Introduction: Reverse Joule Thief

Reverse Joule Thief - no cost by salvaging old PC parts 2012
This is the reverse joule thief I found on YouTube. Supposedly it works better. I wrote this tutorial because I wanted to find a freeway to build the circuit

Step 1: Materials

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One old PC power supply, any will do fine.

Step 2: Disassemble

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Okay. Now you want to get the power supply out of the PC box by unscrewing four screws that hold the PC Power supply in place.

Step 3: Disassemble

Picture of Disassemble

Now that you've got the power supply out of the PC, find the side with the four screws and unscrew them.
Then open the two pieces carefully.

Step 4: Disassemble

Picture of Disassemble

Let's began by extracting the toroid bead from the power supply with a soldering iron. Afterwards take off a few copper wires and leave 2 on in order for the Reverse Joule Thief to work.

Step 5: Disassemble

Picture of Disassemble

Looking through the circuit board to find the resistor,1K, using the soldering iron again we will extract the resistor,1K, for our Reverse Joule Thief.

Step 6: Disassemble

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Again we look through the circuit board to find a transistor, no matter which one,  and use the soldering iron to get it out of the circuit board.

Step 7: Assembly

Picture of Assembly

Now it is time to use the schematic I found on YouTube to build the circuit.
After you are finished, you will have the Reverse Joule Thief circuit ready to use with a 1.5v AA battery free of cost.


abdulbasit.sunny (author)2015-02-28

Hi there!

I wants to know what is reverse joule thief is? Can anyone explain this to me ?

abdulbasit.sunny (author)2015-02-28

Hi there!

I wants to know what is reverse joule thief is? Can anyone explain this to me ?

abdulbasit.sunny (author)2015-02-28

Hi there!

I wants to know what is reverse joule thief is? Can anyone explain this to me ?

abdulbasit.sunny (author)2015-02-28

Hi there!

I wants to know what is reverse joule thief is? Can anyone explain this to me ?

dasimpson1981 (author)2012-02-26

you can also use the ac line filter in a psu it is 2 coils of wire side by side see photo below they look somthing like this you can also use these Axial leaded inuctors

The schematic shown seems very close or exactly the same as other "Joule Thief" schematics I've seen that use a toroid.

But the 170 uH inductors shown puzzle me a little. Are you taking these and winding a second winding over these smaller inductors to get a transformer similar to the toroid transformer in your schematic?

The "Joule Thiefs" I've been working with use an inductor like these but have no other windings anywhere. Also no transistor or resistor is used either. Instead, a modern four legged IC is used and no toroid with windings is necessary.
Further details are not far away. They can be found at:

no remove the toroid and put the inductors side by side wired the same way as the coils and they will transfer magnetic feilds

dasimpson1981 (author)2012-03-27

i have now tested this way of makeing the jt yes it does use less current but to add the led is half the brightness of the normal way to wire it

Thank you for updating me about your testing
correct me if I'm wrong but this means that the light should work longer for a longer period of time even though it is less bright?

it does but when you need this light to see that drop in brightness is not wonted longer battery or not but if we add another winding to the unit for led only and do not put one on the first part of the circuit this can also use less current but up the brightness

dasimpson1981 (author)2012-02-27

from all test i done about 16 wraps of wire is about average for good results

dasimpson1981 (author)2012-02-26

that circuit digram is wromg the led should be on the collector and emmiter of the transister

Okay let's say the diagram is wrong could you give a more detailed explanation why it is wrong and what is doing wrong because the lights still lights up

hard to explain why it is wrong because it takes alot to explain how a jouil thief works i guess it is not really wrong it is just difiernt from the other jt cuircuits they are and trust me they are many i have spent years looking into this device with others the only way to tell if this is wrong or right would be to mesuer the current draw and see if the corect way draws less power or this way if this way draws less then i guess we have a new and better way

westfw (author)dasimpson19812012-02-26

The changed position of the LED is what makes this a "reverse" Joule thief (though it would be nice if the author spelled it that way, or even consistently...) According to the Youtube video referenced, this improves the efficiency. I'd have to measure that to believe it; it looks like it should be pretty equivalent to me... Neither circuit is very good at limiting voltages/currents other than by accident, but I don't see how this modified circuit would provide more than Vled + Vbat across the transistor...

benji.abrams (author)westfw2012-02-26

Thank you for your feedback I am new to this website so you should excuse me if I am not perfect with my tutorial and editing I fixed it up a bit tell me if you see any other things I can fix about this tutorial

dasimpson1981 (author)westfw2012-02-26

bacause in the normal one the higher voltage would be dumped into the - of the battery in the reverse jt the higher voltage is been fead back to the + of the circuit

and it still works because it uses the flyback of the shut off rather then the farwed path of the pulse

dasimpson1981 (author)2012-02-26

this should be the one used

You still didn't answer my question giving me a different diagram doesn't mean that that's an answer please explain what is wrong with the diagram I gave By amps or however you feel fit to explain not just show me whatever you think is the right one and please check out this YouTube video which explains in much more detail than what I can explain about the circuit and tell me what you think about his explanation

amps are the amount of power used from the battery the lower the better this leads to longer life

the impoved idea he has come yup with i feel might over pump voltage into the transister normaly this is below 1.5 volt higher and the transistor heats up now these units can kick anything from 3 volts upto 30 volts now if you say 30 volts 3.7 volt of that the led takes this leads to a higher voltage into the unit then it is realy able to handle

this is what i see and i could be wrong but i am going to try this my self to check i just so happen to have a dead psu laying about

That is great let me know how it unfolded

if you can find one try and find a black toriod from what i have read and things the yellow ones are powded iron and give worse results then the black toriods also another little tip less winds on the base coil in a ratio to the collector coil can slo lead to less power used lots of things you can try with these i have ethern had 10 leds in series run from these

So I need less Winds on my toroid and try to get a darker toroid

they is lots you can try the website i give you will make your head spin with info and many many hours of atempting the results and alot of sure fingures lol

if you would like to mesure the output voltage instead of an led use a diode then a capacitor of very low farad and high voltage this gives you a true reading of the output voltage also an led across the cap can be brighter

Thank you very much for all this useful information

i am a memeber of a website who have done alot of reserch on this ill give you the link as soon as i find it

here you are have fun might take you a few month to read lol have fun

but the units i have made have always been about 25mah draw so lets hope this way is ethern less

dasimpson1981 (author)2012-02-26

i found the best way was to rap 8 turns then leave a long loop then wind another 8 the long loop you strip and use for + and the other to ends go to the transistor
less likley to have it the wrong way round then now haveing the transisot or the led the wrong way round is a diferent matter

dasimpson1981 (author)2012-02-26

a capacitor in the same place as the battery can also help the battery last longer

benji.abrams (author)2012-02-26

This tutorial was meant to educate about the fact that you can get all the materials for free from an old power supply and I did not focus in on how to build this but since you pointed out that it is not so understandable what's going on with the wires I can say this there are two wire is wound around the toroid 29 times around. one wire is thicker than the other so in the and of the wrapping of the wire 29 times around the toroid you take one thickwire and one thin wire from each side and connect them together you get Joule thief coil and I didn't even wrap the wires myself they were already wrapped around the toroid

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