Transformer with planar primary winding
View Patent ↗A transformer, such as a current sense transformer, in which conductive traces disposed within a printed circuit board serve as the primary winding of the transformer. The transformer also includes a secondary winding, for example wound around a hollow pin of a bobbin, through which a leg of a magnetic core is disposed. The magnetic core leg, and in some embodiments also all or a part of the secondary winding, is inserted into a through-hole in the printed circuit board that is surrounded by the primary winding traces.
1. A transformer for use with a printed circuit board having a plurality of through-holes defined therein, said transformer comprising:
a first winding comprising at least one conductive trace at least partially surrounding a first through-hole in the printed circuit board;
a magnetic core element comprising a top member, a bottom member, and first and second legs extending between said top and bottom members, said first leg extending through the first through-hole and said second leg extending through a second through-hole in the printed circuit board, said top and bottom members of said magnetic core element disposed on opposite sides of the printed circuit board;
a second winding concentric with a portion of said magnetic core element and comprising a wire winding including a plurality of turns encircling said first leg of said magnetic core, wherein at least some of the turns of said second winding are disposed within the first through-hole; and
first and second leads connected to respective ends of said second winding.
2. The transformer of claim 1 , wherein all of the turns of said second winding are disposed within the first through-hole of the printed circuit board.
3. The transformer of claim 1 , further comprising:
a bobbin comprising a base and a hollow pin element, said base disposed on one side of the printed circuit board and supporting said first and second leads, said hollow pin element extending from said base and disposed within the first through-hole, said second winding disposed on an outer surface of said pin element, and said first leg of said magnetic core element disposed within said hollow pin element.
4. The transformer of claim 1 , wherein said at least one conductive trace comprises a plurality of conductive traces, each conductive trace disposed in one of a plurality of conductive layers of the printed circuit board, and at least partially surrounding the first through-hole.
5. The transformer of claim 4 , wherein said conductive traces are connected in parallel with one another by edge plating extending around the first through-hole.
6. The transformer of claim 1 , wherein said first winding is a primary winding of said transformer, wherein said second winding is a first secondary winding of said transformer, said transformer further comprising:
a second secondary winding concentric with said first leg of said magnetic core element; and
third and fourth leads connected to respective ends of said second secondary winding.
7. The transformer of claim 1 , wherein said magnetic core element further comprises:
a third leg extending into a third through-hole in the printed circuit board, the third through-hole disposed on an opposite side of the first through-hole from the second through-hole;
wherein said top member is connected to a first end of each of said first, second, and third legs on one side of the printed circuit board;
and wherein said bottom member is connected to a second end of each of said first, second, and third legs on another side of the printed circuit board.
8. A printed circuit board assembly comprising:
a printed circuit board comprising at least one conductive trace, said printed circuit board having a plurality of through-holes defined therein, each through hole extending from a first side of the printed circuit board to a second side of the printed circuit board, said at least one conductive trace at least partially surrounding a first through-hole in said printed circuit board; and
a transformer comprising:
a magnetic core element comprising a top member, a bottom member, and first and second legs extending between said top and bottom members, said first leg extending through the first through-hole in said printed circuit board, said second leg extending through a second through-hole in said printed circuit board;
a first winding comprising said at least one conductive trace;
a second winding concentric with a portion of said magnetic core element and comprising a wire winding including a plurality of turns encircling said first leg of said magnetic core, wherein at least some of the turns of said second winding are disposed within the first through-hole; and
first and second leads connected to respective ends of said second winding.
9. The printed circuit board assembly of claim 8 , further comprising:
a bobbin comprising a base and a hollow pin element, said base disposed on the first side of the printed circuit board and supporting said first and second leads, said hollow pin element extending from said base and disposed within the first through-hole, said second winding disposed on an outer surface of said hollow pin element, and said first leg of said magnetic core element disposed within said hollow pin element.
10. The printed circuit board assembly of claim 8 , wherein said printed circuit board comprises a plurality of conductive layers, said at least one conductive trace comprising a plurality of conductive traces, each conductive trace disposed within one of said conductive layers of said printed circuit board and at least partially surrounding the first through-hole.
11. The printed circuit board assembly of claim 10 , wherein said conductive traces are connected in parallel with one another by edge plating extending around the first through-hole.
12. A method of assembling a printed circuit board assembly, said method comprising:
providing a printed circuit board including at least one conductive trace, the printed circuit board having a plurality of through-holes defined therein, the at least one conductive trace at least partially surrounding a first through-hole in the printed circuit board;
providing a magnetic core element including a top member, a bottom member, a first leg, and a second leg;
inserting the first leg of the magnetic core element through the first through-hole such that the at least one conductive trace at least partially surrounds the first leg, the at least one conductive trace forming a first winding of a transformer;
inserting the second leg of the magnetic core element through a second through-hole in the printed circuit board; and
coupling a second winding to the printed circuit board such that the second winding is concentric with a portion of the magnetic core element, the second winding including a wire winding, wherein coupling the second winding includes coupling the seconding winding to the printed circuit board such that the wire winding includes a plurality of turns encircling the first leg of the magnetic core and at least some of the turns are disposed within the first through-hole; and
connecting first and second leads to respective ends of the second winding.