Author Options:

Joule thief from http://joulethief.com/kit.php? Answered

The joule thief from this website was the first working one I built, mainly because I'd favoured one without a tapped inductor. Anyway, I pulled it out a couple of days ago, and started poking around with it. I noticed that if I put a 10uf  (or maybe it was 1uf or 100uf, sorry, I don't remember) capacitor in parallel with the 0.001uf capacitor, the LED would start to flash. this would not happen with any other value however. Why does this happen?

P.S: I've heard that this joule thief is poorly designed. Is this true?http://talkingelectronics.com/projects/LEDTorchCircuits/LEDTorchCircuits-P1.html



Best Answer 8 years ago

I believe that if you connect it to an o-scope you'll find that it does indeed blink even when it looks solid.  It just blinks faster than your eye can see it.

When you changed the capacity by adding a capacitor you just slowed down the blink to where you can see it.  In otherwords you changed the frequency.

For the thing to work at all it has to be turning on and off rapidly otherwise the coil would not be able to increase the voltage going to the led.

Also, the circuit works so it must be designed pretty well.

The capacitor affects the frequency at which the device operates, like Re says, it's flashing anyway (when working). If you increase the value of the capacitor it takes longer to charge/discharge, you slow it all down.