Cheap Voltage Regulated Joule Thief Power Supply/charger





Introduction: Cheap Voltage Regulated Joule Thief Power Supply/charger

About: Hi, I'm Tamas (Thomas), a 19 years old Hungarian guy. My hobby started more than 10 years ago. I learn electronics, physics, programming, IoT and I'm sharing my projects with you, hope you like it!

Maybe you know the very popular Joule Thief circuit, that usually is used to drive LEDs, but this instructable will show you how to regulate the output voltage up to 30 volts. You can regulate example to 5 volts that is enough to charge a phone or any USB device. It charges slowly but works. Or you can use as a power supply for an Arduino, or for a simple project too. It would be an useful device. I've made a few experiments before the creating the full circuit, so the circuit works fine. The circuit uses a zener diode regulate the output voltage. I will try to describe detalied because it is easy to make a mistake. Don't want to bore you with the working theory, but if you are interested read on wiki or watch this video. You can build this gadget almost free, can find most of the components in a CFL bulb, so let's begin.

Step 1: Tools and Materials


  1. soldering iron and of course solder
  2. a multimeter (optional)
  3. a wire cutter
  4. and.... that is all


  • You can see on the 2nd image that inside the CFL bulb is almost everything, you just need to buy a zener diode, wires and a PCB board. I've used components from a shop, beacause I can't make a clear instructable with short leg components
  • 2N2222 transistor or equivalent, on the transistor in the CFL writes 2222A
  • 47uF capacitor
  • 50-1k resistor
  • 1mm wire
  • USB female jack, if you want to make a charger
  • 1N4001 or any germanium diode
  • toroidal core from the CFL bulb
  • breadboard for testing (optional)
  • PCB board
  • zener diode with a value that you want to regulate the voltage We use the diode as a voltage regulator. Example I use a 5v1 (5.1 volts) zener that can regulate the voltage to about 5 volts that can charge a phone or can drive a Raspberry Pi. If you want to get another voltage example 7 volts for an Arduino, buy a 6v8 zener diode. If you're ready go choose your power supply!

Step 2: Choosing the Power Supply

To operate the circuit you will need a power supply that have enough current to converting to voltage. If you want to operate can use 2 solar panels from old garen lights connected in paralell or use a small DC motor with a propeller on it. This can be used as a hydro or wind turbine. Don't be afraid, if you can't read the circuit diagramm, I will describe step by step the building, so go prototyping!

Step 3: Prototyping on Breadboard and Creating the Inductor


  1. Get two wires, like on the first image and connect together, like on the second image.
  2. Now wrap the toroidal core with the wires and cut the endings, like on the third image.
  3. The starting of the green and red wires is named 1 and 2, and the and the endings are 3 and 4.
  4. Now solder the 2 and 3 together, like on the last image.
  5. And your inductor is done.


  1. Follow the images and the description, you can see the circuit with batteries on the 5th image.
  2. Put your transistor in the breadboard.
  3. Connect the resistor to the base of the transistor.
  4. After this put the soldered leg of the inductor in a free hole and connect to the positive wire of the battery.
  5. Connect the 1 and 4 legs of the inductor to the collector and to the resistor just like on the image.
  6. The negative wire is going to the emitter.
  7. Now you've made a simple Joule Thief, test it, if won't works check the connections. My 3v LED is working.
  8. If works get the cathode of the germanium diode, connect to the collector and put the anode in a free hole.
  9. With a capacitor connect the anode of the diode (positive) and the emitter (negative, GND).
  10. With reversed polarity install the zener diode.

Your protoype now is done! In the next step you can see the testing and the esplanation.

Step 4: Test and Explanation

The germanium diode blocks the current go backwards, and the capacitor with the zener diode ensure proper charging or flowing of the current. The zener's anode must be connected to the positive leg of the capacitor, that means reversed polarity. In this case the voltage is regulated to the zener's value (5v1). My multimeter showed me 5.17 volts, this is a perfect voltage for powering a project or for charging. If you solder anything in paralell to the zener's legs will works. In the next step i will make a USB charger, but you can connect example to an Arduion too.

Step 5: Soldering

Simply solder the components together on a PCB. On the images is described everything you need to know. I think no need more explanation, so go testing!

Step 6: Last Test

Plug your phone in and the charging starts. The ''dead'' battery can drive of course an LED, and if you connect this Joule Thief to a rechargeable battery will charge up in a few hours, you can save a lot of money if you use the ''zombie battery'' charger. Do not forget that is more better with green energy, like on the last image with the generator. Sorry for my potential English mistakes, hope you liked it, (vote on me) and hope you can use this instructable!

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hello. i want to make a rechargeable circuit . The requirements are that it could be able to have a regulated voltage from 3-30 V in order to power up different type of devices and current is variable also. Plus, must be able to perform a overcharge protection at the same time not to spoil the battery .. Can you suggest me how do i start and all the requirements or maybe video for referrence pls ?

1 reply

You could try a pre-made board <a href="">like this</a> on Ebay or Amazon.

How about output amp?

Nice intructable. What would happen if I used an unstable DC source (solar \ turbine) and it went above the voltage I had it set to? Ex. If I have it set to 5v as you do, and for some reason the power coming in goes up to say 6v or even 12v?

3 replies

you can always add a 5v regulator to maintain your output(or input) when your input voltage spikes

mm I'd be scared that it's starting to compound losses....

Why be scared, you can never make an omelet without breaking a few eggs figuratively speaking

Dude, i follow yours steps, but i only get 1,6v from a 1,25v battery, what could be wrong? The toroid may be?

1 reply

yes more than likely, you may have twisted the wrong two wires very easy to do. say you have a red and black wire and you wound them on a toroid say 20 turns, you,ll have two wires on both sides, a red and black on side 1 and a red and black on side 2 take the black wire from side 2 and twist it to the red on side 1 and that,s your battery plus wire will go. here,s a you tube link that shows how to wire what i described hope this helps you out, and the efficiency of this or any joule thief is only limited by the toroid windings so experiment with the coil ratio find what works for you.

Good job young man. Do you know a way to ımprove thıs cırcuıt ın terms of output current such as by usıng a better transıstor or better terroid wıth more wındıngs or perhaps a bıgger capacıtors and maybe maybe dual transıstor paralel. I,ve made thıs but ı would lıke to charge 4 aa wıth 4v solar whıch needs 6v. thanks.

1 reply

Just what i needed! I was given 4 old giant batteries, 2v at 600ah each. My whole solar panel setup lights and stuff is designed for 12v. I solved the charging using Renes re-emf charger that self regulates. However now i need a step up regulator for the output to my lamps and stuff. But i'm completely ignorant of elecronics, i can only follow schematics and assemble without having the slightes clue bout how it works. Is there any chance u could tell me the voltage and amperage ratings i should get for the components with my batteries? Pleaaaaaaaase!????

1 reply

your best bet would be to use a charge controller for solar panels. It will have the proper regulators all built in. Many are available on Amazon for cheap. If you need high power stuff (powering a house or otherwise), then you would need to get higher quality stuff.

owesome...great job... i was looking for this component... cos it very expensive to me to buy a dc to dc converter :)... thanks a lot :)

I use the circuit with free energy generator circuit for cell phone charger, the transistor burn. What reed

I changed the 5v zener to 12v and the 16V 47uF capacitor.. I managed to make it work(I get around 11.35V) but why does the voltage drop to 2.5v when a load is attached?? should I also change the rating of the capacitor used? Thanks!!

1 reply

The voltage drops to about 2.5V because your power supply (the battery or a solar panel) only delivers enough power for your project to run continuous on 2.5V. All that the diode does is make sure the voltage doesn't go over said forward voltage by redirecting it to ground when it does. This way you get small spikes that stop at the desired voltage. By instead using a capacitor at the end stage (which might actually also blow up the capacitor if it doesn't have a high enough rating, but that doesn't seem to be a problem in your case) you store the energy, but when adding a load you also instantly pass it (partially) through. The reason capacitors are used in power supply situations is to keep the voltage constantly high, not constantly low (in this instructable 5V)

i have been thinking about the toroidal thing... What if i replace it with a round magnet(from a speaker), what will be the consequences?