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 high 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 compact SOT23-3 package as well as dice on inked wafers. This way size-sensitive applications can be realised with chip-on-board solutions. This LED driver offers a low-cost two-component-solution (plus LEDs) for small LED flashlights or small-sized torches. Further applications for the PR4401 are LCD backlighting, for example in MP3 players operated with only one alkaline battery cell.