GB2447483A

GB2447483A - Transformer and common mode choke component

Info

Publication number: GB2447483A
Application number: GB0704901A
Authority: GB
Inventors: Araf Sohail
Original assignee: Siconnect Ltd
Current assignee: Siconnect Ltd
Priority date: 2007-03-14
Filing date: 2007-03-14
Publication date: 2008-09-17
Also published as: GB0704901D0

Abstract

An electromagnetic component, or a method of making such a component, comprises winding coils on a magnetic core to provide a transformer and a common mode choke. A first winding may be arranged around a portion of a toroidal magnetic core to provide a secondary coil of a transformer and a second winding is wound on the said core to provide a primary coil of the transformer. The wire ends extending from the said primary coil may be twisted together and wound on to the said core to provide a common mode choke. The core may be made of a homogeneous magnetic material or a composite of materials. The wire ends extending from the secondary coil of the transformer may also be twisted together and wound on the core to provide a further common mode choke. The primary and secondary coil wires of the transformer may also be twisted together prior to winding on the core. The said transformer windings may be formed with the same helical winding sense and they may include tapping means.

Description

An Electromagnetic Component The present invention concerns an

electromagnetic component, and particularly a component combining the function of a high frequency (HF) transformer and a common mode choke.

It is useful in devices requiring power transformation, to be able to combine components making use of induction effects, to establish shared functionality and for enhanced compactness.

For example, it is known to wind wire about a core with magnetic properties, to provide transformer action between two or more windings. For instance, if two wires are wound about the core, a varying current in one wire will induce a potential difference in the other wire.

Further, wire can be wound about a core with magnetic properties, to establish a common mode impedance (choke), presented to currents flowing in the windings formed by the wire. For instance, if two or more wires are wound about the core, such that a current presented to both wires, the common mode choke effect is established.

This effect is suitable for the removal of electrical noise, most particularly common mode noise, which arises for instance environmental electro-magnetic interference.

Such interference can induce or couple electrical noise into the power lines.

Environmental electro-magnetic interference will tend to enter the power line and return to the noise source through a ground path, which will give rise to common mode noise.

Conventionally, transformers and common mode chokes are discrete, separate components.

An aspect of the invention provides an electromagnetic component comprising a magnetic core, a first winding wound about the core to establish a first transformer coil, and a second winding wound firstly wound about the magnetic core to couple with the first winding to establish a second transformer coil, and secondly wound about the magnetic core to establish a common mode choke.

In one embodiment, the first winding establishes the secondary coil of the transformer, whereas the second winding establishes the primary coil of the transformer. The alternative arrangement is also possible.

In one embodiment, the core may be homogenous. In another embodiment, the core may be composite. The core may be arranged to limit induction of eddy currents in said core as a result of a magnetic field generated in said core in use.

In one embodiment, the core is annular. The annular core may be toroidal and, in particular, may be toroidal with circular profile and section.

The core may be of magnetic material, or may be otherwise operable to enhance the

magnetic field generated in the core in use.

The first winding may further be wound about the magnetic core to establish a common mode choke. The first and second windings may be wound together about the magnetic core to establish a common mode choke.

Taps may be providcd in one or more of the windings within the transformer. The first and second windings may be in the same direction, or opposed.

In one embodiment, the portion of the first winding forming the common mode choke is twisted together.

In one embodiment, the respective portions of the first and second windings forming the primary and secondary coils of the transformer are twisted together.

Another aspect of the invention provides a method of constructing an electromagnetic component, comprising winding a secondary winding about an arcuate section of an annular magnetic core, winding a primary winding about the same arcuate section of the annular core in order to establish transformer function between the primary and secondary windings, and further winding the primary winding about a remaining portion of the annular magnetic core in order to form a common mode choke.

An embodiment of the invention will now be described with reference to the accompanying drawings in which: Figure 1 is a circuit diagram illustrating a combined common mode choke and transformer in accordance with the specific embodiment; Figure 2 illustrates a first construction step of formation of the combined component illustrated in Figure 1; Figure 3 illustrates a second construction step of formation of the component illustrated in Figure 1; and Figure 4 illustrates the final step and completion of construction of the component illustrated in Figure 1.

As illustrated in Figure 1, the component comprises the function of a transformer Ti, having a primary coil and a second coil, with NP and NS windings respectively.

The primary coil has lead conductors which each form windings of a common mode choke.

The circuit of Figure 1 is formed by means of a construction method which will now be described.

Firstly, a annular magnetic core 10 is illustrated in Figure 2, on which a secondary winding 20 is wound around through approximately a 60 arc thereof This is illustrated by means of the solid lines in Figure 2. The two ends 22, 24 of the secondary winding are led off to the right as illustrated, i.e. across the centre of the annulus of the magnetic core 10 and past the opposite side thereof.

Then, as illustrated in Figure 3, a primary winding 30 is wound about the same arc of the magnetic core 10 as the secondary winding 20 described above. In this embodiment, the primary winding 30 is wound about the core in the same sense as the secondary winding. It will be appreciated that this is not an essential aspect of the invention, and an opposite sense could be used. Further, whereas five turns are shown in Figure 3 for both the secondary winding (solid line) 20 and the primary winding (broken line) 30, this is not an essential feature of the invention, and the transformer can be formed to step up or step down as required, by means of the provision of unequal turns on each winding of the transformer.

The ends 32, 34 of the conductor forming the primary winding 30 are, as illustrated in Figure 3, temporarily led off to the left, i.e. away from the centre of the annular core 10.

Finally, the two ends 32, 34 of the primary winding are gathered together, and wound about the remaining portion of the annular core. It will be understood that this should be carried out while avoiding entanglement with the free ends 22, 24 of the secondary winding 20. These additional windings form a common mode choke in the conductors leading into the primary winding, as illustrated in Figure 1. Figure 4 therefore illustrates the finished product of the method so described.

Although not illustrated, for reasons of clarity, it may be desirable as a penultimate stage to twist together the ends 32, 34 of the primary winding before winding the turns onto the core to form the common mode choke. This will have a tendency to enhance the common mode character of the choke, as the two ends will then be subject to

substantially the same magnetic field.

In the context of the above embodiment, it will be appreciated by the reader that the common mode choke windings can be a continuation of either the primary or secondary winding. Alternatively, common mode choke windings can be placed on both primary and secondary circuits, by continuing the primary and secondary windings as common mode choke windings in the illustrated fashion. Further, the common mode choke windings are, as illustrated, tightly coupled. It will also be appreciated that it is unnecessary for the common mode choke windings to be arranged symmetrically about the transformer windings, nor is it necessary for the common mode choke windings to extend around the full arcuate extent of the core not used by the transformer windings.

Moreover, as previously noted, the transformer windings may have a non-equal turns ratio, i.e. NP does not need to equal NS. However, as would be expected of a common mode choke, the common mode choke windings should be in unison and therefore provide an equal turns ratio. This will provide the common mode choke function of the component.

Further, whereas the common mode choke windings are illustrated as being wound on portions of the core not utilised for establishment of a transformer, it would also be possible to wind the common mode choke windings (whether of one or both windings of the transformer) over or under the transformer windings.

Other aspects of the invention will be readily appreciated by the skilled person, though these are not specifically mentioned above. The invention should not be read as limited by the foregoing specific description of embodiments thereof, but should instead be understood from the features of the claims appended hereto. The claims are not to be considered as limited by the foregoing description.

Claims

CLAIMS: 6 I. An electromagnetic component comprising a magnetic core, a

first winding wound about the core to establish a first transformer coil, and a second winding firstly wound about the core to couple with the first winding to establish a second transformer coil, and secondly wound about the magnetic core to establish a common mode choke.
2. An electromagnetic component in accordance with claim I wherein the first winding establishes the secondary coil of the transformer, whereas the second winding establishes the primary coil of the transformer.
3. An electromagnetic component in accordance with claim I or claim 2 wherein the core is homogenous.
4. An electromagnetic component in accordance with claim 1 or claim 2 wherein the core is composite.
5. An electromagnetic component in accordance with any one of the preceding claims wherein the core is annular.
6. An electromagnetic component in accordance with claim 5 wherein the annular core is toroidal.
7. An electromagnetic component in accordance with claim 6 wherein the annular core is toroidal with circular profile and section.
8. An electromagnetic component in accordance with any one of the preceding claims wherein the core is operable to enhance the magnetic field generated in the core in use.
9. An electromagnetic component in accordance with any one of the preceding claims wherein the core is constructed of magnetic material.
10. An electromagnetic component in accordance with any one of the preceding claims wherein the first winding is further wound about the magnetic core to establish a common mode choke.
11. An electromagnetic component in accordance with any one of the preceding claims wherein at least one of said first and second windings comprises at least one tapping means, operable to offer electrical connection to a point on said winding.
12. An electromagnetic component in accordance with any one of the preceding claims wherein the first and second windings are in the same helical sense.
13. An electromagnetic component in accordance with any one of the preceding claims wherein the portion of the first winding forming the common mode choke is twisted together.
14. An electromagnetic component in accordance with any one of the preceding claims wherein the respective portions of the first and second windings forming the primary and secondary coils of the transformer are twisted together.
15. A method of constructing an electromagnetic component, comprising winding a secondary winding about an arcuate section of an annular magnetic core, winding a primary winding about the same arcuate section of the annular core in order to establish transformer function between the primary and secondary windings, and further winding the primary winding about a remaining portion of the annular magnetic core in order to form a common mode choke.
16. An electrical component substantially as described herein, with reference to the accompanying drawings.
17. A method of manufacturing an electrical component substantially as described herein with reference to the accompanying drawings.