Ultra-low voltage rectification???

Discussion in 'The Projects Forum' started by JJoll, Feb 18, 2015.

  1. JJoll

    Thread Starter Member

    May 7, 2013
    43
    1
    hi everybody,
    I am getting a a 400mv p-p AC source out of my ipod's audio jack. I am planning to use this to run another sensor. I want to rectify this 400 milli volt signal to a DC signal then pass it through a "LTC3108 - Ultralow Voltage Step-Up Converter and Power Manager Module"- http://www.linear.com/product/LTC3108 to boost my output voltage. What are my options to rectify such a small signal from AC to DC? I know I cannot be using ordinary full/half bridge rectifiers (because of 0.7v drop of diodes). What is a good way of AC to DC, step up conversion for max power delivery? Should I even consider using LTC3108? I was thinking of designing my own transformer where I match impedance of primary winding of transformer with impedance of audio jack for max power delivery. what do you think of that?

    thanks in advance
     
  2. crutschow

    Expert

    Mar 14, 2008
    12,993
    3,227
    How much power do you expect from this?
    The Ipod's audio output power is likely no more than a hundred mW so the maximum DC power you could generate would likely be less than 50mW after conversion losses.
     
  3. ScottWang

    Moderator

    Aug 23, 2012
    4,853
    767
    You said that you wanting to using the 400 mV to run another sensor, what is that sensor used for, to control something?

    400 mV is too low, so you may using a op amp to do a ac amplifier to amplify the signal, after that to do the rectifying and filtering.
     
  4. alfacliff

    Well-Known Member

    Dec 13, 2013
    2,449
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    why not use a transformer to step up the voltage?
     
  5. JJoll

    Thread Starter Member

    May 7, 2013
    43
    1
    More is better at this stage. I am not really expecting anything from this, I am just trying to design something that will give me max power and max current output. Then I will see if I can do anything with it. So really the goal is max output current. I have seen many people making flash lights and etc using headphone jacks.
     
  6. MikeML

    AAC Fanatic!

    Oct 2, 2009
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    Good, because it is a dumb idea, and you ain't gonna get much...
     
    wayneh likes this.
  7. wayneh

    Expert

    Sep 9, 2010
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    Do you really want to risk your expensive iPod to accomplish what a free flashlight will do better?
     
  8. #12

    Expert

    Nov 30, 2010
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    No, he wants to use most of the energy in a battery to run an Ipod to make a microscopic signal and lose half of that microscopic amount of power to run an accumulator for the power by forfeiting the audio information that the Ipod produced.
    Better to just run the flashlight off the battery in the first place.
     
    wayneh likes this.
  9. DickCappels

    Moderator

    Aug 21, 2008
    2,648
    632
    Using a step-up transformer as alfacliff suggested is the most direct solution. The output impedance of iPhones was 16 ohms the last time I checked.

    Texas Instruments has a family of chips that would work well in this application.
    http://www.ti.com/lsds/ti/apps/alternative_energy/harvesting/overview.page

    If you can keep the current in your load to a few tens of microamps, and halfwave doubler made with low power schottky diodes such as the 1N5711 and 1N60 might be a good low-tech choice.
     
  10. GopherT

    AAC Fanatic!

    Nov 23, 2012
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  11. #12

    Expert

    Nov 30, 2010
    16,260
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    @GopherT
    Keep track of that one. We've had so many people lately trying to "harvest" a few milliwatts.
    In an hour, they can harvest less than 1% of the power in a AAA battery.
    Consider the savings!
    If a million people attached the extra parts to get a few milliwatts out of their Ipod, they would used 10,000 less AAA batteries by using 1,000,000 Ipod batteries.
     
    GopherT likes this.
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