# US 2014/0197742 A1 · Led drive circuit > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 2014/0197742 A1 - Document ID: US20140197742A1 - Status: Published application - Kind: A1 - Application number: 13/824,396 - Filed: 2013-01-25 - Published: 2014-07-17 - Earliest claimed: 2013-01-11 - Assignees: Shenzhen China Star Optoelectronics Technology Co., Ltd. - Applicants: Shenzhen China Star Optoelectronics Technology Co., Ltd. - Inventors: Dan Cao; Xiang Yang - Web page: https://patentgrep.com/patent/US20140197742A1 ## CPC - H05B 45/395: Linear regulators - H05B 45/382: with galvanic isolation between input and output - Y02B 20/30: Semiconductor lamps, e.g. solid state lamps [SSL] light emitting diodes [LED] or organic LED [OLED] - H05B: ELECTRIC HEATING; ELECTRIC LIGHT SOURCES NOT OTHERWISE PROVIDED FOR; CIRCUIT ARRANGEMENTS FOR ELECTRIC LIGHT SOURCES, IN GENERAL - Y02B: CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO BUILDINGS, e.g. HOUSING, HOUSE APPLIANCES OR RELATED END-USER APPLICATIONS ## Abstract An LED drive circuit, which comprises a transformer, an MOS tube, a power regulating resistor, a direct current isolation circuit, a rectifying circuit, and a voltage control circuit; when the voltage of the control terminal of the voltage control circuit is higher than the threshold voltage of the MOS tube, the MOS tube is on, a current from an external power supply flows through the first winding of the transformer, the MOS tube and the power regulating resistor successively; when the voltage of the power regulating resistor is close to the voltage of the reference terminal of the voltage control circuit, the MOS tube is cut off, the second winding of the transformer charges the capacitor of the MOS tube via the direct current isolation circuit, the rectifying circuit is on, and the first winding of the transformer supplies power to the LED load via the rectifying circuit. ## Claims ### Claim 1 An LED drive circuit, comprising a transformer, an MOS tube, a power regulating resistor, a direct current isolation circuit, a rectifying circuit, and a voltage control circuit; wherein: the transformer comprises a first winding and a second winding; the first winding is connected at one end to an external power supply and at the other end to a source electrode of the MOS tube, a drain electrode of the MOS tube is grounded via the power regulating resistor; the second winding is grounded at one end, and connected at the other end to a grid electrode of the MOS tube via the direct current isolation circuit; the voltage control circuit comprises a control terminal for controlling on/off of the MOS tube, a reference terminal for regulating voltage of the control terminal, and a ground terminal; the control terminal is connected to the external power supply and the grid electrode of the MOS tube, the reference terminal is grounded via the power regulating resistor, and the ground terminal is grounded directly; the transformer and the voltage control circuit cooperate to control on/off of the MOS tube; when the MOS tube is on, a current from the external power supply flows through the first winding of the transformer, the MOS tube and the power regulating resistor successively, and the rectifying circuit is cut off; when the MOS tube is cut off, the second winding of the transformer charges a capacitor of the MOS tube by the direct current isolation circuit, the rectifying circuit is on, and the first winding of the transformer supplies power to an LED load via the rectifying circuit. ### Claim 2 (depends on 1) The LED drive circuit according to claim 1, wherein the rectifying circuit is a rectifying diode. ### Claim 3 (depends on 1) The LED drive circuit according to claim 1, wherein the voltage control circuit comprises a TL432 chip or a TL431 chip. ### Claim 4 (depends on 1) The LED drive circuit according to claim 1, wherein the direct current isolation circuit comprises a direct current isolation capacitor and a direct current isolation resistor connected in series, the direct current insulation capacitor is connected to the second winding of the transformer, and the direct current insulation resistor is connected to the grid electrode of the MOS tube. ### Claim 5 (depends on 1) The LED drive circuit according to claim 1, wherein the drive circuit comprises a compensating circuit which is connected at its input terminal to the control terminal of the voltage control circuit and at its output terminal to the reference terminal of the voltage control circuit. ### Claim 6 (depends on 5) The LED drive circuit according to claim 5, wherein the compensating circuit comprises a compensating resistor and a compensating capacitor connected in series. ### Claim 7 (depends on 1) The LED drive circuit according to claim 1, wherein the drive circuit comprises a protective circuit for preventing breakdown of the MOS tube, the protective circuit being connected at its input terminal to the control terminal of the voltage control circuit and at its output terminal to the ground terminal of the voltage control circuit. ### Claim 8 (depends on 7) The LED drive circuit according to claim 7, wherein the protective circuit comprises a voltage stabilizing diode and a protective resistor connected in parallel. ### Claim 9 (depends on 1) The LED drive circuit according to claim 1, wherein a control-terminal voltage regulating resistor for regulating voltage of the control terminal of the voltage control circuit is connected between the control terminal of the voltage control circuit and the external power supply. ### Claim 10 (depends on 1) The LED drive circuit according to claim 1, wherein a reference-terminal voltage regulating resistor for regulating voltage of the reference terminal of the voltage control circuit is connected between the reference terminal of the voltage control circuit and the power regulating resistor. ### Claim 11 An LED drive circuit, wherein the drive circuit comprises a transformer, an MOS tube, a power regulating resistor, a direct current isolation circuit, a rectifying circuit, and a voltage control circuit; the source electrode of the MOS tube receives input voltage of the transformer, and the drain electrode of the MOS tube is grounded through the power regulating resistor; the grid electrode of the MOS tube receives output voltage of the transformer via the direct current isolation circuit; the voltage control circuit comprises a control terminal for controlling on/off of the MOS tube, a reference terminal for regulating voltage of the control terminal, and a ground terminal; the control terminal receives the output voltage of the external power supply and is connected to the grid electrode of the MOS tube, the ground terminal is grounded directly, and the reference terminal is grounded via the power regulating resistor; the transformer and the voltage control circuit cooperate to control on/off of the MOS tube; when the MOS tube is on, the input voltage of the transformer forms a current in the transformer, the MOS tube and the power regulating resistor; when the MOS tube is cut off, the output voltage of the transformer charges the capacitor of the MOS tube via the transformer, the direct current isolation circuit and the MOS tube, and meanwhile the transformer supplies power to the LED load via the rectifying circuit. ### Claim 12 (depends on 11) The LED drive circuit according to claim 11, wherein the rectifying circuit is a rectifying diode. ### Claim 13 (depends on 11) The LED drive circuit according to claim 11, wherein the voltage control circuit comprises a TL432 chip or a TL431 chip. ### Claim 14 (depends on 11) The LED drive circuit according to claim 11, wherein the direct current isolation circuit comprises a direct current isolation capacitor and a direct current isolation resistor connected in series, and the direct current insulation capacitor receives the output voltage of the transformer. ### Claim 15 (depends on 11) The LED drive circuit according to claim 11, wherein the drive circuit further comprises a compensating circuit which receives the output voltage of the external power supply at its input terminal and is grounded via the power regulating resistor at its output terminal. ### Claim 16 (depends on 15) The LED drive circuit according to claim 15, wherein the compensating circuit comprises a compensating resistor and a compensating capacitor connected in series. ### Claim 17 (depends on 11) The LED drive circuit according to claim 11, wherein the drive circuit further comprises a protective circuit for preventing breakdown of the MOS tube, the protective circuit receiving the output voltage of the external power supply at its input terminal and being grounded directly at its output terminal. ### Claim 18 (depends on 17) The LED drive circuit according to claim 17, wherein the protective circuit comprises a voltage stabilizing diode and a protective resistor connected in parallel. ### Claim 19 (depends on 11) The LED drive circuit according to claim 11, wherein the control terminal of the voltage control circuit receives the output voltage of the external power supply via the control-terminal voltage regulating resistor which is used for regulating the voltage of the control terminal of the voltage control circuit. ### Claim 20 (depends on 11) The LED drive circuit according to claim 11, wherein a reference-terminal voltage regulating resistor for regulating voltage of the reference terminal of the voltage control circuit is connected between the reference terminal of the voltage control circuit and the power regulating resistor.