LED diode on 1.5V or less – Joule Thief
WANTED – Joule Thief
This is the thief which is responsible for stealing energy from single cell batteries, even in wasted ones.
Simple LED Playground
You Can Use Single Cell Battery for Lighting LED Diode Even if Your Voltage is Low as 0.7V.
One of the best LED diode qualities is their ability to give a proper light at low consumption rates. So if you have a wasted batteries which are not possible to use in your electronic devices, they can be usable, for sure, for bright LED. Voltage is not an issue here, cause we need at least 0.6 – 0.7 V to open transistor. The rest of job is scheduled to inductive element such is simple toroid transformer with few wire wounds.
One LED…One Resistor…One Inductor…One Transistor..
This is the simplest schematic for Joule Thief which I possibly could imagine. There’s only one general purpose transistor, in this case BC547, but should be functional with any other general purpose BJT transistor. Toroid mini-transformer consisting of two windings – one primary and one secondary with very few turns per each – about 7 to 12. Note that windings should be with OPPOSITE DIRECTIONS!
In this case I used toroid core with dimension of 16W x 6 mm H and these measures are with core plastic insulation so real core is smaller. I took double yellow-green wire and put about ten windings of both. After winding I soldered opposite side of yellow and green together in one point to achieve opposite winding directions. Those copper wire (bare wire) was added later to make experiments with more winding and you can disregard it, I just solder it to PCB to keep firm little toroid on surface.
Be sure to make a firm windings for oscillation resistance and wind around toroid core all over. Don forget that windings have to be with opposite directions.
This white plastic piece on top is fastener for wire holding.
How to Pick Correct Resistor Value
Yes, there is a calculation which can’t be of much use because we shouldn’t know right core properties, and needed values of our LED is usually missing. At first I put 1k resistor and one LED is work properly but another don’t (it was different types), so put the 2k2 trimmer and experience that the whole assembling may to work in some cases, with 47 Ohms. While the less value means more current, that shouldn’t be the doctor’s prescription and can permanently damage diode or may not oscillate at all.
Whatever you did with your project don’t blame me – every decision you made is up to you.
Layout on Stripboard-Like PCB
Inspite the simplicity of the project there is layout view too and you can made it on simple stripboard or without board at all – but this is the worst case scenario which should be avoided. If Atarado PICO board is not available make it on custom stripboard (or veroboard) peace of board since it would be more consistence and more durable also.