The Joule Thief is a delightfully simple circuit that can light an
LED that requires 2V or more from a battery that is depleted to 1V or
less. There are three components in addition to the battery and LED: an
NPN transistor, a resistor and a double wound inductor. The key thing
about the inductor is that the same core shares two windings but in
The explanation of how it works is simple enough, as long as you
already understand how inductors and transistors work. In other words,
it isn't simple at all! In short, the double wound inductor and
transistor conspire to generate a transient high voltage spike and so
turn LED on and off so rapidly that the human eye cannot perceive
The idea of such a circuit is approaching its centenary but the name
itself is only around 20 years old. I recommend you check out Big Clive's web site as it was
he who came up with the name "Joule Thief". I also recommend this video in
which he constructs a circuit using some ninja-level soldering
Comment #1 posted on 2023-02-01 19:07:11 by one_of_spoons
I assumed these were more complicated boost modules.
I hadn't realised they were so simple.
I've definitely got a bunch of those components.
Note to Verbose Commenters
If you can't fit everything you want to say in the comment below then you really should record a response show instead.
Note to Spammers
All comments are moderated. All links are checked by humans. We strip out all html. Feel free to record a show about yourself, or your industry, or any other topic we may find interesting. We also check shows for spam :).