Abstract:
A magentic configuration using a plurality of posts and spiting the primary winding on each of the posts and placing the secondary windings together with the rectifiers menas around each posts to minimise the stray and leakage inductance. In this magentic configurations there is a significant reduction of the core material and a reduction of the footprint by a better utilization of the copper. The magentic field is weaving from through a post to the other minimizing the vertical components and forcing the magentic field to be paralel with the winding reducing the ac copper losses. These properties allows this magentic strcuture to be suitable in very high frequency applications and even in application with air core. These magentic structures can be used for transformer inplementation and also for the inductive applications.

Description:
RELATED APPLICATION/CLAIM OF PRIORITY 
       [0001]    This application is related to and claims priority from Provisional application Ser. No. 61955640, filed Mar. 19, 2014, which provisional application is incorporated by reference herein. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The present invention relates mechanical construction and its mechanical results for transformer and inductances with utilization in power conversion, data transition and communication. 
       BACKGROUND OF THE INVENTION 
       [0003]    There is an industry demand for smaller size and lower profile power converters, which require smaller and lower profile magnetic elements, such as transformer and inductors. For a better consistency in production for magnetic elements, the windings are embedded into the multilayers PCB structures. In such applications, the copper thickness is limited. To be able to use thinner copper and limited numbers of layers for higher current applications, there are several solutions. One solution is to split the currents and process each section of it before is provided to the output. The progress in semiconductor industry wherein the footprint of some power devices became very small and the on resistance very small has also shifted the direction in the magnetic technology. The semiconductor devices are capable to process very high currents in a small footprint due to a significant reduction of the on resistance. This requires magnetic structures capable to handle very high current in a very small footprint. To reduce the power dissipation in the copper especially in the multilayer construction using very thin copper the length of the magnetic winding has to be reduced. 
         [0004]    In  FIG. 1  is presented two methods of splitting the current. One is described in U.S. Pat. No. 4,665,357 wherein there are employed multiple independent transformers with the primary in series, referred also as a Matrix transformer. Another methodology is described in U.S. Pat. No. 7,295,094 B2. The structure presented in U.S. Pat. No. 7,295,094B2 has several advantages over the structure presented in U.S. Pat. No. 4,665,357 such the increase of the total magnetizing inductance and a reduction of the magnetic core volume, though limited reduction because all the windings do share the same magnetic core. 
         [0005]    In the patent application Ser. No. 61/821,896 filled May 10, 2013, and U.S. patent application Ser. No. 61/831,527 filled June 5, are presented soft switching topologies wherein the leakage inductance in the transformer has to be very small. The prior art magnetic structures depicted in  FIG. 1  can provide some reduction of the leakage inductance but they cannot offer a significant reduction of the total footprint to allow a reduction of the stray inductance. The stray inductance adds to the leakage inductance and in some application can have a significant percentage of the total parasitic inductance. The latest GAN mosfet technology place another demand on the magnetic structures by pushing the operation frequency higher from hundreds of KHz to Megahertz level. Such high frequency magnetic structures are presented in IEEE Transactions on Power Electronics, Vol_28, NO 9, and September 2013, “A Technology Overview of the Power Chip Development Program”. In these structures, magnetic cores are not used. The structures presented in previous mentioned publication there is a large Rac/Rdc ratio, which is the ratio of the total impedance of the winding including the high frequency losses such as proximity losses and skin effect losses divided by the DC only losses. In operation at higher frequency, that ratio plays an important role. In U.S. Pat. No. 5,381,124 is presented a low profile magnetic structure which employs a four legged magnetic core and as serpentine winding structure. Function of the winding configuration such a structure can benefit of a lower leakage inductance but it does not address the parasitic inductance, which is caused by the interconnection from the transformer to the power semiconductor devices. Another low profile magnetic implementation is described in the U.S. Pat. No. 7,187,263 B2. This is an optimized implementation of the Matrix transformer. In this implementation, the goal was not primarily to minimize the leakage inductance, which is a key element of the in power processing in the resonant topology. This implementation does reduce the stray inductance and the ac losses in the copper. It does not reduce the magnetic core total volume. 
       BRIEF SUMMARY OF THE INVENTION 
       [0006]    The magnetic structures described in this invention provide an improved magnetic core configuration and winding arrangement. The magnetic structures described in this invention do offer a much lower leakage inductance, a better utilization of the copper a smaller footprint and in some implementations are very suitable for air core magnetics for very high frequency operation. The embodiments of this invention can be used for transformer application or inductive elements. 
         [0007]    In one of the basic aspects of the present invention, a magnetic circuit element includes a circuit board, a plurality in excess of two magnetic flux conducting posts penetrating through the circuit board, at least two magnetic flux conducting plates connecting on both sides of the magnetic flux conductive posts, at least two connected primary winding encircling the magnetic posts, and at least two connected secondary winding encircling the magnetic posts. 
         [0008]    In this aspect of the invention, power components are placed in series or in parallel with the winding and become part of the primary or secondary winding. In addition, the entire magnetic structure can be encircled by a suitable shaped, magnetic flux conductive device and interconnections pins are placed inside and outside of the encircling the suitable shaped magnetic flux conductive device, where the pins are connected to a motherboard. Also, the flux conducting plates, or the flux conducting plates and magnetic flux conductive posts can be removed. 
         [0009]    In another basic aspect of the present invention, a magnetic circuit element with center tap topology is provided, including a circuit board, a plurality of magnetic flux conducting posts penetrating through the circuit board, magnetic flux conducting plates connecting on both sides the magnetic flux conductive posts, primary windings encircling the magnetic posts, and secondary windings encircling the magnetic posts, wherein the center tap topology is configured to allow reuse of at least portions of both the primary and secondary windings for current flow in either direction. 
         [0010]    In one of the embodiments of this invention, which is described in  FIG. 3A , and  FIG. 3B  there is a better copper optimization in the center tap topology. In center tap topology the secondary winding is not utilized properly. During one polarity the current flow through one of the secondary winding while, the other part of the secondary is not conducting. In one of the embodiments of this invention, the current in the secondary winding of the transformer circulates in both polarity in the center tap topology leading to a better copper utilization and lower power dissipation. Only a portion of the secondary winding is used for unidirectional current flow. The flooding with the copper over the primary winding will allow current flow freely to cancel the magnetic field of the primary winding to reduce the leakage inductance. Such implementation is presented in  FIG. 6A,6B,6C,6D . In these figures, the copper surrounds the area penetration of the magnetic core. The current flows through the copper around the cores in order to cancel the magnetic field produced by the primary winding. Such a magnetic configuration using a U shape core, and using the copper structures as presented in the drawing have a very low leakage inductance. 
         [0011]    In key one embodiment is depicted in  FIG. 5A ,  FIG. 5B  and  FIG. 5C . This magnetic structure has four posts, which penetrates through the multilayer structure wherein the windings are embedded. This structure is the result of merging four E type magnetic cores, and in the process, a good portion of the magnetic core material is eliminated. That reduces the total footprint of the magnetic structure and reduces to total core loss, which is proportional with the volume of the core material. In this process the secondary winding merge as well as depicted in  FIG. 5B . Each equivalent E shaped core is presented in  FIG. 5C . Though the magnetic core with four legs are depicted in other prior art, the copper structures and the placement of the rectifier means changes the mode of operation and the performances. 
         [0012]    In another embodiment depicted in  FIG. 9A and 9B  is presented the same four-legged magnetic structure wherein the output current flows out of the four openings and under the magnetic rectangular plate with a cutout in the middle to accommodate the four-legged transformer, which represents the output inductor. By placing the output connectors as depicted, the current is split and the magnetic core of the output choke does not have to penetrate the multilayer structure. In this way, we increase the utilization of the copper and decrease the total footprint of the transformer and output choke. This embodiment is very suitable for high output current applications. 
         [0013]    The magnetic configurations using the center posts can be implemented in different configuration as is presented in  FIG. 12 ,  FIG. 13  and  FIG. 14 . 
         [0014]      FIG. 10  depicts a more details drawing of the four-legged magnetic structure employing two magnetic core structures and a multilayer PCB. In  FIG. 11 , the center cutouts in the plates  111  and  113  are eliminated for technological reasons, though there is not a magnetic flux flowing through that section. 
         [0015]    In  FIG. 14  is presented a low profile magnetic structure employing a multitude of center posts. This magnetic structure can be a transformer structure or an inductive structure. On advantage using this configuration as a storage element is the fact that the gap will be distributed among all the center posts. 
         [0016]    The magnetic plate can be removed an in that case we can have only the center posts as in  FIG. 15  or air core as depicted in  FIG. 16 . There is a possibility to have just the center posts with a small plate at one end of it, or both, leaving a gap between the plates. In  FIG. 17  the ac to dc ratio, it is very low for an air core and this magnetic structure is highly suitable for very high frequency applications. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0017]      FIG. 1 : Shows prior art distributed magnetic structures using a multitude of the magnetic elements wherein the primaries are placed in series. 
           [0018]      FIG. 2 : Shows our equivalent schematic of the preferred embodiment wherein the magnetic elements are coupled. 
           [0019]      FIG. 3A : Depicts a transformer, employing center tap including the rectifiers. 
           [0020]      FIG. 3B : Shows the secondary winding implementation of the transformer presented in  FIG. 3A . The secondary winding implementation, in a transformer structure using a U core is one of the embodiments of this invention, wherein the copper utilization of the secondary windings is significantly improved over conventional center tap implementation. 
           [0021]      FIG. 4A : Shows a transformer structure without the center tap using a full bridge rectification. 
           [0022]      FIG. 4B : Shows the secondary winding implementation of the transformer presented in  FIG. 4A . 
           [0023]      FIG. 5A : Shows the equivalent schematic of the four-legged magnetic structure with center tap. 
           [0024]      FIG. 5B : Shows the secondary winding implementation of the four-legged transformer presented in  FIG. 5A . 
           [0025]      FIG. 5C : Shows the equivalent four transformers that are part of the four-legged transformer. 
           [0026]      FIG. 6A through 6D  shows the metal etch layers comprising winding in the transformer using the U core implementation described in  FIG. 3A and 3B . 
           [0027]      FIG. 7A and 7B : Shows the metal etch comprising winding for the four-legged magnetic structure described in  FIG. 5A and 5B . 
           [0028]      FIG. 8A and 8B : Shows the metal etch comprising winding for the four-legged magnetic structure having two turns secondary winding. 
           [0029]      FIG. 9A : Shows our equivalent schematic of the embodiment wherein we introduce a novel implementation for the output inductor. 
           [0030]      FIG. 9B : Shows an implementation of the four-legged magnetics structure from  FIG. 9A  together with a novel output inductor. 
           [0031]      FIG. 10 : Shows three-dimensional drawing of the four-legged magnetic structure. 
           [0032]      FIG. 11 : Shows three-dimensional drawing of the four-legged magnetic structure wherein the cutout in the upper and lower plate is removed. 
           [0033]      FIG. 12 : Shows a potential implementation of the multi legged magnetic structure 
           [0034]      FIG. 13 : Shows another potential implementation of the multi legged magnetic structure. 
           [0035]      FIG. 14 : Shows an implementation of the multi-legged magnetic structure employing ferrite material for the posts and the horizontal plates. 
           [0036]      FIG. 15 : Shows an implementation of the multi-legged magnetic structure employing ferrite material for the posts and without horizontal plates. 
           [0037]      FIG. 16 : Shows an implementation of the multi-legged magnetic structure without any magnetic material. 
           [0038]      FIG. 17 : Shows ratio AC/DC in the secondary winding for the magnetic structures presented in  FIG. 14 , FIG. 15  and  FIG. 16 . 
       
    
    
     DETAILED DESCRIPTION 
       [0039]    Presented in  FIG. 3A  is presented a center tap transformer structure having a primary winding  38 , and two identical secondary windings  34  and  36 . In the secondary side, there are two rectifier means,  30  and  32 . The secondary rectifier means can be schottky diodes, synchronous rectifier using silicon power mosfets, GANs or other technologies. There is a positive output  46 , and a negative output  44 . Typically, the negative output it might be connected to the output ground. In the primary, an AC signal is applied to the primary winding between  40  and  42 , which can be generated, by a full bridge configuration, half bridge or other topologies. In one of the polarities generated by the signal applied to the primary winding  38 , one of the rectifiers means conducts and when the polarity changes the other rectifier means will conduct. Because only one of the secondary winding is conducting current during each polarity the copper in the secondary is not fully utilized. This is one of the major disadvantages of the center tap topology. In addition to that, in center tap topologies there is a leakage inductance between the two secondary windings, which will delay the current flow from a winding to another. In the present embodiment described in  FIG. 3B  these two drawbacks associated with center tap are minimized. In  FIG. 3B  are presented four layers of a multilayer structure, from  50   a  through  50   d,  wherein the secondary winding is implemented. A U core shape magnetic core penetrates through the multilayer PCB through the cutout  54 A and  54 B. In between the legs of the magnetic core there is a conductive material, usually copper connected to the cathodes of the rectifier means, one on layer  50 A connected to the cathode of  30  and another one placed on layer  50   b  connected to the rectifier means  32 . On layer  50   c  and  50   d  there, the cutouts  54 A and  54 B are surrender by conductive material, which is connected to  46 . On layer  50   a  and  50   b  there is a ring of conductive material, which are connected to the anode of the rectifier, means  44 . 
         [0040]    During one of the polarities when the rectifier means  30  conducts the current flows through the conductive material between the lags of the U core from the anode connected to  44  and through the rectifier means,  30 , and further through the via  401  and  402  on layer  50   c  to the  46 . Another path for current flow is through the rectifier means  30  and via  403  and further towards  46 . During the polarity wherein rectifier means  32  is conducting, the current will flow from  44 , through  32 , and further on layer  50   b  through the conductive material,  36 , placed between the cutouts,  54 A and  54 B, and further through via  404  and  405  to layer  50   d  towards  46 . Another path for the current flowing through  32  is through via  406  to layer  50   d  and through the conductive material in between the cutouts  54 A and  54 B towards  46 . Though one turn secondary for this magnetic structure will circle the  54 A and  54 B, the portion of the secondary wherein the current is flowing in only one direction is reduced the conductive material between the cutouts,  54 A and  54 B, such as  34  and  36 . For the rest of the one turn secondary such as the portion of  44  and  46 , which surrounds the cutouts  54 A, and  54 B the current is flowing in both directions. This means that the copper utilization it improved by comparison with more traditional winding technique wherein the entire secondary winding is conducting during only during one polarity. Another advantage of the winding structure presented in  FIG. 3B  is the fact that the copper is placed over the entire section of the primary windings allowing the current to flow in order to cancel the magnetic field produced by the primary winding. In addition to that, the rectifier means  32  and  30  are placed as the part of the secondary winding eliminating the end effect losses and reducing the stray inductance. 
         [0041]    In  FIG. 4A  is presented a transformer structure using full bridge rectification. It is composed by a primary winding  138 , a secondary winding  137 , four rectifier means  133 , 135 , 134 , and  135 . The rectified voltage is connected to  141  and  142 . The primary winding terminations  139  and  140  are connected to an AC source, which can be generated, by a full bridge, half bridge or any other topologies. In  FIG. 4B  is presented the secondary winding arrangement for one turn secondary. For one of the polarities the current is flowing through  136 , the copper section,  137 A and  137 B placed in between the cutouts  54 A and  54 B, and further through  133 , through the via  407  to the layer  410 B towards  141 . During the other polarities the current will flow from  142 , through  135  and further through the copper section,  137 A and  137 B placed between the cutouts  54 A and  54 B, and further through rectifier means  134  and through via  408  to the layer  410 B, towards  141 . In this topology the secondary copper utilization, it is inherently very good because the secondary winding  137  does conduct during both polarities. The winding structure presented in  FIG. 4B  however does incorporate the rectifier means,  133 , 136 , 134  and  135  as part of the secondary winding eliminating the end effects and reducing the stray inductance. 
         [0042]    In  FIG. 5A  is presented the equivalent circuit of one embodiment of this invention wherein a four legged magnetic core structure is used. There are four transformers T 1 , T 2 , T 3  and T 4  which are coupled to each other in series. The T 1  is coupled with T 2 , T 2  is coupled with T 3  and T 3  is coupled with T 4  and further T 4  is coupled with T 1 . In  FIG. 5C  is presented the definition of each transformer from T 1  to T 4 . Each transformer is represented as an E core transformer having as a center post the entire cylindrical leg and two outer posts, which are half of the cylindrical legs in its direct vicinity. The shape of the four legs however can be rectangular or any other shape. Because the transformers T 1 ,T 2 ,T 3  and T 4  doe share sections of the same cylindrical posts, there is a coupling between them. 
         [0043]    The equivalent schematic of the magnetic structure implemented in  FIG. 5B  is presented in  FIG. 5A . An AC signal is applied between  360  and  362 , which can be generated by a full bridge, a half bridge structure, or any other double-ended topology. When a signal with positive polarity at  360  versus  362  is applied the rectifier  376  and  374  are activated and the current flows from the negative voltage V−,  384 , which in many application is connected to the ground, further through the copper section shaped as a cross,  366 A, located on the layer  70   a,  towards the via connection  411 ,  412  and  409 ,  410 . Through the via  411 ,  412  and  409 ,  410  the current flows further on the layer  70 C towards the  382 . A parallel path for the current during this polarity is through the rectifier means  376  and  374 , on the layer  70 C further through  366 B towards  382 . During the other polarity the other rectifier means  380  and  378  are activated and the current will flow further on layer  70   b  through the copper section shaped as a cross  368 A towards via  413 ,  414  and  415 ,  416  and further to the layer  70   d  towards  382 . Another path for the current flowing through  378  and  380  is through  368 B on layer  70   d  towards  382 . 
         [0044]    The current flowing through  384 , 382 , which surrender the four-lagged magnetic structure, and through  366 A,  368 B,  366 B and  368 B is aimed to cancel the magnetic field produced by the primary winding. The fact that the primary winding is split in four sections surrounding the four lagged magnetic core legs  115 A,  115 B,  115 C and  115 D from  FIG. 10 , and on each leg we have current flow into the secondary to suppress the magnetic field created by the primary winding, the leakage inductance in the magnetic structure presented in this patent application, it is very low. The copper arrangement depicted in  FIG. 5B  does allow a very low impedance current flow and in addition to this the rectifier means  376 , 380 , 374  and  378  are part of the secondary winding eliminating in this way the end effects and the stray inductance. The end effect is characterized by the ac losses in the copper after the secondary winding leaves the transformer to make the connection to the secondary means. In this embodiment, there are no end effects because the secondary winding does not leave the magnetic structure, each rectifier means being part of the secondary winding. 
         [0045]    The magnetic structure depicted in  FIG. 5B  does have several advantages over the conventional magnetic using an E core and even U shape cores. First of all the leakage inductance is significantly reduced. In addition to this, the ac losses in the windings are further reduced because the magnetic field intensity between primary and secondary is four times reduced by comparison to one magnetic core structure. In addition to this, the core volume of this configuration is it smaller than smaller than one core configuration. The placement of the rectifier means as a part of the secondary ending eliminated the end effects and the stray inductance between the secondary winding and the rectifier means. The coupling between the four equivalent transformers as depicted in  FIG. 5A  reduces the thickness of the ferrite plates  112  and  113 , which are placed on top of the four cylindrical legs  115 A,  115 B,  115 C and  115 D as depicted in  FIG. 10 . 
         [0046]    In  FIG. 6A through 6D  are presented metal etch layers comprising windings for the transformer structure presented in  FIG. 3A . The winding implementation of  FIG. 6A through 6D  is optimized in respect of layers utilization for the purpose of industrialization. In  FIG. 3B  we are using four layers while in  FIG. 6A  we are using just two layers. In  FIG. 6A  is presented the top layer and layer  2 . On the top layer the cutouts for the magnetic core,  54 A and  54 B are surrender by a copper connected to ground which is  FIG. 3A  is labeled  44 . On the layer  2 , the cutouts for the magnetic core,  54 A and  54 B are surrender by copper connected to  46 , as per  FIG. 3A . The rectifier means  30  and  32  from  FIG. 3A  are implemented by using two synchronous rectifiers in parallel. The copper section,  34 , placed between the cutouts  54 A and  54 B, is connected to the group of via  462 . The drain of the rectifier means  30  is placed on two pads connected to the group of via  460  and  461 . During the polarity wherein the rectifier means  32  are conducting the current is flowing from  44  through the rectifier means  32  further through  34  and through the via  462  to the layer  2  where the current flows to  46 . During the polarity wherein the rectifier means  30  are conducting the current is flowing from  44  through the rectifier means  30  further through  460  and  461  to layer  2  and further through the copper placed between the cutouts,  54 A and  54 B, towards  46 . On  FIG. 6B, 6C  are presented the primary windings, which are incorporated in layer  3 ,  4 ,  5  and  6 . In  FIG. 6D  is presented the secondary winding together with the rectifier meas. These layers are identical to the layer  1 , the top, and layer  2 . However, on these layers, the winding configuration is placed in a mirror arrangement. The massive copper arrangement around the magnetic core legs allows the current to flow optimally and choose its own path in order to cancel the magnetic field produced by the primary winding. This helps in further reducing the leakage inductance in the transformer structure. 
         [0047]    In  FIG. 7  is presented an optimized implementation of the magnetic structure of  FIG. 5B . In  FIG. 7A  the four legged magnetic structure is using just two layers for the secondary winding unlike four layers as depicted in  FIG. 5B . This implementation is for industrialization wherein the cost effectiveness is very important. 
         [0048]    For one of the polarities of the voltage applied to the primary transformer between  360  and  362 ,  FIG. 5A , the rectifier means  376  and  374  conducts and the current will flow from  384  through  376 , 374  through the via  482  and  485  to the second layer. On the second layer, the current will continue to flow in both directions, one between the cutouts  386 A and  386 D and between cutouts  386 B and  386 C towards V+,  382 . During the opposite polarity the current will flow from  384  through rectifier means  380  and  378  towards the via  480 , 481  and respectively  483  and  484 , to the layer  2  and further to V+,  382 . 
         [0049]    The implementation of the secondary winding depicted in  FIG. 7A  has the advantage of using just two layers. In  FIG. 7B  is presented all the layers, starting with to top two layers incorporated secondary winding and the bottom two layers, layer  9  and layer  10  wherein secondary windings are also implemented. The layer  1  and layer  2  and layers  9  and  10  are mirror imagine to each other. The primary windings are implemented on layers  3 , 4 , 5 , 6 , 7  and  8 . 
         [0050]    In  FIG. 8A  is presented one of the embodiments of the four-legged magnetic structure wherein we have two turns in the secondary winding. During one of the voltage polarity injected between  360  and  362  the rectifier means  376  and  374  conduct and the current will flow from  384  through  376 ,  374  and further around the magnetic core cutout  386 A,  386 B and respectively  386 C and  386 D towards via  501 , 502  and respectively  503 , 504  further on the layer  3  where will flow towards V+,  382 . 
         [0051]    During the voltage polarity applied between  360  and  362  when the rectifier means  380  and  378  are conducting the current will flow from  384 , through  380  and  378  and further through via  506  and  507  on layer  2  and further through via  508  on layer  3  towards  382 . 
         [0052]    In  FIG. 8B  is presented the  12  layers winding structure wherein the primary windings are implemented in six of the inner layers and the secondary windings are implemented in the top and bottom three layers. 
         [0053]    In  FIG. 9A  and  FIG. 9B  is presented another embodiment of this invention wherein there is a unique implementation of the output inductor. The entire four-legged magnetic structure,  520  which can be implemented in one of the configuration described in  FIG. 5B, 7A, 7B or 8A, 8B  or any other structure. The rectifier means  76 ,  74 ,  80  and  78  are rectifying the AC voltage injected in the primary winding. There are four pins,  202 A,  202 B,  202 C and  202 D, which are connected to the V−,  84 . There are also four pins  201 A, 201 B,  201 C and  201 D whish are connected to V+,  82  as presented in  FIG. 9A . There is a magnetic core composed by four sections  203 A,  203 B,  203 C and  203 D, which connected together. The entire structure can be formed by one magnetic core or four independent sections placed together. The current flowing towards  201 A,  201 B,  201 C and  201 D will flow under the magnetic core. The pins,  201 A,  201 B,  201 C and  201 D are connected further to the motherboard where they will form Vo+,  521 . The pins connected to the V−, 84 ,  202 A, 202 B, 202 C and  202 D are also connected to the motherboard. The implementation of the output choke using a continuous peace of ferrite material, which does not perforate the multiplayer PCB,  82  it, is unique. In this embodiment we split the output current and by connecting the V−,  84  pins,  202 A,  202 B, 202 C and  202 C and V+, 201 A, 201 B, 201 C and  201 C pins to the mother board we create turns around the magnetic core formed by  203 A, 203 B, 203 C and  203 D. This embodiment is very suitable for very high current application where we reduce the current applied to each pins by a factor of four in this particular implementation. In the case, if we use more than four legs transformer, for example N legged transformer then we can split the current in N section and use N pins to connect to the motherboard the V+and N pins to connect to V−. The arrow placed in the cathode of the rectifier means  76 , 80 , 74  and  78 , in  FIG. 9B  symbolizes the connection to the winding structure of the four legged transformer as presented in  FIG. 5B, 7A and 7B and 8A and 8B . 
         [0054]    In  FIG. 10  is presented the four-legged magnetic configuration. The primary and secondary windings of the transformer are implemented on the multilayer PCB,  111 . There is a four legged magnetic core formed by a magnetic plate  113  and four cylindrical posts,  115 A,  115 B,  115 C and  115 D. There is a cutout  114 B in the plate  113 . The four cylindrical posts penetrate through the holes  386 A,  386 B,  386 C and  386 D. A plate  112  with a cutout  114 A is placed on top making contact with the cylindrical posts directly or using an interface gap. In  FIG. 11  is presented the same structure with the difference that the cutout  114 A and  114 B is eliminated. There is not a magnetic flux through that cutout but for simplicity of the implementation in case of industrialization, the cutouts can be eliminated. 
         [0055]    In  FIG. 12  is presented another arrangement of this multi-legged magnetic structure in a rectangular shape having a multitude of legs. There can be many shapes we can implement this structure, one of them is presented in  FIG. 13 . Each magnetic structure starting with the two legged transformer, four-legged transformer and generally N legged transformer can be multiplied and each section can share the same primary winding. They will form power-processing cells and if they share the same primary winding, the leakage inductance between the primary winding and the secondary winding can be further reduced. The multi-legged magnetic structures can be used as transformers or can be used as inductors. In the inductor implementation the gap can be placed on top of each cylindrical leg and create a very efficient distributed gap minimizing in this way the gap effect. 
         [0056]    In  FIG. 14  is presented a general multi-legged magnetic structure. The windings are implemented in a multiplayer structure which can be embedded also in a multilayer PCB and there are cylindrical magnetic posts and two magnetic plates, one on top and one on the bottom, as depicted in  550  and  551 . 
         [0057]    In  FIG. 15  is presented an implementation wherein the windings are placed in multilayer structure, which can be a multilayer PCB and the magnetic cylindrical post without the ferrite plates on top and bottom, as depicted in  552  and  553 . 
         [0058]    In  FIG. 16  is presented an air core structure wherein the magnetic core material is totally removed and the windings are implemented in a multiplayer structure, which can be multilayer PCB. Such an air core structure has many advantages one of them being much lower AC losses in the winding at high frequency. 
         [0059]    In  FIG. 17  is presented the simulate losses in such structures at 1 Mhz and 10 Mhz using posts and plates of magnetic material, just the magnetic posts of magnetic material and without any magnetic material. 
         [0060]    The major advantage of these magnetic structures, especially for the air core implementation is the fact that the magnetic flux does weave from a loop to another reducing significantly the radiation. This magnetic structure with air core described in  554  contains the magnetic field, and forces it to be parallel with the winding, and it is very suitable for magnetic configuration without magnetic core. In addition to this has a low ac loss for very high frequency application wherein this structure may be used. This magnetic structure will allow power conversion at very high frequency in the range of tens of MHz with high efficiency.