From website
The "Joule Thief" circuit that does not use a transformer to power LED from a single 1.5V battery cell. The circuit consists of two bipolar transistors, coil, two resistors and capacitor to generate higher voltage through 50KHz frequency to power an ordinary LED. Entire circuit draws only about 15 milliamp
Source http://electronics-diy.com/transformerless-joule-thief.php
