# US 10,483,863 B2 · Isolated synchronous rectification-type DC/DC converter > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 10,483,863 B2 - Document ID: US10483863B2 - Status: Granted - Kind: B2 - Application number: 16/100,467 - Filed: 2018-08-10 - Published: 2018-12-06 - Granted: 2019-11-19 - Earliest claimed: 2016-12-16 - Assignees: Rohm Co., Ltd. - Applicants: Rohm Co., Ltd. - Inventors: Hiroki Kikuchi - Web page: https://patentgrep.com/patent/US10483863B2 ## CPC - H02M 3/33592: {having a synchronous rectifier circuit or a synchronous freewheeling circuit at the secondary side of an isolation transformer} - H02J 1/102: being switching converters (H02J1/108, H02J1/12 take precedence) - H02M 1/32: Means for protecting converters other than automatic disconnection - H02M 3/1563: {without using an external clock (H02M3/158 takes precedence)} - H02M 3/3372: {of the parallel type} - H02M 7/21: using devices of a triode or transistor type requiring continuous application of a control signal - H02M 1/0006: {Arrangements for supplying an adequate voltage to the control circuit of converters} - 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) - H02J: ELECTRIC POWER NETWORKS; CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY - Y02B: CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO BUILDINGS, e.g. HOUSING, HOUSE APPLIANCES OR RELATED END-USER APPLICATIONS ## Abstract A secondary controller drives a light emitting element of a photocoupler such that a detection voltage VOUTS corresponding to an output voltage VOUT generated in an output capacitor C approximates to a reference voltage VREF. A primary controller controls a switching transistor M according to a feedback signal VFB. A protection circuit is activated and drives the light emitting element of the photocoupler when detecting an abnormal state. An auxiliary power supply circuit includes a power supply capacitor C provided separately from the output capacitor C and supplies a power supply voltage VCC to the protection circuit and an anode of the light emitting element of the photocoupler. ## Claims ### Claim 1 A secondary controller used in an isolated synchronous rectification-type DC/DC converter, comprising: a control output pin to be coupled to a light emitting element of a photocoupler; a power supply pin to be coupled to receive a power supply voltage; a control input pin to be coupled to receive a detection voltage corresponding to an output voltage of the DC/DC converter; a feedback circuit structured to amplify an error between the detection voltage and a reference voltage and to supply a current corresponding to the error to the light emitting element of the photocoupler; and a power supply path coupled to supply power from the control output pin to the power supply pin. ### Claim 2 (depends on 1) The secondary controller according to claim 1, wherein the power supply path includes a rectifier element. ### Claim 3 (depends on 1) The secondary controller according to claim 1, wherein the power supply path includes a diode having an anode coupled to the control output pin and a cathode coupled to the power supply pin side. ### Claim 4 (depends on 1) The secondary controller according to claim 1, further comprising a protection circuit structured to drive the light emitting element when detecting an abnormal state, and wherein the power supply voltage of the power supply pin is supplied to at least a part of the protection circuit. ### Claim 5 (depends on 4) The secondary controller according to claim 4, wherein the protection circuit is structured to be activated and to drive the light emitting element when detecting an over-voltage state, and wherein the power supply voltage supplied to the power supply pin is decrease slower than the output voltage in a stop state of the DC/DC converter. ### Claim 6 (depends on 5) The secondary controller according to claim 5, wherein the protection circuit includes: an over-voltage detection comparator structured to assert an abnormality detection signal when detecting an over-voltage state; a latch circuit structured to latch the abnormality detection signal; and a protection transistor coupled to the light emitting element and being turned into an on-state according to an output of the latch circuit. ### Claim 7 (depends on 6) The secondary controller according to claim 6, wherein the abnormality detection signal is negated when the power supply voltage falls below a release threshold value. ### Claim 8 (depends on 6) The secondary controller according to claim 6, wherein the abnormality detection signal is negated after a lapse of a predetermined time from its assertion. ### Claim 9 (depends on 5) The secondary controller according to claim 5, the protection circuit includes: a hysteresis comparator structured to assert the abnormality detection signal when a monitoring target voltage exceeds an upper threshold value and to negate the abnormality detection signal when the monitoring target voltage falls below a lower threshold value; and a protection transistor coupled to the light emitting element and being turned into an on-state according to the abnormality detection signal. ### Claim 10 (depends on 1) The secondary controller according to claim 1, wherein the feedback circuit includes: an error amplifier structured to amplify the error between the detection voltage and the reference voltage; and a pass transistor coupled to the control output pin and being driven according to an output signal of the error amplifier. ### Claim 11 (depends on 1) The secondary controller according to claim 1, being accommodated in a same package as a synchronous rectification controller structured to drive a synchronous rectification transistor on a secondary side of the DC/DC converter. ### Claim 12 (depends on 1) The isolated synchronous rectification-type DC/DC converter comprising the secondary controller according to claim 1. ### Claim 13 An isolated synchronous rectification-type DC/DC converter comprising: a transformer having a primary winding and a secondary winding; a switching transistor coupled to the primary winding of the transformer; an output capacitor being charged by a current flowing in the secondary winding of the transformer; a photocoupler having a light emitting element and a light receiving element; a feedback circuit structured to drive the light emitting element of the photocoupler such that a detection voltage corresponding to an output voltage of the output capacitor approximates to a reference voltage; a primary controller coupled to the light receiving element of the photocoupler and structured to control the switching transistor corresponding to a feedback signal based on a state of the light receiving element; a protection circuit structured to be activated and to drive the light emitting element when detecting an abnormal state; an auxiliary power supply circuit including a power supply capacitor provided separately from the output capacitor and structured to supply a power supply voltage generated in the power supply capacitor to at least a part of a power supply line of the protection circuit; and a rectifier element provided between a cathode of the light emitting element of the photocoupler and the power supply line. ### Claim 14 (depends on 13) The DC/DC converter according to claim 13, wherein the power supply voltage decreases slower than the output voltage in a stop state of the DC/DC converter. ### Claim 15 (depends on 14) The DC/DC converter according to claim 14, wherein the power supply voltage from the auxiliary power supply circuit is supplied to an anode of the light emitting element of the photocoupler. ### Claim 16 (depends on 13) The DC/DC converter according to claim 13, wherein the rectifier element includes a diode. ### Claim 17 (depends on 13) The DC/DC converter according to claim 13, wherein the protection circuit includes an abnormality detection circuit structured to maintain assertion of an abnormality detection signal until being reset when detecting the abnormal state; and a protection transistor which is turned into an on-state in an asserted state of the abnormality detection signal, and wherein the power supply voltage may be supplied to the abnormality detection circuit. ### Claim 18 (depends on 17) The DC/DC converter according to claim 17, wherein the abnormality detection signal is negated when the power supply voltage falls below a release threshold value. ### Claim 19 (depends on 17) The DC/DC converter according to claim 17, wherein the abnormality detection signal is negated after a lapse of a predetermined time from assertion thereof. ### Claim 20 (depends on 13) The DC/DC converter according to claim 13, wherein the protection circuit is an over-voltage protection circuit. ### Claim 21 (depends on 13) The DC/DC converter according to claim 13, wherein the auxiliary power supply circuit further includes a charging path from the output capacitor to the power supply capacitor. ### Claim 22 (depends on 21) The DC/DC converter according to claim 21, wherein the charging path includes a rectifier element that allows a current from an output line of the DC/DC converter to the power supply capacitor and blocks a current in the reverse direction. ### Claim 23 (depends on 13) The DC/DC converter according to claim 13, wherein the charging path includes a diode having an anode on the output line side of the DC/DC converter and a cathode on the power supply capacitor side. ### Claim 24 (depends on 13) An electronic device comprising: a load; a diode rectifier circuit structured to performs full-wave rectification of a commercial AC (alternating current) voltage; a smoothing capacitor coupled to smooth an output voltage of the diode rectifier circuit and to generate a DC input voltage; and the DC/DC converter according to claim 13, which steps down the DC input voltage and supplies the stepped-down DC input voltage to the load. ### Claim 25 (depends on 13) A power adapter comprising: a diode rectifier circuit structured to perform full-wave rectification of a commercial AC voltage; a smoothing capacitor coupled to smooth an output voltage of the diode rectifier circuit and to generate a DC input voltage; and the DC/DC converter according to claim 13, which steps down the DC input voltage and supplies the stepped-down DC input voltage to a load. ### Claim 26 A method for controlling an isolated synchronous rectification-type DC/DC converter, the method comprising: controlling a switching transistor coupled to a primary winding of a transformer; rectifying a current flowing in a secondary winding of the transformer to charge an output capacitor and generating an output voltage; generating a power supply voltage by a power supply capacitor provided separately from the output capacitor; supplying the power supply voltage to a secondary controller which drives a light emitting element of a photocoupler and a cathode of the light emitting element; maintaining a state of driving the light emitting element when detecting an abnormal state; and supplying power from a cathode of the light emitting element of the photocoupler to the secondary controller when supply of the power supply voltage to the secondary controller is interrupted.