LED Boost Circuit – Joule Thief

The Nifty-Stuff LED Boost Circuit / Joule Thief is a device designed for two purposes:

1) To suck any and all traces of juice from your “dead” batteries. 

2) To light an LED, with a voltage requirement of higher than 1.5 volts, off of a single 1.5 volt (or less) battery! For example, run a white LED from a single AA battery!

Other boost circuits exist. Some are more efficient but have more parts and are expensive. Others have fewer parts, but are not very efficient or reliable.

This circuit was built to be a perfect balance of price, efficiency, & reliability. Efficiency is around 70% with only 7 parts.

I made a few tap lights for my wife and some other nursing mothers to use at night. These lights are perfect for this application. Not too bright as to blind you when your eyes are adjusted to the dark but sufficient light to accomplish nightly tasks. I received some excellent feedback from one of the mothers:

“This seriously is a “magic” light. I mean, it gives off a decent amount of light, and the fact that it runs ten hours a night for over six weeks on two batteries is pretty crazy. I think this light would be great especially as a night light for kids’ rooms because it’s safe (doesn’t use an outlet), and it’s so cheap to use that you can let it run all night.”

I noticed that I was piling up a HUGE supply of dead alkaline batteries from use in baby toys, flashlights, etc. Being the miser that I am I hate throwing batteries away that still have a bit of juice in them. I was previously using my constant current circuit in a tap light for my wife. I decided to create a new tap light with the Nifty-Stuff LED Boost Circuit. I originally created the boost circuit tap light with two AA batteries in parallel. I stuck two “dead” batteries in the light and gave it to my wife. After a few weeks of use every night the light was still shining bright. At this rate I’d never get through my stockpile of dead batteries! I opened the tap light back up and re-wired the batteries to run in series. This provided more light and would drain the batteries faster. Hahaha… I never thought I’d be designing something to drain batteries faster… how funny!

Word has spread about my custom built lights and my boost circuit, so I’m making it available as a non assembled circuit. You’ll get all the parts needed to build the circuit including a high quality Printed Circuit Board (PCB).  Please keep in mind that this is a VERY tiny circuit, so you’ll need to be pretty handy with a soldering iron to avoid accidentally bridging two connections and shorting something.

The kit with all the parts (including a bright white LED) is currently unavailable.  If you would like to be notified when kits are available please post a comment to this post.   Sorry for any inconvenience

Using this circuit:

This circuit may be driven by voltages up to 3 Volts. While the basic design goal was ‘candle like light from a single cell’, the components used were chosen to allow safe operation from 3 Volts so you can, for example, use it to ‘drain the last bit of energy’ out of used Lithium based cells from flashlights. This means that you can also drive it from a fresh 123 cell at full brightness or two NiMH, alkaline or other cells in series. While the current consumption (and therefore light output) goes down with supply voltage, some light is produced even with very low inputs.

24 thoughts on “LED Boost Circuit – Joule Thief”

  1. How to make a simple light switch from this circuit: connect a photoresistor between the base of the second npn (the one driving the coil) and ground, and the led will light with darkness and go off on daytime. If you want, put a 47k pot in series with the photoresistor to adjust sensitivity.
    It works!!

  2. could i use the joule thief to power 3 leds from two aa bateries, which inturn will be charge by a solar panel 0.25 W 2.5 volt

  3. hey this is a great idea. What is the output voltage from 2 aa size batteries. In trying to power 9 10mm leds using 21/23 (12v) batteries. Also what is the layout for your circuit. It looks like i can get these parts from disposable cameras . If not then could i get a list of parts and a design layout and i can try to make one. Thanks

  4. Is the voltage boost proportional to the light output decrease? Im wondering if the LED output is less (in mcd or lumens) than if you ran the LED at its typical 3-3.5Vf.
    Anyone? Thanks.

  5. #1) When is a kit available, I would like to oder a few of these.

    #2) Can you EXPAND upon this? For example, I’d like to build the most efficient “solar garden lights” I can (I think we can do better than the chinese) — So, a small solar panel to charge the batteries by day, a photocell to turn off the LED by day and turn ’em on at night, and the Joule Theif circuit to get as much time out of the charged batteries as possible. Ideally, I’d like to make the circuit power more than a single LED — most of the Garden lights you get at Walmart are too dim for real lighting purposes, I’d prefer to make a set that give off double or triple the light of the store-bought variety and yet last as long in terms of hours of light.

  6. Hi, i am intresteed in the circuit, it seem s to be very efficient. Please mail me the circuit diagram.

  7. How long can this led run in days on one single AA battery?
    I am looking vor a flashlight that can run on one single AA battery for 5 years.
    Is this in some way possible?
    Can someone help me out, or develop this for me?

  8. I use a simpler circuit to power 14 white led’s from a single AAA battery. I haven’t actually timed how long tha battery lasts but it’s at least 15 hours.

    Check out this link http://www.evilmadscientist.com/article.php/joulethief

    Solar lights already use a variation of the joule thief and the fact that they suck all the enegry out of the battery is why the batteries go bad once the daylight hours are too short recharge them back to full charge.

  9. You can increase the value of the resistor and make the Joule Thief run for a much longer time. But the light output may be so low that it is not useful.

    Use a solar cell to recharge the cell. Those garden lights they sell for a few dollars last for a few years before they go bad.

  10. I love joule thieves! A suggestion: you can get a great $10 alkaline battery charger on amazon that will reinvigorate all those dead batteries.

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