Posted: January 5, 2011 in Uncategorized


Here is small,yet powerful circuit/project that can be used t light a LED from a single AA or AAA can light a LED with a dead cell.
Here’s the Joule thief. It’s like an open PCB torch that will take either an AA or AAA battery in the holder and use whatever power is left in the battery to light a white LED.
The amazing thing about this circuit is that it will run right down to about 0.35V if left running continuously, and will often provide a week of continuous low level light from a battery that would normally be considered dead.
The level of light is initially quite high but gradually reduces as the battery voltage goes lower. However, it can still be used for reading in a dark room, even when the battery is almost completely drained.
Take a metre of the 38swg (0.15mm) enamelled wire and fold it in half making sure that the point of the fold is nice and sharp since it will be used to thread the wire round the ferrite bead. It is important to lay the wire on evenly and pull it firmly round the form since you will need to make twenty turns of the doubled wire and it’s a tight fit.Don’t worry if you make a mess of it, since the ferrite bead can be re-used and you will have lots of spare wire to practice with.
The whole process of winding the bead is the most tricky part of the project and is made slightly more awkward by the fact you are winding two coils on simultaneously.When you pull the loop of wire through the bead be sure to carefully guide the loop through so that it doesn’t twist . When the bead is wound you should have a pair of wires sticking out each end. Crop them to about 2″ (50mm) and tin the ends, then meter them to find which wires are part of the same winding.
Now assemble the joule thief circuit with reference to the circuit diagram given above. And enjoy!!!



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