JPH0943327A - Magneto-resistive current sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve measuring accuracy, to dispense with necessity of a secondary coil for allowing second current to flow, and to decrease the size. SOLUTION: A ferromagnetic body magneto-resistive element unit 10 and an operational amplifying circuit unit 20 are formed on the same chip, individual magneto-resistive bodies 11 to 14 are formed into bridge shapes in the ferromagnetic body magnetoresistance element unit 10, at least one of magneto-resistive bodies has a resistance value different from a resistance value of the other magneto-resistive body, and therefore, the magnetic balancing state can be naturally formed in supplying of the stationary current. Since any hall element is not used as in the past, the change by the temperature is not generated, and the measuring accuracy is high, and any secondary coil for allowing secondary current to flow, which has been required for the magnetic balance in the past, is not required.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetoresistive current sensor which integrates a ferromagnetic magnetoresistive element and a waveform shaping circuit on the same chip and detects a current from a magnetic field change which changes depending on a circuit current. Is.

[0002]

2. Description of the Related Art Conventionally, this type of current sensor has been used for measuring the current of equipment such as an uninterruptible power supply, an extruder, a rolling mill, and an NC machine tool which performs high-speed and large-capacity precision switching. There is. For example, Mechatro Books No8
Is a magnetic flux measurement formula in which the magnetism proportional to the measured current is detected by the Hall element and amplified and output, and the output of the Hall element is amplified and a secondary current is sent to the secondary coil. A magnetic balance type is disclosed in which a Hall element is always placed in a magnetic equilibrium state of zero magnetic field by applying a magnetic flux to output a secondary current.

[0003]

However, when the Hall element is used for magnetic flux detection, it is difficult to improve the measurement accuracy due to the influence of temperature characteristics. On the other hand, in the magnetic balance type, there is a problem that the secondary current that creates the magnetic balance state is required, so that the consumption current increases and that the secondary coil that allows the secondary current to flow is required, and the shape becomes large.

The present invention has been made in view of such a situation, and it has a high measurement accuracy and is used for supplying a secondary current.
The shape of the secondary coil is made smaller by eliminating the need for it.

[0005]

In order to solve such a problem, the present invention comprises a ferromagnetic magnetoresistive element section and an operational amplifier section, and the ferromagnetic magnetoresistive element section is externally proportional to the measured current. The present invention relates to a magnetoresistive current sensor whose resistance value changes when a magnetic field is applied. In order to achieve such an object, a ferromagnetic magnetoresistive element section and an operational amplifier circuit section are formed on the same chip, and the ferromagnetic magnetoresistive element section is made of a Ni-Fe-Co alloy or a Ni-Fe alloy. One of the two thin films is a magnetic resistor with a plurality of linear patterns formed in close proximity to each other, and the magnetic resistors are adjacent to each other, but the pattern formation directions are perpendicular to each other And at least one of them has a resistance value different from that of the other magnetoresistive body. The ferromagnetic magnetoresistive element section uses a Co / Cu or Fe / Cr superlattice instead of the Ni-Fe-Co alloy or the Ni-Fe alloy.

[0006]

FIG. 1 is an equivalent circuit showing the configuration of a magnetoresistive effect current sensor according to the present invention. When a magnetic field is applied, the resistance value of the magnetoresistive effect current sensor changes according to its direction. The ferromagnetic magnetoresistive element section 10 and the operational amplifier circuit section 20 for amplifying its output are formed on the same chip so that they can be integrated. Although not shown, the magnetic field generates a value corresponding to the measured current. As shown in FIG. 2, the ferromagnetic resistance element unit 10 has a plurality of ferromagnetic magnetoresistive thin films adjacent to each other and aligned in parallel to form a magnetoresistor. The magnetic resistors 11 to 14 are formed so as to be perpendicular to each other, and are connected in a bridge shape to detect the direction of the magnetic field.

When a magnetic field in the direction of arrow A in FIG. 2 is applied, the resistance values of the magnetoresistors 11 and 14 aligned in equilibrium with the magnetic field become maximum, and the magnetoresistive element 12 aligned perpendicular to the magnetic field. The resistance values of and 13 are minimum.
On the other hand, when a magnetic field in the direction of arrow B is applied, the resistance values of the magnetoresistors 12 and 13 aligned parallel to the magnetic field become maximum, and the magnetoresistive body 11 aligned perpendicular to the magnetic field.
The resistance values of 14 and 14 are minimum. Generally, the direction of the magnetic field having the maximum resistance value is referred to as the easy magnetization direction, and the direction of the magnetic field having the minimum resistance value is referred to as the difficult magnetization direction.

Each magnetoresistive effect element is [Co (15A) /
Cu (10A) A)] ₅₀ superlattice ferromagnetic thin films are arranged in parallel, and FIG. 3 shows the characteristics of the device at room temperature, where −15 kOe ≦ H ≦ 0.
A linear relationship is obtained with kOe and 0 kOe ≦ H ≦ 15 kOe. Further, the resistance value of the magnetic resistor 11 is adjusted to be smaller than that of the other three magnetic resistors 12 to 14 so that the initial offset voltage is generated.

A power supply terminal 1 shown in FIG. 2 of a ferromagnetic magnetoresistive element portion 10 having these four magnetoresistors 11-14.
5 is connected to the power supply terminal 31 shown in FIG. 1, and the ground terminal 16 shown in FIG. 2 is connected to the ground terminal 33 shown in FIG. 2 is connected to the inverting terminal of the operational amplifier 21 of FIG. 1, and the output terminal 18 of FIG. 2 is connected to the non-inverting terminal of the operational amplifier 21 of FIG. ing.

Next, the operation will be described. In FIG. 1, the resistance values of the magnetic resistors 11 to 14 are R1 to R1, respectively.
When R4 is set and the angle formed with the direction of the symbol A in FIG. 2 is θ, the change in resistance value in the saturated magnetic field is as follows.

R1 (θ) = R1min sin ² θ + R1max cos ² θ R2 (θ) = R2min sin ² (π / 2−θ) + R2max
cos ² (π / 2−θ) R3 (θ) = R3min sin ² (π / 2−θ) + R3max
cos ² (π / 2−θ) R4 (θ) = R4min sin ² θ + R4max cos ² θ where Rn min (n = 1 to 4) is the resistance value when magnetized in the difficult magnetization direction, and Rn max (n = 1 to 4) are design values.

On the other hand, the voltages Vin1 and Vin2 supplied to the inverting input terminal and the non-inverting input terminal of the operational amplifier 21.
Is as follows. Vin1 = Vcc * R3 / (R1 + R3) Vin2 = Vcc * R4 / (R2 + R4) where Vcc is the power supply voltage between the power supply terminal 31 and the ground terminal 33.

Now, when Rn max (n = 1 to 4) = R0 and a magnetic field having a value corresponding to the measurement current is applied,
The maximum change amount ΔV of Vin is as follows, where ΔR is the maximum change amount of the magnetoresistive element. ΔV = | Vin (θ = 0) −Vin (θ = π / 2) | ≈
Vcc * ΔR / R0

FIG. 4 is a diagram showing the principle structure of the magnetoresistive effect current sensor according to the present invention. In actual use, the magnetoresistive effect current sensor shown in FIG. 2 is mounted directly above the structure of FIG. ing. In FIG. 4, a current I is drawn in the direction of the arrow in the figure.
Is supplied, a magnetic field proportional to the measured current I is applied in the direction of hard magnetization indicated by the symbol A.
The resistance value of 1 decreases with the applied magnetic field strength, and the output of the operational amplifier circuit section 20 increases.

In the above embodiments, as the ferromagnetic thin film material, Ni-Fe-Co alloy or Ni-Fe alloy is used for low current to medium current, and Co / Cu superlattice or Fe / Cr is used for medium current or more. It is preferable to use a superlattice from the viewpoint of ensuring linearity.

[0016]

As described above, according to the present invention, the ferromagnetic magnetoresistive element section and the operational amplifier circuit section are formed on the same chip, and the ferromagnetic magnetoresistive element section forms the magnetic resistors in a bridge shape. However, since at least one of them has a resistance value different from the resistance value of other magnetic resistors, it is possible to naturally create a magnetic equilibrium state during the supply of a steady current. Since it does not use, there is no change due to temperature.
In addition, since a secondary coil for flowing a secondary current, which is conventionally required for magnetic balance, is required, it has an effect that the shape can be reduced.

[Brief description of drawings]

FIG. 1 is a circuit diagram of an equivalent circuit showing a configuration of an exemplary embodiment of the present invention.

FIG. 2 is a diagram showing an example of the shape of a ferromagnetic magnetoresistive element section according to the present invention.

FIG. 3 is a graph showing an example of a magnetic resistance curve.

FIG. 4 is a circuit diagram showing a circuit of the magnetoresistive exchange current sensor of the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 10 ... Ferromagnetic substance magnetoresistive element part, 11-14 ... Magnetoresistive body, 20 ... Operation amplifier circuit part, 21 ... Operation amplifier.

Claims (2)

[Claims] 1. A magnetoresistive effect current sensor comprising a ferromagnetic magnetoresistive element section and an operational amplifier section, the resistance value of which changes when an external magnetic field proportional to the measured current is applied to the ferromagnetic magnetoresistive element section. In the above, the ferromagnetic magnetoresistive element section and the operational amplifier circuit section are formed on the same chip, and the ferromagnetic magnetoresistive element section is made of Ni.
-Fe-Co alloy or Ni-Fe alloy thin film made of a magnetoresistor formed by a plurality of linear patterns formed in close proximity to each other. The magnetoresistors are adjacent magnetoresistors. The magnetic resistance is characterized in that the pattern formation directions of the two are perpendicular to each other and at least one of them has a resistance value different from that of the other magnetoresistive body. Effective current sensor. 2. The ferromagnetic magnetoresistive element according to claim 1, wherein the Ni / Fe—Co alloy or the Ni—Fe alloy is replaced by Co / Cu or Fe / Cr.
A magnetoresistive current sensor characterized by using a superlattice.