The following circuit diagram is a LED power supply used to drive a white LED from a single 1.5V DC battery. As we know, a white LED requires 3.6V DC to illuminate. This circuit could easily provide it. To drive the current, a transistor BC338 is needed, a step up transformer (40:60) also required in this circuit. You can also change the transistor type with the higher of lower specBC 337, BC 547/8/9, or 2SC3279.