Dual-permeability core structure for use in high-frequency magnetic components

• US 5,062,197 A
• Filed: 05/07/1990
• Issued: 11/05/1991
• Est. Priority Date: 12/27/1988
• Status: Expired due to Fees

• Current Assignee: North American Power Supplies, Inc.
• Original Assignee: General Electric Company
• Inventors: Charles, Richard J., Ngo, Khai D.
• Primary Examiner(s): Hall, Carl E.
• Application Number:
  US07/519,997
• Time in Patent Office: 547 Days
• Field of Search: 29/606, 29/607, 29/608, 29/602.1, 336/83, 336/233
• US Class Current: 29/606
• CPC Class Codes: H01F 2003/106 Magnetic circuits using combinations of different magnetic materials
• CPC Class Codes: H01F 27/255 made from particles H01F27/26 takes precedence
• CPC Class Codes: H01F 3/10 Composite arrangements of magnetic circuits
• CPC Class Codes: Y10T 29/49073 by assembling coil and core
• CPC Class Codes: Y10T 29/49075 including permanent magnet or core
• CPC Class Codes: Y10T 29/49076 From comminuted material

Abstract

A dual-permeability magnetic core structure is provided for use in small, high-frequency inductors and transformers. The dual-permeability core encloses a winding window containing planar windings and comprises high-permeability and low-permeability sections positioned to produce a highly uniform, or uniformly varying, magnetic field on the winding surfaces. The dual-permeability core products low winding losses and a low AC-to-DC resistance ratio. Fabrication of the dual-permeability core involves a method of controlling the permeability of a magnetic material and a methd of combining structures of two different permeability values.

Claims

1. A method of manufacturing a high-frequency magnetic circuit component, for use as an inductor or a transformer, having a closed-loop, dual-permeability magnetic pot core including therein a winding window which contains a plurality of planar conductors, comprising the steps of:

(a) machining a high-permeability ferrite to form a substantially cylindrical housing comprising an substantially cylindrical peripheral wall and a substantially cylindrical core post located in the interior of said cylindrical housing, said core post being concentric with said cylindrical wall;

(b) providing a temporary base for rigidly mounting said housing thereon;

(c) applying a first low-permeability layer above and adjacent to said temporary base;

(d) inserting at least one conductive winding into said housing, said winding lying above and adjacent to said first low-permeability layer;

(e) applying a second low-permeability layer above and adjacent to said winding; and

(f) removing said temporary base.

2. The method of claim 1 wherein said first and second low-permeability layers each comprise a first mixture composed of a high-permeability ferrite powder and an organic binder.

3. The method of claim 1 wherein said low-permeability layers comprise a low-permeability, sintered ferrite powder.

4. The method of claim 1 wherein said low-permeability layers are rigid structures comprised of a sintered ferrite powder, said structures exhibiting porosity in excess of 20 volume %.

5. The method of claim 2 wherein said high-permeability ferrite powder comprises MO(Fe₂ O₃)₁±

x where x has a value ranging from 0 to about 0.2 and where M is a divalent metal cation selected from the group consisting of Mg, Mn, Fe, Co, Ni, Zn, Cu and including combinations thereof.

6. The method of claim 2 wherein said high-permeability ferrite powder comprises a nickel zinc ferrite.

7. The method of claim 2 wherein said high-permeability ferrite powder comprises a manganese zinc ferrite.

8. The method of claim 2 wherein said ferrite powder comprises ferrite particles having a specific surface area in the range from about 0.2 to about 10 meters² per gram.

9. The method of claim 2 wherein said ferrite powder comprises substantially spheroidal ferrite particles.

10. The method of claim 2 wherein said organic binder comprises an epoxy resin.

11. The method of claim 2 wherein said organic binder comprises a thermoplastic material.

12. The method of claim 2 wherein said ferrite powder is prepared according to the steps of:

providing a high permeability ferrite-forming mixture;

calcining said high-permeability ferrite-forming mixture to form a substantially uniform, high-permeability ferrite; and

comminuting said ferrite to produce a ferrite powder.

13. The method of claim 2 wherein the steps of applying a first low-permeability layer and applying a second low-permeability layer, respectively, each comprises:

packing said ferrite powder into said housing;

infiltrating said packed ferrite powder with said organic binder to form said first mixture; and

permitting said first mixture to solidify.

14. The method of claim 2 wherein the steps of applying a first low-permeability layer and applying a second low-permeability layer, respectively, each comprises:

admixing said ferrite powder and said organic binder to form said first mixture;

allowing said first mixture to solidify;

machining a ring-shaped compact from said first mixture to conform to the shape of the interior of said housing;

inserting said compact into said housing; and

infiltrating said housing with a second mixture comprising a ferrite powder and an organic binder to fill in any gaps between said compact and said housing.

15. The method of claim 2 wherein the steps of applying a first low-permeability layer and applying a second low-permeability layer, respectively, each comprises:

tape casting said ferrite powder with said organic binder to form a ferrite tape comprising said first mixture;

punching a ring-shaped compact from said tape;

inserting said ring-shaped compact into said housing; and

infiltrating said housing with a second mixture comprising a ferrite powder and an organic binder to fill in any gaps between said compact and said housing.

16. The method of claim 2 wherein the steps of applying a first low-permeability layer and applying a second low-permeability layer, respectively, each comprises:

admixing said ferrite powder and said organic binder to form said first mixture;

17. The method of claim 2 wherein said first mixture comprises approximately 40-50% by volume of said ferrite powder and approximately 40-50% by volume of said organic binder.

18. A method of fabricating a high frequency magnetic circuit component, for use as an inductor or a transformer, having a closed-loop, dual-permeability sleeve core including a top, a bottom and two sides, said core including therein a winding window which contains a plurality of planar conductors, comprising the steps of:

(a) machining a low-permeability magnetic material to form two substantially rectangular plates;

(b) forming a sandwich-like structure by stacking said two plates and by mounting at least one conductive winding therebetween, said two plates comprising the top and the bottom of the core;

(c) fixing said sandwich-like structure by applying an organic binder thereto;

(d) machining a high-permeability magnetic material to form two substantially rectangular side members; and

e) mounting said side members to said sandwich-like structure to form the sides of the core.

19. The method of claim 18 wherein said low-permeability magnetic material comprises a mixture of a ferrite powder and an organic binder and wherein said high-permeability magnetic material comprises a sintered ferrite.

20. The method of claim 18 wherein said low-permeability magnetic material and said high-permeability magnetic material each comprise a sintered ferrite.