Planar transformer

Abstract

A set of two planar transformers comprising a magnetic core and at least two printed circuit boards, each printed circuit board comprising: - at least one layer of electrically insulating material and at least one first and second electrically conductive tracks, and - at least one primary winding is formed by the first track and at least one secondary winding formed by the second track, and the magnetic core, comprising: a first part defining a first end of the first transformer, a third part defining a second end of the second transformer, and a second part disposed between the first and third parts and shared between the two transformers, the second part of the magnetic core comprising a plate and several branches perpendicular to the surface of said plate, all or part of these branches passing through both of the printed circuit boards.Abbreviation figure: Figure 1.

Description

Title of the invention: Planar transformer FIELD OF THE INVENTION

[0001] The present invention relates to the field of electrical transformers. More specifically, it relates to a planar electrical assembly for forming a planar electrical transformer. STATE OF THE ART

[0002] Non-planar transformers are generally made with a winding of copper wire in turns around a ferromagnetic core (for example, ferrite). However, this type of coil has a significant footprint, because the winding, also referred to as the coil, extends around the ferromagnetic core in space, in volume, that is to say, in a substantially homogeneous manner in the three dimensions of space.

[0003] Electrical transformers may, for example, be part of an electrical circuit (e.g., an "on-board network") installed in an electric or hybrid vehicle. This circuit allows the conversion of a voltage of 12V or 48V to a voltage greater than 300V, for example, 400V or 800V. This circuit may also allow the conversion of a higher voltage to a lower voltage. Transformers are also sometimes associated with an inverter / rectifier for charging an electrical energy storage unit from an external electrical network. Such an electrical energy storage unit may, for example, have a voltage of 48V or more, for example, a voltage greater than 300V such as 400V, 800V, or more.

[0004] To save space and reduce size, planar electrical transformers comprise a monolithic planar electrical assembly onto which a ferromagnetic core is attached. Such transformers are generally designed to be compact, while taking into account the associated heating and cooling requirements.

[0005] According to the prior art, coils made of thin layers of electrically conductive material, in particular copper, are superimposed and separated by thin layers of electrical insulation. These layers of electrically conductive material are brought into mechanical and electrical contact with each other, for example by welding, to form a spiral suitable for functioning as a coil. This results in substantially flat coils with a small footprint.

[0006] However, to constitute an electrical transformer, it is necessary to have a primary circuit and a secondary circuit magnetically coupled via a ferromagnetic core.

[0007] Thus, to produce a compact electrical transformer, even considering the technology corresponding to substantially flat coils mentioned above, in the prior art, a printed circuit board, or PCB (short for "Printed Circuit Board"), is made. This PCB consists of a substrate, for example, made of pre-impregnated material, in which at least one electrically conductive winding forming a secondary or primary circuit of an electrical transformer is incorporated. At least one other winding forming a primary or secondary circuit, respectively, as well as a ferromagnetic core, are then attached to this PCB to create a complete electrical transformer. Thus, on the PCB that incorporates a secondary or primary winding, another conductive winding, generally made of copper, is brazed, soldered, or even glued to this PCB.

[0008] The ongoing electrification of vehicles is making the use of compact transformers increasingly widespread and is raising various issues, such as reducing their size or improving cooling efficiency. Therefore, there is still a need to improve planar transformers, particularly in these areas.

[0009] The present invention falls within this framework.

[0010] BRIEF DESCRIPTION OF THE INVENTION

[0011] According to a first aspect, the invention relates to a set of two planar transformers comprising a magnetic core and at least two printed circuit boards, each printed circuit board comprising:

[0012] - at least one layer of electrically insulating material and at least one first and a second electrically conductive track, and

[0013] - at least one primary winding is formed by the first track and at least one secondary winding formed by the second track, and

[0014] the magnetic core, comprising: a first part defining a first end of the first transformer, a third part defining a second end of the second transformer, and a second part disposed between the first and third parts and shared between the two transformers, the second part of the magnetic core comprising a plate and several branches perpendicular to the surface of said plate, all or part of these branches passing through one and the other of the printed circuit boards.

[0015] All or part of the branches may extend on either side of the platform. Each branch extends, for example, between an end turned towards the first part of the magnetic core and one end turned towards the third part of the magnetic core.

[0016] The aforementioned assembly may be monolithic. In other words, this assembly may consist of parts rigidly coupled together in the assembled state.

[0017] Each winding can define a spiral.

[0018] For example, one and / or the other of the first and third parts is said to be I-shaped.

[0019] For example, the second part of the magnetic core is devoid of internal air gap.

[0020] According to a second aspect, the invention relates to an electronic circuit comprising at least one additional printed circuit board, the set of two planar transformers according to the first aspect, electrically connected to the additional printed circuit board, and a cooling device in thermal contact with the set of two planar transformers.

[0021] Such a cooling device is also known as a "radiator". Such a radiator allows cooling via ambient air.

[0022] For example, the circuit includes at least one heat transfer device, the heat transfer device being in thermal contact with the cooling device on the one hand and with at least a part of the magnetic core on the other hand.

[0023] For example, the heat transfer device includes one of: a heat pipe, a vapor chamber and the additional printed circuit board.

[0024] For example, at least one heat transfer device includes a heat pipe, said heat pipe being located inside the magnetic core plate. A plurality of heat pipes may be provided, these heat pipes being regularly or irregularly distributed within the magnetic core.

[0025] According to embodiments, at least one heat pipe is located at the intersection between the magnetic core plate and one of its branches.

[0026] For example, a layer of thermal paste or thermal glue is present between at least a part of a printed circuit board and the magnetic core.

[0027] According to embodiments, a thermal interface material is located between at least a part of the magnetic core and the cooling device.

[0028] For example, a thermal interface material is in thermal contact with at least a part of the additional printed circuit board on the one hand and the cooling device on the other hand.

[0029] According to embodiments, a thermal interface material is in thermal contact with at least a part of the heat pipe on the one hand and the cooling device on the other hand.

[0030] For example, each transformer comprises:

[0031] - a single primary winding, and

[0032] - two secondary windings.

[0033] The primary winding is, for example, intended to be electrically connected to a connector for connection to a charging terminal, while one of the secondary windings is intended to be connected to the vehicle's electrical energy storage unit and the other secondary winding is intended to be connected to the vehicle's on-board electrical system. The voltage across this latter secondary winding may then have a significantly lower amplitude than the voltage across the other secondary winding.

[0034] According to a third aspect, the invention relates to an electronic component defining:

[0035] - an electrical energy storage unit charger for powering a vehicle propulsion engine, and

[0036] - a vehicle on-board network DC / DC voltage converter

[0037] the component comprising the electronic circuit according to the second aspect, the first transformer belonging to the electrical energy storage unit charger and the second transformer belonging to the DC / DC voltage converter.

[0038] This component may include a common housing within which the electrical energy storage unit charger and the DC / DC voltage converter are arranged. This common housing may carry connectors for connecting said charger and said converter to the rest of the on-board network. BRIEF DESCRIPTION OF FIGURES

[0039] Other features and advantages of the invention will become apparent from the following detailed description, by way of non-limiting example, and the accompanying figures, among which:

[0040] [Fig. 1] illustrates an electronic circuit comprising a set of two transformers according to a first embodiment,

[0041] [Fig.2] illustrates an electronic circuit comprising a set of two transformers according to a second embodiment,

[0042] [Fig.3] illustrates an electronic circuit comprising a set of two transformers according to a third embodiment,

[0043] [Fig.4] illustrates a first view of an electronic circuit comprising together of two transformers according to a fourth embodiment

[0044] [Fig. 5] illustrates a second view along a section plane A-A' of the circuit electronics comprising a set of two transformers according to the fourth embodiment illustrated [Fig.4]. DETAILED DESCRIPTION OF THE INVENTION

[0045] As will become apparent from this description, the embodiments of the invention offer the possibility of having two transformers in a reduced footprint, both in terms of volume and surface area occupied (compared to two standard transformers). They also allow for the implementation of efficient cooling solutions.

[0046] Embodiments of the invention use a magnetic core structure common to two planar transformers.

[0047] Fig. 1 illustrates a first embodiment of an assembly 1 of two planar transformers. Fig. 1 is a cross-sectional view of the assembly of two planar transformers 1. A magnetic core 11 (for example, made of ferrite – other materials are possible) comprises three parts. A first part 111 is attached to a second part 112 after a printed circuit board 12 has been inserted into it. A third part 113 is also attached to the second part 112 after another printed circuit board 12 has been inserted into it. The second part 112 has a platform 1121 from which branches 1122 extend. These branches 1122 extend on either side of the platform 1121, and the printed circuit boards 12 are inserted onto these branches 1122. In some embodiments, the magnetic core 11 is formed exclusively by the joining of the first part 111, the second part 112, and the third part 113.According to some models, the second part 112 does not have an internal air gap.

[0048] The branches 1122 pass through the printed circuit boards 12 to make contact with the first and third parts 111 and 113 in order to secure the three parts 111, 112, 113. The base of the second part 112 has, for example, a generally parallelepiped shape. It can have other shapes. Generally, the base of the second part 112 has a rectangular cross-section along a horizontal length in the plane illustrated by [Fig. 1]. The branches 1122 extend from this base towards the first part 111 in a vertical direction in the plane illustrated by [Fig. 1]. The branches 1122 also extend in a direction transverse to the rectangular cross-section, that is, in the direction orthogonal to the plane representing the set of two planar transformers 1 in [Fig. 1]. For example, branches 1122 have an overall parallelepiped shape, with a length in the transverse direction to the [Fig.l].Branches 1122 also extend symmetrically from the opposite side of the plate 1121. Thus, the second part 112 has a general shape of an "H" or a double "E". That is to say, its cross-section in a plane of the whole forms a double comb evoking the letter "H" or two "E"s joined by their vertical bars. The branches 1122 of the second part 112 from the... The plates 1121 form the branches 1122 of the double "H" comb (or double "E"). The number of branches 1122 is not limited to four. Thus, for example, [Fig. 1] illustrates a set of two planar transformers 1 with eight branches 1122 (four on each side of the plate 1121).

[0049] The first part 111 of the magnetic core has a generally parallelepiped shape. It can have other shapes. Generally, the first part 111 has a rectangular cross-section (shaped like an "I") along a horizontal length in the plane illustrated by [Fig. 1]. The dimensions of the first part 111 are, for example, close to those of the plate 1121. The branches 1122 of the second part 112 extend from its plate 1121 until they reach the first part 111, which thus closes the double comb or "H" formed by the latter on this side of the plate 1121. The third part 113 has a shape similar to that of the first part 111.

[0050] The first part 111, second part 12 and third part 113 are joined together by any suitable means, for example to the ends of the branches 1122 of the second part 112. Such a means may, for example, be a layer 6 of glue or thermal paste.

[0051] As already indicated, the branches 1122 of the second part 112 pass through the printed circuit boards 12. Thus, the first, second, and third parts 111, 112, and 113 form a magnetic core 11 common to the two transformers. Each printed circuit board 12 has an insulating material and carries electrically conductive traces forming flat windings printed on it and at least partially surrounding the magnetic core 11. Each printed circuit board 12 thus defines a transformer with the magnetic core 11 around which the conductive traces are wound. For each printed circuit board 12, one conductive trace forms a primary winding and another trace forms a secondary winding. In some embodiments, each printed circuit board 12 may comprise a single primary winding and two secondary windings.

[0052] Each printed circuit board 12 can be connected to an additional printed circuit board 3, thus forming an electronic circuit 2. The additional printed circuit board 3 allows control of the transformers of the set of two transformers 1. For example, this printed circuit board 12 may include electronic components specific to power control. Electronic components on the board may define one or more switching arms. Electronic components on the board may define filters.

[0053] The set of two transformers 1 further comprises a cooling device 4, for example a heat-conducting plate (for example in aluminium or other suitable material). The transformers are in thermal contact with this cooling device 4 to enable this cooling.

[0054] In the example shown, the magnetic core is disposed on the additional printed circuit board 3. The additional printed circuit board 3 is, for example, itself disposed on the cooling device 4. To improve heat transfer, a thermal interface 7 may be provided, for example, between the additional printed circuit board 3 and the cooling device 4. It may also be provided between the third portion 113 of the magnetic core 11 and the additional printed circuit board 3. Generally, a thermal interface material may be used between the additional printed circuit board 3 and at least a portion of the magnetic core 11, and between the cooling device 4 and at least a portion of the additional printed circuit board 3.

[0055] Figure 2 illustrates a second embodiment. The elements common to the first embodiment bear the same reference numerals.

[0056] In this example, the additional printed circuit board 3 is not located between the third part 113 and the cooling device 4. It is located between the printed circuit board 12 on the side of the third part 113 and this third part 113. In this embodiment, the third part 113 is in thermal contact with the cooling device 4 in a first part thereof, via the thermal interface 7. The additional printed circuit board 3 is also in contact with the cooling device 4 in another part thereof, also via the thermal interface 7.

[0057] This embodiment saves space since the additional printed circuit board 3 does not constitute an overlay. For example, the core 11 of the transformer assembly passes through the additional printed circuit board 3.

[0058] Respective connection means 15 and 16 between the printed circuit board 12 and additional printed circuit board 3 are also shown.

[0059] Figure 3 illustrates a third embodiment. The elements common to the previous embodiments bear the same reference numerals. In this example, the additional printed circuit board 3 is located between the two printed circuit boards 12. Here too, the overall size is reduced, as the magnetic core 11 passes through the additional printed circuit board 3.

[0060] Figure 4 illustrates a fourth embodiment. The elements common to the previous embodiments bear the same reference numerals.

[0061] In this embodiment, the gaps present in the transformer assembly 1 are filled by a layer of material 17. For example, this material 17 may be present between at least a portion of a printed circuit board 12 and the magnetic core 11. For example, this material 17 may be present between two areas opposite the printed circuit boards 12. This material 17 is, for example, a thermal paste that allows for better heat transfer within the assembly for dissipation. It can also be a thermal adhesive that improves the assembly's strength. All or part of the gaps can be filled. Thus, in the example of [Fig. 4], the gaps between the two printed circuit boards 12 and the magnetic core 1121 are filled. The gaps between the printed circuit board 12 and the first and third parts 111, 113 are not filled. Indeed, heat transfer to the second part 112 is prioritized because it is in contact with a heat transfer device 5.

[0062] In this example, the heat transfer device 5 takes the form of one or more heat pipes. For example, a heat pipe is made of a metal with high thermal conductivity, such as copper or aluminum. It is, for example, a flattened chamber containing passages for the branches 1122 of the second part 112 of the magnetic core 11. The chamber contains a low-boiling-point working fluid. It can also be cylindrical pipes. Heat pipes can also have more complex shapes with portions of different conformations. For example, a cylindrical part and a flattened part to meet the requirements of heat exchange efficiency and the need to reduce size. Simplifying the heat pipe design can also lead to choosing more or less regular conformations in shape.

[0063] In other examples, the heat transfer device 5 may be a vapor chamber. It may also be the additional printed circuit board 3 itself (not shown in [Fig. 4]).

[0064] Returning to the example of the heat pipe(s), these can, for example, be integrated into the magnetic core 11. This could be, for example, a network of heat pipes. Each heat pipe can be located at the intersection of the plate 1121 and a branch 1122 of the second part 112.

[0065] Figure 5 is a longitudinal view of a heat pipe along the section plane A-A' illustrated in Figure 4. As can be seen in this figure, the heat pipe passes completely through the second part 112 of the magnetic core 11 and comes into thermal contact with the cooling device 4, for example via a thermal interface 7. A fastening means 17 can be provided to ensure thermal contact between the heat pipe and the cooling device 4.

[0066] The heat pipe, for example, has a constant cylindrical cross-section. For example, only the part integrated into the magnetic core 11 is cylindrical, while the part external to it is flattened to ensure a larger thermal contact surface with the cooling device 4.

[0067] The embodiments described above can be used in an electronic component comprising an electrical energy storage unit charger for powering a vehicle propulsion motor, and a vehicle on-board DC / DC voltage converter (DC stands for Direct Current). For example, the first transformer in the assembly belongs to the energy storage unit and the second transformer belongs to the DC / DC voltage converter.

[0068] The present invention has been described and illustrated in this detailed description with reference to the accompanying figures. However, the present invention is not limited to the embodiments shown. Other variations, embodiments, and combinations of features can be deduced and implemented by a person skilled in the art upon reading this description and the accompanying figures.

[0069] To satisfy specific needs, a person competent in the field of the invention may apply modifications or adaptations.

[0070] In the claims, the term “include” does not exclude other elements or steps. The various features presented and / or claimed may be advantageously combined. Their presence in the description or in different dependent claims does not preclude the possibility of combining them. The reference symbols shall not be construed as limiting the scope of the invention.

Claims

Demands

1. An assembly of two planar transformers (1) comprising a magnetic core (11) and at least two printed circuit boards (12), each printed circuit board (12) comprising: - at least one layer of electrically insulating material and at least one first and second electrically conductive tracks, and - at least one primary winding is formed by the first track and at least one secondary winding formed by the second track, and the magnetic core (11) comprising: a first part (111) defining a first end of the first transformer, a third part (113) defining a second end of the second transformer, and a second part (112) disposed between the first and third parts and shared between the two transformers, the second part (112) of the magnetic core comprising a plate (1121) and several branches (1122) perpendicular to the surface of said plate,all or part of these branches (1122) passing through both of the printed circuit boards,

2. Assembly of two planar transformers (1) according to claim 1, one and / or the other of the first and third parts being said to be I-shaped.

3. Assembly of two planar transformers (1) according to claim 1 or 2, the second part (112) of the magnetic core (11) being devoid of internal air gap.

4. Electronic circuit (2) comprising at least one additional printed circuit board (3), the set of two planar transformers (1) according to any one of claims 1 to 3, electrically connected to the additional printed circuit board (3) and a cooling device (4) in thermal contact with the set of two planar transformers (1).

5. Electronic circuit (2) according to the preceding claim comprising at least one heat transfer device (5), the heat transfer device (5) being in thermal contact with the cooling device (4) on the one hand and with at least a part of the magnetic core (11) on the other hand.

6. Electronic circuit (2) according to any one of claims 4 or 5 wherein the heat transfer device (5) is selected from a heat pipe, a vapor chamber and the additional printed circuit board (3).

7. Electronic circuit (2) according to the preceding claim in which at least one heat transfer device (5) is a heat pipe, said heat pipe being located inside the plate (1121) of the magnetic core (11).

8. Electronic circuit (2) according to the preceding claim in which at least one heat pipe is located at the intersection between the plate (1121) of the magnetic core and one of its branches (1122).

9. Electronic circuit (2) according to any one of claims 4 to 8 comprising a layer (6) of thermal paste or thermal adhesive between at least a portion of a printed circuit board (12) and the magnetic core (11).

10. Electronic circuit (2) according to any one of claims 4 to 9 in which a thermal interface material (7) is located between at least a part of the magnetic core (11) and the cooling device (4).

11. Electronic circuit (2) according to any one of claims 4 to 10 in which a thermal interface material (7) is in thermal contact with at least a part of the additional printed circuit board (3) on the one hand and the cooling device (4) on the other hand.

12. Electronic circuit (2) according to any one of claims 4 to 11 in which a thermal interface material (7) is in thermal contact with at least a part of the heat pipe on the one hand and the cooling device (4) on the other hand.

13. Electronic circuit (2) according to any one of claims 4 to 12, wherein each transformer comprises: - a single primary winding, and - two secondary windings.

14. Electronic component defining: - an electrical energy storage unit charger for powering a vehicle propulsion motor, and - a vehicle on-board network DC / DC voltage converter, the component comprising the electronic circuit (2) according to any one of claims 4 to 13, the first transformer belonging to the electrical energy storage unit charger and the second transformer belonging to the DC / DC voltage converter.

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