Joule Thief

To light blue and white light-emitting diodes (LEDs) the voltage of 3V is required. By the way, white LED is the same as blue LED with additional luminophore inside. This luminophore is activated by blue light and lights up. Finally it lights as white.

What to do if you wish to connect a white or blue LED to a simple AA or AAA battery or even worse to the dead battery? It’s very simple. It’s enough to assemble a self generator on one transistor and the LED will light. That’s a real sample:

Dziauliu vagis

On the Internet this scheme is often called “Joule Thief”. Though the idea of self generation is well known and used in various strange devices.

What do you need for repeating the experiment? A simple transistor firstly. I used the transistor NPN 2N3904.  Secondly, you need 1K resistor  and  a small transformer wound on a ferrite ring. The ring can be very small, as device is not very powerful. My ring has 2 x 30 winds of thin copper wire.

Wind the transformer as follows: take 1m of  thin wire and fold it in half. So you have two wires. Wind them on the ring simultaneously. When the ring is wound, crop and tin each end of the wires. Connect the beginning of one wind to the end of the other wind and to the positive post of a battery. (Check with a tester or in any other way if the connection was made correctly. You can use coloured wires, it will be easier to recognize them).  The second wire of the transformer should be connected to the resistor, the third – to the collector. Connect Led’s anode (+) to the same collector and free end of the resistor to transistor base (to the central leg). Transistor emitter and LED’s cathode (-) should be connected to the negative post of the battery.

 Scheme is here:

Dziauliu vagis

Theoretical remarks (untested).

You can use PNP transistor, but it will be necessary to reverse emitter with collector, anode with cathode and to connect the power supply in opposite way. You can also use old Russian germanium transistors. Then the device will work more stable at low voltage. Such device could be powered from “primary power sources” as lemons or apples with two different wires inside… 🙂

This entry was posted in Anything. Bookmark the permalink.

2 Responses to Joule Thief

  1. Acme Fixer says:

    When using a PNP, you said to reverse emitter with collector. But the emitter and collector of a PNP should be connected to the same places as for the NPN transistor. The only thing that needs to be reversed is the LED. The battery must be reversed, negative connects to the coil leads.

    Thanks for the good assembly guide, I hope more people try to build this.

  2. Yes, you are right. Also there maybe some translation problems as this article is translated by Agotukas.

Leave a Reply

Your email address will not be published. Required fields are marked *