transformerless joule thief circuits

This a circuit very similar to a Joule Thief, except that it is using 2 transistors, no transformer core, and only one inductor.

Joule Thief based on transformer page is here:

I have built these two circuits today and have combined them into one- first stage is the LED torch to increase voltage, and second stage is a LED blink circuit.


I changed the inductor to 150uH.


The blink circuit is based on the breakdown of the CE junction of a BJT, it is exploited  to discharge a small capacitor into a LED. Since there is some hysteresis the LED blinks (it stays on for small time).

The 47k Ohm resistor in the torch circuit can be changed down to 12K or up to 110 K, which will affect the blink rate.

The components are sold on ebay as a kit, including two small breadboard, and AAA battery holder.

Instructions for the kit:


The transistor with the metal tab is the NPN intended for the LED torch circuit. The transistor with the silver imprint is the PNP, a BC327.

The other transistor type is a 2n3904 (which also could be used for the NPN). Capacitors are some 100pF to 1nF.

there are 3 different resistors for the 47K resistor, 56k which is close (green blue orange), 12K, and 110K.

The small blue resistor is the 680R resistor. There are 3 different kinds of LEDs included, red, blue, and UV.

Both shown circuits can be built, and also combined.

More than one LED could be connected in series too.

One thought on “transformerless joule thief circuits

  1. Hi !

    I bought your components on ebay. I saw you changed the inductor to 150uH. Could you update your circuit schematic with this new component please ? (I think it need to change connections)

    Thanks !


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