Method and system for extending PWM dimming range in LED drivers
First Claim
1. A method for driving a light emitting diode (LED), comprising:
- sensing a rising edge of a pulse width modulation (PWM) signal, wherein, upon sensing the rising edge,initiating a threshold pulse (TP) signal having a configured width started when the rising edge is sensed,generating an LED current with an amplitude at a previously set level, andstarting to charge a capacitor which yields a voltage Vcap;
detecting a falling edge of either the PWM signal or the TP signal, wherein upon detecting the failing edge,stopping charging the capacitor,sampling, after a first delay from the detecting the falling edge, the voltage Vcap,adjusting a level of the amplitude of the LED current based on the sampled voltage Vcap; and
terminating the LED current when it is detected that both the PWM signal and the TP signal reach a low state.
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Accused Products
Abstract
An apparatus for driving a light emitting diode (LED). A rising edge of a pulse width modulation (PWM) signal is first sensed. Upon sensing the rising edge, a threshold pulse (TP) signal is initiated that has a configured width started when the rising edge is sensed, an LED current with an amplitude at a previously set level is generated, and starting to charge a capacitor which yields a voltage Vcap. Subsequently, a falling edge of either the PWM signal or the TP signal is detected. Upon detecting the failing edge, the circuit stops charging the capacitor, samples, after a first delay from the detected falling edge, the voltage Vcap, and adjusts a level of the amplitude of the LED current based on the sampled voltage Vcap. When the falling edges of both the PWM and TP signal are detected, the LED current is terminated.
50 Citations
18 Claims
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1. A method for driving a light emitting diode (LED), comprising:
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sensing a rising edge of a pulse width modulation (PWM) signal, wherein, upon sensing the rising edge, initiating a threshold pulse (TP) signal having a configured width started when the rising edge is sensed, generating an LED current with an amplitude at a previously set level, and starting to charge a capacitor which yields a voltage Vcap; detecting a falling edge of either the PWM signal or the TP signal, wherein upon detecting the failing edge, stopping charging the capacitor, sampling, after a first delay from the detecting the falling edge, the voltage Vcap, adjusting a level of the amplitude of the LED current based on the sampled voltage Vcap; and terminating the LED current when it is detected that both the PWM signal and the TP signal reach a low state. - View Dependent Claims (2, 3, 4, 5, 6, 7)
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8. An apparatus for driving a light emitting diode (LED), comprising:
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a capacitor configured to be charged to yield a voltage Vcap when a rising edge of a pulse width modulated (PWM) signal is detected; a threshold pulse (TP) generator, connecting to the PWM signal, configured to generate a TP signal having a configured width started when the rising edge of the PWM signal is detected, an LED driver configured for generating an LED current with an amplitude at a previously set level when the rising edge of the PWM signal is detected; a single falling edge detector configured for detecting a falling edge of either the PWM signal or the TP signal and producing a first control signal, upon the detection of the falling edge, that is used to stop charging the capacitor; a voltage sampling circuit configured for sampling, after a first delay upon the falling edge of either the PWM or TP signal is detected, the voltage Vcap so that the sampled voltage Vcap is used to adjust the amplitude of the LED current; a dual falling edge detector configured for detecting that both the PWM signal and the TP signal reach a low state and terminating the LED current upon the detection of the low state of both the PWM and the TP signals. - View Dependent Claims (9, 10, 11, 12, 13, 14, 15, 16, 17, 18)
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Specification