The SM8122A is a high efficiency step-up DC/DC converter. Due to high voltage CMOS process realizing 25V output supply as maximum value, 2 to 6 lights of white LED connected in series can be lighted. By connecting in series, current variation among LED is eliminated. Current value sent to white LED can be set by external resistors. In addition, brightness can also be adjusted by control to FB pin or CE pin. Since the SM8122A has an over voltage protection circuit built-in, it dispenses with the existing external ZD (zener diode). Besides, the switching frequency of the SM8122A is higher (2.0MHz) than the existing product (SM8121A), so that it can respond to lower inductance value.