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US 8,575,845 B2Granted
Method and apparatus to measure light intensity
AssigneeTexas Instruments Incorporated
InventorsTobin D. Hagan, David L. Freeman, Marco Corsi
Life of this patent
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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.
Claims13
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.
7 more elements
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;
- wherein the LED further comprises a plurality of LEDs, wherein a step of measuring further comprises measuring the voltage that corresponds to the persistence of at least one of the LEDs;
- wherein the threshold is a sawtooth signal;
- wherein the step of deactivating further comprises:
- generating a sample pulse;
- and
- deactivating the plurality of LEDs in response to the sample pulse;
- 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.
14 more elements
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;
- wherein the threshold is a sawtooth signal;
- 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;
- 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.
14 more elements
Dependencies are inferred from the claim text.