# US 2013/0154483 A1 · Method and apparatus to measure light intensity > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 2013/0154483 A1 - Document ID: US20130154483A1 - Status: Published application - Kind: A1 - Application number: 13/325,934 - Filed: 2011-12-14 - Published: 2013-06-20 - Earliest claimed: 2011-12-14 - Assignees: Texas Instruments Incorporated - Inventors: Tobin D. Hagan; David L. Freeman; Marco Corsi - Web page: https://patentgrep.com/patent/US20130154483A1 ## CPC - H05B 45/14: using electrical feedback from LEDs or from LED modules - H05B 45/39: Circuits containing inverter bridges - H05B: ELECTRIC HEATING; ELECTRIC LIGHT SOURCES NOT OTHERWISE PROVIDED FOR; CIRCUIT ARRANGEMENTS FOR ELECTRIC LIGHT SOURCES, IN GENERAL ## Abstract A method for controlling a light emitting diode (LED) is provided. Initially, the LED, which had been active, is deactivated, and a voltage for a current that corresponds to the persistence of the LED is generated. The voltage is then integrated so as to generate an integrated voltage, and the integrated voltage is compared to a threshold. When the integrated voltage is less than the threshold, the LED is then activated. ## Claims ### Claim 1 An apparatus comprising: a plurality of light emitting diodes (LEDs) coupled in series with one another; a pulse width modulation (PWM) switch that is coupled to at least one of the LEDs; and a controller having: a sample switch that is coupled to at least one of the LEDs; a measurement circuit that is coupled to the sample switch; a sample-and-hold (S/H) circuit that is coupled to the measurement circuit; an integrator that is coupled to the S/H circuit; and a PWM generator that is coupled to the integrator, the PWM switch, and the sample switch, wherein the PWM generator controls the PWM and sample switches. ### Claim 2 (depends on 1) The apparatus of claim 1, wherein the PWM generator further comprises: a comparator that is coupled to the integrator; a logic circuit that is coupled to the comparator, the PWM switch, and the sample switch; and a signal generator that is coupled to the integrator, the comparator, and the logic circuit. ### Claim 3 (depends on 2) The apparatus of claim 2, wherein the logic circuit further comprises: a logic gate that is coupled to the comparator and the comparator; a latch that is coupled to the logic gate, the signal generator, and the sample switch; and an inverter that is coupled between the latch and the PWM switch. ### Claim 4 (depends on 3) The apparatus of claim 3, wherein the controller provides a reference signal to the integrator, a sawtooth signal to the comparator, a reset signal to the logic gate, and a sample set signal to the latch. ### Claim 5 (depends on 4) The apparatus of claim 4, wherein the logic gate is a NAND gate. ### Claim 6 (depends on 5) The apparatus of claim 5, wherein the latch is a reset-set (RS) latch. ### Claim 7 (depends on 6) The apparatus of claim 6, wherein the measurement circuit further comprises: a resistor that is coupled to the sample switch; and an amplifier that is coupled to the resistor. ### Claim 8 A method comprising: deactivating an LED; generating a voltage from a current that corresponds to the persistence of the LED; integrating the voltage so as to generate an integrated voltage; comparing the integrated voltage to a threshold; and activating the LED once the integrated voltage is less than the threshold. ### Claim 9 (depends on 8) The method of claim 8, wherein the LED further comprises a plurality of LEDs, and wherein the step of measuring further comprises measuring the voltage that corresponds to the persistence of at least one of the LEDs. ### Claim 10 (depends on 9) The method of claim 9, wherein the threshold is a sawtooth signal. ### Claim 11 (depends on 10) The method of claim 10, wherein the step of deactivating further comprises: generating a sample pulse; and deactivating the plurality of LEDs in response to the sample pulse. ### Claim 12 (depends on 11) The method of claim 11, wherein the voltage is a cycle voltage for the period between the deactivation and activation of the plurality of LEDs, and wherein the step of generating the voltage further comprises: activating a measuring circuit in response to the sample pulse; and sampling-and-holding the cycle voltage so as to generate an average voltage; and wherein the step of integrating further comprises integrating the average voltage. ### Claim 13 (depends on 12) The method of claim 12, wherein the step of activating further comprises: generating a reset pulse in synchronization with the sample pulse; logically combining the reset pulse with the result of the step of comparing; and deactivating the measurement circuit. ### Claim 14 (depends on 13) The method of claim 13, wherein the step of logically combining further comprises NANDing the reset pulse with the result of the step of comparing. ### Claim 15 An apparatus comprising: means for deactivating a plurality of LEDs; means for generating a voltage from a current that corresponds to the persistence of at least one of the LEDs; means for integrating the voltage so as to generate an integrated voltage; means for comparing the integrated voltage to a threshold; and means for activating the LED once the integrated voltage is less than the threshold. ### Claim 16 (depends on 15) The apparatus of claim 15, wherein the threshold is a sawtooth signal. ### Claim 17 (depends on 16) The apparatus of claim 16, wherein the means for deactivating further comprises: means for generating a sample pulse; and means for deactivating the plurality of LEDs in response to the sample pulse. ### Claim 18 (depends on 17) The apparatus of claim 17, wherein the voltage is a cycle voltage for the period between the deactivation and activation of the plurality of LEDs, and wherein the means for generating the voltage further comprises: means for activating a measuring circuit in response to the sample pulse; and means for sampling-and-holding the cycle voltage so as to generate an average voltage; and wherein the step of integrating further comprises integrating the average voltage. ### Claim 19 (depends on 18) The apparatus of claim 18, wherein the means for activating further comprises: means for generating a reset pulse in synchronization with the sample pulse; means for logically combining the reset pulse with the result of the step of comparing; and means for deactivating the measurement circuit. ### Claim 20 (depends on 19) The apparatus of claim 19, wherein the means for logically combining further comprises means for NANDing the reset pulse with the result of the step of comparing.