# US 8,787,044 B2 · Energy recovery snubber circuit for power converters > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 8,787,044 B2 - Document ID: US8787044B2 - Status: Granted - Kind: B2 - Application number: 12/776,249 - Filed: 2010-05-07 - Published: 2010-12-16 - Granted: 2014-07-22 - Earliest claimed: 2009-05-07 - Assignees: Flextronics AP, LLC - Applicants: Zaohong Yang; Paul Garrity - Inventors: Zaohong Yang; Paul Garrity - Web page: https://patentgrep.com/patent/US8787044B2 ## CPC - H02M 3/33576: {having at least one active switching element at the secondary side of an isolation transformer} - H02M 1/346: {Passive non-dissipative snubbers} - Y02B 70/10: Technologies improving the efficiency by using switched-mode power supplies [SMPS], i.e. efficient power electronics conversion e.g. power factor correction or reduction of losses in power supplies or efficient standby modes - 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) - Y02B: CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO BUILDINGS, e.g. HOUSING, HOUSE APPLIANCES OR RELATED END-USER APPLICATIONS ## Abstract An energy recovery snubber circuit for use in switching power converters. The power converters may include a switch network coupled to a primary winding of an isolation transformer, and rectification circuitry coupled to a secondary winding of the isolation transformer. The energy recovery snubber circuit may include clamping circuitry that is operative to clamp voltage spikes and/or ringing at the rectification circuitry. The clamped voltages may be captured by an energy capture module, such as a capacitor. Further, the energy recovery snubber circuitry may include control circuitry operative to return the energy captured by the energy capture module to the input of the power converter. To maintain electrical isolation between a primary side and a secondary side of the isolation transformer, a second isolation transformer may be provided to return the captured energy back to the input of the power converter. ## Claims ### Claim 1 An energy recovery snubber circuit for use in a switching power converter having an input and an output, the power converter comprising a first transformer having a primary winding and a secondary winding, a controllable switch coupled to the primary winding, and rectification circuitry coupled to the secondary winding, the energy recovery snubber circuit comprising: a voltage clamping element coupled to the rectification circuitry; a capacitive element coupled to the voltage clamping element for storing energy captured by the voltage clamping element; a second transformer having a primary winding coupled to the capacitive element and a secondary winding coupled to the input of the power converter; and control circuitry operably connected to the rectification circuitry, wherein the rectification circuitry triggers the control circuitry to, independent of the amount of energy stored by the capacitive element, selectively cause energy stored by the capacitive element to transfer to the input of the power converter via the second transformer. ### Claim 2 (depends on 1) A circuit as defined in claim 1, wherein the power converter includes a low-pass filter at the output thereof. ### Claim 3 (depends on 2) A circuit as defined in claim 2, wherein the low-pass filter includes an output inductor and an output capacitor. ### Claim 4 (depends on 1) A circuit as defined in claim 1, wherein the power converter includes a rectifier coupled to the secondary winding of the energy recovery snubber circuit. ### Claim 5 (depends on 1) A circuit as defined in claim 1, wherein the rectification circuitry includes a rectifying switch. ### Claim 6 (depends on 5) A circuit as defined in claim 5, wherein the rectifying switch includes a MOSFET. ### Claim 7 (depends on 1) A circuit as defined in claim 1, wherein the controllable switch includes four different switches, two of which are on at a time, one pair of which are on while the other pair is off and one pair of which is off while the other pair is on. ### Claim 8 (depends on 7) A circuit as defined in claim 7, wherein the rectification circuitry includes a first and a second rectifying switch, one of which is on at a time, the first rectifying switch being on when the one pair of switches in the controllable switch are on and the second rectifying switch being on when the other pair of switches in the controllable switch are on. ### Claim 9 (depends on 8) A circuit as defined in claim 8, wherein the first and second rectifying switches include a MOSFET. ### Claim 10 (depends on 1) A circuit as defined in claim 1, wherein the voltage clamping element includes one or more diodes and the control circuitry includes an inverter. ### Claim 11 A switching power converter having an input and an output, the power converter comprising: a first transformer having a primary winding and a secondary winding; a controllable switch coupled to the primary winding; rectification circuitry coupled to the secondary winding; and an energy recovery snubber circuit for the switching power converter, the energy recovery snubber circuit comprising: a voltage clamping element coupled to the rectification circuitry; a capacitive element coupled to the voltage clamping element for storing energy captured by the voltage clamping element; a second transformer having a primary winding coupled to the capacitive element and a secondary winding coupled to the input of the power converter; and control circuitry operably connected to the rectification circuitry, the rectification circuitry triggers the control circuitry to, independent of the amount of energy stored by the capacitive element, selectively cause energy stored by the capacitive element to transfer to the input of the power converter via the second transformer. ### Claim 12 (depends on 11) A circuit as defined in claim 11, wherein the power converter includes a low-pass filter at the output thereof. ### Claim 13 (depends on 12) A circuit as defined in claim 12, wherein the low-pass filter includes an output inductor and an output capacitor. ### Claim 14 (depends on 11) A circuit as defined in claim 11, wherein the power converter includes a rectifier coupled to the secondary winding of the energy recovery snubber circuit. ### Claim 15 (depends on 11) A circuit as defined in claim 11, wherein the rectification circuitry includes a rectifying switch. ### Claim 16 (depends on 15) A circuit as defined in claim 15, wherein the rectifying switch includes a MOSFET. ### Claim 17 (depends on 11) A circuit as defined in claim 11, wherein the controllable switch includes four different switches, two of which are on at a time, one pair of which are on while the other pair is off and one pair of which is off while the other pair is on. ### Claim 18 (depends on 17) A circuit as defined in claim 17, wherein the rectification circuitry includes a first and a second rectifying switch, one of which is on at a time, the first rectifying switch being on when the one pair of switches in the controllable switch are on and the second rectifying switch being on when the other pair of switches in the controllable switch are on. ### Claim 19 (depends on 18) A circuit as defined in claim 18, wherein the first and second rectifying switches include a MOSFET. ### Claim 20 (depends on 11) A circuit as defined in claim 11, wherein the voltage clamping element includes one or more diodes and the control circuitry includes an inverter. ### Claim 21 (depends on 1) A circuit as defined in claim 1, wherein the voltage clamping element is directly coupled to the secondary winding of the first transformer between the secondary winding and the rectification circuitry such that the voltage clamping element receives a non-rectified output of the first transformer.