Step 2: Technical Information

Picture of Technical Information
The principle of operation is very simple.  The circuit is a basic boost switching converter that converts a lower voltage to a higher voltage through the use of switch and inductor.


The Joule Thief circuit uses a programmable boost converter IC. The boost converter is advertised as a 350mA LED Driver, although it’s really just a simple boost controller IC without an external voltage feedback input. The circuit is powered via a single 1.5V AA battery.   L1 is the 3.3uH boost inductor while C2 is a 4.7uF ceramic capacitor used as the boost output filter which provides a DC voltage to the 1W Cree LED.  Potentiometer R2 is used to vary the output brightness of the LED, while C1 is added to provide soft turn-on and turn-off of the LED.

Parts List:
  • (2) Resistor, 0.0 ohm, 0805 (R1,R3)
  • (1) Potentiometer, 1Meg (R2)
  • (1) Capacitor, 1uF, 0805 (C1)
  • (1) Capacitor, 4.7uF, 1206 (C2)
  • (1) Cree 1W LED (D1)
  • (1) Inductor, 3.3uH, 2.5A (L1)
  • (1) Programmable Boost Controller IC
  • (1) Switch
  • (2) AA Battery Clips