TW201440093A - Choke - Google Patents

Abstract

A choke includes a single-piece core made of a same material, the single-piece core having a first board, a second board, and a pillar located between the first and second boards, a winding space located among the first board, the second board and the pillar, wherein the pillar has a non-circular and non-rectangular cross section having a first axis and a second axis substantially perpendicularly intersecting with each other at a center of the cross section of the pillar, and wherein a circumference of the cross section of the pillar includes two arc edges, four first substantially straight edges substantially parallel to the first axis, and two second substantially straight edges substantially parallel to the second axis, each of the first substantially straight edges being a joint of and in direct contact with one of the arc edges and one of the second substantially straight edges.

Description

Choke

The present invention relates to a choke, and more particularly to a choke that enhances saturation characteristics.

The function of the choke is to stabilize the current in the circuit and achieve the effect of filtering out the noise. The effect is similar to that of the capacitor. The same is to store and release the electrical energy in the circuit to adjust the stability of the current, and the electric field is compared with the capacitor. The form of (charge) is used to store electrical energy, and the choke is achieved in the form of a magnetic field.

Chokes are usually used in electronic devices such as DC/DC converters or battery chargers in the early days, and are applied to modems and asymmetric digital subscriber lines (ADSL). Or in a local area network (LAN) transmission device. However, in recent years, chokes have also been more widely used in information technology products such as notebook computers, mobile phones, LCD screens, and digital cameras. As IT products are gradually moving towards thinner and lighter weights, the height and size of chokes will become an important design issue.

As shown in FIG. 1, the choke 1 disclosed in U.S. Patent No. 7,209,022 includes a drum core 10, a wire 12, an exterior resin 14, and a pair of external electrodes 16.

Further, as shown in Fig. 2, the cross section of the column 100 in the drum core 10 is circular. In general, the larger the cross-sectional area of the center pillar 100, the better the characteristics of the choke 1 are. However, since the cross-sectional shape of the center pillar 100 is circular and the winding space S for winding the wire 12 must be retained, the cross-sectional area of the center pillar 100 is thus limited, so that the saturation current cannot be effectively increased.

US Patent Publication No. 7,495,538 (hereinafter referred to as the '538 patent) A drum core having a square center pillar. In the '538 patent, since the cross-sectional shape of the center pillar is square, the wire may be damaged by the sharp corner of the center pillar, and the characteristics of the choke (for example, saturation current, DC impedance, magnetic flux density, etc.) are poor.

Accordingly, it is an object of the present invention to provide a choke that enhances saturation characteristics.

In order to achieve the above object, according to a first embodiment of the present invention, a choke includes a one-piece core made of the same material, the one-piece core having a first plate and a second a plate and a center pillar, the middle column is located between the first plate and the second plate, and a winding space is located between the first plate, the second plate and the center column; The center pillar has a non-circular and non-square cross section perpendicular to an axial direction of the center pillar, the section of the center pillar having a first axis and a second axis, the first axis and the first axis The two axes intersect at a center of the section of the center pillar and are perpendicular to each other; and wherein one of the sections of the center pillar includes two curved sides, four first straight sides, and two second flat sides The four first straight sides are substantially parallel to the first axis, and the second second straight sides are substantially parallel to the second axis, and each of the first straight sides corresponds to the two curved sides One of the sides and one of the two second straight sides.

According to a second embodiment of the present invention, a choke device comprises a one-piece core body made of the same material, the one-piece core body having a first plate piece, a second plate piece and a middle piece a column, the middle column is located between the first plate and the second plate, a winding space is located between the first plate, the second plate and the center column, the single piece core a magnetic permeability between 25 and 60; a wire wound around the center pillar and located in the winding space; and a magnetic material filled in the winding space and covering the wire, one of the magnetic materials The magnetic permeability is between 4 and 21.

The advantages and spirit of the present invention will be further understood from the following detailed description of the invention.

1, 3‧‧‧ Current Circulator

10‧‧‧ drum core

12, 32‧‧‧ wires

14‧‧‧External resin

16‧‧‧External electrode

30‧‧‧ core

34‧‧‧ Magnetic materials

100, 300‧‧‧ column

302‧‧‧ first board

304‧‧‧Second board

306‧‧‧ joints

3040, 3042‧‧‧ corner

A1‧‧‧ first axis

A2‧‧‧ second axis

C‧‧‧ Center

E1‧‧‧ curved sides

E2‧‧‧ first straight side

E3‧‧‧Second straight side

d, L1, L2, t, X, Y‧‧‧ length

H1, H2‧‧‧ thickness

S, S'‧‧‧ winding space

Figure 1 is a cross-sectional view of a conventional choke.

Fig. 2 is a plan view of the choke in Fig. 1.

Figure 3 is a cross-sectional view of a choke according to an embodiment of the present invention.

Fig. 4 is a perspective view of a core body applicable to the choke of Fig. 3.

Fig. 5 is a plan view of the core in Fig. 4.

Figure 6 is a top plan view of two different forms of cores in accordance with another embodiment of the present invention.

Figure 7 is a top plan view of three different forms of cores in accordance with another embodiment of the present invention.

The technical features of the present invention will be described in detail with reference to the accompanying drawings, wherein the same reference numerals are used to designate the same or similar elements. It should be noted that the drawings should be viewed in the direction of the reference numerals.

Please refer to FIG. 3 to FIG. 5, FIG. 3 is a cross-sectional view of the choke 3 according to an embodiment of the present invention, and FIG. 4 is a perspective view of the core 30 applicable to the choke 3 of FIG. Fig. 5 is a plan view of the core 30 in Fig. 4. As shown in FIGS. 3 to 5, the choke 3 includes a core 30, at least one wire 32 (only one is shown in FIG. 3), and a magnetic material 34. The choke 3 is suitable for small size applications. For example, the choke 3 may have a length * width of less than 4 mm * 4 mm and a height of less than 2.5 mm.

In one embodiment, the core 30 includes a center pillar 300, a first panel 302, and a second panel 304. The center pillar 300 is located between the first plate 302 and the second plate 304, and the center pillar 300, the first plate 302 and the second plate 304 are integrally formed. In one embodiment of the invention, the core 30 is a one-piece construction made of the same material. In other words, the combination of the center pillar 300, the first panel 302 and the second panel 304 is a single unitary structure, and there is no gap between the center pillar 300, the junction of the first panel 302 and the second panel 304, or Intermediary material/structure. Further, the center pillar 300, the first panel 302, and the second panel 304 are made of the same material. In one embodiment, the center pillar 300, the first panel 302 and the second panel 304 may be made of the same magnetic material, such as a mixture of a metallic powder and a binder, and the metal powder is in the core. The content in the body 30 is more than 90% by weight, and one of the metal powders has an average particle diameter of between 10 μm and 12 μm. For example, The metal powder may be Fe-Cr-Si alloy, Fe-Al-Cr alloy, Fe-Si-Al alloy, Fe-Ni alloy (Fe-Ni). Alloy), amorphous, nano-crystal, and the like. The bonding agent may be an inorganic binder (for example, a glass binder) that can withstand a high temperature of about 400 ° C to 700 ° C.

As shown in FIG. 5, a first axis A1 and a second axis A2 intersect at a center C of a section of the center pillar 300. The section of the center pillar 300 is perpendicular to one of the axial directions of the center pillar 300. The first axis A1 and the second axis A2 are substantially perpendicular to each other within a manufacturing error range. The length of the first axis A1 is longer than or within the manufacturing error range substantially equal to the length of the second axis A2. One of the sections of the center pillar 300 includes a second curved side edge E1, four first flat side edges E2, and two second flat side edges E3. It should be noted that the first straight side E2 and the second flat side E3 are substantially flat in the manufacturing error range. The four first flat sides E2 are substantially parallel to the first axis A1 within a manufacturing error range, and the second second straight sides E3 are substantially parallel to the second axis A2 within a manufacturing error range. As shown in the embodiment shown in FIG. 5, the first flat side edges E2 located above are substantially aligned with each other in the direction parallel to the first axis A1 within the manufacturing error range, and are located below the other two. A flat side E2 is substantially aligned with each other within a manufacturing error range in a direction parallel to the first axis A1. Each of the first straight sides E2 corresponds to one of the two curved side edges E1 and one of the second second straight sides E2. Each of the curved side edges E1 and the corresponding first straight side edge E2 are joined to a joint 306. The second straight side E3 is shorter than the length of the middle column 300 along the second axis A2. The cross section of the center pillar 300 is substantially symmetrical to the first axis A1 and the second axis A2 within a manufacturing error range. As shown in the embodiment shown in FIG. 5, the first first straight side E2 located above and the other two first straight side edges E2 located below are substantially symmetrical with respect to the first axis A1. The first left straight side E2 of the left side and the other two first straight side sides E2 of the right side are substantially symmetrical with respect to the second axis A2, and the second second straight side edges E3 are substantially opposite to the second side. The axes A2 are symmetrical to each other. Each of the second flat sides E3 is substantially symmetrical with respect to the first axis A1, the two arcuate sides E1 are substantially symmetrical with respect to the first axis A1, and each of the curved sides E1 is substantially opposite to the second axis A2 is symmetrical. In this embodiment, the curved side edge E1 may be an oval-arc shape such that the circumference of the middle pillar 300 is non-circular and non-square. For example, an oval-like shape. Furthermore, the angle between the curved side edge E1 and the corresponding first straight side edge E2 at the joint 306 is greater than 90 degrees. In an embodiment, the end portion of the curved side edge E1 directly connected to the corresponding first straight side edge E2 may have a convex shape. In another embodiment, the end portion of the curved side edge E1 directly connected to the corresponding first straight side edge E2 may have a concave shape (compared to a main portion of the curved side edge E1 having a convex shape), such that The end of the curved side edge E1 having a concave shape and the corresponding first straight side edge E2 may have a relatively smooth transition at the joint 306. In the above embodiment, the pillars 300 in the core 30 can be formed directly in a press molding process. Therefore, the process of the column 300 in the core 30 is simpler than the prior art and can be used to manufacture the core 30 of a small size suitable for the choke 3.

In this embodiment, the inequality 1 defined below can be satisfied: Where Y represents the length of the section along the second axis A2, and d represents Half the length of the second straight side E3 (ie, The difference, and Y is greater than t. In this embodiment, d is between the extension line of one of the two first straight side edges E2 located above and the line parallel to the first axis A1 and passing the apex of the upper curved side edge E1. distance.

Preferably, inequality 2 defined below can be satisfied:

Furthermore, the ratio of the length t of the second straight side E3 to the length X of the section along the first axis A1 is between 0.5 and 0.7.

Furthermore, the ratio of the thickness H1 of the first plate 302 to the length L1 of the first plate 302 is between 0.05 and 0.2, and/or the thickness H2 of the second plate 304 and the length L2 of the second plate 304. The ratio is between 0.05 and 0.2.

Referring again to FIGS. 3 and 5, the wire 32 of the choke 3 is wound around the center pillar 300 and located in the winding space S'. The wire 32 is composed of a copper wire covered with an enamel coating, and the enamel layer is An insulating layer. The wire 32 can be linear or spiral. Since the center pillar 300 is elliptical in shape, when the wire 32 is wound on the center pillar 300, the wire 32 can be closely attached to the outer wall of the center pillar 300 to effectively wrap the wire 32, and the magnetic permeability effect can also be obtained. A lower direct current resistance (DCR) is obtained under the (equivalent permeability effect).

The winding space S' is formed between the first plate 302, the second plate 304, and the center pillar 300. In this embodiment, the magnetic material 34 is filled in the winding space S' and covers the wire 32. The magnetic material 34 may be filled in the winding space S' via a transfer molding process, an injection molding process, or a coating process. The magnetic material 34 contains a thermosetting resin and a magnetic powder. The thermosetting resin is an organic material and does not contain a volatile solvent, and the viscosity of the thermosetting resin is between 12000 centipoise (c.p.s.) and 30,000 c.p.s. before heating. One of the magnetic powders has an average particle size of less than 20 microns. Preferably, the magnetic powder has an average particle size between 4 microns and 10 microns. In this embodiment, the magnetic powder may comprise an iron powder (Fe) or a metallic powder such as Fe-Ni, Fe-Cr-Si, Fe-Cr, Fe-Co-v, Fe. -Ni-Mo, Fe-Si-Al, Fe-B, Fe-Co-B, Fe-Zr-B, nickel-nickel ferromagnetic alloy (Deltamax), special metal (Mu-metal), high magnetic alloy (4 -79 Permalloy), Mo-Permalloy, Supermalloy, Sendust, Power Flux, etc., in which iron powder or metal powder is contained in magnetic material 34. The range is between 50% by weight and 90% by weight, preferably between 60% by weight and 80% by weight, and the content of the thermosetting resin is less than 40% by weight. In this embodiment, the viscosity of the thermosetting resin is between 12000 c.p.s. and 18000 c.p.s. before heating. Preferably, the surface of the iron powder is coated with an insulating substance.

In one embodiment, when a thermosetting resin and iron powder are used to form the magnetic material 34, the thermosetting resin can withstand a high temperature higher than 350 °C. When the heating temperature exceeds the glass transition temperature, in addition to the requirement for the desizing temperature, the use of the iron powder can also make the magnetic permeability of the magnetic material 34 easier to control. In addition, since the viscosity of the thermosetting resin is between 12000 c.ps and 30,000 c.ps, the iron powder is easily mixed with the thermosetting resin to form the magnetic material 34, and the mixing ratio range is tolerated, and the thermosetting resin is easily coated on the winding. Line space S'. Since the content of the thermosetting resin in the magnetic material 34 is less than 40% by weight and does not contain a volatile solvent, the thermal stress generated by the expansion and contraction of the thermosetting resin can be lowered and the probability of pore formation is low during the heat hardening, which can be avoided. Or greatly reducing the occurrence of cracks in the core 30. In addition, in this embodiment, the thermosetting resin is a polymer, such as polymethylallyl (PMA) synthesize resin, and has a linear expansion coefficient of 1*10 ^-5 /°C and 20 *10 ^-5 / °C, and the glass transition temperature is between 130 ° C and 170 ° C. Thereby, when the magnetic material 34 is filled in the winding space S' via the above coating process, the magnetic permeability of the magnetic material 34 is between 4 and 12.

In particular, in this embodiment, the glass transition temperature of the magnetic material 34 is substantially the same as the glass transition temperature of the thermosetting resin, the coefficient of linear expansion is about 13.8*10 ^-5 /°C, and the glass transition temperature is 150 °C.

Further, the magnetic material 34 may be filled in the winding space S' via a transfer molding process. In the transfer molding process, the thermosetting resin may be an epoxy resin, a phenolic resin, or the like, and the magnetic powder material may be iron, an iron-aluminum-niobium alloy, an iron-chromium-niobium alloy, or the like. When the magnetic material 34 is filled in the winding space S' via a transfer molding process, the magnetic permeability of the magnetic material 34 is between 8 and 21.

Furthermore, the magnetic material 34 can be filled in the winding space S' via an injection molding process. In the injection molding process, the thermosetting resin may be Polyamide 6, PA6, Polyamide 12 (PA12), Polyphenylene Sulfide (PPS), Polybutylene terephthalate. Polybutylene terephthalate (PBT), ethylene-ethyl acrylate copolymer (EEA) and/or other suitable resin materials, and the magnetic powder material may be a metal soft magnetic material. The metal soft magnetic material may comprise iron, an iron-aluminum-niobium alloy, an iron-chromium-niobium alloy, stainless steel, and/or other suitable materials. When the magnetic material 34 is filled in the winding space S' via an injection molding process, the magnetic permeability of the magnetic material 34 is between 6 and 18.

In this embodiment, the magnetic permeability of the core 30 is between 25 and 60, and the magnetic permeability of the magnetic material 34 is between 4 and 21. Thereby, the saturation characteristics of the choke 3 can be improved. As noted above, the magnetic permeability of the magnetic material 34 is dependent upon the transfer molding process, the injection molding process, and/or the coating process. Table 1 below shows the saturation characteristics of the choke 3 measured at different current values in accordance with the embodiment of the present invention and the prior art with the magnetic permeability of the corresponding core 30 and the magnetic permeability of the magnetic material 34. The saturation characteristics in Table 1 were measured with a choke 3 having a size of 2 mm * 1.6 mm * 1.0 mm with a specific inductance value of 2.2 μH. Notably, the saturation characteristics of embodiments of the present invention are greater than and superior to the saturation characteristics of the prior art.

It should be noted that since the magnetic material 34 of the embodiment does not use a volatile solvent, it can be directly heated and hardened without being left at room temperature after coating, and there is no crack or deformation after heat hardening. The situation arises. Therefore, in comparison with the prior art, in addition to shortening the process time of the choke 3, the life of the magnetic material 34 is not affected by the proportion of the formulation, and is suitable for mass production.

As shown in the embodiment shown in FIG. 5, at least one corner of the second panel 304 is exposed from the first panel 302 in the viewing direction from the first panel 302 toward the second panel 304 (ie, At least one corner of the second panel 304 is located outside the area covered by the first panel 302. This embodiment The four corners 3040 and 3042 of the second panel 304 are exposed from the first panel 302 in the viewing direction from the first panel 302 toward the second panel 304, but are not limited thereto. In other words, the top/bottom surface of the first panel 302 is smaller than the bottom/top surface of the second panel 304. In this embodiment, the ratio of the top surface/bottom surface of the first plate 302 to the bottom surface/top surface of the second plate 304 is greater than 94% and less than 100%, preferably between 95% and 98. Between % to maintain good saturation characteristics. It should be noted that, in another embodiment, the top surface/bottom surface of the first plate 302 may be larger than the bottom surface/top surface of the second plate 304, and the bottom surface/top surface of the second plate 304 is The ratio of the top surface/bottom surface of the first sheet 302 is still greater than 94% and less than 100%, preferably between 95% and 98% to maintain good saturation characteristics. In other words, the top surface/bottom surface of one of the first plate 302 and the second plate 304 is smaller than the bottom surface/top surface of the other of the first plate 302 and the second plate 304 (the ratio is less than 100 % and greater than 94%, preferably between 95% and 98%).

Referring to Figure 6, Figure 6 is a top plan view of two different forms of core 30 in accordance with another embodiment of the present invention. As shown in FIG. 6, only one corner 3040 of the second panel 304 is exposed from the first panel 302 in the viewing direction from the first panel 302 toward the second panel 304.

Referring to Figure 7, Figure 7 is a top plan view of three different forms of core 30 in accordance with another embodiment of the present invention. As shown in FIG. 7, the shape of the first plate 302 and the second plate 304 may be changed, but the ratio of the top/bottom surface of the first plate 302 to the top/bottom surface of the second plate 304 is shown. It must still be greater than 94% and less than 100%, preferably between 95% and 98% to maintain good saturation characteristics.

Thereby, a plurality of cores 30 can be placed in a plurality of cavities of a mold, and the second plate 304 of each core 30 can be oriented upward by the action of the exposed corners 3040, 3042, such that The counter electrode can be printed on the second plate of the core 30. Thus, the core 30 with the exposed corners 3040, 3042 is suitable for mass production.

As described in embodiments of the present invention, the cross-section of the post in the core is substantially symmetrical with respect to its major axis (e.g., first axis A1) and minor axis (e.g., second axis A2) in the manufacturing error range. In addition, compared to conventional chokes, since the cross section of the column in the core is non-circular and non-square, for example The elliptical shape, etc., the cross-sectional area of the middle column can be effectively increased. Therefore, the saturation current of the choke can be effectively improved. In addition, since the cross section of the center pillar has two opposite curved sides, the wire can be smoothly wound on the center pillar, and the characteristics of the choke (for example, saturation current, DC impedance, magnetic flux density, etc.) are better than conventional ones. The chokes come well.

The above are only the preferred embodiments of the present invention, and all changes and modifications made to the scope of the present invention should be within the scope of the present invention.

3‧‧‧Current

30‧‧‧ core

300‧‧‧中柱

302‧‧‧ first board

304‧‧‧Second board

306‧‧‧ joints

3040, 3042‧‧‧ corner

A1‧‧‧ first axis

A2‧‧‧ second axis

C‧‧‧ Center

E1‧‧‧ curved sides

E2‧‧‧ first straight side

E3‧‧‧Second straight side

d, t, X, Y‧‧‧ length

Claims (28)

A choke device comprising: a one-piece core body made of the same material, the one-piece core body having a first plate piece, a second plate piece and a center column, wherein the center column is located at the first Between a plate and the second plate, a winding space is located between the first plate, the second plate and the center pillar; wherein the center pillar has a non-circular and non-square cross section The section is perpendicular to an axial direction of the center pillar, the section of the center pillar has a first axis and a second axis, and the first axis intersects the second axis at a center of the section of the center pillar And being perpendicular to each other; and wherein one of the sections of the center pillar includes two curved sides, four first straight sides, and two second straight sides, the four first straight sides being substantially parallel The first axis, the two second straight sides are substantially parallel to the second axis, and each of the first straight sides corresponds to one of the two curved sides and the second second straight side One of the sides. The choke of claim 1 wherein the length of the section along the first axis is longer than or substantially equal to the length of the section along the second axis. The choke of claim 1, wherein the second straight side is shorter than the length of the cross section along the second axis and satisfies the following inequality: Where Y represents the length of the section along the second axis, and d represents The difference from the half of the length of the second straight side. The choke of claim 1 wherein the ratio of the length of the second straight side to the length of the section along the first axis is between 0.5 and 0.7. The choke of claim 1, wherein there is no gap or intervening structure between the center post, the junction of the first plate and the second plate. The choke device of claim 1 further comprising: a wire wound on the center pillar and located in the winding space; and a magnetic material filled in the winding space and covering the wire, wherein the magnetic material comprises a resin and a magnetic powder, and the magnetic material One of the magnetic powders has an average particle size of less than 20 microns. The turbulent device of claim 6, wherein the magnetic powder comprises an iron powder or a metal powder, and the magnetic powder is contained in the magnetic material in a range of between 50% by weight and 90% by weight. The choke according to claim 6, wherein a magnetic permeability of the magnetic material is between 4 and 21. The turbulent device of claim 8, wherein the magnetic material is filled in the winding space via a transfer molding process, an injection molding process or a coating process; when the magnetic material is filled in the transfer molding process When the winding space is in the space, the magnetic permeability of the magnetic material is between 8 and 21; when the magnetic material is filled in the winding space via the injection molding process, the magnetic permeability of the magnetic material is between 6 and Between 18; when the magnetic material is filled in the winding space via the coating process, the magnetic permeability of the magnetic material is between 4 and 12. The choke according to claim 1, wherein the one-piece core is made of a metal powder and a mixture of a binder, the metal powder being contained in the one-piece core in an amount of more than 90% by weight, and One of the metal powders has an average particle size between 10 microns and 12 microns. The choke of claim 1 wherein the one-piece core has a magnetic permeability between 25 and 60. The choke of claim 1, wherein a ratio of a top surface of the first sheet to a bottom surface of the second sheet is greater than 94%. The choke according to claim 1, wherein at least one corner of the second plate is exposed from the first plate in a viewing direction from the first plate toward the second plate. The choke of claim 1 wherein the first first straight sides of the first side of the first axis are substantially aligned with each other in a direction parallel to the first axis and are located at the first axis The other two first straight sides of a second side are substantially aligned with each other in a direction parallel to the first axis, the first side being opposite the second side. A choke device comprising: a one-piece core body made of the same material, the one-piece core body having a first plate piece, a second plate piece and a center column, wherein the center column is located at the first Between a plate and the second plate, a winding space is located between the first plate, the second plate and the center pillar, and the magnetic permeability of the one-piece core is between 25 and 60 a wire wound around the center pillar and located in the winding space; and a magnetic material filled in the winding space and covering the wire, the magnetic permeability of the magnetic material is between 4 and 21 between. The turbulent device of claim 15, wherein the center pillar has a non-circular and non-square cross section perpendicular to an axial direction of the center pillar, the section of the center pillar having a first axis and a second axis, the first axis intersecting the second axis at a center of one of the sections of the center pillar and perpendicular to each other. The choke of claim 15 wherein the section is longer or substantially equal to the length of the section along the second axis along the length of the first axis. The turbulent device of claim 16, wherein one of the sections of the center pillar comprises two curved sides, four first straight sides, and two second straight sides, the four first straight The side edges are substantially parallel to the first axis, the two second straight sides are substantially parallel to the second axis, and each of the first straight sides corresponds to one of the two curved sides and the second One of the second straight sides. The choke of claim 18, wherein the second straight side is shorter than the length of the cross section along the second axis and satisfies the following inequality: Where Y represents the length of the section along the second axis, and d represents The difference from the half of the length of the second straight side. The choke of claim 18, wherein the first straight side of the first side of the first axis is two straight The sides are substantially aligned with each other in a direction parallel to the first axis, and the other two first straight sides on a second side of the first axis are substantially aligned with each other in a direction parallel to the first axis, the first One side is opposite the second side. The choke of claim 18, wherein the ratio of the length of the second straight side to the length of the section along the first axis is between 0.5 and 0.7. The choke of claim 15 wherein there is no gap or intervening structure between the center post, the junction of the first sheet and the second sheet. The choke according to claim 15, wherein the magnetic material comprises a resin and a magnetic powder, and one of the magnetic powders has an average particle diameter of less than 20 μm. The choke according to claim 23, wherein the magnetic powder comprises an iron powder or a metal powder, and the content of the magnetic powder in the magnetic material ranges between 50% by weight and 90% by weight. The turbulent device of claim 15, wherein the magnetic material is filled in the winding space via a transfer molding process, an injection molding process or a coating process; when the magnetic material is filled in the transfer molding process When the winding space is in the space, the magnetic permeability of the magnetic material is between 8 and 21; when the magnetic material is filled in the winding space via the injection molding process, the magnetic permeability of the magnetic material is between 6 and Between 18; when the magnetic material is filled in the winding space via the coating process, the magnetic permeability of the magnetic material is between 4 and 12. The turbulent device of claim 15, wherein the one-piece core is made of a metal powder and a mixture of a binder, the metal powder being contained in the one-piece core in an amount of more than 90% by weight, and One of the metal powders has an average particle size between 10 microns and 12 microns. The choke of claim 15 wherein the ratio of the top surface of the first panel to the bottom surface of the second panel is greater than 94%. The choke of claim 15, wherein at least one corner of the second panel is exposed from the first panel in a viewing direction from the first panel toward the second panel.