Transverse shield wire for energy transfer element
Energy transfer elements having a shield to reduce EMI while maintaining a low profile are disclosed. In one example, the transformer may include a transverse shield wire that may be utilized to keep displacement current within the energy transfer element. While windings of the energy transfer element are generally wound axially around the axis of a bobbin in a direction generally perpendicular to the axis of the bobbin, the transverse shield wire may be placed on the bobbin extending over multiple power windings of the energy transfer element in a transverse direction. The transverse shield wire may be situated outside all other windings wound around the bobbin. In some examples, one end of the transverse shield wire may be coupled to a switching node of the energy transfer element while the other end of the transverse shield wire may be coupled to a winding of the energy transfer element.
1. An energy transfer element comprising:
a bobbin;
a primary winding wound around an axis of the bobbin between a first end of the bobbin and a second end of the bobbin;
a secondary winding wound around the axis of the bobbin between the first end of the bobbin and the second end of the bobbin; and
a transverse shield wire having a first end and a second end, wherein the first end of the transverse shield wire is coupled to a first terminal mounted to the bobbin, wherein the second end of the transverse shield wire is coupled to a second terminal mounted to the bobbin, wherein the first end of the transverse shield wire is coupled to the first end of the bobbin, wherein the transverse shield wire extends between the first and second terminals and in a direction transverse to the primary winding and the secondary winding, wherein the transverse shield wire encloses an area that extends between the first and second ends of the bobbin a distance that is less than a distance between the first end of the bobbin and the second end of the bobbin along the axis of the bobbin.
2. The energy transfer element of claim 1 , wherein the transverse shield wire is formed from the same wire as the primary winding.
3. The energy transfer element of claim 1 , wherein the transverse shield wire forms a loop extending in the direction transverse to the primary winding and the secondary winding.
4. The energy transfer element of claim 1 , wherein the transverse shield wire extends over a plurality of turns of the primary winding and a plurality of turns of the secondary winding in the direction transverse to the primary winding and the secondary winding.
5. The energy transfer element of claim 1 , further comprising a first insulating layer wound around the primary winding.
6. The energy transfer element of claim 1 , further comprising an auxiliary winding wound around the axis of the bobbin.
7. The energy transfer element of claim 6 , further comprising a second insulating layer wound around the auxiliary winding, wherein the secondary winding is wound around the second insulating layer.
8. The energy transfer element of claim 1 , further comprising a third insulating layer wound around the secondary winding, wherein the transverse shield wire is placed on the third insulating layer.
9. The energy transfer element of claim 1 , further comprising a balance shield winding wound between the primary winding and the secondary winding.
10. The energy transfer element of claim 1 , further comprising:
a first external node for coupling to an external circuit, wherein a first end of the primary winding is coupled to the first external node; and
a second external node for coupling to the external circuit, wherein a first end of the transverse shield wire is coupled to the second external node, and wherein a second end of the primary winding is coupled to a second end of the transverse shield wire.
11. The energy transfer element of claim 1 , wherein the transverse shield does not enclose the axis of the bobbin.
12. A power converter comprising:
a power switch;
a controller for controlling the power switch; and
an energy transfer element comprising:
a bobbin;
a primary winding wound around an axis of the bobbin between a first end of the bobbin and a second end of the bobbin;
a secondary winding wound around the axis of the bobbin between the first end of the bobbin and the second end of the bobbin; and
a shield wire having a first end and a second end, wherein the first end of the shield wire is coupled to a first terminal mounted to the bobbin, wherein the second end of the shield wire is coupled to a second terminal mounted to the bobbin, wherein the first end of the shield wire is coupled to the first end of the bobbin between the primary winding and the power switch, wherein the shield wire extends between the first and second terminals and in a direction transverse to the primary winding and the secondary winding, wherein the shield wire encloses an area that extends between the first and second ends of the bobbin a distance that is less than a distance between the first end of the bobbin and the second end of the bobbin along the axis of the bobbin.
13. The power converter of claim 12 , wherein the energy transfer element further comprises an auxiliary winding for providing a feedback signal to the controller.
14. The power converter of claim 13 , wherein the energy transfer element further comprises:
a first insulating layer wound around the primary winding, wherein the auxiliary winding is wound around the first insulating layer;
a second insulating layer wound around the auxiliary winding, wherein the secondary winding is wound around the second insulating layer; and
a third insulating layer wound around the secondary winding, wherein the shield wire is placed on the third insulating layer.
15. The power converter of claim 14 , further comprising a balance shield winding wound between the first insulating layer and the second insulating layer.
16. The power converter of claim 15 , wherein a first end of the balance shield winding is coupled to the auxiliary winding, and wherein a second end of the balance shield winding is uncoupled.
17. The power converter of claim 14 , wherein the shield wire is not wound around an axis of the bobbin.
18. The power converter of claim 12 , wherein the shield wire extends over a plurality of turns of the primary winding and a plurality of turns of the secondary winding in the direction transverse to the primary winding and the secondary winding.
19. The power converter of claim 12 , wherein the shield wire forms a loop extending in the direction transverse to the primary winding and the secondary winding.
20. The power converter of claim 12 , wherein the shield wire and the primary winding form a contiguous wire.