# US 8,570,768 B2 · Low-cost transformer assembly > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 8,570,768 B2 - Document ID: US8570768B2 - Status: Granted - Kind: B2 - Application number: 13/088,268 - Filed: 2011-04-15 - Published: 2012-10-18 - Granted: 2013-10-29 - Earliest claimed: 2011-04-15 - Assignees: Power Integrations, Inc. - Applicants: Eng Hwee Quek - Inventors: Eng Hwee Quek - Web page: https://patentgrep.com/patent/US8570768B2 ## CPC - H05K 3/30: Assembling printed circuits with electric components, e.g. with resistors - H01F 27/306: {Fastening or mounting coils or windings on core, casing or other support} - H05K 7/02: Arrangements of circuit components or wiring on supporting structure - H01F 27/065: {Mounting on printed circuit boards} - H01F 27/325: {Coil bobbins (formers for coils in general H01F5/02)} - Y10T 29/49073: by assembling coil and core - Y10T 29/4913: Assembling to base an electrical component, e.g., capacitor, etc. - H05K: PRINTED CIRCUITS; CASINGS OR CONSTRUCTIONAL DETAILS OF ELECTRIC APPARATUS; MANUFACTURE OF ASSEMBLAGES OF ELECTRICAL COMPONENTS - H01F: MAGNETS; INDUCTANCES; TRANSFORMERS; SELECTION OF MATERIALS FOR THEIR MAGNETIC PROPERTIES - Y10T: TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION ## Abstract A transformer assembly is disclosed. An example circuit board assembly includes a circuit board. A drum core inductor is also included and has a drum core, a first winding, and first and second terminals extending from a first end of the drum core inductor. A wire of the first winding is wound around an axis of the drum core. The first winding has first and second ends coupled to the first and second terminals of the drum core inductor, respectively. A bobbin has first and second terminals extending from a first end of the bobbin. A wire of a second winding is wound around an axis of the bobbin. The second winding has first and second ends coupled to the first and second terminals of the bobbin, respectively. The first ends of the drum core inductor and the bobbin are attached to a circuit board such that the drum core inductor is positioned on the circuit board inside an opening of the bobbin defined along the axis of the bobbin. The drum core inductor and the bobbin are detached from one another. ## Claims ### Claim 1 A circuit board assembly, comprising: a circuit board; a drum core inductor having a drum core, a first winding and first and second terminals extending from a first end of the drum core inductor, wherein a wire of the first winding is wound around an axis of the drum core, the first winding having first and second ends coupled to the first and second terminals of the drum core inductor, respectively; and a bobbin having first and second terminals extending from a first end of the bobbin, wherein a wire of a second winding is wound around an axis of the bobbin, the second winding having first and second ends coupled to the first and second terminals of the bobbin, respectively, wherein the first ends of the drum core inductor and the bobbin are attached to a circuit board such that the drum core inductor is positioned on the circuit board inside an opening of the bobbin defined along the axis of the bobbin, wherein the drum core inductor and the bobbin are detached from one another. ### Claim 2 (depends on 1) The circuit board assembly of claim 1 wherein at least one of the drum core inductor and the bobbin are attached to the circuit board with solder at their respective first and second terminals. ### Claim 3 (depends on 2) The circuit board assembly of claim 2 wherein the respective first and second terminals pass through respective openings in the circuit board. ### Claim 4 (depends on 1) The circuit board assembly of claim 1 wherein the first winding is magnetically coupled to the second winding. ### Claim 5 (depends on 1) The circuit board assembly of claim 1 wherein the axis of the drum core inductor and the axis of the bobbin are substantially collinear. ### Claim 6 (depends on 1) The circuit board assembly of claim 1 wherein a length of the first winding along the axis of the drum core inductor is substantially equal to a length of the second winding along the axis of the bobbin. ### Claim 7 (depends on 6) The circuit board assembly of claim 6 wherein a center of the first winding along the axis of the drum core inductor and a center of the second winding along the axis of the bobbin are a substantially equal distance from a surface of the circuit board. ### Claim 8 (depends on 1) The circuit board assembly of claim 1 wherein the bobbin further comprises a first flange at the first end of the bobbin. ### Claim 9 (depends on 8) The circuit board assembly of claim 8 wherein first and second recesses are defined along an edge of the first flange, wherein the wire of the second winding passes into the first and second recesses and the first and second recesses fix a position of the wire of the second winding between the first and second terminals of the bobbin. ### Claim 10 (depends on 8) The circuit board assembly of claim 8 wherein the bobbin further comprises a second flange along the axis of the bobbin, wherein the wire of the second winding is wound around the axis of the bobbin between the first and second flanges. ### Claim 11 (depends on 10) The circuit board assembly of claim 10 wherein third and fourth recesses are defined along an edge of the second flange, wherein the wire of the second winding passes into the third and fourth recesses and the third and fourth recesses fix a position of the wire of the second winding between the first and second terminals of the bobbin. ### Claim 12 (depends on 10) The circuit board assembly of claim 10 wherein the bobbin further comprises a third flange along the axis of the bobbin at a second end of the bobbin such that the second flange is disposed between the first and third flanges, wherein a distance between the second and third flanges along the axis of the bobbin is greater than zero. ### Claim 13 (depends on 1) The circuit board assembly of claim 1 wherein the first end of the drum core inductor includes a standoff. ### Claim 14 (depends on 1) The circuit board assembly of claim 1 further comprising a spacer between the first end of the drum core inductor and the circuit board. ### Claim 15 (depends on 1) The circuit board assembly of claim 1 further comprising a primary side circuit of a switched mode power converter, the primary side circuit including a power switch coupled to the first end of the first winding, the second end of the first winding coupled to an input terminal of the power converter. ### Claim 16 (depends on 15) The circuit board assembly of claim 15 further comprising a secondary side circuit of the switched mode power converter, wherein the second winding is coupled to an output of the switched mode power converter, the secondary side circuit including a rectifier circuit and a filter circuit coupled to the output of the switch mode power converter. ### Claim 17 (depends on 16) The circuit board assembly of claim 16 further comprising a feedback circuit coupled to provide a feedback signal through an isolation circuit to a control circuit coupled to control the power switch in response to the feedback signal. ### Claim 18 (depends on 17) The circuit board assembly of claim 17 further comprising a clamp circuit coupled between the first and second ends of the first winding. ### Claim 19 (depends on 17) The circuit board assembly of claim 17 wherein the isolation circuit comprises an optocoupler coupled between the control circuit and the feedback circuit.