# US 2025/0158531 A1 · Active clamp flyback converter and control method > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 2025/0158531 A1 - Document ID: US20250158531A1 - Status: Published application - Kind: A1 - Application number: 18/936,903 - Filed: 2024-11-04 - Published: 2025-05-15 - Earliest claimed: 2023-11-14 - Assignees: Delta Electronics (Shanghai) Co., Ltd. - Applicants: Delta Electronics (Shanghai) CO., LTD. - Inventors: Liangliang REN; Wei WANG - Web page: https://patentgrep.com/patent/US20250158531A1 ## CPC - H02M 1/342: {Active non-dissipative snubbers} - H02M 3/33592: {having a synchronous rectifier circuit or a synchronous freewheeling circuit at the secondary side of an isolation transformer} - H02M 1/0058: {by employing soft switching techniques, i.e. commutation of transistors when applied voltage is zero or when current flow is zero (using an auxiliary actively switched resonant commutation circuit connected to an intermediate DC voltage or between two push-pull branches of an inverter bridge H02M7/4811; in resonant inverters H02M7/4815; in inverters operating from a resonant DC source H02M7/4826)} - H02M 3/01: {Resonant DC/DC converters} - H02M 3/33569: {having several active switching elements (H02M3/3353 takes precedence)} - H02M 3/33576: {having at least one active switching element at the secondary side of an isolation transformer} - 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 The present disclosure provides an active clamp flyback converter and a control method, and relates to the technical field of converter. The control method includes: in response to that an input voltage of the active clamp flyback converter is less than a preset voltage threshold, or the input voltage of the active clamp flyback converter is less than a product of an output voltage of the active clamp flyback converter and a turns ratio of the transformer, in a same switching cycle, controlling the clamp switch to turn on when the transformer is in a demagnetization stage; and controlling the clamp switch to turn off when a resonant current of the clamp capacitor and a leakage inductance of the transformer reaches a preset current threshold. ## Claims ### Claim 1 A control method for an active clamp flyback converter, wherein the active clamp flyback converter comprises: a transformer, comprising a primary side winding and a secondary side winding coupled with each other; a primary side switch, connected in series to the primary side winding; a clamp branch circuit, connected in parallel to the primary side winding or in parallel to the primary side switch; wherein the clamp branch circuit comprises a clamp switch and a clamp capacitor connected in series; wherein the control method comprises: in response to that an input voltage of the active clamp flyback converter is less than a preset voltage threshold, or the input voltage of the active clamp flyback converter is less than a product of an output voltage of the active clamp flyback converter and a turns ratio of the transformer, performing following steps: in a same switching cycle, controlling the clamp switch to turn on when the transformer is in a demagnetization stage; and controlling the clamp switch to turn off when a resonant current of the clamp capacitor and a leakage inductance of the transformer reaches a preset current threshold. ### Claim 2 (depends on 1) The control method according to claim 1, wherein the active clamp flyback converter further comprises a secondary side circuit, the secondary side circuit is electrically connected to the secondary side winding, wherein the control method comprises: in response to that the input voltage of the active clamp flyback converter is greater than or equal to the preset voltage threshold, and the input voltage of the active clamp flyback converter is greater than the product of the output voltage of the active clamp flyback converter and the turns ratio of the transformer, performing following steps: in a same switching cycle, controlling the clamp switch to turn on after an end of a freewheeling stage of the secondary side circuit; and, controlling the clamp switch to turn off before the primary side switch is turned on. ### Claim 3 (depends on 2) The control method according to claim 2, wherein the control method further comprises: in response to that the input voltage of the active clamp flyback converter is greater than or equal to the preset voltage threshold, and the input voltage of the active clamp flyback converter is greater than the product of the output voltage of the active clamp flyback converter and the turns ratio of the transformer, performing following steps: in a same switching cycle, controlling the clamp switch to turn on when the transformer is in the demagnetization stage; and controlling the clamp switch to turn off when the resonant current of the clamp capacitor and the leakage inductance of the transformer reaches the preset current threshold. ### Claim 4 (depends on 2) The control method according to claim 2, wherein controlling the clamp switch to turn on after the end of the freewheeling stage of the secondary side circuit, comprises: controlling the clamp switch to turn on when a voltage across the primary side switch oscillates to a peak value after the end of the freewheeling stage of the secondary side circuit. ### Claim 5 (depends on 3) The control method according to claim 3, wherein controlling the clamp switch to turn on after the end of the freewheeling stage of the secondary side circuit, comprises: controlling the clamp switch to turn on when a voltage across the primary side switch oscillates to a peak value after the end of the freewheeling stage of the secondary side circuit. ### Claim 6 (depends on 2) The control method according to claim 2, wherein controlling the clamp switch to turn off before the primary side switch is turned on, comprises: determining a conduction duration according to the input voltage of the active clamp flyback converter, the output voltage of the active clamp flyback converter, an equivalent capacitance of the primary side switch, and a magnetic inductance of the transformer; and controlling the clamp switch to turn off when a turn-on duration of the clamp switch reaches the conduction duration before the primary side switch is turned on. ### Claim 7 (depends on 3) The control method according to claim 3, wherein controlling the clamp switch to turn off before the primary side switch is turned on, comprises: determining a conduction duration according to the input voltage of the active clamp flyback converter, the output voltage of the active clamp flyback converter, an equivalent capacitance of the primary side switch, and a magnetic inductance of the transformer; and controlling the clamp switch to turn off when a turn-on duration of the clamp switch reaches the conduction duration before the primary side switch is turned on. ### Claim 8 (depends on 2) The control method according to claim 2, wherein controlling the clamp switch to turn on after the end of the freewheeling stage of the secondary side circuit comprises: when the primary side switch is turned off and a current flowing through the secondary side winding is a positive current, the secondary side circuit is in the freewheeling stage. ### Claim 9 (depends on 3) The control method according to claim 3, wherein controlling the clamp switch to turn on after the end of the freewheeling stage of the secondary side circuit comprises: when the primary side switch is turned off and a current flowing through the secondary side winding is a positive current, the secondary side circuit is in the freewheeling stage. ### Claim 10 (depends on 1) The control method according to claim 1, wherein the control method further comprises: determining whether the transformer is in the demagnetization stage according to a current flowing through a magnetic inductance of the primary side winding. ### Claim 11 (depends on 3) The control method according to claim 3, wherein the control method further comprises: determining whether the transformer is in the demagnetization stage according to a current flowing through a magnetic inductance of the primary side winding. ### Claim 12 (depends on 10) The control method according to claim 10, wherein determining whether the transformer is in the demagnetization stage according to the current flowing through the magnetic inductance of the primary side winding, comprises: the transformer being in the demagnetization stage when the current flowing through the magnetic inductance of the primary side winding is a positive current and presents a downward trend. ### Claim 13 (depends on 11) The control method according to claim 11, wherein determining whether the transformer is in the demagnetization stage according to the current flowing through the magnetic inductance of the primary side winding, comprises: the transformer being in the demagnetization stage when the current flowing through the magnetic inductance of the primary side winding is a positive current and presents a downward trend. ### Claim 14 (depends on 1) The control method according to claim 1, wherein in response to that the input voltage of the active clamp flyback converter is less than the preset voltage threshold, or the input voltage of the active clamp flyback converter is less than the product of the output voltage of the active clamp flyback converter and the turns ratio of the transformer, the active clamp flyback converter operates in a single pulse non-complementary mode. ### Claim 15 (depends on 1) The control method according to claim 1, wherein the preset current threshold is 0 A. ### Claim 16 (depends on 3) The control method according to claim 3, wherein the preset current threshold is 0 A. ### Claim 17 (depends on 1) The control method according to claim 1, wherein in response to that the input voltage of the active clamp flyback converter is less than the product of the output voltage of the active clamp flyback converter and the turns ratio of the transformer, a voltage across the primary side switch oscillates to 0V; in response to that the input voltage of the active clamp flyback converter is greater than or equal to the product of the output voltage of the active clamp flyback converter and the turns ratio of the transformer, the voltage across the primary side switch is unable to oscillate to 0V. ### Claim 18 (depends on 1) The control method according to claim 1, wherein the active clamp flyback converter further comprises a secondary side circuit, and the secondary side circuit comprises an output capacitor; wherein the control method further comprises: in a stage where the primary side switch is turned off and the clamp switch is turned on, the clamp capacitor transmitting energy to at least one of the output capacitor or an output load via the clamp switch. ### Claim 19 An active clamp flyback converter, comprising: a transformer, comprising a primary side winding and a secondary side winding coupled with each other; a primary side switch, connected in series to the primary side winding; a clamp branch circuit, connected in parallel to the primary side winding or in parallel to the primary side switch; wherein the clamp branch circuit comprises a clamp switch and a clamp capacitor connected in series; a control unit, connected to the primary side switch and the clamp switch, wherein the control unit is configured to: in response to that an input voltage of the active clamp flyback converter is less than a preset voltage threshold, or the input voltage of the active clamp flyback converter is less than a product of an output voltage of the active clamp flyback converter and a turns ratio of the transformer, in a same switching cycle, control the clamp switch to turn on when the transformer is in a demagnetization stage; and control the clamp switch to turn off when a resonant current of the clamp capacitor and a leakage inductance of the transformer reaches a preset current threshold. ### Claim 20 (depends on 19) The active clamp flyback converter according to claim 19, wherein the active clamp flyback converter further comprises a secondary side circuit, and the secondary side circuit comprises an output capacitor, wherein in a stage where the primary side switch is turned off and the clamp switch is turned on, the clamp capacitor transmits energy to at least one of the output capacitor or an output load via the clamp switch.