An EMI filter based on a dual-winding folded PCB structure

Abstract

The present invention discloses an EMI filter based on a double-winding folded PCB structure, which includes a magnetic core, a common-mode coupling winding, and a termination structure; the common-mode coupling winding is a PCB winding structure based on an FR4 substrate, and the PCB winding structure is arranged within a fully enclosed structure between the upper and lower magnetic yokes and the side columns, and the middle column passes through the central hole of the PCB winding structure; the PCB winding structure includes a plurality of vertically stacked double-winding folded PCB structures, and the double-winding folded PCB structure is a planar common-mode choke formed by folding an 8-shaped double winding 180° along a folding line to form a vertically stacked structure; the windings on the double-winding folded PCB substrate are cascaded through a first termination structure to achieve the series connection of the number of turns of the common-mode coupling inductance on each PCB board; the second termination structure is the input and output ports of the common-mode coupling winding and is connected to the external converter power bus. The cascaded structure of multiple vertically stacked PCBs effectively solves the contradiction between small volume and high inductance value faced by planar coupled common-mode inductors when using ferrite magnetic cores.

Description

Technical Field

[0001] The present invention relates to the technical field of electromagnetic compatibility of EMI filters, and particularly to an EMI filter based on a double-winding folded PCB structure. Background Art

[0002] At present, high efficiency, high frequency, and high density have become the development and pursuit goals of medium and small power-level power electronic converters. At the same time, with the emergence of a new generation of semiconductor devices, semiconductor MOS devices represented by silicon carbide and gallium nitride devices have pushed the operating frequency of switching power supplies to above hundreds of kHz or even MHz. While the increase in switching frequency brings many benefits such as a reduction in the volume of the power module and an increase in power density, it also brings the transient state of faster switching of the switching device, which will generate extremely fast voltage and current mutations. The voltage and current with a high rate of change will become the electromagnetic interference (EMI) noise source in the converter, resulting in serious electromagnetic interference problems at the input or output end of the converter. Severe electromagnetic interference will affect nearby electronic devices and even cause certain damage to a certain extent.

[0003] In order to suppress electromagnetic interference in switching power supplies and make them meet relevant domestic and international standards, a passive EMI filter is often required to be added between the power supply and the front-stage converter to suppress the flow of EMI noise in the direction of the power supply. Although active filters have also made certain developments and progress in noise suppression in recent years, passive EMI filters are still an indispensable part of the front end of the converter. Therefore, it is very necessary to improve their characteristics.

[0004] Traditional EMI filters are composed of discrete coupled common-mode inductors, common-mode capacitors, differential-mode inductors, and differential-mode capacitors. Their volume often accounts for 1 / 4 to 1 / 3 of the entire converter volume, which is not conducive to the improvement of the power density of the converter; traditional wound inductors also have problems such as difficult control of the coupling coefficient, inability to reach a very high level; obvious parasitic capacitance effect between windings, poor high-frequency characteristics of the inductor; component characteristics are easily affected by near-field coupling; low product consistency, and difficult control of high-frequency characteristics.

[0005] In recent years, relevant scholars have carried out research on the planarization of EMI filters, proposed relevant inductance-capacitance unit integration methods, and realized the integration of planar PCB inductors with common-mode and differential-mode capacitors by means of high-dielectric-constant ceramic substrates; at the same time, research has also been carried out on the improvement of the high-frequency characteristics of planar EMI filters, especially the coupled common-mode inductors therein, and methods such as reducing the positive area of the windings and using air dielectric have been proposed to reduce the parasitic capacitance between windings and other methods to improve the high-frequency characteristics of planar EMI filters.

[0006] However, in relevant research, there is little mention of the design of small-volume and high-inductance coupled common-mode inductors. In existing related designs, the method of increasing the number of turns is mostly to increase the planar area or use high-layer PCB, which cannot meet the requirements of high-power density converters and will also lead to relatively high product processing costs; using amorphous or nanocrystalline magnetic core materials and high-layer single PCB boards to increase the inductance results in high costs; the processing technology required for high-layer single PCB boards is also relatively high, and both the yield and product reliability are reduced. Summary of the Invention

[0007] To address the above issues, the present invention proposes an EMI filter based on a double-winding folded PCB structure. This EMI filter can effectively increase the inductance of the coupled common-mode inductor and reduce the parasitic capacitance in the coupled common-mode inductor winding while ensuring a small volume and good high-frequency characteristics.

[0008] An EMI filter based on a double-winding folded PCB structure includes a magnetic core, a common-mode coupling winding, and a termination structure;

[0009] Among them, the magnetic core adopts a can-shaped structure. The upper and lower yokes and the middle column of the magnetic core are solid cylinders, and the side columns are surrounded by hollow cylinders. Window structures are opened at the termination parts on the side columns, and the rest of the surrounding areas and the parts connected to the upper and lower yokes are all fully enclosed structures;

[0010] The common-mode coupling winding is a PCB winding structure with an FR4 substrate. The PCB winding structure is arranged between the upper and lower yokes and within the fully enclosed structure of the side columns, and the middle column passes through the central hole of the PCB winding structure; the FR4 substrate is arranged within the window structure;

[0011] The PCB winding structure includes a plurality of vertically stacked double-winding folded PCB structures. The double-winding folded PCB structure is a planar common-mode choke formed by folding an 8-shaped double winding 180° along the folding line to form a vertically stacked structure. The first termination structure of the double-winding folded PCB structure cascades the same common-mode inductors on each PCB; the second termination structure is the input and output ports for connecting the common-mode coupling inductor to an external converter.

[0012] As a further improvement of the present invention, the two windings of the 8-shaped double winding are centrosymmetric about the midpoint of the folding line, and the two windings are hinged at the folding line.

[0013] As a further improvement of the present invention, the double-winding folded PCB structure includes a plurality of single PCB boards. Each single PCB board has several layers, and each layer has several turns of windings. The CM coupling windings of the several single PCB boards are staggered, and the windings within each turn and between layers are all in series.

[0014] As a further improvement of the present invention, according to different design requirements for CM or DM planar inductors, the winding directions of the windings on each PCB can be the same or opposite.

[0015] As a further improvement of the present invention, an interleaved via structure is provided on each turn of the winding of the single PCB board, and the CM coupling windings on each layer of the same single PCB board are connected in series between layers through the interleaved via structure.

[0016] As a further improvement of the present invention, the planar common-mode choke integrates a common-mode coupling inductor and a differential-mode filtering capacitor; among them, the coupling common-mode inductor windings on each single-board PCB are arranged in an interleaved manner and are connected between layers through an interleaved via structure; the same common-mode inductors on each PCB single board formed after folding are connected in series in the same direction, and finally a multi-layer and multi-turn common-mode coupling inductor of a multi-PCB board is formed; the differential-mode capacitor is composed of the coupling common-mode inductor L CM1 and the coupling common-mode inductor L CM2 The adjacent facing windings are formed.

[0017] As a further improvement of the present invention, the first termination structure is the cascading port of the CM windings on each single PCB board; the second termination structure is the input and output ports of the common-mode choke.

[0018] As a further improvement of the present invention, through holes are drilled on the FR4 substrate, and the through holes on the windings connect the windings on each layer of the same PCB board, and the termination structure is inserted into the end through holes for cascading between each PCB board or as a connection port to an external converter.

[0019] As a further improvement of the present invention, the material of the magnetic core is a ferrite material.

[0020] As a further improvement of the present invention, the termination structure uses a T2 copper column.

[0021] Compared with the prior art, the present invention has the following beneficial effects:

[0022] The EMI filter based on the double-winding folded PCB structure proposed by the present invention has a winding direction of the figure-eight double windings that can be flexibly designed according to the required common-mode or differential-mode inductance. For the double windings with opposite or same winding directions in the planar unfolded state, after a 180° folding around the y-axis, planar common-mode or differential-mode coupled filter inductance coupling can be respectively achieved; when higher inductance value requirements and overall height constraints are met, the number of folded PCB boards can be expanded, and the designability is good; by adopting a can-shaped closed magnetic core structure and the vertical stacked structure coupling windings formed after "folding", the leakage inductance of the windings can be reduced, the coupling coefficient can be increased, and an equivalent coupled common-mode inductance with a higher inductance value can be achieved; the closed can-shaped magnetic core structure also has good EMI shielding characteristics. Since a high common-mode inductance value is achieved in a small volume, to a certain extent, the extremely high relative magnetic permeability requirement for the magnetic core material can be relaxed; the requirement of fabricating an extremely high number of layers on a single PCB board to meet the high inductance requirement is avoided; the reduction of the requirement for the magnetic permeability of the magnetic core material and the requirement for the PCB board manufacturing process can reduce the production difficulty, improve the product yield, and also significantly reduce the production cost.

[0023] Furthermore, the fully interleaved common-mode coupled inductance winding structure can significantly reduce the parasitic capacitance between the coupled common-mode inductance windings under common-mode excitation, and improve the high-frequency characteristics of the common-mode filter inductance; at the same time, to a certain extent, it increases the equivalent differential-mode filter capacitance under differential-mode excitation, providing conditions for the future integration of a coupled common-mode inductance with good high-frequency characteristics and a larger differential-mode capacitance.

[0024] Furthermore, the termination structure based on T2 copper posts has a certain heat dissipation and mechanical support function while providing a stable and reliable electrical connection. Description of the Drawings

[0025] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for use in the description of the embodiments or the prior art. Obviously, the following drawings are some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0026] Figure 1 It is the overall structural decomposition of the folded EMI filter based on the double-winding folded PCB structure;

[0027] Figure 2 It is the planar figure-eight double common-mode winding before folding of the figure-eight double common-mode winding proposed by the present invention;

[0028] Figure 3 It is the interleaved winding structure on a single PCB of the EMI filter based on the double-winding folded PCB structure proposed by the present invention;

[0029] Figure 4 It is the cross - through via structure of the EMI filter based on the double - winding folded PCB structure;

[0030] Figure 5 It is the finite - element simulation structure of the inductance value of the EMI filter based on the double - winding folded PCB structure proposed by the present invention. (a) is the magnetic flux density vector distribution diagram; (b) is the inductance value of the coupled common - mode inductor.

[0031] Figure 6 It is the winding of the EMI filter based on the double - winding folded PCB structure proposed by the present invention. (a) is the Q3D extraction result of the parasitic capacitance; (b) is the Q3D extraction result of the equivalent differential - mode capacitance. Specific implementation manners

[0032] In order to make the purpose and technical solutions of the present invention clearer and easier to understand, the present invention will be further described in detail below with reference to the drawings and embodiments. The specific embodiments described here are only used to explain the present invention and are not used to limit the present invention.

[0033] In the description of the present invention, it should be understood that the orientation or positional relationship indicated by the terms "center", "longitudinal", "transverse", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", etc. is based on the orientation or positional relationship shown in the drawings. It is only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation. Therefore, it cannot be understood as a limitation to the present invention. In addition, the terms "first" and "second" are only used for descriptive purposes and cannot be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Thus, the features defined with "first" and "second" may explicitly or implicitly include one or more of such features. In the description of the present invention, unless otherwise stated, the meaning of "a plurality" is two or more. In the description of the present invention, it should be noted that, unless otherwise clearly defined and limited, the terms "mounted", "connected" and "coupled" should be understood in a broad sense. For example, it may be a fixed connection, a detachable connection or an integral connection; it may be a mechanical connection or an electrical connection; it may be directly connected or indirectly connected through an intermediate medium, and it may be the internal connection of two elements. For those of ordinary skill in the art, the specific meanings of the above terms in the present invention can be understood according to specific situations.

[0034] The technical solution of the present invention will be clearly and completely described below in conjunction with the accompanying drawings and specific embodiments. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts belong to the scope of the present invention.

[0035] As Figures 1 to 4 shown, an EMI filter based on a dual-winding folded PCB structure provided by the present invention aims to solve the planar design of an EMI filter with requirements of low cost, small volume, and high common-mode inductance value. The structure integrates a common-mode coupling inductor and a differential-mode filtering capacitor, and specifically includes a magnetic core, a common-mode coupling winding, a differential-mode capacitor, and a termination structure.

[0036] Among them, the magnetic core adopts a can-shaped structure. The upper yoke 1, lower yoke 2, and middle column 3 of the magnetic core are solid cylinders, and the side columns 4 are surrounded by hollow cylinders. There are window structures 5 and 6 at the termination parts of the side columns, and the rest of the surrounding and the connection parts with the upper and lower yokes are all fully enclosed structures to reduce leakage inductance and enhance the coupling coefficient of the coupled common-mode inductor; the can-shaped magnetic core can use appropriate high-permeability and low-saturation ferrite materials of each series as the magnetic core material, avoiding the use of more expensive nanocrystalline or amorphous materials.

[0037] In the example, the common-mode coupling winding is a planar winding formed by cascading two PCB boards 7 and 8 with FR4 substrates. The PCB windings 7 and 10 are arranged between the upper and lower yokes 1 and 2 and within the fully enclosed structure of the side columns 4, and the middle column 3 passes through the center hole of the PCB winding structure; the FR4 substrate is arranged within the window structure.

[0038] The PCB winding structure includes a plurality of vertically stacked folded PCB structures. Taking the dual-winding folded PCB structure as an example, when unfolded, one of the two coupled common-mode inductor windings is an 8-shaped winding 11, that is, one of the dual common-mode windings with opposite winding directions and connected in series, is folded 180° along Figure 2 the direction shown in Figure 1The planar common-mode choke of the vertically stacked double-winding folded PCB structure shown in the figure reduces the board area and saves the core volume at the same time. The first FR4 substrate 7 of the double-winding folded PCB structure uses T2 copper posts as the first termination structure 12 to cascade with the second FR4 substrate 10. The formed forward series common-mode choke uses T2 copper posts as the second termination structure 13 as the input and output ports connected to the converter power bus. The termination structures 12 and 13 composed of vias and T2 copper posts can provide certain heat dissipation and mechanical support functions while providing electrical connections. By changing the winding direction of the double winding 11 and changing the winding directions of the two windings 11 under the plane to the same direction, the same structural transformation can realize the vertical stacking of the differential-mode coupling filter inductor and planarize the differential-mode coupling filter inductor.

[0039] The realization of the common-mode coupling inductor is based on the PCB winding structure using FR4 substrates. In order to further enhance the coupling coefficient of the positive and negative bus coupling common-mode inductors (denoted as coupling common-mode inductor 8 and coupling common-mode inductor 9 respectively), a fully interleaved winding structure is adopted, and the winding arrangements of each layer are as Figure 3 shown:

[0040] 81—91—82—92—……—84—94 (8i / 9i, i represents the i-th layer winding of the coupling common-mode inductor 8 / 9). The in-layer and inter-layer windings of the common-mode coupling inductors 8 and 9 are connected in series to increase the number of turns. Crossed via structures 14 are arranged on the inner edges of the inner circles and the outer edges of the outer circles of each layer of windings to realize the series connection of the same coupling common-mode inductor windings on the spacer layers in the interleaved arrangement structure where adjacent layers are different inductance windings.

[0041] The planar common-mode choke integrates a common-mode coupling inductor and a differential-mode filter capacitor. Among them, the common-mode coupling inductor is composed of multiple layers and multiple turns of PCB windings 7 and 10, and is connected by an interleaved via structure 14 between layers. The differential-mode capacitor is composed of the facing windings of the adjacent coupling common-mode inductors 8 and 9 in each layer under the interleaved structure.

[0042] Another advantage of the fully interleaved winding structure of the common-mode coupling inductors 8 and 9 is that under differential-mode excitation, there is a large potential difference between the turns of the common-mode coupling inductors 8 and 9. Therefore, the differential-mode potential difference can be maximally utilized. At the same time, the facing area between the turns of the windings is maximized, and the distance between the windings with differential-mode potential difference is reduced to obtain the largest possible equivalent differential-mode filter capacitor without changing the PCB substrate medium, providing favorable conditions for the integration of the coupling common-mode inductor and the differential-mode capacitor after embedding high-dielectric-constant substrates.

[0043] Under the condition of meeting the requirements of higher inductance value and overall height constraints, the total number of winding turns can be further increased by increasing the number of folded PCB single boards. It is also possible to reduce the processing cost of the PCB while ensuring the number of turns by reducing the number of layers of each single PCB board and increasing the number of PCB single boards at the same time.

[0044] Embodiment

[0045] Reference Figure 2 , which is the PCB winding 11 of the common-mode coupling inductor before folding. Figure 1 FIG. is a schematic diagram of the overall structure of the EMI filter based on the double-winding folded PCB structure proposed by the present invention. Its structure includes a pot-shaped magnetic core (1, 2, 3, 4, 5) made of ferrite material, a symmetric figure-eight double-winding folded PCB structure common-mode winding (7, 8), a low common-mode winding internal parasitic capacitance winding structure, first and second termination structures (12, 13), and an interleaved via structure 14.

[0046] As Figure 2 shown, taking the common-mode coupling inductor as an example, the figure-eight double-winding PCB 11 with opposite winding directions in the plane unfolded state is folded 180° around the y-axis, and folded into a vertical stacking structure as shown in Figure 1 to achieve positive coupling of the coupled common-mode inductor on two PCB single boards. At the same time, in order to adapt to the closed pot-shaped magnetic core, the outer winding is also changed to a circular shape, and the termination structures 12 and 13 are designed as structures based on 3mm diameter T2 copper posts and vias. In the embodiment of the present invention, a design example of a planar common-mode choke with 2 PCB boards 7 and 8 vertically stacked, each single PCB board having 8 layers, each layer containing two turns of windings, and a single coupled common-mode inductor having a total of 16 turns is provided. A pot-shaped closed magnetic core is adopted. Except for the fan-shaped window structure 5 provided at the positions of the first termination structure 12 and the second termination structure 13, the rest of the periphery and the top and bottom are in full-closed contact. The two PCB windings 7 and 8 are centered with the center of the middle column 3 of the magnetic core.

[0047] Reference Figure 1, the two T2 copper posts on the PCB board 7 where the second terminal connection structure 13 is located are the input ports of the common-mode choke, and the two T2 copper posts on the PCB board 10 where the second terminal connection structure 13 is located are the output ports of the common-mode choke; among them, the upper and lower two T2 copper posts on the left side of the second terminal connection structure 13 are the input and output ports of the common-mode coupling inductor 8 respectively, and can be connected to the positive (or negative) power bus of the external converter. The upper and lower two T2 copper posts on the right side of the second terminal connection structure 13 are the input and output ports of the coupled common-mode inductor 9 respectively, and can be connected to the negative (or positive) power bus of the external converter to realize the connection from the power supply to the EMI filter to the power converter; the PCB boards 7 and 10 cascade the coupled common-mode windings on the two PCB boards through the first terminal connection structure 12 to realize the series connection of the turns of the common-mode coupling inductors on each PCB board in the proposed vertical stacking structure. The interleaved winding structure and the folded PCB structure of the common-mode coupling inductors 8 and 9 are also beneficial to realizing the positive strong coupling of the two common-mode windings.

[0048] Reference Figure 3 , as shown in the figure Figure 1 is the longitudinal stretch diagram of the winding structure of the PCB board 7 in Figure 3 . As shown, the turns of the common-mode coupling inductors 8 and 9 are arranged in an interleaved manner. The 1st, 3rd, 5th, and 7th layers are the 1st and 2nd, 3rd and 4th, 5th and 6th, 7th and 8th turns of the common-mode coupling inductor 8 respectively. The turns of each layer and between layers are in a series structure; the 2nd, 4th, 6th, and 8th layers are the 1st and 2nd, 3rd and 4th, 5th and 6th, 7th and 8th turns of the common-mode coupling inductor 9 respectively. The turns of each layer and between layers are in a series structure. As shown in Figure 4 , without using blind buried vias, the series connection of the turns of the same common-mode inductor with intervals is realized through the interleaved via structure 14.

[0049] Reference Figure 5 , (a) is the vector distribution diagram of the magnetic flux density when a common-mode excitation is applied to the 8-shaped double-winding folded PCB structure planar common-mode choke proposed by the present invention, and the winding direction is clockwise; (b) is the inductance value of the coupled common-mode inductor obtained through finite element simulation. It can be seen that when the number of turns of the 8-shaped double-winding folded PCB structure planar common-mode choke proposed by the present invention is 16, even when using a ferrite core with a relative magnetic permeability of 2300, a relatively high common-mode inductance of 5.9289 mH can be obtained. At this time, its overall volume is 24×24×6 mm, which is smaller than the volume of the traditional wound amorphous material common-mode choke; at the same time, the coupling coefficient between the two common-mode windings is about 99.99%, which is a strong coupling.

[0050] Reference Figure 6, as shown in (a), in the case of a small volume and high inductance value, the interleaved winding structure based on the PCB winding can control the parasitic capacitance of the coupled common-mode inductance winding within a small range. The maximum value of the parasitic capacitance between windings under the planar common-mode choke structure proposed by the present invention is 0.59 pF. Compared with the traditional wound coupled common-mode inductor, its high-frequency characteristics have been improved to a certain extent; as shown in (b), by adopting a full interleaved winding structure, a differential-mode capacitance of about 1.87 nF can be integrated on the FR4 dielectric material with a relative dielectric constant of 4.2.

[0051] In summary, the present invention proposes a planar EMI filter based on a double-winding folded PCB structure. By adopting an 8-shaped double-winding folded PCB structure, a coupled common-mode inductor and a differential-mode capacitance with a certain capacitance value are integrated. When the windings are designed with opposite winding directions in the planar unfolded case, the 8-shaped double windings 11 are folded to form a planar common-mode coupled filter inductor with positive coupling under common-mode excitation; the winding direction can also be changed to the same direction in the planar unfolded case, and folded into a planar differential-mode coupled filter inductor with positive coupling under differential-mode excitation according to the same implementation method; the vertically stacked PCB cascade form formed by "folding" can effectively reduce the laying area of the planar common-mode / differential-mode inductor without sacrificing the number of turns, save the core volume and materials, and increase the coupling coefficient between the coupled inductors.

[0052] Taking the design of the planar common-mode choke as an example, the series connection of the common-mode winding turns between each PCB and the connection between the EMI filter and the converter power bus are respectively realized through the first termination structure 12 and the second termination structure 13. The coupled common-mode inductance windings are arranged in an interleaved manner, and the series connection of the same CM inductance windings on the spacer layer is realized through the interleaved vias between layers. The common-mode coupled inductor adopts an interleaved winding stack to suppress the parasitic capacitance between windings and improve the high-frequency characteristics of the coupled common-mode inductor, while also realizing the integration of the common-mode coupled inductor and a differential-mode capacitance with a certain capacitance value; the vertically stacked PCB cascade structure also effectively solves the contradiction between small volume and high inductance value faced by the planar coupled common-mode inductor when using a ferrite core; the use of a can-shaped closed core will further enhance the anti-near-field coupling ability of the filter.

[0053] The above are only the preferred embodiments of the present invention, and do not limit the present invention in any way. Any simple modification, change, and equivalent structural change made to the above embodiments according to the technical essence of the present invention still fall within the protection scope of the technical solution of the present invention.

[0054] The above embodiments are only used to illustrate the technical solution of the present invention and do not limit it. Although the present invention has been described in detail with reference to the above embodiments, those of ordinary skill in the art can still modify the specific implementation of the present invention or make equivalent replacements, and any modification or equivalent replacement that does not depart from the spirit and scope of the present invention is within the protection scope of the claims of the present invention.

Claims

1. An EMI filter based on a double-winding folded PCB structure, characterized in that, It includes a magnetic core, a common-mode coupling winding, and a termination structure; Among them, the magnetic core adopts a can-shaped structure. The upper and lower yokes and the middle column of the magnetic core are solid cylinders, and the side columns are surrounded by hollow cylinders. Window structures are opened at the termination parts of the side columns, and the rest of the periphery and the parts connected to the upper and lower yokes are all fully enclosed structures; The common-mode coupling winding adopts a PCB winding structure with an FR4 substrate. The PCB winding structure is arranged between the upper and lower yokes and within the fully enclosed structure of the side columns, and the middle column passes through the central hole of the PCB winding structure; The FR4 substrate carrying the PCB winding is also arranged within the window structure; The PCB winding structure includes a plurality of vertically stacked double-winding folded PCB structures. The double-winding folded PCB structure is a planar common-mode choke formed by folding an 8-shaped double-winding 180° along the folding line; The short-circuit structure in the structure is realized based on the through-hole-extended copper foil and T2 copper columns of the winding. The first termination structure of the double-winding folded PCB structure cascades the same common-mode inductors on each PCB; The second termination structure is the input and output ports where the common-mode coupling inductor is connected to the external converter.

2. The EMI filter based on the double-winding folded PCB structure according to claim 1, characterized in that: The two windings of the 8-shaped double-winding are centrosymmetric about the midpoint of the folding line, and the two windings are hinged at the folding line.

3. The EMI filter based on the double-winding folded PCB structure according to claim 1, characterized in that: The double-winding folded PCB structure includes a plurality of single PCB boards. Each single PCB board has several layers, and each layer has several turns of windings. The CM coupling windings of several single PCB boards are arranged staggered, and the windings within each turn and between layers are all in series connection.

4. The EMI filter based on the double-winding folded PCB structure according to claim 3, characterized in that: For CM or DM planar inductor design, the winding directions on each PCB can be the same or opposite.

5. The EMI filter based on the double-winding folded PCB structure according to claim 3, characterized in that: Interleaved via structures are provided on each turn of the windings of the single PCB board, and the CM coupling windings of each layer on the same single PCB board are connected in series between layers through the interleaved via structures.

6. The EMI filter based on the double-winding folded PCB structure according to claim 3, characterized in that: The planar common-mode choke integrates a common-mode coupling inductor and a differential-mode filter capacitor; Among them, the coupled common-mode inductance windings on each single-board PCB are arranged staggeredly, and are connected through a staggered via structure between layers; after folding, the multiple single-board PCBs formed are connected in series in the same direction, and finally a multi-layer and multi-turn common-mode coupled inductance of a multi-PCB board is formed; the differential-mode capacitor is composed of the facing windings of the inter-layer coupled common-mode inductance L CM1 and the coupled common-mode inductance L CM2 .

7. The EMI filter based on the double-winding folded PCB structure according to claim 6, characterized in that: The first termination structure is the cascading port of the CM windings on each single PCB board; The second termination structure is the input and output ports of the common-mode choke.

8. The EMI filter based on the double-winding folded PCB structure according to claim 1, characterized in that: Through holes are drilled on the FR4 substrate, and the through holes on the windings connect the windings of each layer on the single PCB board. The copper columns for termination are inserted into the end through holes for cascading between each PCB board.

9. The EMI filter based on the double-winding folded PCB structure according to claim 1, characterized in that: The material of the magnetic core is a ferrite material.

10. The EMI filter based on the double-winding folded PCB structure according to claim 1, characterized in that: The termination structure adopts T2 copper columns.

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