Planar transformer

Abstract

The invention relates to a planar electrical transformer (1) comprising at least one assembly (11) of two folded, cut conductive metal strips (110, 110'), each conductive metal strip (110, 110') comprising at least one helical transfer region (112, 112'), and a magnetic core (10) at least partially surrounding said at least one assembly (11). Figure 2

Description

Title of the invention: Planar transformer

[0001] The invention relates to planar electrical transformers.

[0002] Electrical transformers, essential components in many electronic devices, are devices for increasing or decreasing an alternating voltage using electromagnetic coupling between coils. They generally consist of a primary winding and a secondary winding around a magnetic core. The energy from the primary is transferred to the secondary by electromagnetic induction via the magnetic core.

[0003] In a traditional transformer, the primary winding is made using a conductive wire, often copper. A portion of this wire forms a coil wound around the magnetic core, comprising a certain number of turns. Each turn of the coil corresponds to a loop of the wire. Similarly, the secondary winding is composed of another wire, a section of which is also wound around the magnetic core, forming a series of turns.

[0004] In the case of planar transformers, unlike traditional designs, the coils adopt a flat, or planar, shape and are made of flat conductive elements rather than loops of wire.

[0005] It is known to print the coil of a transformer in the form of a pattern on a planar substrate such as a printed circuit board (PCB). Although this solution has a very small footprint, it does not allow the use of high intensity currents, in particular greater than 100 Amps.

[0006] It is also known to use unitary plates in the shape of a "U" made of copper or aluminum which allow working at high intensities greater than or equal to 100 Amperes. However, the plates require interconnections in order to form turns, and these interconnections are voluminous. Thus, the number of turns in this solution is reduced compared to patterns on PCB, with a low number of turns, which reduces the transmission efficiency and the frequency response.

[0007] There is therefore a need for a planar electrical transformer which allows both operation at high intensities while allowing good transmission efficiency and frequency response.

[0008] To this end, the invention relates to a planar electrical transformer comprising • at least one assembly of two folded cut conductive metal strips, each conductive metal strip comprising at least one helical-shaped transfer region, and • a magnetic core at least partially surrounding said at least one assembly.

[0009] Thanks to the use of folded cut conductive metal strips, the planar electrical transformer of the invention makes it possible to combine the advantages of unitary plates and those of a pattern on a planar substrate: it is thus possible to work at intensities greater than 100 Amperes while maintaining good transmission efficiencies. Indeed, the folding of the strips makes it possible to do without the necessary interconnections between the unitary plates, and to save volume, which makes it possible to increase the number of turns for the same overall volume of the transformer and therefore its transmission capacities. In addition, the possible width of the strips makes it possible to work at intensities equivalent to those of the unitary plates.Finally, the assemblies of the invention make it possible to optimize the leakage inductance and the capacities according to the needs by a range of possibilities offered in the variation of arrangement of the cut strips folded between them within an assembly.

[0010] According to one embodiment of the invention, said at least one transfer region of a conductive metal strip comprises a repetition of folding units, each folding unit forming at least part of a turn of the helical shape and each folding unit being delimited from another folding unit by a folding zone.

[0011] According to one embodiment of the invention, each conductive metal strip of an assembly comprises the same number of transfer regions.

[0012] According to one embodiment of the invention, said at least one transfer region of one of the conductive metal strips of an assembly is at least partially nested with a transfer region of the other conductive metal strip of the assembly.

[0013] According to one embodiment, said at least one transfer region of one of the conductive metal strips of an assembly is superimposed on a transfer region of the other conductive metal strip of the assembly.

[0014] According to one embodiment, the transformer comprises at least two assemblies, and at least two assemblies are superimposed on each other.

[0015] According to one embodiment, at least one of the conductive metal strips of an assembly comprises at least two transfer regions, and where at least two of the transfer regions of the same conductive metal strip are connected in series.

[0016] According to one embodiment, at least one of the conductive metal strips of an assembly comprises at least two transfer regions, and where at least two of the transfer regions of the same conductive metal strip are connected in parallel.

[0017] According to one embodiment, at least one of the two conductive strips of an assembly is covered by an insulator.

[0018] According to one embodiment, the transformer comprises at least two assemblies, where in each assembly one of the conductive strips is a primary and the other conductive strip is a secondary, and where the primary strips of at least two of the assemblies are connected to each other in series or in parallel and / or their secondary strips are connected to each other in series or in parallel. Brief description of the figures

[0019] The invention will be better understood on reading the following description given solely by way of example and with reference to the appended drawings in which:

[0020] [Fig.l] represents an exploded view (A) and an isometric view (B) of a planar electrical transformer according to the invention.

[0021] [Fig. 2] represents three steps (A, B and C) of cutting a conductive strip of a transformer assembly according to a first embodiment of the invention. In Figure 2A is represented a conductive strip in the raw state. In Figure 1B is represented the same strip but where the areas corresponding to the offcuts and that corresponding to the final cut strip are visible. Figure 2C represents the cut strip.

[0022] [Fig. 3] illustrates the folding of the cut strip of Fig. 2C. Fig. 3A shows the strip before folding with an annotation of the fold lines. In Fig. 3B, the strip of Fig. 3A is shown in the folded state along the fold lines.

[0023] [Fig. 4] illustrates a second embodiment of a conductive strip of a transformer assembly according to the invention. In Figure 4A is shown a conductive metal strip on which are shown the areas delimiting the offcuts from that of the final cut strip. In Figure 4B is shown the cut strip thus obtained with an annotation of the fold lines. In Figure 4C is shown the strip of Figure 4B folded along the fold lines.

[0024] [Fig. 5] represents three configurations (A, B and C) of pairs of cut strips of [Fig. 2] before their folding in order to form an assembly of a transformer according to the invention. In Figure 5A, the cut strips are superimposed with an absence of offset, so that all of the turns formed by one of the strips is nested in the turns of the other strip once the two strips are folded. In Figure 5B, the cut strips are superimposed with an offset corresponding to a half turn, so that a half turn of each strip is not nested in a turn of the other strip once the two strips are folded. In Figure 5C, the cut strips are superimposed with an offset corresponding to one turn, so that a turn of each strip is not nested in a turn of the other strip once the two strips are folded.

[0025] [Fig.6] represents the capacitance and leakage inductance (on the ordinate) of several assembly configurations of a transformer according to the invention (on the abscissa). Option No. 2 corresponds to a transformer comprising an assembly with cut strips folded according to the configuration of Figure 5A. Option No. 3 corresponds to a transformer comprising an assembly with cut strips folded according to the configuration of Figure 5B. Option No. 4 corresponds to a transformer comprising an assembly with cut strips folded according to the configuration of Figure 5C. Option No. 5 corresponds to a transformer comprising an assembly with strips cut and superimposed on each other with an offset of two turns before being folded. Option No. 6 corresponds to a transformer comprising an assembly with strips cut and superimposed on each other only after their respective folding. The number after "Cr" and "Lf" refers to the corresponding option. The solid line represents a smoothing of the values ​​obtained for the capacities.The dotted line represents a smoothing of the values ​​obtained for the leakage inductances.

[0026] [Fig.7] represents the capacitance and leakage inductance (on the ordinate) of different assembly combinations of [Fig.6] whose folded cut strips are connected in parallel two by two (on the abscissa). The solid line represents a smoothing of the values ​​obtained for the capacitances. The dotted line represents a smoothing of the values ​​obtained for the leakage inductances.

[0027] [Fig.8] represents the capacitance and leakage inductance (on the ordinate) of different assembly combinations of [Fig.6] whose folded cut strips are connected in series two by two (on the abscissa). The solid line represents a smoothing of the values ​​obtained for the capacitances. The dotted line represents a smoothing of the values ​​obtained for the leakage inductances. Detailed description of the invention

[0028] The following embodiments are examples. Although the description refers to one or more embodiments, this does not necessarily mean that each reference relates to the same embodiment, or that the features apply only to a single embodiment. Simply features of different embodiments may also be combined and / or interchanged to provide other embodiments.

[0029] The invention relates to a planar electrical transformer 1. As shown in [Fig.l], said transformer 1 comprises a magnetic core 10 within which is arranged at least one assembly 11 comprising two conductive strips 110, 110'.

[0030] The strips 110, 110' are in particular made of copper, aluminum or an alloy of these materials.

[0031] Each conductive strip 110, 110' has two free ends 111, 111', at which are in particular contact blades, which provide a connection with an electrical circuit. The ends 111, 111' of a strip 110, 110' may have the same shape or a different shape, in particular configured to allow an offset between them once the strip 110, 110' is folded. This offset between the ends 111, 111' makes it possible in particular to work with high voltages of several hundred Volts while limiting interference.

[0032] Each strip 110, 110' comprises at least one transfer region 112, 112' of helical shape. One of the strips 110 of an assembly 11 is called "primary" and generates a magnetic field within each of its transfer regions 112, which induces an electric current in the other strip 110', called "secondary", by receiving a magnetic field at the level of at least one of its transfer regions 112'. The transfer regions 112 of the primary strip 110 may be intended to induce an electric current in various secondary strips 110' belonging to different assembly 11, or else to another strip 110 alone. Conversely, different transfer regions 112 of a primary strip 110 may be intended to induce an electric current at the level of the same transfer region of the secondary strip 110' of the same assembly 11.For example, one strip 110 may have two transfer regions 112 that sandwich a transfer region 112' of the other strip 110'. These various aspects will be described later.

[0033] The primary strip 110 and the secondary strip 110' of an assembly 11 may have the same shape or different shapes. In particular, the transfer region(s) 112 of one of the strips 110, 110' of an assembly 11 may have different lengths, so that one of the two strips 110, 110' has more turns than the other. The primary strip 110 and the secondary strip 110' may be independently covered with a layer of an insulator, in particular with a thickness of a few microns to 20 microns. Typically, the insulator is a polyimide such as Kapton®, polyethylene terephthalate, paper, a muscovite or phlogopite mica paper composite or even an aluminum oxide.

[0034] We will now turn to [Fig. 2] which illustrates the production of a strip 110 cut according to the first embodiment and the different regions which compose it. The following description is described in relation to a primary strip 110 and applies mutatis mutandis to a secondary strip 110'. In Figure 2A is shown a raw strip 113 of a metallic material. From this raw strip 113 will be cut a strip 110. Figure 2B illustrates the cutting zones which delimit the shape of the strip 110 cut from the offcuts 114 (hatched parts). Figure 2C represents the cut strip 110. In this figure we can see the two ends 111 of the strip 110 and between the two the transfer region 112.

[0035] As can be seen in this figure, the transfer region 112 comprises a repetition of folding unit 115 along the length of the strip 110. As shown in this example, the transfer region 112 may also comprise a portion of at least one of the ends 111 when the latter has a shape participating in the helical shape.

[0036] The folding units 115 of the same transfer region have the same shape. The adjacent folding units 115 are in particular arranged in a different direction or in the same direction. The shape of a folding unit 115 corresponds to at least part of a turn of a coil so that all of the folding units, once folded together, form a succession of turns giving a helical shape. By "helical shape", is meant here any shape of coil, in particular square, circular or even ovoid coils. Each folding unit 115 forms in particular a half-turn or a whole turn. The central lumen and the periphery of the helical shape may have, independently of one another, a circular, ovoid, square or even rectangular shape. They are in particular adapted to the shape of the parts of the magnetic core 10 which they are opposite.

[0037] In the example shown, each folding unit 115 has an “L” shape corresponding to the shape of a half-turn, which is arranged at 90 degrees to the adjacent folding unit(s) 115. The distinction between the folding units 115 appears clearly in FIG. 3A. In this figure, the folding lines 116 arranged in the center of folding zones 117 which separate each folding unit 115 are also shown. Each folding unit 115 is framed by two folding zones 117, in particular also those adjacent to the ends 111 of the strip 110. As can be seen here, the folding lines and the folding zones 117 are in particular perpendicular to the length of the unfolded cut strip 110. Each fold line 116 corresponds to one of the edges of a turn of the helical shape, as seen in Figure 3B where the strip 110 is shown once folded.In this figure 3B, it can be seen that each folding unit 115 is in a plane parallel to that of the other units 115, and that a turn is indeed formed by two units 115. The folding lines 116 are at the center of a folding zone 117 where the strip 110 has a curved shape. The folding of the successive units 115 is done in an opposite direction around each folding line 116, so that the folded shape of the strip 110 corresponds to a crushed accordion.

[0038] In [Fig.4] a second embodiment of a strip 110 is shown, also shown in [Fig.l]. In this embodiment, each unit 115 has a “U” shape, and is arranged at 180° from the adjacent unit 115 or units 115. Here also, as shown in Figure 4C, a turn is formed by folding two adjacent units 115 along the fold line 116 separating them. As can be seen, the folding zone 117 corresponds only to a part of the height of the “U” shape of the folding units 115. In the example shown, the ends 111 are not part of the transfer region 112.

[0039] When a strip 110 comprises several transfer regions 112, these different transfer regions 112 can be electrically connected in parallel or in series. The two strips 110 of the same assembly 11 can have several regions electrically arranged in different configurations. In particular, within an assembly, one of the strips 110 can comprise two transfer regions 112 in parallel, while the other strip 110' can comprise two transfer regions 112' in series. When several transfer regions 112 are arranged in series, they are in particular separated by a connection region framed by two folding zones 117. The connection region can comprise any shape, and can in particular be partially included in at least one of the two transfer regions 112 when its shape participates in the helical shape of said transfer region 112.When several transfer regions 112 are arranged in parallel, their respective ends corresponding to the input of the electric current are connected to each other, and similarly for their respective ends corresponding to the input of the electric current.

[0040] The transfer region(s) 112, 112' of the strips 110, 110' of an assembly 11 may be independently superimposed on each other or at least partially intercalated. These different configurations make it possible to adapt the parameters of the assembly 11 in terms of leakage induction and capacitance to the desired needs, as will be described in detail later. In all cases, the transfer regions 112, 112' of the two strips 110, 110' are assembled so that their respective geomagnetic axes coincide.

[0041] We will now turn to [Fig. 5] which represents several superposition configurations, before their folding together into an assembly, of two cut strips 110, 110' where the transfer regions 112, 112' are at least partially interposed.

[0042] Nevertheless, the intercalation between the transfer regions 112, 112' of two strips 110, 110' can also be obtained by respectively folding the two strips 110, 110' independently, then by intercalating their respective turns of the transfer regions 112, 112' according to the desired configuration. A superposition of the strips 110, 110' will be preferred before a common folding. Indeed, when the transfer regions 112, 112' are superimposed upstream, their folds match so that the contact between the two regions 112, 112' is optimized. This aspect makes it possible to reduce the induction of leakage, compared to the strips 110 which would first be folded then intercalated one inside the other at their transfer region 112, 112'. Thus, according to one embodiment of the invention, the transfer regions 112, 112' of the two strips 110, 110' fit over the entire length of the parts of the strips for which they are interposed.

[0043] When the strips 110, 110' are superimposed on each other before a common folding, they are arranged so that the folding lines of the two strips are consistent, in order to prevent the folding of one of the two strips 110 from causing folding on the other in an undesired area.

[0044] In the examples shown in [Fig. 5], the strips 110, 110' have the same shape and are arranged head to tail. Alternatively, the strips 110, 110' may be arranged in the same direction. Since in this example their ends 111, 111' have a different shape, the head to tail arrangement makes it possible to obtain an offset between these ends 111, 111' once the two strips 110, 110' are folded. In these examples, the strip 110 arranged "below" will be considered primary and the strip 110' arranged above will be considered secondary.

[0045] In Figure 5A, the two strips 110, 110' are superimposed with consistency of all their fold lines 116, 116' which are also superimposed so that the turns of the respective strips 110, 110', once folded, do not have any offset. In Figure 5B, the two strips 110, 110' are offset such that their fold lines 116, 116' are offset by one unit 115, 115'. Thus, the first fold line 116 of the primary strip 110 is not aligned with a fold line 116' of the secondary strip 110'. The second fold line 116 of the primary strip 110 is aligned with the first fold line 116' of the second strip 110', and so on. In the end, a half-turn offset is obtained between the transfer regions 112, 112' once the two folded strips 110 are obtained.As shown, the alignment between the fold lines 116, 116' may not be strict, so that a slight offset may be present, in particular of the thickness of the primary strip 110, which makes it possible to anticipate the final offset in the assembly 11 corresponding to the thickness of the primary strip 110. In FIG. 5C, the superposition of the two strips 110, 110' is carried out with an offset of the fold lines 116, 116') by two units 115, 115', so as to obtain an offset of one turn between the transfer regions 112, 112' once the two folded strips 110, 110'.

[0046] In [Fig. 6] are illustrated the capacitance and leakage inductance values ​​of several configurations of assemblies 11. Option No. 2 corresponds to an assembly 11, with cut strips 110, 110' folded according to the configuration of Figure 5A. Option No. 3 corresponds to an assembly 11 with cut strips 110, 110' folded according to the configuration of Figure 5B. Option No. 4 corresponds to an assembly 11 with cut strips 110 folded according to the configuration of Figure 5C. Option No. 5 corresponds to an assembly 11 with cut strips 110, 110' and superimposed on each other with an offset of two turns before being folded together. Option No. 6 corresponds to an assembly 11 with strips 110, 110' cut and then folded respectively before being superimposed on each other. As [Fig. 6] distinctively shows, the greater the number of turns of the transfer regions 112, 112' of the strips 110, 110' interposed between them, the higher the capacitance value and the lower the leakage inductance value, and vice versa. The intermediate value for these two parameters is obtained for an equivalent number of interposed turns and turns alone (i.e. which are not arranged opposite the turns of the other strip 110, 110') between the two transfer regions 112, 112' of the two strips 110, 110'.

[0047] According to one embodiment of the invention, the transformer 1 comprises at least two assemblies 11. In particular, at least two of the assemblies 11 are superimposed on each other (same geomagnetic axis), or side by side (parallel geomagnetic axes).

[0048] The configuration of the strips 110, 110' in each assembly 11 may be different, in particular with the aim of obtaining particular values ​​in terms of overall capacitance and leakage induction. Furthermore, the primary strips 110 and the secondary strips 110' of the assemblies 11 may be connected to each other respectively in series or in parallel. The series or parallel connection also makes it possible to vary the capacitance and leakage induction values.

[0049] Figures 7 and 8 illustrate the values ​​of capacitance and overall leakage induction obtained with several examples of assembly combination 11 where one of the two corresponds to option No. 2 and the other to option No. 2, No. 4 or No. 6. In [Fig. 7], the primary and secondary strips 110, 110' of the two assemblies 11 are respectively connected to each other in parallel. In [Fig. 8], the primary and secondary strips 110, 110' of the two assemblies 11 are respectively connected to each other in series. For the same sets of configurations of two assemblies, it is noted that placing the primary strips 110 and the secondary strips 110' in parallel makes it possible to increase the capacitance value, while placing them in series makes it possible to reduce the capacitance value and increase the leakage inductance.

[0050] Equivalent results can also be obtained with a single assembly 11 where each strip 110, 110' comprises two transfer regions 112, 112' in parallel (for [Fig.7]), or two transfer regions 112, 112' in series (for [Fig.8]).

[0051] According to one embodiment of the invention, the transformer 1 may further comprise an additional coil associated with at least one of the assemblies 11, in particular in the form of a cut and folded strip 110, 110'. This additional coil may be a primary or a secondary depending on requirements.

Claims

Claims

1. Planar electrical transformer (1) comprising • at least one assembly (11) of two folded cut conductive metal strips (110, 110'), each conductive metal strip (110, 110') comprising at least one transfer region (112, 112') of helical shape, and • a magnetic core (10) at least partially surrounding said at least one assembly (11).

2. An electrical transformer (1) according to claim 1, wherein said at least one transfer region (112) of a conductive metal strip (110, 110') comprises a repetition of folding units (115, 115'), each folding unit (115) forming at least part of a turn of the helical shape and each folding unit (115, 115') being delimited from another folding unit (115, 115') by a folding zone (117).

3. An electrical transformer (1) according to claim 1 or 2, wherein each conductive metal strip (110, 110') of an assembly (11) comprises the same number of transfer regions (112, 112').

4. An electrical transformer (1) according to claim 1 to 3, wherein said at least one transfer region (112, 112') of one of the conductive metal strips (110, 110') of an assembly (11) is at least partially interleaved with a transfer region (112, 112') of the other conductive metal strip (110, 110') of the assembly (11).

5. Electrical transformer (1) according to one of claims 1 to 4, wherein said at least one transfer region (112, 112') of one of the conductive metal strips (110, 110') of an assembly (11) is superimposed on a transfer region (112, 112') of the other conductive metal strip (110) of the assembly (11).

6. Electrical transformer (1) according to one of claims 1 to 5, the transfer regions (112, 112') of the two strips (110, 110') fit over the entire length of the parts of the strips (110, 110') for which they are interposed.

7. Electrical transformer (1) according to one of claims 1 to 6, in which at least one of the conductive metal strips (110, 110') of an assembly (11) comprises at least two transfer regions

8.

9.

10. (112, 112'), and where at least two of the transfer regions of a same conductive metal strip (110, 110') are connected in series. Electrical transformer (1) according to one of claims 1 to 7, wherein at least one of the conductive metal strips (110, 110') of an assembly (11) comprises at least two transfer regions (112, 112'), and where at least two of the transfer regions of a same conductive metal strip (110, 110') are connected in parallel. Electrical transformer (1) according to one of claims 1 to 8, wherein at least one of the two conductive strips (110, 110') of an assembly (11) is covered by an insulator. Electrical transformer (1) according to one of claims 1 to 9, comprising at least two assemblies (11), where in each assembly (11) one of the conductive strips (110) is a primary and the other conductive strip (110') is a secondary, and where the primary strips (110) of at least two of the assemblies (11) are connected to each other in series or in parallel and / or their secondary strips (110') are connected to each other in series or in parallel.

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