JP2001116773A - Current sensor and current detector - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a current sensor and a current detector comprising the current sensor, a drive circuit and a signal processing circuit capable of accurately detecting a magnetic field caused by minute current in the disturbance magnetic field, detecting the minute current and easily mounting on a circuit board in the current sensor using a magnetic impedance element. SOLUTION: The current sensor 1 has coils 6a, 6b energizing current to be measured, and the magnetic impedance elements 4a, 4b differentiating and detecting generated therefrom. The elements 4a, 4b comprise magnetic thin films formed on the same face of the same non-magnetic board 3, respective magnetic field detection directions are made the same direction, and they are arranged along the magnetic field detection direction in parallel. The coils 6a, 6b are wound in mutually reverse directions, and the magnetic field of the mutually reverse direction is applied on the elements 4a, 4b by energization of the current to be measured.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a current sensor used for monitoring and controlling a current, which is incorporated in an electronic device or the like, and in particular, uses a magnetic detecting element and inserts it into a current path of a circuit board or the like to make it small. The present invention relates to a magnetic detection type current sensor for detecting a current, and a current detection device including the current sensor and its driving and signal processing circuits.

[0002]

2. Description of the Related Art In recent years, as the power consumption of electronic devices has been reduced and the precision of power control has been increased, the current used has been reduced, and a current sensor having higher sensitivity has been required. In addition, electronic devices are required to have small size and intelligent performance, and a high-sensitivity current sensor that can be easily mounted on a circuit board or the like is required.

Various micro current sensors using a magnetic detection element have been proposed, but the basic configuration is almost the same. That is, as shown in FIG. 8, a measured current path through which a measured current flows is wound or penetrated through a magnetic core having a gap, and a change in magnetic flux due to the measured current is set in a gap portion of the magnetic core. It is detected by a magnetic detection element. Although a Hall element is mainly used as the magnetic detection element, there is another element using a magnetoresistive element. There is also a method that does not use a magnetic core. A current path to be measured is formed as a coil pattern as shown in FIG. 9 and a magnetic detection element is placed on the coil pattern, or a linear path as shown in FIG. There is one in which magnetic detecting elements are installed on both sides of a current path to be measured.

[0004]

However, in a conventional current sensor using a Hall element or a magnetoresistive element as the magnetic detecting element, the sensitivity of the magnetic detecting element is low, and even if the magnetic flux is concentrated on the magnetic core, several mA is required. Detection is the limit. It is almost impossible to detect a small current by a method without using a magnetic core.

On the other hand, as a method for detecting a minute current of the order of μA, a method using a magnetic impedance element as a magnetic detection element is considered. When a high-frequency current is applied to an element body made of a magnetic material, the impedance between both ends of the element body changes in accordance with an external magnetic field. Therefore, there is a possibility that a more sensitive current sensor can be realized.

[0008] However, if a magnetic impedance element is used as the magnetic detection element in a system in which the magnetic detection element is inserted into the gap of the magnetic core as shown in FIG. 8, the magnetic field detection direction of the magnetic impedance element is the longitudinal direction of the element. In addition, the gap width becomes extremely large, and only sensitivity comparable to that of a conventional sensor can be obtained. Even in the method that does not use a magnetic core, in the configuration in which the elements are arranged on both sides of the current path to be measured as shown in FIG. 10, it is necessary to arrange the longitudinal direction of the magnetic impedance element perpendicular to the current path. Even when the element and the current path are brought close to each other, a magnetic field is applied to only a part of the element, and almost no sensitivity can be obtained. The same applies to the method of FIG.

Further, when detecting a very small current, the disturbance magnetic field becomes extremely large with respect to the magnetic field due to the current to be measured. Therefore, not only is the sensitivity high, but also the disturbance magnetic field is accurately separated to measure the current to be measured. It must be able to detect only a small magnetic field due to Further, when the disturbance magnetic field is removed by differential detection using two magnetic detecting elements, the sensitivity, temperature characteristics, and the like of the magnetic detecting elements usually vary, which becomes a large error factor in detecting a small current. In particular, current detection becomes impossible in a direct current or low frequency range. That is, in order to enable detection on the order of μA, it is indispensable to have a configuration that does not cause an error due to a disturbance magnetic field or a variation in characteristics of the magnetic detection element, in addition to an improvement in sensitivity.

In view of the above circumstances, the present invention relates to a current sensor using a high-sensitivity magneto-impedance element, which accurately detects a magnetic field due to a minute current even in a disturbance magnetic field, and thereby detects a minute current of a μA order. An object of the present invention is to provide a current sensor that can be detected and that can be easily mounted on a circuit board, and a current detection device including the current sensor and its driving and signal processing circuits.

[0009]

According to the present invention, there is provided a current sensor comprising two coils for supplying a current to be measured and a magnetic field generated by the two coils. It has two magneto-impedance elements to be detected, the two magneto-impedance elements are made of a magnetic thin film formed on the same surface of the same non-magnetic substrate, and the respective magnetic field detection directions are the same. , And the two coils are configured to apply mutually opposite magnetic fields to the two magneto-impedance elements when the current to be measured is supplied.

Further, as a more specific configuration, the two coils are arranged side by side along the magnetic field detecting direction such that their respective central axis directions are along the magnetic field detecting directions of the two magnetic impedance elements. A configuration wound around the magneto-impedance element so as to surround each of the magneto-impedance elements, and the two coils are disposed near a surface of the non-magnetic substrate on which the magneto-impedance element is formed. A configuration was adopted in which the coils were wound around the disposed coil bobbins, and were arranged so that their respective central axis directions were along the magnetic field detection direction of the magneto-impedance element and were aligned along the magnetic field detection direction.

[0011] Further, a configuration is adopted in which electrodes formed at both ends of each of the two magneto-impedance elements are directly soldered to a circuit board on which a current sensor is mounted.

[0012] Further, a configuration in which a permanent magnet for applying a bias magnetic field to the magnetic impedance element is provided on the surface of the non-magnetic substrate opposite to the surface on which the magnetic impedance element is provided, more preferably A configuration in which the permanent magnet is formed of a hard magnetic thin film and a configuration in which a bias coil for applying a bias magnetic field to the magnetic impedance element is disposed between the two coils are employed.

The current sensor according to the present invention may further include a current sensor having a configuration other than the configuration in which the bias coil is disposed, and a high-frequency oscillator for applying a high-frequency current to the two magneto-impedance elements. A circuit, two detection circuits for detecting signals extracted from both ends of each of the two magnetic impedance elements, and a differential amplifier circuit for differentially amplifying output signals of the two detection circuits. A current sensor configured to output an output signal of a dynamic amplifier circuit as a current detection signal; and a current sensor according to the present invention, wherein the bias coil is disposed; and an AC bias is applied to the bias coil of the current sensor. A bias application circuit for applying a current; a high-frequency oscillation circuit for applying a high-frequency current to the two magnetic sensing elements; Each of the two detection circuits for detecting a signal extracted from both ends of the magnetic detecting element, the two
A first differential amplifier circuit that differentially amplifies output signals of the two detection circuits, two peak hold circuits that respectively hold positive and negative peak voltages of the output of the first differential amplifier circuit, A second differential amplifier circuit for differentially amplifying the output signals of the two peak hold circuits is provided, and the output signal of the second differential amplifier circuit is output as a current detection signal.

[0014]

Embodiments of the present invention will be described below with reference to the drawings.

<First Embodiment> A first embodiment of a current sensor according to the present invention and a current detecting device using the same will be described with reference to FIGS.

FIG. 1A shows a configuration of the current sensor according to the present embodiment. The current sensor 1 includes a circuit board 14
It consists of the following members indicated by reference numerals 3 to 12 mounted above.

Reference numeral 3 denotes a non-magnetic substrate as a substrate of the magnetic sensing element.

Reference numerals 4a and 4b denote magneto-impedance elements constituting a magnetic detecting element, which are formed on the same surface of the same non-magnetic substrate 3 as magnetic thin films having an elongated serpentine pattern. As a direction,
The respective magnetic field detection directions are arranged in the same direction, and are arranged along the magnetic field detection direction. The inner ends of the magneto-impedance elements 4a and 4b facing each other are connected to each other, a common electrode 5c is drawn out from the connection part, and is formed at the other end of each of the elements 4a and 4b. Are formed with electrodes 5a and 5b (see FIG. 1B). The surface of the non-magnetic substrate 3 on which the magnetic impedance elements 4a and 4b are formed
Placed on the circuit board 14 in a direction perpendicular to the
The three electrodes 5a to 5 of the magnetic impedance elements 4a and 4b
The nonmagnetic substrate 3 is mounted on the circuit board 14 by directly soldering 5 c to the circuit board 14.

Reference numerals 6a and 6b denote coils as current paths through which the current to be measured flows. The directions of the central axes of the coils 6a and 6b are aligned with the magnetic field detection directions of the magnetic impedance elements 4a and 4b. The elements 4a and 4b are arranged side by side so as to surround each of the elements 4a and 4b.
a, 4b (around the non-magnetic substrate 3). The coils 6a and 6b are connected in series as shown in FIG. 1B, but are wound in opposite directions.

Reference numeral 8 denotes a magneto-impedance element 4a, 4b
Is a bias magnet (permanent magnet) for applying a bias magnetic field to the non-magnetic substrate 3 and is provided on the surface of the non-magnetic substrate 3 opposite to the surface on which the magnetic impedance elements 4a and 4b are formed.

Reference numeral 12 denotes a magneto-impedance element 4a, 4
This is a shield for magnetically shielding b from an external magnetic field which becomes a disturbance.

Next, FIG. 1B is an explanatory diagram of the operation principle of the current sensor 1 having the above configuration. At the time of current detection, the two windings wound in opposite directions to each other in a disturbance magnetic field.
A current to be measured is supplied to the two coils 6a and 6b. As a result, magnetic fields ± ΔH in mutually opposite directions are generated from the coils 6a and 6b, respectively, and applied to the magnetic impedance elements 6a and 6b, respectively, and the gradient of the magnetic field as shown in the graph of FIG. It is formed near the impedance elements 6a and 6b. The difference between the magnetic fields due to the position of the gradient of the magnetic field is differentially detected by the two magnetic impedance elements 4a and 4b.

Here, since the gradient of the magnetic field formed by the measured current is local, it can be accurately separated from the disturbance magnetic field. In addition, 2 for differentially detecting the magnetic field
The two magnetic impedance elements 4a and 4b are formed as magnetic thin films adjacent to each other on the same surface of the same non-magnetic substrate 3, so that magnetic field-impedance characteristics, sensitivity,
There is almost no difference in the temperature characteristics between the two elements 4a and 4b. Therefore, very accurate differential detection can be performed. As a result, even if the magnetic field due to the current to be measured is a very small magnetic field with respect to the disturbance magnetic field, it is possible to accurately detect the magnetic field, and effectively use the high-sensitivity magnetic field detection capability of the magnetic impedance element. By utilizing this, current detection on the order of μA can be performed in a wide frequency range from direct current.

Further, in the current sensor 1 of the present embodiment,
By directly soldering the electrodes 5a to 5c of the magneto-impedance elements 4a and 4b to the circuit board 14, the magnetic detection element composed of the elements 4a and 4b, the non-magnetic substrate 3 and the bias magnet 8 is attached to the circuit board 14. Since it is mounted, a holder or the like for mounting the magnetic detection element is not required, the configuration can be simplified, and the mounting of the current sensor can be further facilitated by direct mounting.

Next, FIG. 2 shows a circuit configuration of a current detecting device 2 using the above-described current sensor 1 of FIG.
As shown here, the current detection device 2 includes a high-frequency oscillation circuit 20 that applies a high-frequency current to the magnetic impedance elements 4a and 4b of the current sensor,
The circuit comprises detection circuits 22a and 22b for detecting signals extracted from both ends of a and 4b, and a differential amplifier circuit 24 for differentially amplifying output signals of the detection circuits 22a and 22b.

In this configuration, at the time of current detection, a current to be measured is supplied to the coils 6a and 6b of the current sensor, and a high-frequency current is applied from the high-frequency oscillation circuit 20 to the magnetic impedance elements 4a and 4b. Coil 6a, 6b
The impedance between both ends of the magneto-impedance elements 4a and 4b changes according to the magnetic field generated from, the external magnetic field that becomes a disturbance, and the bias magnetic field of the bias magnet 8, and the amplitude voltage of the high-frequency current changes. The signal is taken out from both ends of the magnetic impedance elements 4a and 4b and detected by the detection circuits 22a and 22b. Further, the output signals of the detection circuits 22a and 22b are
, And an output signal of the differential amplifier circuit 24 is output as a current detection signal.

Here, for the above-mentioned reason, even if the magnetic field due to the measured current is a very small magnetic field with respect to the disturbance magnetic field, the magnetic field is accurately detected by the differential detection by the magnetic impedance elements 4a and 4b. Thus, a minute current of the order of μA can be accurately detected in a wide frequency range from direct current.

FIG. 3 shows an example of measuring a very small current by the current detecting device 2 when a current of 10 μA and 10 Hz is detected. The lower signal is the voltage corresponding to the current value to be measured, and the upper signal is the output of the current detection device. The upper signal waveform exactly corresponds to the lower signal waveform, and the current sensor 1 of FIG.
It can be understood that the configuration of the current detection device 2 accurately separates and detects the magnetic field of the minute current buried in the disturbance magnetic field, and realizes a current resolution on the order of μA.

<Second Embodiment> Next, a second embodiment of the present invention will be described with reference to FIG. FIG. 4 shows the configuration of the current sensor according to the second embodiment. In FIG. 4, portions common or equivalent to those in FIG. 1 of the first embodiment are denoted by common reference numerals, and description of the common portions will be omitted. This is the same in FIG. 5 of a third embodiment described later. Further, the configuration of the driving and signal processing circuit of the current sensor of the current detection device according to the second embodiment is common to the circuit configuration of the first embodiment, and the illustration and description thereof are omitted.

The configuration of the current sensor 1 shown in FIG. 4 differs from that of the first embodiment in that the bias magnet 8 is formed of a hard magnetic thin film and the magnetic impedance elements 4a and 4b of the nonmagnetic substrate 3 are used. It is formed on the surface opposite to the formed surface.

Also, the coils 6a, 6
The coil bobbin 9 is wound around the coil bobbin 9, and the coil bobbin 9 is arranged on the circuit board 14 near the surface of the non-magnetic substrate 3 on which the magnetic impedance elements 4 a and 4 b are formed. That is, the coils 6a and 6b do not surround the magneto-impedance elements 4a and 4b as in the first embodiment, but are arranged near one side of the elements 4a and 4b. The coils 6a and 6b are arranged so that their respective central axis directions (the central axis directions of the coil bobbins 9) are along the magnetic field detection directions of the magnetic impedance elements 4a and 4b.
They are arranged so as to line up along the magnetic field detection direction.

The current sensor 1 according to the present embodiment as described above
According to the configuration described above, there are provided two chip-shaped components, namely, a coil bobbin 9 on which coils 6a and 6b are wound, and a non-magnetic substrate 3 provided with magnetic impedance elements 4a and 4b and a bias magnet 8. The circuit board 14 together with the driving and signal processing circuits of the current sensor of the device
Since it can be directly mounted on an electronic device, it is very easy to incorporate it into an electronic device.

Further, since the diameters of the coils 6a and 6b can be reduced and the lengths of the copper wires of the coils 6a and 6b can be shortened accordingly, the resistance and inductance of the coils 6a and 6b can be set small, and the current path to be measured can be reduced. The inserted load can be reduced.

Further, since the bias magnet 8 is formed as a hard magnetic thin film, installation and position adjustment of the bias magnet become unnecessary, and the configuration of the current sensor can be simplified. Further, in the two magneto-impedance elements 4a and 4b, it is possible to eliminate the deviation of the bias magnetic field due to an error in the installation position of the bias magnet 8.

<Third Embodiment> Next, a third embodiment of the present invention will be described with reference to FIGS.

FIG. 5 shows the configuration of the current sensor 1 according to the third embodiment. In the configuration of the current sensor 1 shown here, the bias magnet 8 in the first embodiment is used.
, A bias coil 10 for applying a bias magnetic field to the magnetic impedance elements 4a and 4b is disposed between the coils 6a and 6b of the current path to be measured, and the non-magnetic substrate 3
It is wound around. The configuration of other parts is the same as the configuration of FIG. 1 of the first embodiment.

FIG. 6 shows a circuit configuration of a current detecting device 2 of a third embodiment using the current sensor 1 of FIG. In this configuration, an AC bias application circuit 28 for applying an AC bias current to the bias coil 10, a high-frequency oscillation circuit 20 for applying a high-frequency current to the magnetic impedance elements 4a and 4b, and signals extracted from both ends of the magnetic impedance elements 4a and 4b Detecting circuits 22a and 22a for detecting
2b, a first differential amplifier circuit 24a that differentially amplifies the output signals of the detection circuits 22a and 22b,
Peak hold circuit 26 for holding positive and negative peak voltages corresponding to the AC bias of the output of 4a
a and 26b, and a second differential amplifier circuit 24b that differentially amplifies the output signals of the peak hold circuits 26a and 26b.

The change in impedance of the magnetic impedance element with respect to the magnetic field, that is, the output characteristic of the detection circuit is a curve as shown in FIG. For this reason, when a wide range of current detection, that is, a wide range of magnetic field detection is performed, linearity cannot be ensured by a normal method using a fixed bias magnetic field. Therefore, a bias magnetic field of a rectangular wave is applied as shown in FIG. 7A, and a difference ΔVp between two operating points Vp (+) and Vp (−) on the plus side and the minus side of the magnetic field on the output characteristic is detected. Thereby, as shown in FIG. 7B, linearity with respect to the magnetic field can be ensured. The same applies to the case where two differential magneto-impedance elements are used as in the present embodiment. When the same rectangular wave magnetic field is applied, the output characteristic having the output characteristic shown in FIG.
This is the same as performing differential detection with one element, and differential detection with good linearity can be performed.

That is, in the configuration of FIG. 6, when the current is detected, the current to be measured is the current sensor coils 6a and 6b.
And the high-frequency current is applied from the high-frequency oscillation circuit 20 to the magneto-impedance elements 4a and 4b,
An AC bias current is applied from the AC bias application circuit 28 to the bias coil 10, whereby a bias magnetic field of a rectangular wave is applied from the bias coil 10 to the magnetic impedance elements 4 a and 4 b. The impedance between both ends of each of the magnetic impedance elements 4a and 4b changes according to the magnetic field generated from the coils 6a and 6b, the external magnetic field as a disturbance, and the bias magnetic field, and the amplitude voltage of the high-frequency current changes. The respective signals are taken out from both ends of the magneto-impedance elements 4a and 4b and are detected by the detection circuits 22a and 22b.
2b, and differentially amplified by the differential amplifier circuit 24a. Further, the peak voltage on the plus side and the minus side of the output signal of the differential amplifier circuit 24a is
a, 26b. The output signals of the peak hold circuits 26a and 26b are
b, and the output signal of the circuit 24b is output as a current detection signal.

According to the present embodiment as described above, by applying the AC bias magnetic field by the AC bias current as described above, the linearity of the output with respect to the current to be measured can be improved, and a wider range of current detection can be achieved. Can be performed.

In the present embodiment, in the two coils 6a and 6b through which the current to be measured flows, induced electromotive forces due to the AC bias magnetic field are generated in directions opposite to each other and cancel each other. It does not affect the current.

[0042]

As is apparent from the above description, according to the present invention, it is possible to accurately detect a minute magnetic field due to a minute current even in a disturbance magnetic field, and to improve the high-sensitivity magnetic field detection capability of a magnetic impedance element. Effectively used, it is possible to detect current on the order of μA in a wide frequency range from DC,
Moreover, an excellent current sensor that is easy to mount on a circuit board,
In addition, the present invention can provide a current detection device including the sensor and its drive and signal processing circuit, and can provide an excellent effect of contributing to higher precision of power control and higher performance of electronic devices.

[Brief description of the drawings]

FIG. 1A is a perspective view showing a configuration of a current sensor according to a first embodiment of the present invention, and FIG. 1B is an explanatory diagram of an operation of the sensor.

FIG. 2 is a block circuit diagram illustrating a circuit configuration of the current detection device according to the first embodiment.

FIG. 3 is a graph showing an example of current detection by the detection device.

FIG. 4 is a perspective view illustrating a configuration of a current sensor according to a second embodiment of the present invention.

FIG. 5 is a perspective view illustrating a configuration of a current sensor according to a third embodiment of the present invention.

FIG. 6 is a block circuit diagram illustrating a circuit configuration of the current detection device according to the first embodiment.

FIG. 7 is a diagram illustrating a detection method using an AC bias magnetic field in the detection device.

FIG. 8 is a schematic configuration diagram showing a configuration of a conventional current sensor.

FIG. 9 is a perspective view showing a configuration of another conventional current sensor.

FIG. 10 is a perspective view showing a configuration of still another conventional current sensor.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 current sensor 2 current detection device 3 non-magnetic substrate 4 a, 4 b magnetic impedance element 5 a to 5 c electrode 6 a, 6 b coil of current path to be measured 8 bias magnet 9 coil bobbin 10 bias coil 12 shield 14 circuit board 20 high-frequency oscillation circuit 22 a, 22 b Detection circuit 24, 24a, 24b Differential amplification circuit 26a, 26b Peak hold circuit 28 AC bias application circuit

Claims (9)

[Claims] 1. A device comprising: two coils for supplying a current to be measured; and two magnetic impedance elements for differentially detecting a magnetic field generated by the two coils, wherein the two magnetic impedance elements are the same non-magnetic substrate. Are arranged along the magnetic field detection direction with the respective magnetic field detection directions being the same direction, and the two coils are energized by the current to be measured. A current sensor configured to apply mutually opposite magnetic fields to the two magneto-impedance elements. 2. The two coils surround each of the magnetic impedance elements so that their respective central axis directions are along the magnetic field detection direction of the two magnetic impedance elements, and are arranged along the magnetic field detection direction. The current sensor according to claim 1, wherein the current sensor is wound around the magneto-impedance element so as to perform the operation. 3. The non-magnetic substrate is wound around a coil bobbin disposed near a surface of the non-magnetic substrate on which the magnetic impedance element is formed, and each of the coils has a center axis direction corresponding to the magnetic field of the magnetic impedance element. The current sensor according to claim 1, wherein the current sensor is arranged so as to be along the detection direction and to be arranged along the magnetic field detection direction. 4. The electrode according to claim 1, wherein electrodes formed at both ends of each of the two magneto-impedance elements are directly soldered to a circuit board on which a current sensor is mounted. The current sensor according to the section. 5. A non-magnetic substrate, wherein a permanent magnet for applying a bias magnetic field to the magnetic impedance element is provided on a surface of the non-magnetic substrate opposite to a surface on which the magnetic impedance element is provided. The current sensor according to any one of claims 1 to 4. 6. The current sensor according to claim 5, wherein the permanent magnet is made of a hard magnetic thin film. 7. The device according to claim 1, wherein a bias coil for applying a bias magnetic field to the magneto-impedance element is arranged between the two coils. Current sensor. 8. The current sensor according to claim 1, a high-frequency oscillation circuit that applies a high-frequency current to the two magnetic impedance elements, and both ends of each of the two magnetic impedance elements. And two differential detection circuits for differentially amplifying the output signals of the two detection circuits, and output the output signal of the differential amplification circuit as a current detection signal. A current detection device characterized by the above-mentioned. 9. A current sensor according to claim 7, a bias application circuit for applying an AC bias current to the bias coil of the current sensor, and a high-frequency oscillation circuit for applying a high-frequency current to the two magnetic detection elements. Two detection circuits for detecting signals taken from both ends of each of the two magnetic detection elements; a first differential amplification circuit for differentially amplifying output signals of the two detection circuits; And a second differential amplifier circuit for differentially amplifying the output signals of the two peak hold circuits, respectively. A current detection device for outputting an output signal of the second differential amplifier circuit as a current detection signal.