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Title:
IMPROVEMENTS RELATING TO TRANSFORMERS/INDUCTORS
Document Type and Number:
WIPO Patent Application WO/1995/028722
Kind Code:
A1
Abstract:
A transformer/inductor comprising magnetic elements having one or more coils, wherein the magnetic elements have a generally U-shaped configuration and are mutually joined and face in mutually opposite directions with the legs of one U-shaped magnetic element lying on the legs of the other U-shaped magnetic element such as to form a closed magnetic circuit. The magnetic elements (15; 16) may each include a projection (12), which may be pointed, for obtaining an adjustable coupling coefficient or factor when using mutually spaced coils, or may lack such projections. The magnetic elements (1, 2; 15, 16) are adapted for mounting on a printed circuit board assembly and can be inserted in holes (19) located in the circuit board assembly from all sides of the board. The holes (19) accomodate coils (17) such as to form a closed magnetic circuit.

Inventors:
Lindqvist, Arne
Application Number:
PCT/SE1995/000422
Publication Date:
October 26, 1995
Filing Date:
April 18, 1995
Export Citation:
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Assignee:
Telefonaktiebolaget, Ericsson L. M.
International Classes:
H01F3/00; H01F27/06; H01F27/26; H01F30/10; (IPC1-7): H01F27/26
Foreign References:
US3478291A
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Claims:
CLAIMS
1. A transformer/inductor comprising magnetic elements having one or more coils, wherein the magnetic elements have a generally Ushaped configuration and are mutually joined and face in mutually opposite directions with the legs of one Ushaped magnetic element lying on the legs of the other U shaped magnetic element such as to form a closed magnetic circuit, characterized in that the magnetic elements (1, 2; 15; 16) may each include a projection (12) for obtaining an adjustable coupling factor when using mutually spaced coils, or may lack such projections; and in that the magnetic elements (1, 2; 15, 16) are adapted for mounting on a printed circuit board assembly and can be inserted in holes (19) located in the circuit board assembly from all sides of the board; and in that the holes (19) accommodate coils (17) such as to form a closed magnetic circuit.
2. A transformer/inductor according to Claim 1, characterized in that the legs of the Ushaped magnetic elements are fastened together with the aid of an adhesive substance.
3. A transformer/inductor according to Claim 2, character¬ ized by clamping means (18) which functions to hold and fasten the legs of the Ushaped magnetic elements together or to fasten said elements to the printed circuit board assembly.
Description:
IMPROVEMENTS RELATING TO TRANSFORMERS/INDUCTORS

DESCRIPTION

TECHNICAL FIELD

The present invention relates to a method of manufacturing a transformer/inductor, and also to a transformer/inductor manufactured in accordance with the method. Transformerε/in- ductors for both heavy current and light current find a wide area of use in electrical technology.

DESCRIPTION OF THE BACKGROUND ART

Transformers are used to switch alternating current from one voltage level to another. A transformer WILL normally include two mutually insulated coils which are mounted on a common, closed sheet-metal core, for instance, a so-called transform¬ er plate. Alternating current passing through one coil generates by induction an alternating voltage of the same frequency in the other coil, with only a small loss. The ratio between the voltages across the coils is essentially equal to the ratio between the number of winding turns on the coils. Large transformers are often immersed in oil, so as to reduce the risk of spark-over and to cool the coil windings. An inductor is often used as a generator or as a barrier element (choke). The transformer core may consist in some suitable magnetic material, or the transformer may have no core and include only coils, depending on the frequency range involved. The inductor is an important component in resonance circuits, among other things.

DISCLOSURE OF THE INVENTION

Transformers and inductors normally have magnetic elements included in a functional circuit. Existing air gaps between the magnetic elements are normally obtained through the

medium of a butt joint or a halved joint, optionally in combination with a specified air gap. The present invention is concerned with transformer/inductor constructions in which the magnetic circuit is closed and an air gap obtained with the aid of mutually overlying parts of the magnetic elements. By placing U-shaped magnetic elements one upon the another and holding the elements together in this position, and orientating said magnetic elements towards one another, there is obtained a closed magnetic circuit and an air gap between said overlying magnetic elements, the surface areas of these parts being greater than the corresponding surface areas that are presented between the ends of mutually contacting magnetic elements a magnetic circuit. In constructions in which parts of the magnetic elements overlie one another, the transition between said magnetic elements is much less sensitive to imperfections in mechanical tolerances than in the case of end-mounted or butt-mounted elements, while, at the same time, the surfaces of the overlying sections of the magnetic elements provide appropriate fastener surfaces for receiving clamping means (or like devices) provided with winding wire connector pins, for instance.

The inventive transformer/inductor lends itself to production in automated production lines with, among other things, its open windings prior to assembly of the magnetic elements, and is thus not expensive and nevertheless retains its functional flexibility. Similarly, the inventive solutions to the aforesaid problem can be applied independently of the magnetic material used, which may be a ferrite, sheetmetal or amorphous material, or a nanocrystalline material.

The illustrated examples enable production costs to be reduced to 30% of the costs entailed by traditional tech¬ niques. Furthermore, the development and use potential of the inventive transformer/inductor are relatively significant, because of the flexible applications achieved at low costs. For instance, the clamp means may include hole-mounted

terminal pins on one side thereof, while the other side may be provided with a pad for surface mounting purposes. The clamp may also be used for automatic connection to coil windings. This enables the same inexpensive product to be used for different mounting alternatives and with different printed circuit boards or printed circuit board assemblies. Suitable areas of use for transformers and inductors con¬ structed in accordance with the invention, with or without pre-magnetization, are line applications, switched mode power supply, toroid substitution, EMC chokes. The inventive transformer/inductor may include means for obtaining an adjustable coupling factor, particular when used with mutually spaced coils, or may lack such means when used in other contexts.

BRIEF DESCRIPTION OF THE DRAWINGS

Fig. 1 illustrates a transformer having a coil body according to the invention, before and after its assembly.

Fig. 2 illustrates a transformer having two coil bodies according to the invention, before and after its assembly.

Fig. 3 illustrates the transformer shown in Fig. 1 in an upright and a horizontal position.

Fig. 4 illustrates an alternative embodiment of the inventive transformer mounted on a printed circuit board assembly.

BEST MODES OF CARRYING OUT THE INVENTION

Figure 1 illustrates the construction of an inventive transformer. The reference numeral 1 identifies a U-shaped angled magnetic element, while the reference numeral 2 identifies a similar U-shaped magnetic element having a coil 3 which can include one or more windings. The reference numeral 4 identifies the legs of magnetic elements and

overlying surfaces on the magnetic element 1. In the assembly of a transformer, the magnetic elements 1 and 2 are laid on one another in mutually opposite directions, with the legs of said elements overlying each other. The magnetic elements 1 and 2 are fastened together with the aid of an adhesive substance, or are secured together with the aid of a clamping means 5 which is optionally separated from the magnetic elements by an insulating material 6. The clamping means 5 may be provided with a hole-mounting pin and/or with a surface-mounting pad 8. The magnetic element may be made of ferrite, magnetic plastic, crystalline sheet etal, amorphous metal or nanocrystalline metal.

Magnetic elements which are injection-moulded from magnetic plastic material have a low production cost and a high surface fineness, which in the case of the inventive con¬ struction which includes mutually overlying surfaces have only a little affect on the magnetic flux. Magnetic elements which are assembled end-to-end require a much greater surface fineness in order to obtain the same magnetic flux or an improved magnetic flux in the magnetic circuit. Ferrite magnetic elements are more expensive. A relatively expensive magnetic element manufacturing process is one in which lasers are used to separate bound and fixated thin amorphous metal strips to form the U-shaped magnetic elements.

Because one or more coils can be wound on one single magnetic element prior to assembly, the costs of manufacturing a transformer are lowered considerably in comparison with a coil which is wound on a closed magnetic body.

Figure 2 illustrates a similar transformer construction to that shown in Figure 1, but with the exception that two separate coils 9, 10 have been wound on the magnetic element 2 and that the second magnetic element has been provided with a centrally positioned, angled projection 12. This construc¬ tion provides a transformer which has an adjustable coupling

coefficient or factor, and which with the pointed configura¬ tion can be current adjusting.

Figure 3 illustrates examples of how inventive transformers may be mounted. Shown to the left in Figure 3 is a horizontal mount while to the right in the Figure is shown a vertical or upstanding mount with the clamping devices 5 secured to an underlying supportive surface 13. As a result of the overlying magnetic parts, the transformer will occupy a smaller space than conventionally constructed transformers.

Figure 4 illustrates an alternative embodiment of an inven¬ tive transformer which is intended to be mounted on a printed circuit board assembly. A circuit board is provided with two rectangular apertures 19 which receive two mutually assembled magnetic elements 15 and 16. Attached to the circuit board 14 is one or two cbils 17 which may include one or more windings. The coils 17 may be provided as separate thin coils placed on and secured to the circuit board, or may be placed between two circuit board layers of a circuit board struc¬ ture. The magnetic elements are placed in holes on the circuit board, one from beneath and one from above, and clamping means 18 or functionally similar means are then placed over respective magnetic elements 15, 16, from above and from beneath, so as to hold the magnetic elements in place and also to affix said elements in relation to the circuit board, which in itself effectively secures the transformer, without needing to fasten the transformer directly on the circuit board.