Planar transformer

Abstract

A set of two transformers (1) comprising a magnetic core (11) and at least one first and one second printed circuit board (12), each printed circuit board comprising: - at least one layer of electrically insulating material, - at least one first and one second electrically conductive tracks, and - at least one primary winding formed by the first track and at least one secondary winding formed by the second track, each of the windings surrounding at least a part of the magnetic core (11), the magnetic core defining with the first printed circuit board the first transformer, and with the second printed circuit board the second transformer, the magnetic core comprising a first part (111), in particular referred to as I-shaped, and a second part (112), in particular referred to as E-shaped and comprising several branches (1121),all or part of these branches (1121) passing through the first and second printed circuit boards. Abbreviated figure: Figure 1,

Description

Title of the invention: Planar transformer technical field

[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.

[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 electrical circuit may allow the conversion of a voltage of 12V or 48V to a voltage greater than 300V, for example, 400V or 800V. This electrical 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 (acronym 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. Summary of the invention

[0010] According to a first aspect, the invention relates to a set of two transformers comprising a magnetic core and at least a first and a second printed circuit board, each printed circuit board comprising:

[0011] - at least one layer of electrically insulating material,

[0012] - at least one first and one second electrically conductive tracks, and

[0013] - at least one primary winding formed by the first track and at least one secondary winding formed by the second track, each of the windings surrounding at least a portion of the magnetic core,

[0014] the magnetic core defining with the first printed circuit board the first transformer, and with the second printed circuit board the second transformer, the magnetic core comprising a first part, in particular said to be I-shaped, and a second part, in particular said to be E-shaped and comprising several branches, all or part of these branches passing through the first and second printed circuit boards.

[0015] For example, the assembly includes a layer of thermal paste or thermal glue between the first part and at least a portion of the second 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] According to a second aspect, the invention relates to an electronic circuit comprising an additional printed circuit board and a set of two transformers, according to the first aspect, the set of two transformers being electrically connected to the additional printed circuit board.

[0019] For example, the circuit includes a cooling device in thermal contact with the set of two transformers. Such a cooling device is also known as a "radiator." Such a radiator allows cooling via ambient air. If necessary, cooling of this radiator by liquid, such as water, may be provided.

[0020] For example, the circuit includes a layer of thermal paste or thermal glue between at least a part of a printed circuit board and the magnetic core.

[0021] According to embodiments, the circuit includes a layer of thermal paste or thermal adhesive disposed at least between two areas facing the printed circuit boards.

[0022] The transfer of calories from the two transformers can be done exclusively by contact of at least one of these two transformers with the cooling device, where appropriate via a thermal interface.

[0023] According to other embodiments, the circuit includes a heat transfer device located between the two printed circuit boards, the heat transfer device being in thermal contact with the two printed circuit boards on one side and the cooling device on the other.

[0024] For example, the heat transfer device includes a heat pipe, for example several heat pipes regularly distributed or not.

[0025] For example, the circuit includes a thermal interface material between the additional printed circuit board and at least a part of the magnetic core.

[0026] According to embodiments, the circuit includes a thermal interface material between the cooling device and at least a portion of the additional printed circuit board.

[0027] For example, the heat transfer device is a graphene sheet.

[0028] For example, the magnetic core is constituted exclusively by the union of the first and second part.

[0029] For example, each printed circuit board includes:

[0030] - a single primary winding, and

[0031] - two secondary windings.

[0032] 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 energy storage unit The vehicle's electrical system is connected to the other secondary winding, which is intended to be connected to the vehicle's on-board electrical system. The voltage across this secondary winding may then be significantly lower than the voltage across the other secondary winding.

[0033] According to a third aspect, the invention relates to an electronic component defining:

[0034] - an electrical energy storage unit charger for powering a vehicle propulsion engine, and

[0035] - a vehicle on-board network DC / DC voltage converter

[0036] 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.

[0037] 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 the figures

[0038] 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:

[0039] [Fig-1] illustrates an electronic circuit comprising two transformers according to a first embodiment,

[0040] [Fig.2] illustrates an electronic circuit comprising two transformers according to a second embodiment,

[0041] [Fig.3] illustrates an electronic circuit comprising two transformers according to a third embodiment,

[0042] [Fig.4] illustrates an electronic circuit comprising two transformers according to a fourth embodiment. Detailed description of the invention

[0043] 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 (compared to two standard transformers). They also allow for the implementation of efficient cooling solutions. Furthermore, the structure of the described embodiments reduces production costs compared to that of two separate transformers.

[0044] Embodiments of the invention use a common magnetic core for two planar transformers.

[0045] Figure 1 illustrates a first embodiment of an electronic circuit 9 comprising a set 1 of two planar transformers. Figure 1 is a cross-sectional view of the assembly. A magnetic core 11 (for example, made of ferrite—other materials are possible) comprises two parts. A first part 111 is attached to a second part 112 after printed circuit boards 12 have been inserted into it. In some embodiments, the magnetic core consists exclusively of the joining of the first and second parts.

[0046] The second part 112 comprises a base from which branches 1121 extend through the printed circuit boards 12 to make contact with the first part 111, thus joining the first and second parts. The base of the second part 112 may, for example, have a generally parallelepiped shape. It may 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 extend from this base to the first part 111 in a vertical direction in the plane illustrated by [Fig. 1]. The branches also extend in a direction transverse to the rectangular cross-section, that is, in the direction orthogonal to the plane representing the assembly in [Fig. 1]. For example, the branches may have a generally parallelepiped shape, with a length in the direction transverse to [Fig. 1].Thus, the second part 112 has a general shape of "E". That is to say, its cross-section in a plane of cutting of the assembly forms a comb resembling the letter "E". The branches of the second part 112 from its base form the branches of the "E" comb. The number of branches is not limited to 3. Thus, for example, [Fig. 1] illustrates an assembly with 4 branches.

[0047] The first part 111 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 base of the second part 112. The branches of the second part 112 extend from its base until they reach the first part 111, which thus closes the comb or "E" formed by it.

[0048] The first and second parts 111 and 112 are joined together by any suitable means, for example at the ends of the branches of the second part 112. Such a means may for example be a layer of glue or thermal paste.

[0049] As already indicated, the branches 1121 of the second part 112 pass through the printed circuit boards 12. Thus, the first and second parts 111 and 112 form a magnetic core common to both boards. Each board has An insulating material supports electrically conductive tracks forming flat windings printed on it and at least partially surrounding the magnetic core. Each board thus defines a transformer with the magnetic core around which the conductive tracks are wound. For each printed circuit board, one conductive track forms a primary winding and another track forms a secondary winding. In some embodiments, each printed circuit board may comprise a single primary winding and two secondary windings.

[0050] Each printed circuit board 12 can be connected to an additional printed circuit board 2, thus forming an electronic circuit. The additional printed circuit board allows the transformers to be controlled. For example, this board 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.

[0051] The assembly of the two transformers further includes a cooling device 3, for example a heat-conducting plate (for example, made of aluminum or other material). The transformers are in thermal contact with this cooling device 4 to enable this cooling.

[0052] In the example shown, the magnetic core is disposed on the additional printed circuit board. The additional printed circuit board is itself disposed, for example, on the cooling device. To improve heat transfer, a thermal interface 6 may be provided, for example, between the additional printed circuit board 2 and the cooling device 3. It may also be provided between the base of the second part 112 of the magnetic core and the additional printed circuit board 2. Generally, a thermal interface material may be used between the additional printed circuit board and at least a part of the magnetic core, and between the cooling device and at least a part of the additional printed circuit board.

[0053] Figure 2 illustrates an electronic circuit according to a second embodiment. Common elements with the first embodiment bear the same references. In this example, the connection 10 between the printed circuit boards 12 and the additional printed circuit board 2 is shown.

[0054] In this embodiment, the gaps present in the transformer assembly are filled by a layer of material 4.

[0055] For example, this material may be present between at least a portion of a printed circuit board and the magnetic core. For example, this material may be present between two opposing areas of the printed circuit boards. This material is, by For example, thermal paste can be used to improve heat transfer and dissipation within the assembly. Alternatively, thermal adhesive can be used to enhance the assembly's strength. All or part of the gaps can be filled. Thus, in the example of [Fig. 2], the gaps between the two printed circuit boards are filled, as are the gaps between the printed circuit board and the base of the second part 112 of the magnetic core. The gaps between the printed circuit board and the first part 111 are not filled. This is because heat transfer to the second part 112 is prioritized, as it is in contact with the cooling device 3. As illustrated by the arrows, heat transfer is downward in the illustration of [Fig. 2].

[0056] Furthermore, in this embodiment, two thermal interfaces 6 are provided between the second part 112 of the core and the additional printed circuit board, as well as between this additional printed circuit board and the cooling device. This improves heat transfer, represented by the downward arrows in the illustration in [Fig. 2].

[0057] Fig. 3 illustrates an electronic circuit according to a third embodiment. The elements common to the previous embodiments bear the same reference numerals. In this example, the printed circuit boards 12 are in contact with a heat transfer device 5. This device is capable of transferring the heat absorbed from the printed circuit boards 12 to the cooling device 3. A fastening element 11 maintains contact between the heat transfer device 5 and the cooling device 3. For example, the heat transfer device 5 is a graphene sheet. For example, the heat transfer device 5 is implemented as a layer sandwiched between the two printed circuit boards 12. Thus, the branches of the second part 112 of the core pass through the heat transfer device 5.

[0058] Figure 4 illustrates a third embodiment. The common elements with The preceding embodiments bear the same reference numerals. In this example, the heat transfer device 5 takes the form of a heat pipe. For example, the 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 of the second part 112 of the magnetic core. The chamber contains a low-boiling-point working fluid.

[0059] 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 of the assembly belongs to the energy storage unit and the second transformer belongs to the DC / DC voltage converter.

[0060] 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.

[0061] To satisfy specific needs, a person competent in the field of the invention may apply modifications or adaptations.

[0062] 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 transformers (1) comprising a magnetic core (11) and at least a first and a second printed circuit board (12), each printed circuit board comprising: - at least one layer of electrically insulating material, - at least one first and a second electrically conductive track, and - at least one primary winding formed by the first track and at least one secondary winding formed by the second track, each of the windings surrounding at least a portion of the magnetic core (11), the magnetic core defining with the first printed circuit board the first transformer, and with the second printed circuit board the second transformer, the magnetic core comprising a first portion (111), in particular referred to as I-shaped, and a second portion (112), in particular referred to as E-shaped and comprising several branches (1121),all or part of these branches (1121) passing through the first and second printed circuit boards.

2. Assembly of two transformers (1) according to the preceding claim comprising a layer (4) of thermal paste or thermal glue between the first part (111) and at least a portion of the second part (112) of the magnetic core (11).

3. Electronic circuit (9) comprising an additional printed circuit board (2) and a set of two transformers (1), according to claim 1 or 2, the set of two transformers (1) being electrically connected to the additional printed circuit board (2).

4. Electronic circuit (9) according to the preceding claim comprising a cooling device (3) in thermal contact with the set of two transformers (1).

5. Electronic circuit (9) according to any one of claims 3 or 4 comprising a layer (4) of thermal paste or thermal adhesive between at least a portion of a printed circuit board (12) and the magnetic core (11).

6. Electronic circuit (9) according to any one of claims 3 to 5 comprising a layer (4) of thermal paste or thermal adhesive arranged at least between two areas opposite the printed circuit boards (12).

7. Electronic circuit (9) according to any one of claims 3 to 5 comprising a heat transfer device (5) located between the two printed circuit boards (12), the heat transfer device (5) being in thermal contact with the two printed circuit boards (12) on the one hand and the cooling device (3) on the other hand.

8. Electronic circuit (9) according to the preceding claim in which the heat transfer device (5) comprises a heat pipe.

9. Electronic circuit (9) according to any one of claims 3 to 8 comprising a thermal interface material between the additional printed circuit board (2) and at least a portion of the magnetic core (11).

10. Electronic circuit (9) according to any one of claims 3 to 9 comprising a thermal interface material between the cooling device (3) and at least a portion of the additional printed circuit board (2).

11. Electronic circuit (9) according to any one of claims 9 or 10 wherein the heat transfer device (5) is a graphene sheet.

12. Electronic circuit (9) according to any one of claims 3 to 11, wherein the magnetic core (11) is constituted exclusively by the union of the first and second part (111, 112).

13. Electronic circuit (9) according to any one of the preceding claims, wherein each printed circuit board 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 (9) according to any one of claims 3 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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