# US 9,882,543 B2 · Magnetic structures for filtering amplifier outputs > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 9,882,543 B2 - Document ID: US9882543B2 - Status: Granted - Kind: B2 - Application number: 14/706,683 - Filed: 2015-05-07 - Published: 2016-11-10 - Granted: 2018-01-30 - Earliest claimed: 2015-05-07 - Assignees: Bose Corporation - Applicants: Bose Corporation - Inventors: Ali Mohammadpour; Michael B. Nussbaum; Remco Terwal - Web page: https://patentgrep.com/patent/US9882543B2 ## CPC - H03H 7/09: Filters comprising mutual inductance - H01F 27/24: Magnetic cores - H01F 37/00: Fixed inductances not covered by group H01F17/00 - H03F 1/565: {using inductive elements} - H03F 3/19: with semiconductor devices only - H03F 3/21: with semiconductor devices only {(H03F3/245 takes precedence)} - H03F 3/217: Class D power amplifiers; Switching amplifiers - H03H 1/0007: {of radio frequency interference filters} - H03H 7/0115: {comprising only inductors and capacitors (H03H7/075, H03H7/09, H03H7/12, H03H7/13 take precedence)} - H03F 2200/171: A filter circuit coupled to the output of an amplifier - H03F 2200/451: the amplifier being a radio frequency amplifier - H03H 2001/0035: {Wound magnetic core} - H03H 2001/0092: {Inductor filters, i.e. inductors whose parasitic capacitance is of relevance to consider it as filter} - H03H: IMPEDANCE NETWORKS, e.g. RESONANT CIRCUITS; RESONATORS (waveguides, resonators, lines or other devices of the waveguide type H01P) - H01F: MAGNETS; INDUCTANCES; TRANSFORMERS; SELECTION OF MATERIALS FOR THEIR MAGNETIC PROPERTIES - H03F: AMPLIFIERS ## Abstract The technology described in this document can be embodied in an apparatus that includes at least four magnetic cores, wherein each core is for supporting an inductor of a filter circuit. Each of the cores include a first section, and a second section separated from the first section by an adhesive layer. The apparatus also includes an air-core structure to store magnetic energy, the air-core structure including a set of focusing projections that define a hollow cavity. The individual focusing projections of the set are disposed on different sides of the hollow cavity to focus magnetic field from the at least four magnetic cores through the hollow cavity. ## Claims ### Claim 1 An apparatus comprising: at least four magnetic cores, each magnetic core supporting an inductor of a filter circuit, wherein each magnetic core comprises: a first section, and a second section separated from the first section by an adhesive layer; and an air-core structure to store magnetic energy, the air-core structure comprising: a set of focusing projections that define a hollow cavity, wherein individual focusing projections of the set are disposed on different sides of the hollow cavity to focus magnetic fields from the at least four magnetic cores through the hollow cavity, wherein each of the inductors corresponding to the at least four magnetic cores comprises a conducting wire wound in a clockwise or anticlockwise direction around a corresponding magnetic core, the direction of winding for at least two inductors being different from the direction of winding of at least two other inductors, and wherein the at least four inductors are inductively coupled to one another. ### Claim 2 (depends on 1) The apparatus of claim 1, wherein the at least four magnetic cores and the air-core structure are spatially distributed in the apparatus such that magnetic flux in a differential mode from each of the at least four magnetic cores passes through the hollow cavity. ### Claim 3 (depends on 1) The apparatus of claim 1, wherein the at least four magnetic cores and the air-core structure are spatially distributed within the apparatus such that in a common mode, a total magnetic flux passing through the hollow cavity is substantially zero. ### Claim 4 An apparatus comprising: at least four magnetic cores, each magnetic core supporting an inductor of a filter circuit, and wherein each magnetic core comprises: a first section, and a second section separated from the first section by an adhesive layer; and an air-core structure to store magnetic energy, the air-core structure comprising: a set of focusing projections that define a hollow cavity, wherein individual focusing projections of the set are disposed on different sides of the hollow cavity to focus magnetic fields from the at least four magnetic cores through the hollow cavity, wherein the filter circuit is disposed between an amplifier circuit and a load that is drivable by the amplifier circuit from two sides of the load, and wherein multiple outputs of the amplifier circuit are interleaved. ### Claim 5 (depends on 4) The apparatus of claim 4, wherein the filter circuit is operable in a common mode and at least one differential mode. ### Claim 6 (depends on 4) The apparatus of claim 4, wherein the load is a bridge-tied load. ### Claim 7 (depends on 4) The apparatus of claim 4, wherein the amplifier circuit comprises at least four buck converters, an output of each buck converter being connected to a corresponding inductor. ### Claim 8 An apparatus comprising: an amplifier circuit comprising at least four amplifiers; a load driven by the amplifier circuit from two sides of the load; and a filter circuit comprising: at least four inductors that are inductively coupled with one another, each of the inductors comprising a conductor wire wound around a core of magnetic material in a clockwise or anticlockwise direction, the direction of winding for at least two inductors being different from the direction of winding of at least two other inductors, a set of focusing projections defining a hollow cavity that stores magnetic energy when subjected to a magnetic flux, at least four input terminals, each input terminal for connecting a corresponding one of the at least four inductors to one of the at least four amplifiers; and at least two output terminals for connecting the filter circuit to the load. ### Claim 9 (depends on 8) The apparatus of claim 8, wherein each of the at least four amplifiers comprises a buck converter. ### Claim 10 (depends on 8) The apparatus of claim 8, wherein the load comprises a bridge-tied load. ### Claim 11 (depends on 10) The apparatus of claim 10, wherein the at least two output terminals of the filter circuit are connected to two terminals of the bridge-tied load. ### Claim 12 (depends on 8) The apparatus of claim 8, wherein outputs of the at least four amplifiers are interleaved. ### Claim 13 (depends on 8) The apparatus of claim 8, wherein the at least four inductors comprise six inductors or eight inductors. ### Claim 14 A filter circuit comprising: at least four inductors that are inductively coupled with one another, each of the inductors comprising a conductor wire wound around a core of magnetic material in a clockwise or anticlockwise direction, a direction of winding for at least two inductors being different from a direction of winding of at least two other inductors; a set of focusing projections defining a hollow cavity that stores magnetic energy when subjected to a magnetic flux; at least four input terminals, each input terminal connected to an output of an amplifier corresponding to one of the at least four inductors; and at least two output terminals for connecting the filter circuit to a load driven from two sides of the load by the amplifiers corresponding to the at least four inductors. ### Claim 15 (depends on 14) The filter circuit of claim 14 wherein the filter circuit is operable in a common mode and at least one differential mode. ### Claim 16 (depends on 15) The filter circuit of claim 15, wherein a common mode inductance of the filter circuit is at least 1.5 times higher than a differential mode inductance for the at least one differential mode. ### Claim 17 (depends on 14) The filter circuit of claim 14, wherein the at least four inductors and the hollow cavity are spatially distributed such that in a common mode, a total magnetic field passing through the hollow cavity is substantially zero. ### Claim 18 (depends on 14) The filter circuit of claim 14, wherein the outputs of the at least four amplifiers are interleaved. ### Claim 19 (depends on 14) The filter circuit of claim 14, wherein (i) the magnetic cores supporting the at least four inductors, and (ii) the hollow cavity are within a structure comprising the magnetic material. ### Claim 20 (depends on 19) The filter circuit of claim 19, wherein individual focusing projections of the set of focusing projections are disposed on opposite sides of the hollow cavity to focus magnetic fields from the at least four magnetic cores through the hollow cavity. ### Claim 21 (depends on 14) The filter circuit of claim 14, wherein a cross-sectional area of the hollow cavity is substantially equal to sum of cross-sectional areas of the at least four magnetic cores. ### Claim 22 (depends on 14) The filter circuit of claim 14, wherein a first set of at least two inductors of the at least four inductors has a clockwise direction of winding and is connected to one of the at least two output terminals, and a second set of at least two inductors, of the at least four inductors different from the first set of at least two inductors, has an anticlockwise direction of winding and is connected to another of the at least two output terminals. ### Claim 23 An apparatus comprising: at least four magnetic cores, each magnetic core supporting an inductor of a filter circuit, wherein each magnetic core comprises: a first section, and a second section separated from the first section by an adhesive layer; and an air-core structure to store magnetic energy, the air-core structure comprising: a set of focusing projections that define a hollow cavity, wherein individual focusing projections of the set are disposed on different sides of the hollow cavity to focus magnetic fields from the at least four magnetic cores through the hollow cavity, wherein a cross-sectional area of the hollow cavity is substantially equal to a sum of cross-sectional areas of the at least four magnetic cores such that flux distribution in the apparatus is uniform.