JP4816952B2 - Current sensor - Google Patents

Description

  The present invention relates to a “magnetic balance type current sensor” used for machine tools, hybrid cars, EV cars, and the like for measuring current with high accuracy in a non-contact manner, and in particular, a spin valve giant magnetoresistive element (Spin-valve). The present invention relates to a current sensor that can accurately measure not only alternating current but also direct current by using -gaint magnetoresistance (hereinafter referred to as SV-GMR element).

  In recent years, there has been a demand for a current sensor capable of accurately measuring a large DC current (eg, several hundred amperes) in a non-contact manner, particularly for a hybrid car. As the background, for example, for high voltage battery (eg 200-400V) current monitoring of hybrid cars, (1) it is a non-contact type because it requires insulation of high voltage system and low voltage system, (2) battery current is Since it is basically direct current, direct current measurement is possible. (3) Battery charge current and discharge current can be measured with high accuracy against temperature fluctuations. This is because accumulation errors accumulate, battery overdischarge and overcharge occur, and the battery life is shortened).

As a magnetic sensing element used in a conventional current sensor, the “Hall element” occupies the majority in the actual market, and recently, there is an element using a magnetoresistive element “MR element”.
MR elements that use the current effect in semiconductors (eg, In-Sb) and "AMR elements" whose resistance varies depending on the current flowing through the metal such as permalloy and the direction of the magnetic field
(Anisotropy magnetoresistance).

  In addition, “GMR elements” that have been researched in recent years include “multilayer GMR elements” (eg, 20-layer multilayer) and “SV-GMR elements”. A multilayer GMR element requires a relatively large magnetic field for resistance change. Therefore, in order to obtain a large magneto-resistance change even in a low magnetic field, the pinned layer (magnetization is constrained) and the free layer (ferromagnetic film sensitively reacting to an external low magnetic field) The SV-GMR element having a structure in which a non-magnetic layer (Cu) having a thickness of nm is sandwiched is developed and employed in a magnetic head of a hard disk drive (HDD).

  A conventional example in which a current sensor is configured using a GMR element will be described below.

JP 2000-56000 A

  In Patent Document 1, a GMR element is inserted with a gap provided in a magnetic yoke, a coil for applying an alternating magnetic field is provided in the magnetic yoke, and only the absolute value of the measured magnetic field can be obtained from the GMR element output. The output component from the GMR element corresponding to the AC magnetic field is extracted through a band-pass filter (BPF), and the phase of the current to be measured can be determined by comparing the phase with the AC component from the coil. is there.

  In this Patent Document 1, as a means for obtaining an absolute value signal of a magnetic field to be measured, a magnetic field generated in a gap by a current to be measured is converted from a magnetic change to a resistance value change by a GMR element, and an amplifier, an AC component removal In this case, the absolute value signal of the magnetic field to be measured (current to be measured) is output through the low-pass filter (LPF).

  FIG. 2 of Patent Document 1 shows the “magnetic field-resistance change characteristic of the GMR element”. The resistance value of this characteristic changes greatly with temperature change. The operating temperature range required for in-vehicle use is, for example, 25 ° C. ± 55 ° C., but at that time, the resistance value of the GMR element greatly changes to ± 10% for the same applied magnetic field. In Patent Document 1, since the “absolute value signal output of the magnetic field to be measured” is made through the amplifier and the low-pass filter in FIG. 1, the error of the current sensor output with respect to the temperature change is very large, and the hybrid car that requires high accuracy is required. Not suitable for battery current monitor.

  In view of the above points, the first object of the present invention is to provide a highly accurate current sensor in which the direction of the current to be measured can be determined and the measurement accuracy of the current to be measured is hardly affected by temperature. To do.

  The second aspect of the present invention is to provide a current sensor having a good temperature characteristic with a relatively simple circuit configuration, using a highly sensitive SV-GMR element (a large resistance change can be obtained even in a low magnetic field). The purpose.

  Furthermore, a third object of the present invention is to provide a current sensor that can reduce the hysteresis with respect to an external magnetic field, which is a drawback of the SV-GMR element, and can prevent a decrease in measurement accuracy due to the hysteresis.

  Other objects and novel features of the present invention will be clarified in embodiments described later.

In order to achieve the above object, a current sensor according to an aspect of the present invention includes:
A magnetic core that generates magnetic flux due to the current to be measured;
An SV-GMR element disposed in the gap of the magnetic core;
An excitation winding and a feedback winding applied to the magnetic core;
A DC bias circuit for applying a DC bias to the SV-GMR element and taking out a resistance change of the SV-GMR element as a voltage change;
AC bias means for applying an AC voltage to the excitation winding;
A DC removal circuit for removing a DC component from the voltage change in the DC bias circuit;
A comparator for shaping the waveform into a square wave voltage by comparing the AC output voltage of the DC removal circuit with a constant level;
A filter circuit that converts a square wave voltage, which is an output of the comparator, into an average DC voltage;
A magnetic balance amplifier for causing a feedback current to flow in the feedback winding so that a difference between a detection output voltage of the filter circuit and a reference voltage becomes zero;
The reference voltage is set to a voltage value at which the feedback current becomes zero when the measured current is zero,
The magnetic balance amplifier controls the magnetic balance state in which the magnetic flux in the gap caused by the current to be measured is canceled by the magnetic flux in the gap caused by the feedback current .

In the current sensor, the SV-GMR element has a magnetoresistive film pattern and a pinned layer magnetization direction perpendicular to each other, and the pinned layer magnetization direction is arranged in a direction substantially parallel to the direction of the magnetic flux in the gap. A magnetic bias may be applied in a direction substantially perpendicular to the pinned layer magnetization direction.

A current sensor according to another aspect of the present invention includes:
A magnetic core that generates magnetic flux due to the current to be measured;
An SV-GMR element disposed in the gap of the magnetic core;
A feedback winding applied to the magnetic core;
A magnetic balance amplifier for causing a feedback current to flow in the feedback winding so that a difference between a detection voltage that changes due to a resistance change of the SV-GMR element and a reference voltage becomes zero;
The reference voltage is set to a voltage value at which the feedback current becomes zero when the measured current is zero,
The magnetic balance amplifier controls the magnetic balance state in which the magnetic flux in the gap caused by the current to be measured is canceled by the magnetic flux in the gap caused by the feedback current ,
In the SV-GMR element, the magnetoresistive film pattern and the pin layer magnetization direction are perpendicular to each other, the pin layer magnetization direction is arranged in a direction substantially parallel to the direction of the magnetic flux generated by the magnetic core, and the pin layer magnetization A magnetic bias is applied in a direction substantially perpendicular to the direction.

  According to the present invention, by using an SV-GMR element as a magnetosensitive element, it is possible to determine a direction of a current to be measured and realize a highly sensitive current sensor.

  Further, if the SV-GMR element is operated by superimposing an AC magnetic flux by an AC bias on the magnetic flux due to the current to be measured, and an AC signal resulting from a resistance change of the SV-GMR element due to the superimposed magnetic field is extracted, the SV- Although the resistance value of the GMR element itself varies greatly with changes in temperature, the rate of change in resistance to a magnetic field hardly varies even with changes in temperature. Therefore, the measurement accuracy of the current to be measured is hardly affected by temperature and is highly accurate. It can be a current sensor.

  Further, the SV-GMR element is configured so that the magnetoresistive film pattern and the pin layer magnetization direction are perpendicular to each other, and the pin layer magnetization direction is set to be substantially the same as the direction of the magnetic flux generated by the current to be measured. If it is arranged and a magnetic bias is applied in a direction substantially perpendicular to the pinned layer magnetization direction, the hysteresis in the relationship between the external magnetic field and resistance of the SV-GMR element can be reduced, and measurement due to the hysteresis Decrease in accuracy can be reduced.

  Hereinafter, as the best mode for carrying out the present invention, an embodiment of a current sensor will be described with reference to the drawings.

  FIG. 1 shows a circuit configuration of a current sensor, and an annular magnetic core with an air gap (a magnetic core that is a closed magnetic circuit other than the air gap) 1 has an electric wire L1 (1 as a current path through which the primary side measured current Ip flows. The primary winding of the turn) is disposed through, and a feedback winding L2 for passing a feedback current Is is wound around the magnetic core 1 by a predetermined number of turns, and an excitation winding L3 for AC bias is provided. It is wound. For example, an oscillator 5 having an oscillation frequency of about 10 kHz is connected to the excitation winding L3 as AC bias means for applying an AC voltage (eg, sine wave, triangular wave, etc.) to the excitation winding L3. For the magnetic core 1, a silicon steel plate, a permalloy core or the like having a high magnetic permeability and a small residual magnetism is used.

  The air gap G formed in the magnetic core 1 passes through the magnetic flux generated by the primary-side measured current Ip and the feedback current Is and the magnetic flux generated by the current in the excitation winding L3 in a superimposed manner. As described above, the SV-GMR element 10 is disposed (fixed in position) in the air gap G. In the present embodiment, an AC magnetic field bias of ± 2 (mT) is applied to the SV-GMR element 10 by flowing an AC current through the excitation winding L3.

  The SV-GMR element includes a magnetic pinned layer whose magnetization direction is fixed in one direction, and a ferromagnetic free layer stacked on the pinned layer via a nonmagnetic material through which a current mainly flows. The pinned layer has a resistance effect film, the magnetization direction of the pinned layer is not changed by the external magnetic field (external magnetic flux), and the magnetization direction of the free layer is changed to the direction of the external magnetic field (external magnetic flux). Here, when the magnetization direction of the pinned layer and the magnetization direction of the free layer (that is, the direction of the external magnetic field) in the magnetoresistive effect film are parallel but opposite in direction, that is, antiparallel, the rate of change in resistance becomes positive. It becomes a high resistance state. When the magnetization direction of the pinned layer and the magnetization direction of the free layer (that is, the direction of the external magnetic field) are parallel and in the same direction, that is, in the forward parallel direction, the resistance change rate becomes negative and a low resistance state is obtained.

  In the present embodiment, as shown in the enlarged view in FIG. 2, the SV-GMR element 10 has a magnetosensitive effect surface 12 on which a magnetoresistive effect film pattern 11 is formed. The longitudinal direction of the meander pattern of the surface 12 is a magnetoresistive effect film) and the pinned layer magnetization direction are perpendicular to each other in the magnetosensitive surface 12.

  Further, the magnetic bias means 6 made of a permanent magnet or an electromagnet has a static magnetic field (DC bias magnetic field) in a direction substantially perpendicular to the pinned layer magnetization direction of the SV-GMR element 10 (however, parallel to the magnetosensitive surface 12). Is applied. This is to reduce the hysteresis of the SV-GMR element 10. Since the end portions of the magnetic core 1 are actually close to each other, they also have a vertical magnetic field component, but there is no effect on the hysteresis reduction effect.

  FIG. 3 shows the relationship between the magnetic flux density in the air gap G and the resistance value of the SV-GMR element inserted in the case where the magnetic bias means 6 is not present and in the case where it is not present.

  FIG. 3A shows the hysteresis characteristic when the magnetic bias means 6 is not provided, and it can be seen that the hysteresis is large. Here, + bias / -bias is applied to the SV-GMR element after a sufficiently large ± 100 (mT) is applied to the SV-GMR element with respect to ± 2 (mT) at which the SV-GMR element is saturated. Is measured.

  In FIG. 3B, a magnetic bias means 6 is provided, and a bias magnetic field in a direction substantially perpendicular to the pinned layer magnetization direction of the SV-GMR element 10 (about 0.8 (mT) at the position of the SV-GMR element). It can be seen that this is a hysteresis characteristic when the voltage is applied, which is clearly smaller and improved as compared with FIG.

  A DC bias circuit 20 in FIG. 1 applies a DC bias to the SV-GMR element 10 and takes out a resistance change of the SV-GMR element 10 as a voltage change. A series connection of the resistor R1 and the SV-GMR element 10 is shown in FIG. A circuit is provided, which is connected between a DC power source Vcc having a constant voltage (for example, DC 5V) and a ground (GND). The voltage at the connection point between the resistor R1 and the SV-GMR element 10 with respect to the ground is taken out and supplied to the AC bypass circuit (DC removal circuit) 30.

  The AC bypass circuit 30 has a DC cut capacitor C1 and a shunt resistor R2. An AC component of the voltage change caused by the resistance change of the SV-GMR element 10 appears at both ends of the shunt resistor R2.

  The AC voltage across the shunt resistor R2 is amplified to an appropriate voltage value by the amplifier circuit 40. The amplifier circuit 40 is, for example, a non-inverting amplifier circuit composed of an operational amplifier 41 and resistors R3 and R4.

  The comparison circuit (comparator) 50 has a waveform shaping function that generates a positive square wave (pulse wave) when the output voltage of the amplifier circuit 40 is higher than the ground level with reference to the ground level. The output is supplied to the low-pass filter circuit 60. The low-pass filter circuit 60 includes a resistor R5 and a capacitor C2 that is charged through the resistor R5.

  The magnetic balance amplifier circuit 70 is a differential amplifier, and the footback current Is is footback-wound so that the difference between the reference voltage Vref and the detected output voltage of the low-pass filter circuit 60 (terminal voltage of the capacitor C2) becomes zero. It flows to L3. A detection resistor R6 for taking out the sensor output voltage is inserted in series with the feedback winding L3.

  Next, the overall operation of the current sensor will be described.

  When the primary side measured current Ip is zero, the AC voltage of the oscillator 5 is applied to the excitation winding L3. As a result, an AC current flows through the excitation winding L3, and the resulting magnetic flux is an annular magnetic core 1 with an air gap. To the SV-GMR element 10 disposed in the air gap G of FIG. At this time, since the pin layer magnetization direction of the SV-GMR element 10 is oriented in a direction substantially parallel to the direction of the magnetic flux generated by the magnetic core 1, the resistance of the SV-GMR element 10 is caused by the periodic change of the magnetic flux. The value also changes periodically. This is taken out as a voltage change by the DC bias circuit 20, and the DC component is removed by the DC cut capacitor C1 of the AC bypass circuit 30. As a result, an AC voltage is obtained at both ends of the shunt resistor R2, and this is the amplifier circuit 40. The AC voltage b1 shown in FIG. 4B is output to the input side of the comparison circuit 50.

  In the comparison circuit 50, when the AC voltage b1 is equal to or higher than the ground potential, the waveform is shaped by converting it to logic level High, and the square wave signal b2 in FIG. 4B is output to the low-pass filter circuit 60, where A detection DC signal b3 obtained by averaging the square wave signal b2 is generated and applied to the inverting input terminal of the magnetic balance amplifier circuit 70. For example, the low-pass filter circuit 60 generates a DC signal having a square wave signal voltage of 5 V, a duty of 50%, 2.5 V, and a duty of 40%, 2 V.

  When the primary-side measured current Ip is zero, the feedback current Is from the magnetic balance amplifier circuit 70 must be zero. At this time, the non-magnetic balance amplifier circuit 70 is set so that the feedback current Is is zero. Sets the reference voltage Vref of the inverting input terminal. That is, the reference voltage Vref is matched with the voltage value of the DC signal b3.

  After such a setting operation of the reference voltage Vref, the actual measurement of the current Ip on the primary side can be made to flow through the electric wire L1 to measure the current.

  When the primary side measured current Ip = 0, the resistance value of the SV-GMR element 10 is changed by the alternating magnetic flux generated by the alternating current of the excitation winding L3 with the magnetic flux density of FIG. However, when the primary-side measured current Ip flows, the magnetic flux generated by the measured current is superimposed on the AC magnetic flux, and the operating point moves from the position where the magnetic flux density = 0 in FIG. Will shift to the side. Since the slope of the curve showing the relationship between the magnetic flux density and the resistance of the SV-GMR element in FIG. 3B changes, the AC voltage waveform extracted by the resistance change of the SV-GMR element 10 when the operating point is shifted. (Voltage waveform obtained across the shunt resistor R2) changes.

Therefore, the detection output voltage of the low-pass filter circuit 60 and the reference voltage Vref do not match, and the reference voltage Vref applied to the non-inverting input terminal in the magnetic balance amplification circuit 70 and the low-pass filter circuit 60 applied to the inverting input terminal. detection output voltage and is constantly fed back current is so that the same potential (flow into or output end) flows in from the output terminal of the magnetic balance amplifier circuit 70, ing a magnetic equilibrium state. In this magnetic equilibrium state, the magnetic flux caused by the primary current to be measured Ip is canceled out by the magnetic flux caused by the feedback current Is, and the state shown in FIG.

Examples of the primary side measured current Ip and the windings provided in the magnetic core 1 are as follows.
Primary side measured current Ip = ± 200A
Number of turns of electric wire L1 (primary winding) Np = 1 turn Feedback current (measurement current) Is (A)
From the principle of ampere-turn such as Ns = 4,000 turns of feedback winding L2 (secondary winding),
Np × Ip = Ns × Is (1)
And the measured current Ip is
Ip = Ns × Is / Np (2)
It becomes. The measured value of the feedback current Is can be taken out as a sensor output voltage proportional to the measured current Ip from both ends of the detection resistor R6 connected in series with the feedback winding L2.

  If the magnetic balance amplifier circuit 70 does not follow and an error of +1 A occurs with respect to the current to be measured, the AC voltage a1, the square wave signal a2, and the DC signal a3 in FIG. Compared with FIG. 4B showing the magnetic equilibrium state, the duty of the square wave signal a2 becomes larger, and the DC signal a3 becomes higher than the reference voltage Vref (= b3). If the magnetic balance amplifier circuit 70 operates normally, the feedback current Is is changed to control the magnetic balance state shown in FIG. 4B.

  On the other hand, if a −1A error occurs with respect to the current to be measured, the AC voltage c1, the square wave signal c2, and the DC signal c3 in FIG. Compared with FIG. 4B showing the magnetic equilibrium state, the duty of the square wave signal c2 becomes smaller, and the DC signal c3 becomes lower than the reference voltage Vref. If the magnetic balance amplifier circuit 70 operates normally, the feedback current Is is changed to control the magnetic balance state shown in FIG. 4B.

  FIG. 5 shows “output characteristics” according to the present embodiment. The feedback current (output current) Is depends only on the turn ratio, while the measured current Ip is ± 200 A, and the feedback current (output current) Is depends only on the turn ratio, and the turn Np = 1 turn of the wire L1 (primary winding), the feedback winding L2 ( Under the measurement condition of the number of turns (secondary winding) Ns = 4000 turns, Is (A) = Ip (A) / 4,000 was obtained with high accuracy. In addition, this characteristic has an effect that the output characteristic only moves in parallel only when the offset fluctuation (Is fluctuation at Ip = 0A) occurs, and the linearity is not affected at all.

  FIG. 6 shows the measurement result of the “offset temperature characteristic”. Current to be measured Ip: With respect to the full scale of ± 200A, the maximum error is -0.1A, and the% error is 0.1 / 200 = 0.05 (%). And highly accurate characteristics were obtained.

  FIG. 7 shows “SV-GMR element hysteresis temperature characteristics”. With reference to + 25 ° C., the resistance value R (Ω) increases by about 10% at + 80 ° C., and conversely, the resistance value R becomes about −10% at −30 ° C., which is greatly reduced. In the present embodiment, attention is paid to the fact that the slope of ΔR / ΔB is constant without depending on the temperature, and only the AC component is extracted by the DC cut capacitor C1 of the AC bypass circuit 30 in FIG. By taking out only the change in the resistance value of the SV-GMR element, the temperature dependence of the DC resistance value R of ± 10% due to the temperature is removed.

  According to this embodiment, the following effects can be obtained.

(1) By using the SV-GMR element 10 as a magnetosensitive element, the direction of the current Ip to be measured can be determined, and a highly sensitive current sensor can be realized. As shown in FIG. 5, the output characteristics depend only on the turn ratio of the electric wire L1 (primary winding) provided in the magnetic core 1 and the feedback winding L2 (secondary winding), and are shown in FIG. Thus, the offset temperature characteristic is also good, and a highly accurate characteristic with respect to temperature change can be obtained.

(2) An AC signal caused by a change in resistance of the SV-GMR element 10 caused by the superimposed magnetic field is generated by superimposing an AC magnetic flux generated by the oscillator 5 serving as an AC bias unit on the magnetic flux generated by the measured current Ip. Take out. Although the resistance value itself of the SV-GMR element largely fluctuates with a temperature change, the resistance change rate with respect to the magnetic field hardly fluctuates even with the temperature change. Therefore, the measurement accuracy of the measured current Ip is the resistance value of the SV-GMR element 10. Thus, it is possible to obtain a highly accurate current sensor that is hardly affected by the temperature change.

(3) The SV-GMR element 10 is configured such that the magnetoresistive film pattern (longitudinal direction) and the pinned layer magnetization direction are perpendicular to each other, and is substantially parallel to the direction of the magnetic flux generated by the current Ip to be measured. The pinned layer magnetization direction is arranged in a direction, and a magnetic bias is applied in a direction substantially perpendicular to the pinned layer magnetization direction by a magnetic bias means 6 made of a permanent magnet or an electromagnet, and an external magnetic field and an SV-GMR element The hysteresis in relation to the resistance can be reduced, and the decrease in measurement accuracy due to the hysteresis can be reduced.

  In the DC bias circuit 20, when the resistance value of the SV-GMR element 10 changes, the voltage at both ends of the series resistor R 1 also changes. Therefore, the voltage change at both ends of the series resistor R 1 is extracted and amplified by the amplifier circuit 40. Is possible.

  If the input impedance of the amplifier circuit 40 is an appropriate value, the shunt resistor R2 in the AC bypass circuit 30 can be omitted.

  If the AC voltage due to the resistance change of the SV-GMR element 10 is large, the amplifier circuit 40 can be omitted.

  Although the embodiments of the present invention have been described above, it will be obvious to those skilled in the art that the present invention is not limited to these embodiments, and various modifications and changes can be made within the scope of the claims.

It is a circuit diagram showing an embodiment of a current sensor according to the present invention. In embodiment, it is a side view which shows arrangement | positioning of the SV-GMR element with respect to the air gap of the annular magnetic core with an air gap, and arrangement | positioning of a magnetic bias means. It is a hysteresis characteristic in the relationship between the external magnetic field and the resistance of the SV-GMR element, where (A) shows a hysteresis curve when there is no magnetic bias means and (B) shows a hysteresis curve when there is a vertical magnetic field by the magnetic bias means. It is a waveform diagram for explaining the operation of the embodiment, (A) is a waveform diagram when a + 1A error occurs, (B) is a waveform diagram during normal operation, (C) is a -1A error temporarily It is a wave form diagram when it generate | occur | produces. It is an output characteristic figure which shows the relationship between the to-be-measured current Ip and footback current Is in embodiment. It is an offset temperature characteristic figure which shows the relationship between the temperature and offset value in embodiment. It is a hysteresis curve figure which shows the hysteresis-temperature characteristic in the relationship between an external magnetic field and the resistance of a SV-GMR element.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Ring core with air gap 5 Oscillator 6 Magnetic bias means 10 SV-GMR element 11 Magnetoresistance effect film pattern 12 Magnetosensitive surface 20 DC bias circuit 30 AC bypass circuit 40 Amplifying circuit 50 Comparison circuit 60 Low pass filter circuit 70 Amplification for magnetic balance Circuit C1, C2 Capacitor L1 Electric wire L2 Feet back winding L3 Excitation winding R1-R6 Resistance Vref Reference voltage

Claims (3)

A magnetic core that generates magnetic flux due to the current to be measured;
A spin valve giant magnetoresistive element disposed within the gap of the magnetic core;
An excitation winding and a feedback winding applied to the magnetic core;
A DC bias circuit for applying a DC bias to the spin valve giant magnetoresistive element and taking out a resistance change of the spin valve giant magnetoresistive element as a voltage change;
AC bias means for applying an AC voltage to the excitation winding;
A DC removal circuit for removing a DC component from the voltage change in the DC bias circuit;
A comparator for shaping the waveform into a square wave voltage by comparing the AC output voltage of the DC removal circuit with a constant level;
A filter circuit that converts a square wave voltage, which is an output of the comparator, into an average DC voltage;
A magnetic balance amplifier for causing a feedback current to flow in the feedback winding so that a difference between a detection output voltage of the filter circuit and a reference voltage becomes zero;
The reference voltage is set to a voltage value at which the feedback current becomes zero when the measured current is zero,
The magnetic balance amplifier controls the magnetic balance state in which the magnetic flux in the gap caused by the current to be measured is canceled by the magnetic flux in the gap caused by the feedback current . The spin valve giant magnetoresistive element has a magnetoresistive film pattern and a pinned layer magnetization direction perpendicular to each other, and the pinned layer magnetization direction is arranged in a direction substantially parallel to the direction of magnetic flux in the gap. The current sensor according to claim 1, wherein a magnetic bias is applied in a direction substantially perpendicular to the direction. A magnetic core that generates magnetic flux due to the current to be measured;
A spin valve giant magnetoresistive element disposed within the gap of the magnetic core;
A feedback winding applied to the magnetic core;
A magnetic balance amplifier that feeds a feedback current to the feedback winding so that a difference between a detection voltage and a reference voltage that change due to a resistance change of the spin valve giant magnetoresistive element becomes zero;
The reference voltage is set to a voltage value at which the feedback current becomes zero when the measured current is zero,
The magnetic balance amplifier controls the magnetic balance state in which the magnetic flux in the gap caused by the current to be measured is canceled by the magnetic flux in the gap caused by the feedback current ,
In the spin valve giant magnetoresistive element, the magnetoresistive film pattern and the pin layer magnetization direction are perpendicular to each other, and the pin layer magnetization direction is arranged in a direction substantially parallel to the direction of the magnetic flux generated by the magnetic core. A current sensor, wherein a magnetic bias is applied in a direction substantially perpendicular to a layer magnetization direction.

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