A Joule Thief is a simple electronic circuit which can convert a low DC voltage into a higher voltage. We can make this circuit using a transistor, an inductor and a few other components.
The interesting thing about this circuit is that we can use a single 1.5V battery to light up a white or blue LED which normally needs around 3V or more.
There are many ways of making a Joule Thief circuit. We can use different transistors, different types of inductors and even modify the circuit for operating multiple LEDs.
So in this article let us look at six different Joule Thief circuit ideas. Each circuit has a different purpose, and you can select the one which suits your requirement. You can also visit the individual articles to see the complete circuit diagrams and working details.
Different Types of Joule Thief Circuits
Joule Thief Circuit Which Can Illuminate Any 3.3V LED or Higher
A normal 1.5V battery cannot directly light up a white or blue LED which needs around 3.3V. But we can use a Joule Thief circuit to increase the voltage and operate such LEDs. This design explains one such arrangement which can be useful for experimenting with different types of higher-voltage LEDs using a low voltage battery.
Read the complete circuit here:
Can We Power a Joule Thief Circuit With a Small DC Motor?
Normally we use a battery for powering a Joule Thief circuit. But can we use a small DC motor for this purpose? Yes, a DC motor can also generate electricity when we rotate its shaft from an external source. This experiment explains how we can use this generated electricity for running a Joule Thief circuit. The output will depend on the motor speed and how much voltage and current it can produce.
Read the complete circuit here:
Joule Thief Circuit Using a Single-Winding Inductor
Most ordinary Joule Thief circuits use two winding sections for getting the required feedback. But in this design we try a different type of inductor arrangement using a single winding with a suitable connection. This is an interesting experiment for understanding how we can use different coil arrangements in a Joule Thief circuit.
Read the complete circuit here:
Illuminating Four 1-Watt LEDs With a 1.5V Cell Using Joule Thief Circuit
Here we have an interesting experiment where we try to operate four 1-watt LEDs using just a 1.5V cell. The Joule Thief circuit is modified for driving multiple high-power LEDs from a low voltage supply. But we must remember that four 1-watt LEDs need considerable power, so the actual brightness will depend on how much current the battery and circuit can supply.
Read the complete circuit here:
Joule Thief Circuit Using 2N3055 Power Transistor
This Joule Thief circuit uses a 2N3055 power transistor instead of an ordinary small signal transistor. The idea here is to experiment with a bigger power transistor for the switching operation. However, the actual output power will depend on the battery, inductor and the way the complete circuit is designed.
Read the complete circuit here:
8X Overunity Circuit Using Joule Thief
This is a different type of Joule Thief experiment which uses an additional resonant arrangement. The original experiment describes a claim of getting around 8 times more output compared to the input. However, this overunity claim has not been independently proved. We must measure the actual input and output power properly before accepting such a result.
Still, the circuit can be interesting for experimenting with resonant switching and modified Joule Thief arrangements.
Read the complete circuit here:
Comparison of the Different Joule Thief Designs
The following table will help us understand the main purpose of each circuit. So you can quickly select the design which you want to experiment with.
| Circuit design | Main purpose | Main feature |
|---|---|---|
| 2N3055 Joule Thief | Power transistor experiment | Uses a 2N3055 |
| DC motor Joule Thief | Alternative power source | Uses a motor as a generator |
| Single-winding Joule Thief | Inductor experiment | Uses a different coil arrangement |
| Four 1-watt LEDs | Multiple LED operation | Experiments with high-power LEDs |
| 3.3V LED Joule Thief | Higher-voltage LED operation | Works from a low voltage source |
| 8X experimental circuit | Resonant switching experiment | Modified Joule Thief arrangement |
How to Select the Right Joule Thief Circuit?
Before selecting a Joule Thief circuit, we must first decide what we want to do with it.
If you just want to light up a small white or blue LED using a single 1.5V cell, then a basic Joule Thief circuit may be enough.
But if you want to operate multiple LEDs or high-power LEDs, then we must check the total output power and the required LED current.
The battery is also very important. A small battery may provide enough voltage to start the circuit, but it may not provide enough current for operating a bigger load.
The inductor is another important part. Its core material, number of turns, wire thickness and winding arrangement can change the output voltage and current.
So, we should always select the complete circuit according to the load requirement. We should not select a circuit just because it is producing a very high voltage.
What You Should Know Before Building a Joule Thief
Before building any Joule Thief circuit, let us understand a few important points.
- A higher output voltage does not mean that we are getting higher output power. When the voltage increases, the available output current generally becomes lower.
- The battery still supplies all the energy required by the circuit. A Joule Thief can use a low battery voltage, but it cannot produce unlimited energy.
- High-power LEDs need proper current control and heat dissipation. Just because an LED is glowing does not mean that it is working safely.
- The transistor must be selected according to the required switching current and voltage. If the current becomes too high, then the transistor may overheat and get damaged.
- The inductor winding and feedback connections must be correct. Otherwise, the circuit may not oscillate properly or may give an unexpected output.
- We should measure the actual output voltage and current with suitable measuring instruments while the circuit is connected to its intended load.
Conclusion
Joule Thief circuits are interesting electronic projects which help us understand how a low DC voltage can be converted into higher voltage pulses using a transistor and an inductor.
We can experiment with different transistors, coil arrangements, LED loads and switching methods to make different types of Joule Thief circuits.
The six designs explained above give us several interesting ideas to try. You can visit the individual articles to see their complete circuit diagrams, component details and working explanations.
So select the circuit according to your requirement, check the component ratings and then start your experiment carefully.
Reference: https://en.wikipedia.org/wiki/Joule_thief
Questions & Answers
Hi dear Swagatam,
Your efforts to develop electronics science are commendable
Joule Thief’s circuits were very interesting. I suggest you design one of them with a germanium transistor, I made one myself and it worked even with less than 0.5 volts
Thank you Dear Amirsaraf, you are absolutely correct!! Germanium BJTs are more efficient than the silicon counterparts….however silicon BJTs are mores easily available than the Germanium ones…thanks for your interesting feedback.
I have created a jewel thief circuit using BC547 and torroid 0.5mm coil 20:20 turns,1K resistor and a 5mm LED. Everything seems to be alright with the circuit. But it does not work with 1.5v. When i use 2.4 v the LED lights on. Of course with 3.7 v the LED is brighter . I have a 1.5-2v solar cell for this circuit. I do not understand the reason for not lighting of the LED with 1.5v. Is there any solution for this problem.
No .It was connecting the common to Vcc and the other two ends, one to 1k resister andother to collector.
In that case I would suggest you to please try the first circuit from the above article, and check the results..
Did you build the first circuit from top? That circuit is tested by me and it worked perfectly well with a 1.5V cell for me, and I could illuminate a watt LED nicely. You can see the results in the first video.
Which ferrite toroid ring did you use, use the T10 or T13 toroid.
Good morning swagatam,
it’s a privilege to people like you still alive. please I need to construct a joule that does not use battery just like that of YouTuber lasersaber so I can further use the output for my generator. where my family live back in our village there’s no light. Lasersaber did put the details or better still maybe I didn’t understand it well please help me with the details. I am new in electronics and everyone in the house is looking up to me
Thank you so much Donald, I appreciate your kind words!
Can you please elaborate on what is your exact requirement, with specifications, for example how do you want the joule thief circuit to work for your specific application? The power output spec needed, and what should be the input supply to the joule thief circuit? I will try to figure it out for you….
Thank you so much, I had issues with my phone so I couldn’t reply but please I am online now.
my input supply is 12 volt from an air batteries. I wanted the JT to work in such a way that the input is sustained after it is removed from the circuitry maybe a high capacitance batteries runs the circuit as it receives charges from the output. some kind of looping back into the input
No problem at all, I will try to solve your confusion.
Actually what you asking is not feasible. If you are thinking of a looping system that would supply you with an unending sustained power, that may not be possible, because the Joule thief output power will be always lower than its input power. I hope I could explain you the truth.
Dear Mr. Swagatam, thanks a lot for this useful and worthy job about the “Joule Thief” circuits!
In “How the Circuit Functions” you wrote, “T1 switches ON and pulls the entire supply voltage to ground and in the course chokes the current across the primary winding of the coil so that the biasing to T2 dries up, shutting off T1 instantaneously”.
Which is in the circuit “T2”? Where is T2 located on the circuit?
This circuit could be used with a bridge rectifier, using, for example, 4 UF4007 and an electrolytic capacitor?
I want to build an LED tester, like one used to test the LED lamps or the backlight LED TV.
Thanks a lot in advance for your attention!
Greetings from Argentina!
Thank you Alejandro, for pointing the typo mistake.
Actually there’s no T2 in the circuit, there’s only one transistor T1, it was probably a typing mistake which I have corrected now.
Yes, you can connect a bridge rectifier at the output with a filter capacitor, and use the boosted DC to test backlight LED strings.
Let me know if you have any further questions, I am always happy to help!
Hi sir , I want a circuit that inputs 0.7v and outputs 1.2v, 1.8v, 3.3v and 5v. How should I design it?
Hi Song,
For that you can specifically use a joule thief circuit and then get those specific supplies through respective zener diodes.
I have another question on the capacitor for the fan circuit. The C1 in the circuit is 470microf, 25V. The capacitors I have on hand are 4700microf, 50V and 2700microf, 10V. Are any of these capacitors suitable ? Why ? Thanks.
You can use 4700uF/50V, it will do the job nicely.
Hi, I am trying to understand the circuit better. You can assume that I am new to circuits. In the circuit with the fan design. The diodes have polarities pointing upwards and the capacitor has polarities pointing downwards. What if the 4 diodes are (a) removed i.e. purely leaving the battery to power the fan and charge the capacitor ?
(b) preserved as in the original setup, but we reverse the polarities i.e. of the diodes and at the same time, connect the fan terminals to the negative ends of the bottom most 2 diodes ?
Please do not feel obliged, but is there a video/ youtube channel on a working prototype of this circuit ?
Thanks.
Hi, In the joule thief circuit with a motor, the motor is used as a generator for charging the battery. Here, the fan (motor) is powering the battery, not the other way round.
If we connect the motor directly without the bridge rectifier, the battery will start getting discharged quickly through the motor winding.
I have added a video just below the diagram for your reference.
Hi every one. How many turns do we need to make the circuit with the 1w, and a 12V dc motor.
Hi, the number of turns will be 20. Just make sure to use bifilar type of wire for the winding. Bifilar means making a thicker wire using many thin wires together. So the wire thickness can be 1mm, built using many thin wires, for example by using 5nos of 0.2mm wires together.
Hi,
“Bifilar winding” means winding with two wires at the same time (bi-filar = 2-“threads”).
What you describe is named “Litze wire”.
Regards,
Sum
Thanks for the info, Yes you are absolutely right….
In your diagram with the cell phone connection above, there is a C2. Is the white portion (plate) of the capacitor C2 supposed to indicate the positive or negative end of the capacitor ?
What about the white portion of C1 found in the diagram with the small dc motor 12V above ? Thanks
The white portion indicates the positive terminal of the capacitor.
Can you please share a simple circuit for a solar light of 1watt LED using the IC QX5252F, AA battery and solar cells. Thanks.
Here’s the circuit which you can try, but I am not sure whether this IC is designed to charge the cell or not through the solar panel. Nothing is specified regarding this in the datasheet of the IC:
Datasheet of the IC:
https://www.mikroshop.ch/pdf/QF5252F.pdf
Hi what happens if we connect the output to a COCKCROFT WALTON MULTIPLIER Circuit im planning to try charge a 60 volt lithium-ion battery …..any one tried this please advise…
It might work to generate the intended high voltage but that simply won’t charge a 60 V li-ion battery due to lack of current.
At least 0.6 volts is needed to trigger a transistor.
I wonder what effect would have adding permanent magnet to toroid. There should be some additional magnetic flux to harvest.
The circuits just shuts off (I just tried). When you add a permanent magnet next to the coil, you are saturating the nucleus and that affects the working of the circuit.
Sounds interesting! That needs to be investigated practically.
I can ask how to calculate the switching frequency. Thank you
I do not have the exact formula for this!
Hi sir, I want to appreciate your efforts, you’ve really done well in helping us expanding our horizon of electrical and electronics knowledge and your circuits works well!!! My question is:- Can the first schematic of the circuit be somehow modified to a buck converter?? Thanks in anticipation
Thank you 2DO, the joule thief circuits are actually boost converters, and there’s isn’t any option to transform them into buck converters.
Alrt, thanks. Can you please give recommendations on how to increase the output current?
Output current can be increased, by using thicker wires for the transformer, and also by using higher current transistor.
Hi Swagatam;
I tried the one of the above circuits which is proper for the small DC motor. The led is ok that lights but there is no voltage between the diodes to the Motor. I also used voltmeter but voltmeter shows zero Volt. Please advise where would be the mistake.
Hi Suat, a motor can consume a significantly high current which can cause massive drop in the joule thief output current. You may have to try some other high current boost converter such as this:
And make sure your input DC has sufficient current to handle the motor load optimally.
Thanks Swagatam. I mean the measurement while there was no load. Although there was no load and there was no output voltage too. On the other hand I also tried the circuit to cellphone there is output voltage measurable. I will try your new offer
Suat, You can try measuring the voltage with an LED connected. If the LED is illuminating then naturally there will be a voltage at the output. Unless the transistor and the coil and the input current are sufficiently upgraded, the circuit will not be able to charge a cellphone or drive a motor.
Hello Swagatam,
I’m planning to make the first circuit you gave above with a suitable mosfet. The input will be 5VDC, and the output will be a battery that will be kept in drop charge. You answered this before. However, I would like to draw a sample circuit and share it on my blog. No matter how inefficient the circuit is, isn’t it also possible to at least be used in trickle charging? Actually, what I want to learn is, could I not use a mosfet instead of a transistor in the circuit?
Hi Shampuan, you can try a mosfet…. however mosfets don’t work with 1.5V or 3V inputs.
Thank you. The input will be 5V and I will apply it to the Gate leg of the mosfet with a 220R resistor. At the output, I will connect a 12V battery for trickle charging. If I give up on this, I might decide to use the TIP41 transistor. The toroid transformer will be a large type that I can get from PC power supplies. Hey! Someone warn me if I talk too much 🙂
With 5V a MOSFET might not conduct well…so a BJT is the right choice…
Can you build a joule thief using a H-Bridge?