Current detection device

This application is based upon and claims the benefit of priority from Japanese Patent Application No. 2019-229597, filed on Dec. 19, 2019; the entire contents of which are incorporated herein by reference.

An embodiment described herein relates generally to a current detection device.

In a current detection device, a current to be detected is supplied to a coil, and the current is detected by detecting a magnetic field generated from the coil. The generated magnetic field is detected by a Hall element, for example. To ensure high-performance and stable operation of the current detection device, in general, there has been known a structure where a shield layer (shield sheet) is disposed between the coil and the Hall element.

In a structure which includes the shield layer, when a current which flows through the coil is an AC current, particularly, a high frequency AC current, an eddy current is generated on the shield layer, so that a magnetic field is generted by the eddy current in a direction opposite to a direction of a magnetic field generated by the current flowing in the coil. Accordingly, since the magnetic field generated by the eddy current is in a direction opposite to the direction of the magnetic field generated by the coil, the magnetic field generated by the eddy current cancels the magnetic field generated by the coil. The magnetic field detected by the Hall element becomes insufficient and hence, an output voltage from a drive circuit of the Hall element is lowered. Accordingly, in the conventional current detection device, the detection of a current is performed by amplifying an output voltage from the drive circuit of the Hall element by an amplifying circuit.

FIG. 1 is a view showing an entire configuration of a current detection device according to an embodiment;

FIG. 2 is a cross-sectional view of the current detection device shown in FIG. 1 taken along a line II-II;

FIG. 3 is a view for describing one example of a state where an eddy current generated in a shield layer is canceled;

FIG. 4 is a view for describing waveforms of eddy currents 31 and 34 generated in the shield layer 17 a by supplying currents I 1 and I 2 to coil patterns 16 a and 16 c;

FIG. 5 is a plan view of a planar coil where each coil pattern has a spiral shape;

FIG. 6 is a plan view of a planar coil where each coil pattern has a rectangular shape; and

FIG. 7 is a plan view of a planar coil where each coil pattern has a hexagonal shape.

A current detection device according to an embodiment includes a first coil, a magnetic field detection element, a shield layer, a second coil, and an operation circuit. The first coil has a planar shape. The magnetic field detection element is disposed in a spaced apart manner from the first coil in a direction orthogonal to a plane of the first coil, and is disposed so as to receive a magnetic field which the first coil generates. The shield layer is disposed between the first coil and the magnetic field detection element. The second coil is disposed in a spaced apart manner from the first coil with respect to an axis perpendicular to the shield layer. The operation circuit operates the second coil.

Hereinafter, the embodiment is described in detail with reference to drawings.

First, a configuration of the current detection device according to the embodiment is described with reference to FIG. 1 and FIG. 2 .

FIG. 1 is a view showing an entire configuration of the current detection device according to the embodiment. FIG. 2 is a cross-sectional view of the current detection device shown in FIG. 1 taken along a line II-II.

The current detection device 1 detects a current I 1 which flows through wirings LI. A current to be detected is a DC current or an AC current. The current detection device 1 is configured of a sheet of substrate 10 having a stacked structure. The current detection device 1 according to the embodiment is used for an overcurrent protection or the like of a PFC (power factor correction) power source, a high-frequency switching power source, an AC/DC adaptor, a control device such as a general-purpose invertor or a motor variable speed device, and a power module.

In the embodiment, the current detection device 1 is formed of a sheet of substrate 10 having a stacked structure. However, for example, the current detection device 1 according to the embodiment may be formed by laminating two substrates or three or more substrates.

The substrate 10 is formed in a rectangular shape, and has a flat surface 10 a on a front surface side and a flat surface 10 b on a back surface side. Note that a shape of the substrate 10 is not limited to the rectangular shape, and may be other shapes such as a circular shape.

On the surface 10 a , an amplifying circuit 11 which amplifies a voltage signal detected by a Hall element 19 described later, a drive circuit 12 which drives the Hall element 19 , and an operation circuit 13 which operates a coil pattern 16 c constituting the second coil described later are disposed.

On the surface 10 s , pads 14 a and 14 b to which two wirings L are connected, wiring patterns 15 a and 15 b which extend from the pads 14 a and 14 b , and a coil pattern 16 a which includes a planar coil having an arcuate shape and straight line portions extending from end portions of the planar coil and disposed parallel to each other are disposed are formed.

Although the coil pattern 16 a includes the straight line portions disposed parallel to each other, the coil pattern 16 a is not limited to such a configuration, and may not include the straight line portions disposed parallel to each other. The coil pattern 16 a may be any coil which can generate a magnetic flux, and a shape of the coil pattern 16 a is not limited to the shape shown in FIG. 1 . The same goes for coil patterns 16 b and 16 c described later.

The coil pattern 16 a constituting the first coil includes one end portion 16 a 1 and an other end portion 16 a 2 , where the one end portion 16 a 1 is connected to the wiring pattern 15 a . With such a configuration, a current I 1 input to the wiring L 1 flows from the one end portion 16 a 1 to the other end portion 16 a 2 of the coil pattern 16 a.

On the surface 10 b , the coil pattern 16 b which includes a planar coil having an arcuate shape and straight line portions extending from end portions of the planar coil and disposed parallel to each other is formed. The coil pattern 16 b constituting the third coil includes the one end portion 16 b 1 and the other end portion 16 b 2 . The one end portion 16 b 1 of the coil pattern 16 b is electrically connected to the other end portion 16 a 2 of the coil pattern 16 a . The other end portion 16 b 2 of the coil pattern 16 b is electrically connected to the wiring pattern 15 b.

More specifically, the one end portion 16 b 1 of the coil pattern 16 b is electrically connected to the other end portion 16 a 2 of the coil pattern 16 a via a plurality of wiring patterns and a plurality of conductors disposed in a plurality of contact holes (that is, via holes). The other end portion 16 b 2 of the coil pattern 16 b is electrically connected to the wiring pattern 15 b via a plurality of wiring patterns and a plurality of conductors disposed in a plurality of contact holes. The drive circuit 12 is electrically connected to the Hall element 19 via a plurality of wiring patterns 20 and a plurality of conductors 21 disposed in a plurality of contact holes. An electrical connection is not limited to the contact holes, and connector parts such as clamping connectors may be used.

With such a configuration, a current I 1 inputted from the other end portion 16 a 2 of the coil pattern 16 a to the coil pattern 16 b flows from the one end portion 16 b 1 to the other end portion 16 b 2 of the coil pattern 16 b . As a result, a direction of the magnetic field generated by the coil pattern 16 a and a direction of a magnetic field generated by the coil pattern 16 b become equal. In the description made hereinafter, the direction of the magnetic fields generated by the coil patterns 16 a and 16 b is referred to as a first direction.

On the surface 10 a , the coil pattern 16 c which includes a planar coil having an arcuate shape and straight line portions extending from end portions of the planar coil and disposed parallel to each other is formed. The coil pattern 16 c is disposed in a spaced apart manner from the coil pattern 16 a with respect to an axis 33 (see FIG. 3 ) perpendicular to a shield layer 17 a.

The coil pattern 16 c constituting the second coil includes one end portion 16 ci and the other end portion 16 c 2 . The one end portion 16 c 1 is connected to a wiring pattern 18 a , and the other end portion 16 c 2 is connected to a wiring pattern 18 b . The wiring patterns 18 a , 18 b are connected to the operation circuit 13 .

The operation circuit 13 is configured of an oscillation circuit or a high-frequency circuit, and supplies a current I 2 to the coil pattern 16 c from the one end portion 16 c 1 to the other end portion 16 c 2 . The current I 2 is supplied to the coil pattern 16 c from the operation circuit 13 disposed on the surface 10 a . However, the embodiment is not limited to such a configuration, and the current I 2 may be supplied to the coil pattern 16 c from the outside of the current detection device 1 .

Between the coil pattern 16 a and the Hall element 19 , the shield layer 17 a is disposed. The shield layer 17 a is provided for shielding an electrostatic noise or an electromagnetic noise from entering the Hall element 19 or the amplifying circuit I 1 which amplifies a voltage signal detected by the Hall element 19 . In the same manner, between the coil pattern 16 b and the Hall element 19 , a shield layer 17 b is disposed. The shield layer 17 b is provided for shielding an electrostatic noise or an electromagnetic noise from entering the Hall element 19 or the amplifying circuit 11 which amplifies a voltage signal detected by the Hall element 19 . The shield layers 17 a and 17 b are formed of a sheet member made of a conductive material such as copper or aluminum. The shield layers 17 a and 17 b are connected to a ground of a product (for example, the substrate 10 or a module) or a ground surface when necessary.

Eddy currents are generated in the shield layers 17 a and 17 b when magnetic fields in the first direction are generated by the coil patterns 16 a and 16 b . Due to such eddy currents generated in the shield layers 17 a and 17 b , magnetic fields in the second direction opposite to the magnetic fields in the first direction are generated.

In the embodiment, the current detection device 1 includes three coil patterns 16 a . 16 b , and 16 c . However, the number of coil patterns is not limited to three, and 0 . 7 , the current detection device 1 may include two coil patterns or four or more coil patterns. In the embodiment, the current detection device 1 includes two shield layers 17 a and 17 b . However, the number of shield layers is not limited to two, and the current detection device 1 may include one shield layer or three or more shield layers.

The magnetic fields in the first direction generated by the coil patterns 16 a and 16 b are cancelled by the magnetic fields generated by the eddy currents in the second direction which is a direction opposite to the first direction. In this manner, the magnetic fields in the first direction are cancelled by the magnetic fields in the second direction. As a result, a magnetic field detected by the Hall element 19 is lowered and hence, the current detection device 1 cannot accurately detect the current I 1 which flows through the coil patterns 16 a and 16 b . In other words, performance of the current detection device 1 is lowered.

In the embodiment, as described later, by supplying the current I 2 from the operation circuit 13 to the coil pattern 16 c , an eddy current is generated in the shield layer 17 a , and the eddy current which is generated by supplying the current I 1 to the coil pattern 16 a can be cancelled so that the magnetic field in the second direction can be reduced.

The Hall element 19 which is a magnetic sensor is disposed in the substrate 10 . The Hall element 19 is disposed to be positioned between the two coil patterns 16 a and 16 b . More specifically, the Hall element 19 is disposed to be positioned between the shield layers 17 a and 17 b . The Hall element 19 which is the magnetic field detection element generates an electromotive force proportional to magnetic flux density, and outputs a voltage signal corresponding to the electromotive force.

In other words, the two respective coil patterns 16 a and 16 b each have the planar coil having an arcuate shape and the straight line portions extending from the end portions of the planar coil and disposed parallel to each other. The Hall element 19 is disposed in a spaced apart manner from the respective coil patterns 16 a , 16 b in the direction orthogonal to planes of the two coil patterns 16 a and 16 b , and are disposed so as to receive magnetic fields which the respective coil patterns 16 a , 16 b generate when a current is supplied to the two coil patterns 16 a and 16 b.

More specifically, a center axis of a magnetic flux which the coil pattern 16 a generates and a center axis of a magnetic flux which the coil pattern 16 b generates are positioned on a same axis, and the Hall element 19 is disposed between the coil patterns 16 a , 16 b , and also disposed on the same axis.

An output signal (voltage signal) of the Hall element 19 is inputted to the amplifying circuit 11 disposed on the substrate 10 via a plurality of wiring patterns and a plurality of conductors disposed in a plurality of contact holes formed in the substrate 10 and in the substrate 10 , and the output signal (voltage signal) is amplified. The Hall element 19 outputs the voltage signal by detecting the magnetic fluxes generated by the current I 1 inputted to the coil patterns 16 a , 16 b However, an amplitude of the voltage is small. Accordingly, the voltage is amplified by the amplifying circuit 11 so that the current I 1 inputted to the coil patterns 16 a , 16 b can be observed.

In the embodiment, the two coil patterns 16 a , 16 b are disposed so as to sandwich the Hall element 19 . However, the number of coil patterns may be one. Although the two shield layers 17 a , 17 b are disposed so as to sandwich the Hall element 19 in the embodiment, the number of shield layer may be one in this case. For example, when the current detection device 1 includes one coil pattern and one shield layer, the one shield layer may be disposed between the one coil pattern and the Hall element 19 .

FIG. 3 is a view for describing one example of a state where an eddy current generated in a shield layer is canceled.

When an electric current I 1 is supplied to the coil pattern 16 a , a magnetic field is generated in the first direction (a direction indicated by symbol 30 ). An eddy current 31 is generated in the shield layer 17 a by being effected by the generated magnetic field. The eddy current 31 generates a magnetic field in a direction which obstructs the magnetic field in the first direction, that is, a magnetic field in the second direction (a direction indicated by symbol 32 ) which is a direction opposite to the first direction.

Accordingly, the magnetic field in the first direction is cancelled by the magnetic field in the second direction so that a magnetic field detected by the Hall element 19 is lowered. As a result, the current detection device 1 cannot accurately detect the current I 1 which flows through the coil patterns 16 a and 16 b.

In the embodiment, the coil pattern 16 c is disposed in a spaced apart manner from the coil pattern 16 a with respect to the axis 33 perpendicular to the shield layer 17 a . By supplying a current I 2 to the coil pattern 16 c , a magnetic field is generated in the first direction, and an eddy current 34 is generated in the shield layer 17 a by being effected by the generated magnetic field.

Although the direction that the eddy current 31 flows and the direction that the eddy current 34 flows are equal, the coil patterns 16 a and 16 c are disposed in a spaced apart manner with respect to the axis 33 perpendicular to the shield layer 17 a and hence, the eddy currents 31 and 34 cancel each other. As a result, a magnetic field in the second direction generated by the eddy current 31 can be reduced.

In this manner, according to the current detection device of the embodiment, a magnetic field detected by the Hall element can be increased.

FIG. 4 is a view for describing waveforms of the eddy currents 31 and 34 generated in the shield layer 17 a by supplying currents I 1 and I 2 to the coil patterns 16 a and 16 c.

A waveform 40 indicates the waveform of the eddy current 31 generated in the shield layer 17 a by supplying the current I 1 to the coil pattern 16 a . The waveform 40 of the eddy current 31 has a frequency f 1 and an amplitude A 1 .

A waveform 41 indicates the waveform of the eddy current 34 generated in the shield layer 17 a by supplying the current I 2 to the coil pattern 16 c The waveform 41 of the eddy current 34 has a frequency f 2 and an amplitude A 2 . As shown in FIG. 4 , a displacement of phase occurs between the waveform 40 of the eddy current 31 and the waveform 41 of the eddy current 34 .

The operation circuit 13 adjusts the current I 2 supplied to the coil pattern 16 c based on a voltage signal which is detected by the Hall element 19 and is amplified by the amplifying circuit 11 . In other words, the operation circuit 13 can control a phase, a frequency, and an amplitude of the eddy current 34 by adjusting the current I 2 supplied to the coil pattern 16 c corresponding to intensity of the eddy current 31 generated by supplying the current I 1 to the coil pattern 16 a.

A cancelling effect of the eddy current 31 and the eddy current 34 becomes maximum when the operation circuit 13 adjusts the current I 2 such that the frequency f 1 of the eddy current 31 and the frequency 2 of the eddy current 34 become equal, the amplitude A 1 of the eddy current 31 and the amplitude A 2 of the eddy current 34 are equal, and a phase of the eddy current 31 and a phase of the eddy current 34 are displaced from each other by 180°. Even in a case where the amplitude A 2 of the eddy current 34 is lower than the amplitude A 1 of the eddy current 31 , the eddy current 31 can be cancelled and hence, a cancelling effect can be acquired.

The coil pattern 16 c may be disposed on the surface 10 b . With such a configuration, an eddy current generated in the shield layer 17 b by supplying a current I 1 to the coil pattern 16 b can be cancelled and hence, the current detection device 1 can detect the current I 1 more accurately.

Each of the coil patterns 16 a , 16 b , and 16 c is configured of the planar coil having an arcuate shape and having a hole at a center of the planar coil; and the straight line portions extending from the end portions of the planar coil having the arcuate shape and disposed parallel to each other. However, the shapes of the respective coil patterns 16 a , 16 b , and 16 c are not limited to such a shape. For example, respective coil patterns 16 a , 16 b , and 16 c may be formed in shapes shown in FIG. 5 , FIG. 6 , and FIG. 7 .

FIG. 5 is a plan view of a planar coil where each coil pattern has a spiral shape. As shown in FIG. 5 , each coil pattern 16 a , 16 b , 16 c forms a three-turn planar coil formed by winding the coil in a spirally curved shape. The number of turns of each coil pattern 16 a , 16 b , 16 c is not limited to three turns, and may be other number of turns.

FIG. 6 is a plan view of a planar coil where each coil pattern has a rectangular shape. As shown in FIG. 6 , each coil pattern 16 a , 16 b , 16 c forms a three-turn planar coil formed in a rectangular shape as a whole by connecting straight lines instead of curved lines. The number of turns of each coil pattern 16 a , 16 b , 16 c is not limited to three turns, and may be other number of turns.

FIG. 7 is a plan view of a planar coil where each coil pattern has a hexagonal shape. As shown in FIG. 7 , each coil pattern 16 a , 16 b , 16 c forms a three-turn planar coil formed in a hexagonal shape as a whole by connecting straight lines instead of curved lines. The number of turns of each coil pattern 16 a , 16 b , 16 c is not limited to three turns, and may be other number of turns. The shape of each coil pattern 16 a , 16 b , 16 c is not limited to hexagonal shape, and may be other polygonal shape such as a triangular shape.

While certain embodiments have been described, these embodiments have been presented by way of example only, and are not intended to limit the scope of the inventions. Indeed, the novel embodiments described herein may be embodied in a variety of other forms; furthermore, various omissions, substitutions and changes in the form of the embodiments described herein may be made without departing from the spirit of the inventions. The accompanying claims and their equivalents are intended to cover such forms or modifications as would fall within the scope and spirit of the inventions.