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Choosing a transformer for energy harvesting

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sandbox

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Hi all,

I am trying to build the energy harvesting circuit from the following pdf : https://web.eecs.umich.edu/~prabal/pubs/papers/kuo10hijack.pdf

It is a energy harvesting circuit for extracting power from the audio jack of a phone

The trouble is that i cant find the part they are using on digikey or anywhere else () . The prime factor for choosing the transformer is that it has a primary inductance of 25uH and 1:20 turns ration, achieves efficient power transfer at a frequency of 20Khz which is close to the upper limit of what a phone's audio jack can produce.

I could however find the following part : LPD6235 https://www.farnell.com/datasheets/1681916.pdf , its not labelled as a transformer but a coupled inductor, is it ok i swap the original part for any variant of these ? if not could you please suggest a part number that i can use as a replacement ?

Thanks in advance for all your help,
sandbox
 
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betwixt

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Forgive me if I'm missing the point but why would you want to convert battery power to audio then back to DC. Surely, just using the battery power directly or through a regulator would be far more efficient.

Brian.
 

sandbox

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The ideas is to build a low power sensor device that can be plugged into any phone and use, using the battery on the phone is not an option since it needs to be hacked to get the power, an additional battery will kind of reduce the shelf life of such a product as well as limit the user experience ...
 

RCinFLA

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Get a phone with USB OTG and take it off of USB jack. Many smartphone have USB on the go.
 

betwixt

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Sandbox, I understand what you are trying to achieve but it will never be cost effective when you use maybe 300% more power than needed and also suffer the potential risks of the phone being damaged or your application being disrupted by other phone functions. All you are doing is sacrificing the phone and it's battery in order to save pennies. A second battery using the same type of charger socket as the phone would be more convenient to the user, they could swap the power cord from one socket to the other. Li-ion/LiPo batteries like the ones inside phones have long shelf life and can survive many charge cycles without significant deterioration.

Brian.
 

mtwieg

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That article suggests impedance matching to the audio output, which sounds like a pretty dubious proposition. I doubt that putting <4ohms on the output is healthy for the driving electronics...

Anyways, that part from coilcraft is pretty special. It was actually developed and produced specifically to be used with this thing from Linear Tech: http://cds.linear.com/docs/en/datasheet/3108fb.pdf
Supposedly Wurth also made some equivalent parts, but I don't see any info on their site...
Finding a replacement will be difficult. The coupled inductor you posted only has a 1:1 ratio, so it wouldn't work. But finding a 1:20 ratio will be difficult. You should at least try and get a few of the real thing from coilcraft (they do not use distributors for US or Canada, you have to go directly to them).
 

js

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That article suggests impedance matching to the audio output, which sounds like a pretty dubious proposition. I doubt that putting <4ohms on the output is healthy for the driving electronics...

primar impedance of transformer with parallel capacitor (about 2uF2) form HIGH impedance state at cca 22kHz so no problem about "over power" driving electronics....
 
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