Modular transformer structure providing enhanced leakage inductance and winding isolation

A transformer structure of modular parts comprises a bobbin for supporting the primary winding, and one or more sets of end pieces sized to successively fit one over another in a nesting arrangement. The end piece flanges provide part of the secondary winding support surface. Further winding surfaces may be provided by adding further sets of end pieces which nest one within the other. The end piece flanges afford added inter-winding isolation. A double flange version of the end pieces affords still greater isolation. While applicable to small-scale transformers, the concept can also be adapted for medium and larger-size transformer designs.

FIELD OF THE INVENTION 
This invention relates to power supply transformers and, more specifically, 
to a modular design for supporting the primary and other windings in 
transformers to provide enhanced inter-winding isolation and which is 
adaptable to multiple applications. 
BACKGROUND OF THE INVENTION 
Small-scale transformers for use in personal computers and similar 
equipments typically must be designed to meet the power supply 
requirements of the particular equipment. Designing and manufacturing 
individually customized transformers is costly, however. Workers in the 
art use where possible pre-existing configurations of winding bobbins, end 
caps, terminal pieces, etc. in new equipment power supplies. Often, 
however, use in further small transformer applications is not possible 
without making costly design adaptations. 
Moreover, in adapting existing small scale transformer structures to new 
applications, it also is necessary for standard safety margins to be met. 
Meeting safety requirements, however, can further complicate the use of 
existing small-scale transformer structures in new equipments. In short, 
the current art lacks a transformer structure which, with little or no 
design modification, can find use in a variety of different equipments and 
also can successfully meet isolation safety margins in any of the design 
variations. 
SUMMARY OF THE INVENTION 
This invention is a small-scale transformer structure made up of modular 
parts. In its basic design, the structure comprises a centerpiece with 
bobbin for containing the primary winding. One or several pairs of end 
pieces along with interwinding tapes that support the secondary winding 
mount on the respective ends of the centerpiece. These end pieces are 
sized to successively fit one over the other in gang fashion to provide 
more winding options. The flange or shoulder of each successive ganged end 
piece provides a pan of the surface for the further winding, and serves as 
margins for meeting safety requirements. The end pieces also contain slots 
or grooves that secure the winding lead wires en route to the terminals. 
In a particular embodiment of the invention, a female fit of the 
bobbin-contacting end pieces over the primary bobbin ends is provided by a 
pair of concentric skirts forming a double flange that extends from the 
end piece. The skirts place continuous insulative material over the 
exterior surface of the bobbin end and also into the underside on the 
bobbin end, to provide added electrical isolation between the windings and 
the core when the transformer is fully assembled. 
The structures are completed by two end caps serving as terminal pieces 
into which the exterior faces of the end pieces fit. In both embodiments, 
the end caps provide a means for mounting of the assembly onto a circuit 
board of the equipment. Besides being modular, the structure reduces or 
eliminates the need for margin tapes and sleevings for meeting insulation 
requirements.

DETAILED DESCRIPTION OF AN ILLUSTRATIVE EMBODIMENT 
FIGS. 1 and 5 illustrate the inventive embodiment in which several end 
pieces with single flange are ganged to provide additional winding 
capability. The centerpiece 10 comprises a 4-sided hollow core with an 
exterior surface 16 and end flanges 11 having wire feed slots 12. An iron 
core (not shown) usually is included in the interior of the centerpiece. 
In accordance with the invention, end pieces (hereinafter referred to as 
"first, second, third, fourth end pieces") may be ganged or stacked onto 
centerpiece 10. Thus, two of the first end pieces 40, consisting of a 
right-hand and a left-hand member, assume a position on either end of the 
centerpiece 10. The end pieces 40 are the interior-most pieces, seating 
next to the bobbin. If further windings are needed, a set of second end 
pieces 41 are ganged atop the end pieces 40. Similarly, if still further 
windings are needed for a given customized transformer, end pieces 42 and 
43 may be successively ganged in sets. FIG. 1 shows several left-hand end 
pieces 40-43 ganged atop each other at the left end of centerpiece 10, 
with the right-hand end pieces 40-43 are depicted in exploded view. 
The end pieces 40-43 each consist of a 4-sided winding surface 14 having an 
outwardly-extending flange 15 formed on one of the ends of the piece 40. 
The flange 15 is slotted to allow passage of the winding leads and 
connection thereof to the terminals 34. The interior of the surface 14 of 
end piece 40 is dimensioned to fit snugly over the windings. Similarly, 
the interiors of each successive end piece 40-43 are dimensioned to fit 
around the next-interior adjacent end piece. 
To complete the assembly, each end of the centerpiece 10 mounts to an end 
cap 30. Centerpiece 10 fits over a rectangular shoulder 31 of the cap and 
abutts against the shoulder flange 32. The base 33 of the end cap 30 from 
which the flange 32 rises, contains several metallic connectors 34 to 
which the windings attach. 
FIG. 3 illustrates one example of the wiring of the transformer 
configuration of FIG. 1. A first primary winding 60 is applied; and one or 
more layers of insulative tape 61 are placed. The innermost end pieces 40 
install over the first primary winding. The secondary winding denoted 63 
installs over the tape layers 61, and extends onto the flange 14 of the 
end piece 40 opposite to where the primary winding is terminated. Further 
tape layers 62 are applied over the secondary windings, the tape extending 
fully over the flanges 14. By fully wrapping the tapes over the flanges of 
the end pieces, spacings required by safety considerations are more 
readily met. 
End piece 41 gangs onto and over the end piece 40. A second primary winding 
64 is placed over the tape layers 62, the tape extending onto the flange 
14 of end piece 41. A final top layer of tape 65 goes over the second 
primary winding 64. The leads of the three windings exit from the assembly 
through convenient ones of the slots 55 formed in the piece parts as shown 
in FIG. 1. 
In accordance with another embodiment of the invention illustrated in FIG. 
2, the end pieces advantageously may include a double flange that envelops 
both sides of the centerpiece end. This variation of end piece, denoted 
50, comprises two concentric skirts or flanges 51, 52 connected by a 
bottom web 53. This variation of end piece may also be ganged, as 
illustrated in FIG. 4. The centerpiece 10 and end cap 30 serve the same 
purpose as already described. A first primary winding 60 is applied. The 
flange 51 of this embodiment of end piece extends into the centerpiece 
interior. The flange 52 rides over the centerpiece end and insulatively 
envelops the end portion of the first primary windings. Then, as in the 
embodiment of FIG. 3, a tape layer 61 is applied, the secondary winding 63 
is laid as previously described, and a further tape layer 62 is applied to 
the secondary winding. If the application requires it, in accordance with 
this version of the invention, another double flange end piece denoted 70 
is installed. The interior skirt 71 of end piece 70 fits within the 
interior skirt 51 of end piece 50. The outside skirt 72 rides atop the rim 
of end piece 50 and extends over any secondary windings that may be 
present. A second primary winding then is applied, beginning on the flange 
72 and extending out over the tape 62. Further end pieces needed in the 
buildup may now be applied in gang fashion in the same manner as just 
described. The outermost winding is protected with a tape application such 
as layer 65. 
The inventive structure allows winding buildups without the end caps 30 
making physical contact with the windings. Advantageously, the end caps 
may be fabricated from phenolic resin material which does not warp from 
contact with solder. The other components may be fabricated from 
Rynite/nylon material. The inventive structure allows margin tape and 
sleeving to be eliminated. Further, the bobbin of the centerpiece 10 may 
be extended horizontally as needed in a given application if it is 
necessary to further reduce the leakage inductance. Alteratively, 
referring to FIG. 6, if higher leakage inductance can be tolerated in a 
given application, the same iron core size (not shown) can be maintained 
and the windings applied one over the other with an increase in the "X" 
dimension (distance between skirts). By increasing the flange width 
dimension "Y" the same transformer design can be used for higher voltage 
applications.