Patent Publication Number: US-9842683-B1

Title: Bobbin and E-core assembly configuration and method for E-cores and EI-cores

Description:
CROSS-REFERENCES TO RELATED APPLICATIONS 
     This application claims benefit of the following patent application which is hereby incorporated by reference: U.S. Provisional Patent Application No. 62/074,749 filed Nov. 4, 2014, entitled “Bobbin and E-Core Assembly Configuration and Method for a Magnetic Component.” 
    
    
     A portion of the disclosure of this patent document contains material that is subject to copyright protection. The copyright owner has no objection to the reproduction of the patent document or the patent disclosure, as it appears in the U.S. Patent and Trademark Office patent file or records, but otherwise reserves all copyright rights whatsoever. 
     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
     Not Applicable 
     REFERENCE TO SEQUENCE LISTING OR COMPUTER PROGRAM LISTING APPENDIX 
     Not Applicable 
     BACKGROUND OF THE INVENTION 
     Conventionally, E-cores used on a magnetic assembly are held together with tape or glue. The E-cores must be held in place during assembly until the tape is secured or until the glue is dried. Adding tape or glue to restrain the E-cores requires additional steps during an assembly process and adds cost to the manufacturing process. Accordingly, a need exists for a low-cost bobbin and core assembly method for E-cores that does not require taping or gluing the cores together. 
     BRIEF SUMMARY OF THE INVENTION 
     A novel bobbin and core assembly method uses only the bobbin to secure the cores together. The bobbin has a channel on each end flange of the bobbin. The channels are perpendicular to a passageway through the bobbin. Each channel has a plurality of crushable ribs that extend outward from the respective end flange and that extend into the respective channel. In an embodiment, eight crushable ribs extend into each channel with four ribs proximate to the top of the channel and with four ribs proximate to the bottom of the channel. 
     The two E-cores are inserted into the bobbin passageway from opposite ends of the bobbin. The two E-cores are moved inwardly until the end surfaces of the outer legs of the two E-cores meet along the outside of the bobbin. The center leg of at least one of the E-cores is shorter than the outer legs to provide a gap between the center leg of the E-core and the other center leg. The two E-cores are secured to the bobbin by frictional engagement of the main bodies of the E-cores with the crushable ribs in the two channels. The bobbin structure and the method of assembling the cores can be used on cores with round, oval, square or rectangular center legs. The bobbin and the method can also be used for EI-core assemblies having one extended E-core with its center leg inserted into the bobbin passageway from one end of the bobbin and having an I-core adjacent the ends of the legs of the E-core in the channel at the opposite end of the bobbin. In either embodiment, the crushable ribs engage the two core bodies and restrain the two core bodies so that no taping or gluing is required. The labor required to assemble the magnetic component is reduced, and no tape or glue is required. The structure and the method of assembly require less material and labor to secure the E-cores together. Accordingly, labor and material costs are reduced. 
     An aspect of the invention in accordance with embodiments disclosed herein is a magnetic assembly that includes a bobbin and first and second cores. Each core has a main body. At least one of the cores has first and second outer legs and a center leg extending from the main body. The bobbin includes a first channel on a first end flange and a second channel on a second end flange. Each channel includes a plurality of crushable ribs that extend into the channel. The first and second cores are inserted into the respective first and second channels to engage and crush the crushable ribs. The crushed ribs frictionally engage the main bodies of the two cores to retain the two cores in a fixed relationship with the bobbin without requiring tape or glue. In one embodiment, both cores are E-cores. In another embodiment, one core is an extended E-core and the other core is an I-core. 
     Another aspect of the invention in accordance with embodiments disclosed herein is a magnetic assembly. The magnetic assembly includes a bobbin, a first core and a second core. The bobbin includes a first outer flange and a second outer flange. A passageway extends through the bobbin from the first outer flange to the second outer flange. At least one winding is wound about the passageway. The bobbin further includes a first plurality of crushable ribs extending outward from the first outer flange in a first channel and a second plurality of crushable ribs extending outward from the second outer flange in a second channel. 
     The first core has a main body and has a first outer leg, a second outer leg, and a center leg extending from the main body. The center leg has an end surface. The center leg of the first core is positioned in the passageway of the bobbin with at least a portion of the main body of the first core positioned in the first channel in crushing frictional engagement with the first plurality of ribs. The second core has a main body. At least a portion of the main body of the second core is positioned in the second channel in crushing frictional engagement with the second plurality of crushable ribs. A facing surface of the second core is positioned proximate to the end surface of the center leg of the first core. 
     In certain embodiments in accordance with this aspect of the invention, the second core is an I-core. In other embodiments in accordance with this aspect of the invention, the second core is an E-core having a first outer leg, a second outer leg, and a center leg. The facing surface of the second core is an end surface of the center leg of the second core. In certain embodiments, each crushable rib has a first thickness at a first end proximate to the respective outer flange and a second thickness at a second end displaced away from the respective outer flange. The second thickness is less than the first thickness. The crushable rib has an engagement surface that slopes between the first end and the second end. The engagement surface engages the main body of the respective core. 
     In certain embodiments, the first plurality of crushable ribs includes at least a first rib positioned above the main body of the first core and a second rib positioned below the main body of the core. The first and second ribs are spaced apart vertically such that the respective second ends of the first and second ribs are spaced apart by a distance greater than the height of the main body of the core and the respective first ends of the first and second ribs are spaced apart by a distance less than the height of the main body of the core. In some embodiments, the first rib is positioned on a lower surface of a ledge extending from the first outer flange, and the second rib is positioned on an upper surface of a connector rail. 
     Another aspect of the invention in accordance with embodiments disclosed herein is a bobbin for a magnetic assembly. The bobbin includes a first outer flange and a second outer flange. A passageway extends through the bobbin from the first outer flange to the second outer flange. At least one winding is wound about the passageway. A first plurality of crushable ribs extends outward from the first outer flange with at least a first of the first plurality of crushable ribs positioned at a level near the top of the passageway and with at least a second of the first plurality of crushable ribs positioned at a level near the bottom of the passageway. A second plurality of crushable ribs extends outward from the second outer flange with at least a first of the second plurality of crushable ribs positioned at a level near the top of the passageway and with at least a second of the second plurality of crushable ribs positioned at a level near the bottom of the passageway. In certain embodiments, the first rib of the first plurality of crushable ribs is mounted on a first connector rail extending from the first outer flange, and the second rib of the first plurality of crushable ribs is mounted on a ledge extending from the first outer flange. In certain embodiments, the first rib of the second plurality of crushable ribs is mounted on a second connector rail extending from the second outer flange, and the second rib of the second plurality of crushable ribs is mounted on a ledge extending from the second outer flange. 
     Another aspect of the invention in accordance with embodiments disclosed herein is a method of assembling a magnetic assembly. The method includes positioning the center leg of an E-core into a passageway of a bobbin with a first outer leg of the E-core positioned on a first side of the bobbin, with a second outer leg of the E-core positioned on a second side of the bobbin, and with a main body of the E-core positioned in a first channel between upper and lower crushable ribs extending from a first end flange of the bobbin. The crushable ribs extending from the first end flange frictionally engage the main body to secure the first E-core to the bobbin. The method further includes positioning a second core on the bobbin with at least a portion of a main body of the second core positioned in a second channel between upper and lower crushable ribs extending from a second end flange of the bobbin. The crushable ribs extending from the second end flange frictionally engage the portion of the main body of the second core to secure the second core to the bobbin. 
     In certain embodiments of the method, the E-core is a first E-core and the second core is a second E-core. The second E-core has a center leg. The method further includes positioning the center leg of the second E-core in the passageway of the bobbin. The center leg of the second E-core has an end surface. The end surface of the center leg of the second E-core is spaced apart from an end surface of the center leg of the first E-core to form a magnetic gap. In certain embodiments, the E-core is an extended E-core having outer legs that extend from the first end flange to the second end flange of the bobbin and having a center leg positioned in the passageway with an end surface of the center leg near the second end flange. The second core is an I-core. The method further includes positioning a central facing surface of the I-core proximate to and spaced apart from the end surface of the center leg of the extended E-core to form a magnetic gap. 
    
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
         FIG. 1  illustrates a perspective view of a conventional magnetic assembly having a bobbin with a coil wound around the bobbin and with two E-cores inserted into a passageway through the bobbin. 
         FIG. 2  illustrates an exploded perspective view of the conventional magnetic assembly of  FIG. 1 . 
         FIG. 3  illustrates a front elevational view of the bobbin of  FIG. 2 . 
         FIG. 4  illustrates a perspective view of an embodiment of a bobbin for a magnetic assembly in accordance with aspects of the present invention, the bobbin having a plurality of upper and lower ribs extending into channels formed on the end flanges of the bobbin. 
         FIG. 5  illustrates an enlarged perspective view of one of the lower ribs of  FIG. 4  taken within the area -- 5 -- in  FIG. 4 . 
         FIG. 6  illustrates an enlarged front elevational view of the lower rib of  FIG. 5 . 
         FIG. 7  illustrates a front elevational view of the improved bobbin of  FIG. 4 . 
         FIG. 8  illustrates a side elevational view of the improved bobbin of  FIG. 4 . 
         FIG. 9  illustrates an exploded perspective view of a magnetic assembly that incorporates that bobbin of  FIGS. 4-8 , the magnetic assembly of  FIG. 9  including two E-cores to be inserted into the bobbin from opposite ends. 
         FIG. 10  illustrates a perspective view of the completed magnetic assembly of  FIG. 9  with the two E-cores inserted into the bobbin and secured by the upper and lower ribs of the bobbin. 
         FIG. 11  illustrates a front elevational view of the magnetic assembly of  FIG. 10 . 
         FIG. 12  illustrates a side elevational view of the magnetic assembly of  FIG. 10 . 
         FIG. 13  illustrates an exploded perspective view of a magnetic assembly that incorporates that bobbin of  FIGS. 4-8 , the magnetic assembly of  FIG. 13  including one extended E-core positioned to be inserted into the channel at the second end of the bobbin and an I-core positioned to be inserted into the channel at the first end of the bobbin. 
         FIG. 14  illustrates a perspective view of the completed magnetic assembly of  FIG. 13  with the extended E-core inserted into the channel at the second end of the bobbin and secured by the upper and lower ribs at the second end of the bobbin and with the I-core positioned in the channel at the first end of the bobbin and secured by the upper and lower ribs at the first end of the bobbin. 
         FIG. 15  illustrates a front elevational view of the magnetic assembly of  FIG. 14 . 
         FIG. 16  illustrates a side elevational view of the magnetic assembly of  FIG. 14 . 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     In the following description, various dimensional and orientation words, such as height, width, length, longitudinal, horizontal, vertical, up, down, left, right, tall, low profile, and the like, may be used with respect to the illustrated drawings. Such words are used for ease of description with respect to the particular drawings and are not intended to limit the described embodiments to the orientations shown. It should be understood that the illustrated embodiments can be oriented at various angles and that the dimensional and orientation words should be considered relative to an implied base plane that would rotate with the embodiment to a revised selected orientation. 
       FIG. 1  illustrates a perspective view of a conventional magnetic assembly  100  having a bobbin  110  with a coil or winding  112  wound around the bobbin  110  between a first end flange  114  and a second end flange  116 . The magnetic assembly  100  further includes a first E-core  120  and a second E-core  122 .  FIG. 2  illustrates an exploded perspective view of the bobbin assembly of  FIG. 1 .  FIG. 3  illustrates a front elevational view of the bobbin of  FIG. 2 . 
     As shown in  FIG. 2 , each of the E-cores  120 ,  122  includes a first outer leg  140  having an end surface  142 , a second outer leg  144  having an end surface  146 , and a center leg  150  having an end surface  152 . The outer legs and the center leg of each E-core extend perpendicularly from a common body portion  160  having a lower surface  162  and an upper surface  164 . The center leg  150  of each E-core is aligned with a passageway  170  through the bobbin between the first end flange  114  and the second end flange  116 . The center legs are inserted into the passageway  170  from opposite ends to form the assembled configuration shown in  FIG. 1 . In many configurations, the center leg of each E-core is shorter than the outer legs of the E-core by a small difference (G/2) such that when the center legs of the two E-cores are positioned in the passageway of the bobbin from opposite ends of the bobbin, the end surfaces of the outer legs abut and the end surfaces of the center legs are spaced apart by a total difference (G) to form a gap between the end surfaces. The gap controls saturation of the core in a known manner. 
     As further shown in  FIGS. 1-3 , the bobbin  110  includes a connector rail  180  at each end of the bobbin. Each connector rail  180  has a plurality of connector pins  182  extending from a lower surface  184 . Some or all of the connector pins  182  are electrically connected to the winding  112  by conductors (not shown). Each connector rail  180  has an upper surface  186 . In the illustrated embodiment, the upper surface  186  of each connector rail  180  extends to and is level with a bottom surface  188  of the passageway  170  of the bobbin. 
     Each of the first end flange  114  and the second end flange  116  of the bobbin  110  includes a plurality of tabs  190 . The tabs  190  extend perpendicularly from the respective flange  114 ,  116 . As shown in  FIG. 3 , each tab  190  has a respective lower surface  192 , which is generally aligned with an upper surface  194  of the passageway  170  of the bobbin. The lower surface  192  of each tab  190  is spaced apart from the upper surface  186  of the connector rail  180  at the respective end of the bobbin  110  by a distance (H) selected to be substantially equal to the height of the common body portion  160  of each of the E-cores  120 ,  122  between the respective lower surface  162  and the respective upper surface  164  of the common body portion. Thus, when the magnetic assembly is assembled as shown in  FIG. 1 , the common body portions of the E-cores fit between the lower surfaces of the tabs and the upper surfaces of the connector rails to position the E-cores vertically with respect to the passageway of the bobbin. 
     Although the two E-cores  120 ,  122  are constrained vertically between the tabs  190  and the connector rails  180 , the E-cores are not constrained horizontally. Thus, the conventional magnetic assembly  100  of  FIGS. 1-3  further includes at least one layer of an adhesive tape  200  that is wrapped around the common body portions  160  and the outer legs  140 ,  144  of the two E-cores after the E-cores are positioned with the respective end surfaces  142 ,  144  of the outer legs of one E-core abutting the respective end surfaces  146 ,  142  of the outer legs of the other E-core. Preferably, multiple layers of the adhesive tape  200  are wound around the E-cores. Alternatively, the end surfaces of the outer legs are glued and the E-cores are held securely in place until the glue sets to permanently engage the end surfaces. In addition, in some embodiments, the lower surfaces  162  and the upper surfaces  164  of the common body portions  160  of the E-cores may be taped or glued to the connector rails and the tabs, respectively, to further secure the E-cores. In either case, the additional steps of taping or gluing require time and effort, and the glue and tape require additional materials. The additional steps and material increase the cost of producing the magnetic assembly  100 . 
       FIG. 4  illustrates a perspective view of an embodiment of a bobbin  300  for a magnetic assembly that reduces the time, effort and materials for producing a magnetic assembly.  FIG. 5  illustrates an enlarged perspective view of one of the lower ribs of  FIG. 4  taken within the area -- 5 -- in  FIG. 4 .  FIG. 6  illustrates an enlarged front elevational view of the lower rib of  FIG. 5 .  FIG. 7  illustrates a front elevational view of the bobbin of  FIG. 4 .  FIG. 8  illustrates a side elevational view of the bobbin of  FIG. 4 . 
     The bobbin  300  of  FIGS. 4-8  includes a first end flange  310  and a second end flange  312 . The first end flange has a first outer surface  314 . The second end flange has a second outer surface  316 . A passageway  320  extends through the bobbin from the first outer surface of the first end flange to the second outer surface of the second end flange. The passageway has a lower inner surface  322  and an upper inner surface  324  ( FIG. 7 ). A winding  326  is wound about the passageway  320  between the first and second end flanges. In the illustrated embodiment, the bobbin  300  may be formed of nylon, such as, for example, commercially available Nylon 6/6 (also known as Nylon 66, Nylon 6-6 or Nylon 6,6). 
     The bobbin  300  further includes a first connector rail  330  at the lower end of the first end flange  310  and a second connector rail  332  at the lower end of the second end flange  312 . Each connector rail has a respective lower surface  334  and a respective upper surface  336 . A plurality of connector pins  338  extend downwardly from the lower surfaces of the connector rails. Some or all of the connector pins are electrically connectable to the winding  326 . The upper surfaces of the connector rails are aligned with the lower inner surface  322  of the passageway  320 . 
     Unlike the previously described conventional bobbin  110 , the bobbin  300  of  FIGS. 4-8  includes a first ledge  340  that extends from the outer surface  314  of the first end flange  310  in parallel to the first connector rail  330 . The first ledge  340  has a lower surface  342  that is aligned with the upper inner surface  324  of the passageway  320 . The first ledge  340  has an upper surface  344 , which is spaced apart from the lower surface  342  of the first ledge  340  by a ledge thickness. The lower surface  342  of the first ledge  340  is spaced apart from upper surface  336  of the first connector rail  330  to form a first horizontal channel  346  across the outer surface  314  of the first end flange  310 . The first horizontal channel  346  is perpendicular to the passageway  320 . 
     The bobbin  300  further includes a second ledge  350  that extends from the outer surface  316  of the second end flange  312  in parallel with the second connector rail  332 . The second ledge  350  has a lower surface  352  that is aligned with the upper inner surface  324  of the passageway  320 . The second ledge  350  has an upper surface  354 , which is spaced apart from the lower surface  352  by the ledge thickness. The lower surface  352  of the second ledge  350  is spaced apart from upper surface  336  of the second connector rail  332  to form a second horizontal channel  356  across the outer surface of the second end flange  312 . The second horizontal channel  356  is perpendicular to the passageway  320  and is parallel to the first horizontal channel  346 . 
     In the illustrated embodiment, the ledge thickness of each of the first ledge  340  and the second ledge  350  is approximately 0.07 inch, and each of the ledges extend outward from the respective end flange by a length of approximately 0.143 inch. The thickness of each ledge with respect to the length is sufficient to cause the ledge to be substantially rigid such that the ledge does not flex when the cores are inserted as described below. In the illustrated embodiment, the respective lower surface of each ledge is spaced apart from respective upper surface of the connector rail by approximately 0.24 inch, which is the nominal height of each of the first channel  346  and the second channel  356 . 
     As shown in  FIGS. 4-8 , a first plurality of ribs  360  extend outward from the outer surface  314  of the first end flange  310  and extend upward from the upper surface  336  of the first connector rail  330 . A second plurality of ribs  362  extend outward from the outer surface  316  of the second end flange  312  and extend upward from the upper surface  336  of the second connector rail  332 . A third plurality of ribs  364  extend outward from outer surface  314  of the first end flange  310  and extend downward from the lower surface  342  of the first ledge  340 . A fourth plurality of ribs  366  extend outward from the outer surface  316  of the second end flange  312  and extend downward from the lower surface  352  of the second ledge  350 . In the illustrated embodiment, each of the first, second, third and fourth plurality of ribs includes four ribs. Each plurality of ribs includes a pair of ribs positioned on either side of a respective end of the passageway  320  and includes a pair of ribs positioned along the edges of the respective first end flange. 
     In the illustrated embodiment, each of the ribs in the first, second, third and fourth plurality of ribs  360 ,  362 ,  364 ,  366  has approximately the same size and shape. One of the ribs  360  in the first plurality of ribs is shown in more detail in the enlarged perspective view of  FIG. 5  and in an enlarged front elevational view of  FIG. 6 . As shown in  FIGS. 5 and 6 , the rib  360  may be a six-sided polyhedron having a first end face  370  (shown partially in dashed lines) in the shape of an isosceles trapezoid in the plane of the outer surface  314  of the first end flange  310 . The first end face  370  has a longer base along the intersection of the upper surface  336  of the first connector rail  330  with the outer surface  314  of the first end flange  310 . The longer base of the first end face  370  has a width of approximately 0.027 inch. The first end face  370  has a shorter base displaced away from the upper surface of the first connector rail. The shorter base of the first end face has a width of approximately 0.015 inch. The shorter base of the first end face  370  is spaced apart from the longer base by approximately 0.02 inch. 
     The rib  360  has a second trapezoidal end face  372  displaced away from the first end face  370  by approximately 0.0785 inch. In the illustrated embodiment, the second end face  372  is parallel to the first end face  370 . However, the second end face  372  may also be at an angle with respect to the first end face  370 . The second end face has a longer base along the upper surface  336  of the first connector rail  330 . The longer base of the second end face  372  has a width of approximately 0.00875 inch. The second end face  372  has a shorter base displaced away from the upper surface  336  of the first connector rail  330 . The shorter base of the second end face  372  has a width of approximately 0.005 inch. In the illustrated embodiment where the second end face is parallel to the first end face, the second base of the second end face is spaced apart from the first base by approximately 0.003 inch. The second end face is spaced apart from the first end face by the length of the rib, which is approximately 0.0785 inch in the illustrated embodiment. 
     The rib  360  has a base face  374  (shown partially in dashed lines), which is coplanar with the upper surface  336  of the first connector rail  330 . The base face is defined by two lines connecting the ends of the longer base of the first end face  370  with the ends of the longer base of the second end face  372 . 
     The rib  360  has an exposed engagement face  376 , which has a first end  380  spaced apart from the base face  374  at the outer surface  314  of the first end flange  310  by the height of first end face  370 . The engagement face  376  has a displaced second end  382 , which is spaced apart from the base face  374  by the height of the second end face  372 . In the illustrated embodiment, the engagement face  376  slopes upward from the second end to the first end face from approximately 0.003 inch above the upper surface  336  of the first connector rail  330  to approximately 0.02 inch above the upper surface of the first connector rail. Thus, the engagement face  376  slopes upward at an angle of approximately 12.22 degrees. The rib  360  has a first side face  384  and a second side face  386  (shown partially in dashed lines) that respectively interconnect a sloped side of the first end face with a corresponding sloped side of the second end face. The foregoing shapes and dimensions are provided for illustration only. The shapes and dimensions may vary in other embodiments. 
     Each of the other ribs in the first plurality of ribs  360  has a size and shape corresponding to the size and shape of the rib illustrated in  FIGS. 5 and 6 . The respective engagement faces  376  of the second plurality of ribs  362  also slope upward from the respective second end  382  to the respective first end  380 . The respective engagement faces of the third plurality of ribs  364  and the fourth plurality of ribs  366  slope downward from the respective second ends to the respective first ends. 
     As illustrated in  FIG. 4  and  FIGS. 6-8 , the ribs  360  on the upper surface  336  of the first connector rail  330  extend upward across the first channel  346  toward the ribs  364 , which extend downward from the lower surface  342  of the first ledge  340 . Similarly, the ribs  362  on the upper surface  336  of the second connector rail  332  extend upward across the second channel  356  toward the ribs  366 , which extend downward from the lower surface  352  of the second ledge  350 . As described above, the nominal height of the first channel  346  between the upper surface of the first connector rail and the lower surface of the first ledge is approximately 0.24 inch. Similarly, the nominal height of the second channel  356  between the upper surface of the second connector rail and the lower surface of the second ledge is also approximately 0.24 inch. The spacing between the lower ribs and the upper ribs at each end of the bobbin varies from the respective second ends  382  to the respective first ends  380  of the engagement faces  376  of the ribs. The combined heights of the second ends of the engagement faces of two opposing ribs cause the heights of the respective channels between the second ends of opposing ribs to be reduced to approximately 0.234 inch (e.g., 0.24−(2×0.003)). The combined heights of the first ends of the engagement faces of two opposing ribs cause the heights of the respective channels between the first ends of opposing ribs to be further reduced to approximately 0.2 inch (e.g., 0.24−(2×0.02)). The effect of the varying spacing between the engagement faces of the opposing ribs is described below. 
       FIG. 9  illustrates an exploded perspective view of a magnetic assembly  400  that incorporates that bobbin  300  of  FIGS. 4-8 . The magnetic assembly of  FIG. 9  includes a first E-core  410  and a second E-core  420 .  FIG. 10  illustrates a perspective view of the magnetic assembly of  FIG. 9  with the components fully assembled.  FIG. 11  illustrates a front elevational view of the magnetic assembly of  FIG. 10 .  FIG. 12  illustrates a side elevational view of the magnetic assembly of  FIG. 10 . 
     The first E-core  410  and the second E-core  420  are similar to the first and second E-cores  120 ,  122  described above with respect to  FIGS. 1 and 2 . In particular, each E-core includes a main body  430  having a lower surface  432  and an upper surface  434 . The main body of each E-core has a height (H) of approximately 0.224 inch between the lower surface and the upper surface. The main body  430  also has an outer surface  436  and an inner surface  438 . A first outer leg  440  extends from the inner surface of the main body  430 . The first outer leg  440  has a first outer leg end surface  442 . A second outer leg  444  extends from the inner surface of the main body. The second outer leg  444  has a second outer leg end surface  446 . A center leg  450  extends from the inner surface  438  of the main body  430 . The center leg  450  has a center leg end surface  452 . 
     As discussed above, the outer legs preferably have the same length with respect to the inner surface of the main body. The center leg of one or both S-cores may be shorter than the outer legs by a small difference (e.g., G/2 in  FIG. 9 ) to form a gap within the passageway when the respective first outer leg surface of each E-core is abutting the respective second outer leg surface of the other E-core. In the illustrated embodiment, a total gap distance (G) is provided between the center leg surfaces. For example, in one embodiment, the total gap distance may be approximately 0.001 inch. The gap controls core saturation in a known manner. In the illustrated embodiment, the three legs have respective lower and upper surfaces that are coplanar with the lower and upper surfaces of the main body. In alternative embodiments (not shown), the center leg may have one surface that is not coplanar with the other surfaces such that the center leg has a height less than the height of the outer legs. 
     In  FIG. 9 , the first E-core  410  is positioned with the respective center leg  450  aligned for insertion into the passageway  320  of the bobbin  300  at the first end flange  310 . The second E-core  420  is positioned with the respective center leg  450  aligned for insertion into the passageway  320  of the bobbin  300  at the second end flange  312 . It should be understood that the positions of the two E-cores are interchangeable in  FIG. 9  and in  FIGS. 10-12 . 
       FIG. 10  illustrates a perspective view of the completed magnetic assembly  400  of  FIG. 9 . In  FIG. 10 , the center leg  450  of the first E-core  410  is inserted into the passageway  320  of the bobbin  300  until the main body  430  is within the first channel  346  and the inner surface  438  ( FIG. 9 ) of the main body of the first E-core abuts the outer surface  314  of the first end flange  310 . The main body of the first E-core is secured by the first plurality of ribs  360  and the third plurality of ribs  364  as described below. The center leg  450  of the second E-core  420  is inserted into the passageway  320  of the bobbin  300  until the main body  430  is within the second channel  356  and the inner surface  438  of the main body of the second E-core abuts the outer surface  316  of the second end flange  312 . The main body of the second E-core is secured by the second plurality of ribs  362  and the fourth plurality of ribs  366  as described below. 
     As discussed above, the height of the main body  430  of the first E-core  410  is approximately 0.224 inch in the illustrated e embodiment. Thus, when the center leg  450  of the first E-core  410  is initially inserted into the passageway  320  of the bobbin  300 , the main body of the first E-core  410  fits easily into the first channel  346  between the second ends  382  of the respective engagement surfaces  376  of the opposing lower ribs  360  and upper ribs  364  because the second ends are spaced apart by approximately 0.234 inch. As the center leg of the first E-core  410  is inserted farther into the passageway  320 , the lower surface  432  of the main body engages the engagement surfaces of the lower ribs, and the upper surface  434  of the main body engages the engagement surfaces of the upper ribs. After engaging the engagement surfaces of the ribs, the upper and lower surfaces of the main body crush the resilient nylon ribs as the main body is forced into the channel. The main body is fully engaged with the ribs when the inner surface  438  of the main body abuts the outer surface  314  of the first end flange  310  of the bobbin proximate to the first ends  380  of the engagement surfaces of the ribs. 
     In like manner, the center leg  450  of the second E-core  420  is inserted into the passageway  320  of the bobbin  300 , and the main body  430  of the second core is inserted into the second channel  356 . The lower surface  432  and the upper surface  434  of the main body of the second E-core are forced into frictional engagement with the engagement surfaces  376  of the lower ribs  362  and the upper ribs  366  which extend into the second channel as described above. 
     The lengths of the outer legs  440 ,  444  of the two E-cores  410 ,  420  are selected so that the first and second end surfaces  442 ,  446  of the outer legs of the first E-core abut the second and first end surfaces  442 ,  446  of the outer legs of the second E-core when the respective inner surfaces  438  of the main bodies  430  are fully engaged with the ribs  360 ,  362 ,  364 ,  366  of the end flanges  310 ,  312  of the bobbin  300 . The frictional engagements of the crushed ribs with the upper surface  334  and lower surface  332  of the main bodies of the two E-cores secure the E-cores in fixed spatial relationships with the bobbin without requiring tape, glue or other additional attachment materials. 
       FIG. 13  illustrates an exploded perspective view of a magnetic assembly  500  that incorporates that bobbin  300  of  FIGS. 4-8 . The magnetic assembly of  FIG. 13  includes one extended E-core  510  to be inserted into the passageway  320  at the end of the bobbin proximate to the second flange  312 . The magnetic assembly  500  includes an I-core  520  positioned at the opposite end of the bobbin  300  proximate to the first flange  310 .  FIG. 14  illustrates a perspective view of the completed magnetic assembly of  FIG. 13 .  FIG. 15  illustrates a front elevational view of the magnetic assembly of  FIG. 14 .  FIG. 16  illustrates a side elevational view of the magnetic assembly of  FIG. 14 . In  FIGS. 13-16 , the extended E-core  510  is positioned proximate to the second end flange  312 , and the I-core  520  is positioned proximate to the first end flange  310 . The positions of the E-core and the I-core can be interchanged or the identifications of the first and second end flanges can be interchanged without affecting the magnetic properties of the structure. 
     The extended E-core  510  of  FIG. 13  is similar to the previously described E-cores. However, the extended E-core has outer legs with lengths selected so that the outer legs of the extended E-core  510  extend for the length of the bobbin  300 . The extended E-core has a main body  530 , which has a lower surface  532 , an upper surface  534 , an outer surface  536  and an inner surface  538 . A first outer leg  540  extends perpendicularly from the main body  530  to a first outer leg end surface  542 . A second outer leg  544  extends from the main body  530  to a second outer leg end surface  546 . A center leg  550  extends from the main body  530  to a center leg end surface  552 . The outer legs and the center leg have respective lower and upper surfaces that are coplanar with the lower and upper surfaces of the main body  530 . The extended E-core  510  has a height between the lower surface and the upper surface of the main body that corresponds to the heights of the previously described E-cores  410 ,  420 . The extended E-core  510  has a width between an outer surface  560  of the first outer leg  540  and an outer surface  562  of the second outer leg  544 . 
     The first outer leg  540  has a length from the inner surface  538  of the main body  530  to the first outer leg end surface  542  that is substantially equal to the length of the passageway  320  of the bobbin  300  from the outer surface  316  of the second end flange  312  to the outer surface  314  of the first end flange  310 . Thus, when the center leg  550  is inserted into the passageway  320  and the main body  530  is inserted into the second channel  356 , the inner surface of the main body abuts the outer surface  316  of the second end flange  314  as shown in  FIG. 14 , and the first outer leg end surface is flush with the outer surface  314  of the first end flange  310 . The second outer leg  544  has a corresponding length such that the second outer leg end surface  546  is also flush with the outer surface of the first end flange. The length of the center leg is shorter than the lengths of the two outer legs by a distance G such that the center leg end surface  552  is recessed slightly with respect to the outer surface of the first end flange. For example, in the illustrated embodiment, the distance G is approximately 0.01 inch. 
     The I-core  520  is a rectangular parallelepiped having only a main body  570 . The main body  570  has a first end surface  572  and a second end surface  574 . The main body  570  of the I-core  520  has a length between the first end surface  572  and the second end surface  574  corresponding to the width of the extended E-core  510  between the outer surfaces  560 ,  562  of the outer legs  540 ,  544 . The I-core  520  has a height between a lower surface  576  and an upper surface  578 . In the illustrated embodiment, the height of the I-core  520  is substantially the same as the height of the extended E-core  510 . The I-core  520  has an outer surface  580  and an inner surface  582 . 
     As shown in  FIG. 14 , the I-core  520  is mounted on the bobbin  300  with a first portion  590  of the inner surface  582  of the I-core abutting the first outer leg end surface  542  of the E-core  510  and with a second portion  592  of the inner surface of the I-core abutting the second outer leg end surface  546  of the E-core. A third portion  594  of the inner surface of the I-core abuts the outer surface  314  of the first end flange  310  between the passageway  320  of the bobbin and the first outer leg  540  of the E-core  510 . A fourth portion  596  of the inner surface of the I-core abuts the outer surface  314  of the first end flange  310  between the passageway  320  and the second outer leg  544  of the E-core  510 . Accordingly, a fifth portion (central facing surface)  598  of the inner surface of the I-core is spaced apart from the recessed center leg end surface  552  by the difference in length of the center leg with respect to the lengths of the two outer legs of the E-core (e.g., the distance G shown in  FIG. 13 ). The spacing produces a magnetic gap between the end surface of the center leg of the E-core and the central facing surface of the I-core. The gap controls saturation of the core in a known manner. 
     As shown in  FIG. 14 , the main body  530  of the extended E-core  510  is positioned in the second channel  356  between the second connector rail  332  and the second ledge  350  with the inner surface  538  of the main body adjacent to the outer surface  316  of the second end flange  312 , as described above. The extended E-core is secured to the second end flange by the friction caused by the crushed second plurality of ribs  362  and the crushed fourth plurality of ribs  366 . 
     As further shown in  FIG. 14 , the main body  570  of the I-core  520  is positioned in the first channel  346  between the first connector rail  330  and the first ledge  340  with the inner surface  582  of the main body of the I-core adjacent to the outer surface  314  of the first end flange  310 . The I-core  520  is secured to the first end flange  310  by the friction caused by the crushed first plurality of ribs  360  and the crushed third plurality of ribs  364 . 
     Although described above in the context of the illustrated embodiments, it should be understood that the core retention ribs can also be used with bobbins and cores of different configurations. For example, the center legs of the two E-cores of  FIGS. 9-12  or the center leg of the E-core of  FIGS. 13-16  and the corresponding passageway through the bobbin may be round in alternative embodiments. The improved bobbin can be modified such that the passageway accommodates a center leg having a shorter height than the heights of the main body and the outer legs to produce a low-profile magnetic assembly. 
     Although illustrated by four crushable ribs above and four crushable ribs below the cores, additional or fewer ribs can be used in alternative embodiments. Furthermore, the opposing ribs in each channel may be offset rather than directly across from each other. 
     Although there have been described particular embodiments of the present invention of a new and useful “Bobbin and E-Core Assembly Configuration and Method for E-Cores and EI-Cores,” it is not intended that such references be construed as limitations upon the scope of this invention except as set forth in the following claims.