Patent Publication Number: US-9847730-B2

Title: Power converter

Description:
TECHNICAL FIELD 
     The present invention relates to a power converter mounted with a noise filter. 
     BACKGROUND ART 
     An electric vehicle or a plug-in hybrid vehicle includes: an inverter device to drive a motor with a high-voltage storage battery for power drive; and a low-voltage storage battery to operate auxiliary machines such as a light and a radio of the vehicle. This kind of vehicle is mounted with a DC-DC converter device that performs power conversion from the high-voltage storage battery to the low-voltage storage battery or power conversion from the low-voltage storage battery to the high-voltage storage battery. 
     The DC-DC converter device includes a high-voltage side switching circuit to convert high-voltage DC voltage to AC voltage, a transformer to convert high AC voltage to low AC voltage, and a low-voltage side rectifier circuit to convert low-voltage AC voltage to DC voltage. In such a DC-DC converter device that converts the voltage by switching a semiconductor device, switching noise generated by switching is needed to be suppressed and a noise filter is needed to be mounted on an output unit. 
     The DC-DC converter is downsized year after year, and downsizing of the noise filter to be mounted is also demanded. As an example of such downsizing, there is a known structure disclosed in PTL 1, for example. The invention disclosed in PTL 1 provides an LC filter device that can have multistage connection by forming a structure in which a coil portion can be integrated. 
     CITATION LIST 
     Patent Literature 
     PTL 1: Publication of Japanese Patent Laid-Open No. 2008-172442 A 
     SUMMARY OF INVENTION 
     Technical Problem 
     A magnetic flux formed by current flowing in a coil of a noise filter forms a closed magnetic circuit inside a magnetic core. However, in the DC-DC converter required to output high DC current, a large-sized magnetic core is needed to be used such that the magnetic core is prevented from magnetic saturation even in the case where magnetic flux density is increased inside the magnetic core due to increase of output current. Due to this, the size of the noise filter is increased, and a factor to hinder downsizing of the DC-DC converter is caused. 
     Solution to Problem 
     The invention according to claim  1  is a power converter that includes: a switching circuit for power conversion having a switching device; and a noise filter provided on a direct current side of the switching circuit and adapted to remove noise. The noise filter includes: a magnetic core formed with a single through-hole and forming a closed magnetic circuit; first wiring running through the through-hole from one first opening to the other second opening thereof, and having one end connected the switching circuit and the other end drawn out from the second opening; second wiring running through the through-hole from the second opening to the first opening thereof, and having one end connected to the other end of the first wiring and the other end drawn out from the first opening as a filter output end; a first capacitor provided between ground and a connecting portion of the first wiring and the second wiring; and a second capacitor provided between the other end of the second wiring and the ground. 
     Advantageous Effects of Invention 
     According to the present invention, the magnetic core of the noise filter can be prevented from magnetic saturation in the power converter mounted with the noise filter, and the power converter can be downsized. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a diagram illustrating an exemplary circuit configuration of a DC-DC converter device  100 . 
         FIG. 2  is a diagram illustrating a wiring structure of a noise filter  140  according to the present embodiment. 
         FIG. 3  is a diagram illustrating an operation principle of the noise filter  140 . 
         FIG. 4  is a diagram illustrating an equivalent circuit of the above-mentioned noise filter  140 . 
         FIG. 5  is a diagram illustrating an equivalent circuit of the noise filter  140  in the case of using a T-type equivalent circuit. 
         FIG. 6  is a diagram illustrating a simple equivalent circuit of the noise filter  140 . 
         FIG. 7  is a diagram illustrating noise transmission amounts calculated by the equivalent circuits in  FIGS. 5 and 6 . 
         FIG. 8  is a perspective view illustrating a noise filter  140  according to a second embodiment. 
         FIG. 9  is an external perspective view illustrating an example of the noise filter  140 . 
         FIG. 10  is an external perspective view illustrating an example of the noise filter  140 . 
         FIG. 11  is an external perspective view illustrating wiring  11 ,  21 ,  31  and a shield plate  71 . 
         FIG. 12  is an enlarged view of a second capacitor substrate  52  mounted with a second capacitor  51 . 
         FIGS. 13( a ) and 13( b )  are explanatory diagrams comparing the noise filter  140  according to the present invention with a noise filter  240  of the related art. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     In the following, embodiments to implement the present invention will be described below with reference to the drawings. 
     First Embodiment 
     In the present embodiment, a DC-DC converter device mounted with a noise filter will be described as an example of a power converter according to the present invention. The DC-DC converter device according to the present embodiment is applied to an electric vehicle, a plug-in hybrid vehicle, and the like. A low-voltage storage battery to operate auxiliary machines such as a light and a radio is mounted on a vehicle, and the DC-DC converter device performs power conversion from a high-voltage storage battery to the low-voltage storage battery and power conversion from the low-voltage storage battery to the high-voltage storage battery. 
     [Circuit Configuration of DC-DC Converter Device] 
       FIG. 1  is a diagram illustrating an exemplary circuit configuration of a DC-DC converter device  100 . The DC-DC converter device  100  includes a power conversion circuit  101  and a noise filter  140 . The power conversion circuit  101  includes a high-voltage side switching circuit  110 , a transformer  120 , and a low-voltage side rectifier circuit  130 . The high-voltage side switching circuit  110  converts, to AC voltage, high-voltage DC voltage received from high-voltage input terminals  111 P,  111 N. The transformer  120  converts high AC voltage to low AC voltage. The low-voltage side rectifier circuit  130  converts low-voltage AC voltage to DC voltage. The low-voltage DC voltage converted by the low-voltage side rectifier circuit  130  is output from a filter output end  82  via the noise filter  140 . 
     (Circuit Configuration of High-voltage Side Switching Circuit) 
     The high-voltage side switching circuit  110  includes four semiconductor switching devices H 1  to H 4  connected as an H-bridge type, and a smoothing input capacitor Cin. For the semiconductor switching device, a MOSFET (field-effect transistor) is used, for example. Further, for the semiconductor switching devices H 1  to H 4 , snubber capacitors are provided in parallel to the respective semiconductor switching devices H 1  to H 4 . AC voltage is generated in a primary side of the transformer  120  by performing phase shift PWM control for the four semiconductor switching devices H 1  to H 4  of the high-voltage side switching circuit  110 . 
     Meanwhile, a resonance choke coil  103  is connected between the high-voltage side switching circuit  110  and the transformer  120 . Zero-voltage switching can be performed in the semiconductor switching devices H 1  to H 4  constituting the high-voltage side switching circuit  110  by using combined inductance of inductance of the resonance choke coil  103  and leakage inductance of the transformer  120 . 
     (Circuit Configuration of Low-Voltage Side Rectifier Circuit) 
     The low-voltage side rectifier circuit  130  includes two rectifier phases formed of MOSFETs and a smoothing circuit including a choke coil Lout and a smoothing capacitor Cout. In the following, a rectifier phase formed by a MOSFET  131  will be referred to as a first rectifier phase, and a rectifier phase formed by a MOSFET  132  will be referred to as a second rectifier phase. 
     Wiring on a high-potential side in each of the rectifier phases (namely, a drain side of the MOSFET) is connected to a secondary side of the rectifier phase  120 . Further, wiring on a low-potential side (ground side) in each of the rectifier phases is joined and connected to the ground via a shunt resistor Rsh. A secondary side center tap terminal of the transformer  120  is connected to the choke coil Lout, and the smoothing capacitor Cout is connected to an output side of the choke coil Lout. 
     Full-wave rectification is performed by the above-described two rectifier phases for alternate current generated on the secondary side of the transformer  120  by phase shift PWM control in the high-voltage side switching circuit  110 . After the full-wave rectification, the alternate current is smoothed by the choke coil Lout and the smoothing capacitor Cout and becomes direct current/voltage. The shunt resistor Rsh is provided in order to detect load current returning from the ground, and indicates, in principle, a current value same as the load current flowing in the choke coil Lout. In other words, the DC-DC converter device  100  according to the present embodiment detects current in the choke coil Lout, and feeds back the value to a control circuit, thereby achieving control of output load current. 
     [Structure and Effects of Noise Filter  140 ] 
       FIG. 2  is a diagram illustrating a wiring structure of the noise filter  140  according to the present embodiment. The noise filter  140  includes a magnetic core  1 , first wiring  11  and second wiring  21  both wound around the magnetic core  1 , and capacitors  41 ,  51 . A through-hole  1 A is formed on the magnetic core  1  that forms a closed magnetic circuit. A first opening  2  is formed on one side of the through-hole  1 A (upper side in the drawing) and a second opening  3  is formed on the other side of the through-hole  1 A (lower side in the drawing). 
     The first wiring  11  is wound around the magnetic core  1  in a manner running through the through-hole  1 A. An end of the first wiring  11  drawn out from the first opening  2  constitutes a filter input end  81 . The filter input end  81  is connected to an output end of the low-voltage side rectifier circuit  130 , namely, an output end of the power conversion circuit  101 . On the other hand, the other end  83  of the first wiring  11  drawn out from the second opening  3  is connected to third wiring  31 . 
     The second wiring  21  is wound around the magnetic core  1  in a manner running through the through-hole  1 A. An end  84  of the second wiring  21  drawn out from the second opening  3  side is connected to the third wiring  31 . On the other hand, the other end of the second wiring  21  drawn out from the first opening  2  forms a filter output end  82 . The first wiring  11  and the second wiring  21  are connected by connecting the other end  83  of the first wiring  11  and the one end  84  of the second wiring  21  to the third wiring  31 . The first capacitor  41  is connected between the third wiring  31  and the ground. Further, the second capacitor  51  is connected between the second wiring  21  and the ground on the filter output end  82  side of the second wiring  21 . 
     Next, an operation principle of the noise filter  140  of the present embodiment will be described using  FIG. 3 . A DC component and an AC component are contained in current received in the filter input end  81 , but a description will be provided by separating the DC component from the AC component. 
     (DC Component) 
     First, the DC component will be described. Here, current flowing in the first wiring  11  is defined as I 1 , and current flowing in the second wiring  21  is defined as I 2 . Further, it is assumed that the number of turns of the first wiring  11  is same as the number of turns of the second wiring  21 . The DC component of the current I 1  flowing in the first wiring  11  generates a magnetic flux Φ DC1  inside the magnetic core  1 . The DC component of current flowing from the other end  83  of the first wiring  11  to the third wiring  31  flows to the second wiring  21  from the one end  84  of the second wiring  21  without being split to the first capacitor  41  connected to the third wiring  31 . The DC component of the current I 2  flowing in the second wiring  21  generates a magnetic flux Φ DC2  inside the magnetic core  1 . 
     The current flowing in the first wiring  11  flows in a direction of the second opening  3  from the first opening  2  inside the through-hole  1 A. Therefore, a direction of the magnetic flux Φ DC1  is a direction indicated by an arrow in the drawing. On the other hand, the current flowing in the second wiring  21  flows in a direction of the first opening  2  from the second opening  3  inside the through-hole  1 A. Therefore, a direction of the magnetic flux Φ DC2  is a direction opposing to the direction of the magnetic flux Φ DC1 . Further, the DC component of the current I 1  has the same value as the DC component of the current I 2 , and further the number of turns of the first wiring  11  is same as the number of turns of the second wiring  21 . Therefore, the magnetic fluxes Φ DC2  and Φ DC1  have equal intensity (magnetic flux density). As a result, a combined magnetic flux of the magnetic flux Φ DC1  and the magnetic flux Φ DC2  becomes zero inside the magnetic core  1 . In other words, the magnetic flux generated by the DC component inside the magnetic core  1  is zero regardless of intensity of AC current, and magnetic saturation caused by the case of having a large amount of AC components (high DC current) is prevented from occurrence. Therefore, there is no need to enlarge the size for saturation control and the magnetic core  1  can be downsized. 
     (AC Component) 
     Next, the AC component will be described. The AC component of the current I 1  flowing in the first wiring  11  generates the magnetic flux Φ AC1  inside the magnetic core  1 . Some of AC components of the current flowing from the other end  83  of the first wiring  11  to the third wiring  31  (indicated by reference sign I 3  in  FIG. 3 ) is split to the first capacitor  41  connected to the third wiring  31 . Therefore, the amount of AC components flowing into the second wiring  21  from the third wiring  31  is reduced. The AC component of the current flowing in the second wiring  21  generates the magnetic flux Φ AC2  inside the magnetic core  1 . As is the case with the magnetic fluxes Φ DC1  and Φ DC2  generated by the above-described DC components, the direction of the magnetic flux Φ AC1  is opposite to the direction of the magnetic flux Φ AC2 , but these magnetic fluxes have different intensity from each other. Due to this, a combined magnetic flux of the magnetic flux Φ AC1  and the magnetic flux Φ AC2  does not become zero, and the first wiring  11  and the second wiring  21  wound around the magnetic core  1  function as inductors against the AC components. Further, a function as a noise filter (LC filter) can be achieved by combining these with the second capacitor  51  connected to the second wiring  21 . 
       FIG. 4  is a diagram illustrating an equivalent circuit of the above-described noise filter  140 . At the filter output end  82 , Lo is connected as a load. The equivalent circuit in  FIG. 4  can perform conversion by using a T-type equivalent circuit of a transformer as illustrated in  FIG. 5 . Here, study will be made on a case where L1=L2=3 μH, coupling coefficient k=0.9, C1=C2=50 μF, and LO=5 μH. In this case, L1−M&lt;M is established because: L1−M=L2−M=(1−k)L1, and M=kL1. 
     Further, in the case of considering a frequency area where impedance of the load L o  is larger than impedance of the second capacitor  51 , the equivalent circuit diagram illustrated in  FIG. 5  can be transformed to a simple equivalent circuit diagram illustrated in  FIG. 6 .  FIG. 7  is a diagram illustrating noise transmission amounts calculated by the equivalent circuits in  FIGS. 5 and 6 . Note that the noise transmission amount is expressed by an absolute value of a ratio |Vo/Vi| between input voltage Vi and output voltage Vo of the noise filter. 
     In  FIG. 7 , a solid line represents the noise transmission amount calculated by the equivalent circuit diagram in  FIG. 5 , and a dotted line represents the amount of transmitted noise calculated by the simple equivalent circuit in  FIG. 6 . Judging from  FIG. 7 , a function as the noise filter is confirmed because the noise transmission amount is suppressed to 0 dB or less when the frequency is 40 kHz or more. Further, when the frequency is 40 kHz or more, results of the respective noise transmission amounts calculated from the equivalent circuit diagrams in  FIGS. 5 and 6  are the same, and it is found that the noise transmission amount can be calculated by the simple equivalent circuit diagram in  FIG. 6 . On the other hand, when the frequency is 40 kHz or less, the noise transmission amount is 0 dB or 0 dB or more, and it is found that the function as the noise filter is available. Particularly, noise peaks caused by circuit resonance are observed near the frequency 14 kHz indicated by reference sign (a) and 30 kHz indicated by reference sign (b) in  FIG. 7 . 
     The noise peak (a) is formed by series resonance generated in mutual inductance M between the first wiring  11  and the second wiring  21 , and the first capacitor C1, and a resonance frequency fa can be calculated by a following formula (1). 
     
       
         
           
             
               
                 
                   
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     Further, the noise peak (b) is almost same as a series resonance frequency fb generated in two inductors (L1-M) and (L2-M) and the second capacitor C2 in the simple equivalent circuit of  FIG. 6 . Here, the resonance frequency fb can be calculated by a following formula (2). By this, the function as the noise filter can be achieved at a desired frequency or more by adjusting a parameter of a circuit element. 
     
       
         
           
             
               
                 
                   
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     Second Embodiment 
     In a power converter according to a second embodiment, a power conversion circuit  101  is same as a first embodiment illustrated in  FIG. 1 , and only a configuration of a noise filter  140  differs from a power converter of the first embodiment. Therefore, in the following, only the noise filter  140  will be described. 
       FIG. 8  is a perspective view illustrating the noise filter  140  according to the second embodiment. In the present embodiment, a member formed by molding a flat bar-shaped member in a U-shape is used as first wiring  11 , second wiring  21 , and third wiring. A magnetic core  1  having a rectangular cylinder shape is formed with a through-hole  1 A having a rectangular cross-sectional surface. The first wiring  11  is arranged so as to run through the through-hole  1 A from a first opening  2  to a second opening  3 . A filter input end  81  of the first wiring  11  projecting from the first opening  2  is connected to an output end of a low-voltage side rectifier circuit  130  illustrated in  FIG. 1 . On the other hand, the other end side of the first wiring  11  projecting from the second opening  3  is integrally connected to the third wiring  31 . 
     The second wiring  21  is arranged so as to run through the through-hole  1 A from the second opening  3  to the first opening  2 . An end of the second wiring  21  projecting from the second opening  3  is integrally connected to the third wiring  31 . On the other hand, a second capacitor  51  is connected between ground and the other end (filter output end  82 ) of the second wiring  21  projecting from the first opening  2 . Further, a first capacitor  41  is connected between the third wiring  31  and the ground. 
     The first wiring  11  and the second wiring  21  are substantially arranged in parallel, and a shield plate  71  is disposed between the first wiring  11  and the second wiring  21  in parallel thereto. The shield plate  71  is connected to the ground. By providing this shield plate  71 , an electric filed on the first wiring  11  side can be separated and blocked from an electric field of the second wiring  21  side. In other words, the shield plate  71  functions as a shield to suppress electric field coupling. 
     In the case where there is electric field coupling between the first wiring  11  and the second wiring  21 , part of noise flowing from the filter input end  81  is transmitted from the first wiring on an input side to the second wiring  21  arranged adjacent thereto via the electric field without passing through the inside of the wiring  11 ,  21  that are inductors. As a result, a noise attenuation effect of the noise filter  140  is deteriorated. However, the first wiring  11  and the second wiring  21  are electrostatically shielded by providing the shield plate  71 , and noise transmission by electric field coupling is prevented. Therefore, the noise attenuation effect can be secured. 
       FIGS. 9 to 12  are diagrams illustrating exemplary implementation of the noise filter  140  illustrated in  FIG. 8 .  FIGS. 9 and 10  are external views of the noise filter  140  fixed to a ground plate  61  having a plate-like shape. The magnetic core  1  is formed of a plurality of core members or an integrated core member. In the example illustrated in  FIG. 9 , the magnetic core  1  is formed of two core members  10  each having a U-shape cross-sectional surface. The first wiring  11 , second wiring  21 , and shield plate  71  are inserted and made to pass through the inside of the through-hole  1 A of the magnetic core  1 . The first capacitor  41  is mounted on a first capacitor substrate  42  disposed on the third wiring  31  side. The second capacitor  51  is mounted on a second capacitor substrate  52  disposed on a side where the filter input end  81  and the filter output end  83  of the wiring  11 ,  21  are provided. 
       FIG. 11  is an external perspective view illustrating the wiring  11 ,  21 ,  31  and the shield plate  71 . The first wiring  11 , second wiring  21 , and third wiring  31  are integrally formed in a bus bar (bar-like or plate-like conductive member) molded in the U-shape. The filter input end  81  and the filter output end  82  are formed on both ends of the bus bar. A portion of the first wiring  11  and a portion of the second wiring  21  are arranged substantially in parallel interposing a gap, and the shield plate  71  is disposed in the gap. 
     At both ends of the shield plate  71 , namely, portions projected to the outside of the through-hole  1 A, fixing portions  71 A,  71 B each bent in an L-shape are formed. The shield plate  71  is fixed to the ground plate  61  by fixing the fixing portions  71 A,  71 B on the ground plate  61  with screws (refer to  FIGS. 9 and 10 ). As a result, the shield plate  71  is electrically connected to the ground plate  61 . 
       FIG. 12  is an enlarged view of the second capacitor substrate  52  mounted with the second capacitor  51 . The second capacitor substrate  52  is formed by mounting capacitors  53   a ,  53   b  on a print circuit board  59  formed with an output terminal side wiring pattern  54 , a ground side wiring pattern  55 , and an intermediate wiring pattern  56 . A plurality of the capacitors  53   a  is connected in parallel between the output terminal side wiring pattern  54  and the intermediate wiring pattern  56 . In the same manner, a plurality of the capacitors  53   b  is arranged in parallel between the intermediate wiring pattern  56  and the ground side wiring pattern. In the case of the example illustrated in  FIG. 12 , three capacitors  53   a ,  53   b  are provided respectively. The above-described second capacitor  51  is formed of these capacitors  53   a ,  53   b.    
     A through-hole  57  is formed on a portion of the output terminal side wiring pattern  54 , and the portion of the output terminal side wiring pattern  54  is fixed to the second wiring  21  with a screw as illustrated in  FIG. 10 . As a result, the output terminal side wiring pattern  54  and the second wiring  21  are electrically connected via the screw. In the same manner, a through-hole  58  is formed also on a portion of the ground side wiring pattern  55 , and the portion of the ground side wiring pattern  55  is fixed to the shield plate  71  with a screw, thereby electrically connecting the ground side wiring pattern  55  to the shield plate  71  via the screw. 
     While detailed illustration is omitted, the first capacitor substrate  42  mounted with the first capacitor  41  also has the same structure as the second capacitor substrate  52 . Further, a portion of an input terminal side wiring pattern formed on the first capacitor substrate  42  is fixed to the third wiring  31  with a screw, and a portion of the ground side wiring pattern formed on the first capacitor substrate  42  is fixed to the shield plate  71  with a screw. With this structure, assembly efficiency of the noise filter can be improved. 
     According to the above-described embodiment, as illustrated in  FIG. 8 , the noise filter  140  disposed on a direct current side of the power conversion circuit  101  and adapted to remove noise includes: the magnetic core  1  formed with the single through-hole  1 A and forming a closed magnetic circuit; the first wiring  11  having one end  81  connected to the power conversion circuit  101  and the other end  83  drawn out from the second opening  3 , and running through the through-hole  1 A from the first opening  2  to the other second opening  3 ; the second wiring  21  having one end  84  connected to the other end  83  of the first wiring  11  and the other end  82  drawn out from the first opening  2  as the filter output end, and running through the through-hole  1 A from the second opening  3  to the first opening  2 ; the first capacitor  41  provided between the ground and a connecting portion of the first wiring  11  and the second wiring  21 ; and the second capacitor  51  provided between the other end  82  of the second wiring  21  and the ground. 
     Meanwhile, in the example illustrated in  FIG. 8 , the one end of the second wiring  21  and the other end of the first wiring  11  are connected via the third wiring  31  functioning as the connecting portion. Further, the first capacitor  41  is provided between the third wiring  31  and the shield plate  71  set to ground potential. 
     By thus forming the noise filter  140 , magnetic fluxes Φ AC1 , Φ DC1  are formed by current flowing in the first wiring  11  and magnetic fluxes Φ AC2 , Φ DC2  are formed by current flowing in the second wiring  21  inside the magnetic core  1  as illustrated in  FIG. 3 . In other words, the first wiring  11 , second wiring  21 , and first capacitor  41  are wired to the magnetic core  1  such that the magnetic flux Φ DC1  and the magnetic flux Φ DC2  by the DC components cancel each other and become substantially zero. Further, some of AC components are split to the ground side by the first capacitor  41 . Therefore, the magnetic flux absolute value of the magnetic flux Φ AC1  is larger than the magnetic flux Φ AC2  and a function as the noise filter is achieved. 
     As a result, the magnetic core  1  can be prevented from magnetic saturation caused by high DC current, and the magnetic core  1  can be more downsized than that of the related art, and the power converter  100  mounted with the downsized noise filter  140  can be provided. Further, in addition to the second capacitor  51  provided on the filter output end  82  side, the first capacitor  41  is provided at the connecting portion of the first wiring  11  and the second wiring  21 , thereby achieving a function as an LC filter for the AC components. 
       FIGS. 13( a ) and 13( b )  are diagrams schematically illustrating magnetic fluxes of DC components formed on a magnetic core in the noise filter  140  according to the present invention and a noise filter  240  in the related art disclosed in PTL 1 described above.  FIG. 13( a )  is the case of the present invention, and same as the one illustrated in  FIG. 3 .  FIG. 13( b )  is the case of the noise filter  240  in the related art. In FIGS.  13 ( a ) and  13 ( b ), a direction of current flowing in wiring  11 ,  242  is the direction toward a back surface orthogonal to a drawing paper, and a direction of current flowing in wiring  21 ,  243  is the direction toward a front surface of the drawing paper. Therefore, a direction of the magnetic flux Φ DC1  is clockwise, and a direction of the magnetic flux Φ DC2  is anti-clockwise. 
     In the noise filter  240  illustrated in  FIG. 13( b ) , two through-holes  241   a ,  241   b  are formed at the magnetic core  241 . Wiring  242  is disposed in the through-hole  241   a  on one side, and wiring  243  is disposed in the other through-hole  241   b  on the other side. Therefore, both magnetic fluxes Φ DC1 , Φ DC2  are concentrated in a magnetic core portion  241   c  between the through-holes  241   a ,  241   b , and in the case of having high DC current, magnetic saturation is likely to occur. On the other hand, in the noise filter  140  according to the present invention illustrated in  FIG. 13( a ) , current directions of the wiring  11 ,  21  arranged inside the single through-hole  1 A are opposite from each other. Therefore, as described above, the magnetic fluxes Φ DC1 , Φ DC2  cancel each other inside the magnetic core  1 . As a result, magnetic saturation can be prevented from occurrence. 
     Further, as illustrated in  FIG. 8 , the shield plate  71  disposed between the first wiring  11  and the second wiring  21  so as to pass through the through-hole  1 A and adapted to prevent the first wiring  11  and the second wiring  21  from electric field coupling is provided. By this, noise transmission from the first wiring  11  to the second wiring  21  caused by electric field coupling can be prevented, and the attenuation effect of the noise filter  140  can be secured. Meanwhile, the same effect can be provided by disposing a shield member for electric field coupling prevention between the first power distribution  11  and the second wiring  21  even in the case where the wiring  11  and  21  are wound around in a coil-like form as illustrated in  FIG. 2 . 
     Further, as illustrated in  FIGS. 2 and 3 , in the case where the noise filter  140  has a structure in which a conductor line is wound around the magnetic core  1 , the first wiring  11  drawn out from the second opening  3  is wound around the magnetic core  1  so as to run through the through-hole  1 A, and then connected to the one end  84  of the second wiring  21  (in  FIGS. 2 and 3 , connected to the one end  84  via the wiring  31 ). On the other hand, the second wiring  21  drawn out from the first opening  2  is wound around the magnetic core  1  so as to run through the through-hole  1 A, and then connected to the second capacitor  51 . 
     Meanwhile, in the example illustrated in  FIG. 2 , the noise filter is formed to have the structure in which the first wiring  11  and the second wiring  21  are respectively wound around the magnetic core  1  twice, but the effects is provided by optional number of turns, not limited to the above-mentioned number of turns. Further, when the number of turns of the first wiring  11  is made same as the number of turns of the second wiring  21 , the magnetic flux by the DC components (obtained by adding the magnetic flux with the magnetic flux) can be made to substantially zero, but not necessarily to be the same. Even when the number of turns is different between the both wiring, the magnetic flux by the DC components can be made little when the difference is small, and magnetic saturation can be prevented from occurrence in the case of having high DC current. 
     Further, as illustrated in  FIG. 11 , the first and second wiring  11  and  12  can be formed integrally by the U-shaped conductive member (bus bar) in which both ends of the two parallel portions are mutually connected at the bent portion, and the one parallel portion may be set as the first wiring  11  and the other parallel portion may be set as the second wiring  21 . In this case, the first capacitor  41  is provided so as to connect the bent portion (third wiring  31 ) of the conductive member to the ground. With this structure, assembly efficiency can be more improved compared to the wound wire type illustrated in  FIG. 2 . 
     Further, the first capacitor substrate  42  is formed with the input terminal side wiring pattern connected to the third wiring  31 , and includes a first print board mounted with the first capacitor  41  so as to be connected to the input terminal side wiring pattern. Further, as illustrated in  FIG. 12 , the second capacitor substrate  52  is formed with the output terminal side wiring pattern  54  connected to the second wiring  21 , and includes the print circuit board  59  mounted with the capacitors  53   a ,  53   b  constituting the second capacitor  51  so as to be connected to the output terminal side wiring pattern  54 . Further, the first print board is fixed to the third wiring  31  such that the input terminal side wiring pattern is electrically connected to the third wiring  31 , and the print circuit board  59  is fixed to the second wiring  21  such that the output terminal side wiring pattern  54  is electrically connected to the second wiring  21 . With this structure, assembly efficiency of the noise filter can be further improved. 
     Moreover, assembly efficiency of the noise filter  140  can be improved by forming the magnetic core  1  from the plurality of core members  10  made of magnetic material. In the example illustrated in  FIG. 9 , a width size between both ends of the shield plate  71  is larger than a diameter size of the through-hole  1 A. Therefore, the cylindrical magnetic core  1  is formed of the two core members  10  having half-cut structure. In the example illustrated in  FIG. 9 , the magnetic core  1  is divided by a dividing surface parallel to an axis of the magnetic core  1 , but may also be divided into a plurality of portions by surfaces orthogonal to the axis. Meanwhile, since the dividing surface is formed in a manner cutting across a magnetic path in the magnetic core  1  illustrated in  FIG. 9 , the dividing surfaces of the core members  10  facing each other at a jointing portion are preferably the same. 
     Meanwhile, according to the above-described embodiments, a full-bridge switching circuit system illustrated in  FIG. 1  is exemplified as a high-voltage side switching circuit system, but in the case of adopting a half-bridge switching system or another type of the switching system as a circuit system, the effects of the above-described noise filter  140  can also be provided in the same manner. Further, in the case of adopting a diode rectification system or another type of the rectification system as a circuit system of the low-voltage side rectifier circuit instead of a synchronous rectification system illustrated in  FIG. 1 , the effects of the above-described noise filter  140  can also be provided in the same manner. Further, needless to mention, there are various possible ways of combining the above-described high-voltage side switching circuit system with the low-voltage side rectifier circuit system. Additionally, according to the above-described embodiments, the example of DC-DC converter device has been described, but not limited thereto, various kinds of power converters provided with a noise filter can be applied. 
     Note that the present invention is not limited to the above-described embodiments and may include various modified examples. For example, the above-described embodiments are described in detail in order to clearly explain the present invention, and are not necessarily limited to those having all the components described. Additionally, some components of one embodiment can be partly replaced with components of another embodiment, and further a component of another embodiment can also be added to components of one embodiment. Further, addition, deletion, and substitution of other components can be made to part of the components of the respective embodiments. 
     REFERENCE SIGNS LIST 
     
         
           1  magnetic core 
           1 A through-hole 
           11  first wiring 
           21  second wiring 
           31  third wiring 
           41  first capacitor 
           42  first capacitor substrate 
           51  second capacitor 
           52  second capacitor substrate 
           54  output terminal side wiring pattern 
           55  ground side wiring pattern 
           61  ground plate 
           71  shield plate 
           100  DC-DC converter device 
           101  power conversion circuit 
           110  high-pressure side switching circuit 
           120  transformer 
           130  low-pressure side rectifier circuit 
           140  noise filter