Compact coupled inductor

Abstract

To provide a method for improving magnetic properties of magnetically active components of converters.SOLUTION: A compact coupled inductor CI with improved properties comprises a base B, a top T, a shared leg SL between the base and the top, two center legs CL1, CL2 between the base and the top, and a first vertical gap GCL in the first center leg CL1 and / or the second center leg CL2. Two coupled inductors are connected such that areas with chamfered edges are arranged one next to another. In the coupled inductor resulting from the connection, chamfered circumferences form two notches arranged on opposite sides of the footprint.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to coupled inductors, and in particular to magnetically coupled inductors that can be used in voltage converters, such as DC-DC converters. [Background technology]

[0002] A DC-DC converter can be used to convert the first DC voltage level to a second DC voltage level, which can be lower or higher than the first DC voltage level.

[0003] DC-DC converters are typically required to be compatible with high-power applications, operate with high power efficiency, and have small spatial dimensions, which can be achieved by reducing losses such as core losses.

[0004] Furthermore, it is essential that the voltage ripple present at the output port is as small as possible.

[0005] From US Pat. No. 5,999,249 and US Pat. No. 5,999,249, for example, coupled inductors are known which are used in DC-DC converters. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] U.S. Patent No. 7,612,640 [Patent Document 2] U.S. Patent No. 6,362,986 Summary of the Invention [Problem to be solved by the invention]

[0007] However, in addition to the above cited objectives, it would be further desirable to have converters with further improved properties, in particular improved magnetic properties of the magnetically active components of the converter. [Means for solving the problem]

[0008] For that purpose, there is provided a coupled inductor according to independent claim 1. The dependent claims provide preferred embodiments.

[0009] The coupled inductor includes a bottom portion and a top portion. The coupled inductor further includes a shared leg between the bottom portion and the top portion, a first central leg between the bottom portion and the top portion, and a second central leg between the bottom portion and the top portion. The coupled inductor further includes a first vertical gap within the first central leg and / or a first vertical gap within the second central leg. The coupled inductor further includes a first coil and a second coil. The first coil is wound around the first central leg. The second coil is wound around the second central leg. The shared leg is disposed between the central legs.

[0010] The first and second coils are electrically connectable or coupleable to other circuit elements of the corresponding DC-DC converter, and the corresponding central legs of the coupled inductors provide magnetic cores utilized to conduct magnetic flux associated with the corresponding coils.

[0011] At least a portion of the bottom and top portions establish additional flux conducting segments to provide improved magnetic flux conductance. The plurality of center legs have corresponding coils wound around the material of the center legs, the center legs being positioned essentially in the center of the corresponding coils.

[0012] The shared legs establish a magnetic flux conduction path available to the magnetic flux associated with the different coils, and thus the corresponding conductance path is "shared" by the different coils.

[0013] The base, legs, and top of the coupled inductor are stacked such that the legs are positioned on or above the base and the top is positioned vertically above the legs, which is parallel to the Z axis and perpendicular to the XY plane.

[0014] The central legs and the shared leg are disposed adjacent to each other on the bottom of the coupled inductor, and the shared leg is disposed between at least two of the central legs in the horizontal direction in the XY plane.

[0015] The leakage inductance of the described coupled inductor can be adjusted by adjusting the spatial cross-sectional area of ​​the legs and the vertical height of at least one gap.

[0016] Additionally, the described coupled inductors reduce fringe losses, which result from magnetic flux that is not contained in a leg, e.g., a shared leg, but extends inside the conductive material of the coil.

[0017] Furthermore, the described coupled inductors may provide improved magnetic coupling, specifically by selecting corresponding parameters such as the cross-sectional area of ​​the legs and / or the height of one or more gaps.

[0018] Thus, a coupled inductor is provided that has reduced leakage losses, improved magnetic coupling, and adjustable leakage inductance compared to known coupled inductors, thereby providing a DC-DC converter with improved electrical characteristics, such as increased power efficiency in a reduced spatial dimension. Thus, an improved, more compact coupled inductor is provided.

[0019] The coupled inductor may include a first vertical gap in the first central leg and a first vertical gap in the second central leg.

[0020] By providing a vertical gap in each of the first and second central legs, a symmetrical structure can be provided with respect to the path of magnetic flux. The vertical gaps in the two legs can have the same height, or the heights of the gaps in the two legs can be different.

[0021] This provides additional degrees of freedom in tailoring the magnetic flux, specifically the path of the magnetic flux. By being able to adjust the spatial dimensions of the gap, leakage inductance, coupling losses, or fringing losses can be adjusted. Furthermore, dimensions can be provided that improve a combination of two or even three of these parameters.

[0022] The ratio of the vertical gap height per leg to the distance between the bottom and top can be from 0% to 80%, more preferably from 0.5% to 1.5%, e.g., 1.0%.

[0023] The unique effect of this dimensional ratio is that magnetic coupling is substantially improved compared to other ratios.

[0024] In this respect, the distance between the bottom and top is essentially equivalent to the length of the leg in the vertical direction.

[0025] For simplicity, the gap in the leg is considered to be part of the leg, and therefore the height of the vertical gap is included in the length of the leg, although it is understood that the gap does not include any material in the leg.

[0026] Providing a ratio between the height of the vertical gap and the distance between the bottom and top, i.e., the ratio between the height of the vertical gap and the length of the legs, provides a useful parameter for optimizing the magnetic properties of the coupled inductor.

[0027] The coupled inductor may further comprise a vertical gap in the shared leg.

[0028] Providing a gap in the shared leg provides an additional degree of freedom to optimize the magnetic flux of the coupled inductor, improving the magnetic properties of the coupled inductor.

[0029] Specifically, a suitable ratio between the height of one or more gaps in the center leg and the height of one or more gaps in the shared leg can be provided as a parameter useful for optimizing the magnetic behavior of the coupled inductor.

[0030] The ratio of the sum of the gap heights in the central leg to the gap heights in the shared leg can be from 0.01% to 50%, for example, 1%, 5%, 10%, 20%, or 40%.

[0031] Correspondingly, the coupled inductor may include one or more additional vertical gaps in the central leg.

[0032] The coupled inductor may also include one or more additional vertical gaps in the shared leg.

[0033] Providing two or more gaps per leg, i.e. per central leg or per shared leg, instead of one larger gap, provides a simple way to achieve reduced fringe loss.

[0034] As previously mentioned, fringe losses result from magnetic flux leaving the provided flux conduction path and entering the conductive material of adjacent coils.

[0035] Dividing the spatial region into a greater number of gaps reduces the total volume of conductive material through which magnetic flux enters adjacent coils, reducing the corresponding deleterious effects on the current flow in the corresponding coils.

[0036] It should be noted that the number of shared legs is not limited to one. Instead, the coupled inductor may include one or more additional shared legs. The shared legs are disposed between the multiple central legs.

[0037] The number of center legs is not limited to two. Alternatively, the number of center legs may be greater than two. Specifically, the number of center legs may be 3, 4, 5, 6, 7, 8, 9, 10, or more. However, the number of center legs is preferably an even number, such as 2, 4, 6, 8, 10, or more. By providing an even number of center legs, corresponding coils wound around the center legs can be electrically connected to enable interleaved switching. A DC-DC converter with coils electrically connected in parallel increases the power capability of the converter. Interleaved switching, i.e., a 180° phase shift between each pair of coils, can substantially reduce output voltage ripple.

[0038] In such multi-phase interleaved applications, one power inductor can be used for each phase, thereby reducing output voltage ripple. The inductive coupling of multiple coils further reduces the magnetic flux in the center leg, resulting in lower magnetic losses and higher power efficiency. Each center leg and each shared leg may have a cross-sectional area at a specific vertical position between the bottom and top. The cross-sectional area of ​​the center leg at a specific vertical position, i.e., vertical height, may be smaller than the cross-sectional area of ​​the shared leg at the same height.

[0039] Specifically, the cross-sectional area of ​​the central leg may be smaller than the cross-sectional area of ​​each of the single shared legs.

[0040] In this manner, the shared legs have a larger cross-sectional area than the center legs, although the number of center legs can be greater than the number of shared legs. Having specific cross-sectional areas for the shared legs and / or center legs provides additional freedom in flux design to improve magnetic properties.

[0041] Specifically, the sum of the cross-sectional areas of all the central legs may be greater than the sum of the cross-sectional areas of all the shared legs.

[0042] Additionally, the sum of the cross-sectional areas of all the common legs may be greater than 0.5 times the sum of the cross-sectional areas of all the central legs.

[0043] Additionally, the sum of the cross-sectional areas of all the shared legs may be less than 1.0 times the sum of the cross-sectional areas of all the center legs.

[0044] In this regard, the reference provided for the cross-sectional area may be a particular vertical position, e.g., the midpoint of the height between the bottom and the top, although a corresponding reference may also be given as a vertical position that may be set between the bottom and the top of the coupled inductor, respectively.

[0045] Additionally, the sum of the heights of the vertical gaps of the shared legs may be greater than the sum of the heights of the vertical gaps of the central legs.

[0046] Also, the total height of the shared leg gaps may be less than 20 times the height of the center leg gap.

[0047] These standards provide an improved magnetic flux conduction path within the coupled inductor to achieve specific requirements (specific tailored leakage inductance, reduced fringe losses, and improved coupling).

[0048] Additionally, the bottom and / or top may have one or more chamfered edges or notches.

[0049] Specifically, the bottom and top portions can have the same footprint. More specifically, the coupled inductor can have a symmetrical structure with respect to the legs, bottom portion, and top portion, with a symmetry plane disposed perpendicular to the Z axis and centered between the bottom and top portions.

[0050] The bottom and top portions may have essentially rectangular footprints with essentially rounded corners, but the two adjacent peripheral edges of the four corners may be chamfered, which is the case when the coupled inductor includes a single shared leg and two center legs.

[0051] When a coupled inductor has four central legs and a single shared leg, the coupled inductor may have an essentially rectangular or quadratic footprint. The footprint is achieved by symmetrically placing two coupled inductors with two central legs adjacent to each other, such that the areas with chamfered edges are adjacent to each other. The chamfered edges form two notches in the coupled inductor, located on either side of the footprint.

[0052] The common leg may project horizontally from the bottom region.

[0053] The vertical gap may have a height of 0.001 mm to 10 mm, preferably 0.1 mm.

[0054] Specifically, the vertical gap in the center leg may be 0.14 mm, and the vertical gap in the shared leg may be 2.5 mm.

[0055] Bottom and top are 18mm 2 (e.g., 3mm x 6mm) to 45,000mm 2 (e.g., 300 mm x 150 mm). A preferred value is 175 mm. 2 from 700mm 2 Up to, for example, 375 mm 2 It could be.

[0056] The coupled inductor may have a height of 3 mm to 150 mm, preferably 12 mm to 18 mm, for example 13.4 mm.

[0057] Furthermore, the coil may comprise or consist solely of a material selected from copper (Cu), aluminum (Al), silver (Ag), finally impure materials, or alloys thereof.

[0058] The conductor of the coil can be a rectangular flat wire, a round wire, or a Litz wire made of the above materials.

[0059] The conductors may be insulated with enamelled insulation.

[0060] The ends of the coil can be used as connectors to a PCB.

[0061] The ends may be coated with a conductive material to promote solderability, and may be coated with Sn or a suitable alloy of Sn, Ni, Cu and / or Ag.

[0062] The legs, bottom, and top can be made of a ferromagnetic material, such as iron (Fe), nickel (Ni), or an alloy containing iron or nickel, or a ferrite ceramic or metal powder composite, preferably MnZn ferrite, although MnZn ferrite is preferred.

[0063] The coils may have interleaved coupling with each other.

[0064] Specifically, each coil may have a specific dedicated coil provided with interleaved switching with a 180° phase shift to reduce output voltage ripple.

[0065] Additionally, the DC-DC converter may include a coupled inductor as described above.

[0066] Note that there may only be one gap in the center leg, small enough to improve coupling.

[0067] The basic operating principles and details of a preferred embodiment of the coupled inductor are explained with reference to the accompanying schematic diagrams. [Brief explanation of the drawings]

[0068] [Figure 1] FIG. 1 is a side view of a coupled inductor CI. [Figure 2] FIG. 2 is a cross-sectional top view of the coupled inductor shown in FIG. [Figure 3] FIG. 3 is a side view of a coupled inductor with four center legs. [Figure 4] FIG. 4 is a cross-sectional top view of a corresponding coupled inductor CI having four central legs. [Figure 5] FIG. 5 is a side view of a coupled inductor with several gaps in the shared leg. [Figure 6] FIG. 6 is a diagram illustrating the electrical configuration of a coil within the circuit environment of selected circuit elements of a DC-DC converter. [Figure 7] FIG. 7 shows a coupled inductor configuration with six central legs. DETAILED DESCRIPTION OF THE INVENTION

[0069] FIG. 1 shows a side view of a coupled inductor CI along the Y-axis. The coupled inductor CI includes a bottom portion B and a top portion T. The top portion T and the bottom portion B are arranged above and below each other in the vertical direction (Z-direction). A first central leg CL1 and a second central leg CL2 are arranged between the top portion T and the bottom portion B in the vertical direction. A shared leg SL is also arranged between the top portion T and the bottom portion B. The shared leg SL is arranged between the first central leg CL1 and the second central leg CL2 in the horizontal direction X. A first coil C1 is wound around the first central leg CL1. A second coil C2 is wound around the second central leg CL2. Therefore, the first central leg and the second central leg are essentially arranged at the centers of the corresponding coils C1 and C2. The shared leg SL is provided to conduct magnetic flux to the first central leg and the second central leg, respectively.

[0070] The first central leg CL1 is provided with a gap GCL, the second central leg CL2 is provided with a further gap GCL, and the shared leg SL is provided with a gap GSL.

[0071] Providing at least one gap in its center leg CL provides a parameter useful for optimizing the magnetic behavior of the coupled inductor. Providing gaps in each of the center legs and adding gaps in the shared leg provides additional degrees of freedom that can be used to optimize leakage inductance, coupling parameters, or both.

[0072] 2 shows cross sections of the center legs CL1, CL2 and the shared leg SL parallel to the XY plane. The cross-sectional area of ​​the shared leg is larger than the cross-sectional area of ​​each of the center legs CL1 or CL2. However, for an optimized magnetic flux conduction path, it is preferable that the cross-sectional area of ​​the shared leg SL is smaller than the sum of the two cross-sectional areas of both center legs.

[0073] Furthermore, the bottom part B has an essentially rectangular footprint with two rounded corners and two chamfered peripheries CE, at the Y positions of which the shared legs SL extend locally along the horizontal direction S.

[0074] On its opposite side, the common leg SL has a protrusion PT at which the common leg SL extends beyond the periphery of the base B.

[0075] Figures 3 and 4 show side and cross-sectional views of an embodiment with four central legs. Specifically, Figure 4 shows an embodiment with four central legs obtained by joining two of the sections shown in Figure 2 together. In that embodiment, the chamfered peripheral areas are joined together to form a cutout that extends into the base. The cutout can have a depth to width ratio of 0.5, meaning that the cutout is twice as deep as it is wide.

[0076] 5 further shows that the gap in the shared leg can be divided into three sub-gaps G1, G2, and G3. This multiple smaller gap reduces fringing losses caused by magnetic flux extending into the material of coil C, rather than a single larger gap.

[0077] Even in the center leg, it is possible to divide a single larger gap into multiple smaller gaps within the center leg.

[0078] The number of gaps in the shared leg or central leg can be 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 or more.

[0079] Figure 6 shows an equivalent circuit diagram of the DC-DC converter DCC. A voltage source VS provides predetermined potentials at two output ports. The output ports of the voltage source VS are electrically connectable to two inductance elements L1 and L2 by switches S1 and S2. The two inductance elements L1 and L2 are realized by two coils C of the aforementioned coupled inductor with two center legs. The two inductance elements are magnetically coupled through the material of the bottom and common legs. The converter DCC also includes two diodes D1 and D2 electrically connected in series between the switches S1 and S2. The two inductance elements L1 and L2 are electrically connected to an output port OUT, which provides a selected secondary DC voltage level for use by an external circuit environment. An additional capacitance element C can be electrically connected to the output port OUT to further reduce voltage ripple.

[0080] Figure 7 shows a coupled inductor with six center legs CL and six coils C. All six center legs share a single common leg SL. Notches N can be placed in the interface regions between the bottoms of adjacent center legs CL.

[0081] The opposing center legs and their corresponding coils are preferably electrically connected in an interleaved arrangement to provide three 180° interleaved coil pairs.

[0082] The coupled inductor and DC-DC converter are not limited to the details of the embodiments described above or shown in the figures. The coupled inductor may include additional electrical connections or ports and additional magnetic flux conducting elements. [Explanation of symbols]

[0083] AC center leg region AS Shared Leg Area B Bottom C Capacitor element C1 First coil C2 Second coil CE chamfered edges CI Coupled Inductor CL1 1st center leg CL2 2nd center leg D1 First diode D2 Second diode G1, G2, G3 shared leg split gap GCL center leg gap GSL Shared Leg Gap L1: First inductance element corresponding to the first coil L2 Second inductance element corresponding to the second coil OUT output port PT protrusion S1 First switch S2 Second switch T top VS voltage source X, Y horizontal direction Z vertical direction

Claims

[Claim 1] A coupled inductor having two coupled inductors, Each of the two coupled inductors has: a bottom portion and a top portion; a shared leg between the bottom and the top; a first central leg between the bottom and the top, and a second central leg between the bottom and the top; a first vertical gap in the first central leg and / or a first gap in the second central leg; a first coil and a second coil, the bottom portion and / or the top portion have one or more chamfered edges; the first coil is wound around the first center leg; the second coil is wound around the second center leg; the shared leg is disposed between the two central legs; A coupled inductor in which the two coupled inductors are connected so that the areas having chamfered peripheral portions are positioned adjacent to each other, thereby forming two notches located on opposite sides of the occupied area of ​​the chamfered peripheral portions within the coupled inductor created by the connection.

Images