Introduction: Joule Thief LED With Dead Battery - No Toriod

It is my first instructable. Basically it is about a Joule Thief to light a LED with one 1.5v battery like what others did. I read thought many instructables. Either I need two transistors or one IC that I don't want or I need a Toroid which I don't have.

Here is another version.

1. Npn transistor x 1 (any kind)
2. resistor 1k ohm x 1
3. Inductor 330uH x 1 (can try any value)
4. 20cm of copper wire ( I cut from a CAT5 cable)
5. LED x 1
6. Battery 1.5v x 1

Step 1: Step 1 to N

Instead of using a toroid,I wrap the copper wire 8 to 10 turns on the inductor as captured.

Connect transistor, resistor and LED as captured, then connect the inductor between resistor and battery positive end, and the copper wire between Collect end of transistor and battery positive end. That is it. Connect the 1.5v battery and see.

The tricks are:
-  increase no of turns of the coil to make LED light up more
- any value of inductor will do as long as it makes the transistor circuit oscilates so the transistor open and close frequently
- any npn transistor will do but if the circuit makes the transistor hot, you need to consider the "heat sink" if you are going to let the LED run for longer time

Step 2: The Diagram

My drawing. Hopefully readable. The end...

Step 3: Enhancement - Brighter Yet Less Heat

The original circuit is for simplicity so not perfect. Transistor will be heat up in an hour.

You can see in fact the coil is almost resistantless like short circuit so all power applies on the transistor.

I think it over then put an inductor in series with the coil. Results in brighter LED yet less heat.

Obviously the inductor puts on some resistance so less current flow that reduce heat. But the inductance increases, so when transistor switches on, more energy is accumulated, then when transistor switches off, more power applies to LED, ie brighter.

One stone two birds. Have fun :D


whalescwh (author)2014-10-24

Read (just now) your comments, think it over about the heat problem, come up another idea :)

I believe the over heat is due to the low resistance of the wire. So I put an Inductor in series with the coin then connect to positive power.

This increases the resistance but most importantly the inductance between positive power and collective pin of the transistor, ie the voltage impose to LED will be higher. Effect is LED lighter but transistor less burn and less heat :>

pandyaketan (author)2014-07-29

This is genius!

I have seen many joule thief circuits, but this one is an underdog!

No IC, No torroid (Ok! Only Air Torroid, no ferrite)!!


If you replace / series / parallel the 1K resistor with a ceramic capacitor (say, 1 nF or 10 nf or even 100 nF cap, like in some other i'bles), that should take care of buffering and heat issues.

I would request you to improvise further to make it suitable for continuous use...

I will surely give it a try, with some tweaks!




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whalescwh (author)2014-06-11

The green one wired up is the inductor. Outlook is like a resistor :)

jwoods10 (author)2014-06-11

What inductor? I only see two resistors...

whalescwh (author)2013-04-23

In fact the transistor is not hot but warm however I don't know and never try to run the setup for 24 hours. So just a reminder / disclaim:)

The transistor I used is s9013 brought online from china.

Nice blog anyway.