# US 7,609,533 B2 · Light-load efficiency improving method and apparatus for a flyback converter > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 7,609,533 B2 - Document ID: US7609533B2 - Status: Granted - Kind: B2 - Application number: 11/882,637 - Filed: 2007-08-03 - Published: 2008-12-04 - Granted: 2009-10-27 - Earliest claimed: 2007-05-29 - Assignees: Richtek Technology Corporation - Inventors: Chao-Hsuan Chuang; Cheng-Hsuan Fan; Hung-Che Chou - Web page: https://patentgrep.com/patent/US7609533B2 ## CPC - H02M 3/33523: {with galvanic isolation between input and output of both the power stage and the feedback loop} - H02M 1/0025: {Arrangements for modifying reference values, feedback values or error values in the control loop of a converter} - H02M 1/0032: {Control circuits allowing low power mode operation, e.g. in standby mode} - 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 flyback converter has a controller to switch a power switch so as to convert an input voltage to an output voltage for a load by monitoring an output voltage dependent signal and a current sensing signal derived from a current flowing through the power switch, a light-load efficiency improving apparatus monitors the load and a supply voltage provided for the controller to selectively clamp the output voltage dependent signal when the load is lower than a first threshold value and the supply voltage is lower than a second threshold value, so as to increase the supply voltage. ## Claims ### Claim 1 A light-load efficiency improving apparatus for a flyback converter which is operative to convert an input voltage to an output voltage for a load by switching a power switch by a controller receiving a supply voltage, an output voltage dependent signal from a feedback input, and a current sensing signal derived from a current flowing through the power switch, the controller turning off the power switch when the output voltage dependent signal is lower than the current sensing signal, the light-load efficiency improving apparatus comprising: a first detecting circuit for detecting the load; a second detecting circuit for detecting the supply voltage; and a circuit for selectively clamping the output voltage dependent signal according to outputs of the first detecting circuit and the second detecting circuit. ### Claim 2 (depends on 1) The light-load efficiency improving apparatus of claim 1, wherein the circuit for selectively clamping the output voltage dependent signal comprises: a voltage source for providing a bias voltage; and a switch between the voltage source and the feedback input, for being turned on when the load is detected lower than a first threshold value and the supply voltage is detected lower than a second threshold value. ### Claim 3 A light-load efficiency improving method for a flyback converter which is operative to convert an input voltage to an output voltage for a load by switching a power switch by a controller receiving a supply voltage, an output voltage dependent signal from a feedback input, and a current sensing signal derived from a current flowing through the power switch, the controller turning off the power switch when the output voltage dependent signal is lower than the current sensing signal, the light-load efficiency improving method comprising the steps of: detecting the load and the supply voltage; and clamping the output voltage dependent signal when the load is detected lower than a first threshold value and the supply voltage is detected lower than a second threshold value, such that the supply voltage rises up until to reach a third threshold value. ### Claim 4 (depends on 3) The light-load efficiency improving method of claim 3, wherein the step of clamping the output voltage dependent signal comprises the step of replacing the output voltage dependent signal with a bias voltage. ### Claim 5 A flyback converter comprising: a power switch; a controller for switching the power switch to convert an input voltage to an output voltage for a load, wherein the controller receives a supply voltage, an output voltage dependent signal from a feedback input, and a current sensing signal derived from a current flowing through the power switch; and a light-load efficiency improving apparatus for selectively clamping the output voltage dependent signal by monitoring the load and the supply voltage. ### Claim 6 (depends on 5) The flyback converter of claim 5, wherein the light-load efficiency improving apparatus comprises: a first detecting circuit for detecting the load; a second detecting circuit for detecting the supply voltage; and a circuit for providing a bias voltage to the feedback input according to outputs of the first detecting circuit and the second detecting circuit. ### Claim 7 (depends on 6) The flyback converter of claim 6, wherein the circuit for providing a bias voltage to the feedback input comprises: a voltage source for providing the bias voltage; and a switch between the voltage source and the feedback input for being turned on when the load is detected lower than a first threshold value and the supply voltage is detected lower than a second threshold value.