The core of the driver PR4401 from Prema consists of a step-up converter with current output, that provides an output voltage of typically 3.6V for white LEDs. The input voltage can be as low as 0.9V, thus allowing a single cell battery operation. Only one external component, an inductor, is required to operate up to three LEDs in series. A regulated current of up to 23mA depending on the inductor value provides a constant LED brightness independent of the supply voltage.

The PR4401 offers a efficiency of about 80% over the whole supply voltage range from 0.9V up to 2V. Thus the typical lifetime is more than 55 hours with an AA alkaline battery. An inductor value of 22µH is recommended for a maximum battery life, while with a 10µH coil higher currents are achieved for maximum brightness of the white LEDs. When the supply voltage drops, the battery current will be reduced to less than 10µA to avoid a deep discharge of the battery.

The PR4401 is available in a SOT23-3 package as well as dice on inked wafers. Samples and demo boards are available upon request.