EMI filter with an integrated structure of common-mode inductors and differential-mode capacitors realized by flexible printed circuit board

1. An EMI (electromagnetic interference) filter with integrated inductors and capacitors realized using at least one flexible printed circuit (FPC), comprising:

a closed magnetic circuit, formed by a first magnetic core and a second magnetic core, comprising a plurality of magnetic core pillars;

at least one of the plurality of magnetic core pillars being wound with the at least one FPC, being a multi-layer serially connected FPC, wherein the at least one FPC is formed by laminating a top insulating layer, 2N copper-foil layers, 2N−1 insulating medium layers, and a bottom insulating layer, wherein N is a positive integer, one of the insulating medium layers is placed between every two neighboring copper-foil layers of the 2N copper-foil layers, and

odd-numbered copper-foil layers of the 2N copper-foil layers are connected to each other on their head and tails ends, respectively, while even-numbered copper-foil layers of the 2N copper-foil layers are connected to each other on their head and tails ends, respectively.

2. The EMI filter of claim 1 , wherein the first and second magnetic cores are both “E” shaped, such that the closed magnetic circuit comprising the plurality of magnetic core pillars consists of three magnetic core pillars.

3. The EMI filter of claim 1 , wherein the first magnetic core is of an “E” shape and the second magnetic core is of an “I” shape, such that the closed magnetic circuit comprising the plurality of magnetic core pillars consists of three magnetic core pillars.

4. The EMI filter of claim 1 , wherein the first and second magnetic cores are both of a “U” shape, such that the closed magnetic circuit comprising the plurality of magnetic core pillars consists of two magnetic core pillars.

5. The EMI filter of claim 1 , wherein the first magnetic cores is of a “U” shape and the second magnetic core is of an “I” shape, such that the closed magnetic circuit comprising the plurality of magnetic core pillars consists of two magnetic core pillars.

6. The EMI filter of claim 1 , wherein N=1.

7. The EMI filter of claim 1 , wherein the insulating medium layers are made of a flexible dielectric material for at least one of the capacitors.

8. An EMI (electromagnetic interference) filter with integrated inductors and capacitors realized using at least one flexible printed circuit (FPC), comprising:

a closed magnetic circuit of a tri-pillar magnetic core formed by a first magnetic core and a second magnetic core, wherein there is an air gap in a middle magnetic core pillar of the tri-pillar magnetic core of the closed magnetic circuit, and

each of two side magnetic core pillars of the tri-pillar magnetic core is respectively wound with a tubular double-faced flexible circuit board comprising the at least one flexible printed circuit, the tubular double-faced flexible circuit board being formed in turn by a first outermost insulating layer, a first copper foil, an insulating medium layer, a second copper foil and a second outermost insulating layer, and at a head end and a tail end of the first copper foil and at a tail end of the second copper foil are respectively welded pads for connecting with an external circuit.

9. The EMI filter of claim 8 , wherein the first magnetic core and the second magnetic core are both E-shaped, so as to form the closed magnetic circuit of the tri-pillar magnetic core.

10. The EMI filter of claim 8 , wherein one of the first magnetic core and the second magnetic core is E-shaped, and the other is I-shaped, so as to form the closed magnetic circuit of the tri-pillar magnetic core.

11. The EMI filter of claim 8 , wherein the insulating medium layer is an organic film capacitor medium material.