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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."

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.
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Hi, will a 1/4 watt inductor be okay assuming I'll be using 330uH?

Dave Kruschke (author)  Patrick JamesO12 days ago

I think that 1/4 watt inductor would be more than enough. If a 3 volt LED draws 20 milliamps, that would be about 6/100ths of a watts.

But, ... you could just try the 1/4 watt inductor and see if you can feel any heat. You won't hurt anything. You could also try different inductors, say from 100uH to 1000uH. I seem to remember getting a brighter LED using a 100uH inductor.

Thanks, Dave. I ordered a bunch of assorted 1/4 watt inductors last week. I can't wait to try them out. Looking forward to more of your instructables.

harmhero3 years 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?

The voltage is doubled by oscillation and cutoff. The extra voltage cannot be read on a DC meter, but a scope will show it as AC. 3 volt LED's can be run. Be careful with yellow and red colors.

And big Ted says always remember to plug your 'scope in first ?

Dave Kruschke (author)  harmhero1 year ago

Try measuring the voltage with your multimeter set to AC instead of DC...

Dave Kruschke (author)  harmhero2 years 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)  harmhero3 years 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...

Pleasing to see some analytical and critical thinking combined with a bit of deconstruction to build understanding, thank you. I'll have a go at building this myself now.

Logical steps for explaining and well illustrated too.

Jan May4 months ago

I love this instructable. I am very much interested in building my own solar garden lights with a 5252F IC,
4v x 40mA solar cells, and "fairy light" strings with about 6 small
LED's in them.

I still have a couple of questions about the 5252F / XXXX chips though.

First of all, does anyone know the differences, if any, between all the variety of XXXX numbers for the 5252F chips, like 1101, 1106, 1120, 1201, 1305, 1306, 2105, etc? I see all kinds available on Ali Express.

Also, does anybody know if they provide any sort of charge controller logic, so they won't overcharge a NiMH AA battery? I am concerned I might have purchased overspec'd solar cells and theoretically could overcharge them.

The possibility of using a temperature sensor and an ATtiny85 to implement my own dT/dt monitoring sounds kind of fun (I could blink the lights in time with the temperature-dependent cricket sounds too), but I'm pretty new to electronics and the complexity of all of that might keep me from ever finishing (or even starting) the project.

Jan, as per the QX5252 datasheet I found on the net, the XXXX number represents the "Lot Number" and the "Year". Quite a few manufacturers are using the "Lot Number" as a "Week Number", therefore based on the number written on the IC, you can determine when the chip was manufactured. For example, 2105 would indicate week #21 of year 2005.

Personally I don't think there is any charge controller logic, so some experiments should be done to play safe. The only thing I can confirm is the fact that there is an "Integrated Schottky Diode" between pins 1 and 2 of the TO-94 package, whereas it would be located between pins 6 and 7 on the DIP8 package. So taking in account the diode's voltage drop and the voltage of the solar cell, I doubt the solar cell would go over the battery's voltage specification.

Also, for NiMH batteries, the charging time is roughly 15 hours at a C/10 rate, therefore if the battery has a 1000maH capacity, it can easily cope with a 100ma charging current. Choosing an inductor that would allow a safe charging current, will make sure that everything operates smoothly.

Using the temperature sensor approach with a uC, is actually fairly complex. I'd prefer the easiest approach, which is making sure just enough current is provided for the charging process. Also, the overall idea is to keep a minimal component count, therefore adding a uC complicate the things since you have to provide power to that IC too, which wouldn't leave you much for the led.

This circuit is based on a QX5252F and I'm actually experimenting with a YX8019, which comes from a different manufacturer but uses a similar concept. Some specs aren't as clear as I would like them to be, but that's OK, if some magic smoke starts to float around, I'll know something didn't go as planned. Just kidding !

Have fun.

Dave Kruschke (author) 4 months ago

First, Jan May, I don't know of any differences in the 5252 ic. But other ics similar to the 5252 can have different pinouts.

I'm not aware of any "charge controller logic" - perhaps the solar cell in a typical garden light isn't strong enough to damage a rechargeable battery. Our "garden lights" have lasted over a year before I changed out just one battery that didn't seem to recharge anymore. Let us know what you find out if you set something up to test this further.

I can understand your talk of harvesting different temperatures and applying the results to some kind of cricket like audio output. But I don't understand what you intend to do with dT/dt, the RATE of temperature change.

In any case, I think you will find a lot of this stuff easier than it sounds after you actually try out some hardware...

JRV315 months ago

Very good instructable, I built it.

I liked the inclusion of the simple circuit in step one.

Thank you.

GregoryI7 months ago

Would that work on making 12VDC into 24VDC to run a PLC in a car, or would that be too much for the IC?

Dave Kruschke (author)  GregoryI7 months ago

I guessing that this IC was specially designed and made for the smallest solar lights using just one rechargeable battery. I have no idea of how it would work with higher voltages. But the size of this IC suggests that the power capacity wouldn't be good enough for some or maybe most 12 or 24 volt devices. Nevertheless, let us know your results if you try out higher voltages...

brhodewalt2 years ago
Fascinating. How did you decide that that was an inductor and not a resistor?
Dave Kruschke (author)  brhodewalt2 years 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

The 5252F coil size determines the output current to the LED's


Hi BurgersBytes, how did you come up with the inductor sizes for the ma output for each size. The manufacturer's spec sheet is much different. For instance the 33 uH is rated at 110 ma. Did you measure each one of these? If so how did you do this?

That is a spec sheet from China. Values are not critical and may vary due to battery or LED types used.

leosedf1 year ago

There is no need for huge coils or toroids, search ebay for "joule thief" and you will know what i mean.

Dave Kruschke (author)  leosedf1 year ago

You are really right about ebay. They sure have some interesting parts there. Thanks for pointing me there...

My Instructable titled "Joule Thief" circuit in a Flashlight Bulb? Yes!!! revealed a "Joule Thief" inside a ordinary looking flashlight bulb.

Any ideas what the efficiency of this asic is? There are dc-dc converters out there that outperform chips like that or joule thiefs with a much cleaner output. Still a joule thief is kinda fun.

kc8hps1 year ago

HI Dave and the group.

I just found the 5252F chips at this link.

http://www.ebay.com/itm/291052254553 it appears they are 100pcs for $11 + $2 shipping. 12 cents a piece didn't seem to expensive to me.

Dave Kruschke (author)  kc8hps1 year ago

I have many more 5252F ICs than I'll ever need. If any readers here would like two of these ICs at no cost beyond the cost of a Self Addresses Stamped Envelope, send me a "post" or "patch"...

Dave Kruschke

I would very much enjoy one of those IC's . what would be the process to obtain a very small # of them from you?

Dave Kruschke (author)  Fearce11 year ago

Send me your mailing address to me using Instructables mail or my email:


When I receive your address, I'll send you an IC...

Dave Kruschke (author)  Dave Kruschke1 year ago

PS; Using my email address works best!

I would like to extend my gratitude to you for sending me those Ic's.

I received them over the weekend. Thank you greatly!

The world could use more generous ppl like you!

Dave Kruschke (author)  Fearce11 year ago

You're Welcome. And thanks for letting me know you received them...

Cheaper than I could sell them. cost me $30 for 100 from China months ago and the next order would have cost me double. Great price!

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.

This battery drain limit is actually a real problem, because you can't drain the battery down below 0.8v or so. A "traditional" Joule Thief will run for ages, taking the battery to almost nothing. One based on the QX5252 will just shut off when it gets to 0.8.

I actually discovered this when I made a few circuits with the 5252 using old dead AAs (non rechargeable). I came back in a few days to find all my lights off - because the batteries had drained to 0.8v or so.

Interestingly, I can make them turn on for a few minutes simply by touching one of the LED leads. It then stays on for several minutes before going back off again.

I'm definitely not an EE-type, but this makes me think there'd be a way to modify the QX5252 based circuit to fool it into thinking the battery isn't dead.

The lower battery limit is to keep the circuit from destroying the rechargeable battery. A lower limit would damage a battery so that it may not recharge at all. I was able to use the chips in power failure circuits with an LDR to have the light only come on when the area is dark too. Pin 1 monitors DC voltages so that voltages below .9 volts will trip the chip on. The LDR connected to the + battery and pin 1 will also keep the chip off in daylight. Pin 1 voltage up to 2 volts will also be used to recharge the battery through the chip. http://petesqbsite.com/phpBB3/viewtopic.php?f=4&t=...

If you want to run a Joule theif battery down to about .6 volts, use a transistor circuit with a wire wound coil or 2 pre-made coils from circuits here:


Yup I get the reason for the cutoff, but I'm using cast off AA's for power so am not using rechargeable batteries - also skipping the solar cells.

I've made plenty of "standard" Joule Thief circuits, but in this particular case I'd like to make 100 of them for a festival. Using the QX5252 is a really cheap and efficient way to make a lot of them, except for the power cutoff. If it could be disabled, these would be ideal.

Basically I can make a QX5252 based circuit, complete with battery holder and all for about $0.65 (quantity 100) and they go together really fast. Toroid based ones, much longer assembly.

And if you put a QX5252 one side by side with a toroid style, the toroid one will keep putting out useful (enough for me) light for days longer.

Dave Kruschke (author)  holtt1 year ago

As you can see below, I hooked up the IC without using Pin 1 at all and now the LED is on all the time. This might work for you and therefore it might not be necessary to tie Pin 1 to Negative , either directly or with a resistor. The wiring below is hardly neat but reveals what I'm talking about here...

IC schematic.jpgIC hookup a.jpgIC hookup b.jpg

Yes that's exactly how I wired mine up. My only comment is that the 0.8-0.9v shutoff happens with this when the battery goes low. It clearly could keep lighting the LED for longer if you didn't mind it going lower.

Pin 1 is pulled low internally when nothing is connected. It can also be turned on or off using digital circuits. The battery voltage is monitored on pin 2 and that will also stop it when the voltage goes below .9 volts. If the battery is removed or completely dead, the charging voltage on pin 1 may turn the LED on also.

Here is a 2 inductor circuit which uses 470uH pre-made coils, but with any transistor there will be a voltage drainage point where it will just refuse to conduct anymore.

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