# US 2021/0242784 A1 · Flyback converter, control circuit and control method thereof > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 2021/0242784 A1 - Document ID: US20210242784A1 - Status: Published application - Kind: A1 - Application number: 17/239,831 - Filed: 2021-04-26 - Published: 2021-08-05 - Earliest claimed: 2018-09-18 - Assignees: Silergy Semiconductor Technology (Hangzhou) LTD - Applicants: Silergy Semiconductor Technology (Hangzhou) LTD - Inventors: Xiangdong Yang; Xiaoru Xu; Yongjiang Bai; Zhiliang Hu - Web page: https://patentgrep.com/patent/US20210242784A1 ## CPC - H02M 3/33507: {with automatic control of the output voltage or current, e.g. flyback converters (H02M3/33561, H02M3/33569 take precedence)} - H02M 3/33523: {with galvanic isolation between input and output of both the power stage and the feedback loop} - H02M 3/33515: {with digital control} - 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 1/342: {Active 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 A control circuit for a flyback converter is configured to adjust a conduction time of an auxiliary switch of the flyback converter in accordance with a drain-source voltage of a main switch of the flyback converter when the main switch is turned on, in order to achieve zero-voltage switching of the main switch. The flyback converter can include: a main power stage having the main switch to control energy storage and transmission of a transformer; and a clamp circuit having an auxiliary switch to provide a release path for releasing energy of leakage inductance of the transformer. ## Claims ### Claim at position 1 -20. (canceled) ### Claim 21 A control circuit for a flyback converter, the control circuit comprising: a) a detection circuit configured to generate a sampling voltage representing a drain-source voltage of a main switch in the flyback converter when the main switch is turned on, and to generate a detection signal in accordance with the sampling voltage; and b) an auxiliary switch control circuit configured to reduce a conduction time of an auxiliary switch in the flyback converter when the detection signal is active, and to increase the conduction time of the auxiliary switch when the detection signal is inactive, in order to achieve zero-voltage switching of the main switch. ### Claim 22 (depends on 21) The control circuit of claim 21, wherein: a) the detection circuit is configured to generate the detection signal based on a comparison between the sampling voltage and a threshold voltage; and b) the auxiliary switch control circuit is configured to adjust the conduction time of the auxiliary switch based on the detection signal. ### Claim 23 (depends on 21) The control circuit of claim 21, wherein the auxiliary switch control circuit comprises a reference voltage regulation circuit configured to adjust a reference voltage signal in accordance with the detection signal, in order to adjust the conduction time of the auxiliary switch in accordance with the reference voltage signal. ### Claim 24 (depends on 23) The control circuit of claim 23, wherein the reference voltage regulation circuit is configured to: a) decrease the reference voltage signal at a rising edge of a turn-on signal of the main switch when the detection signal is active; and b) increase the reference voltage signal at the rising edge of the turn-on signal of the main switch when the detection signal is inactive. ### Claim 25 (depends on 24) The control circuit of claim 24, wherein the auxiliary switch control circuit is configured to control a voltage to increase to the reference voltage signal after the auxiliary switch is turned on, in order to generate a turn-off signal of the auxiliary switch to control the auxiliary switch to be turned off. ### Claim 26 (depends on 22) The control circuit of claim 22, wherein the detection circuit is configured to generate the sampling voltage by sampling a voltage across an auxiliary winding coupled to a secondary winding of a transformer in the flyback converter, such that the sampling voltage characterizes the drain-source voltage of the main switch. ### Claim 27 (depends on 26) The control circuit of claim 26, wherein the detection circuit comprises a first conversion circuit configured to obtain the sampling voltage by remaining a positive voltage part of a first voltage sampled by the voltage of the auxiliary winding, and to make a negative voltage part of the first voltage be zero. ### Claim 28 (depends on 26) The control circuit of claim 26, wherein the detection circuit comprises a sample-and-hold circuit configured to generate the threshold voltage in accordance with the sampling voltage. ### Claim 29 (depends on 26) The control circuit of claim 26, wherein: a) when the sampling voltage is less than the threshold voltage, the detection signal is inactive; and b) when the sampling voltage is not less than the threshold voltage, the detection signal is active. ### Claim 30 (depends on 22) The control circuit of claim 22, wherein: a) the detection circuit is configured to generate the sampling voltage by sampling a drain voltage of the main switch; and b) the sampling voltage characterizes a low voltage part of the drain-source voltage of the main switch. ### Claim 31 (depends on 30) The control circuit of claim 30, wherein the threshold voltage is a predetermined value. ### Claim 32 (depends on 30) The control circuit of claim 30, wherein: a) when the sampling voltage is not less than the threshold voltage, the detection signal is inactive; and b) when the sampling voltage is less than the threshold voltage, the detection signal is active. ### Claim 33 (depends on 21) The control circuit of claim 21, wherein the control circuit is configured to control the auxiliary switch to be turned on at a wave-peak moment of the drain-source voltage of the main switch. ### Claim 34 (depends on 21) The control circuit of claim 21, wherein the control circuit comprises a main switch control circuit configured to generate a turn-on signal of the main switch, in order to control a turn-on moment of the main switch in accordance with the detection signal. ### Claim 35 (depends on 21) The control circuit of claim 21, wherein the auxiliary switch control circuit comprises a wave-peak detection circuit configured to: a) sample a voltage across an auxiliary winding coupled to a secondary winding of a transformer to generate a first voltage characterizing the drain-source voltage of the main switch; and b) generate a wave-peak detection signal in accordance with the first voltage, such that a turn-on signal of the auxiliary switch is generated to control a turn-on moment of the auxiliary switch in accordance with the wave-peak detection signal. ### Claim 36 (depends on 35) The control circuit of claim 35, wherein the wave-peak detection circuit comprises: a) a bias voltage configured to be superimposed on the first voltage to generate a biased sampling voltage; b) a delay circuit configured to delay the first voltage to generate a delayed sampling voltage; and c) a comparator configured to compare the biased sampling voltage against the delayed sampling voltage to generate the wave-peak detection signal. ### Claim 37 (depends on 35) The control circuit of claim 35, wherein the auxiliary switch control circuit is configured to control the auxiliary switch to be turned on in accordance with the wave-peak detection signal and a frequency limit signal. ### Claim 38 (depends on 1) A switching converter, comprising the control circuit of claim 1, and further comprising: a) a main power stage having the main switch, and being configured to control energy storage and transmission of a transformer; and b) a clamp circuit having the auxiliary switch, and being configured to provide a release path for releasing energy of leakage inductance of the transformer. ### Claim 39 (depends on 38) The switching converter of claim 38, wherein: a) the clamp circuit comprises the auxiliary switch and a clamp capacitor; and b) the clamp circuit is coupled in parallel with a primary winding of the transformer. ### Claim 40 (depends on 38) The switching converter of claim 38, wherein: a) the clamp circuit comprises the auxiliary switch and a clamp capacitor; and b) the clamp circuit is coupled in parallel with the main switch.