# How can I calculate a Joule thief

A Joule thief is a simple step-up converter with which you can drive a 3.6 V LED with a 1.5 V battery even if it is spending the last drops of its life. It merely consists of a transistor, a transformer and a resistor.

The circuit is very forgiving especially concerning the number of coils of the transformer. But I was wondering if there is a way to precisely calculate the voltage produced. It would be nice to use an old 1.5 V battery to power a microcontroller. I read people reporting that Zeners would interfere with the oscillating behaviour of the circuit.

Does anyone have deeper knowledge of these kind of circuits? And would it be possible to create a stable 5 volts to power a microcontroller?

The discussion here is the closest I could find and the request is very similar to mine.

• Short answer is yes, it is possible. I've powered an Arduino Mega from an 'empty' penlight cell and a step up converter. But I had the things lying around on my desk and was just fiddling with them, don't know how to spec them. Commented Dec 21, 2012 at 22:23
• did you use a voltage regulator or did you attach the power 'before' the onboard regulator of the arduino? Commented Dec 21, 2012 at 22:41
• just attached it to the 6-20V input. Didn't want to kill the AVR on it, which is spec'd like max. 5V1 and the max. boost converter output was 7V. Commented Dec 21, 2012 at 22:49
• Please ignore my answer, I have voted it for delete. It just another fix. electronics.stackexchange.com/questions/52007/… and I'm too waiting to see the answer how to calculate the real voltage output of joule theft. I think it has more things to do with dynamic resistance of tank circuit and many maths. Hope somebody soon answer this question. Commented Dec 22, 2012 at 20:41
• Please somebody answer this question. This is a real question. I'm too waiting for the answer. Commented Dec 24, 2012 at 19:41