# Trying to build a Joule Thief



## firefly99 (Aug 30, 2017)

I had made several attempts to make Joule thief but all ends in failure. 

I had search through web & finally decide to use the following circuit.




My 1st attempt to use surface mount device & reflow. 
White LED on left PCB, Blue LED on right PCB. The 2 orange thing is the LL4148 diode. The brown rectangle is the capacitor. The black rectangle below is the 5.6kohm resistor. Bottom left is either a 2N3904 or 2N2222A transistor.




Noticed that if I use a 12V A23 battery or 2 AA battery or 9V battery, I could get LED would light up.
But nothing happen when using a single AA or AAA battery.

1st question, what is the purpose of the 2 piece of LL4148 diode ? Circuit should work without these 2 diode.

2nd question, the schematic recommend a MPSA06 transistor. From many internet web pages, it seem 2N3904 or 2N2222A NPN transistor is ok. I had tried both 2N3904 & 2N2222A withour success.

I had a hard time winding the toroid coil. Believe there must be an surface mounted alternative. I am using 2 pieces of 100uH surface mount inductor coil, flat rectangle shape, look like a SMD resistor. The grey rectangle on the right side of the LED & the grey rectangle at the top of pcb at right angle.

Seem there are other surface mount inductor that is more bulky look like a tiny toroid coil.

3rd question, Which type of surface mount inductor to use a) flat rectangle 1206 size or b) more bulky tiny toroid coil.

Any advice would be greatly appreciated. Thank you


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## nein166 (Aug 31, 2017)

Can't help you with smd but it would be cool to pull that off good luck

But I built a joule thief years back with the bifilar wound toroid method it's just a matter of not getting your wires mixed up and they must be insulated against each other. I used wire pulled out of a tiny transformer
Look up additive bifilar wound toroid for a picture


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## firefly99 (Aug 31, 2017)

Ok thanks. YouTube show this circuit was built using normal size components. It was using the 100uH inductor with axial lead. It was proven to work.
Trying my very best to avoid the toroid coil. that why i chosen this joule thief circuit without toroid coil. Hence I thought of replacing it with surface mount inductor or chokes.


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## firefly99 (Aug 31, 2017)

Is the 2 pieces of 1N4148 diodes necessary? Why the diodes cathode is connect to +ve rail?


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## DIWdiver (Sep 1, 2017)

I think the two inductors need to be wound on the same core.

Perhaps something like this? https://www.digikey.com/product-detail/en/bourns-inc/SRF0703A-470M/SRF0703A-470MCT-ND/5031109


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## firefly99 (Sep 2, 2017)

Ok, I will try out the component you recommended. Thanks.


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## PeterFH (Sep 3, 2017)

You need a transformer, not two inductors, they both need to be coupled, that is way you driver is not working. 

Does it need to be a Joule thief? 
You get SMD led drivers that work way better then a joule thief and only need 1-3 additional external components. 

A Prema PR4401 for example is a SOT-23 package that only needs a single inductor as an external component, although some more components are recommended but not necessary. 

If you are interested i can talk a bit more about it.


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## firefly99 (Sep 4, 2017)

Heard of the PR4401, but impossible to get locally. Not listed on RS & Mouser. 
Super interested in Joule Thief. Low components count & simple circuit. So simple, yet it did not work for me. 
I would be grateful if you could provide more information.


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## firefly99 (Sep 4, 2017)

How to build the Joule Thief using surface mount components? What can I use to substitute the transformer coil?


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## firefly99 (Sep 4, 2017)

DIWdiver said:


> I think the two inductors need to be wound on the same core.
> 
> Perhaps something like this? https://www.digikey.com/product-detail/en/bourns-inc/SRF0703A-470M/SRF0703A-470MCT-ND/5031109





PeterFH said:


> You need a transformer, not two inductors, they both need to be coupled, that is way you driver is not working.



DIWdiver / PeterFH, Thank you very much for your suggestion.

I used 2 pieces of 220 inductor coil and finally I managed to make a functional Joule Thief. I left out the 2 pieces of 1N4148 diodes.




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BTW, what is the difference between transformer / inductor / coil ? When you use one of these items, basically you are talking about inductance. Right ?

Sorry, if my questions is stupid. I do not have an EE background. I am trying to learn by tinkering with electronic components. Had taught myself how to solder through hole components. Now want to graduate to surface mount components & reflow soldering.


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## DIWdiver (Sep 4, 2017)

In the simplest terms, a transformer is just multiple inductors wound on the same core.

When we talk about transformers, we typically don't care much about the inductance, as long as it's "high enough". We're typically interested in voltage ratio, ideally equal to the turns ratio between windings. 'Coil' is typically synonymous with 'inductor' and certain types of transformers. There are historical reasons why 'coil' is used in certain applications. For example, the part in your car that creates the high voltage needed to make the spark plugs work is called an ignition coil, not an ignition transformer. Even though it's technically correct, some people would know what you mean if you called it the latter, some would not.

To make it even more confusing, relays have coils not electromagnets, even though the winding is designed to magnetically pull the armature, and has significant inductance that has to be dealt with to make a reliable circuit.

I suspect that at least some of the difference comes from the fact that 'coil' refers to the structure of the device, while 'inductor', 'transformer' and 'electromagnet' refer to the function.


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## firefly99 (Sep 6, 2017)

DIWdiver said:


> In the simplest terms, a transformer is just multiple inductors wound on the same core.
> 
> When we talk about transformers, we typically don't care much about the inductance, as long as it's "high enough". We're typically interested in voltage ratio, ideally equal to the turns ratio between windings. 'Coil' is typically synonymous with 'inductor' and certain types of transformers. There are historical reasons why 'coil' is used in certain applications. For example, the part in your car that creates the high voltage needed to make the spark plugs work is called an ignition coil, not an ignition transformer. Even though it's technically correct, some people would know what you mean if you called it the latter, some would not.
> 
> ...



DIWDiver, Thank you very much for the detailed explanation. Now I had a better understanding.
So for the Joule thief circuit, it would require transformer to work.

Please advise when to use the flat SMD inductor ? I hope I had not wasted money buying a few thousand pieces. 

I had just built 10 more of the Joule thief using transformers & all are working. Noticed that if solder paste is neatly applied. Then the chance of success is higher. If the solder paste is sloppy applied, then the led would be dimmer or not light at all.


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## firefly99 (Sep 10, 2017)

Here are the Joule Thief that I built:




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## firefly99 (Sep 10, 2017)

PeterFH said:


> You need a transformer, not two inductors, they both need to be coupled, that is way you driver is not working.
> 
> Does it need to be a Joule thief?
> You get SMD led drivers that work way better then a joule thief and only need 1-3 additional external components.
> ...



Yes, I am very interested to hear more.


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## PeterFH (Sep 10, 2017)

Give me a day to get my components out of storage and ill take some pictures for you with a diagram.


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## firefly99 (Sep 11, 2017)

PeterFH said:


> Give me a day to get my components out of storage and ill take some pictures for you with a diagram.



Thank you, no hurry, at your convenience.


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