Planar transformer

Abstract

The invention relates to an assembly of transformers comprising a first and a second planar transformer and a heat transfer device, the first transformer comprising a first magnetic core and at least one first printed circuit board associated with the first magnetic core, the second transformer comprising a second magnetic core separate from the first magnetic core and at least one second printed circuit board associated with the second magnetic core, each printed circuit board comprising: - at least one layer of electrically insulating material and at least one first and one 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 extending around at least a portion of the magnetic core associated with the circuit board, the heat transfer device being arranged between the two planar transformers in thermal contact with each of the transformers, the first planar transformer being arranged on a first side of the heat transfer device and the second planar transformer being arranged on a second side of the heat transfer device, opposite the first side.

Description

[0001] Description

[0002] Title of the invention: Planar transformer

[0003]

[0001] FIELD OF THE INVENTION

[0004] [2] 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.

[0005] [3] STATE OF THE TECHNOLOGY

[0006] [4] 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 way in the three dimensions of space.

[0007] [5] 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 may allow the conversion of a voltage of 12V or 48V to a voltage above 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 used in conjunction with an inverter / rectifier to charge an electrical energy storage unit from an external electrical grid. Such an electrical energy storage unit may, for example, have a voltage of 48V or higher, or a voltage above 300V such as 400V, 800V, or higher.

[0008] [6] To save space and reduce bulk, planar electrical transformers consist of 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.

[0009] [7] According to the prior art, coils made of thin layers of electrically conductive material, in particular copper, are layered 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 use as a coil. This results in substantially flat coils with a small footprint.

[0010] [8] However, to constitute an electrical transformer, it is necessary to have a primary circuit and a secondary circuit magnetically coupled via a ferromagnetic core.

[0011] [9] Thus, to produce a compact electrical transformer, even considering the technology corresponding to substantially flat coils mentioned above, in the state of the art, a printed circuit board, or PCB (short for "Printed Circuit Board"), is created. This board 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.

[0012]

[0010] 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 always a need to improve planar transformers, particularly in these areas.

[0013]

[0011] The present invention falls within this framework.

[0014]

[0012] BRIEF DESCRIPTION OF THE INVENTION

[0015]

[0013] According to a first aspect, the invention relates to a set of transformers comprising a first and a second planar transformer and a heat transfer device, the first transformer comprising a first magnetic core and at least one first printed circuit board associated with the first magnetic core, the second transformer comprising a second magnetic core distinct from the first magnetic core and at least one second printed circuit board associated with the second magnetic core, each printed circuit board comprising:

[0016] - at least one layer of electrically insulating material and at least one first and second electrically conductive track, and

[0017] - 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 associated with the printed circuit board, the heat transfer device being disposed between the two planar transformers in thermal contact with each of the transformers, the first planar transformer being disposed on one first side of the heat transfer device and the second planar transformer being disposed on a second side of the heat transfer device, opposite the first side.

[0018]

[0014] The aforementioned assembly may be monolithic. In other words, this assembly may consist of parts rigidly coupled together in the assembled state.

[0019]

[0015] The first and second planar transformers can follow one another along an axis, and the heat transfer device can be arranged between the two planar transformers along this axis.

[0020]

[0016] Each winding can define a spiral.

[0021]

[0017] For example, the magnetic core of each planar transformer comprises a first part, called E-shaped, and a second part called I-shaped.

[0022]

[0018] For example, the magnetic core of each planar transformer is formed by the joining of the first part, referred to as E-shaped, and the second part, referred to as I-shaped.

[0019] According to some embodiments, the assembly comprises a metal casing surrounding the second transformer, said casing being in thermal contact with the heat transfer device. The casing can act, in whole or in part, as a heat sink, allowing heat to be dissipated into the ambient air. If necessary, cooling of this heat sink by a liquid, such as water, can be provided.

[0023]

[0020] According to embodiments, the assembly comprises a layer of thermal paste between at least a part of at least one printed circuit board and the associated magnetic core.

[0024]

[0021] For example, the assembly includes a thermal interface material between at least a part of the magnetic core of at least one transformer and at least a part of the heat transfer device.

[0025]

[0022] For example, the assembly includes a thermal interface material between at least a part of the magnetic core of the first transformer and the metal casing.

[0026]

[0023] According to embodiments, the heat transfer device is a vapor chamber or it includes a heat pipe, for example several heat pipes regularly distributed or not.

[0027]

[0024] In all the foregoing, the heat transfer device can dissipate heat to a cooling device, separate from the heat transfer device. This cooling device can thus act as a heat sink. The cooling device is, for example, the aforementioned metal casing surrounding the second transformer. Alternatively, it could be a metal casing surrounding all or part of one or both of the two transformers. Other embodiments of the cooling device are possible provided they function as a heat sink.

[0028]

[0025] According to a second aspect, the invention relates to an electronic circuit comprising at least one set of transformers as defined above, and at least one additional printed circuit board, the set of transformers being connected to the additional printed circuit board.

[0026] For example, the set of transformers being as described in the first aspect, the heat transfer device being defined by the additional printed circuit board.

[0029]

[0027] For example, each printed circuit board includes:

[0030] - a single primary winding, and

[0031] - two secondary windings.

[0032]

[0028] 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.

[0033]

[0029] 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 motor, and

[0035] - a vehicle on-board network DC / DC voltage converter, the electronic component comprising an 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.

[0036] 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 onboard network.

[0037]

[0030] BRIEF DESCRIPTION OF THE FIGURES

[0031] Other features and advantages of the invention will become apparent from the following detailed description, which is given by way of non-limiting example, and the accompanying figures, among which:

[0038]

[0032] [Fig. 1] illustrates an electronic circuit comprising a set of two transformers according to a first embodiment,

[0039] [Fig. 2] illustrates an electronic circuit comprising a set of two transformers according to a second embodiment.

[0040]

[0033] DETAILED DESCRIPTION OF THE INVENTION

[0041]

[0034] As will become apparent from reading this description, the embodiments of the invention offer the possibility of having two transformers for a reduced footprint, both in terms of volume and surface area occupied, by implementing a common cooling solution.

[0042]

[0035] Embodiments of the invention use a symmetrical structure which allows the fixing of two planar transformers, for example by screwing, clipping or otherwise.

[0043]

[0036] Figure 1 illustrates a first embodiment of an assembly 3 of two planar transformers 1 and 2. Figure 1 is a cross-sectional view of the assembly.

[0044]

[0037] A first magnetic core 11 of the first transformer 1 (for example, made of ferrite – other materials are possible) is composed of two parts. A first part 111 is attached to a second part 112 after a printed circuit board 12 has been inserted into it. In some embodiments, the first magnetic core 11 consists exclusively of the joining of the first and second parts. A second magnetic core 21 of the second transformer 2 (for example, made of ferrite – other materials are possible) is composed of two parts. It is separate from the first magnetic core 11. A first part 211 is attached to a second part 212 after a printed circuit board 22 has been inserted into it. In some embodiments, the second magnetic core 21 consists exclusively of the joining of the first and second parts.

[0045]

[0038] The second part 112 of the first magnetic core 11 has a base from which branches 1121 extend through the printed circuit board 12 to make contact with the first part 111 in order to join the two parts. The base of the second part 112 has, for example, a generally parallelepiped shape. It can take other forms. Generally, the base of the second part 112 has a rectangular cross-section along a horizontal length in the plane shown in Figure 1. The branches 1121 extend from this base towards the first part 111 in a vertical direction in the plane shown in Figure 1. The branches 1121 also extend in a direction transverse to the rectangular cross-section, that is, in the direction orthogonal to the plane representing the assembly in Figure 1.For example, the branches 1121 have an overall parallelepiped shape, with a length in the transverse direction shown in Figure 1. Thus, the second part 112 of the first magnetic core 11 has a general "E" shape. That is, its cross-section in a plane of the assembly forms a comb resembling the letter "E". The branches 1121 of the second part 112 from its base form the arms of the "E" comb. The number of arms is not limited to three. Thus, for example, Figure 1 illustrates an assembly with four arms.

[0046]

[0039] The first part 111 has a generally parallelepiped shape. It can take other forms. Generally, the first part 111 has a rectangular cross-section along a horizontal length (in the shape of an "I") in the plane illustrated by Figure 1. The dimensions of the first part 111 are, for example, close to those of the base of the second part 112. The branches 1121 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.

[0047]

[0040] The first and second parts 111 and 112 are joined together by any suitable means, for example at the ends of the branches 1121 of the second part 112. Such a means may, for example, be a layer 6 of glue or thermal paste.

[0048]

[0041] As already indicated, the branches 1121 of the second part 112 pass through the printed circuit board 12. Thus, the first and second parts 111 and 112 form a magnetic core 11 for the printed circuit board 12. The printed circuit board 12 has an insulating material and carries electrically conductive tracks forming flat windings printed on it. Each of the windings surrounds at least part of the magnetic core 11. It thus defines a first transformer 1 with the magnetic core 11 around which the conductive tracks are wound. One conductive track forms a primary winding and another track forms a secondary winding. In some embodiments, the printed circuit board 12 may comprise a single primary winding and two secondary windings.

[0049]

[0042] The second magnetic core 21 of the second transformer 2 has the same structure as that described previously for the core 11 of the first transformer 1. A first "I"-shaped portion 211 encloses a magnetic circuit of a second "E"-shaped portion 212. This second core 21, together with the printed circuit board 22, forms the second transformer 2. The branches 2121 of the second portion 212 pass through the printed circuit board 22.

[0050]

[0043] The assembly 3 of the two transformers further includes a heat transfer device 4, which may be in the form of a heat-conducting plate. In the example of Figure 1, the heat transfer device 4 is implemented using an additional printed circuit board 8, which will be described later, but other variations are possible in which the heat transfer device is implemented by means other than said board 8, for example, using an aluminum plate or other material, or as described with reference to Figure 2. The transformers 1 and 2 are in thermal contact with this heat transfer device 4, via a thermal interface 7, to allow their cooling.The transformers are arranged on either side of the heat transfer device 4 along an axis along which these transformers 1, 2 follow one another, and the transformers are in contact with opposite sides of the heat transfer device 4.

[0051]

[0044] The heat transfer device 4 is common to both transformers 1, 2. Each transformer is thermally connected to the heat transfer device 4 via the second part 112, 212 in the shape of “E” of their respective core 11, 21. Thus, the second parts 112, 212 are thermally connected to the heat transfer device 4, for example via a thermal interface 7.

[0052]

[0045] Each printed circuit board 12, 22 can be electrically connected to an additional printed circuit board 8, thus forming an electronic circuit 9. The additional printed circuit board 8 allows the transformers 1, 2 to be controlled. For example, this additional printed circuit board 8 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]

[0046] In the example in Figure 1, the heat transfer device 4 includes the additional printed circuit board 8.

[0054]

[0047] In the example shown, a cooling device, for example, a metal case 5, is in thermal contact with the heat transfer device 4. For example, the case 5 houses the second transformer 2. The cooling device 5 allows good heat dissipation from the transformer assembly 3 while maintaining a small footprint.

[0055]

[0048] Generally, the cores 11, 21 of the thermal transformer assembly 3 are in thermal contact with the heat transfer device 4. This thermal contact can be achieved via a thermal interface 7 to improve heat transfer. The cooling device can be in thermal contact with the metal casing 5.

[0056]

[0049] To secure the assembly, means for fastening the transformers 1, 2 may be provided. For example, clips 15 may be provided to hold the transformers together and ensure thermal contact with the heat transfer device 4. Similarly, screws 14 may be provided for the same purpose. The screws 14 pass through the cores 11, 21, for example at the branches 1121, 2121 thereof. The clips 15 hold the transformer assembly 3 from the outside, without passing through the cores 11, 21.

[0057]

[0050] The gaps present in the transformer assembly 3 can be filled by a layer of material 6.

[0058]

[0051] This material 6 may be present between at least one part of a printed circuit board 12, 22 and the magnetic core 11, 21. This material is, for example, a thermal paste that allows for better heat transfer within the assembly to dissipate it. It may also be a thermal adhesive that improves the strength of the assembly. All or part of the gaps may be filled. Thus, in the example of Figure 1, the gap between the first printed circuit board 12 and the base of the second part 112 of the first magnetic core 11 is filled. The same is true for the gap between the second printed circuit board 22 and the base of the second part 212 of the second magnetic core 21. The gaps between the first and second printed circuit boards 12, 22 and respectively the first parts 111, 211 of the first and second magnetic core 11, 21 are not filled.Indeed, heat transfer to the second part 112 is preferred because it is in contact with the heat transfer device 4. As illustrated by the arrows, heat transfer occurs from the first and second printed circuit boards 12, 22 to the heat transfer device 4 and from the first part 211 of the second magnetic core 21 to the metal case 5.

[0059]

[0052] Figure 2 illustrates a second embodiment. The elements common to the first embodiment are identified by the same reference numerals. In this example, the heat transfer device 4 comprises one or more heat pipes. 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. The chamber contains a working fluid with a low boiling point. For example, it is a vapor chamber. The properties of this device can, for example, be less than 500 W / cm². 2 , preferably less than 20 W / cm² 2

[0060]

[0053] In this embodiment as well, each printed circuit board 12 and 22 can be connected to an additional printed circuit board 8, thus forming an electronic circuit 9. The additional printed circuit board 8 allows the transformers 1 and 2 to be controlled. For example, this additional printed circuit board 8 may include electronic components specific to power control. It may also include electronic components specific to controlling the connection and disconnection of electrical signals. The first and second printed circuit boards 12 and 22 are connected to the additional printed circuit board 8 via connection means 16.

[0054] 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 DC / DC voltage converter for the vehicle's on-board network (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.

[0061]

[0055] 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.

[0062]

[0056] To satisfy specific needs, a person competent in the field of the invention may apply modifications or adaptations.

[0063]

[0057] 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. Assembly of transformers (3) comprising a first (1) and a second (2) planar transformers and a heat transfer device (4), the first transformer (1) comprising a first magnetic core (11) and at least one first printed circuit board (12) associated with the first magnetic core (11), the second transformer (2) comprising a second magnetic core (21) distinct from the first magnetic core (11) and at least one second printed circuit board (22) associated with the second magnetic core (21), each printed circuit board (12, 22) comprising: - at least one layer of electrically insulating material and at least one first and 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 part of the magnetic core associated with the printed board, the two planar transformers (1, 2) following one another along an axis and the heat transfer device (4) being disposed between the two planar transformers (1, 2) along this axis, in thermal contact with each of the transformers, the first planar transformer being disposed on one first side of the heat transfer device and the second planar transformer being disposed on a second side of the heat transfer device, opposite the first side.

2. Assembly of transformers according to claim 1, the magnetic core (11, 21) of each planar transformer (1, 2) comprising a first part (111, 211), said to be E-shaped, and a second part (112, 212) said to be I-shaped.

3. Assembly of transformers according to claim 2, the magnetic core (11, 21) of each planar transformer (1, 2) being formed by the union of the first part (111, 211), known as E-shaped, and the second part (112, 212), known as I-shaped.

4. Assembly of transformers according to any one of the preceding claims, comprising a metal casing (5) surrounding the second transformer, said casing being in thermal contact with the heat transfer device.

5. Assembly of transformers according to the preceding claim comprising a thermal interface material between at least a portion of the magnetic core of the first transformer and the metal casing.

6. Transformer assembly according to any one of the preceding claims comprising a layer of thermal paste (6) between at least a part of at least one printed circuit board and the associated magnetic core.

7. Assembly of transformers according to any one of the preceding claims comprising a thermal interface material (7) between at least a portion of the magnetic core of at least one transformer and at least a portion of the heat transfer device.

8. Assembly of transformers according to any one of the preceding claims, comprising a cooling device (5), separate from the heat transfer device (4), and which allows the heat transferred by the heat transfer device (4) to dissipate.

9. Assembly of transformers according to any one of the preceding claims wherein the heat transfer device is a steam chamber or comprises a heat pipe.

10. Electronic circuit (7) comprising at least one set of transformers (3) according to any one of the preceding claims and at least one additional printed circuit board (8), the set of transformers (3) being connected to the additional printed circuit board (8).

11. Electronic circuit according to claim 10, the transformer assembly being according to any one of claims 1 to 8, the heat transfer device being defined by the additional printed circuit board (8).

12. Electronic circuit according to claim 10 or 11, wherein each printed circuit board comprises: - a single primary winding, and - two secondary windings.

13. 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 electronic component comprising an electronic circuit (9) according to any one of claims 10 to 12, the first transformer (1) belonging to the electrical energy storage unit charger and the second transformer (2) belonging to the DC / DC voltage converter.

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