GB2099226A - Ribbon wound transformer and method of making same - Google Patents

Abstract

A transformer has windings formed by conductive wires (14) embedded in a plastic ribbon (10). The wires (14) run the length of the ribbon (10), and are alternated with filaments (16) of dielectric insulation inter-leaved between the wires. The ribbon is rolled up in a tight spiral (22) so that the conductive wires form a plurality of transformer windings (24) of planar spiral configuration with the dielectric filaments defining corresponding spiral disc-like elements (26) between the windings. Adjacent layers of the plastic ribbon roll are bounded together to form a self-supporting structure which is mounted on the transformer core. <IMAGE>

Description

SPECIFICATION Ribbon wound transformer and method of making same This invention relates to transformers. More particularly, this invention relates to a transformer of simple construction, incorporating a set of planar spiral windings capable of handling relatively large currents, and having desirable electrical characteristics including high breakdown voltage and relatively low inter-winding capacitance.

In our copending application No. 8133007, corresponding to United States application Serial No.

206,838, filed November 14, 1980, by Delip Bokil et al, there is disclosed a transformer comprising two rectangular substrates each carrying successive screen-printed, thick-film layers of dielectric insulation material with spiral planar windings embedded therein by use of hybrid processing techniques. This compact rugged tranformer is especially suitable for assembly with integrated circuit components in low-current applications such as isolation amplifiers.

However, there are other applications where higher level currents must be handled, e.g. DC-to-DC converters where current levels may be in the ampere range. It is an object of this invention to provide a transformer which can handle such higher current levels and yet have desirable properties such as high inter-winding breakdown voltage with suitably low inter-winding capacitance.

In carrying out this invention, in one illustrative embodiment thereof, a transformer is provided having windings of conductive wires carried by a ribbon formed of electrically insulating plastic material. The conductive wires are embedded in the ribbon as separate elements in side-by-side disposition extending the length of the ribbon, and alternated with inter-ieaved filaments of dielectric insulation material. The ribbon is rolled up in a tight spiral so that the embedded conductive wires are disposed in spiral configuration to define respective planar transformer windings separated by corresponding planar spiral filaments of dielectric material. The layers of rolled up ribbon preferably are secured together, as by means of inter-layer bonding to form a self-supporting winding structure which is mounted on a magnetic core.

The disc-like layers of spiral dielectric filament between the conductive spiral windings provide good inter-winding breakdown-voltage characteristics, advantageously with low inter-winding capacitance. The overall construction makes possible a simple and rugged transformer capable of economical manufacture. A preferred embodiment of the invention will now be described with reference to the accompanying drawings, in which: Figure 1 is a cross-sectional, isometric view of a section of ribbon constructed in accordance with one embodiment of the present invention; Figure 2 is a cross-sectional, isometric view showing the ribbon of Figure 1 wound into a tight roll to provide a plurality of planar spiral winding layers; and Figure 3 is an exploded, isometric view of a transformer incorporating the present invention.

Referring now to Figure 1,there is shown a ribbon generally indicated at 10 and formed of plastic insulating material 12. Embedded in the plastic are spaced elongate conductive wires 14 extending the length of the ribbon. The wires 14 are alternated across the ribbon with intervening filaments of dielectric insulating material 16, also extending the length of the ribbon.

The ribbon 10 may conventionally be formed by drawing the wires 14 and insulating filaments 16 together, side-by-side, through a bath of molten plastic material having good electrical insulating properties. When the plastic hardens, it protectively surrounds the wires and dielectric filaments. The ribbon 10 formed in this manner may for example accommodate up to twenty wires and dielectric filaments, thus forming up to ten separate transformer windings.

The next step in the procedure is to wind the ribbon 10 into a tight spiral roll 22 as illustrated in Figure 2, thereby forming corresponding planar spiral windings 24 of conductive wire 14, separated by planar disc-like elements 26 of spiral-wound dielectric filaments 16. Winding the ribbon into this form can readily be carried out on a tubular mandrel, using known techniques.

Preferably, adjacent layers of the ribbon are bonded together during winding, to form a selfsupporting solid structure somewhat like a roll of tape. Bonding may for example be effected by spraying the ribbon with a solvent to make it tacky, so adjacent layers will become cemented together as the solvent dries. Alternatively,a the ribbon material can be softened by heating, such as can be produced by passing electric current through the wires 14, or by directing hot air against the ribbon material as it is being wound.

Referring now to Figure 3, the last step in the procedure is to assemble the wound ribbon roll 22 with the transformer core, illustrated here as a pair of three-legged structures 28, 30. Other core structures may of course be used. The resulting complete transformer is a rugged unit, capable of operation at relatively high current levels, having good breakdown voltage characteristics, and suitably low interwinding capacitance.

The conductive wires 14 may for example be common magnet wire, e.g. between 3 to 10 mils in diameter. Such wires typically carry a tough insulation coating about 1/2 mil thick. The diameter of the interleaved dielectric filaments 16 should be about the same as that of the wires 14, and as close as possible thereto, even to the point of touching. The ribbon material thus would not introduce any additional spacing between the wires and the adjacent insulating filaments. If larger wire and filament sizes are utilized, the wire-to-wire spacing would increase due to the increased diameter of the insulating filament, further decreasing the inter-winding capacitance.

The insulating filaments 16 must have good physical flexibility for winding in coil form, a high voltage breakdown characteristic, and a suitably low dielectric-constant for low inter-winding capaci tance. Various materials may be used for this purpose, e.g. certain types of plastics, such as rayon-like material, basically cellulose acetate.

Connections to the outside of the wound roll 22 can be made directly, as through an extended portion 32 of the ribbon. The inside of the roll may have electrical connections made thereto by bringing the inner tail 34 of the ribbon out from the interior of the roll, as indicated in Figure 3. The ribbon can be folded across itself within the interior of the roll (not visible in Figure 3), e.g. at a 450 angle, so that the tail portion 34 will extend parallel to the axis of the roll and thence out from the interior to permit connections to be made to the winding ends.

If desired in order to prevent the folded-over section from establishing any inadvertent electrical connections between the windings, a strip of insulation or other separator may be utilized to cover the foldedover region.

It will be seen from the above description that a transformer has been provided having desirable electrical properties, and which is quite simple and rugged as well as economical to manufacture. Since various changes and modifications to suit particular operating requirements and environments will be apparent to those skilled in the art, the invention should not be considered to be limited to the examples chosen for purposes of illustration, and includes all changes and modifications which do not constitute a departure from the scope of the invention.

Claims (10)

1. A method of making a transformer comprising the steps of: forming a ribbon of insulating material having conductive wire and insulating filament alternatingly embedded therein, extending the length of the ribbon; winding said ribbon in a roll; and mounting said winding on a magnetic core.

2. The method set forth in Claim 1, including bonding adjacent layers of the ribbon to form a self-supporting multi-layer structure.

3. The method set forth in Claim 2, wherein said bonding step comprises applying a solvent on overlying portions of said ribbon as said ribbon is being wound for softening said portions before being rolled together.

4. The method set forth in Claim 2, wherein said bonding step comprises heating said ribbon of insulating material sufficiently so that the layers forming said roll are fused.

5. The method set forth in Claim 4, wherein said heating step is performed by causing an electric current to flow through said conductive wires.

6. Awound ribbon transformer for handling relatively large current levels and providing and increased voltage breakdown level between windings; comprising: a multiple layerwinding comprised of multiple layers of wound ribbon; said ribbon having a plurality of alterating conductive wires and insulating filaments; said ribbon being comprised of insulating material which surrounds said alternating wires and filaments; means for maintaining said ribbon in wound-up roll form; and a magnetic core having said wound ribbon mounted thereon.

7. The wound ribbontransformersetforth in Claim 6, wherein said magnetic core has a central leg which fits into the central opening of said wound ribbon.

8. The wound ribbon transformer set forth in Claim 6 or 7, in which said alternating wire and said filaments have the same diameter.

9. A method of making a transformer, substantially as hereinbefore described with reference to the accompanying drawings.

10. A wound ribbon transformer substantially as hereinbefore described with reference to the accompanying drawings.