# US 2014/0191679 A1 · Dimming circuit and lighting device using the same > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 2014/0191679 A1 - Document ID: US20140191679A1 - Status: Published application - Kind: A1 - Application number: 14/089,800 - Filed: 2013-11-26 - Published: 2014-07-10 - Earliest claimed: 2013-01-07 - Assignees: Lextar Electronics Corporation - Applicants: Lextar Electronics Corporation - Inventors: Chun-Kuang Chen; Po-Shen Chen; Feng-Ling Lin; Hui-Ying Chen - Web page: https://patentgrep.com/patent/US20140191679A1 ## CPC - H05B 45/14: using electrical feedback from LEDs or from LED modules - H05B: ELECTRIC HEATING; ELECTRIC LIGHT SOURCES NOT OTHERWISE PROVIDED FOR; CIRCUIT ARRANGEMENTS FOR ELECTRIC LIGHT SOURCES, IN GENERAL ## Abstract A dimming circuit and a lighting device using the same are provided. The dimming circuit comprises an interface trigger unit, an average duty cycle calculating unit, a control voltage calculating unit and a comparing unit. The interface trigger unit receives an on-time of each pulse width from each period in a PWM signal. The average duty cycle calculating unit is coupled to the interface trigger unit and calculates a ratio of the on-time to the period. The control voltage calculating unit is coupled to the average duty cycle calculating unit, and calculates a desired voltage according to the ratio. The comparing unit is coupled to the control voltage calculating unit, and sends the desired voltage and a differential voltage to a driving circuit. ## Claims ### Claim 1 A light emitting diode (LED) dimming circuit, comprising: an interface trigger unit for receiving an on-time of each pulse width from a plurality of periods of a pulse width modulation (PWM) signal; an average duty cycle calculation unit coupled to the interface trigger unit for calculating a ratio of the on-time e to the periods, wherein the on-time are outputted from the interface trigger unit; a control voltage calculation unit coupled to the average duty cycle calculation unit for calculating a desired voltage according to the ratio obtained by the average duty cycle calculation unit; and a comparison unit coupled to the control voltage calculation unit for calculating a differential voltage between the desired voltage and a feedback voltage and sending the desired voltage and the differential voltage to an LED driving circuit. ### Claim 2 (depends on 1) The LED dimming circuit according to claim 1, further comprising: a feedback unit coupled between the LED driving circuit and the comparison unit for converting a current into the feedback voltage and outputting the feedback voltage to the comparison unit, wherein the current is outputted from the LED driving circuit to an LED. ### Claim 3 (depends on 1) The LED dimming circuit according to claim 1, wherein the interface trigger unit converts the positive edge and the negative edge of each pulse width of the PWM signal into a plurality of trigger signals and calculates the on-time according to the trigger signals. ### Claim 4 A lighting device free of flickering, comprising: an LED: a driving circuit for controlling the LED to emit a light; a dimming circuit, comprising: an interface trigger unit for obtaining an on-time of each pulse width from a plurality of periods of a first PWM signal; an average duty cycle calculation unit coupled to the interface trigger unit for calculating a ratio of the on-time to the periods, wherein the on-time are outputted from the interface trigger unit; a control voltage calculation unit coupled to the average duty cycle calculation unit for calculating a desired voltage according to the ratio obtained by the average duty cycle calculation unit; and a comparison unit coupled to the control voltage calculation unit for calculating a differential voltage between the desired voltage and a feedback voltage of the LED and sending the desired voltage and the differential voltage to the driving circuit; wherein the driving circuit compensates a control voltage outputted to the LED according to the differential voltage, wherein the control voltage is generated according to a second PWM signal, and a frequency of the second PWM signal is higher than that of the first PWM signal. ### Claim 5 (depends on 4) The lighting device free of flickering according to claim 4, wherein the dimming circuit further comprises: a feedback unit coupled between the driving circuit and the comparison unit for converting a current into the feedback voltage and outputting the feedback voltage to the comparison unit, wherein the current is outputted from the driving circuit to an LED. ### Claim 6 (depends on 4) The lighting device free of flickering according to claim 4, wherein the interface trigger unit converts the positive edge and the negative edge of each pulse width of the first PWM signal into a plurality of trigger signals and calculates the on-time from the trigger signals. ### Claim 7 (depends on 4) The lighting device free of flickering frequency according to claim 4, wherein the frequency of the second PWM signal of the driving circuit is higher than 20 kHz, and the frequency of the first PWM signal is lower than 5 kHz. ### Claim 8 (depends on 4) The lighting device free of flickering according to claim 4, wherein the driving circuit comprises a rectifier for converting the external alternating current voltage into a direct current voltage. ### Claim 9 (depends on 8) The lighting device free of flickering according to claim 8, wherein the driving circuit further comprises a power stage, which converts an external voltage into the control voltage of the LED according to the differential voltage and the desired voltage outputted from the comparison unit. ### Claim 10 (depends on 8) The lighting device free of flickering according to claim 8, wherein the driving circuit further comprises a low-pass filter, which makes the waveform of the control voltage approximate a direct current waveform.