# US 2014/0153295 A1 · Buck-Flyback Converter > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 2014/0153295 A1 - Document ID: US20140153295A1 - Status: Published application - Kind: A1 - Application number: 13/690,388 - Filed: 2012-11-30 - Published: 2014-06-05 - Earliest claimed: 2012-11-30 - Assignees: Infineon Technologies North America Corp. - Applicants: Infineon Technologies North America Corp. - Inventors: Mladen Ivankovic; Fred Sawyer - Web page: https://patentgrep.com/patent/US20140153295A1 ## CPC - H02M 3/3353: {having at least two simultaneously operating switches on the input side, e.g. "double forward" or "double (switched) flyback" converter} - 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 3/3372: {of the parallel type} - H02M 3/3378: {in a push-pull configuration of the parallel type (H02M3/3374 takes precedence)} - 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 two-transistor flyback converter includes a transformer having a primary side and a secondary side, a first transistor connected between an input voltage source and a first terminal of the primary side, a second transistor connected between ground and a second terminal of the primary side, and a diode directly connected between the first terminal of the primary side and ground. The first and second transistors are operable to switch on and off simultaneously and with no current return from the primary side to the input voltage source when the input voltage source is less than a reflected voltage from the secondary side. ## Claims ### Claim 1 A two-transistor flyback converter, comprising: a transformer having a primary side and a secondary side; a first transistor connected between an input voltage source and a first terminal of the primary side; a second transistor connected between ground and a second terminal of the primary side; a diode directly connected between the first terminal of the primary side and ground; and wherein the first and second transistors are operable to switch on and off simultaneously and with no current return from the primary side to the input voltage source when the input voltage source is less than a reflected voltage from the secondary side. ### Claim 2 (depends on 1) The two-transistor flyback converter according to claim 1, further comprising a Zener diode connected between a drain of the second transistor and a source of the second transistor. ### Claim 3 (depends on 1) The two-transistor flyback converter according to claim 1, wherein the input voltage source is greater than the reflected voltage from the secondary side plus a voltage spike caused by leakage inductance of the transformer. ### Claim 4 (depends on 1) The two-transistor flyback converter according to claim 1, wherein a breakdown voltage of the second transistor is greater than the reflected voltage from the secondary side plus a voltage spike caused by leakage inductance of the transformer. ### Claim 5 A method of operating a two-transistor flyback converter including a transformer with a primary side and a secondary side, the method comprising: simultaneously switching on a first transistor connected between an input voltage source and a first terminal of the primary side, and a second transistor connected between ground and a second terminal of the primary side to energize the transformer through the primary side; simultaneously switching off the first and second transistors to transfer the energy stored in the transformer to a load connected to the secondary side; and connecting the first terminal of the primary side to ground only through a diode when the first and second transistors are switched off and with no current return from the primary side to the input voltage source when the input voltage source is less than a reflected voltage from the secondary side. ### Claim 6 (depends on 5) The method according to claim 5, further comprising limiting a voltage spike caused by leakage inductance of the transformer to a value less than a breakdown voltage of the second transistor by a Zener diode connected between a drain of the second transistor and a source of the second transistor. ### Claim 7 (depends on 5) The method according to claim 5, wherein the input voltage source is greater than the reflected voltage from the secondary side plus a voltage spike caused by leakage inductance of the transformer. ### Claim 8 (depends on 5) The method according to claim 5, wherein a breakdown voltage of the second transistor is greater than the reflected voltage from the secondary side plus a voltage spike caused by leakage inductance of the transformer. ### Claim 9 A two-transistor flyback converter, comprising: a transformer having a primary side and a secondary side; a first MOSFET having a drain connected to an input voltage source and a source connected to a first terminal of the primary side; and a second MOSFET having a drain connected to a second terminal of the primary side and a source connected to ground so that the primary side is decoupled from the input voltage source by only the first MOSFET and energy is transferred to the secondary side independent of the primary side voltage when the first and second MOSFETs are switched off. ### Claim 10 (depends on 9) The two-transistor flyback converter according to claim 9, further comprising a Zener diode connected between the drain and the source of the second MOSFET. ### Claim 11 (depends on 9) The two-transistor flyback converter according to claim 9, wherein the input voltage source is greater than the reflected voltage from the secondary side plus a voltage spike caused by leakage inductance of the transformer. ### Claim 12 (depends on 9) The two-transistor flyback converter according to claim 9, wherein a breakdown voltage of the second MOSFET is greater than the reflected voltage from the secondary side plus a voltage spike caused by leakage inductance of the transformer. ### Claim 13 (depends on 9) The two-transistor flyback converter according to claim 9, further comprising a diode directly connected between the first terminal of the primary side and ground. ### Claim 14 (depends on 13) The two-transistor flyback converter according to claim 13, wherein the first and second MOSFETs are operable to switch on and off simultaneously and with no current return from the primary side to the input voltage source when the input voltage source is less than a reflected voltage from the secondary side. ### Claim 15 A method of operating a two-transistor flyback converter including a transformer with a primary side and a secondary side, the method comprising: switching on a first MOSFET having a drain connected to an input voltage source and a source connected to a first terminal of the primary side, and a second MOSFET having a drain connected to a second terminal of the primary side and a source connected to ground to energize the transformer through the primary side; switching off the first and second MOSFETs to transfer the energy stored in the transformer to a load connected to the secondary side; decoupling the primary side from the input voltage source by only the first MOSFET when the first and second MOSFETs are switched off; and transferring energy from the primary side to the secondary side independent of the primary side voltage when the first and second MOSFETs are switched off. ### Claim 16 (depends on 15) The method according to claim 15, further comprising limiting a voltage spike caused by leakage inductance of the transformer to a value less than a breakdown voltage of the second transistor by a Zener diode connected between the drain and the source of the second MOSFET. ### Claim 17 (depends on 15) The method according to claim 15, wherein the input voltage source is greater than the reflected voltage from the secondary side plus a voltage spike caused by leakage inductance of the transformer. ### Claim 18 (depends on 15) The method according to claim 15, wherein a breakdown voltage of the second MOSFET is greater than the reflected voltage from the secondary side plus a voltage spike caused by leakage inductance of the transformer. ### Claim 19 (depends on 15) The method according to claim 15, further comprising connecting the first terminal of the primary side to ground only through a diode when the first and second MOSFETs are switched off. ### Claim 20 (depends on 19) The method according to claim 19, further comprising switching the first and second MOSFETs on and off simultaneously and with no current return from the primary side to the input voltage source when the input voltage source is less than a reflected voltage from the secondary side.