TRANSFORMER UNIT FOR A RESONANT CONVERTER

Abstract

A transformer unit for a resonant converter comprising; a primary winding loosely coupled by induction to at least one secondary winding, whereby a leakage inductance is generated, and a shielding element covering at least one of the primary winding or the secondary winding for blocking electromagnetic noise generated by the leakage inductance, wherein the shielding element is thermally coupled to at least one of the primary winding or the secondary winding for transferring heat generated by the transformer unit.

Claims

1. A transformer unit for a resonant converter comprising; a primary winding loosely coupled by induction to at least one secondary winding, whereby a leakage inductance is generated, and a shielding element covering at least one of the primary winding or the secondary winding for blocking electromagnetic noise generated by the leakage inductance, wherein the shielding element is thermally coupled to at least one of the primary winding or the secondary winding for transferring heat generated by the transformer unit.

2. The transformer unit of claim 1, wherein the shielding element further includes a heat sink portion for dissipating the transferred heat to a fluid.

3. The transformer unit of claim 1, wherein the shielding element further includes a clamping portion for pressing the shielding element to the transformer unit.

4. The transformer unit of claim 1, wherein the shielding element is fabricated from a stamped and bent metal sheet.

5. The transformer unit of claim 1, further comprising an elastic thermal coupling element for thermally coupling the shielding element to at least one of the primary winding or the secondary winding.

6. The transformer unit of claim 1, wherein the first winding and the second winding have a common longitudinal axis.

7. The transformer unit of claim 1, further comprising a first bobbin carrying the first winding and a second bobbin carrying the second winding.

8. The transformer unit of claim 7, further comprising an insulation barrier for increasing the creepage distance, wherein the insulation barrier is arranged between the first bobbin and the second bobbin.

9. The transformer unit of claim 1, wherein at least one selected from a group consisting of the primary winding and the secondary winding includes a magnetic core.

10. The transformer unit of claim 8, wherein the magnetic core has a three-legged structure for forming a closed magnetic system.

11. A resonant power converter, comprising: a switch network supplying an alternating voltage to a resonant tank, wherein the resonant tank includes a resonant inductance and at least one reactive element, and a transformer, wherein the resonant inductance and the transformer are formed by the transformer unit of claim 1.

12. A switching power supply, comprising a printed circuit board electrically connecting the resonant power converter of claim 11.

13. The switching power supply of claim 12, wherein the printed circuit board mechanically supports the shielding element.

14. The switching power supply of claim 13, wherein the shielding element is thermally coupled to at least one power electronic component supported by the printed circuit board for transferring heat generated by the power electronic component.

15. The switching power supply of claim 12, wherein a housing element of the switching power supply comprises a second heat sink, wherein the second heat sink is thermally coupled to the shielding element.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0031] The accompanying drawings are incorporated into the specification and form a part of the specification to illustrate several embodiments of the present invention. These drawings, together with the description serve to explain the principles of the invention. The drawings are merely for the purpose of illustrating the preferred and alternative examples of how the invention can be made and used, and are not to be construed as limiting the invention to only the illustrated and described embodiments. Furthermore, several aspects of the embodiments may formindividually or in different combinationssolutions according to the present invention. The following described embodiments thus can be considered either alone or in an arbitrary combination thereof. Further features and advantages will become apparent from the following more particular description of the various embodiments of the invention, as illustrated in the accompanying drawings, in which like references refer to like elements, and wherein:

[0032] FIG. 1 is a schematic circuit diagram of a LLC resonant converter;

[0033] FIG. 2 is an exploded view of a switching power supply with a transformer unit according to the present invention;

[0034] FIG. 3 is an exploded view of a transformer;

[0035] FIG. 4 is a schematic perspective view of a bobbin;

[0036] FIG. 5 is a further schematic perspective view of the bobbin;

[0037] FIG. 6 is a schematic planar view of the bobbin;

[0038] FIG. 7 is a further schematic planar view of the bobbin;

[0039] FIG. 8 is a further schematic planar view of the bobbin;

[0040] FIG. 9 is a further schematic planar view of the bobbin;

[0041] FIG. 10 is a sectional view along the line X-X of FIG. 7.

DETAILED DESCRIPTION

[0042] The present invention will now be explained in more detail with reference to the Figures and firstly referring to FIG. 2. FIG. 2 shows an exploded view of a switching power supply 400. The switching power supply 400 comprises a housing formed by a cover element 402 and a bottom element 404. The housing elements are made of an isolating material such as a plastic. The housing elements serve to mechanically support and protect the integrated parts. In particular, the cover element 402 comprises a heat sink element 406, also referred to as second heat sink 406, and the bottom element 404 supports a printed circuit board (PCB) 500. The PCB serves for mechanically supporting and electrically contacting the transformer unit 100.

[0043] The transformer unit 100 comprises a transformer 200 and a shielding element 300. The transformer 200 is described in detail with reference to FIG. 3. The transformer 200 comprises a primary winding 202 and a secondary winding 204. In particular, the transformer 200 transfers electrical energy between the primary winding 202 and the secondary winding 204 through electromagnetic induction. A varying current in the primary winding 202 of the transformer produces a varying magnetic field, which in turn induces a varying electromotive force or voltage in the secondary winding 204. Although not shown in the drawings, the varying current is for example generated by a switch network supplying an alternating voltage. The switch network is, for example, mounted on the PCB 500.

[0044] As further shown in FIG. 3, the primary winding 202 and the secondary winding 204 of the transformer 200 share a common longitudinal axis 206. In other words, the poles of the windings are arranged side by side. By this arrangement the primary winding 202 and the secondary winding 204 are inductively coupled.

[0045] Furthermore, the primary winding 202 and the secondary winding 204 are spaced by a distance 208. This distance 208 causes a loose coupling of the windings, whereby the leakage inductance is generated. Furthermore, the distance 208 is in a range of 1 to 10 millimeters and is preferably 6.5 mm, and thus, the requirements of a clearance distance between the primary winding 202 and the secondary winding 204 for the application of a battery charger for a bicycle or the like are met.

[0046] Additionally, the transformer 200 comprises two three-legged magnetic cores 220. Each core 220 comprises a cylindrical central part 222, which is received by the windings 202 and 204. Furthermore, each core 220 comprises a yoke 226, which connects the central part 222 with two rectangular side legs 224. As best shown in FIG. 2, the three-legged magnetic cores 220 form a closed shell surrounding the windings of the transformer. The windings 202 and 204 are surrounded by the magnetic cores 220, and thus, the transformer 200 is constructed in a shell form.

[0047] Although not shown in the figures, the central part 222 is not limited to a cylindrical shape. For example, the central part may have any other polygonal shape. Same applies for the shape of the side legs 224, which can also have cylindrical shape or any other polygonal shape.

[0048] As shown in FIG. 3, the primary winding 202 and the secondary winding 204 are carried by a bobbin 230. Thus, the bobbin 230 defines the positioning and stabilizes the windings 202 and 204 of the transformer 200. The bobbin is described with reference to FIGS. 4 to 10.

[0049] The bobbin 230 has a first cylindrical part 232 for carrying the first winding 202 and a second cylindrical part 234 for carrying the second winding 204. The first cylindrical part 232 comprises at a first base a first flange portion 235 and at a second base a second flange portion 236. The second cylindrical part 234 comprises at a first base a third flange portion 237 and at a second base the fourth flange portion 238.

[0050] As best shown in FIG. 6, the bobbin 230 further comprises a connecting element 239 arranged between the second flange portion 236 and the third flange portion 237. The connecting element 239, the second flange portion 236, and the third flange portion 237 form an insulation barrier 233. By the insulation barrier 230, and in particular due to the second and third flange portion 236 and 237, the clearance distance between the primary winding 202 and the secondary winding 204 is increased, and thus, the requirements for the clearance distance for the application of a battery charger for a bicycle or the like are met.

[0051] Consequently, the connecting element of the insulation barrier 233 serves to generate the leakage inductance and the second flange portion 236 and the third flange portion 237 increases the clearance distance, and thus, enable a safe and compact design.

[0052] As shown in FIG. 8 and in FIG. 10, a sectional view of the connecting element 239 along the line X-X of FIG. 7, the first cylindrical part 232, the second cylindrical part 234, and the connecting element 239 comprises a feed through 240 for receiving the cylindrical central part 222 of the magnetic core 220. Thus, the feed through 240 increases the efficiency of the transformer 200.

[0053] As shown in FIG. 5, the first flange portion 235 comprises a first connector stripe 242 and the fourth flange portion 238 comprises a second connector stripe 244. As shown in FIG. 2, the bobbin 230 is mechanically connected by the first connector stripe 242 and by the second connector stripe 244 to the printed circuit board 500.

[0054] Advantageously, the bobbin 230 is made of an insulating material such as a plastic. Although not shown in the figures, the bobbin 230 comprises conductive elements for electrically contacting the windings 202 and 204 with the PCB 500. The bobbin 230 with the conductive elements is, for example, manufactured by injection molding or a casting process.

[0055] Additionally, as shown in FIG. 3 the transformer 200 comprises a cover 210 for housing the windings 202 and 204, the magnetic cores 222 and the bobbin 230. The cover 210 may be from an isolating material such as a plastic and may comprise a shielding foil. The cover comprises an opening 203 for thermally contacting the transformer 200.

[0056] Further, as shown in FIG. 2, the transformer unit 100 comprises the shielding element 300. The shielding element 300 comprises a heat sink portion 310 and a clamping portion 320.

[0057] The heat sink portion 310 having the shape of a U with a central heat sink plate 312 facing the poles of the windings 202 and 204 and two wing plates 314 extending in the direction of the longitudinal axis of the windings 202 and 204. In particular, the wing plates 314 increase the surface of the heat sink portion 310 thereby allowing a more efficient dissipation of heat. The U-shape of the heat sink portion allows a compact design of the switching power supply.

[0058] The heat sink portion 310 of the shielding element 300 further comprises a plurality of pins 316 for thermally and/or electrically contacting the PCB 500 and for mechanically supporting the shielding element 300. Thus, the shielding element 300, which comprises the heat sink portion 310, can be electrically grounded and mechanically stabilized.

[0059] The clamping portion 320 having the shape of U comprises a central clamp portion 322 extending in a direction perpendicular to the longitudinal axis of the first winding 202, a first connecting portion 324 facing the first winding 202 and a second connecting portion 326 facing the second heat sink 406.

[0060] Advantageously, the shielding element 300 with the heat sink portion 310 and the clamping portion 320 is fabricated from a stamped and bent metal such as aluminum.

[0061] As shown in FIG. 2, the shielding element 300 is thermally coupled by a first elastic thermal coupling element 602 to the primary winding 202. In particular, the cover 210 of the transformer 200 comprise an opening 203 for receiving the first elastic thermal coupling element 602 and the first connecting portion 324 of the shielding element 300. Consequently, heat generated by the primary winding 202 of the transformer 200 can be efficiently transported via this thermal connection to the heat sink portion 310 of the shielding element 300.

[0062] Additionally, the first connection portion 324, which is made of a metal such as aluminum, covers the first winding 302, and thus, blocks the electric field of the EMI noise caused by the leakage inductance. As already discussed above, the shielding element 300 is grounded via at least one of the plurality of pins 316. Additionally, the central plate 312 of the heat sink portion 310 of the shielding element 300, which is also made of a metal such as aluminum, covers one pole of the primary winding 302, and thus, also blocks the electric field of the EMI noise caused by the leakage inductance.

[0063] Consequently, the shielding element 300 efficiently shields the EMI noise generated by the leakage inductance and cools directly the primary winding 202 of the transformer. Additionally, the secondary winding 204 is indirectly cooled by the connection via the magnetic cores 220.

[0064] Furthermore, as shown in FIG. 2, the shielding element 300 is thermally coupled by a second elastic thermal coupling element 604 to the second heat sink 406. Thus, the heat dissipation rate can be increased.

[0065] Additionally, the clamping portion 320 is arranged between the second heat sink 406 and the first winding 202. Thus, the contact pressure between the first connection portion 324 and the first winding 202 can be increased and the contact pressure between the second connection portion 326 and the second heat sink 406 can be increased. By increasing the contact pressure also the thermal coupling can be increased. Thus, the heat can be transported more efficiently to the heat sink 310 and the second heat sink 406.

[0066] Although not shown in the figures, the PCB 500 may comprise at least one resonance capacitance and one power electronic including at least one switching element, for example a MOSFET. As shown in FIG. 2, the shielding element 300 comprises pins 316, which are received by the PCB 500. Thus, the heat sink portion 310 of the shielding element 300 is also used to dissipate heat generated by the power electronic components supported by the PCB 500.

REFERENCE NUMERALS

[0067]

TABLE-US-00001 Reference Numerals Description 100 transformer unit 200 transformer 202 primary winding 203 first opening 204 secondary winding 206 longitudinal axis 208 distance 210 cover 220 three-legged magnetic core 222 cylindrical central part 224 rectangular side legs 226 yoke 230 bobbin 232 first cylindrical part 234 second cylindrical part 235 first flange portion 236 second flange portion 237 third flange portion 238 fourth flange portion 239 connecting element 242 first connector stripe 244 second connector stripe 300 shielding element 310 heat sink portion 312 central plate 314 wing plates 320 clamping portion 322 central clamp portion 324 first connecting portion 326 second connecting portion 400 switching power supply 402 cover element 404 bottom element 406 second heat sink 602 first thermal coupling element 604 second thermal coupling element