Patent Publication Number: US-2015078054-A1

Title: Common mode inductor device

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a National Stage Application of International Patent Application No. PCT/EP2013/057089, filed on Apr. 4, 2013, which claims priority pursuant to Article 8 of the Patent Cooperation Treaty, 35 U.S.C. §119(a), and 119(e) to United Kingdom Patent Application No. 1206474.7 and U.S. Provisional Patent Application No. 61/623,277, respectively, both filed on Apr. 12, 2012. Each of the above-cited priority applications are hereby incorporated by reference in their entireties. 
    
    
     BACKGROUND 
     Several types of converters are known for use in power supply systems, where there is a need to convert an AC power to a controlled DC power. The AC power will usually be supplied from an AC power source, such as the mains. The DC power is supplied to equipment such as telecommunication equipment, broad band data communication equipment (GSM/UMTS base stations etc), military equipment, medical equipment etc. 
     There are several requirements for such power supply systems. First of all, the efficiency should be high, i.e. the losses should be low. The power supply system described in WO 2009/028954 and WO 2009/058024 has an efficiency of ca 96% and is marketed and sold by Eltek Valere under the name FlatPack 2 HE. The power supply system is provided as a power supply unit for insertion into a rack. The unit has an height of 1U (the standard height of one shelf in a rack, corresponding to 44.5 mm), a length of 328 mm and a width of 109 mm so that four such units may be provided next to each other in a 19″ rack. The unit may deliver a power of 2 kW or 3 kW at −48V DC. 
     One or more embodiments of the present invention provide a smaller unit having substantially the same power as the above power supply system and with a relatively high efficiency. More specifically, the new unit should be 1U high. The length should be 220 mm so that the unit and the rack may be provided in a 30 cm power cabinet. In addition, the width should be 72 mm in order to provide that six such units may be provided next to each other in a 19″ rack. The unit should be able to supply a power of 2-3000 W at −48V DC. Hence, the available volume for the components is reduced by approximately 55%. 
     One or more embodiments of the invention reduce costs. One contribution to cost reduction is the reduced size. Another contribution to cost reduction is to use cheaper electronic components such as processor units etc. However, such electronic components are simpler, and consequently, effort must be put into using the electronic components smarter. One way of achieving this is to reduce the number of calculations needed for controlling the power supply system. 
     The power supply system comprises a fan for blowing air through the unit. The fan is normally located on the front side of the unit and blows air out through the rear side of the unit. The increased power density (power per volume unit) of the unit makes it difficult to achieve a satisfying air flow through the unit. 
     In order to be able to achieve the above, a redesign of the printed circuit card and the organization of the electronic components were necessary. Some of the largest components in such power supply systems are the common mode inductor devices, of which the power supply system must have three (two on the primary side of the converter and one on the secondary side of the converter). 
     A common mode inductor device, often referred to as a common mode choke, is used to prevent electromagnetic interference (EMI) and radio frequency interference (RFI) from power supply lines and for preventing of malfunctioning of electronic equipment. They pass differential currents (i.e. equal currents, but opposite directions), while blocking common-mode currents. 
     A photo of a prototype of the power supply unit  1  having the desired size of 1U high, 220 mm long and 72 mm wide is shown in  FIG. 1 . The unit has a first side plate  3   a,  a second side plate  3   b  and a bottom plate  3   c  with a printed circuit board  2 . In  FIG. 1 , the roof plate of the unit is removed. Three prior art common mode inductor devices  10  are standing on the printed circuit board  2  between the first side plate  3   a  and the second side plate  3   b  in order to illustrate the dimensions of the common mode inductors  10  in relation to the available space. As shown, the common mode inductors  10  will obstruct the air flow through the converter. This is especially the case when the power is high, such as 2500 W or higher, since the size of the common mode inductor devices increases as the power increases. 
     A prior art common mode inductor device  10  is shown in  FIG. 2 . The common mode indictor device  10  comprises a torus-shaped core  11  of a magnetic material, a first winding  21  wound around the core and a second winding  22  wound around the core. The ends of the windings are guided through openings in the printed circuit board  2  and are electrically connected to the printed circuit board  2 . 
     One or more embodiments of the invention provide an improved common mode inductor device which contributes to solving the above problems and which makes it possible to provide a power supply unit with the specifications mentioned above. 
     SUMMARY 
     One or more embodiments of present invention relates to a common mode inductor device including a magnetic core forming a continuous loop, a first winding wound around the magnetic core and a second winding wound around the magnetic core. The magnetic core includes a first leg section, a second leg section, a third leg section and a fourth leg section. The first winding is wound around the first leg section, the second winding is wound around the second leg section, the third leg section is provided between a first end area of the first leg section and a first end area of the second leg section, and the fourth leg section is provided between a second end area of the first leg section and a second end area of the second leg section. 
     In one aspect, the first leg section is provided substantially in parallel with the second leg section. 
     In one aspect, the first leg section, the second leg section, the third leg section and the fourth leg section is forming a rectangular prism with an opening, where edges of the leg sections are chamfered or rounded. 
     In one aspect, the inductor device further including a separation plate provided between the first winding and the second winding. 
     In one aspect, the separation plate is fixed between the third and fourth leg sections. 
     In one aspect, the inductor device further including a mounting plate connected to the fourth leg section. 
     In one aspect, the mounting plate includes openings, where terminals of the first winding and terminals of the second winding are guided through the openings in the mounting plate. 
     In one aspect, the third leg section includes an outer, substantially planar contact surface. 
     In one aspect, the magnetic core is made of a press-moulded magnetic powder. 
     In one aspect, the respective ends of the first and second winding are provided adjacent to the fourth leg section. 
     In one aspect, the fourth leg section includes a base element protruding away from the first and second leg sections, where the base element includes an outer, substantially planar contact surface. 
     In one aspect, the width of the third leg section is larger than the width of the first leg section. 
     In one aspect, the cross sectional area of the core is substantially constant around its circumference. 
     In one aspect, the rear surface of the core is planar. 
     One or more embodiments of the present invention also relates to a power supply unit including a housing including a roof plate, a bottom plate, two side plates, a rear plate and a front plate. An AC-DC converter including electronic components is connected to a printed circuit board, where the electronic components of the AC-DC converter and the printed circuit board are provided within the housing. The AC-DC converter includes at least two common mode inductor devices according to those described above, where the common mode inductor devices are connected to the printed circuit board. 
     In one aspect, the outer, substantially planar contact surface of the third leg section is provided in contact with the roof plate. 
     In one aspect, a heat conducting and electrically insulating material is provided between the outer, substantially planar contact surface of the third leg section and the roof plate. 
     In one aspect, the base element of the fourth leg section is supported in an opening of the printed circuit board. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Embodiments of the invention will now be described in detail with reference to the enclosed drawings, where: 
         FIG. 1  is a photo of a prototype of the new power supply system, wherein prior art common mode inductor devices are used; 
         FIG. 2  is illustrates one prior art common mode inductor device; 
         FIG. 3  illustrates a front view of a first embodiment of the invention; 
         FIG. 4  illustrates a perspective view of a second embodiment of the invention, where the windings are omitted; 
         FIG. 5   a  illustrates a front view of a third embodiment of the invention, where the windings are omitted; 
         FIG. 5   b  illustrates a side view of  FIG. 5   a , still with the windings omitted; 
         FIG. 5   c  illustrates a perspective view from below of the third embodiment of  FIGS. 5   a  and  5   b , still with the windings omitted; 
         FIG. 6  corresponds to the embodiment in  FIG. 5   a , where the windings also are shown and where the inductor device is fixed to a printed circuit board; 
         FIG. 7  illustrates a prior art common mode inductor device for comparison with  FIG. 6 ; 
         FIGS. 8   a  and  8   b  illustrate a fourth embodiment of the invention with the windings omitted. 
     
    
    
     DETAILED DESCRIPTION 
     In embodiments of the invention, numerous specific details are set forth in order to provide a more thorough understanding of the invention. However, it will be apparent to one with ordinary skill in the art that the invention may be practiced without these specific details. In other instances, well-known features have not been described in detail to avoid obscuring the invention. 
     It is now referred to  FIG. 3 . Here it is shown a common mode inductor device  10  comprising a magnetic core  11 , a first winding  21  wound around the magnetic core  11  and a second winding  22  wound around the magnetic core  11 . The first winding  21  comprises ends  21   a,    21   b  for connection to a printed circuit board  2  (illustrated in  FIGS. 4 and 6 ) and the second winding  22  comprises ends  22   a,    22   b  for connection to the printed circuit board  2 . 
     The magnetic core  11  comprises a first leg section  12 , a second leg section  13 , a third leg section  14  and a fourth leg section  15 . These leg sections  12 ,  13 ,  14 ,  15  are substantially elongated, each having their respective longitudinal axis I 12 , I 13 , I 14 , I 15  as illustrated in  FIG. 3 . 
     The first leg section  12  has a first end area  12   a  and a second end area  12   b.  The second leg section  13  has a first end area  13   a  and a second end area  13   b.  The third leg section  14  has a first end area  14   a  and a second end area  14   b.  The fourth leg section  15  has a first end area  15   a  and a second end area  15   b.    
     The first leg section  12  may be provided in parallel with the second leg section  13 , that is, the longitudinal axis I 12  is in parallel with the longitudinal axis I 13 . Moreover, the third leg section  14  may be provided in parallel with the fourth leg section  15 , that is, the longitudinal axis I 14  is in parallel with the longitudinal axis I 15 . Moreover, the longitudinal axis I 12  of the first leg section  12  is perpendicular to the longitudinal axis I 14  of the third leg section  14  and hence also perpendicular to the longitudinal axis I 15  of the fourth leg section  15 . 
     The third leg section  14  is provided between the first end area  12   a  of the first leg section  12  and a first end area  13   a  of the second leg section  13 . The fourth leg section  15  is provided between the second end area  12   b  of the first leg section  12  and a second end area  13   b  of the second leg section  13 . 
     It should be noted that the core  11  is forming a continuous loop. That is, the leg sections  12 ,  13 ,  14 ,  15  are forming one continuous loop without air gaps in order to improve the magnetic properties of the core. Preferably, the entire core  11  is produced in one process, for example by a press-molding process of magnetic powder. In such a process, there is no assembly of four separate leg sections. 
     Alternatively, it may be possible to provide the core  11  as an assembly of leg sections. 
     Consequently, the first leg section  12 , the second leg section  13 , the third leg section  14  and the fourth leg section  15  is forming a rectangular prism with an opening  25 . It should be noted that the edges of the leg sections  12 ,  13 ,  14 ,  15  may be chamfered or rounded as shown in  FIG. 3  and  FIG. 5   a ,  5   c  for improving the magnetic properties of the core and in order to reduce the distance between the core and the windings  21 ,  22  wound around the core  11 . 
     The first winding  21  is wound around the first leg section  12  and the second winding  22  is wound around the second leg section  13 . Hence, the first and second windings  21 ,  22  are substantially parallel to each other, as shown in  FIG. 3  and  FIG. 6 . The fourth leg section  15  may be adapted to be connected to or supported by the printed circuit board  2 . The respective ends  21   a,    21   b,    22   a,    22   b  of the first and second winding  21 ,  22  are hence provided adjacent to the fourth leg section  15 . 
     It is now referred to  FIG. 4 , illustrating a sketch of a second embodiment. Here the core is angular, in practice the core  11  will have more rounded or chamfered edges similar to the first embodiment described above or the third embodiment described below. As in the first embodiment, the first winding  21  is wounded around the first leg section  12  and the second winding  22  is wounded around the second leg section  13 . However, the windings  21 ,  22  is omitted from  FIG. 4  in order to show the core  11 . 
     In the second embodiment, the common mode inductor device comprises a separation plate  32  provided between the first and second winding  21 ,  22 , that is between the first leg section  12  and the second leg section  13 . In the present embodiment, the separation plate  32  is fixed between the third and fourth leg sections  14 ,  15 . The separation plate  32  is made of a plastic material or other known 
     PCB-material, with appropriate thermal properties, flammability properties and electrically insulating properties. Moreover, it should be mechanically rigid to provide mechanical support for the core  11 . 
     In the second embodiment, the common mode inductor device comprises a mounting plate  30  connected to the fourth leg section  15 . The mounting plate  30  provides a mechanical support of the inductor device in relation to the printed circuit board  2 . 
     In  FIG. 4  it is shown that the mounting plate  30  comprises openings  31 , where the terminals  21   a,    21   b  of the first winding  21  and the terminals  22   a,    22   b  of the second winding  22  are guided through the openings  31  in the mounting plate  30 . The ends of the windings are then guided further through the printed circuit board  2  as is known for a skilled person. The mounting plate  30  comprises four openings  31 , one for each end  21   a,    21   b,    22   a,    22   b  of the windings  21 ,  22 . 
     It should be noted that the first embodiment of  FIG. 3  also may comprise a separation plate  32  and/or a mounting plate  30 . 
     It is now referred to  FIG. 5   a - c , and  FIG. 6 . The core  11  of  FIG. 5   a  corresponds to the core  11  above, in that the longitudinal axis I 12 , I 13  of the first and second leg section  12 ,  13  are considered to be parallel to each other, even though these leg sections  12 ,  13  are slightly curved. The purpose of the curved leg section  12 ,  13  is to create a small space  34  between the turns of each of the windings  21 ,  22  in the area close to the separation plate  32  as shown in  FIG. 6 . The space  34  between each turn of the windings  21 ,  22  improves the cooling of the inductor device. 
     In the third embodiment, the fourth leg section  15  comprises a base element  17  protruding away from the first and second leg sections  12 ,  13 , that is, towards the printed circuit board  2 . The base element  17  is a part of the continuous core  11 . The base element  17  is configured to be supported in an opening of the printed circuit board  2 . For example, the base element  17  may be glued to the printed circuit board  2 , alternatively, the base element  17  and the opening of the printed circuit board  2  may be shaped so that the base element  17  may be pressed firmly into the opening, and thereby be held supported in the opening in the printed circuit board  2  (i.e. a press fit type of support). 
     In  FIG. 6  it is shown that the base element  17  is protruding from the underside of the printed circuit board  2 . The base element  17  is comprises an outer, substantially planar contact surface  19  arranged for contact with the bottom plate  3   c  of  FIG. 6  either directly or via a gap filling material in order to transport heat from the inductor to the bottom plate  3   c.    
     In the third embodiment, as shown in  FIG. 5   b , it is also the third leg section  14  protrudes from the first and second leg sections  12 ,  13 . Here it is shown that the width W 14  of the third leg section  14  is larger than the width W 12  of the first leg section  12 . It should be noted that the cross sectional area of the core  11  is substantially constant around its circumference. 
     In  FIGS. 5   a ,  5   b  and  5   c , the front surface of the core is denoted with FS and the rear surface is denoted with RS. 
     In  FIG. 6  it is also shown that the inductor device comprises a mounting plate  30 . The mounting plate  30  makes the handling of the core  11  with mounting plate  32  easier during assembly, and may increase the assembly efficiency. Moreover, the mounting plate  32  may also provide electrical insulation. 
     In all the embodiments above, the third leg section  14  comprises an outer, substantially planar contact surface  16 . The contact surface  16  is arranged to be in contact with the roof plate  3   d  of  FIG. 6  either directly or via a gap filling material in order to transport heat from the inductor to the roof plate  3   d.  The gap filling material must be thermally conducting; in addition it may be electrically insulating and/or shock absorbing. 
     In the third embodiment, the base element  17  may be in contact with the bottom plate  3   c  either directly or via the gap filling material. 
     A prior art common mode inductor is illustrated in  FIG. 7  for comparison with the third embodiment of the invention shown in  FIG. 6 . Here, also the roof panel  3   d  and the bottom panel  3   c  are shown, to illustrate the relatively small space available to these components. 
     By means of the features of the core  11 , the windings  21 ,  22  may have more turns than prior art inductor devices. In  FIG. 6  the windings  21 ,  22  each have  13  turns, while the corresponding windings of  FIG. 7  have  7  turns. The increased width W 14  allows that the length of each leg section  12 ,  13  to be increased. The base element  17  being lowered into and below the printed circuit board  2  allows that the length of each leg section  12 ,  13  to be increased further. 
     Also the cooling of the inductor device of  FIG. 6  is improved over the inductor device in  FIG. 7 , since the area of the core being available for transporting heat to the housing is substantially increased. 
     It is now referred to  FIGS. 8   a  and  8   b . The core  11  corresponds to the core  11  of  FIG. 5   a ,  5   b ,  5   c , the difference is that the rear surface RS facing down in  FIG. 8   a  and facing up in  FIG. 8   b , is planar. Hence, the third leg section  14  is only protruding from the front surface FS of the first and second leg sections. The planar rear surface RS provides an easier production process. 
     One or more embodiments of the present invention also relates to a power supply unit  1  comprising a housing  3  and an AC-DC converter. The housing  3  comprises a roof plate  3   d,  a bottom plate  3   c,  two side plates  3   a,    3   b,  a rear plate and a front plate. A fan is provided in the front plate of the housing  3 . Ventilating openings provided in the rear plate of the housing  3  for allowing the air to be blown through the housing  3  by means of the fan. 
     The AC-DC converter comprises electronic components connected to a printed circuit board  2 , where the electronic components of the AC-DC converter and the printed circuit board  2  is provided within the housing  3 . 
     The AC-DC converter further comprises three common mode inductor devices  10  of one of the embodiments described above, where the common mode inductor devices  10  are connected to the printed circuit board  2 . 
     As mentioned above, the outer, substantially planar contact surface  16  of the third leg section  14  is provided in contact with the roof plate  3   d.  A heat conducting and electrically insulating material is provided between the outer, substantially planar contact surface  12  of the third leg section  14  and the roof plate  3   d.  Moreover, moreover, the base element  17  of the fourth leg section  15  is supported in an opening of the printed circuit board  2 . 
     While the invention has been described with respect to a limited number of embodiments, those skilled in the art, having the benefit of this disclosure, will appreciate that other embodiments can be devised which do not depart from the scope of the invention as disclosed herein. Accordingly, the scope of the invention should be limited only by the attached claims.