Abstract:
A high-density pass-through filter apparatus slips over the terminal blade of a standard pass-through electrical connector within an opening in the bulkhead of an electronic module to which the connector is fastened. The filter apparatus retains a large number of axially oriented and axially terminated capacitive filter components which are electrically coupled at one end to the connector terminal and at the other end to a peripheral ring that resiliently engages the periphery of the bulkhead opening.

Description:
TECHNICAL FIELD 
     The present invention relates to capacitive pass-through filters, and more particularly to high-density pass-through filters for high current pass-through electrical connectors. 
     BACKGROUND OF THE INVENTION 
     Pass-through electrical connectors designed to be mounted on the case or bulkhead of an electronic module are frequently provided with capacitive pass-through filter elements for suppressing high frequency energy electromagnetically coupled to the connector terminals or the cables coupled to them. Incorporating the filter components into the connector itself is beneficial from an electrical standpoint because the filter components can be densely packed in relatively close proximity to the connector terminal. However, connectors with integral filter components tend to be both large and costly, particularly in the case of high current connectors. Accordingly, what is needed is a more cost effective way of providing high-density pass-through filtering for electrical connectors. 
     SUMMARY OF THE INVENTION 
     The present invention provides an improved high-density pass-through filter apparatus that slips over the terminal blade of a standard pass-through electrical connector within an opening in the bulkhead of an electronic module to which the connector is fastened. The filter apparatus retains a large number of axially oriented and axially terminated capacitive filter components which are electrically coupled at one end to the connector terminal and at the other end to a peripheral ring that resiliently engages the periphery of the bulkhead opening. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is an exploded isometric view of the filter apparatus of the present invention. 
         FIG. 2  is a fully assembled isometric view of the filter apparatus of  FIG. 1 . 
         FIG. 3  an exploded isometric view of a pass-through electrical connector, the filter apparatus of  FIGS. 1-2 , an optional grounding ferrule and the metal case of an electronic module. 
         FIG. 4  is a partially assembled isometric view of the electrical connector, filter apparatus, grounding ferrule and module case of  FIG. 3 . 
         FIG. 5  is a fully assembled isometric view of the electrical connector, filter apparatus, grounding ferrule and module case of  FIG. 3 . 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring to the drawings, and particularly to  FIGS. 1 and 2 , the reference numeral  10  generally designates a preferred embodiment of a high-density pass-through filter apparatus according to the present invention. The filter apparatus  10  of the illustrated embodiment is configured to receive a rectangular connector terminal blade and to fit within a circular bulkhead opening, but it will be appreciated that other configurations are also possible. 
     As best seen in the exploded view of  FIG. 1 , the filter apparatus  10  includes an insulative base plate  12 , a plurality of axially oriented and axially terminated (i.e., surface-mount) capacitors  14 , two conductive pads  16 ,  18 , a set of terminal contactors  20   a ,  20   b , and a bulkhead contactor  22 . These components are axially joined as explained below to form the assembled filter apparatus  10  depicted in  FIG. 2 . 
     Base plate  12  has a large rectangular axial through-hole  24  sized in cross-section to loosely receive the external terminal of a standard pass-through electrical connector, and a plurality of small square or rectangular axial through-holes  26  sized in cross-section to snugly receive the axially oriented capacitors  14 . Additionally, each axial face of base plate  12  includes a raised peripheral shoulder  28  and a raised shoulder  30  surrounding the large rectangular through-hole  24 . The capacitors  14  are identical in size, and each has an axial dimension (length) slightly larger than the axial dimension of the base plate through-holes  26 . 
     The conductive pads  16  and  18  are identical, each sized to fit radially within the raised peripheral shoulders  28 , and each having a large rectangular axial through-hole  32 ,  34  sized in cross-section to receive the raised shoulders  30 . The conductive pads  16  and  18  are mounted on opposite axial faces of the base plate  12 , with the raised shoulders  30  of base plate  12  passing through the respective through-holes  32 ,  34 . When so assembled, the conductive pads  16  and  18  are peripherally bounded by the respective raised peripheral shoulders  28  of base plate  12 , and are physically in contact with the terminals formed on opposite axial ends of the capacitors  14 . Since the capacitors  14  are each contacted at one end by the conductive pad  16  and at the other end by the conductive pad  18 , they are electrically connected in parallel between the two conductive pads  16  and  18 . Preferably, conductive pads  16  and  18  are formed of a compliant material such as conductive foam to ensure reliable electrical contact with the terminals of capacitors  14  despite minor variations in the capacitor dimensions. The conductive pads  16  and  18  can be snapped or glued in place within the raised peripheral shoulders  28 . Alternatively, the conductive pads  16  and  18  can be formed by dispensing a layer of conductive adhesive, or even solder, on the opposing axial faces of base plate  12 . 
     The terminal contactors  20   a ,  20   b  each include a semi-circular base portion  36   a ,  36   b  and a linear array of axially extending prongs  38   a ,  38   b . The base portions  36   a ,  36   b  of contactors  20   a ,  20   b  abut the outboard face of conductive pad  16  within the raised peripheral shoulder  28  of base plate  12 , with the prongs  38   a ,  38   b  extending into the large rectangular axial through-hole  24  of base plate  12 . As explained below, the prongs  38   a ,  38   b  electrically contact the external terminal of the electrical connector so that the terminal is electrically connected to each of the capacitors  14  through the conductive pad  16 . The contactors  20   a ,  20   b  can snap into place within the raised peripheral shoulders  28 , or can be held in place with a conductive adhesive. In the case where the conductive pad  16  is formed of conductive adhesive or solder, the conductive pad  16  will serve not only to electrically tie the contactors  20   a ,  20   b  to the capacitor terminals, but also to physically secure the contactors  20   a ,  20   b  in place. 
     The bulkhead contactor  22  has a circular base portion  40  with a large rectangular axial through-hole  42  sized in cross-section to receive the raised shoulder  30  of base plate  12 , and a circular peripheral array of axially extending prongs  44 . The bulkhead contactor  22  is brought into abutment with the conductive pad  18 , with the raised shoulder  30  of base plate  12  passing through the through-hole  42 . When so assembled, the prongs  44  engage the radial or lateral periphery of base plate  12 , and the bulkhead contactor  22  is electrically connected to each of the capacitors  14  through the conductive pad  18 . The prongs  44  and the periphery of base plate  12  can be provided with complementary snap features to mechanically fasten the contactor  22  to the base plate  12 . Alternately or in addition, conductive adhesive may be used to secure contactor  22  to the conductive pad  18  and/or base plate  12 . And in the case where the conductive pad  18  is formed of conductive adhesive or solder, the conductive pad  18  will serve not only to electrically tie the bulkhead contactor  22  to the capacitor terminals, but also to physically secure the bulkhead contactor  22  in place. 
       FIGS. 3 ,  4  and  5  illustrate an application of the filter apparatus  10  to an electrical connector  50  such as a DC power bus connector that is attached to the sidewall  52  of a cast-metal (aluminum or zinc, for example) housing  54 . The plastic body of connector  50  is insert molded around a single electrical terminal having an exposed rectangular blade  56 , and includes a header  58  and a mounting flange  60 . The filter apparatus  10  is slipped over the terminal blade  56  as seen in  FIGS. 3-4 , and the peripheral prongs  44  of bulkhead contactor  22  electrically contact the inner periphery of a sidewall opening  62  through which the terminal blade  56  passes when the connector  50  is mounted on sidewall  52  as seen in  FIG. 5 . In the illustrated embodiment, a grounding ferrule  64  is placed in the opening  62  to serve as an electrical intermediary between the housing  54  and the prongs  44  of bulkhead contactor  22 , but the use of grounding ferrule  64  is optional. Once the connector  50  is secured in place on sidewall  52 , the inboard end of terminal blade  56  is fastened to a bus structure  66  in housing  54  as shown in  FIG. 5 . 
     In summary, the present invention achieves a very cost effective way of providing high-density pass-through filtering for an electrical connector. Packaging the filter apparatus  10  as a component that slips over a terminal blade  56  of a pass-through electrical connector  50  allows the use of an inexpensive standard connector, and the dense arrangement of axially oriented and axially terminated capacitive filter components results in a filter with both low inductive impedance and high capacitance. 
     While the present invention has been described with respect to the illustrated embodiment, it is recognized that numerous modifications and variations in addition to those mentioned herein will occur to those skilled in the art. For example, the described approach to pass-through filtering may be extended to connectors having more than one terminal, the connector terminal may be round instead of rectangular, and so on. Accordingly, it is intended that the invention not be limited to the disclosed embodiment, but that it have the full scope permitted by the language of the following claims.