# US 5,703,765 A · Flyback converter having a regulated output voltage > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 5,703,765 A - Document ID: US5703765A - Status: Granted - Kind: A - Application number: 08/676,353 - Filed: 1996-07-18 - Granted: 1997-12-30 - Earliest claimed: 1994-01-20 - Assignees: Siemens Aktiengesellschaft - Inventors: Josef Preis - Web page: https://patentgrep.com/patent/US5703765A ## CPC - H02M 3/33561: {having more than one ouput with independent control} - H02M 1/009: {having two or more independently controlled outputs (for DC-DC converter with intermediate AC H02M3/33561)} - 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 Flyback converter has a regulating arrangement which is connected to an output and whose duty ratio is limited to a predetermined upper limit. A series circuit has a diode and an RC series circuit is connected to the rectifier diode of the main circuit (3) on the secondary side in order to supply the regulating arrangement with an auxiliary voltage which is greater than the output voltage. A further diode (44) leads from the series circuit to an output (a) of the auxiliary circuit (4). The flyback converter is suitable in particular for supplying ASICs, which require a relatively low supply voltage. ## Claims ### Claim 1 A flyback converter, comprising: an electronic switch which is connected in series with a primary winding of a transformer in a main circuit on a primary side of the transformer, the electronic switch being controllable by a control device; on a secondary side of the transformer a main circuit which is connected to a secondary winding of the transformer, the main circuit having a first diode in a series path and an energy-storage capacitor in a subsequent parallel path, connected in parallel with an output in the transformer; a regulating arrangement connected to an output of the flyback converter, the regulating arrangement supplied with an auxiliary voltage, a duty ratio of the control voltage which controls the electronic switch being limited to a predetermined upper limit; an auxiliary circuit having an input connected to the first diode of the main circuit on the secondary side and the auxiliary circuit having one pole of an output connected to the input; the auxiliary circuit having an RC series circuit in a series path on the input side, a second diode in the downstream parallel path, a third diode in a series path following the parallel path, and a capacitor in parallel with the output; the regulating arrangement having an auxiliary voltage input supplied with an auxiliary voltage which is a sum of the output voltage of the flyback converter and the output voltage of the auxiliary circuit; the second diode polarized such that the second diode is reverse biased when the first diode is forward biased; the third diode polarized such that the third diode is reverse biased when the second diode is forward biased. ### Claim 2 (depends on 1) The circuit arrangement as claimed in claim 1, wherein a limit of the duty ratio is at least approximately 0.5. ### Claim 3 (depends on 1) The circuit arrangement as claimed in claim 1, wherein a zener diode is arranged in parallel with the output of the auxiliary circuit. ### Claim 4 (depends on 1) The circuit arrangement as claimed in claim 1, wherein the supply voltage input of a regulator of the regulating arrangement is connected to the auxiliary voltage input of the regulating arrangement. ### Claim 5 (depends on 1) The circuit arrangement as claimed in claim 1, wherein a light-emitting diode of an optocoupler is connected to the output of the regulating arrangement, and wherein a series circuit which has the light-emitting diode of the optocoupler and a resistor is connected to the auxiliary voltage input of the regulating arrangement. ### Claim 6 (depends on 1) The circuit arrangement as claimed in claim 1, wherein the regulator is formed by a reference element, and wherein the control voltage output of the reference element is connected via a resistor to the auxiliary voltage input of the regulating arrangement. ### Claim 7 (depends on 1) The circuit arrangement as claimed in claim 1, wherein an output voltage of the flyback converter is less than 5 V, and the auxiliary voltage is at least 5 V. ### Claim 8 A flyback converter, comprising: an electronic switch which is connected in series with a primary winding of a transformer in a main circuit on a primary side of the transformer, the electronic switch being controllable by a control device; on a secondary side of the transformer a main circuit which is connected to a secondary winding of the transformer, the main circuit having a first diode in a series path and an energy-storage capacitor in a subsequent parallel path, connected in parallel with an output in the transformer; a regulating arrangement connected to an output of the flyback converter, the regulating arrangement supplied with an auxiliary voltage, a duty ratio of the control voltage which controls the electronic switch being limited to a predetermined upper limit; an auxiliary circuit having an input connected to the first diode of the main circuit on the secondary side and the auxiliary circuit having one pole of an output connected to the input; the auxiliary circuit having an RC series circuit in a series path on the input side, a second diode in the downstream parallel path, a third diode in a series path following the parallel path, and a capacitor in parallel with the output; the regulating arrangement having an auxiliary voltage input supplied with an auxiliary voltage which is a sum of the output voltage of the flyback converter and the output voltage of the auxiliary circuit; the second diode polarized such that the second diode is reverse biased when the first diode is forward biased; the third diode polarized such that the third diode is reverse biased when the second diode is forward biased; and a zener diode arranged in parallel with the output of the auxiliary circuit. ### Claim 9 (depends on 8) The circuit arrangement as claimed in claim 8, wherein a limit of the duty ratio is at least approximately 0.5. ### Claim 10 (depends on 8) The circuit arrangement as claimed in claim 8, wherein the supply voltage input of a regulator of the regulating arrangement is connected to the auxiliary voltage input of the regulating arrangement. ### Claim 11 (depends on 8) The circuit arrangement as claimed in claim 8, wherein a light-emitting diode of an optocoupler is connected tot he output of the regulating arrangement, and wherein a series circuit which has the light-emitting diode of the optocoupler and a resistor is connected to the auxiliary voltage input of the regulating arrangement. ### Claim 12 (depends on 8) The circuit arrangement as claimed in claim 8, wherein the regulator is formed by a reference element, and wherein the control voltage output of the reference element is connected via a resistor to the auxiliary voltage input of the regulating arrangement. ### Claim 13 (depends on 8) The circuit arrangement as claimed in claim 8, wherein an output voltage of the flyback converter is less than 5 V, and the auxiliary voltage is at least 5 V. ### Claim 14 A flyback converter, comprising: an electronic switch which is connected in series with a primary winding of a transformer in a main circuit on a primary side of the transformer, the electronic switch being controllable by a control device; on a secondary side of the transformer a main circuit which is connected to a secondary winding of the transformer, the main circuit having a first diode in a series path and an energy-storage capacitor in a subsequent parallel path, connected in parallel with an output in the transformer; a regulating arrangement connected to an output of the flyback converter, the regulating arrangement supplied with an auxiliary voltage, a duty ratio of the control voltage which controls the electronic switch being limited to a predetermined upper limit; an auxiliary circuit having an input connected to the first diode of the main circuit on the secondary side and the auxiliary circuit having one pole of an output connected to the input; the auxiliary circuit having an RC series circuit in a series path on the input side, a second diode in the downstream parallel path, a third diode in a series path following the parallel path, and a capacitor in parallel with the output; the regulating arrangement having an auxiliary voltage input supplied with an auxiliary voltage which is a sum of the output voltage of the flyback converter and the output voltage of the auxiliary circuit; the second diode polarized such that the second diode is reverse biased when the first diode is forward biased; the third diode polarized such that the third diode is reverse biased when the second diode is forward biased; and the supply voltage input of a regulator of the regulating arrangement connected to the auxiliary voltage input of the regulating arrangement. ### Claim 15 (depends on 14) The circuit arrangement as claimed in claim 14, wherein a limit of the duty ration is at least approximately 0.5. ### Claim 16 (depends on 14) The circuit arrangement as claimed in claim 14, wherein a zener diode is arranged in parallel with the output of the auxiliary circuit. ### Claim 17 (depends on 14) The circuit arrangement as claimed in claim 14, wherein a light-emitting diode of an optocoupler is connected tot he output of the regulating arrangement, and wherein a series circuit which has the light-emitting diode of the optocoupler and a resistor is connected to the auxiliary voltage input of the regulating arrangement. ### Claim 18 (depends on 14) The circuit arrangement as claimed in claim 14, wherein the regulator is formed by a reference element, and wherein the control voltage output of the reference element is connected via a resistor to the auxiliary voltage input of the regulating arrangement. ### Claim 19 (depends on 14) The circuit arrangement as claimed in claim 14, wherein an output voltage of the flyback converter is less than 5 V, and the auxiliary voltage is at least 5 V.