# US 2021/0242766 A1 · Switching control circuit and power supply circuit > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 2021/0242766 A1 - Document ID: US20210242766A1 - Status: Published application - Kind: A1 - Application number: 17/130,647 - Filed: 2020-12-22 - Published: 2021-08-05 - Earliest claimed: 2020-02-04 - Assignees: Fuji Electric Co., Ltd. - Applicants: Fuji Electric Co., Ltd. - Inventors: Takato SUGAWARA - Web page: https://patentgrep.com/patent/US20210242766A1 ## CPC - H02M 1/08: Circuits specially adapted for the generation of control voltages for semiconductor devices incorporated in static converters - H02M 3/33523: {with galvanic isolation between input and output of both the power stage and the feedback loop} - H02M 1/0006: {Arrangements for supplying an adequate voltage to the control circuit of converters} - H02M 1/322: {Means for rapidly discharging a capacitor of the converter for protecting electrical components or for preventing electrical shock} - H02M 3/335: using semiconductor devices only - H02M 1/0096: {Means for increasing hold-up time, i.e. the duration of time that a converter's output will remain within regulated limits following a loss of input power} - 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 circuit having a first capacitor, a transformer including a primary coil having a voltage of the first capacitor applied thereto, a secondary coil and an auxiliary coil, a second capacitor having a voltage from the auxiliary coil applied thereto, a transistor controlling an inductor current flowing through the primary coil, a control circuit outputting a first control signal when supply of the input voltage is unstopped, or is stopped yet a voltage of the second capacitor reaches a first level, and outputting a second control signal thereafter when the voltage of the second capacitor further reaches a second level, a first drive circuit outputting a first drive signal for switching control of the transistor in response to the first control signal, and a second drive circuit outputting a second drive signal for controlling on-resistance of the transistor to discharge the first capacitor, in response to the second control signal. ## Claims ### Claim 1 A switching control circuit for controlling a power supply circuit that includes a first capacitor configured to smooth an input voltage of the power supply circuit, a transformer including a primary coil provided on a primary side thereof, a secondary coil provided on a secondary side thereof, and an auxiliary coil, the primary coil being configured to have a voltage of the first capacitor applied thereto, a second capacitor configured to have a voltage from the auxiliary coil applied thereto, and a transistor configured to control an inductor current flowing through the primary coil, the switching control circuit being configured to perform switching control of the transistor, the switching control circuit comprising: a control circuit configured to output a first control signal, when the input voltage is supplied to the power supply circuit, or when supply of the input voltage is stopped yet a first condition that a voltage of the second capacitor reaches a first level is satisfied, and output a second control signal, when the supply of the input voltage is stopped, the first condition is satisfied, and thereafter a second condition that the voltage of the second capacitor reaches a second level higher than the first level is satisfied; a first drive circuit configured to output a first drive signal for performing the switching control of the transistor, in response to the first control signal; and a second drive circuit configured to output a second drive signal for controlling on-resistance of the transistor to discharge the first capacitor, in response to the second control signal. ### Claim 2 (depends on 1) The switching control circuit according to claim 1, wherein the second drive circuit outputs the second drive signal to thereby cause the inductor current for discharging the first capacitor to be at a predetermined value. ### Claim 3 (depends on 1) The switching control circuit according to claim 1, wherein the second control signal is output, when the supply of the input voltage is stopped and a third condition that the voltage of the second capacitor has not decreased to the first level is satisfied. ### Claim 4 (depends on 3) The switching control circuit according to claim 3, wherein the voltage of the second capacitor is at a third level when the power supply circuit generates an output voltage at a target level, the third level being higher than the second level. ### Claim 5 (depends on 3) The switching control circuit according to claim 3, further comprising: an interruption detection circuit configured to detect that supply of an alternating-current (AC) voltage is stopped, when the input voltage is the AC voltage, and a hysteresis comparator configured to output a signal, which is at a first logic level when the voltage of the second capacitor becomes lower than the first level, and at a second logic level when the voltage of the second capacitor becomes higher than the second level. ### Claim 6 (depends on 2) The switching control circuit according to claim 2, wherein the second drive circuit includes a timer circuit configured to measure time of a predetermined cycle repeatedly, the predetermined cycle including a first time period and a second time period, and a drive signal generating circuit configured to generate the second drive signal to cause the inductor current to be at the predetermined value, during the first time period of the predetermined cycle, and to stop generation of the inductor current, during the second time period of the predetermined cycle. ### Claim 7 (depends on 2) The switching control circuit according to claim 2, further comprising: a determination circuit configured to determine whether discharge of the first capacitor is completed, wherein the second drive circuit stops generation of the inductor current when the determination circuit determines that the discharge of the first capacitor is completed. ### Claim 8 (depends on 1) The switching control circuit according to claim 1, wherein when the first drive circuit outputs the first drive signal in response to the first control signal under the first condition, the voltage of the second capacitor rises. ### Claim 9 (depends on 8) The switching control circuit according to claim 8, wherein the control circuit outputs the second control signal, when the voltage of the second capacitor rises under the first condition, to thereby cause the second condition to be satisfied. ### Claim 10 A switching control circuit for controlling a power supply circuit that includes a first capacitor configured to smooth an input voltage of the power supply circuit, a transformer including a primary coil provided on a primary side thereof, a secondary coil provided on a secondary side thereof, and an auxiliary coil, the primary coil being configured to have a voltage of the first capacitor applied thereto, a second capacitor configured to have a voltage from the auxiliary coil applied thereto, and a transistor configured to control an inductor current flowing through the primary coil, the switching control circuit being configured to perform switching control of the transistor, the switching control circuit comprising: a control circuit configured to output a first control signal when the input voltage is supplied to the power supply circuit, and output a second control signal when supply of the input voltage is stopped, a first drive circuit configured to output a first drive signal for performing the switching control of the transistor, in response to the first control signal, and a second drive circuit configured to output a second drive signal for controlling on-resistance of the transistor repeatedly to pass the inductor current intermittently to thereby discharge the first capacitor, in response to the second control signal. ### Claim 11 (depends on 10) The switching control circuit according to claim 10, wherein a switching frequency of the transistor is equal to or greater than 100 times of a frequency at which the inductor current is passed intermittently. ### Claim 12 A power supply circuit comprising: a first capacitor configured to smooth an input voltage of the power supply circuit; a transformer including a primary coil provided on a primary side thereof, a secondary coil provided on a secondary side thereof, and an auxiliary coil, the primary coil being configured to have a voltage of the first capacitor applied thereto; a second capacitor configured to have a voltage from the auxiliary coil applied thereto; a transistor configured to control an inductor current flowing through the primary coil; a control circuit configured to output a first control signal, when the input voltage is supplied to the power supply circuit, or when supply of the input voltage is stopped yet a first condition that a voltage of the second capacitor reaches a first level is satisfied, and output a second control signal, when the supply of the input voltage is stopped, the first condition is satisfied, and thereafter a second condition that the voltage of the second capacitor reaches a second level higher than the first level is satisfied; a first drive circuit configured to output a first drive signal for performing switching control of the transistor, in response to the first control signal; and a second drive circuit configured to output a second drive signal for controlling on-resistance of the transistor to discharge the first capacitor, in response to the second control signal.