Transformer and associated production method

Abstract

A transformer for switched-mode power supplies includes a magnetizable core having a winding axis, at least one primary winding, which is formed by a primary winding conductor which at least partly surrounds the winding axis of the core, and at least one secondary winding, which is formed by a secondary winding conductor. The secondary winding conductor surrounds the primary winding conductor. The secondary winding is formed in one layer, and a cross section of the secondary winding conductor is rectangular, in particular square.

Claims

1. A transformer for switched-mode power supplies, the transformer comprising: a magnetizable core having a single winding axis; at least one primary winding formed by a primary winding conductor at least partly surrounding the winding axis of the core; at least one secondary winding formed by a secondary winding conductor, wherein the secondary winding conductor surrounds the primary winding conductor, the secondary winding is formed in one layer, and a cross section of the secondary winding conductor is rectangular, and a planar cooling element arranged parallel to the winding axis of the core and extending over the at least one secondary winding in the direction of the winding axis of the core, wherein the planar cooling element is thermally coupled to the at least one secondary winding on a side of the at least one secondary winding facing radially away from the winding axis of the core, wherein a region of the magnetizable core axially overlapped by the at least one secondary winding is not directly thermally coupled to the planar cooling element by a conductive heat transfer path that bypasses the at least one secondary winding.

2. The transformer according to claim 1, wherein the cross section of the secondary winding conductor is square.

3. The transformer according to claim 1, wherein the secondary winding conductor is solid.

4. The transformer according to claim 3, wherein the at least one secondary winding is formed from a solid material block, structured to form the secondary winding conductor, and the structuring of the solid material block is carried out by material removing machining.

5. The transformer according to claim 4, wherein the material removing machining is at least one of drilling, cutting, milling or electric discharge machining.

6. The transformer according to claim 1, wherein the at least one secondary winding is formed from a diecast shaped article.

7. The transformer according to claim 1, wherein the transformer has a nominal output, the cross section of the secondary winding conductor being dimensioned such that a current-carrying capacity of the secondary winding conductor is higher than necessary for the nominal output.

8. The transformer according to claim 1, wherein the secondary winding conductor is formed of aluminum, copper, or titanium.

9. The transformer according to claim 1, further comprising: a heat-conductive electric insulator arranged between the cooling element and the secondary winding.

10. The transformer according to claim 9, wherein the electric insulator is an electrically insulating heat-conductive foil.

11. The transformer according to claim 1, wherein the secondary winding forms a heat sink.

12. The transformer according to claim 1, wherein a distance between the primary winding and the core and a distance between the secondary winding and the primary winding are selected to minimize leakages.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 shows schematically an illustration of a transformer according to the invention;

(2) FIG. 2 shows schematically an exploded illustration of the transformer shown in FIG. 1; and

(3) FIG. 3 shows schematically an electric equivalent circuit of the transformer shown in FIGS. 1 and 2.

DETAILED DESCRIPTION OF THE DRAWINGS

(4) FIG. 1 shows a transformer 1 for switched-mode power supplies comprising a magnetizable ferrite core 2 having a limb that defines a winding axis 3, a first primary winding 4a (see FIG. 2), which is formed by a first primary winding conductor made of litz wires that are insulated a number of times and which directly surrounds the winding axis 3 of the core 2, a second primary winding 4b, which is formed by a second primary winding conductor made of litz wires that are insulated a number of times and which directly surrounds the winding axis 3 of the core 2. The first primary winding 4a and the second primary winding 4b are arranged axially adjacently on the limb. A first solid secondary winding 5a is made of aluminum and is formed by a first secondary winding conductor 6a, and a second solid secondary winding 5b is made of aluminum and is formed by a second secondary winding conductor 6b.

(5) Furthermore, bores 9a and 9b are provided as connection points for the first and second secondary winding 5a and 5b, respectively.

(6) Insulation elements 10 serve to electrically insulate between the primary and secondary circuit.

(7) The secondary winding conductors 6a and 6b surround their associated primary winding conductors, such that they are arranged axially adjacently over the limb. The secondary winding conductors 6a and 6b are each formed in one layer and each have, in the winding direction, a rectangular cross section which is changeable in the winding direction.

(8) The transformer has a specific nominal output, wherein the cross section of the secondary winding conductors 6a and 6b is dimensioned in such a way that the current-carrying capacity thereof is greater than is necessary for the nominal output.

(9) For efficient cooling, a planar cooling element 7 is further provided, which is to be thermally coupled to the side or surface of the secondary windings 5a and 5b facing away from the winding axis 3 of the core 2. A heat-conductive electric insulator in the form of an electrically insulating heat-conductive foil 8 is provided between the cooling element 7 and the secondary windings 5a and 5b. Corresponding cooling elements can be provided on the upper face and/or the lower face of the secondary windings 5a and 5b.

(10) The secondary windings 5a and 5b are each formed from a solid aluminum material block, which is suitably structured by drilling, cutting, electric discharge machining and/or milling.

(11) The cross section of the secondary winding conductors 6a and 6b, or the minimum cross section thereof over the entire winding, is dimensioned in such a way that, at a given working frequency, the effective replacement area (skin depth) due to the skin effect is much smaller than the geometric cross section of the solid secondary winding conductors 6a and 6b. The dominating alternating current loss thus flows in the outer region of the winding in the direction of the core region of the winding and lastly along the winding to the heat sink in the form of the cooling element 7.

(12) FIG. 2, for clarification, shows an exploded illustration of the transformer shown in FIG. 1.

(13) FIG. 3 shows an electric equivalent circuit of the transformer 1 shown in FIGS. 1 and 2 with the primary windings 4a and 4b and the secondary windings 5a and 5b.

(14) The embodiments shown have solid secondary-side windings 5a and 5b, which lie directly over the primary windings 4a and 4b, respectively, which are formed from litz wires insulated a number of times. The primary windings 4a and 4b are arranged with minimal spacing over the ferrite core 2.

(15) Due to straight surfaces of the solid secondary windings 5a and 5b, a simple and efficient coupling to the cooling surface 7 is possible. The (minimum) cross section of the solid secondary windings 5a and 5b is intentionally overdimensioned here in order to thus achieve an efficient heat flow within the secondary windings 5a and 5b. The windings 5a and 5b are insulated with respect to the cooling area 7 by way of a thin heat-conductive foil 8 or ceramic material.

(16) Due to the minimal distances between the windings 4a, 4b, 5a and 5b and the transformer core 2, optimal cooling is ensured on the one hand, and on the other hand the leakages are minimized or the coupling between the primary and secondary side is maximized.

(17) The shown embodiments enable simple cooling of the transformer 1 via the solid secondary windings 5a and 5b, which can be effectively thermally coupled.

(18) The transformer core 2 may likewise be thermally coupled very easily, such that optimal cooling of the overall component is possible. Furthermore, due to the large cross section of the secondary windings 5a and 5b, aluminum can be used, which saves weight and costs.

(19) The transformer 1 for switched-mode power supplies has at least one solid (secondary) winding, the cross section of which is selected in such a way that a transport of the heat loss produced during operation to a planar heat sink is possible without the need for additional coolants.

(20) Of course, just one individual primary and secondary winding or more than two primary and secondary windings may also be provided.