Abstract:
A method of fabricating conducting crossover structures for power inductors comprises providing a first lead frame array including first lead frames, providing a second lead frame array including said second lead frames, stamping one side of a second lead frame array to define first and second terminals of said second lead frames, at least one of coating, spraying, applying and/or attaching an insulating material to said first lead frame array to form a first laminate, stamping said first laminate in a direction from said insulating material towards said first lead frame array to define first and second terminals of said first lead frames; and arranging said insulating material of said first laminate adjacent to and in contact with said one side of said second lead frame array to form a second laminate.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a divisional of U.S. patent application Ser. No. 11/367,176, filed Mar. 3, 2006, which is a divisional of U.S. patent application Ser. No. 10/875,903, filed on Jun. 24, 2004, which is a continuation-in-part of U.S. patent application Ser. No. 10/744,416, filed on Dec. 22, 2003, which is a continuation-in-part of U.S. patent application Ser. No. 10/621,128 filed on Jul. 16, 2003, all of which are incorporated herein by reference in their entirety. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates to inductors, and more particularly to power inductors having magnetic core materials with reduced levels of saturation when operating with high DC currents and at high operating frequencies. 
     BACKGROUND OF THE INVENTION 
     Inductors are circuit elements that operate based on magnetic fields. The source of the magnetic field is charge that is in motion, or current. If current varies with time, the magnetic field that is induced also varies with time. A time-varying magnetic field induces a voltage in any conductor that is linked by the magnetic field. If the current is constant, the voltage across an ideal inductor is zero. Therefore, the inductor looks like a short circuit to a constant or DC current. In the inductor, the voltage is given by: 
             v   =     L   ⁢         ⅆ   i       ⅆ   t       .             
Therefore, there cannot be an instantaneous change of current in the inductor.
 
     Inductors can be used in a wide variety of circuits. Power inductors receive a relatively high DC current, for example up to about 100 Amps, and may operate at relatively high frequencies. For example and referring now to  FIG. 1 , a power inductor  20  may be used in a DC/DC converter  24 , which typically employs inversion and/or rectification to transform DC at one voltage to DC at another voltage. 
     Referring now to  FIG. 2 , the power inductor  20  typically includes one or more turns of a conductor  30  that pass through a magnetic core material  34 . For example, the magnetic core material  34  may have a square outer cross-section  36  and a square central cavity  38  that extends the length of the magnetic core material  34 . The conductor  30  passes through the central cavity  38 . The relatively high levels of DC current that flow through the conductor  30  tend to cause the magnetic core material  34  to saturate, which reduces the performance of the power inductor  20  and the device incorporating it. 
     SUMMARY OF THE INVENTION 
     A power inductor according to the present invention includes a first magnetic core material having first and second ends. An inner cavity is arranged in the first magnetic core material that extends from the first end to the second end. A first notch is arranged in the first magnetic core material that projects inwardly towards the inner cavity from one of the first and second ends. A first conductor passes through the inner cavity and is received by the first notch. 
     In other features, a second notch is arranged in the first magnetic core material that projects inwardly towards the inner cavity from the other of the first and second ends. The first conductor is also received by the second notch. The first conductor is not insulated. A third notch is arranged in the first magnetic core material that projects inwardly towards the inner cavity from the one of the first and second ends. A fourth notch is arranged in the first magnetic core material that projects inwardly towards the inner cavity from the other of the first and second ends. A second conductor passes through the inner cavity and is received by the third and fourth notches. 
     In still other features of the invention, the first conductor passes through the inner cavity at least two times and is also received by the third and fourth notches. An additional 2n+1 notches are arranged in the first magnetic core material that project inwardly towards the inner cavity. The first conductor is also received by the 2n+1 additional notches. The first conductor passes through the inner cavity n+1 times. A slotted air gap in the first magnetic core material extends from the first end to the second end. An eddy current reducing material is arranged adjacent to at least one of an inner opening of the slotted air gap in the inner cavity between the slotted air gap and the first conductor and an outer opening of the slotted air gap. The eddy current reducing material has a permeability that is lower than the first magnetic core material. 
     In yet other features, a second notch is arranged in the first magnetic core material that projects inwardly from one of the first and second ends. A second conductor passes through the inner cavity and is received by the second notch. A projection of the first magnetic core material extends outwardly from a first side of the first magnetic core material between the first and second conductors. The eddy current reducing material has a low magnetic permeability. The eddy current reducing material comprises a soft magnetic material. The soft magnetic material comprises a powdered metal. The first conductor includes an insulating material arranged on an outer surface thereof. A cross-sectional shape of the first magnetic core material is one of square, circular, rectangular, elliptical, and oval. A DC/DC converter comprises the power inductor. 
     In still other features of the invention, a first end of the first conductor begins and a second end of the first conductor ends along an outer side of the first magnetic core material. A system comprises the power inductor and further comprises a printed circuit board. The first and second ends of the first conductor are surface mounted on the printed circuit board. First and second ends of the first conductor project outwardly from the first magnetic core material. The first and second ends of the first conductor are surface mounted on the printed circuit board in a gull wing configuration. 
     In yet other features, a system comprises the power inductor and further comprises a printed circuit board. The at least one of the first and second ends of the first conductor are received in plated-through holes of the printed circuit board. A cross-sectional shape of the first notch is one of square, circular, rectangular, elliptical, oval, and terraced. A second magnetic core material is located at least one of in and adjacent to the slotted air gap. The first magnetic core material comprises a ferrite bead core material. The first magnetic core material and the second magnetic core material are self-locking in at least two orthogonal planes. Opposing walls of the first magnetic core material that are adjacent to the slotted air gap are “V”-shaped. The second magnetic core material is “T”-shaped and extends along an inner wall of the first magnetic core material. 
     In still other features of the invention, the second magnetic core material is “H”-shaped and extends partially along inner and outer walls of the first magnetic core material. The second magnetic core material includes ferrite bead core material with distributed gaps that lower a permeability of the second magnetic core material. The distributed gaps include distributed air gaps. Flux flows through a magnetic path in the power inductor that includes the first and second magnetic core materials. The second magnetic core material is less than 30% of the magnetic path. 
     In yet other features, flux flows through a magnetic path in the power inductor that includes the first and second core materials. The second magnetic core material is less than 20% of the magnetic path. The first and second magnetic core materials are attached together using at least one of adhesive and a strap. The first notch is formed in the first magnetic core material during molding and before sintering. 
     Further areas of applicability of the present invention will become apparent from the detailed description provided hereinafter. It should be understood that the detailed description and specific examples, while indicating the preferred embodiment of the invention, are intended for purposes of illustration only and are not intended to limit the scope of the invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The present invention will become more fully understood from the detailed description and the accompanying drawings, wherein: 
         FIG. 1  is a functional block diagram and electrical schematic of a power inductor implemented in an exemplary DC/DC converter according to the prior art; 
         FIG. 2  is a perspective view showing the power inductor of  FIG. 1  according to the prior art; 
         FIG. 3  is a cross sectional view showing the power inductor of  FIGS. 1 and 2  according to the prior art; 
         FIG. 4  is a perspective view showing a power inductor with a slotted air gap arranged in the magnetic core material according to the present invention; 
         FIG. 5  is a cross sectional view of the power inductor of  FIG. 4 ; 
         FIGS. 6A and 6B  are cross sectional views showing alternate embodiments with an eddy current reducing material that is arranged adjacent to the slotted air gap; 
         FIG. 7  is a cross sectional view showing an alternate embodiment with additional space between the slotted air gap and a top of the conductor; 
         FIG. 8  is a cross sectional view of a magnetic core with multiple cavities each with a slotted air gap; 
         FIGS. 9A and 9B  are cross sectional views of  FIG. 8  with an eddy current reducing material arranged adjacent to one or both of the slotted air gaps; 
         FIG. 10A  is a cross sectional view showing an alternate side location for the slotted air gap; 
         FIG. 10B  is a cross sectional view showing an alternate side location for the slotted air gap; 
         FIGS. 11A and 11B  are cross sectional views of a magnetic core with multiple cavities each with a side slotted air gap; 
         FIG. 12  is a cross sectional view of a magnetic core with multiple cavities and a central slotted air gap; 
         FIG. 13  is a cross sectional view of a magnetic core with multiple cavities and a wider central slotted air gap; 
         FIG. 14  is a cross sectional view of a magnetic core with multiple cavities, a central slotted air gap and a material having a lower permeability arranged between adjacent conductors; 
         FIG. 15  is a cross sectional view of a magnetic core with multiple cavities and a central slotted air gap; 
         FIG. 16  is a cross sectional view of a magnetic core material with a slotted air gap and one or more insulated conductors; 
         FIG. 17  is a cross sectional view of a “C”-shaped magnetic core material and an eddy current reducing material; 
         FIG. 18  is a cross sectional view of a “C”-shaped magnetic core material and an eddy current reducing material with a mating projection; 
         FIG. 19  is a cross sectional view of a “C”-shaped magnetic core material with multiple cavities and an eddy current reducing material; 
         FIG. 20  is a cross sectional view of a “C”-shaped first magnetic core including a ferrite bead core material and a second magnetic core located adjacent to an air gap thereof; 
         FIG. 21  is a cross sectional view of a “C”-shaped first magnetic core including a ferrite bead core material and a second magnetic core located in an air gap thereof; 
         FIG. 22  is a cross sectional view of a “U”-shaped first magnetic core including a ferrite bead core material with a second magnetic core located adjacent to an air gap thereof; 
         FIG. 23  illustrates a cross sectional view of a “C”-shaped first magnetic core including a ferrite bead core material and “T”-shaped second magnetic core, respectively; 
         FIG. 24  illustrates a cross sectional view of a “C”-shaped first magnetic core including a ferrite bead core material and a self-locking “H”-shaped second magnetic core located in an air gap thereof; 
         FIG. 25  is a cross sectional view of a “C”-shaped first magnetic core including a ferrite bead core material with a self-locking second magnetic core located in an air gap thereof; 
         FIG. 26  illustrates an “O”-shaped first magnetic core including a ferrite bead core material with a second magnetic core located in an air gap thereof; 
         FIGS. 27 and 28  illustrate “O”-shaped first magnetic cores including ferrite bead core material with self-locking second magnetic cores located in air gaps thereof; 
         FIG. 29  illustrates a second magnetic core that includes ferrite bead core material having distributed gaps that reduce the permeability of the second magnetic core; 
         FIG. 30  illustrates first and second magnetic cores that are attached together using a strap; 
         FIG. 31  is a perspective view showing the magnetic core material of a power inductor with one or more notches arranged in at least one side of the magnetic core material; 
         FIG. 32  is a cross-sectional view of the power inductor in  FIG. 31  including one or more conductors that pass through the inner cavity of the magnetic core material and that are received by the notches; 
         FIG. 33  is a side cross-sectional view of the power inductor in  FIG. 32  showing ends of the conductors beginning and terminating along an outer side of the magnetic core material; 
         FIG. 34  is a functional block diagram and electrical schematic of the power inductor in  FIGS. 32 and 33  implemented in an exemplary DC/DC converter; 
         FIG. 35  is a bottom cross-sectional view of a power inductor including a single conductor that is threaded through the inner cavity multiple times and that is received by each of the notches; 
         FIG. 36  is a functional block diagram and electrical schematic of the power inductor in  FIG. 35  implemented in an exemplary DC/DC converter; 
         FIG. 37  is a side view of the power inductor in  FIG. 33  surface mounted on a printed circuit board; 
         FIG. 38  is a side view of the power inductor in  FIG. 33  surface mounted on a printed circuit board in a gull wing configuration; 
         FIG. 39  is a side view of the power inductor in  FIG. 33  connected to plated-through holes of a printed circuit board; 
         FIG. 40  illustrates the dot convention applied to a power inductor with two straight conductors; 
         FIG. 41  illustrates a chip that is connected to the power inductor of  FIG. 40 ; 
         FIG. 42  illustrates the desired dot convention for a power inductor with two conductors; 
         FIG. 43  illustrates a power inductor with crossing conductors; 
         FIG. 44  illustrates a chip connected to the power inductors of  FIG. 43 ; 
         FIG. 45  is a side cross-sectional view of first and second lead frame conductors that are separated by insulating material; 
         FIGS. 46A and 46B  are plan views of the first and second lead frame conductors, respectively; 
         FIG. 46C  is a plan view of a crossover conductor structure; 
         FIG. 47A  is a side cross-sectional view of a first laminate including a first lead frame and insulating material; 
         FIG. 47B  illustrates stamping of the first laminate of  FIG. 47A  in a direction from the insulating material side towards the first lead frame; 
         FIG. 48A  is a side cross-sectional view of a second lead frame; 
         FIG. 48B  illustrates stamping of the second lead frame; 
         FIG. 49  illustrates attachment of the first laminate to the second lead frame to form a second laminate; 
         FIGS. 50A and 50B  illustrate first and second arrays of lead frames, respectively; and 
         FIGS. 51A-51C  show alternate lead frame arrays. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The following description of the preferred embodiment(s) is merely exemplary in nature and is in no way intended to limit the invention, its application, or uses. For purposes of clarity, the same reference numbers will be used in the drawings to identify the same elements. 
     Referring now to  FIG. 4 , a power inductor  50  includes a conductor  54  that passes through a magnetic core material  58 . For example, the magnetic core material  58  may have a square outer cross-section  60  and a square central cavity  64  that extends the length of the magnetic core material. The conductor  54  may also have a square cross section. While the square outer cross section  60 , the square central cavity  64 , and the conductor  54  are shown, skilled artisans will appreciate that other shapes may be employed. The cross sections of the square outer cross section  60 , the square central cavity  64 , and the conductor  54  need not have the same shape. The conductor  54  passes through the central cavity  64  along one side of the cavity  64 . The relatively high levels of DC current that flow through the conductor  30  tend to cause the magnetic core material  34  to saturate, which reduces performance of the power inductor and/or the device incorporating it. 
     According to the present invention, the magnetic core material  58  includes a slotted air gap  70  that runs lengthwise along the magnetic core material  58 . The slotted air gap  70  runs in a direction that is parallel to the conductor  54 . The slotted air gap  70  reduces the likelihood of saturation in the magnetic core material  58  for a given DC current level. 
     Referring now to  FIG. 5 , magnetic flux  80 - 1  and  80 - 2  (collectively referred to as flux  80 ) is created by the slotted air gap  70 . Magnetic flux  80 - 2  projects towards the conductor  54  and induces eddy currents in the conductor  54 . In a preferred embodiment, a sufficient distance “D” is defined between the conductor  54  and a bottom of the slotted air gap  70  such that the magnetic flux is substantially reduced. In one exemplary embodiment, the distance D is related to the current flowing through the conductor, a width “W” that is defined by the slotted air gap  70 , and a desired maximum acceptable eddy current that can be induced in the conductor  54 . 
     Referring now to  FIGS. 6A and 6B , an eddy current reducing material  84  can be arranged adjacent to the slotted air gap  70 . The eddy current reducing material has a lower magnetic permeability than the magnetic core material and a higher permeability than air. As a result, more magnetic flux flows through the material  84  than air. For example, the magnetic insulating material  84  can be a soft magnetic material, a powdered metal, or any other suitable material. In  FIG. 6A , the eddy current reducing material  84  extends across a bottom opening of the slotted air gap  70 . 
     In  FIG. 6B , the eddy current reducing material  84 ′ extends across an outer opening of the slotted air gap. Since the eddy current reducing material  84 ′ has a lower magnetic permeability than the magnetic core material and a higher magnetic permeability than air, more flux flows through the eddy current reducing material than the air. Thus, less of the magnetic flux that is generated by the slotted air gap reaches the conductor. 
     For example, the eddy current reducing material  84  can have a relative permeability of 9 while air in the air gap has a relative permeability of 1. As a result, approximately 90% of the magnetic flux flows through the material  84  and approximately 10% of the magnetic flux flows through the air. As a result, the magnetic flux reaching the conductor is significantly reduced, which reduces induced eddy currents in the conductor. As can be appreciated, other materials having other permeability values can be used. Referring now to  FIG. 7 , a distance “D 2 ” between a bottom the slotted air gap and a top of the conductor  54  can also be increased to reduce the magnitude of eddy currents that are induced in the conductor  54 . 
     Referring now to  FIG. 8 , a power inductor  100  includes a magnetic core material  104  that defines first and second cavities  108  and  110 . First and second conductors  112  and  114  are arranged in the first and second cavities  108  and  110 , respectively. First and second slotted air gaps  120  and  122  are arranged in the magnetic core material  104  on a side that is across from the conductors  112  and  114 , respectively. The first and second slotted air gaps  120  and  122  reduce saturation of the magnetic core material  104 . In one embodiment, mutual coupling M is in the range of 0.5. 
     Referring now to  FIGS. 9A and 9B , an eddy current reducing material is arranged adjacent to one or more of the slotted air gaps  120  and/or  122  to reduce magnetic flux caused by the slotted air gaps, which reduces induced eddy currents. In  FIG. 9A , the eddy current reducing material  84  is located adjacent to a bottom opening of the slotted air gaps  120 . In  FIG. 9B , the eddy current reducing material is located adjacent to a top opening of both of the slotted air gaps  120  and  122 . As can be appreciated, the eddy current reducing material can be located adjacent to one or both of the slotted air gaps. “T”-shaped central section  123  of the magnetic core material separates the first and second cavities  108  and  110 . 
     The slotted air gap can be located in various other positions. For example and referring now to  FIG. 1A , a slotted air gap  70 ′ can be arranged on one of the sides of the magnetic core material  58 . A bottom edge of the slotted air gap  70 ′ is preferably but not necessarily arranged above a top surface of the conductor  54 . As can be seen, the magnetic flux radiates inwardly. Since the slotted air gap  70 ′ is arranged above the conductor  54 , the magnetic flux has a reduced impact. As can be appreciated, the eddy current reducing material can arranged adjacent to the slotted air gap  70 ′ to further reduce the magnetic flux as shown in  FIGS. 6A  and/or  6 B. In  FIG. 10B , the eddy current reducing material  84 ′ is located adjacent to an outer opening of the slotted air gap  70 ′. The eddy current reducing material  84  can be located inside of the magnetic core material  58  as well. 
     Referring now to  FIGS. 11A and 11B , a power inductor  123  includes a magnetic core material  124  that defines first and second cavities  126  and  128 , which are separated by a central portion  129 . First and second conductors  130  and  132  are arranged in the first and second cavities  126  and  128 , respectively, adjacent to one side. First and second slotted air gaps  138  and  140  are arranged in opposite sides of the magnetic core material adjacent to one side with the conductors  130  and  132 . The slotted air gaps  138  and/or  140  can be aligned with an inner edge  141  of the magnetic core material  124  as shown in  FIG. 11B , or spaced from the inner edge  141  as shown in  FIG. 11A . As can be appreciated, the eddy current reducing material can be used to further reduce the magnetic flux emanating from one or both of the slotted air gaps as shown in  FIGS. 6A  and/or  6 B. 
     Referring now to  FIGS. 12 and 13 , a power inductor  142  includes a magnetic core material  144  that defines first and second connected cavities  146  and  148 . First and second conductors  150  and  152  are arranged in the first and second cavities  146  and  148 , respectively. A projection  154  of the magnetic core material  144  extends upwardly from a bottom side of the magnetic core material between the conductors  150  and  152 . The projection  154  extends partially but not fully towards to a top side. In a preferred embodiment, the projection  154  has a projection length that is greater than a height of the conductors  150  and  154 . As can be appreciated, the projection  154  can also be made of a material having a lower permeability than the magnetic core and a higher permeability than air as shown at  155  in  FIG. 14 . Alternately, both the projection and the magnetic core material can be removed as shown in  FIG. 15 . In this embodiment, the mutual coupling M is approximately equal to 1. 
     In  FIG. 12 , a slotted air gap  156  is arranged in the magnetic core material  144  in a location that is above the projection  154 . The slotted air gap  156  has a width W 1  that is less than a width W 2  of the projection  154 . In  FIG. 13 , a slotted air gap  156 ′ is arranged in the magnetic core material in a location that is above the projection  154 . The slotted air gap  156  has a width W 3  that is greater than or equal to a width W 2  of the projection  154 . As can be appreciated, the eddy current reducing material can be used to further reduce the magnetic flux emanating from the slotted air gaps  156  and/or  156 ′ as shown in  FIGS. 6A  and/or  613 . In some implementations of  FIGS. 12-14 , mutual coupling M is in the range of 1. 
     Referring now to  FIG. 16 , a power inductor  170  is shown and includes a magnetic core material  172  that defines a cavity  174 . A slotted air gap  175  is formed in one side of the magnetic core material  172 . One or more insulated conductors  176  and  178  pass through the cavity  174 . The insulated conductors  176  and  178  include an outer layer  182  surrounding an inner conductor  184 . The outer layer  182  has a higher permeability than air and lower than the magnetic core material. The outer material  182  significantly reduces the magnetic flux caused by the slotted air gap and reduces eddy currents that would otherwise be induced in the conductors  184 . 
     Referring now to  FIG. 17 , a power inductor  180  includes a conductor  184  and a “C”-shaped magnetic core material  188  that defines a cavity  190 . A slotted air gap  192  is located on one side of the magnetic core material  188 . The conductor  184  passes through the cavity  190 . An eddy current reducing material  84 ′ is located across the slotted air gap  192 . In  FIG. 18 , the eddy current reducing material  84 ′ includes a projection  194  that extends into the slotted air gap and that mates with the opening that is defined by the slotted air gap  192 . 
     Referring now to  FIG. 19 , the power inductor  200  a magnetic core material that defines first and second cavities  206  and  208 . First and second conductors  210  and  212  pass through the first and second cavities  206  and  208 , respectively. A center section  218  is located between the first and second cavities. As can be appreciated, the center section  218  may be made of the magnetic core material and/or an eddy current reducing material. Alternately, the conductors may include an outer layer. 
     The conductors may be made of copper, although gold, aluminum, and/or other suitable conducting materials having a low resistance may be used. The magnetic core material can be Ferrite although other magnetic core materials having a high magnetic permeability and a high electrical resistivity can be used. As used herein, Ferrite refers to any of several magnetic substances that include ferric oxide combined with the oxides of one or more metals such as manganese, nickel, and/or zinc. If Ferrite is employed, the slotted air gap can be cut with a diamond cutting blade or other suitable technique. 
     While some of the power inductors that are shown have one turn, skilled artisans will appreciate that additional turns may be employed. While some of the embodiments only show a magnetic core material with one or two cavities each with one or two conductors, additional conductors may be employed in each cavity and/or additional cavities and conductors may be employed without departing from the invention. While the shape of the cross section of the inductor has be shown as square, other suitable shapes, such as rectangular, circular, oval, elliptical and the like are also contemplated. 
     The power inductor in accordance with the present embodiments preferably has the capacity to handle up to 100 Amps (A) of DC current and has an inductance of 500 nH or less. For example, a typical inductance value of 50 nH is used. While the present invention has been illustrated in conjunction with DC/DC converters, skilled artisans will appreciate that the power inductor can be used in a wide variety of other applications. 
     Referring now to  FIG. 20 , a power inductor  250  includes a “C”-shaped first magnetic core  252  that defines a cavity  253 . While a conductor is not shown in  FIGS. 20-28 , skilled artisans will appreciate that one or more conductors pass through the center of the first magnetic core as shown and described above. The first magnetic core  252  is preferably fabricated from ferrite bead core material and defines an air gap  254 . A second magnetic core  258  is attached to at least one surface of the first magnetic core  252  adjacent to the air gap  254 . In some implementations, the second magnetic core  258  has a permeability that is lower than the ferrite bead core material. Flux flows  260  through the first and second magnetic cores  252  and  258  as shown by dotted lines. 
     Referring now to  FIG. 21 , a power inductor  270  includes a “C”-shaped first magnetic core  272  that is made of a ferrite bead core material. The first magnetic core  272  defines a cavity  273  and an air gap  274 . A second magnetic core  276  is located in the air gap  274 . In some implementations, the second magnetic core has a permeability that is lower than the ferrite bead core material. Flux  278  flows through the first and second magnetic cores  272  and  276 , respectively, as shown by the dotted lines. 
     Referring now to  FIG. 22 , a power inductor  280  includes a “U”-shaped first magnetic core  282  that is made of a ferrite bead core material. The first magnetic core  282  defines a cavity  283  and an air gap  284 . A second magnetic core  286  is located in the air gap  284 . Flux  288  flows through the first and second magnetic cores  282  and  286 , respectively, as shown by the dotted lines. In some implementations, the second magnetic core  258  has a permeability that is lower than the ferrite bead core material. 
     Referring now to  FIG. 23 , a power inductor  290  includes a “C”-shaped first magnetic core  292  that is made of a ferrite bead core material. The first magnetic core  292  defines a cavity  293  and an air gap  294 . A second magnetic core  296  is located in the air gap  294 . In one implementation, the second magnetic core  296  extends into the air gap  294  and has a generally “T”-shaped cross section. The second magnetic core  296  extends along inner surfaces  297 - 1  and  297 - 2  of the first magnetic core  290  adjacent to the air gap  304 . Flux  298  flows through the first and second magnetic cores  292  and  296 , respectively, as shown by the dotted lines. In some implementations, the second magnetic core  258  has a permeability that is lower than the ferrite bead core material. 
     Referring now to  FIG. 24 , a power inductor  300  includes a “C”-shaped first magnetic core  302  that is made of a ferrite bead core material. The first magnetic core  302  defines a cavity  303  and an air gap  304 . A second magnetic core  306  is located in the air gap  304 . The second magnetic core extends into the air gap  304  and outside of the air gap  304  and has a generally “H”-shaped cross section. The second magnetic core  306  extends along inner surfaces  307 - 1  and  307 - 2  and outer surfaces  309 - 1  and  309 - 2  of the first magnetic core  302  adjacent to the air gap  304 . Flux  308  flows through the first and second magnetic cores  302  and  306 , respectively, as shown by the dotted lines. In some implementations, the second magnetic core  258  has a permeability that is lower than the ferrite bead core material. 
     Referring now to  FIG. 25 , a power inductor  320  includes a “C”-shaped first magnetic core  322  that is made of a ferrite bead core material. The first magnetic core  322  defines a cavity  323  and an air gap  324 . A second magnetic core  326  is located in the air gap  324 . Flux  328  flows through the first and second magnetic cores  322  and  326 , respectively, as shown by the dotted lines. The first magnetic core  322  and the second magnetic core  326  are self-locking. In some implementations, the second magnetic core  258  has a permeability that is lower than the ferrite bead core material. 
     Referring now to  FIG. 26 , a power inductor  340  includes an “O”-shaped first magnetic core  342  that is made of a ferrite bead core material. The first magnetic core  342  defines a cavity  343  and an air gap  344 . A second magnetic core  346  is located in the air gap  344 . Flux  348  flows through the first and second magnetic cores  342  and  346 , respectively, as shown by the dotted lines. In some implementations, the second magnetic core  258  has a permeability that is lower than the ferrite bead core material. 
     Referring now to  FIG. 27 , a power inductor  360  includes an “O”-shaped first magnetic core  362  that is made of a ferrite bead core material. The first magnetic core  362  defines a cavity  363  and an air gap  364 . The air gap  364  is partially defined by opposed “V”-shaped walls  365 . A second magnetic core  366  is located in the air gap  364 . Flux  368  flows through the first and second magnetic cores  362  and  366 , respectively, as shown by the dotted lines. The first magnetic core  362  and the second magnetic core  366  are self-locking. In other words, relative movement of the first and second magnetic cores is limited in at least two orthogonal planes. While “V”-shaped walls  365  are employed, skilled artisans will appreciate that other shapes that provide a self-locking feature may be employed. In some implementations, the second magnetic core  258  has a permeability that is lower than the ferrite bead core material. 
     Referring now to  FIG. 28 , a power inductor  380  includes an “O”-shaped first magnetic core  382  that is made of a ferrite bead core material. The first magnetic core  382  defines a cavity  383  and an air gap  384 . A second magnetic core  386  is located in the air gap  384  and is generally “H”-shaped. Flux  388  flows through the first and second magnetic cores  382  and  386 , respectively, as shown by the dotted lines. The first magnetic core  382  and the second magnetic core  386  are self-locking. In other words, relative movement of the first and second magnetic cores is limited in at least two orthogonal planes. While the second magnetic core is “H”-shaped, skilled artisans will appreciate that other shapes that provide a self-locking feature may be employed. In some implementations, the second magnetic core  258  has a permeability that is lower than the ferrite bead core material. 
     In one implementation, the ferrite bead core material forming the first magnetic core is cut from a solid block of ferrite bead core material, for example using a diamond saw. Alternately, the ferrite bead core material is molded into a desired shape and then baked. The molded and baked material can then be cut if desired. Other combinations and/or ordering of molding, baking and/or cutting will be apparent to skilled artisans. The second magnetic core can be made using similar techniques. 
     One or both of the mating surfaces of the first magnetic core and/or the second magnetic core may be polished using conventional techniques prior to an attachment step. The first and second magnetic cores can be attached together using any suitable method. For example, an adhesive, adhesive tape, and/or any other bonding method can be used to attach the first magnetic core to the second core to form a composite structure. Skilled artisans will appreciate that other mechanical fastening methods may be used. 
     The second magnetic core is preferably made from a material having a lower permeability than the ferrite bead core material. In a preferred embodiment, the second magnetic core material forms less than 30% of the magnetic path. In a more preferred embodiment, the second magnetic core material forms less than 20% of the magnetic path. For example, the first magnetic core may have a permeability of approximately 2000 and the second magnetic core material may have a permeability of  20 . The combined permeability of the magnetic path through the power inductor may be approximately 200 depending upon the respective lengths of magnetic paths through the first and second magnetic cores. In one implementation, the second magnetic core is formed using iron powder. While the iron powder has relatively high losses, the iron powder is capable of handling large magnetization currents. 
     Referring now to  FIG. 29 , in other implementations, the second magnetic core is formed using ferrite bead core material  420  with distributed gaps  424 . The gaps can be filled with air, and/or other gases, liquids or solids. In other words, gaps and/or bubbles that are distributed within the second magnetic core material lower the permeability of the second magnetic core material. The second magnetic core may be fabricated in a manner similar to the first magnetic core, as described above. As can be appreciated, the second magnetic core material may have other shapes. Skilled artisans will also appreciate that the first and second magnetic cores described in conjunction with  FIGS. 20-30  may be used in the embodiments shown and described in conjunction with  FIGS. 1-19 . 
     Referring now to  FIG. 30 , a strap  450  is used to hold the first and second magnetic cores  252  and  258 , respectively, together. Opposite ends of the strap may be attached together using a connector  454  or connected directly to each other. The strap  450  can be made of any suitable material such as metal or non-metallic materials. 
     Referring now to  FIG. 31 , a power inductor  520  includes notches  522  arranged in a magnetic core material  524 . For example, the magnetic core material  524  may include first, second, third, and fourth notches  522 - 1 ,  522 - 2 ,  522 - 3 , and  522 - 4 , respectively, (collectively notches  522 ). The notches  522  are arranged in the magnetic core material  524  between an inner cavity  526  and an outer side  528  of the magnetic core material  524 . The first and second notches  522 - 1  and  522 - 2 , respectively, are arranged at a first end  530  of the magnetic core material  524  and project inwardly. The third and fourth notches  522 - 3  and  522 - 4 , respectively, are arranged at a second end  532  of the magnetic core material  524  and also project inwardly. 
     While the notches  522  in  FIG. 31  are shown as rectangular in shape, those skilled in the art appreciate that the notches  522  may be any suitable shape including circular, oval, elliptical, and terraced. In an exemplary embodiment, the notches  522  are molded into the magnetic core material  524  during molding and before sintering. This approach avoids the additional step of forming the notches  522  following molding, which reduces time and cost. The notches  522  may also be cut and/or otherwise formed after molding and sintering if desired. While two pairs of notches are shown in  FIG. 31 , one notch, one pair of notches and/or additional notch pairs may be used. While the notches  522  are shown along one side of the magnetic core material  524 , one or more notches  522  may be formed on one or more sides of the magnetic core material  524 . Furthermore, one notch  222  may be formed on one side at one end of the magnetic core material  524  and another notch  522  may be formed on another side at the opposite end of the magnetic core material  524 . 
     Referring now to  FIGS. 32 and 33 , first and second conductors  534  and  536 , respectively, pass through the inner cavity  526  along the bottom of the inner cavity  526  and are received by the notches  522 . For example, the notches  522  may control a position of the first and second conductors  534  and  536 , respectively. The first conductor  534  is received by the first and third notches  522 - 1  and  522 - 3 , respectively, and the second conductor  536  is received by the second and fourth notches  522 - 2  and  522 - 4 , respectively. The notches  522  preferably retain the first and second conductors  534  and  536 , respectively, which prevents the first conductor  534  from contacting the second conductor  536  and avoids a short-circuit. In this case, insulation on the conductor is not required to insulate the first conductor  534  from the second conductor  536 . Therefore, this approach avoids the additional step of removing insulation from the ends of insulated conductors when making connections, which reduces time and cost. However, insulation may be used if desired. 
     While not shown in  FIGS. 31-33 , the power inductor  520  may include one or more slotted air gaps arranged in the magnetic core material  524 . For example, the one or more slotted air gaps may extend from the first end  530  to the second end  532  of the magnetic core material  524  as shown in  FIG. 4 . The power inductor  520  may also include an eddy current reducing material that is arranged adjacent to an inner opening and/or an outer opening of a slotted air gap as shown in  FIGS. 6A and 6B . The slotted air gap may be arranged on the top of the magnetic core material  524  and/or one of the sides of the magnetic core material  524  as shown in  FIGS. 10A and 10B . 
     A second cavity may be arranged in the magnetic core material  524  and a center section of the magnetic core material  524  may be arranged between the inner cavity  526  and the second cavity. In this case, the first conductor  534  may pass through the inner cavity  526  and second conductor  536  may pass through the second cavity. The first and second conductors,  534  and  536 , respectively, may include an outer insulating later as shown in  FIG. 16 . The magnetic core material  524  may also comprise a ferrite bead core material. The power inductors of  FIGS. 31-39  may also have other features shown in  FIGS. 1-30 . 
     Referring now to  FIG. 34 , the first and second conductors  534  and  536 , respectively, may form a coupled inductor circuit  544 . In one implementation, the mutual coupling is approximately equal to 1. In another implementation, the power inductor  520  is implemented in a DC/DC converter  546 . The DC/DC converter  546  utilizes the power inductor  520  to transform DC at one voltage to DC at another voltage. 
     Referring now to  FIG. 35 , a bottom cross-sectional view of the power inductor  520  is shown to include a single conductor  554  that passes through the inner cavity  526  twice and that is received by each of the notches  522 . In an exemplary embodiment, a first end  556  of the conductor  554  begins along the outer side  528  of the magnetic core material  524  and is received by the second notch  522 - 2 . The conductor  554  passes though the inner cavity  526  along the bottom of the inner cavity  526  from the second notch  522 - 2  and is received by the fourth notch  522 - 4 . The conductor  554  is routed along the outer side  528  of the magnetic core material  524  from the fourth notch  522 - 4  and is received by the first notch  522 - 1 . The conductor  554  passes through the inner cavity  526  along the bottom of the inner cavity  526  from the first notch  522 - 1  and is received by the third notch  522 - 3 . 
     The conductor  554  continues from the third notch  522 - 3  and a second end  558  of the conductor  554  terminates along the outer side  528  of the magnetic core material  524 . Therefore, the conductor  554  in  FIG. 35  passes through the inner cavity  526  of the magnetic core material  524  at least twice and is received by each of the notches  522 . The conductor  554  may be received by additional notches  522  in the magnetic core material  524  to increase the number of times that the conductor  554  passes through the inner cavity  526 . 
     Referring now to  FIG. 36 , the conductor  554  may form a coupled inductor circuit  566 . In one implementation, the power inductor  520  may be implemented in a DC/DC converter  568 . 
     Referring now to  FIGS. 37-38 , the power inductor is surface mounted on a printed circuit board  570 . In  FIG. 39 , the power inductor is mounted to plated through holes (PTHs) of the printed circuit board  570 . In  FIGS. 37-39 , similar reference numbers are used as in  FIGS. 32 and 33 . In an exemplary embodiment and referring now to  FIG. 37 , the first and second ends of the first and second conductors  534  and  536 , respectively, begin and terminate along the outer side  528  of the magnetic core material  524 . This allows the power inductor  520  to be surface mounted on the printed circuit board  570 . For example, the first and second ends of the first and second conductors  534  and  536 , respectively, may attach to solder pads  572  of the printed circuit board  570 . 
     Alternatively and referring now to  FIG. 38 , the first and second ends of the first and second conductors  534  and  536 , respectively, may extend beyond the outer side  528  of the magnetic core material  524 . In this case, the power inductor  520  may be surface mounted on the printed circuit board  570  by attaching the first and second ends of the first and second conductors  534  and  536 , respectively, to the solder pads  572  in a gull wing configuration  574 . 
     Referring now to  FIG. 39 , the first ends and/or the second ends of the first and second conductors  534  and  536 , respectively, may also extend and attach to plated-through holes (PTHs)  576  of the printed circuit board  570 . 
     Referring now to  FIGS. 40 and 41 , the dot convention is applied to a power inductor  600  in  FIG. 40  including first and second conductors  602  and  604 , respectively. To connect a chip  610  as shown in  FIG. 41 , printed circuit board (PCB) traces  612 - 1 ,  612 - 2  and  612 - 3  (collectively PCB traces  612 ) are sometimes employed. As can be seen in  FIG. 41 , wiring provided by the PCB traces  612  is not properly balanced. The imbalanced wiring tends to reduce the coefficient of mutual coupling and/or to increase losses due to skin effects at high frequencies. 
     Referring now to  FIGS. 42 ,  43  and  44 , a desired dot convention for a power inductor  620  including first and second conductors  622  and  624  is shown. In  FIG. 43 , the first and second conductors  622  and  624 , respectively, are crossed to allow an improved connection to a chip. In  FIG. 41 , PCB traces  630 - 1 ,  630 - 2  and  630 - 3  (collectively PCB traces  630 ) are used to connect the conductors  622  and  624  to the power inductor  620 . The PCB traces  630  are shorter and more balanced than those in  FIG. 41 , which allows the coefficient of mutual coupling to be closer to 1 and reduces losses due to skin effects at high frequencies. 
     Referring now to  FIGS. 45-46 , a crossed conductor structure  640  according to the present invention is shown. In  FIG. 45 , a side cross-sectional view of the crossed conductor structure  640  is shown to include first and second lead frames  644  and  646 , respectively, that are separated by an insulating material  648 . In  FIGS. 46A and 46B , plan views of the first and second lead frames  644  and  646 , respectively, are shown. The first lead frame  644  includes terminals  650 - 1  and  650 - 2  that extend from a body  654 . The second lead frame  646  includes terminals  656 - 1  and  656 - 2  that extend from a body  658 . While a generally “Z”-shaped configuration is shown for the lead frames  644  and  646 , other shapes can be used. In  FIG. 46C , a plan view of the assembled crossover conductor structure  640  is shown. 
     Several exemplary approaches for making the crossover conductor structure  640  will be described below. The first and second lead frames  644  and  646  may be initially stamped. The insulating material  648  is subsequently positioned there between. Alternately, the insulating material can be applied, sprayed, coated and/or otherwise applied to the lead frames. For example, one suitable insulating material includes enamel that can be readily applied in a controlled manner. 
     Alternately, the first and second lead frames  644  and  646  and the insulating material  648  can be attached together and then stamped. The first lead frame  644  (on a first side) is stamped approximately ½ of the thickness of the laminate from the first side towards a second side to define the shape and terminals of the first lead frame  644 . The second lead frame  646  (on the second side) is stamped approximately ½ of the thickness of the laminate from the second side towards the first side to define the shape and terminals of the second lead frame  646 . 
     Referring now to  FIGS. 47A-49 , an alternate method of construction is shown. The first lead frame  644  is initially attached to the insulating material  648  before stamping. The first lead frame  644  and the insulating material  648  are stamped in a direction indicated in  FIG. 47B  such that stamping deformation (if any) occurs in a direction away from the second lead frame (after assembly) to reduce the potential for short circuits. In other words, the stamping is done on the insulation side towards the first lead frame  644 . Likewise the second lead frame  646  is stamped in the proper orientation to reduce the potential for short circuits. The stamp side of the second lead frame is arranged in contact with the insulating material. The stamping deformity (if any) in the first and second lead frames are outwardly directed. Referring now to  FIG. 49 . the first lead frame  644  and the insulating material  648  and the second lead frame  646  are arranged adjacent to each other to form a laminate. 
       FIG. 50A  illustrates a first lead frame array  700  including first lead frames  644 - 1 ,  644 - 2 , . . . , and  644 -N, where N&gt;1. In  FIG. 50B , a second lead frame array  704  includes second lead frames  646 - 1 ,  646 - 2 , and  646 -N. As can be appreciated, the lead frame arrays  700  and  704  may alternatively include alternating first and second lead frames that are offset by one position. An insulating material  648  can be attached to the first and/or second lead frame array  700  and  704 , respectively, and/or to individual lead frames. Alternately, an insulating material can be applied, sprayed and/or coated onto one or more surfaces of one and/or both of the lead frames. Tab portions  710 - 1 ,  710 - 2 ,  710 - 3  and  710 - 4  (collectively tab portions  710 ) may be used to attach the terminals or other portions of individual lead frames to feed strips  712 - 1 ,  712 - 2 ,  712 - 3 , and  712 - 4  (collectively feed strips  712 ), respectively. The shape of the lead frames, the terminals and the tab portions are defined during stamping. In this embodiment, stamping is performed prior to joining the lead frames and insulating material. The feed strips  712  may optionally include holes  713  for receiving positioning pins of a drive wheel (not shown). Adjacent lead frames are optionally spaced from each other as identified at  714  and/or tab portions can be provided. 
     Referring now to  FIGS. 51A-51C , additional tab portions  720 - 1  and  720 - 2  removably connect adjacent lead frames. Additionally, the lead frames are shown to include insulating material  728  that has been applied, sprayed and/or coated onto one or more surfaces of one and/or both of the lead frames. Alternately, insulating material  648  can be used. In the exemplary embodiment, facing surfaces of the lead frames are coated with the insulating material. For example, the insulating material can be enamel. 
     In addition to the methods described above, first and second lead frame arrays and insulating material can be arranged together and then stamped approximately ½ of a thickness thereof from both sides to define the shape of the lead frame arrays. Alternately, the insulating material can be applied to one or both lead frame arrays, stamped, and then assembled in an orientation that prevents stamping deformity from causing a short circuit as described above. Still other variations will be apparent to skilled artisans. 
     Those skilled in the art can now appreciate from the foregoing description that the broad teachings of the present invention can be implemented in a variety of forms. Therefore, while this invention has been described in connection with particular examples thereof, the true scope of the invention should not be so limited since other modifications will become apparent to the skilled practitioner upon a study of the drawings, the specification and the following claims.