WO2014072062A1

WO2014072062A1 - A smd current sensor device and uses thereof

Info

Publication number: WO2014072062A1
Application number: PCT/EP2013/003365
Authority: WO
Inventors: Sébastien Daniel Emilien CASTRES; Patrick Jean Pierre Amédée FOUASSIER; José Ramón FERNANDEZ DE LA FUENTÉ
Original assignee: Premo, Sl
Priority date: 2012-11-12
Filing date: 2013-11-08
Publication date: 2014-05-15
Also published as: DE112013005380T5; CN104813176A; ES2405837A1; ES2405837B1; CN104813176B

Abstract

The SMD current sensor device comprises: - a magnetic core; and - first (31) and second (43) windings respectively wound around first and second sections of the magnetic core. Most of first winding (31) is over moulded with an electrically insulating material defining a first envelope (3) defining a through hole (33) for the introduction therein of the first section of the magnetic core, and the device comprises an electrically insulating support (44) around which the second winding (43) is wound and which defines a through hole (42) for the introduction therein of the second section of the magnetic core, both through holes (33, 42) being aligned to each other. The uses of the SMD current sensor device are for sensing an excess of electrical current circulating through the first winding and for accurately measuring the magnitude of said electrical current.

Description

A SMD current sensor device and uses thereof

Field of the Art

The present invention generally relates, in a first aspect, to a SMD (Surface Mounting Device) current sensor device, i.e. a device designed to be arranged and soldered over a printed circuit board by a SMD technique, comprising two windings wound around a magnetic core, and more particularly to a SMD current sensor device structurally formed to constitute a compact and small device offering a high efficiency, by means, among others, of providing an electrically insulating barrier between the two windings which allows them to be placed close to each other.

Second and third aspects of the invention relate to different uses of the SMD current measuring device of the first aspect.

Background of the Invention

There are several devices in the prior state of the art regarding electrical current sensor devices, some of which include current transformers, also called instrument transformers, for measuring electric currents, such as that disclosed in U.S. Patent No. US 4,630,218.

Moreover, it is well known that switching protective systems including this kind of current sensors are arranged in modern power supplies, such as in the power line current fed power supplies disclosed by U.S. Patent Application Pub. No. US 2012/23661 1 A1 .

In applications such as inverters and DC/DC battery chargers for Electric vehicles and hybrid vehicles (also known as HEV: "Hybrid - Electric Vehicles") current sensors are required to occupy as little space as possible and support the most power possible. Additionally, to have a proper switching management digital controls are required to be better than conventional PWM controls and that this control be carried out by sampling the current flowing through the conductors at a very high frequency (between 70 KHz and 200 KHz).

Most of sensors known in the art are difficult to use in applications that require a sensor that is a surface mount device due to size restrictions. The requirements of the various international standards regarding distances between windings, distance between core and windings, etc. prevent the use of conventional devices for that purpose.

However, some current sensor devices are known which are really suitable for

SMD, such is the case of the ones disclose by the next cited patents. U.S. Patent No. US 7,622,910 B2 discloses an integrated current sensor device, apt for surface mounting, comprising a magnetic core and first and second windings wound around respective first and second sections of the magnetic core.

US 7,622,910 B2 states that the core and its windings are properly insulated, but no particular structural arrangement of said elements (windings and core) neither to achieve such insulation nor for their assembly within the substrate of the integrated device is disclosed, other that by reference to the integrated circuit "Sentron CSA-1 V- SO", which is said to be modified by including there into an AC inductor, hence it is implicitly assumed that the insulation to the windings and core is provided by the substrate of the integrated circuit itself or of other layered element added during the manufacturing thereof.

The use of an integrated circuit manufacturing process for manufacturing the device of US 7,622,910 B2 has many drawbacks, including those associated to costs, restrains and complexity inherent to such processes. Also, the maximum electrical values which an integrated current sensor device can stand are lower in comparison with a non-integrated one, due to thermal, geometrical and other kind of constraints.

EP 1 105 893 B1 discloses an inductive component production process comprising moulding a molten hot melt adhesive under pressure in a metal mould enclosing a magnetic core wound by one or more windings. For an embodiment, the inductive component disclosed by EP 1 105 893 B1 is said to be directly suitable for SMD, by providing a mould with blind holes and laying the connections form the winding or windings therein.

No intermediate insulation between the windings or between the windings and the magnetic core is disclosed at all in EP 1 105 893 B1 , the only moulding process disclosed therein being performed once the windings are wound around the core.

Description of the Invention

It is an object of the present invention to offer an alternative to the prior state of the art, with the purpose of providing a SMD current sensor device, which provides particular structural arrangements for the inner elements thereof, i.e. for the magnetic core and windings, which allows its manufacturing as a compact and small device offering a high efficiency, and meeting the requirements of various international standards in regards to insulation criteria like dielectric strength and/or physical construction criteria like creepage distance, clearance, distance through the insulation.

To that end, the present invention relates to a SMD electrical current sensor device, comprising: - a magnetic core;

- a first winding wound around at least a first section of said magnetic core; and

- a second winding wound around at least a second section of said magnetic core;

Contrary to the SMD current sensor devices disclosed by the prior art, in the one proposed by the present invention at least part of the first winding is over moulded with an electrically insulating material defining a first envelope confining at least part of the first winding therein, said first envelope defining a through hole for the introduction therein of a first portion of the magnetic core, and the SMD current sensor device comprises an electrically insulating support around which the second winding is wound and which defines a through hole for the introduction therein of a second portion of the magnetic core, wherein said through holes of the first and second windings are aligned to each other.

The first envelope provides an insulating solid barrier that physically separates the first winding from the second winding. This barrier provides a higher electric insulation which allows reducing the distance between both windings, as the electric insulation between them is increased in comparison to a situation when none of the windings were over moulded with an insulating material.

Hence, the present invention provides a current sensor device with an arrangement which enables the incorporation of a current sensor having the dimensions of a SMD device, maintaining the characteristics of safety and compliance with the parameters proposed by standards such as IEC-61558 and UL-1950.

Preferably, the magnetic core and first and second windings form a current transformer, where the first winding acts as the primary winding and the second winding is the secondary winding of the current transformer, although implementations other than a current transformer, for current sensing, are also possible by using the magnetic core and windings of the device of the invention, for less preferred embodiments.

For an embodiment, said electrically insulating support is attached to the first envelope, i.e. the electrically insulating support and the envelope are two independent pieces attached to each other, while for another embodiment the electrically insulating support is integral to the first envelope, i.e. they are both built as one-piece.

The magnetic core comprises, for an embodiment, at least one magnetic elongated member comprising said first and second sections.

Although for an embodiment said first and two sections correspond to different regions of a one-piece magnetic elongated member, for another embodiment the magnetic core is split in first and second magnetic sub-cores comprising respective magnetic elongated parts with free ends abutting to each other within said aligned through holes for forming said magnetic elongated member, wherein each of said magnetic elongated parts corresponds to a respective of said first and second sections of the magnetic core.

Preferably, the magnetic core is removably attached to the first envelope of the first winding and to the electrically insulating support of the second winding, by the introduction of its first and second sections through, respectively, the aligned through holes thereof.

For another embodiment, the SMD current sensor device of the present invention comprises first and second support elements, each supporting one of said magnetic elongated parts at respective ends thereof opposite to said free ends.

Said first and second support elements are, for an embodiment, part of, respectively, said first and second magnetic sub-cores and are integral with the corresponding magnetic elongated part forming respective one-piece elements therewith which, when assembled together, form a closed magnetic circuit.

For a preferred embodiment, each of said magnetic one-piece elements is an E- shaped piece where, in a cross-sectional plane cutting the three legs thereof and on which the magnetic flux will circulate, the central leg has a width that doubles the width of each lateral leg, such that when both E-shaped pieces are arranged facing each other contacting at the free ends of their respective arms/legs, form a closed magnetic circuit where the magnetic flux density generated by the first/primary winding within the central leg returns through both lateral legs at half the induction value.

For an alternative embodiment, said first and second support elements are nonmagnetic elements which are attached to the magnetic elongated parts of, respectively, the first and second magnetic sub-cores.

For a preferred embodiment, the first winding is made up of one turn and the second winding is made up of more than one turn. More particularly, the second winding is made up of at least fifty turns for applications in the HEV industry.

The second winding is also insulated with an electrically insulating material. It could be also over moulded, for an embodiment.

Said insulations or over mouldings are independent to each other, i.e. at least performed in separated ways, and they provide an increase in the physical barrier between the windings and the windings and the magnetic core, making the SMD current sensor device of the invention apt to stand higher electrical currents, thus limiting the possible occurrence of electric arcing. According to an embodiment, the magnetic core is formed with a Manganese- Zinc alloy or amorphous cobalt.

As per an embodiment, the electrically insulating support of the second winding is a winding former around which the second winding is formed.

Said winding former is made up, for an embodiment, with a material comprising a liquid crystal polymer or other plastic materials compliant with SMD soldering process like reflow or vapour-phase soldering methods, i.e. high thermal index plastics according to IEC85 standard and also compliant with the self-extinguish criteria according to the UL94 standard.

For an embodiment, the first winding comprises copper, nickel, silver, gold and/or a tin alloy.

The principle of the current sensor of the present invention is based, for a preferred embodiment, on the use of an instrumentation transformer. Thereby there is not handling of the electric current passing through a conductor, the measurement is performed from the magnetic field induced by said current in a core.

A second aspect of the invention relates to a use of the SMD current sensor device of the first aspect for sensing an excess of electrical current circulating through the first winding, for example for protection against overheating.

Additionally the present invention besides providing a current sensor device used for sensing an excess of electrical current can also be applied for current measuring. This type of measurement allows the measurement of very high currents without having direct contact with them as, if such contact is done, related devices should have a considerable volume.

Hence, a third aspect of the invention relates to a use of the SMD current sensor device of any of the previous claims, for accurately measuring the magnitude of the electrical current circulating through the first winding, to use the reading, for instance, in a control loop of associated switching power supplies.

Brief Description of the Drawings

· The previous and other advantages and features will be better understood from the following detailed description of embodiments, with reference to the attached drawings, which must be considered in an illustrative and non-limiting manner, in which:

Figure 1 is a perspective view which shows the SMD current sensor device of the first aspect of the invention, for an embodiment;

Figure 2 is a top view of the device of Figure 1 ; Figure 3 is a perspective exploded view of the device of the first aspect of the invention for the same embodiment of Figures 1 and 2;

Figure 4 shows, by means of a perspective view, some of the elements shown in Figure 3, particularly those including the first and second windings;

Figure 5 shows the same elements than Figure 4 but by means of a top view, where three aligned through holes, for the insertion of the magnetic core, are drawn in dashed lines;

Figure 6 is a cross sectional view taken along cutting plane line VI-VI of Figure 5. Figure 7 is a cross sectional view taken along cutting plane line VII-VII of Figure 5;

Figure 8 is a cross sectional view taken along cutting plane line VIII-VIII of Figure

5; and

Figure 9 is a perspective view which shows all the elements shown in Figure 3, except cover 2, once assembled.

Detailed Description of Several Embodiments

Appended Figures show the different elements of the SMD current sensor device 1 of the invention, for and embodiment for which it comprises, as seen mainly in Figure 3

- a magnetic core split in first and second magnetic sub-cores comprising respective magnetic elongated parts 51 1 , 521 ;

- a first winding 31 over moulded with an electrically insulating material defining a first envelope 3 confining most of the first winding 31 therein (as seen in Figure 6), except for the free ends 31 a and 31 b, where said first envelope 3 defines, as shown in Figure 6, a through hole 33 for the introduction therein of the magnetic elongated part 51 1 ;

- an electrically insulating support 44; and

- a second winding 43 wound around said electrically insulating support 44 and which defines a through hole 42 (as seen in Figure 7) for the introduction therein of said magnetic elongated part 521.

For the illustrated embodiment, furthermore, the first winding 31 is made up with one turn while the second winding 43 may comprise between 50 and 200 turns. The skilled in the art will be able to calculate the ratio of the number of turns of the first and second windings for other embodiments.

As shown in Figure 8, through holes 33 and 42 are aligned to each other, such that when both magnetic elongated parts 51 1 , 521 are inserted there through their free ends abut to each other within the aligned through holes 33, 42. These magnetic elongated parts 51 1 , 521 may be attached to the inner contours of the through holes windings 33 and 42 by a structural adhesive or epoxy glue.

A cover 2 is provided for housing and retaining together, in this case by snap fitting, the different elements of the current sensor device 1 , and in particular sub cores, as shown in Figures 1 and 2.

As shown in Figure 3, the SMD current sensor device 1 comprises first and second support elements 51 , 52, each having two parallel arms 51 a-51 b; 52a-52b interconnected through a traverse 51 c, 52c to which one of the magnetic elongated parts 51 1 , 521 is connected at respective ends thereof opposite to their free ends, such that the magnetic elongated parts 51 1 , 521 extends in parallel and in the same direction than the parallel arms 51 a-51 b; 52a-52b to form an E-shaped piece with them and with the respective traverse 51 c; 52c. Both E-shaped pieces are arranged facing each other, and when assembled, as shown in Figure 9, contacting at the free ends of their respective arms 51a-51 b; 52a-52b and magnetic elongated parts 51 1 , 521 .

These E-shapes for the first and second support elements 51 , 52 provides a particularly advantageous embodiment, as the final assembled, i.e. the shape of the two E-shape pieces once assembled contacting to each other, is closer to the cubic or rectangular prism form of the typical surface mount devices. Thus in addition, these E- shapes allow for a symmetrical device 1 and the magnetic core be easily removable, if required, for replacement.

For a preferred embodiment, the first 51 and second 52 support elements are part of, respectively, the first and second magnetic sub-cores and are integral with the corresponding magnetic elongated part 51 1 , 521 forming respective magnetic one-piece elements therewith each being an E-shaped piece which, as shown in Figure 3, has a central leg 51 1 , 521 with a width Wc that doubles the width Ws of each lateral leg 51 a, 51 b, 52a, 52b, such that when both E-shaped pieces are arranged facing each other contacting at the free ends of their respective arms/legs, form a closed magnetic circuit where the magnetic flux density generated by the first/primary winding 31 within the central leg, formed by 51 1 plus 521 , returns through both lateral legs, 51 a plus 52a and 51 b plus 52b, at half the induction value.

For another embodiment, the first 51 and second 52 support elements are nonmagnetic elements attached to the magnetic elongated parts 51 1 , 521 of, respectively, the first and second magnetic sub-cores.

As can be seen in Figure 3, the present invention provides a single package for each of the windings 31 , 43, so there Is a physical barrier between them that prevents electric arcing or generate losses. This is particularly relevant because the device of the present invention is preferably used in applications standing in the range of 100 to 1000V with a RMS current (to detect/measure up to 50A.

This single package includes the primary winding fully over moulded comprising an insulator which has a dielectric strength of between 2 and 4 kV, a creepage distance of at least 5mm to the secondary winding and to the core and therefore meet the requirements provided by standards such as IEC-61558 and UL-1950 .

Figure 4 shows in detail the device of Figure 3 without the magnetic core and the cover 2, so that one can observe the details of the windings 31 , 43 and the elements associated thereto, such as the first insulating envelope 3 and the electrically insulating support 44 or winding former which in a particularly preferred embodiment is made from a liquid crystal polymer (also known as LCP, for the English expression "Liquid Crystal Polymer"), phenol or any other material resistant to high temperature and flame retardant. This former 44 must withstand continuous temperatures of approximately between -40°C and + 155°C.

Figure 5 shows a top view of the elements shown in Figure 4, where two of the five pins 41 (such as the second and fourth of the row of five pins) are connected (connection not shown) to the free ends of the second or secondary winding 43, on which, in use, it will be obtained an output current proportional to the current passing through the first or primary winding 31 by the principle of electromagnetic induction. The former 44 of the secondary winding 43 is mechanically connected to the five pins 32 to provide a better mechanical fastening, however these pins 32 have no direct electrical connection, for the embodiment illustrated.

The first winding 31 is a planar metallic strip which, as shown in Figures 1 to 9, has free ends 31 a, 31 b which are not over moulded, remain out of the envelope 3 and constitute two respective metallic pins for SMD use, in order to be electrically connected, by welding, to respective tracks of a circuit board to make current pass there through.

Figure 6 is a cross sectional view taken along cutting plane line VI-VI of Figure 5, and shows how the first winding 31 is embedded into the first envelope 3, following a development having an omega shape, or similar, such an omega shape being commonly used to define a regular shape, for example, for a metal profile.

This omega shape allows surrounding magnetic elongated part 51 1 following a development there around of what electromagnetically is understood as one turn.

As shown in Figures 5 and 6, the first envelope 3 comprises two upper planar walls 3a, 3b and, between them, a protuberant central portion 3c surrounding the central part of the first winding 31 . When assembled, as shown in Figure 9, wherein each of the two parallel arms 51 a-51 b of the first support element 51 is supported on one of said two upper planar walls 3a, 3b and on a respective adjacent side wall 3d , 3c2 of the protuberant central portion 3c, thus contributing to give an overall structural robustness to the device 1 .

The primary winding is preferably provided for supporting DC currents of approximately 50 A RMS, therefore it has been chosen, preferably, to have a cross section of approximately 3 · 0.4 mm2 with a material such as copper plus nickel flash, tin alloy, silver or gold to ensure that it can be weld properly and ensure good electrical (ohmic resistivity) and thermal performances (thermal conductivity).

Additionally, the frequency operating range must be of approximately between 10

KHz and 250 KHz to meet industry requirements.

The metal strip forming the first winding 31 , is obtained through a conventional process of pressing and bending and is usually made of stainless steel.

Figure 7 shows a cross sectional view taken along cutting plane line VII-VII of Figure 5, which shows how the electrically insulating support 44, also called winding former, defines the above mentioned a through hole 42 aligned with through hole 33.

Said Figure 7 and also Figures 3, 4 and 5 show the electrically insulating support 44 attached or integral to a support piece 4 having two upper planar surfaces 4a, 4b and, between them, a central arch portion 4c with a central through hole 55 aligned with through holes 33, 42, wherein each of the two parallel arms 52a-52b of the second support element 52 is supported on one of said two upper planar surfaces 4a, 4b and on a respective adjacent side wall 4c1 , 4c2 of the central arch portion 4c, with the same purpose of contributing to give an overall structural robustness to the device 1 . This insulating support 44 is used to carry the second or secondary winding 43.

For the embodiment of Figure 8, electrically insulating support 44, support piece

4 and first envelope 3 are built as a one-piece element, where respective through holes 55, 42 and 33 form a single and common through hole.

A recess area R1 is defined on the upper surface of support piece 4 passing under the central arch, in order to act as a guide for the magnetic elongated part 521 for easing its insertion into through holes 55 and 42. With the same purpose another recess area R2 is defined on the upper surface of the first envelope 3, as shown in Figure 5.

Metallic pins 41 for SMD soldering are mechanically attached to said support piece 4, such that they extend as shown in all the appended figures. A stated above at least two of said metallic pins 41 are connected to the free ends of the second winding 43.

Claims

1. - A SMD current sensor device, comprising:

- a magnetic core;

- a first winding (31 ) wound around at least a first section of said magnetic core; and

- a second winding (43) wound around at least a second section of said magnetic core;

characterized in that at least part of said first winding (31 ) is over moulded with an electrically insulating material defining a first envelope (3) confining said at least part of the first winding (31 ) therein, said first envelope (3) defining a through hole (33) for the introduction therein of said first section of said magnetic core, and in that the SMD current sensor device comprises an electrically insulating support (44) around which said second winding (43) is wound and which defines a through hole (42) for the introduction therein of said second section of the magnetic core, wherein said through holes (33, 42) of said first (31 ) and second (43) windings are aligned to each other.

2. - The SMD current sensor device of claim 1 , wherein said electrically insulating support (44) is attached or integral to said first envelope (3).

3. - The SMD current sensor device of claim 1 or 2, wherein said magnetic core comprises at least one magnetic elongated member comprising said first and second sections.

4. - The SMD current sensor device of claim 3, wherein said magnetic core is split in first and second magnetic sub-cores comprising respective magnetic elongated parts (51 1 , 521 ) with free ends abutting to each other within said aligned through holes (33, 42) for forming said magnetic elongated member, wherein each of said magnetic elongated parts (51 1 , 521 ) corresponds to a respective of said first and second sections of the magnetic core.

5. - The SMD current sensor device of claim 4, comprising first and second support elements (51 , 52), each supporting one of said magnetic elongated parts (51 1 , 521 ) at respective ends thereof opposite to said free ends.

6. - The SMD current sensor device of claim 5, wherein said first (51 ) and second (52) support elements are part of, respectively, said first and second magnetic sub-cores and are integral with the corresponding magnetic elongated part (51 1 , 521 ) forming respective one-piece elements therewith.

7. - The SMD current sensor device of claim 5, wherein said first (51 ) and second (52) support elements are non-magnetic elements attached to the magnetic elongated parts (51 1 , 521 ) of, respectively, the first and second magnetic sub-cores.

8. - The SMD current sensor device of claim 6 or 7, wherein each of said first (51 ) and second (52) support elements has two parallel arms (51 a-51 b; 52a-52b) interconnected through a traverse (51 c; 52c), said magnetic elongated part (51 1 , 521 ) being connected to said traverse (51 c; 52c) such that it extends in parallel and in the same direction than said parallel arms (51 a-51 b; 52a-52b) to form an E-shaped piece with them and with said traverse (51 c; 52c), wherein both E-shaped pieces are arranged facing each other, and contacting at the free ends of their respective arms (51 a-51 b; 52a-52b) and magnetic elongated parts (51 1 , 521 ).

9. - The SMD current sensor device of claim 8, wherein said first envelope (3) comprises at least two upper planar walls (3a, 3b) and, between them, a protuberant central portion (3c) surrounding at least part of said first winding (31 ), wherein each of said two parallel arms (51a-51 b) of said first support element (51 ) is supported on one of said at least two upper planar walls (3a, 3b) and on a respective adjacent side wall (3d , 3c2) of said protuberant central portion (3c).

10. - The SMD current sensor device of claim 9, wherein said electrically insulating support (44) is attached or integral to a support piece (4) having at least two upper planar surfaces (4a, 4b) and, between them, a central arch portion (4c) with a central through hole (55) aligned with said through holes (33, 42), wherein each of said two parallel arms (52a-52b) of said second support element (52) is supported on one of said at least two upper planar surfaces (4a, 4b) and on a respective adjacent side wall (4c1 , 4c2) of said central arch portion (4c).

1 1.- The SMD current sensor device of claim 10, comprising metallic pins (41 ) for

SMD soldering, wherein at least part of said metallic pins (41 ) are electrically connected to at least the free ends of said second winding (43) and mechanically attached to said support piece (4).

12. - The SMD current sensor device of any of the previous claims, wherein the free ends (31 a, 31 b) of said first winding (31 ) are not over moulded, remain out of said envelope (3) and constitute two respective metallic pins for SMD soldering.

13. - The SMD sensor current device of claiml , wherein the first winding (31 ) is made up of one turn and the second winding (43) is made up of more than one turn.

14. - The SMD sensor current device of any of the previous claims, wherein said second winding (43) is also over moulded with an electrically insulating material.

15. - The SMD sensor current device of any of the previous claims, wherein the magnetic core is removably attached to the first envelope (3) of the first winding (31 ) and to the electrically insulating support (44) of the second winding (43), by the introduction of its first and second sections through, respectively, the aligned through holes (33, 42) thereof.

16. - The SMD sensor current device of any of the previous claims, wherein the magnetic core is formed with a Manganese-Zinc alloy and/or amorphous cobalt.

17. - The SMD sensor current device of claim 1, wherein said electrically insulating support (44) of the second winding (43) is a winding former.

18.- The SMD sensor current device of claim 17, wherein said winding former is made up with a material comprising a liquid crystal polymer.

19. - The SMD sensor current device of any of the previous claims, wherein the first winding (31 ) comprises nickel, silver, gold and/or a tin alloy.

20. - The SMD current sensor device of any of the previous claims, wherein said magnetic core and first (31 ) and second (43) windings form a current transformer.

21. - Use of the SMD current sensor device of any of the previous claims, for sensing an excess of electrical current circulating through the first winding.

22. - Use of the SMD current sensor device of any of claims 1 to 20, for accurately measuring the magnitude of the electrical current circulating through the first winding.