How to make a Joule Thief

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 .

Comments

[kev88]

what if i remove the toroid? will it still works.

[neumanngregor]

There are some experiments, with a ferrite bar, nai, wood and even air core, but the efficency will be dramaticaly decreased ...

[kev88]

what i mean is to completely removed the toroid and boost the current with just the transistor

[neumanngregor]

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.

[ifarhan1]

can i replace the led with something else?

[neumanngregor]

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

[ifarhan1]

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

[mvj]

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

[neumanngregor]

A LM317 is not a transistor, it is a 3-Terminal Adjustable Regulator ( datasheet : http://www.national.com/ds/LM/LM117.pdf  ) 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 cudent get his name (i used my multimeter to get HFE value 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 "datasheet" (ex. "BC109 datasheet").

[acmefixer]

In step 3 I didn't see anything giving the thickness or length of the wire.  The wire and toroid core determine the frequency, which isn't important.  I've been experimenting with the cores I got from goldmine-elec.com for five for a dollar.  These are large and very high permeability. I wound it full of telephone wire, and the JT frequency was so low I could hear it with an earphone.  More info in my blog here.

[neumanngregor]

Watson im a big fan of your blog, i find really usefull the material you post on there. I use the 2cm external diameter cores that i got from AT and ATX PC sorces and from CRT monitors, i got my hands on a big number of them i "cleande" them of usefull things b4 sending them to recycle. The wire i use is standard emaeled and the size is around 1/3 of a mm (sorry i used only a ruler, dont have better measurement devices). The telophon wire is not really good for JT, in my view, it jst take too mutch space when winding the toroid. If you have a email or msn i whud enjoy to talk more about electronics with you (send me a pm with contact info if you wanna)

[acmefixer]

When you put multiple LEDs in series, the voltage adds up.  For blue or white LEDs it is about 3 volts per LED.  Some transistors have a maximum voltage of only 20 volts,so use caution and do not exceed the maximum voltage for the transistor.  Keep in mind that 6 series LEDs is over 18 volts.

I connect multiple LEDs in parallel and they all light up fine, as long as the LEDs are from the same maker and made about the same time.  The Joule Thief's pulsed output helps distribute the current evenly over all the LEDs.

[neumanngregor]

You are absolutely right aobut not going over the maximal voltage of the transistor, thats the same as going over the maximal amperage of the transistor. Shure you can add up leds in series and in parallel, heven as combo. I dont understand why ppl need to light up 20 leds, you can make enough light with max 3 ultra bright leds too. The ideea of a JT, in my own view, is to light up a led with with somthing thats is SMALLER that 2-3 AA or AAA batterys in a holder and some leds. I like to have a small device that helps up and that use "dead" batterys.

In my new instructable (hope i will upload all stuff this week) i gonna show ppl how to have a JT with a battery drain of 2.60 mA.

[V-Man737]

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.

[neumanngregor]

C9013 (100Mhz) i think it whud work ( datasheet here : http://www.futurlec.com/Transistors/C9013.shtml) 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

The transistors i listed are very cheap the 2N2222 (250Mhz) in plastic package is realy cheap, and the 2N3094 (300 Mhz)

[V-Man737]

Thanks, good to know! I'll let you know how it turns out for me.