This is a pocket-sized LED flashlight operating with only one AAA battery. However, the super high luminosity LEDs(blue,green or white) require at least 3.5 volts of forward voltage. This flashlight is boosting input voltage up to operating voltage of a LED with simple DC-DC converter. Circuit Diagram Right image shows the circuit diagram for the LED light. It is a typical blocking oscilator. High voltage pulse appears at collector of the Q1 is rectified by D1 and charged into C3. T1 is a hand-winded transformer. Please try to build the transformers to find the best condition, a drum core will be easy to build. Q1 is a low voltage strobe transister, any other transisters may down effeciency. The output current can be adujusted by R1.