Transformerless Adjustable Joule Thief





Introduction: Transformerless Adjustable Joule Thief

Did you have problems winding the toroidal transformer of a regular joule thief? If so then this instructable is for you! And if not it is also an interesting circuit to see.

In this instructable I will show you how I made the simplest joule thief I know of with only an inductor!

Step 1: Demonstration

A joule thief is a circuit which boosts up voltage usually from a single AA cell to a higher voltage. It is most often used to drive LEDs with single "dead" battery.

Although the regulation is not as visible as it should. It's because I used a new battery. If you want to dim the light completely, use a 10kΩ potentiometer.

Step 2: Parts List

For this instructable you will need:


male headers (or you can just solder wires)

1x - BC327 small signal PNP transistor (others might work also but not as good)

1x - BC337 small signal NPN transistor (others might work also but not as good)

1x - 33µH inductor

1x - 470pF ceramic capacitor

1x - 47kΩ resistor

1x - 5kΩ or 10kΩ potentiometer or 2.2kΩ resistor(if brightness adjustment is not necessary)

Step 3: Schematic and Component Layout

The schematic is very plain and so is the component layout. I used the PCB layout as a guide for perfboard. I don't think making a custom PCB is worth it this time.

The original schematic can be found here: talking electronics

To make the schematic and component layout I used a free program CadSoft Eagle which I would recommend to anyone making schematics or PCBs.

Step 4: Conclusion

Although this may not be the most efficient joule thief ever, it gets the job done without the need of a toroid. The already small PCB could be made even smaller if SMD parts were used(but in reallity not by much).

Don't forget to post your results into the comments.



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    18 Discussions

    I took you statement that SMD would not reduce by much as a challenge. SO...

    I now have a PCB and thru away 77% of the size with;

    0604 size Rs and Cs ,

    SC70 size transistors

    0805 size LED

    SOD323 size inductor

    It is only .35 x .35 inch and still has .1 spaced headers.

    Hows that for reduction?

    Never tell an engineer it can't be done.

    7 replies

    update; here is the layout image, also got it just a bit smaller .337 x .324 inch

    anyone that wants the eagle files to make it smaller send me a note with where to send it.


    fantastic but can u build it with those tiny components? not really practical at 0201. perhaps for machine placed projects.

    i'm so tempted to break into my supply of 0201 components lol


    nothing like a challenge. Here it is with 0201 .262 x .325 inch


    On the contrary sir. That is how you get new inventions materialized.
    Now I bet you can't build me an antigravity device strong enough to lift my truck into space.

    well OK.
    i think you may have me on that one

    However being an Electronics Engineer and not a physicist,
    You never what the future may bring.

    I'm glad that you took my statement as a challenge. One thing I was not aware of with the SMD design is that the most space is saved by the height.
    Don't forget to show use your version, I'm very curious!

    As I don't have a powersupply capable of outputting 0.5V I can't really tell you but 0.5V is below the required 0.7V by the PN junction so I suppose it won't work?
    I'm not sure but I think that the regular joule thief can work with 0.5V without any special transistors.
    But if you want to know you should really try it out and let us know.

    ahh good point, ok let's say 1v. I'm thinking fuel cell or pv applications and the cells are .5v running

    i made one of these with germanium transistors 50 years ago using a very low voltage. also made one with Silicon.. NPN+PNP. it had a very long time constant. it was about 15 to 20 minutes before we heard a click. the inductor needs to saturate in this design same as the regular "joule thief" it is really just a simple relaxation oscillator

    Very nice and tiny build! Usefull! Tks for sharing :)