The Simple Joule Thief.




About: I'm a big Arduino fan. I'm always looking for new and exciting things to do with electronics and Arduino. I also like video gaming on my PC and Xbox. I also ride my bike almost every day, and sometimes swim/...

The Joule Thief is such an easy and simple device, but what it does is amazing. It can use a battery that is not usable in any other electronic device and give it life again. It can even take a battery that won't even power a basic LED by itself when it is brand new (1.5 volt AA) and amplify the power so that it can.

This "Joule Thief" circuit, using a battery that won't work in any other device, can power a blue or white LED for approximately 8 days straight before it stops working. It could probably power a red LED for at least 10-12 days. You could also use it to power a microcontroller (such as an AVR or PIC MCU).

This is an entry in the LED Contest with Elemental LED and the Hurricane Lasers contest, so if you like it, vote!

Step 1: Why Is It Called a Joule Thief?

The reason the Joule Thief is called what it is is because of what it does. (That sentence was confusing) (:

Basically, what the Joule Thief does is it "steals" every last Joule of energy from your batteries. The explanation of what a joule is can be found on the Wikipedia page here. The quickest explanation I can think of is that a Joule is a form of energy that, in the way we use it, can be used to power electrical devices. I won't go into any more detail here because it gets very complicated.

Step 2: Parts List

To make this "Joule Thief", you will need:

1x 470uH inductor (looks like a fat resistor)
1x 2.2K resistor
2x 1K resistor
2x basic NPN transistor (2N3904, 2N2222, 2N4401, etc.)
1x 1000pf (same thing as 1nf or 0.001uf) ceramic capacitor
1x AA battery + holder (or any other 1.5 volt battery)
As many LEDs as your heart desires.

Step 3: Make It on a Breadboard!

It is super simple to make on a breadboard because it has such a low parts count. Look at the schematic to figure it out.

Step 4: Make It Permanent!

I have included the .sch and .brd files for making your own PCB. You can send the .brd file to the OSHPark website here, and they will make 3 copies of the board for $2.30 with free shipping. Not even kidding, it's that cheap.

Step 5: It's Done!

See, wasn't that easy?

You can also use a 2x AA battery pack instead for enhanced brightness. I'm not sure how many batteries you can go up to until the LEDs burn out, but you can sure test it yourself! :)

Step 6: BONUS! Use It to Power Your Projects!

You can add this Joule Thief to any of your projects that use microcontrollers also! Add it to my LED dice project here and get a super-green Dice circuit!

You could also probably make a super-high-power Joule Thief power supply with a 9 or 12 volt battery instead!

2 People Made This Project!


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10 Discussions


3 years ago on Introduction

One joule = one watt for one second. It is a unit of work as is a kilowatt-hour. How is that complicated??


4 years ago on Introduction

I built another Joule Thief instructable using a self wound coil. As soon as I get the choke I'm going to build this.

It's based on the same principal as the fly back diode attached to a relay.


4 years ago on Introduction

hi there,

is it possible to make a joule thief that will work from 48 vdc -128 vdc and handle 500 amps?


Robert Powell

4 years ago

If you use a 2n4401 transistor you will burn out the led at 2.3 vdc because 2n4401 can handle more amps. But idk with 2n3904 or 2n2222 so idk. :-)


5 years ago on Introduction

i use 2N3904 as the transister, but it doesn't work!!

the radio man

5 years ago on Step 3

nice project im doing it now unfortunatly i dont have LOL only have 1 red and im happy i can power it for more than 15 days (because im not using a dead 1)

2 replies
Dave Kruschke

Reply 6 years ago on Introduction

I've read where there are a few people that seemed to be highly focused on a narrow definition of Joule Thief. But isn't the main focus here intended to be on electronics rather than grammar or semantics? Besides, the meanings of names often change over time. Like, "I'm using a mouse to operate my computer even though we don't live with mice and I'm not really computing anything. Surely using these words this way isn't seriously confusing or worth fussing over. If something acts almost exactly like a "Joule Thief," why default to a more general term like Voltage Converter...


Reply 6 years ago on Step 2

Thank you for telling me this. I did not know that this circuit is not a joule thief. And also thank you for the information on the resistor/transistor thing. I will try it with a higher value tomorrow.