Squeeze More Juice Out of a Dead Battery!

A joule-thief circuit uses a transformer with primary and secondary windings on an iron core and a switching transistor to step up the voltage from a nearly depleted 1.5 V AA cell, enabling it to power a 3 V white LED. The transformer induces a higher voltage in the secondary coil via a changing magnetic field, while the transistor maintains oscillation to draw the remaining chemical energy from the battery.