White-LED driver provides 64-step dimming


Posted on Mar 12, 2013

The circuit of Figure 1 is designed for portable-power applications that require white LEDs with adjustable, logarithmic dimming levels. The circuit drives as many as four white LEDs from a 3.3V source and adjusts the total LED current from 1 to 106 mA in 64 steps of 1 dB each. The driver is a charge pump that mirrors the current ISET (sourced from IC3`s SET terminal) to produce a current of (215·ISET±3%) through each LED. Internal circuitry maintains the SET terminal at 0.6V. To control the LED brightness, op amp IC2 monitors the difference between the high-side voltage and the wiper voltage of digital potentiometer IC1. The op amp then multiplies that voltage by a gain to set the maximum output current. Zero resistance at the potentiometer`s W1 terminal corresponds to minimum LED current and, therefore, minimum brightness.






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