Many consumer products using white light LEDs for illumination and backlighting provide gradual LED illumination at turnon and turnoff. This gradual illumination is usually achieved with the aid of a Microprocessor that provides PWM dimming control. This circuit uses the Texas Instruments TPS61040 white light LED Driver to provide gradual illumination at turnon and turnoff without the use of a Microprocessor
The following circuit generates a 101mA constant current to drive up to 6 white LEDs for portable applications such PDAs and digital cameras. The input operating range is 1.8 V to 6 V, which covers two-cell alkaline and NiMh inputs (1.8 V to ~3 V), three-cell alkaline and NiMh inputs (2.7 V to ~4.8 V), and single-cell Li-Ion inputs (3 V~4.2 V). This boost converter uses R1 to set a constant current through the LEDs A detailed description of this circuit CAN be found in the TPS61040 data sheet ( SLVS413 ).
TPS61040 Constant Current LED Drive Supply