"Joule Thief" Circuits, crude to modern...

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It seems that many "Joule Thief" circuits depend on a clunky (bulky and heavy) toroid or "donut" that has to be carefully wound with copper wire. But now there are several very small 4 legged ICs available that do the job using only a simple inductor, single cell battery and a LED. In effect, the 4 legged IC replaces the clunky toroid.

I came across these ICs when I disassembled some solar powered yard lights. I looked for a toroid but only found a four legged IC and a part that looked like a resistor but actually was a very physically small inductor (coil). Both of these parts along with wire attachment points were soldered to a small circuit board. I was able to remove parts, attach wires to them and assemble them on a Radio Shack type of "Breadboard" to test and better understand this circuit.

But then I created a very crude and minimal circuit to better understand some of the key parts of a "Joule Thief."
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Step 1:

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I used a Yellow LED that requires 2 volts (or a little more). My 1.5 volt "Rocket Battery" has been worn down to 1.4 volts. As a result, the LED is off and is not even close to conducting any current. Points A and B on the inductor coil L are at pretty much the same voltage, 1.4 volts compared to "ground" or the minus of the battery.

When the switch is pushed and and held ON, briefly, current flows through the coil and creates a magnetic field around the coil. Points A and B are still positive with point A being slightly more positive than point B.

But when the switch is released and turned OFF, the magnetic field suddenly collapses and creates a 1.4 volt voltage with a reverse polarity. This means that point B is now 1.4 volts higher (more positive) than point A. It is as if the coil has become like a temporary battery connected in series with the actual battery, presenting 2.8 volts to the LED. The LED reacts to this by flashing on for a very short moment. Pushing the switch again repeats this cycle. If I could push the switch rapidly enough, the LED would appear to be solidly ON.

The pictures that follow will reveal how simple it would be to recreate this. The coil or inductor is 12 feet of 24 gage wire wrapped (200 turns) around a 1/4 inch diameter soft iron nail.
Dave Kruschke (author) 21 days ago

You are right about the inductor replacing the toroid but ONLY if the toroid inductor has a single winding. Other joule thief circuits with only one transistor seem to require a toroid with TWO windings.

The IC is an integrated circuit that does much more than a single transistor could do. If you search online for the 5252F IC, you might be able to download or view a pdf that explains this much better than I could. But let me know if you are looking for a 5252F IC...

dudes21 days ago

actually the inductor is what replaces the toroid "donut". the four pronged ic replaces a transistor, which is how it switches on and off fast.

correct me if im wrong

BurgersBytes3 months ago
That 5252F chip does more than just drive the LED. It also limits battery drain to .8 volts to lessen the chance of damage. I am currently waiting on an order of them from China if anybody is interested.

A photocell resistor can be run from + battery to pin 1 to turn the LED on only at night instead of using a solar cell to do it. Any device can be hooked to pin 1 to bring it high for off and low for on. The pin does not require a resistor to take the voltage low either. No connection brings it low so your Joule thief worked.
Joe Blogs5 months ago
I found this IC in a cheap garden light so it was not necessary to buy it in from another country.
manicmonday8 months ago
Can the inductor replace the toroid even if you don't have the 4 pin IC, and instead have the 3 pin transistor?
Dave Kruschke (author)  manicmonday8 months ago
Please check out my Instructable that features a "Joule Thief" that uses two transistors, two resistors, one capacitor, one inductor and one LED.

Dave Kruschke (author)  manicmonday8 months ago
Yes! Please check out my Instructable that features a "Joule Thief" that uses two transistors, two resistors, one capacitor, one inductor and one LED.

brhodewalt8 months ago
Also, in your schematic in Step 5, what is the purpose of the connection to pin 2 on the IC?
Dave Kruschke (author)  brhodewalt8 months ago
Pin 2 is for the connection to the positive terminal of the 1.5 volt battery.
Pin 3 is for the connection to the negative terminal of the 1.5 volt battery.
Pin 2 and Pin 3 are basically for the battery power supply.
Pin 4 gets repeatedly grounded to negative, connecting the battery directly to coil L momentarily. When pin 4 ungrounds coil L, the magnetic field created collapses and and results in voltage in series with the battery to flash the LED...
Joule Thief IC.jpg
brhodewalt8 months ago
Fascinating. How did you decide that that was an inductor and not a resistor?
Dave Kruschke (author)  brhodewalt8 months ago
I reversed drew the schematic from a solar light "joule thief" and was stuck when I view what look just like a resistor and nothing else. I had never seen an inductor that looked like a resistor. I then made a crude "equivalent" circuit using only a battery, LED, switch and the mystery part. My crude "equivalent" circuit was able to momentarily flash the LED that requires about three volts. I asked myself, "if L were really a resistor, how could the LED ever get 3 volts?" Against what I thought I knew, I decided that maybe L was an inductor. Then I looked up inductors in parts catalogs and sure enuf, they had inductors for sale that looked like resistors...
Joule Thief IC.jpgSmall 330 uH Inductor.jpgJoule Thief Crude.jpg
harmhero1 year ago
I build a tiny Joule Thief, it works grea on one AA battery!

But what I don't understand is why the output voltage is the same as the input, 1.5 volts?
Dave Kruschke (author)  harmhero11 months ago
Ha! I just happened to think: What did you use to measure the voltage when you measured 1.5 volts? The output of the Joule Thief is not a steady DC voltage but a voltage that fluctuates rapidly. Some meters only measure the average value of a fluctuating voltage so while the average reading might be 1.5 volts but the peak voltage (that is high enough to light the LED) is maybe 2.0 volts or higher. However, this momentary peak voltage might not be seen on the meter display. I suspect that using an oscilloscope would reveal these peak voltages I'm referring to here.
Dave Kruschke
Dave Kruschke (author)  harmhero1 year ago
Could you describe your circuit or better yet, provide a schematic?

On the other hand, without further info, I wonder what your output voltage would be when your battery voltage depletes to 1.0 volts. Sooner or later, the battery voltage will drop but if you are still getting 1.5 volts, something is working right to at least some degree...
Dave Kruschke (author)  acmefixer1 year ago
I thought that Colin was simply offering a simple circuit to power many LEDs with just "one" battery using a crude, easy to wind inductor. It never occurred to me that Colin was offering this as some kind of high efficiency device. I liked seeing Colin's circuit but haven't done any work with it.
I seemed to remember you, Acmefixer, mentioning something about the importance of keeping resistances low in "joule thiefs." If this is true, wouldn't an "iron" core winding have less resistance than an air core winding for a needed, fixed inductance? Of course, if the oscillating frequency is high enough to cause the "iron" core to saturate, this would be a different matter.
I would agree that Colin seems to spend more time than helpful to me criticizing what he considers "bad designs" (see FM transmitters on Colin's Talking Electronics Website for examples of this). I'd much prefer to see designs that he built that work.
Nevertheless, I think that the good in Colin's website significantly outweighs the "bad"...
Dave Kruschke (author)  acmefixer1 year ago
Not so fast, Acmefixer. I was thinking of a situation where one decides they want/need an inductor having a fixed value, say 200 uH, for a project. At this point, they might be able to consider an air core inductor with many turns of wire or some kind of "iron" core with less turns of wire. Less turns of the same diameter wire WILL have less dc ohm resistance and also less overall impedance. Yeah, I know that the desired frequency, if "high," might rule out using an "iron" core due to saturation. If frequency issues weren't significant, I'd pick the "iron" core over the air core because I'd need less wire.
As far as the word "efficiency" is concerned, I never thought I had a good idea of what Colin really meant here and didn't really care, especially since "efficiency" doesn't seem to represent the same thing to all people (much like the words "Joule Thief"). Again, I was most interested in the simplicity of his hardware, specifically the inductor where he used a RustyBolt.
Your suggestion that Colin "criticize his own work instead of others" might well apply to yourself. To me, you two seem "birds of the same feather" as both of you seem rather Fixated on criticizing the work of others. And while I don't think highly of the helpfulness of some of the criticism by you and Colin, I'd still recommend some readers to visit both the sites maintained by you two. Specifically, I just read your 3-23-13 posting on your blog about using the Grease Spot technique from Physics to compare LED brightness. To me, this writing was well done and didn't contain any crappy criticism what-so-ever. I'd recommend anyone with a deeper curiosity about using LEDs and "Joule Thieves" to leave this Instructable and visit your blog as they will find interesting information uncluttered with criticism, unlike your contributions at this Instructable. Finally, should you attempt to criticize Colin's work at his website, Talking Electronics, you will be there for years as he seems to have years and years of work deposited there...
Dave Kruschke
buttonmak1 year ago
Hello, can this setup run a 13w CFL?

Dave Kruschke (author)  buttonmak1 year ago
I don't have any suggestions for doing this, especially if just one AA type of battery is used. For years I used a penlight that powered a bulb rated for 1/4 amp at 2.5 volts. So the battery here was only putting out 1/4 times 2.5 or 5/8ths of a watt, rather far from the 13 watts you desire. The other issue that I can't address is getting you the voltage you would need to run your CFL...
colin551 year ago
Here's a Joule Thief with 10 LEDs on a 9v battery.
Dave Kruschke (author)  colin551 year ago
Well, I wasn't ready for the circuit above but when I went to Colin Mitchell's Talking Electronics website (, I found there a "Joule Thief" circuit there that doesn't require an IC and doesn't require any kind of transformer.

I built this "Joule Thief" circuit using some parts having different values but the circuit worked really fine. This project is revealed in my latest Instructable, "Joule Thief - no IC and no transformer.

I certainly recommend Colin Mitchell's Talking Electronics website as it is very rich with examples and explanations of a huge variety of circuits...
Dave Kruschke (author)  colin551 year ago
Your interesting project makes me wonder how low the 9 volt battery can go before your device no longer oscillates. Your project also prompted me to finally do something with inductors. My inductor project turned out a little different than yours but has "resonant frequency" properties in common. I made a RFID reader Detector,

I hope to get around to doing something with your project...
bud man1 year ago
Hi I'm new to replying to your site. I spent meny hours trying to find out what those chips were. Than finding them is another problem. I found them in china. But than one has to look at thier pricing & shipping. The shipping Hurts. I have purchased a bunch of ic driver chips & chokes from a company in china. The parts were very cheap. The shipping is another matter. I have 100 ea. of an AN608 , 100 ea. of an CL0116 , I like this one best . And the last is XY3688E this is a voltage booster for use with a multi colored led that changes by itself. I also bought the chokes from the same company. ANA608 100ea. $0.20ea. CL0116 100ea. $0.05 ea. XY3688E 100ea. $0.08ea. all the chokes were at 50 ea. $0.04 ea. I also found some of the circuits for each on the web. Like I said the shipping is the killer. I can supply anyone info on the web site if you want it.
Dave Kruschke (author)  bud man1 year ago
Please do reveal any website that will reveal access information about the driver ICs and chokes you have mentioned. Also let us know if you would sell a few of your parts to readers. Finally, I'm very curious about the uH values of the chokes that you have. Are these chokes like the chokes in this Instructable that look like 1/2 watt resistors?

I agree that finding these ICs presents quite a challenge but it looks like you were very successful...
Small 330 uH Inductor.jpg
Dave Kruschke (author) 1 year ago
In any case, I finally got a chance to apply the Joule Thief in a practical way. My magnifying glass has a 222 incandescent light that runs of of two 1.5 volt AA batteries. But the bulb burned out (one spec I read said they only last five hours and I believe it). So instead of going to Radio Shack for a $2 replacement bulb, I deconstructed a solar light that I picked up at a flea market for 50 cents. It uses a bright white LED, just one 1.5 volt AA battery and a tiny circuit board with the same four legged IC as above along with a tiny inductor that looks like a resistor. Since I was only going to use one AA battery, the room for the other AA battery was just enough for the little circuit board containing the above mentioned parts. The room was tight and there wasn't any room for any larger circuit board, toroid or "transformer-on-a-bolt." I was able to use the original switch as I broke the light bult and soldered connections to it. The original switch wouldn't work without a "bulb."

Lets see if I can add some pictures below here:

Joule thief retrofit a sm.jpgJoule thief retrofit b sm.jpgJoule thief retrofit c sm.jpg
ctudoran1 year ago
Do you have an idea about how much current can this solar panel circuit can drive? I am thinking of lighting up a few leds (5 of them).
westfw1 year ago
Note that the original joule thief can use quite tiny hand-wound transformers; it doesn't need to be either clunky, heavy, or toroidal. Here's a photo of one I mad quite some time ago; the transformer is that little black square thing in the bottom center, next to the green LED. The bigger ones are easier to work with.

There are actually a LOT of ICs that implement "single cell boost regulator" circuits. They do tend to be less hobbyist friendly than the one here, and usually have 5 or 6 wires. And they tend to be more expensive that the JT circuit built from scavenged parts. For instance, consider the MCP1623 from microchip:
You can see how a 4-pin version would be possible (get rid of "enable", make the feedback internal...)
Dave Kruschke (author)  westfw1 year ago
You've made some good points. Since most of the "Joule Thief" circuits I've seen on line do use toroids that are larger, clunkier and heavier than yours, it may be likely that the authors of these circuits would greatly appreciate instructions from you for building your transformer. This could be simple; like a list revealing wire size(s) and length(s), number of turns for each winding along with a description of your core or "toroid" and how to wind it.

And yes, the four legged IC I removed from solar light circuit was "less hobbyist friendly" as there was hardly any space to solder wires to it. I then soldered it back into the small circuit board and soldered wires to larger areas of the small circuit board. However, if one buys brand new QX5252F ICs from Andy, mentioned below, these new ICs come with long legs that can be easily bent so that wires can be easily attached - or, this IC can easily be "speared" directly into a breadboard such as yours...
westfw1 year ago
Is the chip that you found actually something that we can buy somewhere?
Dave Kruschke (author)  westfw1 year ago
You can email Andy at for ordering 100 ICs or more. I found Andy to be very reliable and prompt. I counted and tested every IC I received from him. I counted 102 and all 102 worked in my breadboard circuit.
For smaller numbers, you could send an email to
killbox westfw1 year ago
looks just like the chip i found in the Dollar Tree, $1 solar yardlights.

im a little surprised its doing what this instructable claims, i thought it was just a fancy switch (if current is going to one leg then turn off led and pipe power to battery. else turn on LED)

but im only 1/2 way through the instructable and very interested in trying this out when i find a free moment.
nevermind about my skepticism, looks like i was right about the ic, and the EU is using a coil. so everything is peachy! Great idea!
Dave Kruschke (author)  killbox1 year ago
To me, the most important aspect of this "fancy switch" is that allows one to use a simple, one winding small inductor instead of the heavy, clunky donut-like toroid with two windings. If the EU is still using a toroid, I predict that they won't be using it for long...
Dave Kruschke (author)  killbox1 year ago
Your are right, the chip is like (but not necessarily identical) to the chip found in the $1 solar yardlights. Watch out for the IC pinouts as they are not the same on all IC found in these solar lights. If you look carefully at the tiny circuit board in the solar light, you can deconstruct the connections and make a schematic that will reveal the actual pinouts.

I can't disagree with the term "fancy switch" as the IC is switching the inductor lead (that is not connected to B+) to B- about 60 to over 100 thousand times per second, depending on the type of LED load. This "fancy switch" also allows the solar cell to control operation...

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