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.
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.
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>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>
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>
The 2N3906 is a PNP transistor. The circuit requires a NPN transistor like the 2N3904 or the 2N2222.
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?
<p>I have used 13003 transistor on a joule thief circuit, so I know it works, dead CFL's are not very reliable source for transistors as sometimes when the bulbs goes bad, transistors burn out too. (Often it's the transistors that fail in these bulbs). Also take note that pinout on these transistors are not standardized between manufactures, I have TO-92 13001 that has pinout reversed (BCE).</p>
<p>I need your suggestion and help, from a source I am getting 100 mV and 50 microAmp (&micro;A) not milliAmp (mA) current continuous mode. Can I use jewel thief circuit to light a LED. if yes please let me know the resistor in ohm, diode specification and led specification so that i can make the circuit and how many wire turns will be required. To enhance the density, can I use capacitor for this small production of what specification. Please help</p>
<p>You need bigger power supply, the Joule Thief circuit only increases voltage, not current, if the current is too low the circuit simply doesn't operate. Also it's not that efficient as it also draws current.</p>
<p>Jewel thief :D</p>
<p>haha ... i noticed it a little later.. </p>
<p>You must know that a white led's voltage need to be around 3 V, and it draws about 20 ma to be lit up. Can you tell me what power source you have, and what project you re working on, so we can help</p>
Could I substitute the 2N3904 transistor for a TIP3055?
<p>It's a NPN 15A 60V transistor and it should work fine. </p>
<p>As long as it is a NPN, you can use it. Check the pinout schematic. The higher rate the transistor can handle the better</p>
<p>is it easy to make a stress meter using a joule thief circuit??</p>
Great Instructable thanks! What would be a better transistor if I want to make a very high voltage joule thief? Can you show me how to make a joule thief that can power a fan (pref adjustable)? I have lots of PC fans (12v) that I would love to be able to run with just 1 or 2 AA batteries!
I made it, but it only works with 2 AA batterys and it doesn't even light up a bit with 1 battery.... Thanks man!
<p>Interesting and enjoyable</p>
<p>Great project, I made it. I am going to leave it on and see how long the battery lasts. I let you know when it dies.</p>
<p>still alive?</p>
<p>Help please. I don't know an awful lot about electronics, I'm on a learning curve. I teach DT to primary children and I want to make a windmill that will light up an LED. The frame and windmill itself is the easy part for me, but is this what I should be looking at to light it up and will a joule thief help?</p>
Joule thief requires a pre-existing energy density... if the energy is generated on demand, a joule thief will not help. You may add an intermediary such as a polarized capacitor (high Mfs..like 4700mF) between the 'generator' and joule thief. But an energy potential (joules) must exist. A capacitor works like a battery, but charges much more quickly, and doesn't store as much energy potential all at once. But the capacitor would create a buffer from which to feed the joule thief.
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Pull apart a fish tank pump ($10.00) and you'll see the magnet that moves back and forth to make the pump work. Mount magnets on a wheel (alternating polarities) and allow them to pass by the transformer looking oscillator, as the wheel turns. The faster, the more power. But this setup should light a led and/or charge a Battery (must use a rectifier for it to work...see bridge rectifier). Entire setup less than $20.00... even less if you own an old fish tank pump :-)
<p>i used bc549 transistor, toroid from broken cfl lamps, and only 6 turns of wire on it because the toroid is so small, but it works, thank's</p>
i used also C945, C1815, and C9014 transistors and it works well, just watch out for these transistor's pinout, and i used it as a dimlight for our room at night,,
<p>Hey, I try to reproduce your experience but i don't find the toroid bead, please can you give me the reference of the toroid bead ? </p>
How many volt it can produce?
<p>the circuit is basicly a high freq oscillator circiuit around 40 kHz depending on the number of turns on the toroide. if a higher voltage source is used the current thru the transistor will increase making it go pop the 1k resistor is used to bias the transistor and can be increases to reduce current draw also a power transistor can be used for higher current tolerance.</p>
<p>I used a BC547 transistor. Is it OK? </p>
<p>Can we use a metal hexagonal bolt instead of Toroid...?????</p>
<p>You can, but it isn't as efficient as a ferrit bead(toroid).</p>
<p>Can I use a ferrit bar instead of a toroid ?</p>
<p>I made it, and it works great. Thanks so much for the pictures, because they helped a lot. I used a toroid that I had from an old ripped apart CFL (9 turns of thicker gauge wire from a larger toroid from a power supply), and the 2N3904 transistor, with an LED from an optical mouse. I used many different NPN transistors and that was the one with the best results. I did not have either of the two that you suggested (2N4401 or BC337). They would probably give better results, but it works very well as is. I started with a AA battery that measured .8V. It's been on now for 48 hours! I plan on getting a board so I can solder this together for use in another project. Great instructable.</p>
<p>Help me understand the role of the transistor? Is this specific to the joule thief? Running and LED directly from battery source (with resistor) doesn't seem to require the transistor, so I'm curious about what changes with the joule thief to make the transistor a requirement?</p>
<p>My understanding: LED's require &gt;3V to work. Joule Thiefs use one battery (1.5V or less) by charging the coil and adding its discharge to the battery's charge to power the LED.</p><p>The transistor does the switching from charge to discharge. The LED is actually blinking really fast like AC florescent bulbs do, but just too fast to see. </p>
<p>The LED will only light up if the battery voltage exceeds te forward voltage of the LED. Think of it as a threshold. So connecting a 1.5V battery to an LED with a forward voltage of 3V won't light it up. The Joule thief circuit here pulses the power through the coil, which causes a voltage spike, which is high enough to light up LEDs with a forward voltage much higher than the battery can provide directly. Furthermore, it can keep doing so untill the battery is almost completely drained, in effect 'stealing' every last bit of energy from the battery. It is so good at cranking up the voltage, it can work with batteries that are too discharged for most other devices. </p>
<p>I used a picture of your Joule Thief circuit in my latest instructable:</p><p><a href="http://www.instructables.com/id/Battery-Clips/" rel="nofollow">http://www.instructables.com/id/Battery-Clips/</a></p><p>I gave you credit and provided a link to this instructable.</p><p>I also enjoyed, and benefited greatly from, your instructable on better photography.</p><p>My Joule Thief kept the LED on for 68 hours. </p>
<p>Will using it reduce amps?? Please help.</p>
<p>Made it but have hard time to measure output voltage. My true RMS multimeter show me exactly the same output voltage as the input voltage. But it make sense, as the output is a pulse, the mean of the output may actually be equal to the input. Am I right ? If so I may read my VC850 to find a way to measure peak voltage.</p>
I got the same reading as well
madeor on a proto board and in the process I made an improv AA battery holder.
<p>I like high voltage, can I use my transformer in place of the toroid?</p>

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