Joule Thief using Starship coil, lighting 36 LEDs from one AA
At Sunrise:Off-Grid I ended up mentioning this fascinating little circuit to many people, but hadn’t taken an example with me. The JT allows a single 1.5 volt battery to power one or more 3volt LEDs for many hours. The light won’t stop until the battery drops to approx 0.4 volts.
The construction is very simple indeed, and quite fun – you have to wind a little torroid with wire and a ferrite ring. You need one transistor, one resistor, an LED and your battery. You can also use a Rodin Starship coil in place of the torroid, allowing the whole thing to use wire with no ferrite ring. The image here shows a JT made this way. The picture shows a single AA (reading about 1 volt) lighting 36x 3 volt LEDs. I would have tried more but I ran out of LEDs! Interestingly, the whole lot were only drawing about 20 milliamps at 1 volt – less than the normal load of a single 3 volt LED!
If you go to http://www.evilmadscientist.com/article.php/joulethief you will find full instructions and parts needed to build your first one. The instructions are all over the web, but this was where I found it and they’re very clear. It is easy enough for a child to make and intriguing enough to keep an adult entertained and bewildered for hours…
