Current transducer with in-plane gradient sensor

Abstract

A current transducer (1) comprising a magnetic field gradient sensor (2) and a primary conductor (5), the primary conductor having a first branch (6a), a second branch (6b) and a bridging branch (8) interconnecting one end of the first branch (6a) to one end of the second branch (6b), the first and second branches separated by a gap (G), the first branch (6a) comprising a first joining section (24a) connected to the bridging section, configured to direct a primary current obliquely and outwardly with respect to a centre line (C), and the second branch comprising a second joining section (24b) connected to the bridging branch (8) configured to direct a primary current obliquely and inwardly with respect to the centre line such that a magnetic crossfield generated by the primary current flowing in the bridging branch is cancelled by magnetic crossfields generated by the primary current flowing in the first and second joining sections respectively.

Description

[0001] CURRENT TRANSDUCER WITH IN-PLANE GRADIENT SENSOR

[0002] The present invention relates to a current transducer with an in-plane magnetic field gradient sensor and an integrated in-plane primary conductor.

[0003] It is known to provide current transducers with an in-plane magnetic field sensor configured for measuring a magnetic field generated by a primary conductor positioned adjacent the in-plane magnetic field sensor. The primary conductor typically has a U-shaped portion with parallel first and second branches joined together at one end by a bridging portion. The gradient sensor has a first sensing element positioned adjacent and overlapping one of the primary conductor branches and a second sensing element positioned adjacent and overlapping the other primary conductor branch. The current in the first and second branches flows in opposite directions and a magnetic field gradient is thus generated in a direction transverse to the first and second branches and may thus be picked up by the in-plane magnetic field sensor. The bridging portion that interconnects the first and second primary conductor branches however also generates a magnetic field (a magnetic crossfield) that combines with the magnetic field of the branches. The result is such that the magnetic fields lines do not cross the first and second branches orthogonally from the first in-plane sensing element to the second in-plane sending element, which adversely affects the magnetic field gradient measurement. This so- called crossfield effect of the bridging branch is undesirable and in order to reduce the crossfield effect, it is known to lengthen the primary conductor branches to increase the distances between the magnetic field gradient sensors and the bridging section. This however leads to the need for a larger surface area current transducer and longer primary conductor arrangements, and in certain applications there is a desire to have more compact and less costly current transducers. Also, the longer conductor length increases both the electric and thermal resistance of the primary conductor, resulting in reduced current carrying capacity before temperature limits are exceeded. Moreover, even with longer primary conductors, there is often still a residual crossfield effect that adversely affects the measurement accuracy of the current transducer.

[0004] It may be noted that the magnetic field sensors measure the field along an axis perpendicular to the bridge extension, and that crossfield is the component of the magnetic field perpendicular to this measurement direction. A perfect sensor would only be sensitive to the field along the intended direction, but in reality the crossfield is an influence quantity that changes the sensitivity of the sensor. Because the cross field is created by the same current that is to be measured, the sensitivity variation imposed by the crossfield is dependent on the amplitude of the current to be measured. The result is a non-linear response of the sensor, which is detrimental to measurement accuracy.

[0005] In view of the foregoing, it is an object of this invention to provide a current transducer with an in-plane magnetic field gradient sensor and an integrated in-plane primary conductor that is accurate.

[0006] It is advantageous to provide a current transducer with an in-plane magnetic field gradient sensor and an integrated in-plane primary conductor that is cost effective to produce.

[0007] It is advantageous to provide a current transducer with an in-plane magnetic field gradient sensor and an integrated in-plane primary conductor that that may be easily installed and connected on a circuit board of an external electronic system.

[0008] Objects of this invention have been achieved by providing a system according to claim 1. Dependent claims set forth various advantageous features of embodiments of the invention.

[0009] Disclosed herein is a current transducer comprising a magnetic field gradient sensor and a primary conductor, the primary conductor having a first branch, a second branch and a bridging branch interconnecting one end of the first branch to one end of the second branch, the first and second branches separated by a gap, the first branch comprising a first joining section connected to the bridging section, configured to direct a primary current obliquely and outwardly with respect to a centre line, and the second branch comprising a second joining section connected to the bridging branch configured to direct a primary current obliquely and inwardly with respect to the centre line such that a magnetic crossfield generated by the primary current flowing in the bridging branch is cancelled by magnetic crossfields generated by the primary current flowing in the first and second joining sections respectively.

[0010] The magnetic field gradient sensor comprises a first in-plane sensor positioned overhead and overlapping the first joining section and a second in-plane sensor positioned overlapping and overhead the second joining section.

[0011] In an advantageous embodiment, the first and second branches of the primary conductor have inner edges separated by a gap and the joining sections extend obliquely and outwardly from the first and second branches towards the bridging section. In an advantageous embodiment, the first and second branches of the primary conductor have outer and inner lateral slots that are offset in the direction of the centre line, the outer lateral slots being positioned further away from the bridging branch than the inner slot, the joining sections being positioned between ends of the inner and outer lateral slots.

[0012] In an advantageous embodiment, the first in-plane sensor and second in-plane sensor are Tunnel Magnetroesistance (TMR) magnetic field detectors.

[0013] In an advantageous embodiment, the current transducer further comprises a signal conditioning IC.

[0014] In an advantageous embodiment, the magnetic field gradient sensor is separate from the signal conditioning IC and connected thereto with bond wires.

[0015] In an advantageous embodiment, the magnetic field gradient sensor is mounted on a surface of the primary conductor separated therefrom by an insulating layer.

[0016] In an advantageous embodiment, the current transducer further comprises a signal conditioning integrated circuit (IC) incorporating or connected to the magnetic field gradient sensor and further connected to a secondary conductor arrangement of the transducer.

[0017] In an advantageous embodiment, the primary conductor, secondary conductor arrangement, and magnetic field gradient sensor are overmolded by an insulating housing except for connection terminals of the primary conductor and secondary conductor arrangement.

[0018] In an advantageous embodiment, the primary conductor and secondary conductor arrangement are formed from a lead frame.

[0019] In an advantageous embodiment, the primary conductor comprises a shape that has mirror image symmetry about the centre line.

[0020] In an advantageous embodiment, the primary conductor first branch comprises a first connection end terminal and the primary conductor second branch comprises a second connection end terminal a width of each of the first and second connection end terminal being over 30% of a total width of the current transducer. Further objects and advantageous features of the invention will be apparent from the claims, from the detailed description, and annexed drawings, in which:

[0021] Figure 1a is perspective view of a current transducer according to an embodiment of the invention;

[0022] Figure 1 b is a top view of a current transducer according to an embodiment of the invention;

[0023] Figure 2 is a top view of a current transducer according to another embodiment of the invention;

[0024] Figure 3 is a top view of a primary conductor of the embodiment of figure 1 ;

[0025] Figure 4 is a top view of a primary conductor of the embodiment of figure 2;

[0026] Figure 5 is a top view of a portion of the embodiment of figure 3 showing the general direction of current flow;

[0027] Figures 6a and 6b are illustrations of primary conductors showing computer simulated in-plane magnetic flux density components, figure 6a showing a primary conductor shape without features of the invention and figure 6b showing a primary conductor with features according to an embodiment of the invention.

[0028] Referring to the figures, a current transducer 1 according to embodiments of the invention comprises a magnetic field gradient sensor 2, a primary conductor 5, and a housing 4 enclosing or encapsulating the magnetic field gradient sensor and a portion of the primary conductor. The housing 4 may comprise an overmolding as is per se well known in the art of current transducers.

[0029] The current transducer may further comprise a signal conditioning integrated circuit (IC) 3 electrically connected to the magnetic field gradient sensor 2 or incorporating the magnetic field gradient sensor. In other words, the magnetic field gradient sensor may either form one or more separate components connected to the signal conditioning IC, for instance via bond wires, or in a variant the magnetic field gradient sensor may be integrally formed within an integrated circuit whereby elements of the magnetic field gradient sensor are formed within zones of the integrated circuit. The current transducer 1 further comprises a secondary conductor arrangement 14 electrically connected to the signal conditioning IC and / or to the magnetic field gradient sensor for power and signal communication. Electrical interconnections between the signal conditioning IC 3, magnetic field gradient sensor 2 and secondary conductor arrangement 14 may be effected by various per se known interconnects 16 such as bond wires or solder beads in a flip-chip interconnection. In preferred embodiments, the interconnects 16 between the signal conditioning IC and the secondary conductor arrangement is performed with bond wires such that the signal conditioning IC 3 may be positioned close to the primary conductor 5 and further away from the secondary conductor arrangement 14.

[0030] The primary conductor 5 and secondary connector arrangement 14 may be stamped and formed from a lead frame, in other words cut-out of a strip of sheet metal as perse well known in the art of current transducers.

[0031] In the illustrated embodiments, the secondary conductor arrangement 14 has connection terminals provided with surface mount pads exposed on a mounting side 18 of the housing 4. The primary conductor 5 has first and second connection end terminals 10a, 10b that may advantageously be in the form of surface mount connection pads configured for surface mount connection of the current transducer on an external circuit board. Such surface mount connection configurations are also well known in the field of current transducers. The primary conductor and secondary conductor arrangement may however have connection terminals with other forms and configurations, such as with pin contacts, for connection to external circuit, without departing from the scope of the invention.

[0032] As well known in the art of current transducers, the primary conductor is configured to the connected to a conductor carrying a current to be measured that flows through the primary conductor and generates a magnetic field that is correlated to the amplitude of the primary current to be measured.

[0033] The magnetic field gradient sensor 2 comprises a first in-plane sensor 2a and a second inplane sensor 2b, configured to measure a magnetic field within a measurement plane / WPthat extends across and overlies (or underlies) the first in-plane sensor 2a and the second in-plane sensor 2b. The measurement plane is a plane parallel to a major surface of the primary conductor 5 which in the illustrated embodiments is parallel to the mounting side 18 of the current transducer. The first and second in-plane sensors may, in an advantageous embodiment, be TMR (Tunnel Magnetoresistance) magnetic field sensors which are perse well known for in-plane magnetic field measurement.

[0034] The primary conductor 5 has a first branch 6a, a second branch 6b and a bridging branch 8 interconnecting one end of the first branch to one end of the second branch, such that the primary conductor has a substantially U-shaped portion. The ends of the first and second branches opposite the bridging branch 8 are each connected to a connection end terminal, the first branch 6a connected to a first connection end terminal 10a and the second branch 6b connected to a second connection end terminal 10b. As mentioned previously, the connection end terminals may for instance have the form of surface mount pads for surface mount connection to conductive traces on a circuit board. A width of each of the first and second connection end terminal may advantageously be over 30% of a total width of the current transducer in order to provide good electrical and especially thermal connection to an external circuit board on which the transducer is intended to be connected.

[0035] The first in-plane sensor 2a is positioned overhead (overlapping) the first branch 6a of the primary conductor and the second in-plane sensor 2b is positioned overhead (overlapping) the second branch 6b of the primary conductor. The first and second in-plane sensors may be mounted on an upper surface of the primary conductor, separated therefrom by an insulating layer. The insulating layer may for instance be a polyimide layer or another polymer layer typically of less than 0.5 mm thickness.

[0036] In advantageous embodiments, the first in-plane sensor 2a and second in-plane sensor 2b are made of a semiconductor chip having for instance a silicon substrate on which TMR sensors are realized. The first branch 6a and second branch 6b may extend substantially parallel to each other and symmetrically arranged and shaped about a centre line C. The centre line may however not necessarily correspond to a line that extends through a centre of the current transducer housing.

[0037] Each branch has an inner edge 22, the inner edges of the first and second branches facing each other and are separated by a gap G. The end of the first branch 6a has a first joining section 24a forming the interconnection with the bridging branch 8, and the end of the second branch 6b has a second joining section 24b forming the interconnection with the bridging branch 8. The first and second joining sections 24a, 24b are configured to direct the primary current at an inclined angle with respect to the centre line C such that, the magnetic field component that is orthogonal to the sensing direction, has a net component close to zero. This is achieved because the current through the primary underneath the sensor is at an angle such that it generates a larger cross field component than if the current was parallel to the center line C, but that cross field component is of equal magnitude and in the opposite direction as the cross field component produced by the bridging portion of the conductor, where the current turns away from the direction parallel to the centre line C. Therefore, for a primary current flowing through the first branch 6a from the first connection end terminal 10a towards the bridging branch 8, the joining section 24a is configured to direct the primary current I outwardly with respect to the centre line C such that the orthogonal vector component of the current flow points away from the centre line, in an opposite direction to the vector component of the current flowing in the bridging branch. Similarly, the current flow Ij2 vector component orthogonal to the centre line in the joining section on the second branch side is in an opposite direction to the vector component of the current 4 flowing in bridging branch. The effect of the current flow components orthogonal to the centreline C in the joining sections is to cancel the crossfield effect in the bridging section, such that the magnetic field lines between the first and second branches overhead the joining sections is substantially orthogonal to the centre line C as best seen in figure 6b. The magnetic field of the crossfield in the bridging branch 8 is thus cancelled by the oblique current flows I , Ij2 created by the joining sections 24a, 24b that divert the current away, respectively towards the centre line C in opposition to the current flow 4 direction in the bridging branch 8.

[0038] In a first embodiment as illustrated in figures 1b, 3 and 5, the oblique current flow is created by outer and inner lateral slots 28, 30 that are offset in the direction of the centre line, the outer lateral slots being positioned further away from the bridging branch 8 then the inner slot. In the illustrated embodiment, the outer lateral slot 28 extends from outer edges 20 of the respective branches towards the inner edges 22 and the inner lateral slots 30 extend from the inner edges 22 towards the respective outer edges 20, the joining sections 24a, 24b being positioned between ends of the inner and outer lateral slots.

[0039] In the second embodiment illustrated in figures 2 and 4 the joining sections 24a, 24b are inclined outwardly with respect to the centre line C such that the primary current flow through these joining sections has an oblique angle with respect to the centre line, configured to generate a magnetic field that cancels the magnetic crossfield generated by the current flowing in the bridging section, in the vicinity of the joining sections.

[0040] Thus, the first and second in-plane sensors 2a, 2b are positioned overhead the first and second branches of the primary conductor overhead their respective joining sections 24a, 24b interconnecting the branches to the bridging branch 8. In view of the cancellation of the crossfield effect, the primary conductor may have a more compact and shorter length than in conventional solutions. Although the primary and secondary conductor have being described as being formed from lead frames, in variants it is possible to have the primary and / or secondary conductor formed by other perse known technologies such as by depositing metal tracks on a substrate.

[0041] List of references used

[0042] Current transducer 1

[0043] Magnetic field gradient sensor 2 First in-plane sensor 2a Second in-plane sensor 2b

[0044] Signal conditioning IC 3

[0045] Overmold housing 4

[0046] Mounting side 18

[0047] Primary conductor 5

[0048] First branch 6a

[0049] Outer edge 20

[0050] Inner edge 22

[0051] Second branch 6b

[0052] Outer edge 20

[0053] Inner edge 22

[0054] Bridging branch 8

[0055] First joining section 24a

[0056] Outer lateral slot 28

[0057] Inner lateral slot 30

[0058] Second joining section 24b

[0059] Outer lateral slot 28

[0060] Inner lateral slot 30

[0061] First Connection end terminal 10a

[0062] Surface mount pad

[0063] Second connection end terminal 10b

[0064] Surface mount pad

[0065] Secondary conductor arrangement 14 Connection terminals

[0066] Surface mount pads

[0067] Interconnects 16

[0068] Bond wires

[0069] Centreline C

Claims

Claims1 . A current transducer (1) comprising a magnetic field gradient sensor (2) and a primary conductor (5), the primary conductor having a first branch (6a), a second branch (6b) and a bridging branch (8) interconnecting one end of the first branch (6a) to one end of the second branch (6b), the first and second branches separated by a gap (G), the first branch (6a) comprising a first joining section (24a) connected to the bridging section, configured to direct a primary current obliquely and outwardly with respect to a centre line (C), and the second branch comprising a second joining section (24b) connected to the bridging branch (8) configured to direct a primary current obliquely and inwardly with respect to the centre line such that a magnetic crossfield generated by the primary current flowing in the bridging branch is cancelled by magnetic crossfields generated by the primary current flowing in the first and second joining sections respectively, wherein the magnetic field gradient sensor (2) comprises a first in-plane sensor (2a) positioned overhead and overlapping the first joining section (24a) and a second in-plane sensor (2b) positioned overlapping and overhead the second joining section (24b).

2. The current transducer according to claim 1 wherein the first and second branches (6a, 6b) of the primary conductor (5) have inner edges (22) separated by a gap (G) and the joining sections (24a, 24b) extend obliquely and outwardly from the first and second branches towards the bridging section.

3. The current transducer according to claim 1 wherein the first and second branches (6a, 6b) of the primary conductor (5) have outer and inner lateral slots (28, 30) that are offset in the direction of the centre line, the outer lateral slots being positioned further away from the bridging branch than the inner slot, the joining sections (24a, 24b) being positioned between ends of the inner and outer lateral slots.

4. The current transducer according to any preceding claim wherein the first in-plane sensor (2a) and second in-plane sensor (2b) are Tunnel Magnetroesistance (TMR) magnetic field detectors.

5. The current transducer according to any preceding claim further comprising a signal conditioning IC (3).

6. The current transducer of the preceding claim wherein the magnetic field gradient sensor is separate from the signal conditioning IC and connected thereto with bond wires.

7. The current transducer according to any preceding claim wherein the magnetic field gradient sensor (2) is mounted on a surface of the primary conductor separated therefrom by an insulating layer.

8. The current transducer according to any preceding claim wherein the current transducer further comprises a signal conditioning integrated circuit (IC) (3) incorporating or connected to the magnetic field gradient sensor (2) and further connected to a secondary conductor arrangement (14) of the transducer.

9. The current transducer according to any preceding claim wherein the primary conductor (5), secondary conductor arrangement (14), and magnetic field gradient sensor (2) are overmolded by an insulating housing (4) except for connection terminals of the primary conductor and secondary conductor arrangement.

10. The current transducer according to any preceding claim wherein the primary conductor and secondary conductor arrangement are formed from a lead frame.

11. The current transducer according to any preceding claim wherein the primary conductor (5) comprises a shape that has mirror image symmetry about the centre line.

12. The current transducer according to the preceding claim wherein the primary conductor first branch comprises a first connection end terminal (10a) and the primary conductor second branch comprises a second connection end terminal (10b) a width of each of the first and second connection end terminal being over 30% of a total width of the current transducer.

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