Yes, it's the infamous Joule Thief, in Instructable form! For those of you who don't know, the Joule Thief is a tiny little circuit that allows you to drive a white or blue LED from voltages as low as 0.5 volts. You think those batteries are dead? Don't throw them out yet! Hook them up to the Joule Thief to squeeze every last drop of energy out of them!

The idea and circuit came from this Make weekend project. Why don't you pay them a visit?

Step 1: Parts and Tools

For this project you will need very few tools and parts, as you will see in the picture below.
But for those of you who like it in text, here it is:

Helping Hands (Optional)
Soldering Iron
A Blue or White LED (Other colors are fine, too)
2N3904 Transistor or equivalent
1k Resistor (Brown-Black-Red)
Toroid Bead
Thin wire, two colors (magnet wire works)

You can get the toroid and transistor from a dead CFL; the transistor is usually labeled 13002.

Also, if you use a 2N4401 or BC337 transistor, your LED will be brighter because they can handle more amps.


<p>Hi,</p><p>i added 2 Leds, a potentiometer and two switches to make an reading/night light robot out of scrap parts. :D Thank you !</p>
Fun little project! Worked great first try!
<p><strong>I hope this comment helps</strong>. Mine didn't worked at first but after some CRITICAL fixes: 1) Bigger toroidal and thinner wires. And MOST IMPORTANT 2) The transistor wired as shown will NOT work in many cases because Base, Collector and Emitter are NOT in the same place. You need to know where the BCE are and is recommended to see a diagram for this circuit. I used both ferrite core and transistor from a dead CFL and did the test with a &quot;dead&quot; 1.5v battery and a UV LED. My transistor was a 13002.</p>
I've been back over it numerous times. Can anyone tell me what's wrong here? I know the circuit is terminated properly as it works with 3v. Just won't work with 1.5v :(
<p>What transistor type you've used? </p>
Same as instructions. 2N3904. I used wire from cat 5 cable which seems thin enough but I could be wrong?
<p>connections seems to be ok but leds negative side is connected to emiter transistor and minus from battery? I've meet sometime problems with ring toroid can't light a joule thief. Check other toroid ring and transistor fault if any. I've made a bigger joule thief inverter on cilindric toroid primary-45meters x wires(0,28mm) and secondary 24turns 0,68 mm over primary connections from secondary just like joule thief and I can light 3w-5w bulb leds from 1,5v battery over 4 hours light. Joule thief it's an easy schematic but any foult cannot make it work. Don't give up. Try harder. Cheers</p>
Mine is coming on but it is not getting brighter and the voltage is the same. I use a 13003 transistor. Please some help.
<p>Use a potentiometer 1k for adjusting brightness or even better 100ohms pot.</p>
<p>Hi, I tried making the same circuit but i don`t know what is wrong it`s not working i used the npn 2n2222 instead of a npn 2n3904 and i followed the same steps shown here but i can`t figure out why my circuit isn`t working? plz help i need it urgently!</p>
<p>No importa el transistor, siempre y cuando sea NPN, lo que debe estar sucediendo es que una de las bobinas est&aacute; en vertida, as&iacute; que cambia el orden de solo una bobina</p>
<p>You need a wire from the LED's negative to the battery.</p>
<p>I used a 2N3904 or 2N2222 going into a tip 31. It ran a solar led garden light that had a joule thief in it ran by my second joule thief. I got rid of the battery and replaced it with a 100F capacitor charged to 1v. It draws 2.6 miliamps. </p>
<p>My transformor was a bifillar toroid over rubberized ferite. And the choke was from a pc tower power supply. With a few of 10 pf capacitors. I just posted the circuit as the board migh be too confusing with that darlington array on it or what was a modifed darlinton pair. And that may not be perfectly drawn. PNP transistors would have worked better I think also. </p>
<p>You can use the digikey site to draw circuits as well. </p>
<p>Would it be better to use a N channel MOSFET in place of the NPN bipolar transistor? There's usually a 5V reverse bias limit on the base-emitter junction, a FET could allow more negative voltages on its gate (e.g with a. lower turns ratio), plus it's more efficient because there's no saturation voltage drop. I guess you'd also have to watch that the steady state (DC) condition of the transistor being on permanently which could short the battery, but a nice little circuit!</p>
<p>Hey thank you for your help with building my little dog light, now an Instructable!</p><p> <a href="http://www.instructables.com/id/Joule-Thief-Dog-Light">http://www.instructables.com/id/Joule-Thief-Dog-Li...</a></p><p>I couldn't have done it without your own great Instructable.</p>
<p>i have been trying with many transistor/wire/battery nothink working :c </p><p>What's wrong ?</p>
<p>emitter/collecter seems both to be connected to -</p>
<p>emitter/collecter seems both to be connected to -</p>
<p>What resistor are you using?</p>
<p>You could check all components, if there is current through them.Try &quot; ordinary&quot; wire ,instead of cobber wire for the toroid, unless you have current flowing through ofc ( they can be a bit difficult to get stripped right ),Check led works ( i dunno why you shrinktubed it ) it is easier not to, when starting up, get polarity right. :) That is all i can be helpfull with. Hope it works out fine.</p>
<p>Resistor is 1.2k the only one i was having on hand , i just tryed with some other wire same result , led is ok , i also tryed with a 920 ohm same result .</p><p>I have no luck with that sort of circuit i think :,), </p>
<p>Your circuit dosent quite seem right, from what i can see.This is what i can show.Remember transistor NPN.</p>
<p>Ok here they are,all 3 J-Thieves.Was fun to make them.I want to make more, smaller,wierder.</p><p>Can any tell how bedst to measure lightintensity without a lightmeter? To measure effency in circuit?</p><p>If it is possible</p>
<p>Wanted to make a smaller but as i am learning it will come.</p><p>Actually fun to make your own pcb.</p>
<p>Another J-thief.Random,casual,carefully handpicked vintage components. :)</p><p>Solderwork looks crappy and is.I`m a novice.</p><p>J-thief rox.</p>
<p>hello , could a s9014 work ?</p><p>thanks</p>
<p>:) my 1.st.Tis loads fun.Just the beginning.</p><p>Ty for tutorials.</p>
<p>Ps it is a 1 watt button led.</p>
I used BC549C to build a Joule Thief.
Does not work with 1.5V and 421 2DT nor with BC 337-40, only at 3-5V.
<p>In my experience dead CFL's are not a reliable source for toroid's as they are often too small to be useful in a project like this.</p>
Would a 2N3906B work i don't know about transiters
<p>You can, but you have to reverse the polarity of the supply and the LED on the circuit.</p>
<p>Here's a schematic for a PNP version: <a href="http://2.bp.blogspot.com/-nKDPBXQ1fhg/VLyHUdlfIZI/AAAAAAAABsY/7D6-sx2EI1s/s1600/pnp-joule-thief-wiring.png" rel="nofollow">http://2.bp.blogspot.com/-nKDPBXQ1fhg/VLyHUdlfIZI/...</a></p>
<p>Here's a schematic for a PNP version: <a href="http://2.bp.blogspot.com/-nKDPBXQ1fhg/VLyHUdlfIZI/AAAAAAAABsY/7D6-sx2EI1s/s1600/pnp-joule-thief-wiring.png" rel="nofollow">http://2.bp.blogspot.com/-nKDPBXQ1fhg/VLyHUdlfIZI/...</a></p>
The 2N3906 is a PNP transistor. The circuit requires a NPN transistor like the 2N3904 or the 2N2222.
Hey :) I am making a mini wind turbine and my motor generates about a 1V . With the joule thief I get 1.5V . How to get ~4.5V ? How to do it? Is it possible?
Increase the number of turns on your toroid and use a higher rated transistor. With 200 turns of the primary coil and 8 of the secondary, you can get approximately 110v, enough to power a CFL from an AA battery...but only for about 20 minutes. A D battery has a larger energy density and capacity, and may last upto an hour powering a CFL. The circuit doesn't actually do any boosting. It merely oscillates the voltage at a high frequency, which tricks electronics into powering up. A rapid recording would show that the light actually turns on and off at such a high rate, to our eyes appears to be lit solid.
<p>would adding a small capacitor help then? Or would it drain it too fast, maybe if the capacitor was minimal, you wouldn't want the cap to be Over charging, just right on the threshold.</p>
And by secondary and primary what do you mean........ Could you tell which one goes for the base and which one for the collector?
Did it work?we have common problem.im also making wind turbine and my motor generate also about 1V.<br>charingweedworm69@gmail.com
<p>Here is the schematic. This is all over the net. I would like to make this with 2 batteries for even longer life, but I suspect this will significantly increase the LED current. Any ideas?</p>
<p>Connect your 2 batteries in parallel. Voltage will be the same. Assuming you have 2 1.5V batteries, connecting in parallel will give you 1.5V but with a higher amps. </p>
<p>The pictures are great, thanks. But, this really needs a real schematic. I can't quite tell how you're connecting the coil. </p>
<p>I used 2N2222 transistor. The circuit was not working. why?</p>
<p>Why don't you just recommend using the 2N4401 transistor instead of the 2N3904? Is the 2N3904 more common to see in stores?</p>
Would a CTBC 547B LE work, i got it with DIY kit still in new condition <br>
I used transistors of dead cfl lamps which is 13002,13003.. but the joule thief isn't working.. can i use any other transistors thats NPN or is it specific to use 2N3904, 2N4401?

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