Transformerless Adjustable Joule Thief

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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:

perfboard

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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    19 Discussions

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    theykk

    5 months ago

    i try but doesnt working

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    mickeypop

    2 years ago

    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
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    mickeypopmickeypop

    Reply 2 years ago

    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.

    temp3.png
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    JohnC430mickeypop

    Reply 2 years ago

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

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    TaylorH52mickeypop

    Reply 2 years ago

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

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    mickeypopTaylorH52

    Reply 2 years ago

    Taylor

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

    temp.png
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    josephleboldmickeypop

    Reply 2 years ago

    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.

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    mickeypopjosephlebold

    Reply 2 years ago

    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.

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    DIY Circuitsmickeypop

    Reply 2 years ago

    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!

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    DIY CircuitsH2Powerman

    Reply 2 years ago

    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.

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    H2PowermanDIY Circuits

    Reply 2 years ago

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

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    JohnC430DIY Circuits

    Reply 2 years ago

    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

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    dpizetta

    2 years ago

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