WO2001071736A1

WO2001071736A1 - Tansformer with molded flanges and method

Info

Publication number: WO2001071736A1
Application number: PCT/US2001/005463
Authority: WO
Inventors: Donald Burnell Rigdon; Patrick L. Pfeifer; Melvin P. Pedersen; Michael Rowe; Kim Stuart Dockter
Original assignee: Midcom, Inc.
Priority date: 2000-03-17
Filing date: 2001-02-21
Publication date: 2001-09-27
Also published as: AU2001238566A1

Abstract

An improved transformer (20), as well as an improved method of forming a transformer, that results in an increased winding (40) a rea, reduced transformer size, and a reduced amount of labor, thereby reducing costs. Moreover, the improved transformer still satifies agency safety insulation requirements with respect to creepage and clearance between primary and secondary windings. Moreover, the improved transformer still satisfies agency safety insulation requirements between primary and secondary windings with respect to distance through insulation, and electrical strength.

Description

TRANSFORMER WITH MOLDED FLANGES AND METHOD

This application is being filed as a PCT International Application in the name of Midcom, Inc., a U.S. national corporation, on February 21, 2001, designating all countries except the U.S.

Field

This invention relates to a transformer and a method of forming a transformer. More particularly, the invention relates to a transformer where the required creepage and clearance distance is reduced or eliminated entirely, as well as to a method of forming such a transformer.

Background

Various safety agencies require certain creepage and clearance distances between two conductors where electrical safety is a concern. As defined by the International Electro-technical Commission (IEC), creepage is the shortest path between two conductors or conductive parts, as measured along the surface of the insulation (IEC 950). In addition, IEC 950 defines clearance as the shortest distance between two conductors or conductive parts, as measured through air. These distance requirements contribute to the crowding commonly found on printed circuit boards and PC-Cards due to the increased size of the transformers in which creepage and clearance is required between hazardous voltage primary winding(s) and the low voltage secondary winding(s).

The creepage and clearance distance requirements can be eliminated entirely if the transformer is formed with what is termed a "cemented joint". A cemented joint is a joint which may be regarded as a solid barrier with regard to electrical insulation (IEC 950, clause 2.9.7). If a joint in a transformer qualifies as a cemented joint, the need for creepage and clearance distance is eliminated, and the minimum dimension of the cemented joint is then equal to the required through insulation distance which is typically much less than what the required creepage and clearance distance would be. If the joint does not qualify as a cemented joint, the creepage and clearance distances of a transformer can still be reduced if the transformer qualifies as an enclosed and sealed part (IEC 950, clause 2.9.6) in which the ingress of dirt and moisture are prevented. Figure 4 illustrates a partial sectional view of a bobbin 2 on a prior art line transformer. In this transformer, shelf tape is disposed at each end of the bobbin 2 to form tape shelves 4, 6. The tape shelves 4, 6 each have a length l_t that is a minimum of 0.100 inches in order to achieve the 2.5 mm creepage and clearance distance to satisfy agency requirements. Due to the length l_t of the shelves 4, 6, the length that is available for winding is reduced by 0.200 inches minimum. A wire 8 is then wound on the bobbin 2 between the shelves 4, 6, and two layers of thin-sheet material 10 are then placed over the wire and the tape shelves. This process is repeated until the desired electrical specifications are achieved. However, this prior art process is extremely labor intensive since the tape shelves 4, 6 are formed by hand on the bobbin before each winding is applied. Further, the tape shelves 4, 6 consume winding area and decrease the width of the winding 8.

What is needed is a transformer, and an associated method, which complies with safety agency requirements and which allows for a reduction in the size of the transformer. In a line transformer, such a size reduction would allow an increase in the number of parts on a customer's printed circuit board. Further, the method should be less labor intensive than conventional methods, and should result in a transformer with an increased winding area while having a reduced size, while still reducing or eliminating the agency requirements for creepage and clearance distance.

Summary

The invention provides an improved transformer, as well as an improved method of forming a transformer, that results in an increased winding area, reduced transformer size, and a reduced amount of labor thereby reducing costs. Moreover, the improved transformer still satisfies agency safety requirements.

When a joint of the transformer qualifies as a cemented joint, such as according to IEC 950, clause 2.9.7. the need for creepage and clearance inside the transformer is eliminated, thereby providing the largest transformer size reduction. Alternatively, if the transformer qualifies as an enclosed and sealed part, such as according to IEC 950, clause 2.9.6, the creepage and clearance distances between the hazardous voltage winding(s) and the low voltage winding(s). while still applicable, are nevertheless reduced. In one aspect of the invention, as defined in the accompanying claims, a transformer comprises a bobbin having first and second opposite ends, with a first flange being disposed adjacent one of the first and second opposite ends of the bobbin. A conductive winding is disposed on the bobbin, and an insulator is disposed on and covers the winding and covers at least a portion of the first flange. Further, a first molded flange is disposed adjacent the end of the bobbin at which the first flange is disposed, with the first molded flange covering at least a portion of the first flange that is covered by the insulator.

In another aspect of the invention, as defined in the accompanying claims, a method of forming a transformer comprises providing a transformer bobbin with first and second opposite ends, with a first flange disposed adjacent the first end of the bobbin and a second flange disposed adjacent the second end of the bobbin: winding a conductor onto the bobbin between the first flange and the second flange; covering the conductor and at least a portion of the first flange and the second flange with an insulator; and molding a flange on the insulator adjacent the first end of the bobbin so as to cover at least a portion of the first flange that is covered by the insulator.

In yet another aspect of the invention, as defined in the accompanying claims, a method of forming a transformer comprises providing a transformer bobbin having opposite ends and a flange disposed at one end of the bobbin, winding a conductor onto the bobbin, covering the conductor and at least a portion of the flange with an insulator, and covering at least a portion of the flange that is covered by the insulator with a molded flange.

In another aspect of the invention, as defined in the accompanying claims, a method of forming a cemented joint in a transformer comprises providing a transformer bobbin having opposite ends and a flange disposed at each end. winding a conductor onto the bobbin between the flanges, covering the conductor and at least a portion of each of the flanges with an insulating material, and at least partially covering the portion of at least one of the flanges that is covered by the insulating material with a molded flange.

Further, in a transformer having a bobbin with opposite ends and a flange disposed at each end, a winding wound onto the bobbin between the flanges, and insulating material covering the winding and covering at least a portion of each of the flanges, a method of reducing or eliminating creepage and clearance distance in the transformer comprises covering at least a portion of the insulating material and at least a portion of each of the flanges covered by the insulating material with cover flanges disposed adjacent the ends of the bobbin, where the cover flanges are formed by molding.

These and various other advantages and features of novelty which characterize the invention are pointed out with particularity in the claims annexed hereto and forming a part hereof. However, for a better understanding of the invention, its advantages and objects attained by its use, reference should be made to the drawings which form a further part hereof, and to the accompanying description, in which there is described a preferred embodiment of the invention.

Brief Description of the Drawings

Figure 1 is a perspective view of a base bobbin prior to applying the first winding.

Figures 2A-E illustrate various steps in forming the transformer. Figure 3 is a partial view of an alternative transformer design in accordance with the principles of the invention.

Figure 4 is a partial sectional view of a prior art transformer bobbin.

Detailed Description

The invention will now be described with reference to Figures 1 and 2A-E. The invention is described herein in relation to a transformer 20, particularly a line coupling transformer. However, the invention could be used on other line coupling devices, or with other electrical devices having a pair of conductors in which a creepage and clearance distance requirement must be met.

The transformer 20 includes a bobbin 22 that is supported by flanges 24 that extend upwardly from a pair of rails 26. Terminals 28 are connected to the rails 26 to enable coupling of the transformer 20 to an adjacent component. The bobbin 22 defines an open interior 30 extending between first and second opposite ends 32, 34 of the bobbin.

The steps involved in forming the transformer will be explained in relation to Figures 2A-E. As shown in Figure 2A, a first flange 36 is disposed at the first end 32 of the bobbin 22 and a second flange 38 is disposed at the second end 34. A conductive winding 40 is then wound onto the bobbin 22 between the flanges 36, 38. An insulator 42 is then applied so that it is disposed on and covers or overlaps the winding 40, as well as covers or overlaps at least a portion of each of the flanges 36, 38.

Thereafter, as shown in Figure 2B, flanges 44, 46 are molded onto both sides of the bobbin 22, with the flanges 44, 46 being disposed on the insulator 42 and covering or overlapping at least a portion of each of the flanges 36, 38. The interface between the molded flanges and the insulator 42 creates a cemented joint, provided that the interface satisfies the criteria set forth in IEC 950, clause 2.9.7.

With reference to Figure 2C, a second conductive winding 48 is then wound between the flanges 44, 46. and an additional insulator 50 is applied so that it is disposed on and covers the winding 48, as well as covers at least a portion of each of the flanges 44, 46.

Additional flanges 52. 54 are then molded onto both sides of the bobbin 22, as shown in Figure 2D. with the flanges 52. 54 being disposed on the insulator 50 and covering or overlapping at least a portion of each of the flanges 44, 46. Finally, as shown in Figure 2E, a final conductive winding 56 is wound between the flanges 52, 54. and a final insulator 58 is applied onto the winding 56.

As shown in Figure 2B. the molded flanges 44, 46 cover/overlap the entire width of the flanges 36, 38, respectively. In particular, the width of the flanges 44, 46 is greater than the width of the flanges 36, 38. Therefore, the flanges 44, 46 also cover/overlap the entire portions of the flanges 36. 38 that are covered/overlapped by the insulator 42. Likewise, as shown in Figure 2D, the width of the molded flanges 52. 54 is approximately equal to the width of the molded flanges 44. 46 such that the flanges 52. 54 substantially cover/overlap the entire extent of the flanges 44, 46 underneath. Thus, the flanges 52. 54 also cover/overlap the entire portions of the flanges 44, 46 that are covered/overlapped by the insulator 50.

However, the flanges need not cover/overlap the entire extent of the flanges over which they are disposed, and the flanges need not cover the entire portion of the flanges covered by the insulators. For instance, as shown in Figure 3, a partial view of a transformer is shown, with the transformer including a conductive winding 70, a flange 72 and an insulator 74 that covers/overlaps a portion of the flange 72. A molded flange 76 covers/overlaps a portion of the insulator 74 and the flange 72. As illustrated, the width of the flange 76 is less than the width of the flange 72 it covers. Thus, a portion of the flange 72. indicated by gap d in Figure 3, is left uncovered by the flange 76 whereby the flange 76 only covers/overlaps a portion P of the flange 72 that is covered by the insulator 74.

In the construction of Figure 3, the flange 76 provides a stepped transformer design in which the width of the windings increase. Moreover, the flanges 44, 46, 52, 54 in Figures 2A-E could be designed similarly to the flange 76, in which case the flanges disposed thereunder would have a construction similar to flange 72. It is to be noted that the flanges 72, 76 each define a shelf 78 and a shoulder 80 at the end of the shelf, as do the flanges 44, 46, 52, 54 illustrated in Figures 2A-E. The flanges 36, 38 can also include this shelf and shoulder design. However, it is contemplated that the flanges 52. 54 could be formed without the shoulder, in which case the final insulator 58 would extend between the flanges 24.

Returning to Figure 2B. the flanges 36, 38 preferably have a minimum width w of approximately at least 0.016 inches as required by the particular application and relevant standard, while the bobbin 22 has a minimum wall thickness t_w of approximately at least 0.016 inches. It is contemplated that the bobbin 22 could have only a single flange at one of its opposite ends, instead of two flanges 36, 38.

The conductive windings 40, 48, 56, 70 are each preferably formed of a number of turns of a wire or other conductive element made from an electrically conducting material, such as copper or other suitable metallic material. Other conducting materials could be used to form the wire if desired.

The insulators 42, 50, 58, 74 are each formed from an insulating material, preferably a thin film material, such as 3M #56 or #74 tape produced by 3M Corporation of St. Paul, Minnesota. It is to be realized that other thin film insulating materials could be used as well. Two layers of the thin film material are preferably used to form each insulator 42, 50, 58. 74. However, depending upon the thickness and dielectric strength of the thin film material used and the electrical requirements, it is contemplated that a single layer of thin film material, or more than two layers of thin film material, could be used. Further, the edges of each of the insulators 42, 50, 58, 74 cover a minimum of 0.016 inches of the respective flanges (36, 38), (44, 46), (52, 54), 72. The 0.016 inches is the minimum through insulation distance required by safety agencies.

The flanges 44, 46, 52. 54, 76 are molded from a suitable plastic material, such as Rynite® thermoplastic polyester resin, onto the respective insulators 42. 50, 58, 74. The molded flanges preferably have a minimum width Wf of approximately 0.016 inches; more preferably, the width _f is approximately 0.035 inches.

The molded flange/insulator interface can be qualified as a cemented joint. When qualified as a cemented joint, the creepage and clearance distance can be eliminated, and the 0.016 inch thick cemented joint through insulation distance provided by the insulator satisfies agency requirements, which allows for a smaller transformer.

Cemented Joint A relevant test, provided by IEC 950. clause 2.9.7, for qualifying an interface as a cemented joint is conducted on samples as follows:

I. Thermal cycling (10 cycles of the following steps)

1. 68 hours at a predetermined temperature Tl (depending upon the specified operating conditions of the transformer)

2. 1 hour at 25 °C + 2 °C

3. 2 hours at 0 °C + 2 °C

4. not less than 1 hour at 25 °C + 2 °C Immediately thereafter, the relevant electric strength test is performed on the samples, except that it is multiplied by a factor of 1.6.

On other samples, the following humidity conditioning test is conducted:

II. Humidity Conditioning

1. 48 hours at 91 % to 95% relative humidity (RH), at a temperature T between 20 °C and 30 °C (maintained within 1 °C) at which condensation does not occur. Once humidity conditioning is complete, the relevant electric strength test is immediately performed on the samples, except that it is multiplied by a factor of 1.6.

If the transformers pass both of these electric strength tests, the molded flange/insulator interface is considered to be a cemented joint, thereby eliminating the creepage and clearance distance requirements. On the other hand if the interface does not qualify as a cemented joint, the creepage and clearance distances can still be reduced if a transformer qualifies as being enclosed and sealed.

Creepage and Clearance Reduction

A relevant test for qualifying a part as "enclosed and sealed" is provided by IEC 950, clause 2.9.6. An enclosed and sealed part adequately prevents ingress of dirt and moisture. Preventing ingress of dirt and moisture allows the creepage and clearance distances internal to the transformer to be reduced. In order to determine whether a transformer is enclosed and sealed, the following testing provided by IEC 950, clause 2.9.6, is performed:

I. Thermal cycling (10 cycles of the following steps)

2. 1 hour at 25 °C + 2 °C

3. 2 hours at 0 °C + 2 °C

4. not less than 1 hour at 25 °C + 2 °C After 10 cycles, the sample is allowed to cool to room temperature, and is then subjected to the following humidity conditioning test:

II. Humidity Conditioning

1. 48 hours at 91 % to 95% relative humidity (RH), at a temperature T between 20 °C and 30 °C (maintained within 1 °C) at which condensation does not occur. Once humidity conditioning is complete, the relevant electric strength test is performed. If the transformer passes the electric strength test, the transformer is considered to be enclosed and sealed. After the flanges 44, 46 are molded, the remaining windings 48, 56, insulators 50, 58 and flanges 52, 54 are applied as necessary in order to achieve the desired electrical specifications of the transformer. Thus, it is contemplated by the inventors that a transformer could be designed with one or more of the remaining windings 48, 56, insulators 50, 58 and flanges 52, 54, depending upon the desired electrical specifications of the transformer. Further, it is contemplated by the inventors that a transformer could be designed with the winding 40. insulator 42 and flanges 44, 46 of Figures 2 A and 2B if the electrical specifications are met thereby, without the remaining windings, insulators and flanges.

Alternatively, it is contemplated by the inventors that the insulators 42, 50, 58 could be made of a molded material, such as plastic. In this instance, the insulators could be of unitary construction with the respective molded flanges, in which case the insulators would be molded with the flanges.

All references to IEC 950 herein are to the 4th amendment of the 2nd edition. There are also various national standards based upon IEC 950, such as UL 1950/CSA 22.2 No. 950. EN 60950, and AS/NZS 3260. It is contemplated by the inventors that other suitable testing standards could be used in order to determine whether the interface qualifies as a cemented joint and whether the transformer is enclosed and sealed.

The above specification, examples and data provide a complete description of the manufacture, construction and use of the invention. Since many embodiments of the invention can be made without departing from the spirit and scope of the invention, the invention resides in the claims hereinafter appended.

Claims

WE CLAIM:

1. A transformer, comprising: a bobbin having first and second opposite ends, a first flange disposed adjacent one of said first and second opposite ends of said bobbin; a conductive winding disposed on said bobbin; an insulator disposed on and covering the winding and covering at least a portion of said first flange; and a first molded flange adjacent the end of said bobbin at which said first flange is disposed, said first molded flange covers at least a portion of said first flange that is covered by said insulator.

2. The transformer according to claim 1 , wherein said insulator comprises a film material.

3. The transformer according to claim 1, wherein said insulator comprises a molded material.

4. The transformer according to claim 1, further including a second flange disposed at the end of said bobbin opposite the end at which said first flange is disposed; and the insulator covers at least a portion of said second flange; and a second molded flange covers at least a portion of said second flange that is covered by said insulator.

5. The transformer according to claim 4, wherein said conductive winding is disposed between said first and second flanges.

6. The transformer according to claim 4, wherein said first and second molded flanges are formed from plastic.

7. The transformer according to claim 4, wherein said first and second molded flanges are of unitary construction with said insulator.

8. The transformer according to claim 4, further including: an additional conductive winding disposed on said insulator, said additional conductive winding being disposed between said first and second molded flanges; an additional insulator disposed on and covering the additional conductive winding and covering at least a portion of said first and second molded flanges; and additional molded flanges covering at least a portion of said first and second molded flanges that are covered by said additional insulator.

9. The transformer according to claim 8, further including a second additional conductive winding disposed on said additional insulator, said second additional conductive winding being disposed between said additional molded flanges, and a second additional insulator disposed on and covering the second additional conductive winding and covering at least a portion of said additional molded flanges.

10. The transformer according to claim 2, wherein the insulator comprises at least one layer of the film material.

1 1. The transformer according to claim 10, wherein the insulator comprises two layers of the film material.

12. The transformer according to claim 1, wherein the first molded flange is disposed on the insulator.

13. The transformer according to claim 1 , wherein the first molded flange has a thickness that is greater than a thickness of the insulator.

14. A method of forming a transformer, comprising: providing a transformer bobbin with first and second opposite ends, a first flange disposed adjacent the first end of said bobbin and a second flange disposed adjacent the second end of said bobbin; winding a conductor onto the bobbin between the first flange and the second flange; covering the conductor and at least a portion of the first flange and at least a portion of the second flange with an insulator; and molding a flange on the insulator adjacent the first end of the bobbin so as to cover at least a portion of the first flange that is covered by the insulator.

15. The method according to claim 14, further including: molding another flange on the insulator at the second end of the bobbin so as to cover at least a portion of the second flange that is covered by the insulator.

16. The method according to claim 15, further including: winding a second conductor onto the insulator between the molded flanges; covering the second conductor and at least a portion of the molded flanges with an additional insulator; and molding additional flanges onto the additional insulator so as to cover at least a portion of each of said molded flanges that are covered by the additional insulator.

17. The method according to claim 16, further including: winding a third conductor onto the additional insulator between the additional molded flanges; and covering the third conductor and at least a portion of the additional molded flanges with an insulator.

18. The method according to claim 15, wherein molding the flanges comprises molding the flanges from plastic.

19. A method of forming a transformer, comprising: providing a transformer bobbin having opposite ends and a flange disposed at one end of the bobbin; winding a conductor onto the bobbin; covering the conductor and at least a portion of the flange with an insulator; and covering at least a portion the flange that is covered by the insulator with a molded flange.

20. A method of forming a cemented joint in a transformer, comprising: providing a transformer bobbin having opposite ends and a flange disposed at each end; winding a conductor onto the bobbin between the flanges: covering the conductor and at least a portion of each of the flanges with an insulating material; and at least partially covering the portion of at least one of the flanges that is covered by the insulating material with a molded flange.

21. In a transformer having a bobbin with opposite ends and a flange disposed at each end, a winding wound onto the bobbin between the flanges, and insulating material covering the winding and covering at least a portion of each of the flanges, a method of reducing or eliminating creepage and clearance distance in the transformer, comprising: covering at least a portion of the insulating material and at least a portion of each of the flanges covered by the insulating material with cover flanges disposed adjacent the ends of the bobbin, said cover flanges being formed by molding.