# US 9,049,766 B2 · Avoid audio noise of a LED driver during PWM dimming > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 9,049,766 B2 - Document ID: US9049766B2 - Status: Granted - Kind: B2 - Application number: 13/921,523 - Filed: 2013-06-19 - Published: 2013-12-26 - Granted: 2015-06-02 - Earliest claimed: 2012-06-21 - Assignees: Richtek Technology Corporation - Applicants: Richtek Technology Corporation - Inventors: Tsung-Wei Huang; Shui-Mu Lin; Huan-Chien Yang; Nang-Ching Yeung; Ti-Ti Liu - Web page: https://patentgrep.com/patent/US9049766B2 ## CPC - H05B 45/46: having LEDs disposed in parallel lines - H05B 45/38: using boost topology - 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 A LED driver using a PWM signal for dimming control includes a power converter and a current regulator. The power converter provides an output voltage and a load current for a plurality of LEDs. The current regulator provides a load current dependent signal for the power converter to speed up load transient response caused by variation of the load current, to reduce the ripple of the output voltage, and thereby to avoid audio noise during PWM dimming. ## Claims ### Claim 1 A LED driver using a PWM signal for dimming control, the LED driver comprising: a power converter providing an output voltage and a load current for a plurality of LEDs, the power converter comprising: an operational amplifier amplifying a difference between a reference voltage and a feedback signal related to the output voltage to thereby generate a compensation voltage; and a PWM logic circuit connected to the operational amplifier and configured to generate a control signal according to the compensation voltage and a ramp signal, the control signal having a duty ratio for regulating the output voltage; and a current regulator having a plurality of control terminals connected to the plurality of LEDs respectively, and configured to be responsive to the PWM signal to adjust a plurality of LED currents which flow through the plurality of control terminals respectively and determine the load current, and to generate a sense signal related to the load current, the sense signal being applied to the power converter to adjust the duty ratio. ### Claim 2 (depends on 1) The LED driver of claim 1, wherein the power converter employs the sense signal to adjust the compensation voltage to thereby adjust the duty ratio. ### Claim 3 (depends on 2) The LED driver of claim 2, further comprising a dynamic headroom controller connected to the plurality of control terminals and configured to detect voltages at the plurality of control terminals to generate a detection signal determining the reference voltage. ### Claim 4 (depends on 3) The LED driver of claim 3, wherein the dynamic headroom controller comprises: a voltage detector connected to the plurality of control terminals and configured to detect the voltages at the plurality of control terminals to extract a minimum voltage therefrom; a comparator connected to the voltage detector and configured to compare the minimum voltage with a second reference voltage to thereby generate a comparison signal; a counter and logic circuit connected to the comparator and configured to provide a digital signal and to adjust the digital signal according to the comparison signal; and a digital-to-analog converter connected to the counter and logic circuit and configured to convert the digital signal into the detection signal. ### Claim 5 (depends on 1) The LED driver of claim 1, wherein the power converter employs the sense signal to adjust the ramp signal to thereby adjust the duty ratio. ### Claim 6 (depends on 5) The LED driver of claim 5, further comprising a dynamic headroom controller connected to the plurality of control terminals and configured to detect voltages at the plurality of control terminals to generate a detection signal for adjusting the feedback signal. ### Claim 7 (depends on 6) The LED driver of claim 6, wherein the dynamic headroom controller comprises: a voltage detector connected to the plurality of control terminals and configured to detect the voltages at the plurality of control terminals to extract a minimum voltage therefrom; a comparator connected to the voltage detector and configured to compare the minimum voltage with a second reference voltage to thereby generate a comparison signal; and a filter connected to the comparator and configured to filter the comparison signal to generate the detection signal. ### Claim 8 (depends on 1) The LED driver of claim 1, wherein the current regulator comprises: a current generation circuit generating a first current; a current mirror connected to the current generation circuit and configured to mirror the first current to generate the sense signal when the PWM signal is triggered; and a plurality of Switch circuits connected to the current mirror and the plurality of control terminals and configured to determine the LED currents which flow through the plurality of control terminals respectively according to a voltage related to the first current. ### Claim 9 (depends on 1) The LED driver of claim 1, wherein the current regulator increases the load current step by step when the PWM signal is triggered and decreases the load current step by step when the PWM signal is terminated. ### Claim 10 A method for a LED driver using a PWM signal for dimming control, the method comprising the steps of: A.) providing an output voltage and a load current for a plurality of LEDs; B.) detecting the output voltage to generate a feedback signal; C.) amplifying a difference between a reference voltage and the feedback signal to thereby generate a compensation voltage; D.) according to the compensation voltage and a ramp signal, generating a control signal having a duty ratio for regulating the output voltage; E.) responsive to the PWM signal, adjusting a plurality of LED currents which flow through the plurality of LEDs respectively and determine the load current; and F.) generating a sense signal related to the load current to adjust the duty ratio. ### Claim 11 (depends on 10) The method of claim 10, wherein the step F comprises adjusting the compensation voltage responsive to the sense signal to thereby adjust the duty ratio. ### Claim 12 (depends on 11) The method of claim 11, further comprising detecting voltages at output terminals of the plurality of LEDs to generate a detection signal for determining the reference voltage. ### Claim 13 (depends on 12) The method of claim 12, wherein the step of detecting voltages at output terminals of the plurality of LEDs to generate a detection signal for determining the reference voltage comprises the steps of: detecting the voltages at the output terminals of the plurality of LEDs to extract a minimum voltage therefrom; comparing the minimum voltage with a second reference voltage to generate a comparison signal; adjusting a digital signal according to the comparison signal; and converting the digital signal into the detection signal. ### Claim 14 (depends on 10) The method of claim 10, wherein the step F comprises adjusting the ramp signal responsive to the sense signal to adjust the duty ratio. ### Claim 15 (depends on 14) The method of claim 14, further comprising detecting voltages at output terminals of the plurality of LEDs to generate a detection signal for adjusting the feedback signal. ### Claim 16 (depends on 15) The method of claim 15, wherein the step of detecting voltages at output terminals of the plurality of LEDs to generate a detection signal for adjusting the feedback signal comprises the steps of: detecting the voltages at the output terminals of the plurality of LEDs to extract a minimum voltage therefrom; comparing the minimum voltage with a second reference voltage to thereby generate a comparison signal; and filtering the comparison signal to generate the detection signal. ### Claim 17 (depends on 10) The method of claim 10, further comprising increasing the load current step by step when the PWM signal is triggered and decreasing the load current step by step when the PWM signal is terminated.