Apparatus and methods for controlling LED light flux

An LED light flux setting system comprising:

• a microprocessor configured to generate a generator output signal, the generator output signal formed as a base rectangular waveform gated by a modulating rectangular waveform, the base rectangular waveform having a first frequency more than 10 kHz and the modulating rectangular waveform having a second frequency less than one-tenth of the first frequency, the microprocessor being controllable to vary a duty cycle of the base rectangular waveform and a frequency and duty cycle of the modulating rectangular waveform;
• a low-pass filter having a cut-off frequency between the first frequency and the second frequency, the low-pass filter coupled to the rectangular pulse generator system and configured to receive a filter input signal representative of the generator output signal and produce a filter output signal representative of the filter input signal with frequencies above the cut-off frequency being attenuated compared to frequencies below the cutoff frequency, the low-pass filter including a capacitor and a resistive voltage divider, the resistive voltage divider applying a portion of a voltage of the filter input signal to the capacitor;
• a voltage-controlled current source coupled to the low-pass filter and responsive to a control voltage signal representative of the filter output signal for generating an LED drive signal having a current level representative of a voltage level of the control voltage signal;
• and
• at least one LED configured to conduct the LED drive signal, the at least one LED producing a light flux determined by the current level of the LED drive signal.

An LED light flux setting method comprising:

• generating, by a rectangular pulse generator system, a base rectangular waveform having a first frequency and a first duty cycle;
• gating the base rectangular waveform with a modulating rectangular waveform having a second frequency less than the first frequency and a second duty cycle, the gated base rectangular waveform forming a generator output signal;
• filtering a filter input signal representative of the generator output signal with a low-pass filter having a cutoff frequency to produce a filter output signal representative of the filter input signal with frequencies above the cut-off frequency being attenuated compared to frequencies below the cutoff frequency;
• generating an LED drive signal having a current level representative of a voltage level of a control voltage signal representative of the filter output signal;
• and
• producing a light flux determined by the current level of the LED drive signal by conducting the LED drive signal in at least one LED.