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.