EP3893256A1

EP3893256A1 - Semi-planar transformer

Info

Publication number: EP3893256A1
Application number: EP20168512.0A
Authority: EP
Inventors: Manuel Escudero Rodriguez; Matteo-Alessandro Kutschak; David Meneses Herrera
Original assignee: Infineon Technologies Austria AG
Current assignee: Infineon Technologies Austria AG
Priority date: 2020-04-07
Filing date: 2020-04-07
Publication date: 2021-10-13

Abstract

A transformer comprises a first winding and a second winding. The first winding comprises at least one metal plate. The second winding comprises at least two winding turns of a wire. The wire traverses the metal plate and the winding turns are arranged on opposite sides of the metal plate.

Description

Technical Field

This disclosure relates generally to the field of transformers, and in particular to the field of semi-planar transformers.

Background

Transformers are widely used in electronic equipment. A variety of different transformer designs is known in the art in view of different types of transformer windings or transformer cores. The transformer design affects the transformer efficiency as well as the cost of manufacture of the transformer. In general, a transformer in which a coil needs to be wound by hand is more expensive than a transformer design that allows the core windings to be applied by automated manufacturing.

Summary

According to an aspect of the disclosure a transformer comprises a first winding and a second winding. The first winding comprises at least one metal plate. The second winding comprises at least two winding turns of a wire. The wire traverses the metal plate. The winding turns are arranged on opposite sides of the metal plate.
According to another aspect of the disclosure, an electrical device comprises a circuit carrier and a transformer mounted on the circuit carrier. The transformer comprises a first winding and a second winding. The first winding comprises at least one metal plate. The second winding comprises at least two winding turns of a wire. The wire traverses the metal plate. The winding turns are arranged on opposite sides of the metal plate. The circuit carrier is provided with a first winding interconnect which is configured to electrically connect the metal plates.
According to still another aspect of the disclosure, a method of manufacturing a transformer comprises arranging at least one metal plate as a first winding of the transformer. A wire is provided as a second winding of the transformer. At least a first wire turn is wound adjacent to a first side of the metal plate. The metal plate is traversed by the wire. At least a second wire turn is wound adjacent to a second side of the metal plate opposite the first side of the metal plate.

Brief description of the drawings

The elements of the drawings are not necessarily to scale relative to each other. Like reference numerals designate corresponding similar parts. The features of the various illustrated embodiments can be combined unless they exclude each other and/or can be selectively omitted if not described to be necessarily required. Embodiments are depicted in the drawings and are exemplarily detailed in the description which follows.

Figure 1A is a schematic top view of an exemplary transformer illustrating a planar winding and two turns of a helical winding.
Figure 1B is a schematic side view from the viewing direction V of the exemplary transformer of Figure 1A.
Figure 2A is a top view of an exemplary transformer having a shell type core.
Figure 2B is a bottom view of the exemplary transformer of Figure 2A.
Figure 2C is a perspective view of the exemplary transformer of Figure 2A and Figure 2B.
Figure 3 is a schematic top view of an exemplary transformer illustrating a planar winding including a plurality of metal plates and a single layer helical winding formed by a wire.
Figure 4 is a schematic top view of an exemplary transformer illustrating a planar winding including a plurality of metal plates and a two layer helical winding formed by a wire.
Figure 5 is a side view of the exemplary transformer of Figure 4 from cutting line A-A of Figure 4.
Figure 6 is a schematic top view of an exemplary transformer illustrating a planar winding including a plurality of metal plates and a three layer helical winding formed by a wire.
Figure 7 is a schematic illustration of a single layer helical winding design.
Figure 8 is a schematic illustration of a double layer helical winding design.
Figure 9A is a schematic perspective view of an example of a semi-planar transformer.
Figure 9B is a schematic side view of the semi-planar transformer of Figure 9A.
Figure 9C is a plan view of a metal plate forming part of the first winding.
Figure 9D is a schematic side view of the metal plate of Figure 9C.
Figure 10 is a perspective top view on an exemplary transformer having a transformer-internal first winding interconnect configured to electrically connect the metal plates.
Figure 11 is a perspective bottom view of a circuit carrier on which an exemplary transformer is mounted, wherein the circuit carrier provides for a transformer-external first winding interconnect.
Figure 12 is diagram illustrating the efficiency of a DC-DC voltage converter using a transformer in accordance with the disclosure.
Figure 13 is a flowchart of an exemplary method of manufacturing a transformer in accordance with the disclosure.

Detailed description

It is to be understood that the features of the various exemplary embodiments and examples described herein may be combined with each other, unless specifically noted otherwise.
As used in this specification, the terms "electrically connected" or "electrically coupled" or similar terms are not meant to mean that the elements are directly contacted together; intervening elements may be provided between the "electrically connected" or "electrically coupled" elements, respectively. However, in accordance with the disclosure, the above-mentioned and similar terms may, optionally, also have the specific meaning that the elements are directly contacted together, i.e. that no intervening elements are provided between the "electrically connected" or "electrically coupled" elements, respectively.
In particular, transformers having a semi-planar design and manufacturing methods for transformers having a semi-planar design are described herein. Semi-planar means that at least one winding of the transformer is a planar winding while at least one other winding of the transformer is a non-planar winding.
Figures 1A and 1B illustrate an example of an exemplary transformer 100 including a planar winding and two turns of a non-planar winding. The at least one winding of the transformer 100 which is a planar winding is formed by a metal plate 120. The at least one winding of the transformer 100 which is a non-planar winding is formed by a wire 140.
The wire 140 has a first terminal 142 and a second terminal 144. The wire 140 may be a continuous wire 140. The wire 140 may have a constant thickness and/or metal line cross-section along its extension. The wire 140 typically is an electrically insulated wire (e.g. a sheathed wire cable) which may include an insulation foil covering a core metal line to prevent electrical contact to the metal plate 120 and/or any potential short circuit between wire portions of the second winding which is formed by the wire 140.
Further, the transformer 100 may include a magnetic core 160. The magnetic core 160 may run through the planar first winding and the helical second winding. Various different core designs are feasible and described in more detail further below.
Referring to Figure 1B, the metallic plate 120 may have the form of a ring segment 126. The ring segment 126 may have a cutout 126A. The cutout 126A separates opposite ends of the ring segment 126, i.e. makes the ring segment 126 to distinguish from a closed ring.
As shown in Figure 1B, the wire 140 traverses the metal plate 120 formed as a ring segment 126 through the cutout 126A at a traversal portion 146 of the wire 140. Differently put, the cutout 126A disconnecting the opposite ends of the ring segment 126 allows the wire 140 of the second winding to traverse the metal plate 120 so that at least one winding turn of the wire 140 is arranged on one side of the metal plate 120 and another winding turn of the wire 140 is arranged on the opposite side of the metal plate 120.
As illustrated in Figure 1B, the ring segment 126 may have a first terminal 122 and a second terminal 124 at the opposite ends of the ring segment 126. The first and second terminals 122, 124 may, e.g., protrude over the circumference 126C of the ring segment 126. A slit 130 may be formed between opposite sides of the first and second terminals 122, 124. The cutout 126C of the ring segment 126 may form a part of the slit 130 extending between the first and second terminals 122, 124.
The ring segment 126 may have a variety of different circumferential shapes. It may have a partly or fully circular shape as shown, e.g., in Figures 1B, 5 and Figures 9A-9C, respectively. It may further have, e.g., a partly or fully elliptical shape or a partly or fully polygonal, rectangular or quadratic shape, in particular with rounded corners.
It is to be noted that the term helical winding is used in a broad meaning in this disclosure. Helical may mean that the wire 140 of the second winding may intersect a plane defined by the metal plate 120. For instance, the winding turns of the wire 140 may be in at least two different planes which are parallel to the plane defined by the metal plate 120 of the planar first winding, while the traversal portion 146 may be inclined against this plane.
Referring to Figures 2A-2C, a transformer 200 may include a number N of metal plates, N being an integer equal to or greater than 2 and/or equal to or less than 3, 4, 5, 6, ..., 10, 20 .... In the example shown in Figures 2A-2C, e.g. N = 6 metal plates 120 are provided.
The metal plates 120 may be parallel to each other. Each metal plate 120 may be planar.
The winding turns of the wire 140 are arranged in the spaces between the metal plates 120. By way of example, M = N -1 spaces are defined by the metal plates 120. Each space may contain at least one turn of the wire 140.
If the second winding is a single layer helical winding, the transformer 200 may, e.g., include a number of M winding turns of the wire 140. If the second winding is a multi-layer helical winding, the total number of winding turns may, e.g., equal the number of layers times M.
The transformer 200 is, e.g., equipped with a shell type magnetic core 260. The shell type magnetic core 260 includes a central magnetic core 160 as depicted in Figures 1A-1B and a core shell enclosing the first winding (e.g. metal plate(s) 120) and the second winding (e.g. turns of wire 140) in the lateral dimensions. The core shell may be closed, i.e. may completely surround the first and second windings in the lateral dimensions.
In the embodiment shown in Figures 2A-2C, the metal plates 120 are each electrically separated (disconnected) from each other. In this case, the electrical connections between the metal plates 120 (i.e. the individual ring segments 126 forming the metal plates 120) will be provided by a transformer-internal or transformer-external interconnect (both not shown). This will be described in more detail further below in conjunction with Figures 10 and 11.
The wire 140 may form the primary winding of the transformer 200, while the metal plates 120 may form the secondary winding of the transformer 200. However, in other embodiments it is also possible that the first winding is the primary winding of the transformer 200 (i.e. the input winding) and that the second winding is the secondary winding of the transformer 200 (i.e. the output winding).
For example, the transformer 200 can be a component of a voltage converter configured to down-convert or up-convert a voltage Vin coupled to the primary winding to an output voltage Vout coupled to the secondary winding. The voltage converter may, e.g., be a DC-DC voltage converter or an AC-DC voltage converter or a DC-AC voltage converter or an AC-AC voltage converter.
The transformer 200 may be designed for a variety of different applications and technical requirements. By way of example, the wire 140 may have a metal line cross-section of equal to or greater than 0.7 mm² or 1.0 mm² or 1.3 mm².
The wire 140 may, e.g., be a litz wire containing a plurality of strands. The litz wire may, e.g., have 100 to 200 strands (in this example e.g. 175 strands) of a diameter of, e.g., 0.1 mm each.
Generally, the metal plates 120 may be individual parts which are prefabricated. A metal plate 120 may be formed in one piece, i.e. may be an integral part. A metal plate 120 may be a punched part. A metal plate 120 may have a thickness equal to or greater than or less than 0.3 mm or 0.5 mm or 0.7 mm or 0.9 mm.
The transformer 200 may, e.g., be equipped with a magnetic core 260 which is a prefabricated part. For example, a ferrite pot core (PQ) can be used. In this example, a PQ 35/28 is used. Other core sizes, such as, e.g., PQ 20/16, PQ 20/20, PQ 26/20, PQ 26/25, PQ 32/20, PQ 32/30, PQ 35/35, PQ 40/40, or PQ 50/50, are also feasible. Moreover, core geometries other than the PQ geometry may be used.
Referring to Figure 3, an exemplary transformer 300 may include a first winding which comprises a plurality of metal plates 120 forming a first planar winding, and a wire 140 forming a second winding which is a single layer helical winding. As apparent from Figure 3, the wire 140 runs through slits 130 arranged between opposite ends of the ring segments 126 of the metal plates 120. The opposite ends of the ring segments 126 may be shaped to form the first and second terminals 122, 124 of the ring segments 126. Similar as in transformer 200, e.g. a shell type magnetic core 260 may be used.
Referring to Figure 4, a transformer 400 may be equipped with a double-layer helical second winding. The second wire layer is indicated by reference sign 140'.
A side view of the transformer 400 from cutting line A-A of Figure 4 is shown in Figure 5. The wire 140' of the second wire layer is arranged radially atop the wire 140 of the first wire layer. In view of other features and characteristics of the transformer 400, reference is made to the description of the transformers 100, 200 and 300 to avoid reiteration.
Figure 6 illustrates a schematic top view of an exemplary transformer 600. The transformer 600 may be identical to transformers 200, 300, 400 except that a triple-layer helical winding as the second winding is used. The wire 140" of the third wire layer is arranged radially atop the wire 140' of the second wire layer. Again, reference is made to the description above in order to avoid reiteration.
All the examples of transformers 100, 200, 300, 400, 600 are semi-planar transformers. The semi-planarity of the transformer design allows the transformers to be manufactured by an automated manufacturing method. More specifically, the second winding of the transformers 100, 200, 300, 400, 600 may be wound around the magnetic core 160 by using an automated winding machine. This allows to significantly reduce the cost of manufacture of a semi-planar transformer as exemplified by transformers 100, 200, 300, 400, 600 disclosed herein.
In contrast, fully planar transformers, e.g. transformers which use a planar second wire winding, e.g. a wire winding which is not provided with the traversal portions 146, cannot be manufactured in an automated way. Rather, each winding turn of such planar second wire winding has to be applied separately by hand.
Referring to Figure 7, a single layer helical winding may consist of winding turns in an axial direction along a screw line (or with a slanted portion corresponding to the traversal portion 146). There is only one layer of winding turns. The double helical winding as illustrated in Figure 8 uses two layers of winding turns. Generally, a multi-layer helical winding may have the advantage over a single layer helical winding that it reduces eddy current loss in the wire 140.
Referring to Figure 9A, an exemplary transformer 900 may have a stacked design. The transformer 900 may comprise two transformers as described above (e.g. transformer 200) and, e.g., a resonant inductor 920. A schematic side view of the transformer 900 of stacked design with optional resonant inductor 920 is shown in Figure 9B.
A metal plate 120 forming part of the first winding of the transformer 900 (or any other transformer 100, 200, 300, 400, 600 disclosed herein) is illustrated in Figure 9C. The metal plate 120 may have an inner opening of radius R1, a circumference 126C of radius R2, first and second terminals 122, 124 of length D1 and width D2, and a slit 130 of width D3. A cutout 930 may be designed as a proximal partial broadening of the slit 130. The cutout 930 may have a width D4. The metal plate 120 may have a bottom half width D5.
By way of example, R1 = 7.3 mm and/or R2 = 10.25 mm and/or D1 = 6.0 mm and/or D2 = 4.0 mm and/or D3 = 2.5 mm and/or D4 = 6.0 mm and/or D 5 = 11.75 mm. All these dimensions are exemplary dimensions and may, e.g., be varied by equal to or less than ±50%, ±40%, ±30%, ±20%, or ±10%.
A thickness T of the metal plate 120 may, e.g., be 0.6 mm, see Figure 9D. The thickness T of the metal plate 120 may, e.g., be subjected to a same range of variation as specified above.
The transformer 100, 200, 300, 400, 600, 900 as described herein may be used as a LLC main transformer intended for use in, e.g., a high voltage DC-DC converter of a switch mode power supply (SMPS) for, e.g., telecom or industrial applications. The input voltage of such high voltage DC-DC converter may, e.g., range between 350 V and 410 V. The output voltage may, e.g., range between 44 V and 58 V. The maximum output current may, e.g., be about 55 A, and the maximum output power may, e.g., be around 3 kW. The power density may, e.g., be equal to or greater than 30 W/inch³. All these quantities are exemplary quantities and may be subjected to variations of, e.g., equal to or less than ±50%, ±40%, ±30%, ±20%, or ±10%. Further, the high voltage DC-DC converter may be a down converter as exemplified above or an up-converter.
Figure 10 illustrates a transformer 200' which comprises a first winding interconnect 1020 configured to electrically connect the metal plates 120. More specifically, the first winding interconnect 1020 may connect a first terminal 122 of a particular ring segment 126 to a second terminal 124 of a neighbouring ring segment 126, respectively.
The first winding interconnect 1020 between the ring segments 126 of the metal plates 120 may be designed as a part of the transformer 200'. In this case, the first winding interconnect 1020 between the first and second terminals 122, 124 may be mounted to the transformer (e.g. the transformer 200, see Figure 2A) after the wire 140 has been wound in the spaces between the metal plates 120. Differently put, the transformer 200' may be identical with the transformer 120 except that the transformer 120' is equipped with the transformer-internal first winding interconnect 1020.
The transformer-internal first winding interconnect 1020 may, e.g., be a wire interconnect as illustrated in Figure 10. In other embodiments, the transformer-internal first winding interconnect 1020 may be implemented by conducting paths on a carrier (not shown), e.g. a PCB (printed circuit board) or any other carrier mentioned further below with respect to a transformer-external first winding interconnect. In this case, to produce the transformer 200' with a transformer-internal first winding interconnect 1020, such carrier with conducting paths may be mounted to e.g. the transformer 200 (see Figure 2A) after the wire 140 has been wound in the spaces between the metal plates 120.
Figure 11 illustrates an electrical device 1100 comprising a circuit carrier 1110 on which a transformer (here exemplary transformer 200) is mounted. Further, additional device-specific circuitry 1150 may be mounted on the circuit carrier 1110.
The circuit carrier 1110 provides for a transformer-external first winding interconnect. That is, the metal plates 120 of the first winding of the transformer (e.g. transformer 200 of Figure 2A) are only interconnected to form a continuous winding once the transformer 200 is mounted on the circuit carrier 1110. To this end, the circuit carrier 1110 is provided with conducting paths 1120. The conducting paths 1120 are arranged to connect a first terminal 122 of a particular ring segment 126 to a second terminal 124 of a neighbouring ring segment 126, respectively.
The circuit carrier 1110 may, e.g., be any circuit carrier used in the art for (power) circuitry, e.g. may comprise a PCB (printed circuit board) or a ceramics carrier or a plastics carrier.
The electrical device 1100, which uses the transformer as a circuit component, may be implemented on the circuit carrier 1110. In this case, the circuit carrier 1110 may provide both for a transformer-external first winding interconnect and for a mounting platform of the device-specific circuitry 1150.
For instance the electrical device 1100 may, e.g., be a LLC voltage converter. A LLC voltage converter may include the transformer (e.g. transformer 200 as shown in Figure 11) and device-specific circuitry 1150 such as, e.g., a power switching bridge stage, an LLC stage (also known as LLC tank), a rectifier stage and an output capacitor. The power switching bridge stage includes power transistors. The LLC stage includes a resonant capacitor, a resonant inductance, and a primary inductance. The resonant inductance of the LLC stage may, e.g., be implemented by resonant inductor 920 of stacked design transformer 900.
Figure 12 illustrates the efficiency of an exemplary LLC 3kW DC-DC down converter having an input voltage of 400 V and an output voltage of 51.5 V. The measured efficiency of a half-bridge LLC using the proposed stacked magnetic structure of Figure 9A is shown by the dashed line. With the proposed magnetic structure, an efficiency of 98.22% at 50% load can be achieved. The efficiency is almost as high as the efficiency (solid line) of the same LLC 3kW DC-DC down converter using, however, a transformer having a fully planar design (i.e. a planar first metal plate winding and a planar second multiple wire winding).
This high efficiency can be achieved at reasonable cost. The semi-planar transformer design allows to provide for a low cost planar first winding comprising or consisting of metal plates and a non-planar second winding configured as a helical wire winding which can be manufactured at low cost in mass production exploiting automated wiring techniques.
Figure 13 is a flowchart of an exemplary method of manufacturing a transformer in accordance with the disclosure.
At S1 at least one metal plate (or a plurality of metal plates) is arranged as a first winding of the transformer.
At S2 a wire is provided as a second winding of the transformer.
At S3 at least a first wire turn is wound adjacent to a first side of the metal plate.
At S4 the wire traverses the metal plate.
At S5 at least a second wire turn adjacent to a second side of the metal plate opposite the first side of the metal plate is wound.
As already mentioned, S3-S5 may be carried out by automated coil winding technology allowing to significantly reduce the cost of transformer fabrication.
The following examples pertain to further aspects of the disclosure:
Example 1 is a transformer comprising a first winding, the first winding comprises at least one metal plate; and a second winding, the second winding comprises at least two winding turns of a wire, the wire traversing the metal plate, the winding turns are arranged on opposite sides of the metal plate.
In Example 2, the subject matter of Example 1 can optionally include wherein the metal plate comprises a cutout which is passed through by the wire.
In Example 3, the subject matter of Example 1 or 2 can optionally include wherein the metal plate is shaped as a ring segment having a first terminal and a second terminal at opposite ends of the ring segment.
In Example 4, the subject matter of Examples 2 and 3 can optionally include wherein a slit is formed between the opposite ends of the ring segment, and wherein the cutout is designed as a proximal partial broadening of the slit.
In Example 5, the subject matter of any preceding Example can optionally include wherein the second winding is a single layer helical winding.
In Example 6, the subject matter of any of Examples 1 to 4 can optionally include wherein the second winding is a multilayer helical winding.
In Example 7, the subject matter of any preceding Example can optionally include wherein the first winding comprises a plurality of metal plates which are each separated by at least one winding turn of the second winding.
In Example 8, the subject matter Example 7 can optionally include wherein the metal plates are electrically disconnected from one another or wherein the transformer comprises a first winding interconnect configured to electrically connect the metal plates.
In Example 9, the subject matter of any preceding Example can optionally include wherein the first winding is a secondary winding of the transformer and the second winding is a primary winding of the transformer or wherein the first winding is a primary winding of the transformer and the second winding is a secondary winding of the transformer.
Example 10 is an electrical device comprising: a circuit carrier; and a transformer mounted on the circuit carrier, the transformer comprising: a first winding, the first winding comprises at least one metal plate; and a second winding, the second winding comprises at least two winding turns of a wire, the wire traversing the metal plate, the winding turns are arranged on opposite sides of the metal plate, wherein the circuit carrier is provided with a first winding interconnect which is configured to electrically connect the metal plates.
In Example 11, the subject matter of Example 10 can optionally include wherein the circuit carrier is a printed circuit board or a ceramics carrier or a plastics carrier.
Example 12 is a method of manufacturing a transformer, the method comprising arranging at least one metal plate as a first winding of the transformer; providing a wire as a second winding of the transformer; winding at least a first wire turn adjacent to a first side of the metal plate; traversing the metal plate by the wire; and winding at least a second wire turn adjacent to a second side of the metal plate opposite the first side of the metal plate.
In Example 13, the subject matter of Example 12 can optionally include wherein winding the at least first wire turn, traversing the metal plate by the wire and winding the at least second wire turn are carried out by an automated wire winding machine.
In Example 14, the subject matter of Example 12 or 13 can optionally include wherein the first winding comprises a plurality of spaced-apart metal plates, the method comprising winding the wire between the spaced-apart metal plates to form a single layer helical second winding.
In Example 15, the subject matter of Example 12 or 13 can optionally include wherein the first winding comprises a plurality of spaced-apart metal plates, the method comprising winding the wire between the spaced-apart metal plates to form a multilayer helical second winding.
Although specific embodiments have been illustrated and described herein, it will be appreciated by those of ordinary skill in the art that a variety of alternate and/or equivalent implementations may be substituted for the specific embodiments shown and described without departing from the scope of the present invention. This application is intended to cover any adaptations or variations of the specific embodiments discussed herein. Therefore, it is intended that this invention be limited only by the claims and the equivalents thereof.

Claims

A transformer, comprising:
a first winding, the first winding comprises at least one metal plate; and

a second winding, the second winding comprises at least two winding turns of a wire, the wire traversing the metal plate, the winding turns are arranged on opposite sides of the metal plate.
The transformer of claim 1, wherein the metal plate comprises a cutout which is passed through by the wire.
The transformer of claim 1 or 2, wherein the metal plate is shaped as a ring segment having a first terminal and a second terminal at opposite ends of the ring segment.
The transformer of claims 2 and 3, wherein a slit is formed between the opposite ends of the ring segment, and wherein the cutout is designed as a proximal partial broadening of the slit.
The transformer of any of the preceding claims, wherein the second winding is a single layer helical winding.
The transformer of any of claims 1 to 4, wherein the second winding is a multilayer helical winding.
The transformer of any of the preceding claims, wherein the first winding comprises a plurality of metal plates which are each separated by at least one winding turn of the second winding.
The transformer of claim 7, wherein the metal plates are electrically disconnected from one another or wherein the transformer comprises a first winding interconnect configured to electrically connect the metal plates.
The transformer of any of the preceding claims, wherein the first winding is a secondary winding of the transformer and the second winding is a primary winding of the transformer or wherein the first winding is a primary winding of the transformer and the second winding is a secondary winding of the transformer.
An electrical device comprising:
a circuit carrier; and

a transformer mounted on the circuit carrier, the transformer comprising:
a first winding, the first winding comprises at least one metal plate; and

a second winding, the second winding comprises at least two winding turns of a wire, the wire traversing the metal plate, the winding turns are arranged on opposite sides of the metal plate, wherein

the circuit carrier is provided with a first winding interconnect which is configured to electrically connect the metal plates.
The electrical device of claim 10, wherein the circuit carrier is a printed circuit board or a ceramics carrier or a plastics carrier.
A method of manufacturing a transformer, the method comprising:
arranging at least one metal plate as a first winding of the transformer;

providing a wire as a second winding of the transformer;

winding at least a first wire turn adjacent to a first side of the metal plate;

traversing the metal plate by the wire; and

winding at least a second wire turn adjacent to a second side of the metal plate opposite the first side of the metal plate.
The method of claim 12, wherein winding the at least first wire turn, traversing the metal plate by the wire and winding the at least second wire turn are carried out by an automated wire winding machine.
The method of claim 12 or 13, wherein the first winding comprises a plurality of spaced-apart metal plates, the method comprising:
winding the wire between the spaced-apart metal plates to form a single layer helical second winding.
The method of claim 12 or 13, wherein the first winding comprises a plurality of spaced-apart metal plates, the method comprising:
winding the wire between the spaced-apart metal plates to form a multilayer helical second winding.