Joule Thief flashlight

Joule Thief flashlight

Maker Jimmie Rodgers posted this flashlight variation of the Joule Thief to the MAKE Flickr pool.

Joule Thief – Link


  • Make a Joule Thief – Weekend Projects Video Podcast – Link

12 thoughts on “Joule Thief flashlight

  1. Kozz says:

    If one were to power a Joule Thief with a brand new AA battery, would there be any potential harm to the life of the LED? I’m not much of an electronics geek.

  2. paolo says:

    Well, normally, LEDs take 3 to 3.5 volts of potential to function at full capacity. I guess it would depend how powerful the joule thief is. Just take your multimeter out :P

    To optimize it, one could put several smaller joule thieves and determine how many joule thieves the current goes through before going to the LED, that wouldn’t need the resistor (or the resistor could have a switch to have more possibilities) and allow a larger flexibility in power source and probably have an even better power efficiency, just a thought.

  3. p914 says:

    Kozz, I think the answer is yes, and you’d be wasting energy as well.

  4. Collin Mel says:

    Sweet! I was wondering when someone would make one of these.

    Now to throw it into an altoids can or little RS box

  5. DonH says:

    Didn’t RTFA, but here are some comments that occur to me after reading about them in other places: A suppression ferrite has a large value of the imaginary term of Kappa(m). This does not make it a good choice for a magnetic material for a switcher. In the photograph, regular wire is being used on a seemingly overlarge ferrite core. This would create an undesired amount of parasitic capacitance, resulting in losses. Use magnet wire, square magnet wire is best. There are possibly other issues, but these are the most glaring. If this is a one-one X-former, the wires should probably be twisted together before being wrapped on the core, to increase capacitive coupling between the windings.

  6. Norry says:

    It seems that you are not so causious about quality but Podcast can make it so why not Podcast Hosting on

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Gareth Branwyn is a freelance writer and the former Editorial Director of Maker Media. He is the author or editor of over a dozen books on technology, DIY, and geek culture. He is currently a contributor to Boing Boing, Wink Books, and Wink Fun. And he has a new best-of writing collection and “lazy man’s memoir,” called Borg Like Me.

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