# US 11,451,134 B2 · Method and device for discharging output capacitor of power supply > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 11,451,134 B2 - Document ID: US11451134B2 - Status: Granted - Kind: B2 - Application number: 16/435,380 - Filed: 2019-06-07 - Published: 2020-12-10 - Granted: 2022-09-20 - Earliest claimed: 2019-06-07 - Assignees: NXP B.V. - Applicants: NXP B.V. - Inventors: Jeroen Kleinpenning; Jacobus Govert Sneep; Tsung-Pin Tang - Web page: https://patentgrep.com/patent/US11451134B2 ## CPC - H02M 1/32: Means for protecting converters other than automatic disconnection - H02M 7/217: using semiconductor devices only - H02M 3/33523: {with galvanic isolation between input and output of both the power stage and the feedback loop} - H02M 3/33592: {having a synchronous rectifier circuit or a synchronous freewheeling circuit at the secondary side of an isolation transformer} - H02M 1/322: {Means for rapidly discharging a capacitor of the converter for protecting electrical components or for preventing electrical shock} - 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 Embodiments of a method and a device are disclosed. In an embodiment, a method for discharging an output capacitor of a power supply is disclosed. The power supply includes a primary side for receiving a signal to be converted and a secondary side for outputting a converted signal. The method involves detecting whether synchronous rectification (SR) circuitry at the secondary side is inactive, determining that the primary side is disconnected from a mains voltage when the SR circuitry is detected to be inactive, and discharging an output capacitor at the secondary side based on the determination that the primary side is disconnected from the mains voltage. ## Claims ### Claim 1 A method for discharging an output capacitor of a power supply, the power supply having a primary side configured to receive a signal to be converted and a secondary side configured to output a converted signal, the method comprising: detecting that the synchronous rectification (SR) circuitry at the secondary side is inactive after no switching activity is sensed for a predetermined time at drains of the SR circuitry; determining that the primary side is disconnected from a mains voltage after the SR circuitry is detected to be inactive; and discharging an output capacitor at the secondary side based on the determination that the primary side is disconnected from the mains voltage. ### Claim 2 (depends on 1) The method of claim 1, wherein the primary side is determined to be disconnected from the mains voltage when the SR circuitry performs no switching activity for a predetermined duration. ### Claim 3 (depends on 2) The method of claim 2, wherein discharging the output capacitor comprises: detecting an amount of time that the SR circuitry performs no switching activity; and discharging the output capacitor when the amount of time exceeds a threshold. ### Claim 4 (depends on 1) The method of claim 1, wherein the output capacitor is discharged by a constant power load. ### Claim 5 (depends on 1) The method of claim 1, wherein the output capacitor is discharged by a constant current load. ### Claim 6 (depends on 1) The method of claim 1, wherein the output capacitor is discharged by a resistor load. ### Claim 7 (depends on 1) The method of claim 1, wherein the output capacitor is discharged by at least one of a power load, a current load, a resistor load, or any combination thereof. ### Claim 8 (depends on 1) The method of claim 1, wherein a current for discharging the output capacitor decreases at a high junction temperature. ### Claim 9 A power supply, comprising: a primary side configured to connect to a mains voltage and receive a voltage signal to be converted; a secondary side configured to output a converted voltage signal; and a transformer connected between the primary side and the secondary side and configured to convert the voltage signal, wherein the secondary side comprises: an output capacitor, synchronous rectification (SR) circuitry configured to rectify the converted voltage signal from the transformer, detection circuitry configured to detect that the SR circuitry is inactive after no switching activity is sensed for a predetermined time at drains of the SR circuitry, determining circuitry configured to determine that the primary side is disconnected from the mains voltage after the SR circuitry is detected to be inactive, and discharging circuitry configured to discharge the output capacitor based on the determination that the primary side is disconnected from the mains voltage. ### Claim 10 (depends on 9) The power supply of claim 9, wherein the determining circuitry is configured to determine that the primary side is disconnected from the mains voltage when the SR circuitry performs no switching activity for a predetermined duration. ### Claim 11 (depends on 10) The power supply of claim 10, wherein the discharging circuitry is configured to: detect an amount of time that the SR circuitry performs no switching activity; and discharge the output capacitor when the amount of time exceeds a threshold. ### Claim 12 (depends on 9) The power supply of claim 9, wherein the output capacitor is discharged by a constant power load. ### Claim 13 (depends on 9) The power supply of claim 9, wherein the output capacitor is discharged by a constant current load. ### Claim 14 (depends on 9) The power supply of claim 9, wherein the output capacitor is discharged by a resistor load. ### Claim 15 (depends on 9) The power supply of claim 9, wherein the output capacitor is discharged by at least one of a power load, a current load, a resistor load, or any combination thereof. ### Claim 16 (depends on 9) The power supply of claim 9, wherein a current for discharging the output capacitor decreases at a high junction temperature. ### Claim 17 (depends on 9) The power supply of claim 9, wherein the discharging circuitry sets a delay time that is longer than a maximum time of a non-switching portion of a burst mode or of a low frequency mode whereby discharge is not triggered during no-load operation. ### Claim 18 (depends on 9) The power supply of claim 9, wherein the detection circuitry is configured to detect the mains voltage disconnect at the secondary side without a communication signal from the primary side. ### Claim 19 A power supply, comprising: a primary side configured to connect to an input voltage and receive a voltage signal to be converted; and a secondary side configured to output a converted voltage signal, the secondary side comprising a controller configured to: detect that synchronous rectification (SR) circuitry at the secondary side is inactive after no switching activity is sensed for a predetermined time at drains of the SR circuitry, determine that the primary side is disconnected from the input voltage after the SR circuitry is detected to be inactive, and discharge an output capacitor at the secondary side based on the determination that the primary side is disconnected from the input voltage. ### Claim 20 (depends on 19) The power supply of claim 19, wherein the controller is configured to determine that the primary side is disconnected from the input voltage when the SR circuitry performs no switching activity for a predetermined duration. ### Claim 21 (depends on 20) The power supply of claim 20, wherein the controller configured to discharge the output capacitor is further configured to: detect an amount of time that the SR circuitry performs no switching activity; and discharge the output capacitor when the amount of time exceeds a threshold. ### Claim 22 (depends on 19) The power supply of claim 19, wherein the controller is configured to discharge the output capacitor by at least one of a power load, a current load, a resistor load, or any combination thereof.