Patent Publication Number: US-6657529-B1

Title: Magnetic component

Description:
FIELD OF TECHNOLOGY 
     The invention relates to a magnetic component. 
     BACKGROUND AND SUMMARY 
     Magnetic components (coils or transformers) are also provided for use in high frequency clocked electronic circuits, for example, parts of combinatorial circuits. In many electronic devices of the consumer electronics industry, parts of combinatorial circuits are used nowadays. A large problem is then caused by the electromagnetic disturbances resulting from the high-frequency switching mode. This problem becomes particularly serious when the parts of combinatorial circuits are built-in in monitors, television sets or audio sets, because the video and audio quality respectively may be influenced. More particularly radio reception is strongly affected in the long-wave and medium-wave range, because this frequency range lies in the neighborhood of switching frequencies or their first harmonics. To the most important noise sources belong the magnetic components which generate a very strong magnetic stray field. 
     A method usually implemented for reducing this magnetic stray field comprises creating a short-circuit winding around the coil or the transformer respectively, with the aid of a conductive foil, usually a copper strip. This method, however, is not at all sufficient for lowering the magnetic field to a level that is no longer detected by the medium-wave antenna of the audio device. A further efficient method comprises that the magnetic component is built-in in a closed screen housing. Added to the disadvantage of extra cost and weight is here particularly the poorer heat dissipation. 
     From WO 81/02648 (compare its FIG. 1) is known a magnetic component with a U core in which a winding is deposited on two opposite core limbs. When there is a current flowing through the windings, the generated stray fields are mutually partly compensating so that the resulting stray field outside the magnetic component is reduced. 
     SUMMARY OF THE INVENTION 
     It is an object of the invention to provide a further variant for a magnetic component, in which the generated stray field outside the component is minimized. 
     The object is achieved in that at least two windings electrically connected in series are provided and in that the magnetic component has a core on which the windings are arranged so that in the case of a current flowing through the windings, the generated magnetic stray fields outside the component at least partly compensate each other, while the core has at least one inside limb portion and at least two outside limb portions and the windings are arranged on the inside limb portion and/or the outside limb portions. 
     The desired effect of stray field reduction outside the magnetic component can be obtained with the aid of cores for magnetic components, for example, E or P cores which are customary in the market. A winding is then suitably subdivided so that spatially separated winding portions are formed which are no longer directly magnetically coupled i.e. the same magnetic flow no longer passes through them. Outside the magnetic component, an effective compensation of the magnetic fields generated by the respective windings can thus be achieved, so that the resulting magnetic stray field outside the component is largely minimized. There are component variants which can be manufactured cost effectively and effectively reduce the stray field. More particularly, the individual windings have, in essence, equal inductance values, so that with symmetrical component structures an optimum compensation of the generated stray fields outside the magnetic component is achieved. With asymmetric arrangements, however, different inductance values may regularly be selected. 
     In an embodiment of the invention, there are two cores which have corresponding inside and outside limb portions. The inside limb portions carry each a winding for guiding a magnetic flow and between the two core portions a third core portion is arranged which is I-shaped in cross-section. This embodiment is preferably realized by means of an E core between whose core halves the core portion having an I shape in cross-section is arranged. 
     Another variant of embodiment of the invention provides that two inside core portions are provided which have corresponding inside and outside limb portions pointing inwards, that on the outside of the inside core portions further core portions are arranged which have further inside and outside limb portions corresponding to the inside and outside limb portions of the inner core portions and that the windings are arranged on the inside core portions. This embodiment provides a further improved reduction of the stray field outside the magnetic component. The component core is preferably realized by means of two E cores i.e. by means of four E core halves lying on top of each other, whose inside and outside limb portions all point to the inside of the component. 
     A further reduction of the outside stray field may be achieved in that the outside limb portions of the core portions carry at least part of the windings. When the inside and outside limb portions of the core portions then carry windings, the stray field reduction is optimized further. The idea according to the invention, however, also includes the case where only the outside limbs carry windings. The invention also relates to a core for one of the variants of a magnetic component described above. 
    
    
     BRIEF DESCRIPTION OF THE DRAWING 
     Examples of embodiment of the invention will be further explained with reference to the drawings, in which: 
     FIG. 1 shows a magnetic component according to the invention having a core comprising two E cores, 
     FIG. 2 shows a magnetic component according to the invention having a core comprising two E core halves and one I-shaped core half, 
     FIG. 3 shows a magnetic component according to the invention having a core comprising four E core halves and 
     FIG. 4 shows a magnetic component according to the invention with which windings have also been deposited on the outside limbs. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The magnetic component shown in FIG. 1, which is arranged as a coil here, has a core comprising two E cores  1  and  2 . On the inside limb (portion) of the E core  1  is wound a winding  3  which is electrically connected in series to a winding  4 , while the winding  4  is wound on the inside limb (portion) of the E core  2 . The outside limb (portions) of the two E cores  1  and  2  have no windings. The two E cores  1  and  2  are arranged so that the inside and outside limb portions corresponding to each other lie opposite each other and their axes are running in parallel. 
     Furthermore, FIG. 1 shows for the case where a current I flows through the windings  3  and  4 , the basic pattern of the magnetic flux generated by the flowing current. In the upper E core  1 , the thus generated magnetic flux in the inside limb is directed from top to bottom, thus in the direction of the other E core  2 . At the bottom of the inside limb of the E core  1 , this flux is split up and is led here for one half to the left outside limb and for the other half to the right outside limb of the E core  1 . The magnetic partial fluxes led via the two outside limbs are directed from bottom to top in the two outside limbs of the E core  1  and are united at the upper end of the inside limb of the E core  1  to the magnetic flux running through the inside limb, so that the magnetic circuit covered by the E core  1  is closed. Since the same current flows through the winding  4  as through the winding  3 , and in the present case the two windings also have the same inductance values, the distribution of magnetic flux in E core  2  corresponds to the distribution of magnetic flux in the E core  1 . However, the magnetic fluxes flowing through the inside or outside limb respectively of the E core  2  are oppositely directed, that is to say, the magnetic flux flowing through the inside limb of the E core  2  is directed from bottom to top on the magnetic partial fluxes in the outside limbs of the E core  2  are directed from top to bottom. In such a magnetic component the magnetic stray fields generated by the windings  3  and  4  largely compensate each other outside the magnetic component, so that the resulting magnetic stray field outside the magnetic component is reduced to a minimum. 
     FIG. 2 shows a preferred embodiment of the magnetic component according to the invention with an intersection running through the magnetic component. In this variant of embodiment, a core with two E core halves  10  and  11  is provided, between which a core portion  12  having an I-shaped cross-section is arranged. The inside limb portion of the E core half  10  carries a winding  13  and the inside limb portion of the E core half  11  carries a winding  14 . Similarly to the magnetic component shown in FIG. 1, also here the two windings are electrically connected in series. An air gap (references  15  and  16 ) is provided between the inside limb portions of the two respective core halves  10  and  11  and the core portion  12 . 
     If a current I flows through the windings  13  and  14  (corresponds to the arrangement of windings  3  and  4  and the current flow shown in FIG.  1 ), as is shown in FIG. 2, the result is that in the inside limb of the core half  10  a magnetic flux is generated directed from top to bottom and pointing in the direction of the core half  11 . The magnetic flux entering the core half  12  via the air gap  15  is led in the present symmetrical core arrangement in equal amounts in the direction of the left and right outside limb portions of the core halves  10  and  11 . For optimizing the pursued compensation of the outside magnetic stray field, the thickness d of the core portion  12  is to be selected smallest possible, while the reduction of the thickness d has its limits where the generated losses in the core portion  12  are no longer acceptable, or the inductance values to be generated by means of the windings  13  and  14  are no longer realizable. 
     The embodiment as shown in FIG. 2 leads to a reduction of the outside magnetic stray field that can be compared to that of the embodiment shown, in FIG.  1 . However, the embodiment shown in FIG. 2 offers the advantage that the core portions  10 ,  11  and  12  used are available as cost-effective mass-produced articles and for the core arrangement are used only, for example, an E core and a core portion having an I-shaped cross-section. 
     A further improved reduction of the outside stray field is found in the magnetic component shown in FIG.  3 . This has a core formed by four E core halves. First an E core is provided formed in customary fashion by two core halves  20  and  21 , while on the outside of the core half  20  an E core half  22  of a second E core is arranged and on the outside of the E core half  21 , the second core half  23  of the second E core is put accordingly. The head ends of corresponding inside and outside core portions of the four E core halves are opposite each other and on one line. An air gap is provided between the inside limb portions of the two inside E core halves  20  and  21 , between the inside limb portion of the E core half  22  and of the E core half  20 , and between the inside limb portion of the E core half  23  and of the E core half  21 . Electrically series-arranged windings  24 ,  25 ,  26  and  27  are arranged on the inside limb portions of all four E core halves  20 ,  21 ,  22  and  23  so that magnetic fluxes through the inside limb portions of the E core halves  20  and  21  have the same direction. Similarly, the magnetic fluxes through the inside limb portions of the E core halves  22  and  23  show the same direction. In the present example of embodiment with the symmetrical core arrangement which comprises four identical E core halves, the windings  24  to  27  carried by the respective inside limb portions have identical numbers of turns. 
     FIG. 4 represents a further variant of embodiment and shows a magnetic component with an E core  30 , whose inside limb carries a winding  31  and whose two outside limbs carry windings  32  and  33 . The windings  31  to  33  are electrically connected in series and wound so that magnetic fluxes run through the windings  32  and  33  in the same direction (in FIG. 4 from bottom to top) and that the respective magnetic flux runs in opposite direction through the middle winding  31  (in FIG. 4 from top to bottom). With this variant of embodiment it becomes clear that the inventive idea can be developed such that also the outside limb (portions) of a branched core of a magnetic component according to the invention can always carry part of the windings connected in series. This presents new possibilities of embodiment also for the variants of embodiment shown in FIGS. 1 to  3 . 
     In lieu of E core portions, also portions of comparable types of cores, for example of P cores, can be used for the component according to the invention. Furthermore, the described embodiments may also be easily extended to transformers in the customary fashion.