GB2264396A - Centre-tapped, z-folded, multi-layer winding for a multi-pole transformer - Google Patents

Abstract

A transformer includes a multi-layer primary winding having at least one turn about each pole of at least two pairs of magnetic poles (20-21, 22-23). A center-tapped secondary winding (30) is constructed from a plurality of secondary conductive film portions (32) disposed on one surface of a secondary dielectric membrane (34) and z-folded to form a multi-layer secondary winding interleaved with the multi-layer primary winding. The secondary winding has a pair of first terminals (36) along alternate edges perpendicular to the folds on opposite sides of the multi-layer winding stack, a pair of center-tap terminals (38) and a pair of third terminals (40) along each fold of the stack. Holes are provided in the folds of the primary winding in order to allow electrical connection of the first terminals. Furthermore, holes are provided in alternate folds of the secondary winding in order to allow electrical connection of the center-tap and third terminals, respectively. <IMAGE>

Description

LOW-PROFIt. MULTI-POLE TRANSFORMER WITH CENTER-TAPPED SECONDAR Related cations This application is related to commonly assigned, copending Patent Application No. ~~~~~~~ (docket no. 20,467 USSN 07/838656) of W.A. Roshen and A.J. Yerman and to commonly assigned, copending Patent Application No. ~ (docket no. 20,748 USSN 07/838958) of A.J. Yerman and W.A.

Roshen, both filed concurrently herewith and incorporated by reference herein.

Field of the Invention The present invention relates generally to magnetic components and, more particularly, to a low-profile transformer having a z-foldable, center-tapped secondary winding.

Background of the Invention Commonly assigned, copending U.S. patent 5126715 of A.J. Yerman and W.A. Roshen, Serial No.

07/548,461, now allowed and incorporated by reference herein, describes a low-profile, multi-pole, conductive-film transformer. The transformer of Serial No. 07/548,461 includes a continuous, serpentine primary winding that is configured and z-folded to form a multi-pole, multi-layer winding having separate secondary winding layers interleaved therewith. Conductive connecting strips are used to electrically connect the separate secondary winding layers together. In another commonly assigned, copending U.S.

patent application (A.J. Yerman and W.A. Roshen, US Serial No. 07/838958 (docket no. RD-20748), cited hereinabove), a continuous, z-foldable secondary winding configuration is described that allows for very simple and reliable high current and low-resistance connections between secondary winding layers.

Although the improved conductive-film transformer configurations described in the hereinabove cited patent applications are useful for many high-frequency applications, it is desirable for many power electronics applications to use a transformer having center-tapped windings. Therefore, it is desirable to provide a conductive-film transformer having center-tapped windings.

Summary of the Invention A high-frequency, low-profile transformer includes a primary winding comprising a continuous primary conductive film having a generally serpentine configuration and being disposed on a primary dielectric membrane. The primary conductive film is z-folded to form a multi-layer primary winding having at least one turn about each pole of at least two pairs of magnetic poles. A center-tapped secondary winding comprises a plurality of secondary conductive film portions disposed on a secondary dielectric membrane and zfolded to form a multi-layer secondary winding interleaved with the multi-layer primary winding.Each of the secondary conductive film portions is configured to form a current path having at least two winding turns in series about one pole of each pair of the magnetic poles such that the two winding turns of each current path are situated on adjacent layers of the secondary winding stack. In addition, the secondary winding has a pair of first terminals along alternate edges perpendicular to the folds on opposite sides of the multilayer winding stack, a pair of center-tap terminals along each fold of the stack, and a pair of third terminals along each fold of the stack. Vias are provided in the folds of the primary winding in order to allow electrical connection of the first terminals. Furthermore, vias are provided in alternate folds of the secondary winding in order to allow electrical connection of the center-tap and third terminals, respectively.

grief DescriDtion of the Drawings The features and advantages of the present invention will become apparent from the following detailed description of the invention when read with the accompanying drawings in which: Figure 1 is a top plan view of one embodiment of a primary winding useful in a transformer according to the present invention; Figure 2a is a top plan view of one embodiment of a secondary winding useful in a transformer according to the present invention; Figure 2b is a bottom view of the secondary winding of Figure 2a; Figure 3a is a cross sectional, perspective view of a transformer according to the present invention including a primary winding such as that of Figure 1 and a secondary winding such as that of Figure 2; Figure 3b is a full perspective view of the transformer of Figure 3a;; Figure 4 is a top plan view of an alternative embodiment of a primary winding useful in a transformer according to the present invention; and Figure 5 is a top plan view of an alternative embodiment of a secondary winding useful with the primary winding of Figure 4.

Detailed Deseription of the Invent, on Figure 1 illustrates a primary winding 10 similar to that employed in the transformer according to the hereinabove cited U.S. patent application of A.J. Yerman and W.A. Roshen, Serial No. 07/548,461, which is useful in a high-frequency, low-profile transformer according to the present invention. In particular, primary winding 10 includes a continuous primary conductive film 12 having a generally serpentine configuration disposed on a dielectric membrane 14. Although primary winding 10 is shown as having a primary conductive film disposed on only one side of dielectric membrane 14, another primary conductive film (not shown) may be situated on the other side of dielectric membrane 14, if desired.Dotted lines 16 and 17 represent fold lines for z-folding the primary conductive film, as described in patent application Serial No. 07/548,461, cited hereinabove. Specifically, fold lines 16 indicate folding in one direction; and fold lines 17 indicate folding in the opposite direction. Primary winding 10 is thus configured to have at least one winding turn about each of two pairs of magnetic poles 20-21 and 22-23. Openings for poles 20-23 are sized to receive core posts of a suitable magnetic core, such as, for example, the magnetic core described in patent application Serial No. ~~~~~~ (docket no. RD-20,467), cited hereinabove. By way of illustration, X'5 are provided to indicate that the direction of magnetic flux within the respective poles extends downward, and dots are provided to indicate that the direction of magnetic flux within the respective poles extends upward. Each arrow indicates the corresponding direction of current flow. Primary winding terminals 26 and 28 extend outward from one end, i.e., the bottom or top, of the multi-layer primary winding stack after folding. As shown, each fold 16 and 17 of primary winding 10 further includes a single cut 29 for providing access to secondary winding terminals, as described hereinbelow.

Figure 2a illustrates a top view and Figure 2b illustrates a bottom view of one embodiment of a centertapped secondary winding 30 which is to be z-folded along fold lines 16' and 17' and interleaved with primary winding 10 of Figure 1 to form a low-profile transformer according to the present invention. Center-tapped winding 30 comprises a plurality of secondary conductive film portions 32 disposed on one surface of a secondary dielectric membrane 34.

However, similar to primary winding 10, it is to be understood that although a secondary conductive film is shown as being disposed on only one surface of dielectric membrane 34, another secondary conductive film may be situated on the other surface of dielectric membrane 34, if desired.

Each of the secondary conductive film portions is configured to form a current path having at least two winding turns about one pole of each pair of poles such that the two winding turns of each current path are situated on adjacent layers of the secondary winding stack. In particular, each current path extends from a first terminal 36 situated on an edge of the secondary winding, around a pole (e.g., 23) to a center-tap terminal 38 situated on a fold (e.g., 16'), and around the same pole to a third terminal 40 situated toward the center of the fold. Hence, there are two center-tapped winding turns in series about each magnetic pole.

In accordance with the present invention, vias are provided in the folds of the primary and secondary windings in order to provide access to the secondary winding terminals after folding, thus enabling the parallel connection thereof in the stack. In particular, as shown in Figure 1, vias 29 in the primary winding may comprise a single cut toward the center of each primary winding fold for connection of first terminals 36, as described hereinbelow. On the other hand, as shown in Figure 2b, secondary winding vias 41 are only necessary in alternate folds of the secondary winding for connection of the center-tap and third terminals, respectively.

Secondary winding 30 is z-folded in a fashion similar to the windings of patent application Serial No.

07/548,461, cited hereinabove, to form a multi-layer secondary winding which is interleaved with a multi-layer primary winding. For example, Figure 3 illustrates a transformer according to the present invention having zfolded and interleaved primary and secondary windings, such as those illustrated in Figures 1 and 2, respectively. In particular, primary winding 10 is interleaved with secondary winding 30 so that fold lines 16 and 17 (Figure 1) are respectively displaced 90 with respect to fold lines 16' and 17', respectively. Additional dielectric layers (not shown) provide insulation between primary and secondary conductive films that face each other, as needed.

Easy and reliable, high-current, low-resistance connections are made between secondary winding layers. In particular, on the side of the secondary winding stack having conductive film portions 32 folded toward each other so that they face inward (shown as the right side in Figures 3a and 3b), conductive bridges 50 and 51, respectively, in combination with vias 41, are used to connect third terminals 40 and center-tap terminals 38 respectively together along alternate folds. A conductive connecting strip 52 is soldered to conductive bridges 50 in order to couple third terminals 40 in parallel; and connecting strips 54 are soldered to conductive bridges 51 in order to couple centertap terminals 38 in parallel.However, on the side of the secondary winding stack having conductive film portions 32 folded away from each other so that they face outward (shown as the left side in Figures 3a and 3b), connecting strips 52 and 54 are respectively soldered directly to conductive film portions 32 at the third terminals 40 and center-tap terminals 38, respectively; i.e., no additional conductive bridges are needed. On the other two sides of the winding stack, connecting strips 56 are soldered to first terminals 36 through vias 29 in primary winding 10 in order to connect first terminals 36 in parallel.

Figure 4 illustrates an alternative embodiment of a primary winding 10', and Figure 5 illustrates an alternative embodiment of a secondary winding 30' useful in a transformer according to the present invention. Vias in primary winding 10' of Figure 4 include a pair of cuts 29' and 29'' situated along each fold on opposite sides of the primary winding stack. Like the single-cut vias 29 described hereinabove with reference to Figure 1, vias 29' and 29'' provide accesss to secondary winding layers for the parallel connection of first terminals 36' in the multi-layer winding stack, as needed. Conductive films 32' of secondary winding 30' of Figure 5 are configured similarly to conductive films 32 of Figure 2 in order to provide two winding turns about each pole of each pole-pair. In Figure 5, however, first terminals 36' are situated closer to the secondary winding folds, which may be preferable for some applications in order to reduce the stray inductance of interconnections to rectifying diodes, for example.

While the preferred embodiments of the present invention have been shown and described herein, it will be obvious that such embodiments are provided by way of example only. Numerous variations, changes and substitutions will occur to those of skill in the art without departing from the invention herein. Accordingly, it is intended that the invention be limited only by the spirit and scope of the appended claims.

Claims (9)

CLAIMS:

1. A transformer, comprising: a primary winding comprising a continuous primary conductive film having a generally serpentine configuration and being disposed on a primary dielectric membrane, said primary conductive film being z-folded to form a multi-layer primary winding having at least one turn about each pole of at least two pairs of magnetic poles;; a center-tapped secondary winding comprising a plurality of secondary conductive film portions disposed on a secondary dielectric membrane, said secondary winding being z-folded to form a multi-layer secondary winding interleaved with said multi-layer primary winding, each of said secondary conductive film portions being configured to form a current path having at least two winding turns in series about one pole of each pair of said poles such that said two winding turns of each current path are situated on adjacent layers of said secondary winding, said secondary winding having a pair of first terminals along alternate edges perpendicular to the folds on opposite sides of the multi-layer winding stack, a pair of center-tap terminals along each fold of said stack, and a pair of third terminals along each fold of said stack;; said primary winding having primary via means for allowing electrical connection of said first terminals together in said stack; and said secondary winding having secondary via means for allowing electrical connection of said center-tap and third terminals, respectively, in said stack.

2. The transformer of claim 1, further comprising separate respective conductive connecting strips for connecting said first, center-tap, and third terminals together, respectively.

3. The transformer of claim 1 wherein said first terminals are situated centrally along each edge of the multi-layer winding stack and said primary via means comprises a single cut centrally in each said fold of said primary winding.

4. The transformer of claim 1 wherein said first terminals are situated on opposite sides of each edge of the multi-layer winding stack and said primary via means comprises a pair of cuts along opposite sides of each fold of said primary winding.

5. The transformer of claim 1 wherein said third terminals are situated centrally along each fold of said secondary winding, and said center-tap terminals are situated on either side of said third terminals.

6. A center-tapped winding for a magnetic circuit component, comprising: a plurality of conductive film portions disposed on a dielectric membrane, said winding being z-folded to form a multi-layer winding, each of said conductive film portions being configured to form a current path having at least two winding turns in series about one pole of each pair of said poles such that said two winding turns of each current path are situated on adjacent layers of said winding, said winding having a pair of first terminals along alternate edges perpendicular to the folds on opposite sides of the multilayer winding stack, a pair of center-tap terminals along each fold of said stack, and a pair of third terminals along each fold of said stack.

7. The center-tapped winding of claim 6 wherein said third terminals are situated centrally along each fold of said winding, and said center-tap terminals are situated on either side of said third terminals.

8. A transformer substantially as hereinbefore described with reference to the drawings.

9. A center-tapped winding substantially as hereinbefore described with reference to the drawings.