|Created||April 02, 2012|
|Last modified||April 02, 2012|
|Tags||flashlight joule joule-thief led light thief|
A simple Joule Thief circuit that uses bootstrap feedback to drive the transistor for added efficiency. There is a slight under-voltage (-6.6v instead of -5v) at the Base-Emitter junction but the transistor seems to handle it OK.
The coil can be from 50uH to 200uH per leg. It can be made by winding 12ft (3,5m) of a pair of wires around a 1" (25mm) form to make a 50uH air-core inductor. Make sure you connect the circuit to align the dots at the start of each wire.
The transistor must be rated for over 600mA and has a high frequency gain of 150 or more. Vce (at 500mA) dictates efficiency and the 'end-point' of battery life.
The 1N4148 will work OK but best efficiency is with a 1-amp schottky diode at D7.
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