The UTC L5100 is a STEP-UP DC/DC Converter and designed for driving white LEDs with a constant current. It can drive several LEDs in series by a Li-Ion cell. UTC L5100 switches at a high frequency 1.2MHz, so it can allowing the use of tiny external components. The output capacitor can be as small as 0.22F, saving space and cost compare with alternative other solutions. The low 95mV feedback voltage minimizes power loss in the current setting resistor can have better efficiency.