Patent Publication Number: US-10763028-B2

Title: Magnetic component and magnetic core of the same

Description:
RELATED APPLICATIONS 
     The present application is a continuation-in-part application of U.S. application Ser. No. 15/092,629, filed Apr. 7, 2016, which claims priority to Chinese Application Serial Number 201510169368.5, filed Apr. 10, 2015 and Chinese Application Serial Number 201510446385.9, filed Jul. 27, 2015, which is herein incorporated by reference. The present application claims priority to Chinese Application Serial Number 201610173671.7, filed Mar. 24, 2016, which is herein incorporated by reference. 
    
    
     BACKGROUND 
     Field of Invention 
     The present disclosure relates to a power technology. More particularly, the present disclosure relates to a magnetic component and a magnetic core of the same. 
     Description of Related Art 
     In recent years, miniaturization of power converter is an important trend of the development of power technology. In a power converter, magnetic components occupy a certain degree of the volume and contribute a certain degree of the loss. Therefore, the design and improvement of the magnetic components become very important. 
     In some application scenarios, such as an application with large current condition, a plurality of interleaved parallel-connected circuits are used to decrease the occurrence of the ripples. In common designs of the magnetic components, in order to guarantee the unsaturation and low loss of the magnetic material, the volume of the magnetic components has to be increased to decrease the magnetic induction in the magnetic core. As a result, it is needed to achieve the balance between high efficiency and high power density. 
     Accordingly, what is needed is a switching mode power supply and an integrated device of the same to address the above issues. 
     SUMMARY 
     An aspect of the present invention is to provide a magnetic core. The magnetic core includes a plurality of magnetic core units each having at least one non-shared magnetic core part that is not shared with the neighboring magnetic core unit, wherein a reluctance of the shared magnetic core part is smaller than the reluctance of a non-shared magnetic core part of the magnetic core units, and directions of a direct current magnetic flux in the shared magnetic core part of the neighboring two magnetic core units are opposite. 
     Yet another aspect of the present invention is to provide a magnetic component. The magnetic component includes a magnetic core and a plurality of windings. The magnetic core includes a plurality of magnetic core units each having at least one non-shared magnetic core part that is not shared with the neighboring magnetic core unit, wherein a reluctance of the shared magnetic core part is smaller than the reluctance of a non-shared magnetic core part of the magnetic core units, and directions of a direct current magnetic flux in the shared magnetic core part of the neighboring two magnetic core units are opposite. Each of the windings is disposed to be correspondingly wound at the non-shared magnetic core part of the magnetic core unit. 
     These and other features, aspects, and advantages of the present invention will become better understood with reference to the following description and appended claims. 
     It is to be understood that both the foregoing general description and the following detailed description are by examples, and are intended to provide further explanation of the invention as claimed. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention can be more fully understood by reading the following detailed description of the embodiment, with reference made to the accompanying drawings as follows: 
         FIG. 1  is a circuit diagram of a multi-phase paralleled power converter in an embodiment of the present invention; 
         FIG. 2  is a diagram of the structure of a multi-phase inductor used in the multi-phase paralleled power converter in an embodiment of the present invention; 
         FIG. 3A  is a diagram of the multi-phase inductor in  FIG. 2  and a part of the magnetic flux distribution therein in an embodiment of the present invention; 
         FIG. 3B  is a diagram of an equivalent magnetic circuit model of the multi-phase inductor in an embodiment of the present invention; 
         FIG. 4  is a diagram of the magnetic component used in the multi-phase paralleled power converter in an embodiment of the present invention; 
         FIG. 5  is a diagram of the magnetic component used in the multi-phase paralleled power converter in an embodiment of the present invention; 
         FIG. 6A - FIG. 6G  are diagrams of a single magnetic core unit respectively in an embodiment of the present invention; 
         FIG. 7A  and  FIG. 7B  are diagrams of the magnetic core in an embodiment of the present invention; 
         FIG. 8  is a diagram of the magnetic core in an embodiment of the present invention; 
         FIG. 9  is a diagram of the magnetic core in an embodiment of the present invention; 
         FIG. 10  is a diagram of the magnetic core in an embodiment of the present invention; 
         FIG. 11  is a diagram of the magnetic core in an embodiment of the present invention; 
         FIG. 12  is a diagram of the magnetic core in an embodiment of the present invention; 
         FIG. 13  is a diagram of the magnetic core in an embodiment of the present invention; 
         FIG. 14A  is a diagram of the magnetic core in an embodiment of the present invention; 
         FIG. 14B  is a diagram of the manufactured structure of the magnetic core illustrated in  FIG. 14A  in an embodiment of the present invention; 
         FIG. 15A  is a diagram of the magnetic core in an embodiment of the present invention; 
         FIG. 15B  is a diagram of the manufactured structure of the magnetic core illustrated in  FIG. 15A  in an embodiment of the present invention; 
         FIG. 15C  is a diagram of the magnetic core in an embodiment of the present invention; 
         FIG. 15D  is a diagram of the magnetic core in an embodiment of the present invention; 
         FIG. 15E  is a diagram of a top cover in an embodiment of the present invention; 
         FIG. 15F  is a diagram of a magnetic circuit model of the magnetic core unit in an embodiment of the present invention; 
         FIG. 15G  is a diagram of a magnetic circuit model of the magnetic core unit in an embodiment of the present invention; 
         FIG. 15H  is a diagram of a magnetic circuit model of the magnetic core unit in an embodiment of the present invention; 
         FIG. 15I  is a diagram of a magnetic circuit model of the magnetic core unit in an embodiment of the present invention; 
         FIG. 16  is a structure of a six-phase integrated inductor in an embodiment of the present invention; 
         FIG. 17  is a structure of a six-phase integrated inductor in another embodiment of the present invention; 
         FIG. 18  is a diagram of partial magnetic flux distribution of the six-phase integrated inductor in  FIG. 16  in an embodiment of the present invention; 
         FIG. 19  is a diagram illustrating the structure of an inductor winding and the magnetic core unit of the six-phase integrated inductor illustrated in  FIG. 16  in an embodiment of the present invention; 
         FIG. 20  is a diagram illustrating the structure of an inductor winding and the magnetic core unit of the six-phase integrated inductor illustrated in  FIG. 16  in another embodiment of the present invention; 
         FIG. 21  is a diagram illustrating a three-dimensional diagram of the inductor winding in  FIG. 20  in an embodiment of the present invention; 
         FIG. 22  is a diagram illustrating a diagram of an unfolded inductor winding illustrated in  FIG. 21  in an embodiment of the present invention; and 
         FIG. 23  is diagram of a structure of a two-phase integrated inductor in an embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION 
     The magnetic component in the present disclosure includes a magnetic core and a winding. The magnetic core includes a plurality of magnetic core units. A part of the direct current (DC) magnetic flux (B DC ) of the magnetic component cancels out due to the same shared magnetic core part shared by the two neighboring magnetic core units. The DC magnetic induction cancellation enhance the saturation performance. Further, the effect of DC bias on magnetic core loss is also reduced. Therefore, the volume of the magnetic core and the whole magnetic component can be reduced. By using different types of windings, the magnetic component can become magnetic apparatus having different functions. For example, when the winding is a transformer winding, the magnetic component is used as a transformer. When the winding is an inductor winding, the magnetic component is used as an inductor. An inductor in a three-phase interleaved buck circuit is used as an example to describe the magnetic component. 
     Reference is now made to  FIG. 1 .  FIG. 1  is a circuit diagram of a power converter in an embodiment of the present invention. The direct current to direct current (DC/DC) power converter includes an inductor module  10 , a plurality of switches  12   a ,  12   b ,  12   c ,  14   a ,  14   b ,  14   c  and load  16 . 
     The inductor module  10  includes a plurality of inductors  100   a - 100   c . One terminal of each of the inductors  100   a - 100   c  is electrically connected together to form a multi-phase paralleled output terminal OUT of the DC/DC power converter. As a result, the inductor module  10  is the output inductor corresponding to the multi-phase paralleled output terminal OUT of the DC/DC power converter. 
     The switches  12   a - 12   c  and the corresponding switches  14   a - 14   c  form a multi-phase paralleled power conversion circuits. The multi-phase paralleled output terminal OUT is the output of the power conversion circuits. In the present embodiment, as illustrated in  FIG. 1 , each of the inductors  100   a - 100   c  is electrically connected to the corresponding switches  12   a - 12   c  and  14   a - 14   c . Taking the inductor  100   a  as an example, the inductor  100   a  is electrically connected to the switches  12   a  and  14   a . The inductors  100   a - 100   c  are further coupled to a multi-phase paralleled input terminal IN through the switches  12   a - 12   c . In the present embodiment, the multi-phase paralleled input terminal IN receives an input voltage Vin. 
     The load  16  is electrically connected to the inductor module  10  at the multi-phase paralleled output terminal OUT. In an embodiment, the DC/DC power converter further includes other load components, such as but not limited to the capacitor  18  illustrated in  FIG. 1  to stabilize the circuit. 
     It is appreciated that the disposition of the inductor module  10  in the power converter is merely an example. In other embodiments, the inductor module  10  can be directly electrically connected to the multi-phase paralleled input terminal IN to use as input inductors and are electrically coupled to the multi-phase paralleled output terminal OUT through the switches  12   a - 12   c  and  14   a - 14   c.    
     The inductor module  10  can be implemented by a magnetic component  2  illustrated in  FIG. 2 . Reference now is made to  FIG. 2 .  FIG. 2  is a diagram of the magnetic component  2  used in the inductor module  10  in an embodiment of the present invention. The magnetic component  2  includes a plurality of inductor windings  20   a ,  20   b  end  20   c  and a magnetic core  22 . The inductor windings  20   a - 20   c  and the magnetic core  22  are integrated to form the inductors  100   a - 100   c  illustrated in  FIG. 1 . 
     The number of the windings  20   a - 20   c  is corresponding to the number of the inductors  100   a - 100   c  in the inductor module  10  illustrated in  FIG. 1 . In an embodiment, the inductor windings  20   a - 20   c  includes a copper sheet, a litz wire, a PCB winding, a circular conductor, a bunched conductor or a flat wire. 
     In the present embodiment, the magnetic core  22  includes three magnetic core units  220   a ,  220   b  and  220   c . The magnetic core units  220   a - 220   c  include the corresponding windows  24   a ,  24   b  and  24   c . Each of the magnetic core units  220   a - 220   c  has a closed geometrical structure to form one of the windows  24   a - 24   c . It is appreciated that though there are three windows in the present embodiment, the magnetic core units do not necessarily have the closed geometrical structure to form the windows. The magnetic core units can be an open structure without forming the windows. 
     As illustrated in  FIG. 2 , each of the magnetic core units  220   a - 220   c  is a quadrangle formed by four magnetic pillars that have a through hole, in which the through hole forms the window to dispose the inductor windings. The magnetic core unit  220   a  corresponds to the window  24   a . The magnetic core unit  220   b  corresponds to the window  24   b . The magnetic core unit  220   c  corresponds to the window  24   c . Each of the windows  24   a - 24   c  includes at least one of the inductor windings  20   a - 20   c . For example, the window  24   a  holds the winding  20   a . The window  24   b  holds the winding  20   b . The window  24   c  holds the winding  20   c.    
     Two of the neighboring magnetic core units have a shared magnetic core part. For example, the magnetic core units  220   a  and  220   b  have a shared magnetic core part  26   a ; the magnetic core units  220   b  and  220   c  have a shared magnetic core part  26   b . In addition, two of the neighboring magnetic core units further have at least a non-shared magnetic core part. For example, the magnetic core unit  220   a  includes non-shared magnetic core parts  27   a ,  28   a  and  29   a  that are not shared with the magnetic core unit  220   b . The magnetic core unit  220   b  includes non-shared magnetic core parts  27   b  and  29   b  that are not shared with the magnetic core units  220   a  and  220   c . The magnetic core unit  220   c  includes non-shared magnetic core parts  27   c ,  28   c  and  29   c  that are not shared with the magnetic core unit  220   b . In other words, in the present embodiment, the magnetic core units  220   a  and  220   b  have a shared magnetic core part  26   a  and the magnetic core units  220   b  and  220   c  have a shared magnetic core part  26   b . For the magnetic core unit  220   b , the magnetic pillars  26   a  and  26   b  are common magnetic pillars shared with other magnetic core units. 
     In the embodiment illustrated in  FIG. 2 , the shared magnetic core part  26   a  of the two neighboring magnetic core units  220   a  and  220   b  is a common magnetic pillar, and the non-shared magnetic core parts  27   a ,  29   a  and  28   a  are a first magnetic pillar, a second magnetic pillar and a t bird magnetic pillar respectively. The first magnetic pillar  27   a  and the second magnetic pillar  29   a  are perpendicular to the common magnetic pillar  26   a  that is used as the shared magnetic core part. The third magnetic pillar  28   a  is parallel to the common magnetic pillar. The reluctance of the shared magnetic core part of each of the magnetic core units  220   a - 220   c  is smaller than the reluctance of the non-shared magnetic core part thereof. Taking the magnetic core units  220   a  and  220   b  as an example, the reluctance of the shared magnetic core parts  26   a  is smaller than the reluctance of the non-shared magnetic core parts  27   a ,  28   a  and  29   a  of the magnetic core units  220   a  and  220   b . Correspondingly, in order to meet the relation of the reluctances of the shared magnetic core part and the non-shared magnetic core part described above, material of different permeability can be used to manufacture the shared magnetic core part and the non-shared magnetic core part respectively. For example, the shared magnetic core part is manufactured by high permeability material and the non-shared magnetic core part is manufactured by low permeability material. The initial permeability of the high permeability material, e.g. ferrite, is larger than 50. The initial permeability of the low permeability material, e.g. powder material, is larger than or equal to 1 and is smaller than or equal to 50. In an embodiment, the shared magnetic core part  26   a  is formed by the material having the initial permeability higher than that of the non-shared magnetic core part to keep the reluctance of the shared magnetic core part  26   a  smaller than that the reluctance of the non-shared magnetic core part. 
     Besides, in order to meet the relation of the reluctances of the shared magnetic core part and the non-shared magnetic core part described above, the shared magnetic core part and the non-shared magnetic core part can be manufactured by using the material having the same permeability and disposing magnetic sections having lower permeability at the non-shared magnetic core part. The magnetic sections can be a first low permeability structure that has the permeability between 1˜50. In other words, though the shared magnetic core part and the non-shared magnetic core part use the material having the same permeability, the requirement that the reluctance of the shared magnetic core part is smaller than the reluctance of the non-shared magnetic core part is still met since the magnetic sections (such as one section or more than one sections of air gaps) having the low permeability are disposed at the non-shared magnetic core part. In other words, under the condition that the air gaps are disposed at the non-shared magnetic core part, the shared magnetic core part and the non-shared magnetic core part can be manufactured by using the material having the same permeability to simplify the manufacturing process of the magnetic cores. 
     For example, in the embodiment illustrated in  FIG. 2 , the non-shared magnetic core parts  29   a ,  29   b  and  29   c  of each of the magnetic core units  220   a - 220   c  includes the first low permeability structures  222   a ,  222   b  and  222   c  that has the lowest permeability in the magnetic core units  220   a - 220   c  to meet the requirement of the inductance value and prevent the magnetic core units from saturation. In an embodiment, the permeability of the first low permeability structures  222   a ,  222   b  and  222   c  is smaller than or equal to 50. In one embodiment, the first low permeability structures  222   a ,  222   b  and  222   c  are air gaps. Since the permeability of the shared magnetic core parts is very high and the non-shared magnetic core parts include the first low permeability structures, the reluctance of the shared magnetic core parts far smaller than the reluctance of the non-shared magnetic core parts. Usually the reluctance of the shared magnetic core parts is 1/10 of the reluctance of the non-shared magnetic core parts. 
     Due to the numerical relation of the reluctance of the shared magnetic core parts and the non-shared magnetic core parts, i.e. the reluctance of the non-shared magnetic core parts is far larger than the reluctance of the shared magnetic core parts, different magnetic core units can share the magnetic pillars without affecting the circuit function. Such a feature is further described in detail in the following paragraphs in the aspect of the magnetic flux distribution. 
     Reference is now made to  FIG. 3A-3B  at the same time.  FIG. 3A  is a diagram of the multi-phase inductor  2  in  FIG. 2  and partial magnetic flux therein in an embodiment of the present invention.  FIG. 3B  is a equivalent model of the multi-phase inductor  2  in  FIG. 2  in an embodiment of the present invention. 
     As illustrated in  FIG. 3A , the winding  20   a  is disposed at the window  24   a , the winding  20   b  is disposed at the window  24   b  and the winding  20   c  is disposed at the window  24   c . The current flowing through each of the windings  20   a ,  20   b  and  20   c  includes a direct current (DC) component and an alternating current (AC) component, and the DC component of each of the windings  20   a ,  20   b  and  20   c  is supposed to flow into the paper perpendicularly. Taking the winding  20   a  as an example, the DC component generates three magnetic fluxes in the magnetic cores, which are fluxes  300   a ,  300   b  and  300   c  respectively. In order to simplify the discussion, only the magnetic flux distributed in the core is analyzed, and without considering the magnetic fluxes distributed in the air. 
     The magnetic flux  300   a  only couples with itself and is a leakage flux corresponding to the leakage inductance. The magnetic fluxes  300   b  and  300   c  are mutual magnetic fluxes generated by the winding  20   a  coupling with the other two windings  20   b  and  20   c , respectively, and the mutual magnetic fluxes are corresponding to respective mutual inductances of the corresponding windings. 
     As illustrated in the equivalent magnetic circuit model, F is the magnetomotive force (MMF) of the windings  20   a . Ra is the total reluctance of the non-shared magnetic core part of the magnetic core unit  220   a  and is determined by the first low permeability structure  222   a . Rb is the total reluctance of the non-shared magnetic core part of the magnetic core unit  220   b  and is determined by the first low permeability structure  222   b . Rc is the total reluctance of the non-shared magnetic core part of the magnetic core unit  220   c  and is determined by the first low permeability structure  222   c . r 12  is the reluctance of the shared magnetic core part of the magnetic core units  220   a  and  220   b , and r 23  is the reluctance of the shared magnetic core part of the magnetic core units  220   b  and  220   c . Since the shared magnetic core part includes high permeability material and the non-shared magnetic core part includes the first low permeability structure, the reluctances r 12  and r 23  of the shared magnetic core part is far smaller than the reluctances Ra, Rb and Rc of the non-shared magnetic core parts. As a result, among the three magnetic fluxes  300   a ,  300   b  and  300   c  generated by the winding  20   a , the leakage flux  300   a  is large and the mutual fluxes  300   b  and  300   c  are small. Accordingly, though the magnetic core units  220   a  and  220   b  shares one shared magnetic core part  26   a , the coupling of these two magnetic core units is small. The inductor of the shared magnetic pillar can accomplish the circuit function equivalent to the discrete inductor. 
     The following paragraph describes the advantage of the shared magnetic core parts included in the neighboring magnetic core units. Reference is now made to  FIG. 3A . The largest magnetic flux in the magnetic fluxes generated by a current is defined as the main magnetic flux. As a result, the main magnetic flux generated by the winding  20   a  is  300   a . Similarly, the main magnetic flux generated by the winding  20   b  is  302 . The paths of the magnetic fluxes  300   a  and  302  include a common magnetic pillar, i.e. the shared magnetic core part  26   a . In the shared magnetic core part  26   a , the directions of the magnetic fluxes  300   a  and  302  are opposite to cancel out each other. As a result, the magnetic induction B in the shared magnetic core part  26   a  decreases, and the effects of DC bias on core loss decrease and the saturation current increase as well. As a result, the volume of the magnetic core can be decreased. Accordingly, the volume of the inductor illustrated in  FIG. 3A  can be decreased by letting the neighboring magnetic core units share the shared magnetic core part having the high permeability, in which the shared magnetic core part is disposed at the path of the main magnetic flux of each of the magnetic core units. In order to accomplish a certain inductance and to prevent the magnetic core from saturation, a first low permeability structure is disposed at least a part of the non-shared magnetic core part of each of the magnetic core unit to increase the reluctance of the non-shared magnetic core part. 
     Reference is now made to  FIG. 4 .  FIG. 4  is a diagram of the magnetic component  4  in an embodiment of the present invention. The magnetic component  4  includes a plurality of windings  20   a - 20   c  and a magnetic core  40 . 
     In the present embodiment, the magnetic core  40  includes three magnetic core units  400   a - 400   c . The magnetic core units  400   a - 400   c  include the corresponding windows  42   a - 42   c . The windings  20   a - 20   c  are disposed in the windows  42   a - 42   c  respectively. The magnetic core units  400   a - 400   c  are presented by a triangle formed by three magnetic pillars. The neighboring two magnetic core units, such as the magnetic core units  400   a  and  400   b , have a shared magnetic core part  44   a . The magnetic core units  400   b  and  400   c  have a shared magnetic core part  44   b . As described in the previous embodiments, the shared magnetic core parts  44   a  and  44   b  can be fabricated by the material having a higher initial permeability as compared to the non-shared magnetic core part and then have a lower reluctance. Of course in the present embodiment, two magnetic pillars of the magnetic core unit  400   b  are both the shared magnetic core parts. 
     Reference is now made to  FIG. 5 .  FIG. 5  is a diagram of the magnetic component  5  in an embodiment of the present invention. The magnetic component  5  includes a plurality of windings  20   a - 20   c  and a magnetic core  50 . 
     In the present embodiment, the magnetic core  50  includes three magnetic core units  500   a ,  500   b  and  500   c  and the corresponding windows  52   a ,  52   b  and  52   c . The windings  20   a - 20   c  are disposed in the windows  52   a - 52   c  respectively. The magnetic core units  500   a - 500   c  is a pentagon formed by five magnetic pillars. The neighboring two magnetic core units, such as the magnetic core units  500   a  and  500   b , have a shared magnetic core part  54   a . The magnetic core units  500   b  and  500   c  have a shared magnetic core part  54   b . As described in the previous embodiments, the shared magnetic core parts  54   a  and  54   b  can be fabricated by the material having a higher initial permeability as compared to the non-shared magnetic core part and then have a lower reluctance. 
     In other embodiments the number and the shape of the magnetic core units of the magnetic core can be adjusted according to practical applications and are not limited to the number and the shape described in the above embodiments. 
     Reference is now made to  FIG. 6A - FIG. 6G .  FIG. 6A - FIG. 6G  are diagrams of a single magnetic core unit  6  respectively in an embodiment of the present invention. 
     In the present embodiment, the magnetic core unit  6  is a quadrangle that includes four magnetic pillars  60   a ,  60   b ,  60   c  and  60   d . In an embodiment, the magnetic pillars  60   c  is the shared magnetic core part shared by other magnetic core units (not illustrated), and the magnetic pillars  60   a ,  60   b  and  60   d  are the non-shared magnetic core part of the magnetic core unit. As a result, the magnetic pillars  60   a ,  60   b  and  60   d  may dispose the first low permeability structure (e.g. air gap). The disposition method of the first low permeability structure, such as the number and the position of the first low permeability structure, can be adjusted based on different requirements. 
     Taking  FIG. 6A  as an example, the first low permeability structure  600  is an air gap disposed at the center of the magnetic pillar  60   a . In  FIG. 6B , the first low permeability structure  600  is disposed at one terminal of the magnetic pillar  60   a  near to magnetic pillar  60   d . In  FIG. 6C , the first low permeability structure  600  including a single air gap is disposed at a quarter of length of the magnetic pillar  60   a  relative to one terminal of the magnetic pillar  60   a.    
     In  FIG. 6D , the first low permeability structures  600  and  602  each including a single air gap are disposed at the centers of the magnetic pillars  60   a  and  60   b  respectively. In  FIG. 6E , the first low permeability structures  602  and  604  each including a single air gap are disposed at the centers of the magnetic pillars  60   b  and  60   d  respectively. In  FIG. 6F , the first low permeability structures  600 ,  602  and  604  each including a single air gap are disposed at the centers of the magnetic pillars  60   a ,  60   b  and  60   d  respectively. 
     The first low permeability structures mentioned in the above embodiments are examples of discretely disposing the first low permeability structures on the magnetic core units. 
     In  FIG. 6G , the low permeability structure  606  including three air gaps  610   a ,  610   b  and  610   c  is disposed at the center of the magnetic pillar  60   a . In the present embodiment, the first low permeability structure is the example of intensively disposing the first low permeability structures on the magnetic core units. 
     Various combinations of the positions and the numbers of the first low permeability structures and the numbers of the air gap included in the first low permeability structures mentioned above can be used according to different conditions and are not limited thereto. Surely, the air gap in the first low permeability structures can also be stuffed by other material having a low permeability. 
       FIG. 7A  and  FIG. 7B  are diagrams of the magnetic core  7  in an embodiment of the present invention. In the present embodiment, the magnetic core  7  includes six magnetic core units  700   a ,  700   b ,  700   c ,  700   d ,  700   e  and  700   f  and corresponding windows  72   a ,  72   b ,  72   c ,  72   d ,  72   e  and  72   f . The magnetic core units  700   a - 700   f  form a quadrangle. In the present embodiment, the central axes of the windows of the illustrated magnetic core  7  are parallel to each other. 
     Each of the magnetic core units  700   a - 700   f  includes a first low permeability structure. In  FIG. 7 , each of the magnetic core units  700   a - 700   f  includes two first low permeability structure, each of which has a single air gap and is disposed at a terminal of a pair of non-shared magnetic core parts perpendicular to the shared magnetic core part, such as the first low permeability structures  720   a  and  720   b  corresponding to the magnetic core unit  700   a . In  FIG. 7B , each of the magnetic core units  700   a - 700   f  includes a plurality of distributed first low permeability structures disposed at the center of the same non-shared magnetic core part perpendicular to the shared magnetic core part, for example, the first low permeability structure  722  of the magnetic core unit  700   a  includes three air gaps distributed at the center of the same non-shared magnetic core part. In other words, the air gaps of each of the magnetic core units in  FIG. 7B  are disposed at the same side. 
       FIG. 8  is a diagram of the magnetic core  8  in an embodiment of the present invention. In the present embodiment, the magnetic core  8  includes six magnetic core units  800   a ,  800   b ,  800   c ,  800   d ,  800   e  and  800   f  and corresponding windows  82   a ,  82   b ,  82   c ,  82   d ,  82   e  and  82   f . The magnetic core units  800   a - 800   f  form a quadrangle. In the present embodiment, each of the magnetic core units  800   a - 800   f  has two or more neighboring magnetic core units connected thereto. Taking the magnetic core unit  800   a  as an example, the magnetic core unit  800   a  has two neighboring magnetic core units  800   b  and  800   d  connected thereto. The magnetic core unit  800   b  has three neighboring magnetic core units  800   a ,  800   c  and  800   e  connected thereto. 
     Each of the magnetic core units  800   a - 800   c  includes a plurality of first low permeability structures distributed at the center of the same side of the non-shared magnetic core part, such as the first low permeability structure  820   a  corresponding to the magnetic core unit  800   a . Each of the magnetic core units  800   d - 800   f  includes a plurality of first low permeability structures distributed at the center of the same side of the non-shared magnetic core part, for example, the first low permeability structure  820   b  corresponding to the magnetic core unit  800   d  includes three air gaps disposed at the center of the same non-shared magnetic core part. 
     As a result, the magnetic core units  800   a - 800   f  of the magnetic core  8  have more shared magnetic core parts to further shrink the size of the magnetic core  8 . 
       FIG. 9  is a diagram of the magnetic core  9  in an embodiment of the present invention. In the present embodiment, the magnetic core  9  includes six magnetic core units  900   a ,  900   b ,  900   c ,  900   d ,  900   e  and  900   f  and corresponding windows, such as the window  92  corresponding to the magnetic core unit  900   a . The magnetic core units  900   a - 900   f  form a quadrangle. In the present embodiment, each of the magnetic core units  900   a - 900   f  has two neighboring magnetic core units connected thereto to form a cubic. Taking the magnetic core unit  900   a  as an example, the magnetic core unit  900   a  has two neighboring magnetic core units  900   b  and  900   f  connected thereto. The magnetic core unit  900   c  has two neighboring magnetic core units  900   b  and  900   d  connected thereto. 
     Each of the magnetic core units  900   a - 900   f  includes a plurality of first low permeability structures disposed at the center of the same side of the non-shared magnetic core part, such as the first low permeability structure  920  corresponding to the magnetic core unit  900   a.    
     In the magnetic core  9 , the central axis of some of the windows of the magnetic core units  900   a - 900   f  are parallel, while the central axis of some of the windows are perpendicular. For example, the central axis of the windows of the magnetic core units  900   a  and  900   b  are perpendicular to each other, and the central axis of the windows of the magnetic core units  900   b  and  900   c  are parallel to each other. As a result, the magnetic core units  900   a - 900   f  of the magnetic core  9  together form a cubic to further shrink the size of the magnetic core  9 . 
       FIG. 10  is a diagram of the magnetic core  1000  in an embodiment of the present invention. In the present embodiment, the magnetic core  1000  includes six magnetic core units  1000   a ,  1000   b ,  1000   c ,  1000   d ,  1000   e  and  1000   f  and corresponding windows, such as the window  1002  corresponding to the magnetic core unit  1000   d . The magnetic core units  1000   a - 1000   f  form a quadrangle. In the present embodiment, the magnetic core units  1000   a - 1000   c  are on the same plane, and the magnetic core unit  1000   b  has the neighboring magnetic core units  1000   a  and  1000   c  connected thereto. The magnetic core units  1000   d - 1000   f  are all on another plane, and the magnetic core unit  1000   e  has the neighboring magnetic core units  1000   b  and  1000   f  connected thereto. The magnetic core units  1000   e  and  1000   f  are respectively adjacent to the magnetic core units  1000   a  and  1000   c.    
     The magnetic core units  1000   a - 1000   c  and the magnetic core units  1000   d - 1000   f  are perpendicular to each other. As a result, the central axes of the windows that the magnetic core units  1000   a - 1000   c  and the magnetic core units  1000   d - 1000   f  corresponding to are perpendicular to each other to form an irregular three-dimensional shape. 
     In the present embodiment, each of the magnetic core units  1000   a - 1000   f  includes a plurality of first low permeability structures disposed at the center of one non-shared magnetic core part, such as the first low permeability structure  1020  corresponding to the magnetic core unit  1000   d  illustrated in  FIG. 10 . 
     As a result, the magnetic core units  1000   a - 1000   f  included in the magnetic core  1000  can form an irregular three-dimensional shape according to the practical requirements. 
       FIG. 11  is a diagram of the magnetic core  1100  in an embodiment of the present invention. In the present embodiment, the magnetic core  1100  includes three magnetic core units  1100   a - 1100   c  and corresponding windows, such as the window  1102  corresponding to the magnetic core unit  1100   a . The magnetic core units  1100   a - 1100   c  is a rectangle. In the present embodiment, for the non-shared magnetic core parts of the magnetic core units  1100   a  and  1100   b , a shared magnetic core part  1104   a  between the magnetic core units  1100   a  and  1100   b  is partially shared. For the non-shared magnetic core part of the magnetic core unit  1100   b , a magnetic core part  1104   b  between the magnetic core units  1100   b  and  1100   c  is partially shared. In other words, in the magnetic core  1100  illustrated in  FIG. 11 , the shared magnetic core parts and the non-shared magnetic core parts are formed at different positions of the same magnetic pillar. 
     Further, various combination of the numbers and the positions of the first low permeability structures included in the magnetic core units  1100   a - 1100   c  can be used. It is appreciated that though some of the magnetic pillars of the magnetic core units  1100   a - 1100   c  include the shared magnetic core parts  1104   a  and  1104   b , the first low permeability structures can still be formed on the non-shared magnetic core part of these magnetic pillars. 
     As a result, the magnetic core units  1100   a - 1100   c  included in the magnetic core  1100  can be formed with a partially shared manner according to the practical requirements. 
       FIG. 12  is a diagram of the magnetic core  1200  in an embodiment of the present invention. In the present embodiment, the magnetic core  1200  includes three magnetic core units  1200   a - 1200   c  and corresponding windows, such as the window  1202  corresponding to the magnetic core unit  1200   a . The magnetic core units  1200   a - 1200   c  is a rectangle. In the present embodiment, for the magnetic pillars of the magnetic core units  1200   a  and  1200   b , the shared magnetic core part  1204   a  between the magnetic core units  1200   a  and  1200   b  is partially shared. For the magnetic pillars of the magnetic core units  1200   b  and  1200   c , the shared magnetic core part  1204   b  between the magnetic core units  1200   b  and  1200   c  is partially shared. 
     Further, various combination of the numbers and the positions of the first low permeability structures included in the magnetic core units  1200   a - 1200   c  can be used. It is appreciated that though some of the magnetic pillars of the magnetic core units  1200   a - 1200   c  includes the shared magnetic core parts  1204   a  and  1204   b , the first low permeability structures can still be formed on the non-shared part of these magnetic pillars. 
     As a result, the magnetic core units  1200   a - 1200   c  included in the magnetic core  1200  can be formed with a partially hared manner according to the practical requirements. 
       FIG. 13  is a diagram of the magnetic core  7 ″ in an embodiment of the present invention. 
     In the present embodiment, the magnetic core  7 ″ includes six magnetic core units  700   a ,  700   b ,  700   c ,  700   d ,  700   e  and  700   f  and corresponding windows  72   a ,  72   b ,  72   c ,  72   d ,  72   e  and  72   f . The magnetic core units  700   a - 700   f  is a quadrangle. Each of the magnetic core units  700   a - 700   f  includes two first low permeability structures each having a single air gap and each disposed at a terminal of a pair of non-shared magnetic core parts perpendicular to the shared magnetic core part, such as the first low permeability structures  720   a  and  720   b  corresponding to the magnetic core unit  700   a  that is disposed at the terminal of the two non-shared magnetic core units perpendicular to the shared magnetic core part  704 . 
     However, in the present embodiment, taking the shared magnetic core part  704  of the magnetic core units  700   a  and  700   b  as an example, the shared magnetic core part  704  includes a second low permeability structure  1300 . As a result, in an embodiment, the permeability of the first low permeability structure  720   a  of the non-shared magnetic core part is U1 the permeability of the other non-shared magnetic core part of the magnetic core unit  700   a  is U3, U3&gt;U1. The permeability of the second low permeability structure  1300  of the shared magnetic core part is U2, the permeability of the other part of the shared magnetic core part is U4, U4&gt;U2 The cross-sectional area and the length of the non-shared magnetic core part of the magnetic core unit  700   a  are S1 and L1, and the cross-sectional area and the length of the shared magnetic core part  704  are S2 and L2, the reluctance Rm1 of the non-shared magnetic core part would be (2*L1)/(U1*S1) under the condition that U3 is far larger than U1. The reluctance Rm2 of the shared magnetic core part  704  would be L2/(U2*S2) under the condition that U4 is far larger than U2. After the adjustment of the lengths L1 and L2 and the cross-sectional areas S1 and S2, the reluctance Rm2 of the shared magnetic core part  704  can be smaller than the reluctance Rm1 of the non-shared magnetic core part. 
       FIG. 14A  is a diagram of the magnetic core  400  in an embodiment of the present invention.  FIG. 14B  is a diagram of the manufactured structure of the integrated magnetic core  1400  illustrated in  FIG. 14A  in an embodiment of the present invention. 
     In the embodiment illustrated in  FIG. 14A , the magnetic core  1400  includes two magnetic core units  1400   a - 1400   b  and corresponding windows that further include the corresponding inductor windings  1420   a  and  1420   b . The magnetic core units  1400   a - 1400   b  include first low permeability structures  1422   a  and  1422   b  respectively. The first low permeability structures  1422   a  and  1422   b  are disposed at the non-shared magnetic core parts parallel to the shared magnetic core part respectively. The inductor windings  1420   a  and  1420   b  are wound at the non-shared magnetic core parts perpendicular to the shared magnetic core part respectively. 
     In order to manufacture the magnetic core  1400  in  FIG. 14A , the implementation is realized by fabricating the magnetic core base  1430  and the magnetic core top cover  1440  illustrated in  FIG. 14B  respectively. The magnetic core top cover  1440  can be an I-shaped magnetic core and the magnetic core base  1430  can be an E-shaped magnetic core. The magnetic core base  1430  includes a central pillar, two side pillars and a connection part connecting the central pillar and the two side pillars. The central pillar of the E-shaped magnetic core is the shared magnetic core part, and the two side pillars, the connection part connecting the central pillar and the two side pillars and the magnetic core top cover are the non-shared magnetic core part. The first low permeability structures  1422   a  and  1422   b  are disposed at the two side pillars of the E-shaped magnetic core. The inductor windings  1420   a  and  1420   b  are wound at the connection part of the E-shaped magnetic core. 
     As illustrated in  FIG. 14B , the vertical distances of the side pillars of the two sides of the magnetic core base  1430  relative to the magnetic core top cover  1440  are H1 and H2 respectively. In order to keep the inductance value of the two inductors identical to each other, it may be necessary to keep H1=H2. Since the top surfaces of the side pillars and the top surface of the central pillar are not at the same plane, the polishing of the side pillars has to be performed by two steps, which easily results in the inequality between H1 and H2 due to the tolerances of the manufacturing of the magnetic core. As a result, though the magnetic core  1400  illustrated in  FIG. 14A  and  FIG. 14B  can guarantee the volume decrease under the high power condition, the manufacturing process has higher requirements. 
     Reference is now made to  FIG. 15A  and  FIG. 15B .  FIG. 15A  is a diagram of the magnetic core  1500  in an embodiment of the present invention.  FIG. 15B  is a diagram of the manufactured structure of the magnetic core  1500  illustrated in  FIG. 15A  in an embodiment of the present invention. 
     In the embodiment illustrated in  FIG. 15A , the magnetic core  1500  includes two magnetic core units  1500   a - 1500   b  and corresponding windows that further include the corresponding inductor windings  1520   a  and  1520   b . The magnetic core units  1500   a - 1500   b  include a shared magnetic core part  1510   a  that can be a common magnetic pillar. The magnetic core units  1500   a - 1500   b  further include non-shared magnetic core parts  1511   a ,  1512   a ,  1513   a ,  1511   b ,  1512   b  and  1513   b  that can be formed by a magnetic pillar respectively. The magnetic core units  1500   a - 1500   b  respectively include at least one magnetic material having the permeability ranging from 1˜50, such as a first low permeability structure. In the magnetic core  1500  illustrated in  FIG. 15A , the magnetic core units  1500   a - 1500   b  include the first low permeability structures  1522   a  and  1522   b  respectively. The first low permeability structures  1522   a  and  1522   b  are disposed at the non-shared magnetic sere parts that are perpendicular to the shared magnetic core part. The inductor windings  1520   a  and  1520   b  are wound at the non-shared magnetic core parts that are perpendicular to the shared magnetic core part. 
     In order to manufacture the magnetic core in  FIG. 15A , the implementation is realized by fabricating the magnetic core base  1530  and the magnetic core top cover  1540  illustrated in  FIG. 15B  respectively. The magnetic core top cover  1540  can be an I-shaped magnetic core and the magnetic core base  1530  can be an E-shaped magnetic core. The magnetic core base  1530  includes a central pillar two side pillars and a connection part connecting the central pillar and the two side pillars. The central pillar of the E-shaped magnetic core is the shared magnetic core part, and the two side pillars, the connection part connecting the central pillar and the two side pillars and the magnetic core top cover are the non-shared magnetic core part. The first low permeability structures  1522   a  and  1522   b  are disposed at the magnetic core top cover  1540 . The inductor windings  1520   a  and  1520   b  are wound at the connection part of the E-shaped magnetic core. 
     As illustrated in  FIG. 15B , the heights of the side pillars and the central pillar of the magnetic core base  1530  should be the same. By polishing the three surfaces at the same time, the inequality of the pillars during the fabrication of the magnetic core can be solved to keep the heights thereof same. Further, the magnetic core top cover  1540  is formed by adhering the magnetic cores  1541 ,  1542  and  1543  with glue. In order to keep the same inductance value of the two inductors, the widths D1 and D2 of the first low permeability structures  1522   a  and  1522   b  of the magnetic core top cover  1540  needs to be controlled to be identical to each other. In another method, spherical particles that are nonconductive and nonmagnetic insulator and have a diameter of D1 are mixed in the binder to fix the distance between the parts to be adhered in the magnetic core. The consistency of the inductance value of the inductors is increased. 
     Only if following the principle of sharing the magnetic pillars, the position of the first low permeability structure can be disposed at any place of the non-shared magnetic core part. Therefore, different shapes of the magnetic core can be formed when a plurality of magnetic core units share the magnetic pillar. In  FIG. 14B , the first low permeability structures  1422   a  and  1422   b  illustrated in  FIG. 14A  are disposed at the connection part of two side pillars of the magnetic core base  1430  and the magnetic core top cover  1440  of the magnetic core  1400 . In  FIG. 15A , the first low permeability structures  1522   a  and  1522   b  are disposed at the magnetic core top cover  1540 . Though the two magnetic cores are equivalent from the point of view of the magnetic path, the implementations of the fabrication are different. As a result, the magnetic core  1500  having the first low permeability structures  1522   a  and  1522   b  disposed at the magnetic core top cover  1540  illustrated in  FIG. 15A  has better control over the accuracy of the inductance value and the greater convenience of the manufacturing process than the magnetic core  1400  having the first low permeability structures  1422   a  and  1422   b  formed at the side pillars illustrated in  FIG. 14A . 
     Besides, for the windings in the window of the magnetic cores, the first low permeability structures bring fringing flux that results in the increase of the eddy loss of the inductor windings. The distance to the first low permeability structures is closer, the loss of the inductor windings is larger. Supposed that between  FIG. 14A  and  FIG. 15A , the sizes are identical except that the position of first low permeability structures of the magnetic core are different. When the vertical distance from the inductor winding  1420   b  to the first low permeability structure  1422   b  in  FIG. 14A  is Hw1, and the vertical distance from the inductor winding  1520   b  to the first low permeability structure  1522   b  in  FIG. 15A  is Hw2, it is obvious that Hw2&gt;Hw1. As a result, the eddy loss of the inductor windings in  FIG. 15A  is smaller. 
     In the aspect of the expansion of the magnetic core, the magnetic core  1400  illustrated in  FIG. 14A  can not be expanded to three or more phases of magnetic cores along the horizontal dimension, as the first low permeability structure is disposed at the side pillars of the magnetic core base  1430 . The magnetic core  1400  can only be expanded along the direction perpendicular to the horizontal dimension, in which when one phase is added, additional polishing is needed in the manufacturing process. The complexity of the manufacturing of the magnetic core and the difficulty of controlling the consistency of the inductance value are correspondingly increased. 
     The two shared magnetic cores in  FIG. 15A  can not only be expanded along the direction vertical to the horizontal dimension, but also can add one or more magnetic core units along the horizontal dimension. It is easy to perform expansion to three or more phases of integrated magnetic cores. 
       FIG. 15C  is a diagram of the magnetic core  1500 ′ in an embodiment of the present invention. The magnetic core  1500 ′ is the expansion of the magnetic core  1500  in  FIG. 15A  and is a three-phase magnetic core that includes the magnetic core units  1500   a - 1500   c  and the corresponding windows and includes the corresponding inductor windings  1520   a - 1520   c . The magnetic core units  1500   a - 1500   c  includes the first low permeability structures  1522   a - 1522   c  respectively. The expansion along the horizontal dimension is very elastic and convenient. No addition adjustment during the fabrication of the whole magnetic core is needed. 
       FIG. 15D  is a diagram of the magnetic core  1500 ″ in an embodiment of the present invention. The magnetic core  1500 ″ is the mirror expansion on the basis of the magnetic core  1500 ′ in  FIG. 15C  along the direction vertical to the horizontal dimension. The magnetic core  1500 ″ has magnetic core units  1500   a - 1500   f  and the corresponding windows and includes the corresponding inductor windings  1520   a - 1520   f . The magnetic core units  1500   a - 1500   f  includes the first low permeability structures  1522   a - 1522   f  respectively. Compared to the magnetic core in  FIG. 15D  with magnetic core in  FIG. 5C , the phase number of the core is doubled only one polishing process is added. The fabrication process is relatively easier. 
     In addition, it needs to point out that when three or more phases magnetic cores are expanded along the x dimension (taking the three-phase core illustrated in  FIG. 15C  as an example), the top cover is as shown in  FIG. 15E . The length of the first low permeability structure  1522   a  of the magnetic core unit  1500   a  is D31 the length of the first low permeability structure  1522   b  of the magnetic core unit  1500   b  is D32 and the length of the first low permeability structure  1522   c  of the magnetic core unit  1500   c  is D33. The conventional design is to keep D31, D32 and D33 as identical as possible during fabrication. Under an ideal condition that the effect of the tolerance is neglected, it can be known from the symmetry of the structure that the inductance value of the magnetic core units  1500   a  and  1500   c  are the same. Since the magnetic core unit  1500   b  is not completely symmetrical to them, the inductance value Lb of the magnetic core unit  1500   b  is not identical with the inductance value La of the magnetic core unit  1500   a.    
       FIG. 15F  is a diagram of a magnetic circuit model of the magnetic core unit  1500   a  in an embodiment of the present invention. The total reluctance Za is the total impedance from Port  1  (as illustrated in  FIG. 15G ). Similarly,  FIG. 15H  is a diagram of a magnetic circuit model of the magnetic core unit  1500   b  in an embodiment of the present invention. The total reluctance Zb is the total impedance from Port  2  (as illustrated in  FIG. 15I ). According to the relation of the parallel and serial connection of the magnetic path, Za is larger than Zb. The inductance value of the magnetic core unit is inversely proportional to the total reluctance of the magnetic path. As a result, La&lt;Lb, and Lb=(1+α)*La. Normally, the range of α is 0.1%˜10%. In the actual inductor specification, the inductors having the same size have an inductance bias of 10%. As a result, in common situations, the bias of the inductance value La and Lb is acceptable. However, for the multi-phase inductors connected in parallel and the inductors having higher requirement of the control of the inductance accuracy, the bias of the inductance needs to be modified. The practical method is to design the length D32 of the first low permeability structure  1522   b  of the magnetic core unit  1500   b  to be (1+α) times of the length D31 of the first low permeability structure  1522   a  of the magnetic core unit  1500   a . As a result, in the embodiment of the magnetic core  1500 ′ in  FIG. 15C , the reluctance of the first low permeability structure  1522   b  of the magnetic core unit  1500   b  that has two neighboring magnetic core units is larger than the reluctance of the first low permeability structures  1522   a  and  1522   c  of the magnetic core units  1500   a  and  1500   c  respectively that each of them has only one neighboring magnetic core unit. So on and so forth, in order to guarantee the balance of the inductance with the magnetic core units having less neighboring magnetic core units and the magnetic core units having more neighboring magnetic core units, the reluctance of the first low permeability structures in the magnetic core units having more neighboring magnetic core units may be designed to be larger than the reluctance of the first low permeability structures in the magnetic core units having less neighboring magnetic core units. For example, a length of air gap (i.e. first low permeability structure  1522   b  in  FIG. 15C ) of magnetic core unit  1500   b  may be made longer than each of the lengths of air gaps (i.e. first low permeability structures  1522   a  and  1522   c ) of magnetic core unit  1500   a  and  1500   c , but the disclosure is not limited thereto. 
     Surely, in other embodiments, the condition that the reluctance of the first low permeability structures in one of the magnetic core units is larger than the reluctance of the first low permeability structures in another one of the magnetic core units can be realized when the permeability of the material of the first low permeability structures in one of the magnetic core units is smaller than the permeability of the material of the first low permeability structures in another one of the magnetic core units. 
     The advantage of the present disclosure is to shrink the size of the multiple of integrated inductors by using the design of the magnetic core. 
     The implementation of the inductor windings of multi-phase integrated inductor is described in the following paragraphs. 
     Reference is now made to  FIG. 16 .  FIG. 16  is a diagram of a six-phase integrated inductor in an embodiment of the present invention. The integrated inductor includes an integrated magnetic core and inductor windings. The structure of the six-phase integrated inductor is similar to the magnetic core illustrated in  FIG. 7B  and includes six magnetic core units arranged along the same direction. The neighboring two magnetic core units share the shared magnetic core part  1502  that has a high permeability. The first low permeability structures  1504  are air gaps and are disposed at the non-shared magnetic core part perpendicular to the shared magnetic core part  1502  and all air gaps are at the same side of the magnetic core. Each of the windows of the integrated magnetic core further includes a corresponding inductor winding  1505 . Each of the inductor windings  1505  is wound at the non-shared magnetic core part of the corresponding magnetic core unit that has no air gap thereon. 
     The magnetic core of the integrated inductor can be formed by an I-shaped magnetic core top cover  1503  and a magnetic core base  1501 . A plurality of air gaps are disposed at the I-shaped magnetic core top cover to form the first low permeability structure  1504 . The magnetic core base  1501  includes a substrate and seven magnetic pillars thereon, wherein two of them are non-shared magnetic core part and five of them are shared magnetic core part. In an embodiment, the magnetic core base  1501  can be formed by six U-shaped magnetic cores. Each of the U-shaped magnetic core has two magnetic pillars and a connection part connecting the two magnetic pillars. In these six U-shaped magnet cores, the outer side pillar of the first magnetic core, the outer side pillar of the last magnetic core and the connection part of each U-shaped magnet core are non-shared magnetic core parts. The other magnetic pillars of the six U-shaped magnet cores form the shared magnetic core parts. In other embodiments, the magnetic core base  1501  can be formed by combining three E-shaped magnetic cores or by combining U-shaped and E-shaped magnetic cores. 
     The integrated inductor can be disposed at a multi-phase paralleled input end or a multi-phase paralleled output end of a power transformer. The current flowing through the windings of the integrated inductor includes a DC component and an AC component, wherein the DC component has the same current direction and the AC component has the predetermined phase difference. 
     Reference is now made to  FIG. 17 .  FIG. 17  is a diagram of a six-phase integrated inductor in another embodiment of the present invention. The integrated inductor includes an integrated magnetic core and inductor windings. Similar to the six-phase integrated inductor illustrated in  FIG. 16 , the integrated inductor includes an I-shaped magnetic core top cover  1603  and a magnetic core base  1601 . The magnetic core base  1601  includes two non-shared magnetic core parts and five shared magnetic core parts. A plurality of air gaps are disposed at the I-shaped magnetic core top cover  1603  and used as the first low permeability structure  1604 . The difference between the integrated inductor in  FIG. 16  and  FIG. 17  is that: in  FIG. 17 , each of the inductor windings  1605  is wound at the magnetic core top cover  1603  that has the air gaps. Comparing to the embodiment in  FIG. 16 , the present embodiment can decrease the leakage magnetic flux of each of the magnetic core units to improve the resistance to the interference, the performance of electromagnetic compatibility and decrease the magnetic coupling between each of the magnetic core units. 
     Reference is now made to  FIG. 18 .  FIG. 18  is a diagram of magnetic flux distribution of the first phase inductor windings  1505  of the six-phase integrated inductor after taking the mutual magnetic flux diffusing in the air into consideration. As illustrated in  FIG. 16 , the fluxes generated by the inductor winding  1505  can be divided into six parts, in which Φ 11  is the leakage magnetic flux that only couples to the inductor winding  1505  itself that corresponds to the leakage inductance. Φ 12 , Φ 13 , Φ 14 , Φ 15  and Φ 16  are the mutual magnetic fluxes between the inductor winding  1505  and other inductor windings and correspond to the mutual inductances of the corresponding inductor windings (please refer to  FIG. 3A , in which the mutual magnetic fluxes in the core are very small according to the previous analysis and are ignored due to the simplification). Though the shared magnetic core part of the neighboring magnetic core units are the magnetic pillars having high permeability, the mutual magnetic fluxes are still large such that the magnetic coupling cannot be ignored since the air gaps of each of the magnetic core units are not surrounded by the inductor windings. Especially under the high frequency condition, when the inductor volume is small and the distance between the magnetic core units having different phases is close, the coupling coefficient of the neighboring two magnetic core units can reach the range of 0.2-0.5. For the structure illustrated in  FIG. 17 , since the air gaps of each of the magnetic core units are surrounded by the inductor windings, the leakage flux is smaller. The coupling coefficient can be decreased to the range of 0-0.15, such as 0.12, 0.10, 0.08, 0.06, etc, and have less influence on the circuit. The performance is identical to the discrete inductor. 
     Reference is now made to  FIG. 19 .  FIG. 19  illustrates the structure of an inductor winding and the magnetic core unit of the six-phase integrated inductor illustrated in  FIG. 16 . In a six-phase integrated inductor, such as the six-phase integrated inductor in  FIG. 16  ( FIG. 17 ), the inductor winding  1605  may be flat wires. The cross-sectional surface of the flat wires is rectangular, a width of the flat wires is w, and a thickness of the flat wires is h, w&gt;h. As illustrated in  FIG. 19 , the advantage of using flat wires to form the inductor winding  1605  is that after the conductor is bent to form the inductor winding, two pads  1606  (illustrated in  FIG. 17 ) can be formed directly and can be welded to the PCB directly. 
     In the six-phase integrated inductors in  FIG. 16  and  FIG. 17 , the two pads of the inductor winding is bent inward of the inductor. In another embodiment, the inductor winding pads can be bent outward as well. When the inductor winding surrounds the air gaps (illustrated in  FIG. 17 ), the fringing flux of the air gaps can introduce additional loss on the inductor winding. Three methods are used to decrease such a loss in the present embodiment: 
     Firstly, the direction of the width W of the inductor winding and the first low permeability structure, i.e. the magnetic pillar that the air gaps are disposed, are kept parallel. Since the high frequency current distributes on the conductor surface close to the air gaps, the conduction area of the high frequency current increases and the loss decreases when the plane that the width of the conductor is located faces the first low permeability structure. 
     Secondly, a suitable distance s1 is kept between the inductor winding and the first low permeability structure, i.e. the air gaps, as illustrated in  FIG. 19 . For example, the distance s1 and the width w of the inductor winding satisfy the condition of s1&gt;w/5. Generally, under such a condition, the loss generated by the fringing flux of the air gaps can be ignored. 
     Thirdly, flat wires with groove can be used to form the inductor winding, as illustrated in  FIG. 20  and  FIG. 21 .  FIG. 21  illustrates a three-dimensional diagram of the inductor winding in  FIG. 20 . The groove  1801  is located in the flat wires that used as the inductor winding  1605 . The grooves can be U-shaped, and the depth s2 is larger than ⅕ of the width w of the inductor winding. Generally, under such a condition, the loss generated by the fringing flux of the air gaps can be ignored. The shape of the grooves  1801  is not limited to U-shape and can be arc or other shapes. The width w1 of the groove  1801  can be larger than the width of the air gaps. The advantage of using the flat wires with the grooves to manufacture the inductor winding is that: when the winding and the magnetic core are assembled, the winding can abut on the magnetic pillar with air gaps so as to control the distance between the winding and the magnetic pillar having the first low permeability structure (i.e. air gaps). 
     Reference is now made to  FIG. 22 .  FIG. 22  is a diagram of an unfolded inductor winding illustrated in  FIG. 21 . A section of straight flat wire having a groove can be bent in order to obtain the winding structure illustrated in  FIG. 21 . In order to be bent easily and to decrease the degree of deformation, an opening, such as a V-shaped opening  1802 , can be disposed in the straight flat wire having the groove. In an embodiment, the V-shaped opening  1802  can be 90 degrees. The size of the V-shaped opening can increase or decrease according to the practical requirements. Further, the shape of the opening is not limited to V-shape, and can be arc shape or other shapes. 
     Reference is now made to  FIG. 23 .  FIG. 23  is diagram of a structure of a two-phase integrated inductor in an embodiment of the present invention. The magnetic core  2101  of the two-phase integrated inductor includes two magnetic core units each having an air gap  2102 . The two air gaps  2102  are disposed at the central position of the non-common magnetic pillars of the two magnetic core units respectively that are in parallel with the common magnetic pillars therein. The two inductor windings  2103  and  2104  are both flat wires and are wound at the non-common magnetic pillars having the air gaps. The direction of the width W of the inductor winding is in parallel with the non-common magnetic pillar that the air gaps are disposed. The integrated inductor can be used in a multi-phase paralleled buck circuit, a multi-phase paralleled boost circuit or other circuits that are similar to these two circuits. Since the magnetic coupling between different phases integrated inductor is weak, the integrated inductor is equivalent to a discrete inductor. There is no requirement of the phase difference of the switch signal of each of the parallel-connected paths. For example, in an embodiment, the switch signals of different parallel-connected paths are synchronized. In another embodiment the switch signals of different parallel-connected phases have a certain delay. For example, the delay time is T/N, in which T is the switch period and N is the number of parallel-connected paths. 
     Although the present invention has been described in considerable detail with reference to certain embodiments thereof, other embodiments are possible. Therefore, the spirit and scope of the appended claims should not be limited to the description of the embodiments contained herein. 
     It will be apparent to those skilled in the art that various modifications and variations can be made to the structure of the present invention without departing from the scope or spirit of the invention. In view of the foregoing, it is intended that the present invention cover modifications and variations of this invention provided they fall within the scope of the following claims.