Milen @ instructables.com writes:
Normally the Joule thief produces output voltage, which value is difficult to predict. Without load (the LED) I have measured voltages over 30 V. I wanted to create a Joule thief, which can be used to supply some small electronic devices, but having well defined and stable output voltage. There are known some solutions in which instead the LED load, a one-diode rectifier is used, and the output voltage is stabilized by the use of Zenner diode. I did not like this solution, because through the Zenner diode flows always a constant DC current, what reduces drastically the efficiency of the device and empties fast the supply battery. I was looking for other, better solution of the output voltage stabilization (limitation).
High efficiency regulated Joule thief - [Link]
Dave Kruschke writes:
Yep, no transformer and no hard to get IC. But, … two transistors and other parts are required. I actually found this circuit by accident while roaming Colin Mitchell’s Talking Electronics website (talkingelectronics.com). This website is very rich with examples and explanations of a huge variety of circuits. In fact, this website is so abundant in circuits that later on, I couldn’t find the circuit revealed here. Anyhow, I believe that the TE circuit can be considered “robust” as it works even if different parts are used.
“Joule Thief” – no IC and no Transformer - [Link]
Making LED devices portable can be a little bulky due to the batteries. The Joule Thief solves that, by boosting a single AA battery’s voltage to a high enough level to light a LED. Check it out.
Joule Thief – use LEDs with only one AA battery! - [Link]
This is a 1.2-volt single transistor flyback (Joule Thief) circuit that features a third coil. With it, flash duration and brightness is much enhanced, even with just a 10uF capacitor, as can be seen in the following schematic
1.2v LED Flasher – Joule thief - [Link]