A Joule Thief (JT) is a step-up voltage transformer based on the working mode of a PWM (Pulse Width Modulation), it produce a oscillation in a inductor with the help of a transistor (2N3904, 2N2222, ...) then the output of the inductor is your new voltage. The result is that you can light a white, blue or even a ultraviolet LED with a single 1.5V cell (AA, AAA or any type of cell, i have used a watch cell too). This "voltage booster" circuit is not very efficient but it can use batterys that are near depleted. I whud not power up a microcontroler are anything that whud be disturbed by the voltage and power oscillation of the output, there are some dedicated step-up voltage boosters like the IC from Maxim with a 90% efficiency. With a bigger inductor and another transistor it is possible to get some very high voltage, i have see on the web some JT that can light up a neon tube from a 12v bike lead acid battery.

Step 1: Tools

Solder iron, Dremel, Hot Glue, Cutter or Exacto Knive and ... a pair of hands .
It is said that you got your toroid from a dead cfl. Have you tried smaller toroids? Like half the size of your cfl toroid? (Just thinking ahead for a peoject where space is at a premium.)
I had a even smaller one, the outer diameter is 5mm, but it is a pain in the aXX to wind it. :D it works well, the small one, i even used just a fer-rite rod and it worked too.
A 555 ic, can do that mutch better for that, hope you dont belive the "overunity bla bla" if you drive a bigger load the power drain is bigger on the battery. A JT can drive a cfl easy if it is made for that purpose. Some ppl used the flyback transformer as inductor for a jt, but you need a better transistor for that, not the usual 2n3904 or 2n2222.
So you can use a joule thief as a flyback driver.
what if i remove the toroid? will it still works.
There are some experiments, with a ferrite bar, nai, wood and even air core, but the efficency will be dramaticaly decreased ...
what i mean is to completely removed the toroid and boost the current with just the transistor
Ohh you meen a 1 transistor amp, that is not the same as a JT, in JT's the transistor and the inductor are used to make a oscilation, and the resultants "spikes" are used to light up the LED. The gain of a single transistor amp is not tha hight as a JT. Dont mix audio amps with PWM.
can i replace the led with something else?
As long as it is a diode it is ok, if you want to feed the voltage to somthing else, keep in mind that the voltage it is not DC and it has some big freqvency, i dont recomand to try to power somting that can be damaged easly
if the voltage is not in DC, is it in AC? My idea is to connect the joule thief to my created earth battery to charge a cell phone that use voltage under 3volt. Can it be done? Please help me.... thanx
Hi,I'm new to the electronics thing and I was wandering if I could use a LM317 transistor instead of the 2N3904, I live in S.A. and cant realy find a 2N3904. Can someone please direct me to site from which I can learn and understand more about electronics,tnx
A LM317 is not a transistor, it is a 3-Terminal Adjustable Regulator ( datasheet : <a href="http://www.national.com/ds/LM/LM117.pdf " rel="nofollow">http://www.national.com/ds/LM/LM117.pdf&nbsp;</a> ) but i used some outher transistors too, like 2N2222 or BC547C, even a unknown transistor i recovered, it whas fit in a heat sink and i&nbsp;cudent get his name (i used my multimeter to get&nbsp;HFE value&nbsp;and pinout). If you have not found any of the transistors then just experiment with things you can recover from electro junk :) , read the datasheets to know the pinout of them, easy way put on google the name of the transistor folowed by the word &quot;datasheet&quot; (ex. &quot;BC109 datasheet&quot;).
How would a C9013 transistor do in this? I'd like to see a more comprehensive list of transistors that would work, just for those of us whose sources for components are broken childrens' toys.
C9013 (100Mhz) i think it whud work ( datasheet here : <a rel="nofollow" href="http://www.futurlec.com/Transistors/C9013.shtml)">http://www.futurlec.com/Transistors/C9013.shtml)</a> if it dont oscilate then try to lower the resistor value at the base of the transistor or add a small capacitor (a ceramic capacitor like 104 ... as a thumb rule is better get a biger Mhz value and try to get a transistor with the voltage range you need <br/><br/>The transistors i listed are very cheap the 2N2222 (250Mhz) in plastic package is realy cheap, and the 2N3094 (300 Mhz)<br/>
Thanks, good to know! I'll let you know how it turns out for me.

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