Low-profile coupled inductors with leakage control

A low-profile coupled inductor includes a magnetic core and first and second windings. The magnetic core includes first and second end flanges, a winding form element, a first outer plate, and a first leakage post. The winding form element is disposed between and connects the first and second end flanges in a first direction. The first outer plate is disposed over and faces the first and second end flanges in a second direction. The first leakage post is disposed between the winding form element and the first outer plate in the second direction. The first winding is wound around the winding form element, between the first end flange and the first leakage post, and the second winding is wound around the winding form element, between the first leakage post and the second end flange. Each of the windings is wound around a common axis extending in the first direction.

BACKGROUND

Mobile electronic devices such as mobile telephones and tablet computers require extensive power management circuitry. For example, mobile electronic devices often include multiple switching power converters, such as for controlling battery charging and for providing point-of-load regulation for processors and other integrated circuits. Power management circuitry often occupies a signification portion, e.g., up to 40%, of a mobile electronic device's volume.

Switching power converters typically include one or more inductors to store energy in magnetic form. For example, a buck DC-to-DC converter includes an inductor as part of an output filter for removing AC components from the converter's switching waveform. Inductors are typically among the largest components within DC-to-DC converters. Therefore, it is desirable to minimize inductor size. However, it is difficult to reduce inductor size without degrading inductor performance and/or significantly increasing inductor cost. For example, reducing the cross-sectional area of an inductor's magnetic core typically increases the magnetic core's reluctance, thereby increasing core losses. As another example, decreasing winding cross-sectional area increases the winding's DC resistance, thereby increasing copper losses.

It is known that a single coupled inductor can replace multiple discrete inductors in a switching power converter, to improve converter performance, reduce converter size, and/or reduce converter cost. Examples of coupled inductors and associated systems and methods are found in U.S. Pat. No. 6,362,986 to Schultz et al., which is incorporated herein by reference. Some examples of coupled inductor structures are found in U.S. Patent Application Publication Number 2004/0113741 to Li et al., which is also incorporated herein by reference.

In contrast to discrete inductors, coupled inductors have two distinct inductance values, i.e., magnetizing inductance and leakage inductance. Magnetizing inductance is associated with magnetic coupling of the windings and results from magnetic flux generated by current flowing through one winding linking each other winding of the coupled inductor. Leakage inductance, on the other hand, is associated with energy storage and results from magnetic flux generated by current flowing through one winding not linking any of the other windings of the coupled inductor. Both magnetizing inductance and leakage inductance are important parameters in switching power converter applications of coupled inductors. Specifically, leakage inductance values typically must be within a limited range of values to achieve an acceptable tradeoff between low ripple current magnitude and adequate converter transient response. The magnetizing inductance value, on the other hand, typically must be significantly larger than the leakage inductance values to achieve sufficiently strong magnetic coupling of the windings, to realize the advantages of using a coupled inductor instead of multiple discrete inductors.

While use of a coupled inductor in a switching power converter offers many advantages, conventional coupled inductors typically having a higher profile (height) than discrete inductor counterparts. Many mobile electronic devices, though, have stringent low-profile requirements, often dictating that component profile not exceed one millimeter. Therefore, coupled inductor have not obtained large market share in low-profile applications. Additionally, conventional coupled inductors are often more expensive than discrete inductors having similar properties, and therefore coupled inductors are not widely used in low-current, i.e., less than 10 amperes per phase, applications.

SUMMARY

In an embodiment, a low-profile coupled inductor includes a magnetic core, a first winding, and a second winding. The magnetic core includes first and second end flanges, a winding form element, a first outer plate, and a first leakage post. The winding form element is disposed between and connects the first and second end flanges in a first direction. The first outer plate is disposed over and faces the first and second end flanges in a second direction, where the second direction is orthogonal to the first direction. The first leakage post is disposed between the winding form element and the first outer plate in the second direction. The first winding is wound around the winding form element, between the first end flange and the first leakage post, and the second winding is wound around the winding form element, between the first leakage post and the second end flange. Each of the first and second windings is wound around a common axis extending in the first direction.

In an embodiment, a low-profile coupled inductor includes a magnetic core, a first winding, and a second winding. The magnetic core includes first and second end flanges, a winding form element, an outer plate, and a first leakage post. The winding form element is disposed between and connects the first and second end flanges in a first direction. The outer plate at least partially surrounds each of the first and second end flanges and the winding form element, as seen when the low-profile coupled inductor is viewed cross-sectionally in the first direction. The first leakage post is disposed between the winding form element and the outer plate. The first winding is wound around the winding form element, between the first end flange and the first leakage post, and the second winding is wound around the winding form element, between the leakage post and the second end flange. Each of the first and second windings is wound around a common axis extending in the first direction.

In an embodiment, a low-profile coupled inductor includes a magnetic core, a first winding, and a second winding. The magnetic core includes first and second end flanges, a winding form element, and a first outer plate. The winding form element is disposed between and connects the first and second end flanges in a first direction. The first outer plate is disposed over and faces the first and second end flanges in a second direction, where the second direction is orthogonal to the first direction. The first winding is wound around the winding form element, and the second winding is wound around the winding form element. Each of the first and second windings is wound around a common axis extending in the first direction.

DETAILED DESCRIPTION OF THE EMBODIMENTS

Applicant has developed low-profile coupled inductors which at least potentially overcome one or more of the disadvantages of conventional coupled inductors discussed above. Certain embodiments of the low-profile coupled inductors have a profile of less than 1 mm and are therefore potentially suitable for use in applications with stringent low-profile requirements, such as mobile telephone and tablet computer applications. Additionally, certain embodiments of the low-profile coupled inductors allow windings to be wound directly on the magnetic core, thereby promoting manufacturing simplicity, low manufacturing cost, low material cost, and ease of forming multiple turns. Furthermore, the low-profile coupled inductors advantageously allow leakage inductance to be adjusted substantially independently of magnetizing inductance during coupled inductor design and/or manufacture.

FIG. 1shows a perspective view of a low-profile coupled inductor100with leakage control.FIG. 2shows an exploded perspective view of coupled inductor100, andFIG. 3shows a cross-sectional view of coupled inductor100taken along line1A-1A ofFIG. 1. Coupled inductor100includes a magnetic core102including a first end flange104, a second end flange106, a winding form element108, a first outer plate110, and a first leakage post112. First end flange104and second end flange106are separated from each other in a first direction114, and winding form element108is disposed between and connects first and second end flanges104and106in first direction114. First outer plate110is disposed over and faces first and second end flanges104and106in a second direction116, orthogonal to first direction114. First leakage post112is attached to winding form element108, such that first leakage post112is disposed between winding form element108and first outer plate110in second direction116. First end flange104is separated from first outer plate110in second direction116by a first magnetizing gap118, and second end flange106is separated from first outer plate110by a second magnetizing gap120in second direction116. First leakage post112is separated from first outer plate110by a first leakage gap122in second direction116. In some alternate embodiments, such as embodiments where magnetic core102is formed of magnetic material having a distributed gap, one or more of first magnetizing gap118, second magnetizing gap120, and first leakage gap122are omitted. First leakage post112could be replaced with two or more leakage posts, such as respective leakage posts coupled to each of winding form element108and first outer plate110, without departing from the scope hereof.

In some embodiments, magnetic core102is a homogenous core, i.e., each of first and second end flanges104and106, winding form element108, first outer plate110, and first leakage post112are formed of the same magnetic material, such as a ferrite magnetic material. However, in some other embodiments, magnetic core102is a non-homogenous core, i.e., two or more of its elements are formed of different magnetic materials. For example, in a particular embodiment, first and second end flanges104and106, winding forming element108, and first leakage post112are formed of a ferrite magnetic material, while first outer plate110is formed of a magnetic paste. Although the various components of magnetic core102are delineated in the figures to help a viewer distinguish these elements, lines separating elements of magnetic core102do not necessarily represent discontinuities in magnetic core102. For example, first and second end flanges104and106and winding form element108could be part of a single monolithic magnetic structure.

Low-profile coupled inductor100further includes a first winding124and a second winding126each wound around a common axis128extending in first direction114(seeFIG. 3). First and second windings124and126are not shown in the perspective views ofFIGS. 1 and 2, to better show magnetic core102. First winding124is wound around winding form element108, between first end flange104and first leakage post112, and second winding126is wound around winding form element108, between first leakage post112and second end flange106. Although first and second windings124and126are each illustrated as forming six turns around common axis128, the number of turns formed by each winding could vary without departing from the scope hereof. For example, in one alternate embodiment, each of first and second windings124and126forms only a single turn around common axis128.

FIG. 4is a cross-sectional view like that ofFIG. 3, but further illustrating approximate magnetic flux paths in low-profile coupled inductor100. Leakage magnetic flux130associated with first winding124, as well as leakage magnetic flux132associated with second winding126, flows through first leakage post112and first leakage gap122. Consequentially, leakage inductance values can be adjusted during design and/or manufacture of low-profile coupled inductor100simply by adjusting the configuration of first leakage post112and/or first leakage gap122. For example, if an increase in leakage inductance values is desired, magnetic permeability of first leakage post112can be increased, cross-sectional area of first leakage post112can be increased, and/or thickness of first leakage gap122, in second direction116, can be decreased. It should be appreciated that these multiple avenues for adjusting leakage inductance values enable fine control of leakage inductance values, which may be of particular benefit since leakage inductance is a critical parameter in switching power converter applications, as discussed above. In many conventional coupled inductors, in contrast, it is difficult to finely control leakage inductance values.

It should further be appreciated that magnetizing flux134, which links both of first winding124and second winding126, does not flow through first leakage post112or first leakage gap122. Consequently, leakage inductance values can advantageously be adjusted independently of magnetizing inductance values, by adjusting the configuration of first leakage post112and/or first leakage gap122. Thickness of first magnetizing gap118and second magnetizing gap120, in second direction116, can be selected to achieve a desired magnetizing inductance and/or resistance to magnetic saturation. For example, thickness of first magnetizing gap118and thickness of second magnetizing gap120can be decreased to increase the value of magnetizing inductance. As another example, thickness of first magnetizing gap118and thickness of second magnetizing gap120can be increased to reduce likelihood of magnetic saturation at high current levels. It is anticipated that the respective thicknesses of first magnetizing gap118and second magnetizing gap120will typically be smaller than thickness of first leakage gap122.

Low-profile coupled inductor100may achieve additional advantages. For example, winding form element108has a low profile136, as can be seen in the cross-sectional view ofFIG. 3, thereby minimizing length and associated resistance of first and second windings124and126, while also helping minimize profile136of coupled inductor100. In some embodiments, profile136is less than one millimeter. Additionally, there is little separation between first outer plate110and the remainder of magnetic core102, which also helps minimize profile136. Furthermore, the fact that both first winding124and second winding126are wound around common axis128potentially enables both windings to be simultaneously wound, thereby promoting manufacturing efficiency and simplicity. Moreover, first end flange104, first leakage post112, and second end flange106help confine first winding124and second winding126to their respective positions on winding form element108, thereby reducing, or even eliminating, the need for additional features to control winding position. Additionally, the fact that first and second windings124and126are wound around a portion of magnetic core102, instead of embedded in the magnetic core, allows greater flexibility in choosing magnetic material forming magnetic core102, thereby allowing, for example, use of a ferrite magnetic material. Furthermore, leakage post112helps prevent current crowding, and associated resistance, in first and second windings124and126.

The configuration of magnetic core102also advantageously allows 360-degree access to winding form element108before first outer plate110is installed, thereby potentially enabling first and second windings124and126to be wound directly on magnetic core102, such as by rotating magnetic core102around common axis128. In many conventional coupled inductors, in contrast, the magnetic core blocks access to at least part of the core's winding portion, necessitating that windings be wound separately from the magnetic core and subsequently installed on the magnetic core. Additionally, the ability to wind first and second windings124and126directly on magnetic core102facilitates forming the windings with multiple turns, to achieve large inductance values. It can be difficult or impossible to form windings with multiple turns, however, on some conventional coupled inductors that require that windings be wound separate from the magnetic core.

FIG. 5is a perspective view of a low-profile coupled inductor500, which is similar to low-profile coupled inductor100ofFIG. 1, but with different locations of first outer plate110and first leakage post112. Specifically, coupled inductor500includes a magnetic core502, which is like magnetic core102, but with first outer plate110and first leakage post112disposed on the side, instead of on the top, of winding form element108.FIG. 6shows an exploded perspective view of coupled inductor500, andFIG. 7shows a cross-sectional view of coupled inductor500taken along line5A-5A ofFIG. 5. First outer plate110is disposed over and faces first and second end flanges104and106in a second direction516, orthogonal to first direction114. First end flange104is separated from first outer plate110in second direction516by a first magnetizing gap518, and second end flange106is separated from first outer plate110by a second magnetizing gap520in second direction516. First leakage post112is separated from first outer plate110by a first leakage gap522in second direction516. First and second windings124and126are not shown in the perspective views ofFIGS. 5 and 6, but the windings are visible in the cross-sectional view ofFIG. 7. The fact that first outer plate110and first leakage post112are disposed on the side, instead of on the top, of winding form element108may result in a profile536of coupled inductor500being smaller than profile136of coupled inductor100, assuming otherwise identical configuration.

Either of low-profile coupled inductor100or500could be modified to include a second outer plate analogous to first outer plate110, but disposed on the opposite side of winding form element108from first outer plate110. For example,FIG. 8shows a perspective view of a low-profile coupled inductor800including two outer plates.FIG. 9show an exploded perspective view of coupled inductor800, andFIG. 10shows a cross-sectional view of coupled inductor800taken along line8A-8A ofFIG. 8. In some embodiments, low-profile coupled inductor800has a profile836of less than one millimeter.

Coupled inductor800includes a magnetic core802including a first end flange804, a second end flange806, a winding form element808, a first outer plate810, a second outer plate838, a first leakage post812, and a second leakage post840. First end flange804and second end flange806are separated from each other in a first direction814, and winding form element808is disposed between and connects first and second end flanges804and806in first direction814. First outer plate810and second outer plate838are disposed on opposite sides of winding form element808, such that each outer plate810and838is disposed over and faces first and second end flanges804and806in a second direction816, orthogonal to first direction814. First leakage post812is attached to winding form element808, such that first leakage post812is disposed between winding form element808and first outer plate810in second direction816. Similarly, second leakage post840is attached to winding form element808, such that second leakage post840is disposed between winding form element808and second outer plate838in second direction816. One or both of first leakage post812and second leakage post840could each be replaced with two or more leakage posts, without departing from the scope hereof.

First end flange804is separated from first outer plate810in second direction816by a first magnetizing gap818, and second end flange806is separated from first outer plate810by a second magnetizing gap820in second direction816. Similarly, first end flange804is separated from second outer plate838in second direction816by a third magnetizing gap842, and second end flange806is separated from second outer plate838by a second magnetizing gap844in second direction816. First leakage post812is separated from first outer plate810by a first leakage gap822in second direction816, and second leakage post840is separated from second outer plate838by a second leakage gap846in second direction816. In some alternate embodiments, such as embodiments where magnetic core802is formed of magnetic material having a distributed gap, one or more of first magnetizing gap818, second magnetizing gap820, third magnetizing gap842, fourth magnetizing gap844, first leakage gap822, and second leakage gap846are omitted. Although the various components of magnetic core802are delineated in the figures to help a viewer distinguish these elements, lines separating elements of magnetic core802do not necessarily represent discontinuities in magnetic core802. For example, first and second end flanges804and806and winding form element808could be part of a single monolithic magnetic structure.

Low-profile coupled inductor800further includes a first winding824and a second winding826each wound around a common axis828extending in first direction814(seeFIG. 10). First and second windings824and826are not shown in the perspective views ofFIGS. 8 and 9to better show magnetic core802. First winding824is wound around winding form element808, between first end flange804and first and second leakage posts812and840, and second winding826is wound around winding form element808, between first and second leakage posts812and840and second end flange806. Although first and second windings824and826are each illustrated as forming six turns around common axis828, the number of turns formed by each winding could vary without departing from the scope hereof.

FIG. 11is a cross-sectional view like that ofFIG. 10, but further illustrating approximate magnetic flux paths in low-profile coupled inductor800. Leakage magnetic flux830associated with first winding824, as well as leakage magnetic flux832associated with second winding826, both flow through first leakage post812, first leakage gap822, second leakage post840, and second leakage gap846. Magnetizing flux834, on the other hand, does not flow through any of first leakage post812, first leakage gap822, second leakage post840, or second leakage gap846. Consequentially, leakage inductance values of low-profile coupled inductor800can advantageously be adjusted during design and/or manufacture, independent of magnetizing inductance, simply by adjusting the configuration of first leakage post812, first leakage gap822, second leakage post840, and/or second leakage gap846. For example, leakage inductance could be decreased by increasing the thickness of first and/or second leakage gaps822and846in second direction816. Magnetizing inductance could be adjusted by adjusting the configuration of first magnetizing gap818, second magnetizing gap820, third magnetizing gap842, and/or fourth magnetizing gap844. For example, magnetizing inductance could be decreased by increasing the thickness of first magnetizing gap818, second magnetizing gap820, third magnetizing gap842, and/or fourth magnetizing gap844, in second direction816.

Use of dual first and second outer plates810and838, instead of just a single outer plate, provides dual paths for magnetic flux. Consequentially, low-profile coupled inductor800will have lower core losses and more even flux density distribution than coupled inductor100or500, assuming all three coupled inductors haves similar leakage inductance values, magnetizing inductance values, and case sizes.

Applicant has additionally discovered that it may be advantageous to split control of magnetizing gap thickness and leakage gap thickness between the winding form element and the outer plate(s). Splitting gap thickness control in such manner overcomes possible manufacturing difficulties associated with controlling multiple gap thicknesses from a single element.

FIGS. 12 and 13each illustrate a respective example of splitting control of gap thickness between the winding form element and one or more plates.FIG. 12is a cross-sectional view of a low-profile coupled inductor1200, which is similar to low profile coupled inductor500ofFIG. 5, but with first leakage post112connected to first outer plate110instead of to winding form element108. This configuration splits control of gap thickness between winding form element108and first outer plate110. Specifically, thickness of a first magnetizing gap1218and a second magnetizing gap1220are controlled by the configuration of winding form element108, while control of a first leakage gap thickness1222is controlled by configuration of first outer plate110.

FIG. 13is a cross-sectional view of a low-profile coupled inductor1300, which is similar to low-profile coupled inductor800ofFIG. 8, but with first leakage post812connected to first outer plate810, and second leakage post840connected to second outer plate838, instead of with both first leakage post812and second leakage post840connected to winding form element808. This configuration splits control of gap thickness between winding form element808and first and second outer plates810and838. Specifically, thickness of magnetizing gaps1318,1320,1342, and1344is controlled by the configuration of winding form element808, while thickness of a leakage gaps1322and1346is controlled by configuration of first outer plate810and second outer plate838.

The low profile coupled inductors discussed above could also be modified such that thickness of the magnetizing gaps is controlled by one or more outer plates. Such modifications, however, may reduce or eliminate the ability of the end flanges to control winding position.

Applicant has further discovered that leakage gap thickness can be controlled at least partially by forming a recess in the outer plates.FIGS. 14 and 15each illustrate a respective embodiment including an outer plate forming a recess. In particular,FIG. 14is a cross-sectional view of a low-profile coupled inductor1400, which is similar to low profile coupled inductor500ofFIG. 5, but with first outer plate110replaced with a first outer plate1410forming a recess1448extending into first outer plate1410in a direction1416. First leakage post112is also replaced with a first leakage post1412, which is connected to winding form element108and faces recess1448. Accordingly, a thickness of first leakage gap1422, and thereby leakage inductance values of coupled inductor1400, can be controlled by adjusting the configuration of winding form element108and/or first outer plate1410.

FIG. 15is a cross-sectional view of a low-profile coupled inductor1500, which is similar to low profile coupled inductor800ofFIG. 8, but with first outer plate810replaced with a first outer plate1510and second outer plate838replaced with second outer plate1538. First outer plate1510forms a first recess1548extending into first outer plate1510in a direction1516, and second outer plate1538forms a second recess1550extending into second outer plate1538in direction1516. First leakage post812is also replaced with a first leakage post1512, and second leakage post840is replaced with second leakage post1540. First leakage post1512is connected to winding form element808and faces first recess1548, and second leakage post1540is connected to winding form element808and faces second recess1550. Accordingly, a thickness of first leakage gap1522, and thereby the leakage inductance values of coupled inductor1500, can be controlled by adjusting the configuration of winding form element808and/or first plate1510. Similarly, a thickness of second leakage gap1546, and thereby the leakage inductance values of coupled inductor1500, can be controlled by adjusting the configuration of winding form element808and/or second plate1538.

The low-profile coupled inductors discussed above could be modified to include an outer plate at least partially surrounding the end flanges and winding form element. This modification promotes low magnetic flux density and even magnetic flux density distribution in a manner similar to that of using two outer plates.FIGS. 16 and 17illustrate one example of a low-profile coupled inductor including an outer plate surrounding the ends flanges and winding forming elements.FIG. 16is a top plan view of a low-profile coupled inductor1600, andFIG. 17is a cross-sectional view of low-profile coupled inductor1600taken along line16A-16A ofFIG. 16.

Low profile coupled inductor1600includes a magnetic core1602including a first end flange1604, a second end flange1606, a winding forming element1608, an outer plate1610, and a first leakage post1612. First end flange1604and second end flange1606are separated from each other in a first direction1614, and winding form element1608is disposed between and connects first end flange1604and second end flange1606in first direction1614. Each of first end flange1604, second end flange1606, and winding form element1608has a circular shape, as seen when low-profile coupled inductor1600is viewed cross-sectionally in first direction1614. Outer plate1610has a tubular shape and surrounds each of first end flange1604, second end flange1606, and winding form element1608, when low-profile coupled inductor1600is viewed cross-sectionally in first direction1614. First leakage post1612is connected to winding form element1608and extends along an outer circumference of winding form element1608, so that first leakage post1612forms a ring disposed between winding form element1608and outer plate1610, as seen low-profile coupled inductor1600is viewed cross-sectionally in first direction1614.

First end flange1604is separated from outer plate1610in a second direction1616by a first magnetizing gap1618, where second direction1616extends radially from a center axis1628extending in first direction1614. Additionally, second end flange1606is separated from outer plate1610by a second magnetizing gap1620in second direction1616. First leakage post1612, in turn, is separated from outer plate1610by a first leakage gap1622in second direction1616. In some alternate embodiments, such as embodiments where magnetic core1602is formed of magnetic material having a distributed gap, one or more of first magnetizing gap1618, second magnetizing gap1620, and first leakage gap1622are omitted. First leakage post1612could be replaced with two or more leakage posts, such as respective leakage posts coupled to each of winding form element1608and outer plate1610, without departing from the scope hereof. In an alternate embodiment, first leakage post1612is connected to outer plate1610, instead of winding form element1608. Although the various components of magnetic core1602are delineated in the figures to help a viewer distinguish these elements, lines separating elements of magnetic core1602do not necessarily represent discontinuities in magnetic core1602. For example, first and second end flanges1604and1606and winding form element1608could be part of a single monolithic magnetic structure.

Low profile coupled inductor1600further includes a first winding1624and a second winding1626each wound around center axis1628. First winding1624is wound around winding form element1608, such that first winding1624is disposed between first end flange1604and first leakage post1612in first direction1614. Similarly, second winding1626is wound around winding form element1608, such that second winding1626is disposed between first leakage post1612and second end flange1606in first direction1614.

FIG. 18is a cross-sectional view like that ofFIG. 17, but further illustrating approximate magnetic flux paths in low-profile coupled inductor1600. Leakage magnetic flux1630associated with first winding1624, as well as leakage magnetic flux1632associated with second winding1626, both flow through first leakage post1612and first leakage gap1622. Magnetizing flux1634, on the other hand, does not flow through either first leakage post1612or first leakage gap1622. Consequentially, leakage inductance values of low-profile coupled inductor1600can advantageously be adjusted during design and/or manufacture, independent of magnetizing inductance, simply by adjusting the configuration of first leakage post1612and/or first leakage gap1622. For example, leakage inductance could be decreased by increasing the thickness of first leakage gap1622in second direction1616. Magnetizing inductance can be adjusted by adjusting the configuration of first magnetizing gap1618and/or second magnetizing gap1620. For example, magnetizing inductance could be decreased by increasing the thickness of first magnetizing gap1618and/or second magnetizing gap1620in second direction1616.

Low-profile coupled inductor1600may achieve advantages similar to those discussed above with respect to low-profile coupled inductor100. For example, leakage inductance values can be adjusted independently of magnetizing inductance values, as discussed above. Additionally, the fact that both first winding1624and second winding1626are wound around common center axis1628potentially enables both windings to be simultaneously wound, thereby promoting manufacturing efficiency and simplicity. Furthermore, first end flange1604, first leakage post1612, and second end flange1606help confine first winding1624and second winding1626to their respective positions on winding form element1608, thereby reducing, or even eliminating, the need for additional features to control winding position. Moreover, the fact that first and second windings1624and1626are wound around a portion of magnetic core1602, instead of embedded in the magnetic core, allows greater flexibility in choosing magnetic material forming magnetic core1602. Additionally, the configuration of magnetic core1602advantageously allows 360-degree access to winding form element1608before outer plate1610is installed, thereby potentially enabling first and second windings1624and1626to be wound directly on magnetic core1602, such as by rotating magnetic core1602around center axis1628.

FIG. 19is a perspective view of a low-profile coupled inductor1900, which is similar to coupled inductor1600ofFIG. 16, but has a rectangular shape instead of a round shape.FIG. 20is a cross-sectional view of low-profile coupled inductor1900taken along line20A-20A ofFIG. 19, andFIG. 21is a cross-sectional view of low-profile coupled inductor1900taken along line21A-21A ofFIG. 19. Low profile coupled inductor1900includes a magnetic core1902including a first end flange1904, a second end flange1906, a winding forming element1908, a tubular outer plate1910, a first leakage post1912, and a second leakage post1940. First end flange1904and second end flange1906are separated from each other in a first direction1914, and winding form element1908is disposed between and connects first end flange1904and second end flange1906in first direction1914. Each of first end flange1904, second end flange1906, and winding form element1908has a rectangular shape, as seen when coupled inductor1900is viewed cross-sectionally in first direction1914. Outer plate1910surrounds each of first end flange1904, second end flange1906, and winding form element1908, when low-profile coupled inductor1900is viewed cross-sectionally in first direction1914. First leakage post1912and second leakage post1940are each disposed on opposite sides of winding form element1908, such that each leakage post1912and1940is disposed between winding form element1908and outer plate1910, in a second direction1916orthogonal to first direction1914.

First end flange1904is separated from outer plate1910in second direction1916and in a third direction1917by a first magnetizing gap1918, and second end flange1906is separated from outer plate1910by a second magnetizing gap1919in second direction1916and in third direction1917. Third direction1917is orthogonal to both first direction1914and second direction1916. First leakage post1912is separated from outer plate1910by a first leakage gap1922in second direction1916, and second leakage post1940is separated from outer plate1910by a second leakage gap1946in second direction1916. (SeeFIG. 20). In some alternate embodiments, such as embodiments where magnetic core1902is formed of magnetic material having a distributed gap, one or more of first magnetizing gap1918, second magnetizing gap1919, first leakage gap1922, and second leakage gap1946are omitted. One or more of first leakage post1912and second leakage post1940could be replaced with two or more leakage posts without departing from the scope hereof.

Low-profile coupled inductor1900further includes a first winding1924and a second winding1926similar to first winding1624and second winding1626of low-profile coupled inductor1600, respectively. Specifically, each of first winding1924and second winding1926is wound around a common axis1928extending in first direction1914. First winding1924is wound around winding form element1908, such that first winding1924is disposed between first end flange1904and first and second leakage posts1912and1940in first direction1914. Similarly, second winding1926is wound around winding form element1908, such that second winding1926is disposed between first and second leakage posts1912and1940and second end flange1906, in first direction1914.

FIG. 22is a perspective view of a low-profile coupled inductor2200, which is similar to low-profile coupled inductor1900ofFIG. 19, but with outer plate1910replaced with an outer plate2210which only partially surrounds first end flange1904, second end flange1906, and winding form element1908. Specifically, outer plate2210forms a rectangular C-shape, as seen when coupled inductor2200is view cross-sectionally in first direction2214. As a result, one side of coupled inductor2200is open, such as to allow for electrical connections with a printed circuit board or other electronic circuitry.FIG. 23is a cross-sectional view of low-profile coupled inductor2200taken along line23A-23A ofFIG. 22, andFIG. 24is a cross-sectional view of low-profile coupled inductor2200taken along line24A-24A ofFIG. 22.

First end flange1904is separated from outer plate2010in second direction2216and in a third direction2217by a first magnetizing gap2218, and second end flange1906is separated from outer plate2210by a second magnetizing gap2219in second direction2216and in third direction2217. Third direction2217is orthogonal to both first direction2214and second direction2216. First leakage post1912is separated from outer plate2210by a first leakage gap2222in second direction2216, and second leakage post1940is separated from outer plate2210by a second leakage gap2246in second direction2216. (SeeFIG. 23). In some alternate embodiments, one or more of first magnetizing gap2218, second magnetizing gap2219, first leakage gap2222, and second leakage gap2246are omitted. One or more of first leakage post1912and second leakage post1940could be replaced with two or more leakage posts without departing from the scope hereof.

The exemplary low-profile coupled inductors illustrated inFIG. 1-24are symmetrical. However, any of the coupled inductors disclosed herein could be modified to be asymmetrical, such as to achieve asymmetrical leakage inductance values or to enable use of two different winding configurations. For example,FIG. 25is a cross-sectional view of a low-profile coupled inductor2500, which is similar to low-profile coupled inductor800ofFIG. 8, but having asymmetrical windings and winding windows. Specifically, first winding824is replaced with first winding2524formed of low-gauge wire and forming five turns, while second winding826is replaced with second winding2526formed of relatively high-gauge wire and forming many turns. Additionally, first leakage post812and second leakage post840are disposed off-center along a width2552of coupled inductor2500, so that a first winding window2554for first winding2524is smaller than a second winding window2556for second winding2526. This asymmetric nature of coupled inductor2500may be desirable, for example, in applications where first winding2524must support large current values and small leakage inductance is desired, and where second winding2526need only support small current value and large leakage inductance is desired. The other low-profile coupled inductors disclosed herein could be modified to be asymmetrical in a similar manner to that ofFIG. 25.

With the exception of second winding2526in low-profile coupled inductor2500ofFIG. 25, the windings in the low-profile coupled inductors ofFIG. 1-25form a single row of turns along their respective winding form elements. This configuration advantageously minimizes winding thickness in a direction orthogonal to the common axis and also promotes strong magnetic coupling of windings. However, it may be desirable in some applications for the windings to form two or more rows of turns, to minimize winding thickness in a direction parallel to the center axis.

For example,FIG. 26is a perspective view of a low-profile coupled inductor2600, which is similar to low-profile coupled inductor500ofFIG. 5, but has been rotated by 90 degrees. Low profile coupled inductor2600includes a first winding2624and a second winding2626in place of first winding124and second winding126, respectively. Each of first winding2624and second winding2626forms multiple turns in a plane orthogonal to a profile2658of the coupled inductor, to help minimize profile2658.

Similarly,FIG. 27is a perspective view of a low-profile coupled inductor2700, which is similar to low-profile coupled inductor800ofFIG. 8, but has been rotated by 90 degrees. Low profile coupled inductor2700includes a first winding2724and a second winding2726in place of first winding824and second winding826, respectively. Each of first winding2724and second winding2726forms multiple turns in a plane orthogonal to a profile2758of the coupled inductor, to help minimize profile2758.

The low-profile coupled inductors disclosed herein optionally further include electrical contacts (not shown), such as solder tabs or through-hole pins, for interfacing the windings with external circuitry. The contacts are applied, for example, using known techniques for disposing electrical contacts on magnetic elements. In certain embodiments, these electrical contacts are disposed on the winding form element so that only the winding form element need be coupled to a supporting substrate, such as a printed circuit board. This configuration advantageously isolates the end flanges and outer plate(s) from the supporting substrate and its associated thermal and mechanical strain, thereby promoting stable magnetizing and leakage gap thickness.

While the low-profile coupled inductors discussed above include at least one leakage post, each of these coupled inductors could be modified to omit its respective one or more leakage posts. For example,FIG. 28is a cross-sectional view of a low-profile coupled inductor2800, which is similar to low-profile coupled inductor100ofFIG. 1, but does not include a leakage post. In particular, low-profile coupled inductor2800includes a magnetic core2802including a first end flange2804, a second end flange2806, a winding form element2808, and a first outer plate2810. First end flange2804and second end flange2806are separated from each other in a first direction2814, and winding form element2808is disposed between and connects first and second end flanges2804and2806in first direction2814. First outer plate2810is disposed over and faces first and second end flanges2804and2806in a second direction2816, orthogonal to first direction2814. First end flange2804is separated from first outer plate2810in second direction2816by a first magnetizing gap2818, and second end flange2806is separated from first outer plate2810by a second magnetizing gap2820in second direction2816.

Low-profile coupled inductor2800further includes a first winding2824and a second winding2826each wound around a common axis2828extending in first direction2814. First winding2824is separated from second winding2826in first direction2814by a separation distance2860. Leakage inductance values of first winding2824and second winding2826are adjusted during the design or manufacture of coupled inductor2800, for example, by adjusting separation distance2860. For example, if greater leakage inductance is desired, separation distance2860can be increased. Alternately or additionally, leakage inductance can be adjusted during coupled inductor design or manufacture by adjusting the configuration, such as cross-sectional area, of first end flange2804and/or second end flange2806. Although low-profile coupled inductor2800is illustrated as being symmetrical, it would be modified to be asymmetrical without departing from the scope hereof.

The low-profile coupled inductors disclosed above are advantageously capable of achieving controlled leakage inductance values which are relatively large, such as for use in multi-phase converter applications where the coupling factor between the phases is higher than required, where the coupling factor is the ratio of magnetizing inductance to leakage inductance. In some applications, there may be a need for leakage inductance values to be relatively small, such as in low-profile coupled inductors having an extreme aspect ratio or a magnetic core formed of a low permeability magnetic material, to achieve a sufficiently large coupling factor.

Therefore, Applicant has additionally developed low-profile coupled inductors with interleaved windings which are capable of achieving relatively large controlled coupling factors. For example,FIG. 2900is a cross-sectional view of a low-profile coupled inductor2900, which is similar to low-profile coupled inductor2800ofFIG. 28, but with selective interleaving of windings.

Low-profile coupled inductor2900includes a magnetic core2902including a first end flange2904, a second end flange2906, a winding form element2908, and a first outer plate2910. First end flange2904and second end flange2906are separated from each other in a first direction2914, and winding form element2908is disposed between and connects first and second end flanges2904and2906in first direction2914. First outer plate2910is disposed over and faces first and second end flanges2904and2906in a second direction2916, orthogonal to first direction2914. First end flange2904is separated from first outer plate2910in second direction2916by a first magnetizing gap2918, and second end flange2906is separated from first outer plate2910by a second magnetizing gap2920in second direction2916.

Low profile coupled inductor includes a first winding2924and a second2926wound around winding form element2908and a common axis2928extending in first direction2914. First winding2924and second winding2926are interleaved within an interleaved portion2960of winding window2962, but the windings are not interleaved outside of interleaved portion2960. Magnetic flux will leak from winding form element2908to first outer plate2910between windings outside of interleaved portion2960. Within interleaved portion2960, in contrast, the magnetic flux will couple from one winding to the other, resulting in magnetizing inductance.

Coupling factor can advantageously be controlled by varying the portion of first and second windings2924and2926that are interleaved, or in other words, by varying the portion of winding window2962occupied by interleaved portion2960. For example, coupling factor can be increased during the design or manufacture of low-profile coupled inductor2900by increasing the portion of first and second windings2924and2926which are interleaved, or in other words, by increasing the size of interleaved portion2960. Maximum coupling factor can be achieved by fully interleaving first and second windings2924and2926.

Accordingly, coupled inductor parameters can be controlled in low-profile coupled inductor2900in a way that can increase the coupling factor for cases where the initial coupling factor is lower than desired. Additionally, the other low-profile coupled inductors disclosed herein could be modified so that their respective windings are interleaved in a similar manner. By the appropriate application of interleaving and/or leakage control posts, it is possible to independently control magnetizing and leakage inductances in a variety of structures where the magnetic properties prior to application of these methods may have exhibited either higher or lower than optimal coupling.

One possible application of the low-profile coupled inductors disclosed herein is in multi-phase switching power converter applications, including but not limited to, multi-phase buck converter applications, multi-phase boost converter applications, or multi-phase buck-boost converter applications. For example,FIG. 30illustrates one possible use of low-profile coupled inductor100(FIG. 1) in a multi-phase buck converter3000. Each of first winding124and second winding126is electrically coupled between a respective switching node Vxand a common output node Vo. A respective switching circuit3002is electrically coupled to each switching node Vx. Each switching circuit3002is electrically coupled to an input port3004, which is in turn electrically coupled to an electric power source3006. An output port3008is electrically coupled to output node Vo. Each switching circuit3002and respective inductor is collectively referred to as a “phase”3010of the converter. Thus, multi-phase buck converter3000is a two-phase converter.

A controller3012causes each switching circuit3002to repeatedly switch its respective winding end between electric power source3006and ground, thereby switching its winding end between two different voltage levels, to transfer power from electric power source3006to a load (not shown) electrically coupled across output port3008. Controller3012typically causes switching circuits3002to switch at a relatively high frequency, such as at one hundred kilohertz or greater, to promote low ripple current magnitude and fast transient response, as well as to ensure that switching induced noise is at a frequency above that perceivable by humans. Additionally, in certain embodiments, controller3012causes switching circuits3002to switch out-of-phase with respect to each other in the time domain to improve transient response and promote ripple current cancellation in output capacitors3014.

Each switching circuit3002includes a control switching device3016that alternately switches between its conductive and non-conductive states under the command of controller3012. Each switching circuit3002further includes a freewheeling device3018adapted to provide a path for current through its respective winding124or126when the control switching device3016of the switching circuit transitions from its conductive to non-conductive state. Freewheeling devices3018may be diodes, as shown, to promote system simplicity. However, in certain alternate embodiments, freewheeling devices3018may be supplemented by or replaced with a switching device operating under the command of controller3012to improve converter performance. For example, diodes in freewheeling devices3018may be supplemented by switching devices to reduce freewheeling device3018forward voltage drop. In the context of this disclosure, a switching device includes, but is not limited to, a bipolar junction transistor, a field effect transistor (e.g., a N-channel or P-channel metal oxide semiconductor field effect transistor, a junction field effect transistor, a metal semiconductor field effect transistor), an insulated gate bipolar junction transistor, a thyristor, or a silicon controlled rectifier.

Controller3012is optionally configured to control switching circuits3002to regulate one or more parameters of multi-phase buck converter3000, such as input voltage, input current, input power, output voltage, output current, or output power. Buck converter3000typically includes one or more input capacitors3020electrically coupled across input port3004for providing a ripple component of switching circuit3002input current. Additionally, one or more output capacitors3014are generally electrically coupled across output port3008to shunt ripple current generated by switching circuits3002.

Buck converter3000could be modified to use one of the other low-profile coupled inductors disclosed herein, such as low-profile coupled inductor500,800,1200,1300,1400,1500,1600,1900,2200,2500,2600,2700,2800, or2900. Additionally, buck converter3000could also be modified to have a different multi-phase switching power converter topology, such as that of a multi-phase boost converter or a multi-phase buck-boost converter, or an isolated topology, such as a flyback or forward converter without departing from the scope hereof.

Moreover, the low-profile coupled inductors disclosed herein could be used in heterogeneous converter applications, such as to achieve magnetic coupling of multiple single-phase converters having different topologies. For example, asymmetrical low-profile coupled inductor2500(FIG. 25) could be shared by a boost converter and an inverter, where first winding2524forms part of the boost converter, and second winding2526forms parts of the inverter. The asymmetrical nature of low-profile coupled inductor2500allows the properties of each inductor therein, such as leakage inductance and current carrying capability of each inductor, to be tailored for its respective converter.

Combinations of Features

Features described above may be combined in various ways without departing from the scope hereof. The following examples illustrate some possible combinations:

(A1) A low-profile coupled inductor may include a magnetic core, a first winding, and a second winding. The magnetic core may include (1) first and second end flanges, (2) a winding form element disposed between and connecting the first and second end flanges in a first direction, (c) a first outer plate disposed over and facing the first and second end flanges in a second direction, the second direction orthogonal to the first direction, and (d) a first leakage post disposed between the winding form element and the first outer plate in the second direction. The first winding may be wound around the winding form element, between the first end flange and the first leakage post, and the second winding may be wound around the winding form element, between the first leakage post and the second end flange. Each of the first and second windings may be wound around a common axis extending in the first direction.

(A2) In the low-profile coupled inductor denoted as (A1), the first leakage post may be separated, in the second direction, from one of the winding form element and the first outer plate by a first leakage gap.

(A3) In the low-profile coupled inductor denoted as (A2), the first leakage post may be attached to the winding form element and may be separated from the first outer plate by the first leakage gap.

(A4) In the low-profile inductor denoted as (A3), the first outer plate may form a first recess extending into the first outer plate in the second direction, and the first leakage post may face the first recess in the second direction.

(A5) In the low-profile coupled inductor denoted as (A2), the first leakage post may be attached to the first outer plate and separated from the winding form element by the first leakage gap.

(A6) In any of the low-profile coupled inductors denoted as (A1) through (A5), the first outer plate may be separated from the first end flange by a first magnetizing gap in the second direction, and the first outer plate may be separated from the second end flange by a second magnetizing gap in the second direction.

(A7) In any of the low profile inductors denoted as (A1) through (A6), the winding form element and the first and second end flanges may be formed of a ferrite magnetic material, and the first outer plate may be formed of a magnetic paste.

(A8) In any of the low-profile coupled inductors denoted as (A1) through (A7), each of the first and second windings may form multiple turns around the winding form element.

(A9) In any of the low-profile coupled inductors denoted as (A1) through (A8), the magnetic core may further include (1) a second outer plate disposed over and facing the first and second end flanges in the second direction, such that the first and second end flanges and the winding form element are each disposed between first and second outer plates in the second direction, and (2) a second leakage post disposed between the winding form element and the second outer plate in the second direction.

(A10) In the low profile inductor denoted as (A9), the second leakage post may be separated from one of the winding form element and the second outer plate by a second leakage gap in the second direction.

(A11) In the low-profile coupled inductor denoted as (A10), the second leakage post may be attached to the winding form element and may be separated from the second outer plate by the second leakage gap.

(A12) In either of the low profile inductors denoted as (A10) or (A11), the second outer plate may form a second recess extending into the second outer plate in the second direction, and the second leakage post may face the second recess in the second direction.

(A13) In the low-profile coupled inductor denoted as (A10), the second leakage post may be attached to the second outer plate and separated from the winding form element by the second leakage gap.

(A14) In any of the low-profile coupled inductors denoted as (A9) through (A13), the second outer plate may be separated from the first end flange by a third magnetizing gap in the second direction, and the second outer plate may be separated from the second end flange by a fourth magnetizing gap in the second direction.

(B1) A low-profile coupled inductor may include a magnetic core, a first winding, and a second winding. The magnetic core may include (1) first and second end flanges, (2) a winding form element disposed between and connecting the first and second end flanges in a first direction, (c) an outer plate at least partially surrounding each of the first and second end flanges and the winding form element, as seen when the low-profile coupled inductor is viewed cross-sectionally in the first direction, and (d) a first leakage post disposed between the winding form element and the outer plate. The first winding may be wound around the winding form element, between the first end flange and the first leakage post, and the second winding may be wound around the winding form element, between the leakage post and the second end flange. Each of the first and second windings may be wound around a common axis extending in the first direction.

(B2) In the low-profile coupled inductor denoted as (B1), each of the first and second end flanges may have a circular shape, as seen when the low-profile coupled inductor is viewed cross-sectionally in the first direction, and the outer plate may have a ring shape, as seen when the low-profile coupled inductor is viewed cross-sectionally in the first direction.

(B3) In the low-profile coupled inductor denoted as (B1), each of the first and second end flanges may have a rectangular shape, as seen when the low-profile coupled inductor is viewed cross-sectionally in the first direction, and the outer plate may have a rectangular shape, as seen when the low-profile coupled inductor is viewed cross-sectionally in the first direction.

(B4) In the low-profile coupled inductor denoted as (B3), the outer plate may have a C-shape, as seen when the low-profile coupled inductor is viewed cross-sectionally in the first direction.

(B5) In the low-profile inductor denoted as (B4), each of the first and second end flanges may have a rectangular shape, as seen when the low profile coupled inductor is viewed cross-sectionally in the first direction, and the outer plate may have a rectangular C-shape, as seen when the low-profile coupled inductor is viewed cross-sectionally in the first direction.

(C1) A low-profile coupled inductor may include a magnetic core, a first winding, and a second winding. The magnetic core may include (1) first and second end flanges, (2) a winding form element disposed between and connecting the first and second end flanges in a first direction, and (c) a first outer plate disposed over and facing the first and second end flanges in a second direction, the second direction orthogonal to the first direction. The first and second windings may each be wound around the winding form element, such that the first winding is separated from the second winding in the first direction by a separation distance. Each of the first and second windings may be wound around a common axis extending in the first direction.

(C2) In the low-profile coupled inductor denoted as (C1), the first outer plate may be separated from the first end flange by a first magnetizing gap in the second direction, and the first outer plate may be separated from the second end flange by a second magnetizing gap in the second direction.

(C3) In either of the low profile inductors denoted as (C1) or (C2), the winding form element and the first and second end flanges may be formed of a ferrite magnetic material, and the first outer plate may be formed of a magnetic paste.

(C4) In any of the low-profile coupled inductors denoted as (C1) through (C3), each of the first and second windings may form multiple turns around the winding form element.

(C5) In any of the low-profile coupled inductors denoted as (C1) through (C4), the magnetic core may further include a second outer plate disposed over and facing the first and second end flanges in the second direction, such that the first and second end flanges and the winding form element are each disposed between first and second outer plates in the second direction.

(C6) In any of the low-profile coupled inductors denoted as (C1) through (C5), at least a portion of the first and second windings may be interleaved.

(D1) A multi-phase switching power converter may include any one of the low-profile coupled inductors denoted as (A1) through (A14), (B1) through (B5), and or (C1) through (C6).

(D2) In the multi-phase switching power converter denoted as (D1), each winding may be electrically coupled between a respective switching node and a common output node.

(D3) The multi-phase switching power converter denoted as (D2) may further include a respective switching circuit electrically coupled to each switching node.

(D4) The multi-phase switching power converter denoted as (D3) may further include a controller for causing each switching circuit to repeatedly switch its respective winding end between two different voltage levels, to transfer power from an electric power source to a load.

(D5) Any of the multi-phase switching power converters denoted as (D1) through (D4) may be a multi-phase buck converter.

Changes may be made in the above low-profile coupled inductors and associated methods without departing from the scope hereof. It should thus be noted that the matter contained in the above description and shown in the accompanying drawings should be interpreted as illustrative and not in a limiting sense.