Abstract:
Provided is an electronic device that is provided with a filter circuit that suppresses the effects of electromagnetic noise propagated through space from a circuit board and reduces parasitic inductance, and can output a voltage with adequately reduced noise. To solve the above problem, in an electronic device provided with a cabinet ( 101 ), a circuit board ( 132 ) provided in the cabinet, an output terminal ( 122 ) that passes through a through hole provided in the cabinet and outputs the output of the circuit board to the outside, the present invention constructs a loop composed of a filter means ( 142 ) having a filter capacitor ( 142   a ), an output terminal, a cabinet, and wires ( 142   b,    142   c ) for connecting these parts. The wire ( 142   c ) connected to the cabinet is connected to a position close to the output terminal, and reduces the size of the loop. In addition, a shield ( 102 ) is provided between the filter means and the circuit board.

Description:
TECHNICAL FIELD 
       [0001]    The present invention relates to noise filters in an electronic device that performs power conversion and the like. 
       BACKGROUND ART 
       [0002]    An electric vehicle and/or a plug-in hybrid vehicle have mounted thereon an inverter device that drives a motor with a high-voltage battery for power drive and a low-voltage battery for operating auxiliary machines, such as a light and a radio of the vehicle. Such a vehicle has mounted thereon a DC/DC converter device (power conversion device) that performs the power conversion from a high-voltage battery to a low-voltage battery or the power conversion from a low-voltage battery to a high-voltage battery. 
         [0003]    Some power conversion devices have coupled thereto filter circuits, such as an input filter circuit on the input side of a power conversion circuit and an output filter circuit on the output side of the power conversion circuit, as one of the purposes for reducing noise that mixes into an electronic device and the like arranged outside the power conversion device (e.g., see Patent Literature 1). 
       CITATION LIST 
     Patent Literature 
       [0000]    
       
         Patent Literature 1 JP-2004-368388 
       
     
       SUMMARY OF INVENTION 
     Technical Problem 
       [0005]    In an input filter circuit and an output filter circuit coupled to a power conversion device, the parasitic inductance of the filter circuit might increase and the noise radiated from a power conversion circuit and propagating in space and/or the electromagnetic noise caused by an eddy current flowing in a housing might be superimposed on the filter circuit, so that the electromagnetic induction might degrade the filter performance. 
         [0006]    The present invention has been made in order to solve the above-described problem, and provides an electronic device that reduces noise radiated from a circuit and thereby secures the noise reduction effect of a filter. 
       Solution to Problem 
       [0007]    In order to solve the above-described problem, the present invention employs the configurations defined by the appended claims. According to an aspect of the present invention, an electronic device includes: a housing; a circuit board provided in the housing; and an external terminal for outputting an output of the circuit board to an outside or for entering the circuit board from an outside, the external terminal extending through a through-hole provided in the housing, wherein a filter unit with a filter capacitor, the external terminal, the housing, and wirings for couples these parts constitute a loop, and wherein a wiring coupled to the housing is coupled to a position close to the external terminal so as to reduce the loop. 
       Advantageous Effects of Invention 
       [0008]    According to an aspect of the present invention, spatially-coupling of the noise from a circuit board to a filter unit and the like can be suppressed and thereby the noise reduction effect of the filter can be secured. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0009]      FIG. 1  is an external perspective view of a DC/DC converter device according to an embodiment of the present invention. 
           [0010]      FIG. 2  is a view illustrating the circuit configuration of the DC/DC converter device according to the embodiment of the present invention. 
           [0011]      FIG. 3  is an exploded view illustrating the component arrangement in the DC/DC converter device according to the embodiment of the present invention. 
           [0012]      FIG. 4  is a perspective view illustrating the component arrangement in a housing of the DC/DC converter device according to the embodiment of the present invention. 
           [0013]      FIG. 5  is a perspective view illustrating the component arrangement in the housing of the DC/DC converter device according to the embodiment of the present invention, and an external view of an output bus bar and output terminal for outputting the output of a step-up circuit board to the outside and a filter circuit comprising a ferrite and a capacitor substrate. 
           [0014]      FIG. 6  is a view illustrating the component arrangement of a step-up circuit section according to the embodiment of the present invention. 
           [0015]      FIG. 7  is a perspective view illustrating the component arrangement of an output filter according to the embodiment of the present invention. 
           [0016]      FIG. 8  is a perspective view illustrating the component arrangement of the output filter according to the embodiment of the present invention. 
           [0017]      FIG. 9  is a cross sectional view illustrating the connection between the output filter and the output terminal according to the embodiment of the present invention. 
           [0018]      FIG. 10  is a cross sectional view illustrating the connection between an output filter and an output terminal  122  according to an alternative embodiment of the present invention. 
       
    
    
     DESCRIPTION OF EMBODIMENTS 
       [0019]    Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. 
         [0020]      FIG. 1  is a perspective view illustrating an external view of a DC/DC converter device  100 . The DC/DC converter device is applied to an electric vehicle and the like, and performs the power conversion from a high-voltage battery to a low-voltage battery or the power conversion from a low-voltage battery to a high-voltage battery. 
         [0021]    The DC/DC converter device  100  is described.  FIG. 2  is a view illustrating the circuit configuration of the DC/DC converter device  100 . As illustrated in  FIG. 2 , the DC/DC converter device  100  of the embodiment corresponds to a bidirectional DC/DC converter device. Therefore, a step-down circuit and a step-up circuit employ a synchronous rectification configuration instead of a diode rectification configuration. Moreover, in order to obtain a high output power by HV (High Voltage)/LV (Low Voltage) conversion, high-current components are employed for switching elements to increase the size of a smoothing coil. 
         [0022]    Specifically, both the HV side and the LV side employ an H-bridge type synchronous rectification switching circuit configuration (H 1 -H 4 ) using a MOSFET with a recovery diode. In switching control, zero-cross switching is achieved at a high switching-frequency (100 kHz) using a LC series resonant circuit (Cr, Lr), so as to improve the conversion efficiency and thereby reduce the heat loss. In addition, an active clamp circuit is provided so as to reduce the loss due to a circulating current during the step-down operation, and furthermore the occurrence of a surge voltage during switching is suppressed so as to reduce the breakdown voltage of the switching elements, thereby achieving a reduction in the breakdown voltage of the circuit components and miniaturizing the DC/DC converter device. 
         [0023]    Furthermore, in order to secure a high output power on the LV side, a full-wave rectification type current doubler scheme is employed. Note that, in achieving an increase in output power, a high output power is secured by simultaneously activating a plurality of switching elements in parallel. In the example of  FIG. 2 , four switching elements are arranged in parallel, like SWA 1 -SWA 4  and SWB 1 -SWB 4 . Moreover, an increase in output power is achieved by arranging two circuits of switching elements and small-sized reactors, i.e., smoothing reactors, (L 1 , L 2 ) in parallel so as to have symmetry. By arranging two circuits of small-sized reactors in this manner, miniaturization of the entire DC/DC converter device can be achieved as compared with the case of arranging one large-sized reactor. 
         [0024]      FIGS. 3 ,  4 , and  5  are views illustrating the component arrangement in the DC/DC converter device  100 .  FIG. 3  is an exploded perspective view of the DC/DC converter device  100 . 
         [0025]    As illustrated in  FIG. 3 , the circuit components of the DC/DC converter device  100  are housed in a metal (e.g., aluminum die-cast) housing  101 . A case cover  111  is fixed to the opening of the housing  101  with a volt. A main transformer  133 , an inductor element  134 , a step-down circuit section  131  having switching elements H 1 -H 4  mounted thereon, a step-up circuit section  132  having a switching element  136  mounted thereon, and the like are placed in the bottom surface section inside the housing  101 . 
         [0026]    Note that, for the correspondence with the circuit diagram of  FIG. 2 , the main transformer  133  corresponds to a transformer Tr, the inductor element  134  corresponds to the reactors L 1  and L 2  of the current doubler, and the switching element  136  corresponds to the switching element SWA 1 -SWA 4  and SAWB 1 -SWB 4 , respectively. The switching elements S 1 , S 2 , and the like of  FIG. 2  are also mounted on the step-up circuit section  132 . 
         [0027]    The switching elements H 1 -H 4  are provided inside the step-down circuit section  131 . The switching elements H 1 -H 4  are mounted on a metal substrate  139  having patterns formed therein, and the back side of the metal substrate is fixed to the housing bottom surface so as to closely contact thereto. The step-up circuit section  132 , on which the switching element  136  is mounted, also comprises a metal substrate similarly. 
         [0028]    A control circuit that controls the switching elements provided in the step-up circuit section  132  and in the step-down circuit section  131  is mounted on the control circuit board  130 . The control circuit board  130  is fixed onto a metal base plate  137 . The base plate  137  is fixed by a plurality of supports  101   a  projecting upward from the bottom surface of the housing  101 . Thus, the control circuit board  130  will be arranged above the heat generating components (the main transformer  133 , the inductor element  134 , and the like) arranged in the housing bottom surface section, via the base plate  137 . 
         [0029]    Because the base plate  137  is formed of metal, the heat generated in the control circuit board  130  is transferred to the support  101   a  and the housing  101 . Moreover, the base plate  137  functions as a shielding member for radiation heat from the heat generating components provided in the housing bottom surface section, and also functions as a shield that shields the switching radiation noise from the switching elements by using copper material and the like. 
         [0030]      FIG. 4  is a perspective view illustrating the component arrangement of the step-up circuit section  132  in the DC/DC converter device  100  and an external view of the housing (case)  101 .  FIG. 5  is a perspective view illustrating the component arrangement of the step-up circuit section  132  in the DC/DC converter device  100 , and an external view of an output bus bar  121  and output terminal  122  for outputting the output of the step-up circuit section  132  to the outside, and the LC filter circuit comprising a ferrite core  141  and an output filter  142 .  FIG. 6  is a plan view of the step-up circuit section  132 . 
         [0031]    The ferrite core  141  and the output filter  142  constitute the LC filter circuit that is installed in order to reduce the output noise of the DC/DC converter device  100 , and constitutes a π-type LC filter circuit together with the smoothing capacitor  138  mounted on the substrate of the step-up circuit section  132 . Note that the circuit configuration is intended to reduce noise in the output and therefore is not limited to the π-type LC filter circuit. The output terminal  122  functions as an output terminal in converting the power from the HV side to the LV side, while in converting the power from the LV side to the HV side, it functions as an input terminal. While the converter of the embodiment is capable of performing power conversion in both directions, i.e., to the HV side and to the LV side, there is also a converter that performs power conversion in only one direction. 
         [0032]    Between the LC filter circuit and the step-up circuit section  132 , a shield wall  102  formed integrally with the housing  101  is formed. The output bus bar  121  bypasses the shield wall  102 , and electrically couples the step-up circuit section  132 , the ferrite core  141 , the output filter  142 , and the output terminal  122 . With the shield wall  102 , as illustrated in  FIG. 5 , even when the LC filter circuit, the step-down circuit section  131 , and the step-up circuit section  132  are inside one and the same housing of the housing  101 , it is possible to prevent the switching radiation noise due to the switching elements of the step-down circuit section  131  and the step-up circuit section  132  from being superimposed on the LC filter circuit and prevent the noise reduction effect of the filter from being unable to be obtained. Accordingly, there is no need to prepare a separate housing for the LC filter circuit. 
         [0033]    At least if the output terminal  122 , in which the current whose noise is removed by the LC filter circuit flows, is isolated by the shield wall  102  from the step-up circuit section  132  and the like, the shield effect can be obtained. However, preferably, shielding also the output filter  142  and the ferrite core  141  with the shield wall  102  would further increase the shielding distance near the output terminal  122  and thus further increase the shielding effect. Note that, in the embodiment, the smoothing capacitor  138  is situated at a position branched from the path from the step-up circuit section  132  to the output terminal  122 . Therefore, even if the smoothing capacitor  138  is shielded, the effect is small, and furthermore because the smoothing capacitor  138  is provided on the board of the step-up circuit section  122 , the smoothing capacitor  138  is not an object to be shielded with the shield wall  102 . 
         [0034]    Moreover, using a conductive seal material in order to fill the gap between the shield wall  102  and the case cover  111 , the shield effect can be increased further. 
         [0035]    Note that the shield wall  102  may be formed integrally with the base plate  137 . In this case, because the base plate  137  is fixed to the housing  101  with a screw (not shown), the position of the screw is the most potentially-stable position in the base plate  137 . Therefore, in the case where the shield wall  102  is formed from the base plate  137 , a screw hole is preferably installed close to the shield wall  102 . 
         [0036]    The shield wall  102  is preferably formed from both the housing  101  and the base plate  137 . By installing the shield wall  102  and the shield wall of the base plate  107  so as to intersect with each other when seen from the housing, the distance of the LC filter circuit from the step-down circuit section  131  and the step-up circuit section  132  that are noise sources can be increased, the noise to be mixed can be reduced, and the shield effect can be increased. 
         [0037]    Note that, in the embodiment, as illustrated in  FIG. 4 , the DC/DC converter device  100  includes the output terminal  122  for outputting the output of the step-up circuit section  132  to the outside, the output terminal  122  extending through the through-hole  103  provided from the housing  101 . In the periphery of the through-hole  103 , a projection  104  is formed so as to cover the output terminal, where the housing is thickened. Thus, even if noise is spatially superimposed between the filter circuit and the through-hole  103 , the noise can be prevented from leaking to the outside. 
         [0038]    Moreover, as illustrated in  FIGS. 4 ,  5 , and  6 , a GND boss  105  and a GND boss installing hole  105   a  are arranged in the center of the step-up circuit section  132 . Thus, bus bars  123  on the board of the step-up circuit section  132  arranged between two inductor elements  134  for voltage conversion and the smoothing capacitor  138  can be symmetrically arranged, and the values of the parasitic inductance of the respective bus bars  123  can be set equal. Accordingly, the loss can be reduced. 
         [0039]    Because the chassis of a vehicle usually the largest conductor inside the vehicle, in a vehicle with a DC/DC converter the housing  101  coupled to the chassis is most potentially-stable. Therefore, one end of the smoothing capacitor  138  is coupled to GND (ground), and by installing the GND boss  105  very close to this place, the parasitic inductance between the smoothing capacitor  138  and GND can be minimized. Thus, the noise reduction effect of the smoothing capacitor  138  can be secured. 
         [0040]    Moreover, the GND boss  105  is installed in proximity to the smoothing capacitor  138 , so that there is no need for the GND bus bar  124 , which couples the smoothing capacitor  138  and the GND boss  105 , to be installed running in parallel to the bus bar  123 . It is therefore possible to prevent the switching noise from the bus bar  123  from electromagnetically coupling to the GND bus bar  124 . Accordingly, potential fluctuations of the housing  101  can be prevented and the noise level of the DC/DC converter device  100  can be reduced. 
         [0041]      FIG. 7  and  FIG. 8  are the perspective views illustrating an external view of the output filter  142 . Ceramic capacitors  142   a  are mounted on a filter substrate  142   d . The filter substrate  142   d  includes a filter output bus bar  142   b  for electrically coupling the capacitor  142   a  and the output terminal  122 , a GND bus bar  142 C for electrically coupling the capacitor  142   a  and the housing  101 , and a fixture  142   e  for mechanically fixing the filter substrate  142   d  to the housing  101 . 
         [0042]      FIG. 9  is a cross sectional view illustrating the connection between a capacitor substrate  142  and the output terminal  122 . The arrows in the view each indicate the direction in which a noise current flowing into the filter circuit flows. 
         [0043]    As illustrated in  FIG. 9 , the filter output bus bar  142   b  and the GND bus bar  142 C are arranged so as to face in proximity to each other. This enables to reduce the area of a loop formed by the filter output bus bar  142   b , the filter base plate  142 , and the GND bus bar  142 C. Therefore, the superposition of switching noise from the step-down circuit section  131  and/or the step-up circuit section  132  can be reduced. 
         [0044]    As illustrated in  FIG. 9 , the output terminal  122  and the filter substrate  142   d  are coupled via the filter output bus bar  142   b  and the GND bus bar  142 C. Moreover, in order to fix, to the housing  101 , the output terminal  122  and the filter output bus bar  142   b  coupled to the output terminal  122 , an output terminal upper part  122   a  is fixed to an output terminal lower part  122   b  fixed to the housing  101 , by fastening a large screw  144  across the bus bar  142   b . Accordingly, the output terminal  122  and the filter output bus bar are fixed to the projection  104  via an insulator  143 . Due to a high-current output from the DC/DC converter device, the large screw  144  has a diameter large than the screw for fixing the step-up circuit section and the like to the housing. Although a torque will be generated by this large screw, the bus bar can withstand this torque. 
         [0045]    In order to secure the performance of the capacitor  142   a , a certain degree of size is required and a plurality of capacitors may be used. Moreover, there are many capacitors each having terminals on both sides, in the market. When coupled to the output terminal  122  and the housing  101  using such a capacitor, the connection position with the housing is likely to be far away from the output terminal and thus the area of a loop formed by the output terminal, the capacitor, the housing, and the wiring will increase. Then, the parasitic inductance of the filter circuit will increase, and the noise radiated from the power conversion circuit and propagating in space and/or the electromagnetic noise caused by an eddy current flowing in the housing might be superimposed on the filter circuit, so that the electromagnetic induction might degrade the filter performance. 
         [0046]    In the embodiment, the connection position between the GND bus bar  142 C and the housing  101  is set closer to the output terminal  122  than the capacitor  142   a  and the substrate  142   d  so as to reduce the loop. Accordingly, the parasitic inductance and electromagnetic induction can be reduced and the filtering function can be secured. Here, the position close to the output terminal  122  indicates the fact that the shortest distance to either one part of the output terminal  122  is small when viewed three-dimensionally. 
         [0047]    Moreover, the filter output bus bar  142   b  and the GND bus bar  142 C are arranged so as to face each other, so that the noise currents flowing into the filter circuit flow opposite to each other. As a result, a U-turn current is formed between the filter output bus bar and the GND bus bar. Accordingly, a magnetic flux generated in the periphery of the filter output bus bar and a magnetic flux generated in the periphery of the GND bus bar cancel out each other, so that a reduction in the parasitic inductance can be achieved. 
         [0048]    Note that, as illustrated in  FIG. 9 , the connection position between the filter output bus bar  142   b  and the filter substrate  142   d  and the connection position between the GND bus bar  142 C and the filter substrate  142   d  are on the same side of the filter substrate  142   d . Thus, the both bus bars will be mounted facing each other until reaching a position where both bus bars are coupled to the substrate. Therefore, the superposition of noise and an increase of inductance can be prevented. 
         [0049]    Moreover, the filter substrate  142   d  comprises two layers, wherein inner layer wirings of the substrate are mounted so as to face each other on the output side where the capacitor  142   a  is coupled to the filter output bus bar  142   b  and on the GND side where the capacitor  142   a  is coupled to the GND bus bar  142 C. Thus, an increase in the parasitic inductance of the substrate pattern of the filter substrate  142   d  can be also prevented. 
         [0050]    Note that, as the filter substrate  142   d , a more-layer substrate instead of a two-layer substrate may be used. Because the use of a multilayer substrate can shorten the distance between layers to enhance the coupling between the output side and the GND side, an increase in the parasitic inductance can be further prevented. 
         [0051]    The substrate  142   d  of the output filter is arranged so that the plane direction thereof is set along the longer direction of the output terminal  122 . This is because arranging the substrate  142   d  so as to face a direction different from the direction of the substrate of the step-up circuit section  132  is more space-saving. In particular, as with the embodiment, the substrate  142   d  may be arranged perpendicular to the substrate of the step-up circuit  132  and the like so as to be set along the output terminal  122 . 
         [0052]    When the housing  101  includes the projection  104  projecting inward, the GND bus bar  142 C may be coupled to the upper surface of the projection  104 . Because the projection  104  has the through-hole  103  through which the output terminal  122  extends, the projection  104  can be coupled to a position close to the output terminal  122  and is also suitable for vertically placing the substrate  142   d  as illustrated in  FIG. 9 . 
         [0053]    Moreover, as illustrated in  FIG. 9 , in the base plate  137 , other than the shield wall  102  formed between the output filter  142  and the step-up circuit section  32 , a shield wall  137   a  is formed for the purpose for separating the output filter  142  from the output terminal  122  and the output bus bar  121 . Thus, without preparing a separate housing, the output filter  142  can be placed in a room substantially separated from the room of the step-down circuit section  131  and the step-up circuit section  132 , so that the superposition of noise onto the filter substrate  142   d  can be reduced and a voltage with sufficiently reduced noise can be output from the DC/DC converter device. 
       Other Embodiments 
       [0054]    The DC/DC converter device according to an aspect of the present invention can be modified to DC/DC converter devices according to various kinds of embodiments. For example, as illustrated in  FIG. 10 , the filter substrate  142   d  may be mounted in parallel to the housing bottom surface in accordance with the space of the housing. Also in this case, the connection portion between the GND bus bar  142   d  and the housing  101  is closer to the output terminal  122  than the capacitor  142   a , and the loop is also reduced. 
         [0055]    Moreover, the filter substrate  142   d  and the output terminal  122  may be directly coupled without via the filter output bus bar  142   b  and the GND bus bar  142 C. The inductance corresponding to the filter output bus bar and the GND bus bar can be reduced and the filter substrate  142   d  can be mounted. 
         [0056]    Note that, instead of mounting a ceramic capacitor onto the substrate, a filter capacitor integrated with the bus bar may be used. A filter output bus bar and a GND bus bar are caused to face each other and mounted integrally with a filter capacitor, so that the superposition of noise can be prevented, an increase in inductance can be also prevented, and the same effect as the effect obtained when a ceramic capacitor is used can be obtained. 
         [0057]    Moreover, when the output power of the DC/DC converter device is small and the filter substrate  142   d  can withstand the torque of the large screw of the output terminal, the output terminal and the capacitor substrate  142  can be integrated. Therefore, the filter output bus bar  142   b  and the GND bus bar  142 C may be omitted. Omission of the both bus bars enables to further reduce the parasitic inductance. 
         [0058]    Note that, the above description is just exemplary, and is neither limited to nor constrained from the correspondence between the contents of the above-described embodiments and the contents of the claims at all in interpreting the invention. For example, in the above-described embodiments, the LV side of the DC/DC converter has been taken as an example and described, but the present invention may be applied to the HV side. Moreover, a power conversion device mounted in vehicles, such as PHEV or EV, has been described as an example, but the present invention is not limited thereto and can be also applied to the power conversion devices used for construction machinery and the like, and the vehicles of a railroad, and furthermore can be also applied to electronic devices other than the power conversion devices. 
       REFERENCE SIGNS LIST 
       [0000]    
       
         
           
               100 : DC/DC converter device 
               101 : housing 
               102 : shield wall 
               103 : through-hole 
               104 : projection 
               105 : GND boss 
               105   a : GND boss installing hole 
               111 : top cover 
               121 : output bus bar 
               122 : output terminal 
               123 : bus bar 
               124 : GND bus bar 
               130 : control circuit substrate 
               131 : step-down circuit section 
               132 : step-up circuit section 
               133 : main transformer 
               134 : inductor element for voltage conversion 
               135 : power semiconductor module 
               136 : switching elements H 1 -H 4   
               137 : base plate 
               137   a : shield wall 
               141 : ferrite core 
               142 : output filter 
               142   a : ceramic capacitor 
               142   b : filter output bus bar 
               142 C: GND bus bar 
               142   d : output filter substrate 
               143 : insulator 
               144 : large screw