LED Brightness Control by Variable Frequency Modulation
AssigneeMicrochip Technology Incorporated
InventorCharles R. Simmers
Life of this patent
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Abstract
Perceived intensity (brightness) of light from a light emitting diode (LED) is controlled with a pulse train signal having fixed pulse width and voltage amplitude and then increasing or decreasing the frequency (increasing or decreasing the number of pulses over a time period) of this pulse train signal so as to vary the average current through the LED. This reduces the level of electro-magnetic interference (EMI) at any one frequency by varying the pulse train energy spectrum over a plurality of frequencies.
Claims20
An apparatus for controlling brightness of a light emitting diode (LED), comprising:
- a pulse generating circuit having a trigger input and a pulse output, wherein a plurality of trigger signals are applied to the trigger input and a plurality of pulses are thereby generated at the pulse output, wherein each of the plurality of pulses has a constant width and amplitude;
- a pulse on-time integrator having a pulse input coupled to the pulse output of the pulse generating circuit and an integration time interval input, wherein the pulse on-time integrator generates an output voltage proportional to a percent of when the amplitudes of the plurality of pulses are on over an integration time interval;
- an operational amplifier having negative and positive inputs and an output, the negative input is coupled to the output voltage from the pulse on-time integrator and the positive input of the operational amplifier is coupled to a voltage signal representing a desired light brightness from a light emitting diode (LED);
- and
- a voltage controlled frequency generator having a frequency control input and a frequency output, wherein the frequency control input is coupled to the output of the operational amplifier, and the frequency output generating the plurality of the trigger signals is coupled to the trigger input of the pulse generating circuit, whereby the voltage controlled frequency source causes the pulse generating circuit to produce the plurality of pulses necessary for producing the desired light brightness from the LED.
An apparatus for controlling brightness of a light emitting diode (LED), comprising:
- a pulse generating circuit having a trigger input and a pulse output, wherein a plurality of trigger signals are applied to the trigger input and a plurality of pulses are thereby generated at the pulse output, wherein each of the plurality of pulses has a constant width and amplitude;
- a light brightness detector adapted to receive light from a light emitting diode (LED) and output a voltage proportional to the LED light brightness;
- an operational amplifier having negative and positive inputs and an output, the negative input is coupled to the voltage proportional to the LED light brightness and the positive input of the operational amplifier is coupled to a voltage signal representing a desired light brightness from the LED;
- and
- a voltage controlled frequency generator having a frequency control input and a frequency output, wherein the frequency control input is coupled to the output of the operational amplifier, and the frequency output generating the plurality of the trigger signals is coupled to the trigger input of the pulse generating circuit, whereby the voltage controlled frequency source causes the pulse generating circuit to produce the plurality of pulses necessary for producing the desired light brightness from the LED.
A microcontroller for controlling brightness of a light emitting diode (LED), comprising:
- a microcontroller having a output and an input, the output is coupled to a light emitting diode (LED) and the input is coupled to a LED light brightness control signal;
- and
- the microcontroller generates a plurality of pulses, wherein each of the plurality of pulses has a constant width and amplitude, and light brightness from the LED is proportional to a percent of time that the plurality of constant width and amplitude pulses are on over an integration time interval.
Dependencies are inferred from the claim text.