# US 7,609,535 B2 · Method and apparatus for providing input EMI filtering in power supplies > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 7,609,535 B2 - Document ID: US7609535B2 - Status: Granted - Kind: B2 - Application number: 10/948,945 - Filed: 2004-09-23 - Published: 2005-02-24 - Granted: 2009-10-27 - Earliest claimed: 2002-11-18 - Assignees: Power Integrations, Inc. - Inventors: Balu Balakrishnan - Web page: https://patentgrep.com/patent/US7609535B2 ## CPC - H02M 1/44: Circuits or arrangements for compensating for electromagnetic interference in converters or inverters - H02M 1/126: {using passive filters} - H02M: APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF (transformers H01F; dynamo-electric converters H02K47/00; controlling transformers, reactors or choke coils, control or regulation of electric motors, generators or dynamo-electric converters H02P) ## Abstract A power supply electromagnetic interference (EMI) filter circuit and technique. In one embodiment, a method of filtering EMI in a power supply includes rectifying an AC signal from an AC source, smoothing the rectified AC signal with a bulk storage capacitor to provide a DC output as an input to a power conversion circuit and filtering the EMI generated by the power conversion circuit from reaching the AC source by using the bulk capacitor and one or more inductors in combination with the AC source capacitance as an EMI filter. In one embodiment the method also includes the use of one or more of the inductors as a fusing element. ## Claims ### Claim 1 A power supply circuit comprising: an input terminal to be directly coupled to an AC source having a distributed source capacitance; an EMI filter coupled to the input terminal, wherein the EMI filter consists of an inductor and a capacitor, wherein a first terminal of the inductor is coupled to the input terminal such that a current flow through the inductor is substantially equal to a current flow through the input terminal, and wherein a second terminal of the inductor is coupled to the capacitor, wherein the EMI filter forms a pi filter with the distributed source capacitance of the AC source when the input terminal is coupled to the AC source such that a current flowing through the AC source is substantially equal to the current flow through the input terminal, and wherein the inductor is an input fuse that becomes an open circuit to limit an abnormal amount of current to all other components of the power supply circuit; and a power conversion circuit coupled to the EMI filter, wherein the capacitor is coupled between the inductor and the power conversion circuit to provide bulk storage for a direct current (DC) input of the power conversion circuit. ### Claim 2 (depends on 1) The power supply circuit of claim 1, wherein the inductor is coupled directly to the input terminal to protect all other components of the power supply circuit from the abnormal amount of current flow. ### Claim 3 (depends on 1) The power supply circuit of claim 1, further comprising a rectifier coupled to the EMI filter to rectify an AC signal received from the AC source. ### Claim 4 (depends on 3) The power supply circuit of claim 3, wherein the rectifier is coupled between the second terminal of the inductor and the capacitor. ### Claim 5 (depends on 3) The power supply circuit of claim 3, wherein the rectifier is a half wave rectifier circuit. ### Claim 6 (depends on 3) The power supply circuit of claim 3, wherein the rectifier is a full wave rectifier circuit. ### Claim 7 A power supply circuit, comprising: a rectifier circuit; and a single electromagnetic interference (EMI) filter circuit coupled to the rectifier circuit, the EMI filter circuit consisting of: an inductor having a first terminal to be coupled to an alternating current (AC) source having an AC source capacitance; and a bulk storage capacitor coupled across an output of the rectifier circuit, wherein an EMI pi filter is formed with the AC source capacitance, the inductor, and the bulk storage capacitor when the first terminal of the inductor is coupled to the AC source. ### Claim 8 (depends on 7) The power supply circuit of claim 7, wherein the bulk storage capacitor is coupled to provide bulk storage for the DC input of the power supply conversion circuit. ### Claim 9 (depends on 7) The power supply circuit of claim 7, wherein the bulk storage capacitor is a single capacitor. ### Claim 10 (depends on 7) The power supply circuit of claim 7, wherein a second terminal of the inductor is coupled to an input of the rectifier. ### Claim 11 (depends on 7) The power supply circuit of claim 7, wherein the rectifier is half wave rectifier circuit. ### Claim 12 (depends on 11) The power supply circuit of claim 11, wherein the half wave rectifier circuit includes a plurality of inputs and a corresponding plurality of outputs, wherein the half wave rectifier circuit comprises one or more diodes coupled between each of the inputs and the corresponding outputs of the half wave rectifier circuit. ### Claim 13 (depends on 7) The power supply circuit of claim 7, wherein the rectifier is a full wave rectifier circuit. ### Claim 14 (depends on 7) The power supply circuit of claim 7, wherein the inductor includes a wire gauge such that the inductor is adapted to function as a fuse to limit an abnormal amount of current flow due to a fault in a power supply component. ### Claim 15 (depends on 14) The power supply circuit of claim 14, wherein the inductor is covered with a flame retardant material. ### Claim 16 (depends on 14) The power supply circuit of claim 14, wherein the inductor is covered with a heatshrink material.