Introduction: Make a Joule Thief

Picture of Make a Joule Thief

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

Picture of 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.

Step 2: Wind the Toroid

Picture of Wind the Toroid

The first step is to wind the toroid. I found mine in an old computer power supply, and it works fine for me. Toroids are donut-shaped objects like in the picture, and can be attracted by a magnet.

You can find toroids in a few places. Old computer motherboards, XBOX and X360 motherboards have them (don't take them unless it's dead!). You can find toroids in computer power supplies, or you could buy them at your nearest RadioShack.

Take your two strands of wire, and twist the ends together. You don't have to do this, but it makes winding a little easier.

Thread the twisted end through the toroid, then take the other two ends (Not twisted together) and wind it once around the toroid. Don't twist the wires; make sure that two wires of the same color are not right next to each other.

Keep winding, making sure you wind the coils tight. It will still work if they are kind of loose, but it is better to have them tight.

Ideally, you want about 8-11 turns on your toroid. Even if you can fit more, don't put more on. Make sure the turns are spaced evenly around the toroid.

Once you wind around the whole toroid, cut off the extra wire, making sure you leave a couple of inches for soldering.

Strip some insulation off the wires, then take a wire from each side, making sure they are of the OPPOSITE COLOR. Twist them together, and then you're done with the toroid.

Step 3: Solder It All Together

Picture of Solder It All Together

Now we are going to solder the whole thing together. You could put it on a board if you like, but in this Instructable, we're going to free-hand solder it. Or whatever you call it. You can follow these written instructions, or take a look at the pictures. They explain it very well.

First, take the two outer leads of the transistor and bend them outwards a little ways, and bend the middle lead backwards. Bend the LED's leads outwards, too. You don't have to, but it makes it easier to solder.

Take one of the wires coming from the toroid that is alone; that is, not twisted together with another wire. Solder it to one side of the resistor. Solder the other end of the resistor to the middle lead of the transistor.

Take the other single wire from the toroid, and solder it to the collector of the transistor. Solder the positive side of the LED to the collector as well, and solder the negative side to the emitter.

All that's left to do now is solder an extension wire to the negative side of the LED. Take a piece of that wire you had earlier and solder it to the transistor's emitter.

Step 4: Try It Out!

Picture of Try It Out!

And that's it! You're finished with your Joule Thief. Touch the twisted wires coming from your toroid to the positive side of a battery, and the extension wire to the negative side. If all is working well, the LED will light up! If not, try using thinner wire on your toroid. I've included a schematic in the pictures if you prefer.


shreyask9 (author)2017-02-10

Correction in the schematic of circuit:- The LED is supposed to be connected in reverse manner.(if you're using NPN transistor) i.e. anode to the emitter of transistor and cathode to the collector of transistor or vice versa if PNP transistor...

Wolf6774 (author)shreyask92017-10-22

Actually, it can work both ways. With mine i found it works better if i connect the Anode to the collector, and the cathode to the emitter.

just a voltage (author)2017-10-02

Hi Can I connect this set up to a dc motor? will the effect be the same?

alaafprojs (author)2017-06-04

Is it possible to make it w/o the toroid bead

alaafprojs (author)alaafprojs2017-06-04

Yes It is!(I just tried it with a transformer

shreyask9 made it! (author)2017-02-10

Works like charm....
I salvaged ferrite toriod from CFL ballast circuit and made 10 turnes on it... Ive used 2n2222a transister and high intensity red led from old broken computer mouse.. the circuit works on old batteries to suck out every joule of energy from it.

T0BY (author)2016-11-23

Genius! I am very impressed!

FrancisP40 (author)2016-11-08

How big should the ferrite core must be and how many windings needed?

ihaveaplace (author)2016-07-11

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 :(

miked2001 (author)ihaveaplace2016-11-07

Does the LED have an internal resistor?

Have you tried lighting the LED with a 2.0 volt supply or a 3 volt coin cell?

More turns in the winding might do the trick, (longer wires).

kyooby (author)ihaveaplace2016-08-11

What transistor type you've used?

ihaveaplace (author)kyooby2016-08-11

Same as instructions. 2N3904. I used wire from cat 5 cable which seems thin enough but I could be wrong?

kyooby made it! (author)ihaveaplace2016-08-12

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

stannickel made it! (author)2016-11-03

My first joule thief. It must work. It powers a 3 volt LED with a single 1.5 volt AA battery. I used a VN10KM Power FET for the transistor. The designations for Base Collector Emitter in an FET are Gate Drain Source from what I could find on the web. Anyway, it works!

gizu_one made it! (author)2016-10-16


i added 2 Leds, a potentiometer and two switches to make an reading/night light robot out of scrap parts. :D Thank you !

GaryDP made it! (author)2016-10-09

Fun little project! Worked great first try!

Lucio MartinC (author)2016-09-11

I hope this comment helps. 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 "dead" 1.5v battery and a UV LED. My transistor was a 13002.

The weekend mechanic (author)2016-04-28

Mine is coming on but it is not getting brighter and the voltage is the same. I use a 13003 transistor. Please some help.

Use a potentiometer 1k for adjusting brightness or even better 100ohms pot.

ajay_1558 (author)2016-05-23

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!

Rogermatz (author)ajay_15582016-06-12

No importa el transistor, siempre y cuando sea NPN, lo que debe estar sucediendo es que una de las bobinas está en vertida, así que cambia el orden de solo una bobina

StefanD27 (author)ajay_15582016-05-25

You need a wire from the LED's negative to the battery.

TravisM18 made it! (author)2016-05-21

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.

TravisM18 (author)TravisM182016-05-21

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.

TravisM18 (author)TravisM182016-05-21

You can use the digikey site to draw circuits as well.

MarkP188 (author)2016-04-20

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!

Pricklysauce (author)2016-03-26

Hey thank you for your help with building my little dog light, now an Instructable!

I couldn't have done it without your own great Instructable.

ralrigs (author)2016-02-23

i have been trying with many transistor/wire/battery nothink working :c

What's wrong ?

6teeth (author)ralrigs2016-03-14

emitter/collecter seems both to be connected to -

6teeth (author)ralrigs2016-03-14

emitter/collecter seems both to be connected to -

6teeth (author)ralrigs2016-02-23

What resistor are you using?

6teeth (author)6teeth2016-02-23

You could check all components, if there is current through them.Try " ordinary" 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.

ralrigs (author)6teeth2016-02-23

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 .

I have no luck with that sort of circuit i think :,),

6teeth made it! (author)ralrigs2016-02-24

Your circuit dosent quite seem right, from what i can see.This is what i can show.Remember transistor NPN.

6teeth made it! (author)2016-02-27

Ok here they are,all 3 J-Thieves.Was fun to make them.I want to make more, smaller,wierder.

Can any tell how bedst to measure lightintensity without a lightmeter? To measure effency in circuit?

If it is possible

6teeth made it! (author)2016-02-26

Wanted to make a smaller but as i am learning it will come.

Actually fun to make your own pcb.

6teeth made it! (author)2016-02-23

Another J-thief.Random,casual,carefully handpicked vintage components. :)

Solderwork looks crappy and is.I`m a novice.

J-thief rox.

ralrigs (author)2016-02-22

hello , could a s9014 work ?


6teeth made it! (author)2016-02-06

:) my loads fun.Just the beginning.

Ty for tutorials.

6teeth (author)6teeth2016-02-06

Ps it is a 1 watt button led.

FlorinCB made it! (author)2016-02-01

I used BC549C to build a Joule Thief.

FlorinCB (author)2016-01-26

Does not work with 1.5V and 421 2DT nor with BC 337-40, only at 3-5V.

TheG16 (author)2016-01-25

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.

Dylanjcasey117 (author)2015-01-03

Would a 2N3906B work i don't know about transiters

MartinL10 (author)Dylanjcasey1172015-09-21

You can, but you have to reverse the polarity of the supply and the LED on the circuit.

The 2N3906 is a PNP transistor. The circuit requires a NPN transistor like the 2N3904 or the 2N2222.

justas.uzusienis (author)2015-03-10

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.

About This Instructable




Bio: Sometimes my Instructables are few and far between, but I try to make them as well as I can. Hopefully you can be inspired or ... More »
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