the magnetic field detection bridge circuit 123 shown in FIG. 2, a power source Vdd is connected to a connection point between the magnetoresistive effect element 122b and the magnetoresistive effect element 122c, and the magnetoresistive effect element 122a and the magnetoresistive effect element 122d are connected to each other. A ground (GND) is connected to a connection point between the two. Further, in this magnetic field detection bridge circuit 123, one output (Out1) is taken out from the connection point between the magnetoresistive effect elements 122a and 122b, and another output (Out2) from the connection point between the magnetoresistive effect elements 122c and 122d. ) Is taken out. These two outputs are amplified by the amplifier 124 and supplied to the feedback coil 121 as a current (feedback current). This feedback current corresponds to a voltage difference corresponding to the induced magnetic field H. At this time, a cancellation magnetic field that cancels the induction magnetic field H is generated in the feedback coil 121. Then, the current to be measured I is measured by the detection unit (detection resistor R) based on the current flowing through the feedback coil 121 when the induced magnetic field H and the canceling magnetic field cancel each other.

  As shown in the enlarged view of FIG. 2, the magnetoresistive effect elements 122a to 122d are formed by folding back a plurality of strip-like long patterns (stripes) arranged so that their longitudinal directions are parallel to each other. GMR element having a shape) is preferable. In this meander shape, the sensitivity axis direction (Pin direction) is a direction (stripe width direction) orthogonal to the longitudinal direction (stripe longitudinal direction) of the long pattern. In this meander shape, the induced magnetic field H and the canceling magnetic field are applied so as to be along a direction (stripe width direction) orthogonal to the stripe longitudinal direction.

  In this meander shape, in consideration of linearity, the width in the sensitivity axis direction (Pin direction) is preferably 1 μm to 10 μm. In this case, considering linearity, it is desirable that the longitudinal direction of the meander shape is perpendicular to the direction of the induction magnetic field H and the direction of the cancellation magnetic field. By adopting such a meander shape, the output of the magnetoresistive effect element can be taken with a smaller number of terminals (two terminals) than the Hall element.

  The electromagnets 13a and 13b are disposed on a substrate (not shown) so as to sandwich the magnetoresistive elements 122a to 122d. The electromagnets 13a and 13b are arranged so as to apply a magnetic field from a direction substantially orthogonal to the sensitivity axis direction of the magnetoresistive effect elements 122a to 122d. The electromagnets 13a and 13b are connected to the switching control circuit 221 (see FIG. 5) of the control unit 200, and are applied to the magnetoresistive elements 122a to 122d according to output signals output from the magnetoresistive elements 122a to 122d. The magnetic field strength to be adjusted is configured to be adjustable.

  In the current sensor 1 having such a configuration, as shown in FIG. 1, an induced magnetic field H generated from the current I to be measured is received by the magnetoresistive effect elements 122a to 122d, and the induced magnetic field H is fed back and fed back to the feedback coil. A cancel magnetic field is generated from 121, and the two magnetic fields (induction magnetic field H, cancel magnetic field) are canceled out and adjusted appropriately so that the magnetic field applied to the magnetoresistive effect elements 122a to 122d becomes zero.

  The current sensor 1 having the above configuration uses a magnetoresistive effect element 122a to 122d as a magnetic detection element, in particular, a magnetic field detection bridge circuit having a GMR (Giant Magneto Resistance) element or a TMR (Tunnel Magneto Resistance) element. Thereby, the highly sensitive current sensor 1 is realizable. In addition, the current sensor 1 includes a magnetic field detection bridge circuit 123 including four magnetoresistive elements 122a to 122d having the same film configuration. In addition, the current sensor 1 having the above configuration can be reduced in size because the feedback coil 121, the magnetic field detection bridge circuit 123, and the electromagnets 13a and 13b are formed on the same substrate. Furthermore, since the current sensor 1 has a configuration without a magnetic core, it can be reduced in size and cost.

  In the current sensor having the four magnetoresistive effect elements 122a to 122d arranged in this way, the magnetic resistance from the feedback coil 121 is set so that the voltage difference between the two outputs (Out1, Out2) of the magnetic field detection bridge circuit 123 becomes zero. A canceling magnetic field is applied to the effect elements 122a to 122d, and the current to be measured I is measured by detecting the value of the current flowing through the feedback coil 121 at that time.

  As shown in FIG. 1, when the current I to be measured flows through the conductor 11, an induction magnetic field H and a cancel magnetic field are applied to the four magnetoresistive effect elements 122a to 122d, respectively. At this time, when the combined magnetic field intensity of the induced magnetic field H generated by the current I to be measured and the canceling magnetic field becomes zero, the midpoint potential difference of the magnetic field detection bridge circuit 123 becomes zero.

  FIG. 3A is an explanatory diagram of a wiring pattern of the magnetic field detection bridge circuit 123 in the current sensor 1 according to the embodiment of the present invention, and FIG. 3B is an AA line in FIG. It is a schematic diagram of an arrow cross section. As shown in FIG. 3A, the magnetic field detection bridge circuit 123 of the current sensor according to the present embodiment has wiring that is symmetric with respect to the power supply point (Vdd). Magnetoresistive elements 122a to 122d are formed so that the extending direction of the coil pattern of feedback coil 121 (feedback direction of feedback current) and the meander stripe longitudinal direction are along. Here, as shown in FIG. 3B, a feedback coil 121 is disposed on the magnetoresistive effect elements 122a to 122d.

  Further, a wiring pattern 60 is formed to connect the magnetoresistive effect elements 122a to 122d and to connect to a power supply point (Vdd) or Gnd. The wiring pattern 60 is symmetric with respect to the power supply point. As a result, the wiring lengths on both sides of the power supply point are substantially the same, so that there is no difference in wiring resistance between the power supply points. As a result, the midpoint potential shift due to the difference in wiring resistance is eliminated, and current measurement can be performed with higher accuracy.

  Next, the detection principle of the current sensor 1 according to the present embodiment will be described with reference to FIGS. 4 (a) and 4 (b). 4A and 4B are explanatory diagrams of the detection principle of the current sensor 1 according to the present embodiment. 4 (a) and 4 (b), only one electromagnet 13a is shown for convenience of explanation. 4A and 4B show the relationship between the induced magnetic field H from the measured current I in the magnetoresistive effect element 122a and the electromagnet 13a, the magnetoresistive effect elements 122b to 122d are also shown. The current I to be measured is detected by the same principle.

As shown in FIGS. 4A and 4B, in the current sensor 1 according to the present embodiment, the magnetic field H1 generated by the electromagnet 13a is applied orthogonally to the induced magnetic field H from the current to be measured. Then, a magnetization vector M having a predetermined angle θ with respect to the sensitivity axis direction is formed from the induced magnetic field H from the current I to be measured and the magnetic field H1 generated by the electromagnet. At this time, the resistance R of the magnetoresistive effect element 122a is expressed by the following relational expression (1), and changes depending on the angle θ formed by the magnetization vector M and the sensitivity axis direction. For this reason, when the magnetic field H1 applied from the electromagnet 13a is small, the angle θ formed by the sensitivity axis direction and the magnetization vector M is close to 0, and the detection sensitivity is increased.
R = R0− (ΔR / R) cos θ (1)
(In Formula (1), R0 is an initial resistance, and ΔR is a resistance change, which is a constant determined by the material and configuration of the magnetoresistive element.)

  As shown in FIG. 4A, when the magnetic field H1 applied from the electromagnet 13a is small, the induction magnetic field H from the current I to be measured and the magnetic field H1 generated by the electromagnet 13a are predetermined with respect to the sensitivity axis direction. A magnetization vector M having an angle θ1 is formed. On the other hand, as shown in FIG. 4B, when the magnetic field H1 applied from the electromagnet 13a is large, the angle θ2 formed by the sensitivity axis direction and the magnetization vector M becomes larger than the above θ1, and the relational expression ( 1) The detection sensitivity of the magnetoresistive effect element 122a becomes smaller. In this case, when a large current is generated, even if the induced magnetic field H from the current I to be measured is large, the angle θ formed by the sensitivity axis direction and the magnetization vector M is difficult to become zero. Magnetic saturation of the effect element 122a can be suppressed. Therefore, the measurement range of the current sensor 1 can be expanded.

  Next, the control of the output signal of the current sensor 1 when measuring the current to be measured will be described in detail. FIG. 5 is a functional block diagram of the current sensor 1 according to the present embodiment. As shown in FIG. 5, the current sensor 1 includes a sensor unit 12a that detects an induced magnetic field H from the current I to be measured, a control unit 200 that controls an output signal of the sensor unit 12a, and an output from the sensor unit 12a. Electromagnets 13a and 13 for applying a magnetic field to the magnetoresistive elements 122a to 122d of the sensor unit 12a according to the signal are provided.

  The sensor unit 12a includes a feedback coil 121 arranged to generate a magnetic field in a direction that cancels the magnetic field generated by the current I to be measured, and four magnetoresistive effect elements 122a to 122d that are magnetic detection elements. 123.

  The control unit 200 amplifies the differential output of the magnetic field detection bridge circuit 123 of the sensor unit 12a, converts the feedback current of the feedback coil 121 and the differential / current amplifier 211, and converts the feedback current of the sensor unit 12a into a voltage. I / V amplifier 212, switching control circuit 221 for switching the amount of current supplied to electromagnets 13a and 13b according to the output signal from differential / current amplifier 211, and amplification for amplifying the differential output of I / V amplifier 212 Circuit 222.

  The feedback coil 121 is disposed in the vicinity of the magnetoresistive effect elements 122a to 122d of the magnetic field detection bridge circuit 123, and generates a cancel magnetic field that cancels the induced magnetic field H generated by the current I to be measured. The resistance values of the magnetoresistive elements 122a to 122d change due to the application of the induced magnetic field H from the current I to be measured. By configuring the magnetic field detection bridge circuit 123 with the four magnetoresistive elements 122a to 122d, a highly sensitive current sensor can be realized. Further, by using the magnetoresistive effect elements 122a to 122d, it is easy to arrange the sensitivity axis in a direction parallel to the substrate surface on which the current sensor is installed, and it becomes possible to use a planar coil.

  The magnetic field detection bridge circuit 123 includes two outputs that generate a voltage difference according to the induced magnetic field H generated by the current I to be measured. Two outputs of the magnetic field detection bridge circuit 123 are amplified by the differential / current amplifier 211, and the amplified outputs are given to the feedback coil 121 as current (feedback current). This feedback current corresponds to a voltage difference corresponding to the induced magnetic field H. At this time, a cancellation magnetic field that cancels the induction magnetic field H is generated in the feedback coil 121. Then, the current flowing through the feedback coil 121 when the induced magnetic field H and the canceling magnetic field cancel each other is converted into a voltage by the I / V amplifier 212, and this voltage becomes the sensor output.

  In the differential / current amplifier 211, the power supply voltage is set to a value close to the reference voltage for I / V conversion + (maximum value within the rated value of feedback coil resistance × feedback coil current at full scale), thereby providing feedback. The current is automatically limited, and the effect of protecting the magnetoresistive effect elements 122a to 122d and the feedback coil can be obtained. Here, the differential of the two outputs of the magnetic field detection bridge circuit 123 is amplified and used as a feedback current. However, only the midpoint potential is output from the bridge circuit, and the potential difference from a predetermined reference potential is used. It may be a feedback current.

  The switching control circuit 221 includes a determination circuit that determines whether the magnitude of the output signal from the magnetoresistive effect elements 122a to 122d is greater than a predetermined threshold. The switching control circuit 221 applies the current from the electromagnets 13a and 13b to the magnetoresistive effect elements 122a to 122d by switching the amount of current supplied to the coils of the electromagnets 13a and 13b according to the output signal from the differential / current amplifier 211. Control the magnetic field strength. By performing such control, it is possible to adjust the detection sensitivities of the magnetoresistive elements 122a to 122d according to the output of the sensor unit 12a that changes according to the induced magnetic field H from the current to be measured. Thereby, when the current I to be measured is a large current, the detection sensitivity of the magnetoresistive effect elements 122a to 122d is reduced by increasing the magnetic field applied from the electromagnets 13a and 13b to the magnetoresistive effect elements 122a to 122d. It becomes possible. When the current I to be measured is a small current, the detection sensitivity of the magnetoresistive effect elements 122a to 122d can be increased by reducing the magnetic field applied from the electromagnets 13a and 13b. Therefore, the detection range of the current sensor 1 can be expanded. As will be described later, when the current to be measured of the current sensor 1 is measured, when the cancel magnetic field from the feedback coil 121 is not used, it is used as a current output signal supplied from the switching control circuit 221 to the electromagnets 13a and 13b. May be.

  Next, a control flow at the time of measuring the current to be measured of the current sensor 1 according to the present embodiment will be described in detail with reference to FIG. FIG. 6 is a diagram illustrating an example of a control flow at the time of measuring the current to be measured by the current sensor 1 according to the present embodiment.

  As shown in FIG. 6, after starting measurement of the current to be measured, the current to be measured I is measured by the sensor unit 12a (step ST1). Next, the switching control circuit 221 determines whether or not the output signal from the sensor unit 12a is greater than a predetermined threshold value S1 (step ST2). In step ST2, when the output signal from the sensor unit 12a is larger than the predetermined threshold value S1, the amount of current supplied to the electromagnets 13a and 13b is increased (step ST3). In step ST2, when the output signal from the sensor unit 12a is equal to or less than the predetermined threshold S1, the measurement of the measured current I is continued by the sensor unit 12a with the current supply amount constant to the electromagnets 13a and 13b ( Step ST1).

  Next, after supplying the current to the electromagnets 13a and 13b, the switching control circuit 221 determines whether or not the output signal from the sensor unit 12a is larger than a predetermined threshold S1 with a predetermined time constant (step S4). In step ST4, when the output signal from the sensor unit 12a is larger than the predetermined threshold value S1, the amount of current supplied from the switching control circuit 221 to the electromagnets 13a and 13b is increased and the electromagnets 13a and 13b to the magnetoresistive effect element 122a. The magnetic field applied to -122d is increased (step ST3). As a result, the angle θ formed by the sensitivity axis direction of the magnetoresistive effect elements 122a to 122d and the magnetization vector M composed of the magnetic field H1 from the electromagnets 13a and 13b and the induced magnetic field H from the measured current I increases. The detection sensitivity of the magnetoresistive effect elements 122a to 122d is lowered. Therefore, even when the measured current I is large, the magnetic saturation of the magnetoresistive elements 122a to 122d can be suppressed.

  If the output signal of the sensor unit 12a is equal to or smaller than the predetermined threshold value S1 in step ST4, it is next determined whether or not the output signal of the sensor unit 12a is smaller than the predetermined threshold value S2 (step ST5). In step ST5, when the output signal of the sensor unit 12a is smaller than the predetermined threshold value S2, the amount of current supplied to the electromagnets 13a and 13b is decreased (step ST6). As a result, the strength of the magnetic field applied from the electromagnets 13a and 13b to the magnetoresistive effect elements 122a to 122d is reduced, so that the sensitivity axis direction of the magnetoresistive effect elements 122a to 122d, the magnetic field H1 from the electromagnets 13a and 13b, and the measurement target. The angle θ formed by the magnetization vector M composed of the induction magnetic field H from the current I is small. Therefore, the detection sensitivity of the magnetoresistive effect elements 122a to 122d is improved.

  In step ST5, when the output signal of the sensor unit 12a is equal to or greater than a predetermined threshold value, the measurement of the measured current I by the sensor unit 12a is continued with the current supply amount being constant (step ST1). Thus, in the current sensor 1 according to the present embodiment, the switching control circuit 221 controls the amount of current supplied to the electromagnets 13a and 13b and adjusts the detection sensitivity of the magnetoresistive effect elements 122a to 122d. The measurement current I is measured. With such control, for example, in an electric vehicle or the like, when the measured current I is stopped at a small current, the output signal from the sensor unit 12a becomes a minute value (threshold value S1 or less). The detection sensitivity can be improved by increasing the detection sensitivity of 122d. Further, when the electric vehicle is started with the current I to be measured being a large current, the output signal becomes larger than the predetermined threshold value S1, so that the magnetoresistive effect element 122a from the sensor unit 12a is applied by applying a magnetic field from the electromagnet 13a. It becomes possible to suppress magnetic saturation of ˜122d. For this reason, even when the current sensor 1 is used in an electric vehicle, it is possible to realize a current sensor that can accurately detect a small current and can also measure a large current.

  In the control flow described above, the example in which the output signal from the sensor unit 12a is compared with the threshold value S1 with a predetermined time constant has been described. However, the output signal from the sensor unit 12a is continuously compared with the predetermined threshold value S1. It is also possible to perform feedback control. In this case, the detection sensitivity of the magnetoresistance effect elements 122a to 122d can be continuously adjusted by continuously adjusting the application of the magnetic field H1 from the electromagnets 13a and 13b to the magnetoresistance effect elements 122a to 122d. Magnetic saturation of the magnetoresistive effect elements 122a to 122d can be effectively suppressed. In this case, an output signal from the sensor unit 12a is detected with a predetermined time constant, and the electromagnets 13a and 13b are switched from the switching control circuit 221 based on the amount of change in the output signal between each time point detected continuously. You may make it control the electric current supply amount to.

  By the way, in the magnetic balance type current sensor, the feedback coil 121 generates heat due to the increase in the current I to be measured, and the heat generation of the feedback coil 121 raises the temperature of the magnetoresistive effect elements 122a to 122d, and the magnetoresistive effect element 122a. A phenomenon occurs in which the output signal of ˜122d becomes small. For this reason, in order to improve the measurement accuracy of the current sensor 1, it is desirable to suppress the heat generation of the feedback coil 121. Furthermore, when the current I to be measured is a large current, sufficient measurement accuracy may not be obtained only with the canceling magnetic field from the feedback coil 121.

  Next, another example of the control flow when measuring the current to be measured of the current sensor 1 according to the present embodiment in consideration of the characteristics of the magnetic balance type current sensor will be described. FIG. 7 is a diagram showing another control flow at the time of measuring the current to be measured by the current sensor 1 according to the embodiment of the present invention. In this example, the detection sensitivity of the magnetoresistive effect elements 122a to 122d is controlled by applying the magnetic field H1 by the electromagnets 13a and 13b and using the canceling magnetic field from the feedback coil 121 in combination.

  As shown in FIG. 7, in this example, after starting measurement of the current to be measured, the current I to be measured is measured by a canceling magnetic field from the feedback coil 121 in a state where the coils of the electromagnets 13a and 13b are not energized (step ST11). Next, the switching control circuit 221 determines whether or not the output signal from the sensor unit 12a is greater than a predetermined threshold value S3 (step ST12). In step ST12, when the output signal from the sensor unit 12a is larger than the predetermined threshold value S3, the cancel magnetic field from the feedback coil 121 is stopped and current supply to the electromagnets 13a and 13b is started (step ST13). In step ST13, the current that flows from the switching control circuit 221 to the electromagnets 13a and 13b is used as the feedback current. In step ST12, when the output signal from the sensor unit 12a is equal to or smaller than the predetermined threshold value S3, the measurement is continued without supplying current to the electromagnets 13a13b (step ST11).

  Next, after supplying current to the electromagnets 13a and 13b, the switching control circuit 221 determines whether or not the output signal from the sensor unit 12a is larger than a predetermined threshold value S4 with a predetermined time constant (step ST14). In step ST14, when the output signal from the sensor unit 12a is larger than the predetermined threshold value S4, the amount of current supplied from the switching control circuit 221 to the electromagnets 13a and 13b is increased, and the magnetoresistive effect element 122a from the electromagnets 13a and 13b. The magnetic field H1 applied to -122d is increased (step ST13). As a result, the angle θ formed by the sensitivity axis direction of the magnetoresistive effect elements 122a to 122d and the magnetization vector M composed of the magnetic field H1 from the electromagnets 13a and 13b and the induced magnetic field H from the measured current I increases. The detection sensitivity of the magnetoresistive effect elements 122a to 122d is lowered.

  In step ST14, when the output signal of the sensor unit 12a is equal to or smaller than the predetermined threshold value S4, it is determined whether or not the output signal of the sensor unit 12a is smaller than the predetermined threshold value S5 (step ST15). In step ST15, when the output signal of the sensor unit 12a is smaller than the predetermined threshold value S5, the amount of current supplied from the switching control circuit 221 to the electromagnets 13a and 13b is stopped and a cancel magnetic field is generated from the feedback coil 121. The current I to be measured is measured (step ST16). As a result, the magnetic field H1 applied from the electromagnets 13a and 13b to the magnetoresistive effect elements 122a to 122d is reduced, so that the sensitivity axis direction of the magnetoresistive effect elements 122a to 122d, the magnetic field H1 from the electromagnets 13a and 13 and the measurement target. The angle θ formed by the magnetization vector M composed of the induced magnetic field H from the current I decreases, and the detection sensitivity increases. In this way, the current I to be measured is measured while controlling the amount of current supplied to the electromagnets 13a and 13b by the switching control circuit 221 until the end of measurement.

  In this example, when the current I to be measured is a large current and the output signals of the magnetoresistive elements 122a to 122d exceed a predetermined threshold value S3, the cancel magnetic field from the feedback coil 121 is stopped, and the electromagnet 13a, The measured current I is measured by the magnetic field H1 from 13b. Thus, when the measured current I is a large current, the heat generation in the current sensor 1 can be suppressed by measuring the measured current I without using the canceling magnetic field from the feedback coil 121. As a result, the measurement error of the current I to be measured when the current I to be measured is a large current can be reduced, and the measurement accuracy of the current sensor can be further improved. Further, in this example, even when the measured current I is a large current and the induced magnetic field cannot be canceled by the cancel magnetic field from the feedback coil 121, the electromagnet 13a, By applying a magnetic field from 13b, the current I to be measured can be accurately measured.

  The present invention can be similarly applied not only to a magnetic balance type current sensor but also to a magnetic proportional type current sensor that measures a current I to be measured by outputs of two magnetoresistive effect elements proportional to an induced magnetic field H. As shown in FIG. 8, the current sensor 2 has a configuration in which the feedback coil is removed from the configuration shown in FIG. The magnetic field detection bridge circuit 123 of the magnetic proportional current sensor has four magnetoresistive elements 122a to 122d, and is symmetrical with respect to the power supply point (Vdd) as in the configuration shown in FIGS. Has some wiring. Further, the electromagnets 13a and 13b are arranged so as to apply the magnetic field H1 from the direction orthogonal to the sensitivity axis direction of the four magnetoresistive elements 122a to 122d. As described above, even when the present invention is applied to a magnetic proportional current sensor, an effect can be obtained in the same manner as in the case of a magnetic balanced current sensor.

  Thus, in the current sensor 1 according to the present embodiment, the magnetoresistive elements 122a to 122d of the sensor unit 12a are changed from the electromagnets 13a and 13b to the magnetoresistive elements 122a according to the magnitude of the current I to be measured. The current I to be measured is measured while adjusting the magnetic field H1 applied to .about.122d. Thereby, by the magnetic field H1 from the electromagnets 13a and 13b, the sensitivity vector direction of the magnetoresistive effect elements 122a to 122d and the magnetization vector M composed of the magnetic field H1 from the electromagnets 13a and 13b and the induced magnetic field H from the current I to be measured. , The detection sensitivity of the magnetoresistive effect elements 122a to 122d with respect to the induced magnetic field H from the current I to be measured changes. Therefore, even when the measured current I is a large current, the magnetic saturation of the magnetoresistive effect elements 122a to 122d can be suppressed. Further, since the detection sensitivity of the current I to be measured can be adjusted by applying the magnetic field H1 by the electromagnets 13a and 13b without changing the distance between the magnetoresistive elements 122a to 122d and the conductor 11, the current sensor 1 can be downsized. Is possible. Therefore, it is possible to realize a current sensor that has a wide measurement range and can be miniaturized.

  In particular, in the current sensor 1 according to the present embodiment, the measured current I can be measured without using the canceling magnetic field from the feedback coil 121 by using the electromagnets 13a and 13b in the magnetic balance type current sensor. It becomes possible. Thereby, the fall of the detection sensitivity of the magnetoresistive effect elements 122a-122d by the heat_generation | fever of the feedback coil 121 which arises when the to-be-measured current I is a large current can be suppressed. For this reason, the difference in detection sensitivity between the magnetoresistive effect elements 122a to 122d can be reduced, and a current sensor with high measurement accuracy can be realized.

  The present invention is not limited to the above embodiment, and can be implemented with various modifications. For example, the materials, connection relations, thicknesses, sizes, manufacturing methods, and the like in the above embodiments 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.

  INDUSTRIAL APPLICABILITY The present invention has an effect that it can measure a wide range of currents to be measured and can be downsized, and can be applied particularly to a current sensor that detects the magnitude of a current for driving a motor of an electric vehicle. is there.

DESCRIPTION OF SYMBOLS 1, 2 Current sensor 11 Conductor 12 Feedback circuit 12a Sensor part 13a, 13b Electromagnet 60 Wiring pattern 121 Feedback coil 122a-122d Magnetoresistive element 123 Magnetic field detection bridge circuit 124 Amplifier 200 Control part 211 Differential / current amplifier 212 I / V Amplifier 221 Switching control circuit 222 Amplifier circuit

Claims (4)

  A magnetic field detection bridge circuit including at least one magnetoresistive effect element whose resistance value is changed by applying an induction magnetic field from a current to be measured; at least one electromagnet for applying a magnetic field to the magnetoresistive effect element; and the magnetic field detection bridge A current sensor comprising switching control means for controlling a magnetic field strength applied from the electromagnet to the magnetoresistive element in accordance with an output signal output from a circuit.   A feedback coil is disposed near the magnetoresistive effect element and generates a canceling magnetic field that cancels the induced magnetic field. The feedback coil is energized by a voltage difference obtained by the magnetic field detection bridge circuit, and the induced magnetic field is generated. The current sensor according to claim 1, wherein the current to be measured is measured based on a current flowing through the feedback coil when an equilibrium state in which the canceling magnetic field and the canceling magnetic field cancel each other is achieved.   The magnetoresistive element has a shape formed by folding a plurality of strip-like long patterns arranged so that the longitudinal directions thereof are parallel to each other, and the induction magnetic field and the canceling magnetic field are orthogonal to the longitudinal direction. The current sensor according to claim 2, wherein the current sensor is applied along a direction.   2. The current sensor according to claim 1, wherein the current to be measured is measured by the magnetic field detection bridge circuit based on outputs of the two magnetoresistive elements proportional to the induced magnetic field.

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