I am working on a project that need to get energy harvest from smartphone headset jack.I find hijack project has a solution.the energy harvest circuit of it is below: enter image description here

it use coilcraft transformer LPR6235PMR. datesheet is below:


I built a circuit exactly the same and use my phone to generate an sine signal with 22khz.It turned out works fine partly.It indeed convert AC to DC.But power efficiency is only 10% probably.I find out the main problem is the transformer:If input frequency of sine signal is 580khz. everything is fine. But if frequency is 22khz as hijack's suggestion.the voltage draw about 80% percent at L1 part then increase 20 times. So turns ratio is only 1:4.

at first, I wonder whether or not LPR6235 can be as step up converter of smartphone audio output. Then I find lumu use this transformer.(LPR6235LMR turns ratio 1:10 almost the same) enter image description here

someone also had used it and worked fine. http://www.avrfreaks.net/forum/harvesting-power-headphone-output

("My coil samples arrived from CoilCraft, part number LPR6235-253PMLB(20:1). Feeding the primary with with one channel of 20KHz sine(highest frequency my iPod Sig. Gen. app will do) at max amplitude results in a no-load secondary of 13.6V p-p. This drops to around 10.5V with a 2k2 load resistor. I reckon that, since I'm going to need one schottky anyway with a FET bridge, I might as well use a conventional bridge, since: a) That will only introduce another approx. 0.5V drop. b) I only need 3 to 3.5V anyway. I will try paralleling up the L and R channels to see what effect that has. John")

so I guess it should work. But I can't find what the problem is.why my transformer exactly the same one doesn't has 1:20 turns ratio.


  • \$\begingroup\$ Output from a smartphone at 22kHz will be rather weak. Try a lower frequency, say maybe 10kHz. \$\endgroup\$ – JRE Oct 27 '16 at 11:01

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