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SMPS On Signal Line

Discussion in 'Electronic Design' started by James, Jan 30, 2007.

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  1. James

    James Guest

    Hi All,
    Is it possible to run a buck-boost or flyback SMPS from a 0.2Vpp
    signal line? My signal has bandwith from 1-5K with low output
    impedance. I am looking to trickle charge a 3.3V battery. I would be
    happy if I could get a couple of mA at 3 to 5 volts.

    I also am looking for this to be in a small package. The switcher
    would need to fit in a footprint of about 25 X 25 mm.

    Am I dreaming or is this possible?


    James
     
  2. Phil Allison

    Phil Allison Guest

    ** Groper Alert !


    ** So, you are asking for about 8 mW to be delivered from a 70 mV rms
    source - hmmmmmm.

    Means the 70 mV signal source will have to supply over 100 mA, so must be
    *well under* 1 ohm impedance.

    Sure you are not dreaming ?

    If by some chance you are not, then an audio step up transformer followed
    by a bridge rectifier is the simplest way.

    The ratio will need to be around 40:1, for charging to occur on signal
    peaks.

    Lotsa luck.



    ........ Phil
     
  3. As long as you can power the control circuitry from the battery, then
    it could be possible. I.e, you might not be able to "start up" from a
    dead battery without another external power source.

    It *might* even be possible to startup directly from the 0.2V somehow,
    anyone? I seem to recall a thread about this here before.
     
  4. Actually I missed that your 0.2V is an AC signal, so Phils transformer
    suggestion is more appropriate.
     
  5. tlbs101

    tlbs101 Guest

    I am actually experimenting with something quite similar right now,
    only my input signal a little higher -- closer to a schottky diode
    drop, so I am using a ladder multiplier. (I have other problems to
    deal with, such as: my input voltage range is nominally 0.5 but can
    reach several volts, so I need protection/pre-regulation after the
    multiplier.)

    I like the idea of using an audio transformer -- I had considered that
    before, and now I think I'll revisit that. Thanks, Phil.

    Tom P.
     
  6. James

    James Guest

    Thanks for the comments, my output impedance is about an ohm and my
    signal source is good for 10ma. As you pointed out this will not get
    me to 2mA at 3V. I am looking at moving to a 1.8V micro. With the
    voltage reduction and a closer look at sleep modes for the micro I
    should be able to get my current consumption down to 300 - 500uA.
    Even with these changes I think I will still be a bit short of full
    power from the signal line. I think I will still pursue a signal
    line charging approach as it looks to me like I will be able to extend
    my battery life by a factor of 3-5X.

    James
     
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