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I saw a tiny joule thief here: http://www.bigclive.com/joule.htm.  I wanted to replicate the size, but leave the application open for use in different projects.  By following this excellent instructable: http://www.instructables.com/id/Make-a-Joule-Thief/ I was able to fit my circuit inside a 5x5 square of perfboard. It happily powers 3 leds in parallel. 
i just made one in a 3x4 piece of perfboard
That looks awesome!! Makes me want to go even smaller...Where is the resistor though? Underneath the board disqualifies you from competition(!)
<p>it is hidden behind the transistor :-)</p>
guys i want to makeone of this but i only have C1815,A1510Y transistor.. and dont know the resistor to use because i dont know the color to choose..
Cool
This is very neat, very clean looking as well! <br>I was wondering if you remembered where you got your ferrite bead from. I can't seem to find any. Also, I noticed you have only 5 wraps where most other thiefs use upwards of 20, does that effect the performance at all?
Hi! Thank you! I found the tiny ferrite bead inside a Philips &quot;Genie&quot; 11w CFL bulb. The instructable I followed recommended 6-11 turns on the bead, with 11 being the maximum advised. I used the smallest wire available to me and just squeezed 5 turns. It has been running 3 UV leds in parallel for a few nights now from an otherwise dead battery. Everything seems to work OK, but I'm not really sure how to test performance to be honest!
Okay, thank you! The only ferrite I have been able to find is much too big, I will continue to scavenge :)
Connecting three white LEDs in series is very bad for the Joule Thief because it requires over ten volts to light, and that same voltage is reflected back into the winding to the base. The base to emitter junction is rated for 5 volts maximum, and this JT exceeds that maximum by more than double. This is very unhealthy for the transistor, and so it is when the clip leads become disconnected while it is running. Do a big favor for the transistor and solder the LEDs in permanently. And connect them in parallel; you will get a brighter light with no more current. Thank you for the instructable.
Thank you so much for your very informative and helpful comment! I will be sure to take your advice.
Connecting three white LEDs in series is very bad for the Joule Thief because it requires over ten volts to light, and that same voltage is reflected back into the winding to the base. The base to emitter junction is rated for 5 volts maximum, and this JT exceeds that maximum by more than double. This is very unhealthy for the transistor, and so it is when the clip leads become disconnected while it is running. Do a big favor for the transistor and solder the LEDs in permanently. And connect them in parallel; you will get a brighter light with no more current. Thank you for the instructable.

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