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Very Low Power Switched Mode Power Supply

Discussion in 'Electronic Design' started by [email protected], Apr 27, 2008.

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  1. Guest


    Does anyone know of a Switched Mode Power Supply that will operate on
    really low input voltage, say about 1 or volts and has no constraints
    on power output?

  2. Guest

    This has been discussed here, albeit some time ago. The only difficult
    part is getting the thing to start up. If you don't mind including a
    rechargeable battery there's no real problem; otherwise you've got to
    go for an inverter based on normally "on" parts, like junction FETs or
    depletion mode MOSFETs.

    I've not worked on the problem, so this is just what I remember, and
    isn't all that reliable. Win Hill and Joerg might know more - they did
    chime in on the 31 May 2006 thread "Low voltage step up design?"
  3. Joerg

    Joerg Guest

    There are plenty of step-up chips that start at less than a volt but
    they usually have one thing in common: They do require a bit of
    quiescent from the output side, mostly a few ten uA. That can be a
    problem in battery apps where you have to guarantee a continuous and
    stable output voltage. Browse National or TI, take a look around their
    step-up switcher chips.

    If power consumption is a really tough issue you are often back to the
    old JFET and have to coax it into a burst mode where the length of the
    bursts depend on whether the output voltage has dropped below a lower
    window limit or not. IOW it's going to have hysteretic behavior.
  4. MooseFET

    MooseFET Guest

    The basic two transistor multivibrator oscillator will start and run
    as low as about 0.8V. Using one of those you can make a simple
    booster supply to run the control electronics on. A cross coupled
    pair of 2N2222s and a transformer can get you a 10V supply to run
    stuff on.

    The main supplies pass elements can be MOSFETS or BJTs.
  5. Check L6920 from ST.

    Vladimir Vassilevsky
    DSP and Mixed Signal Design Consultant
  6. Texas TPS61200 - 0.3v min input
  7. Tim Williams

    Tim Williams Guest

    A chopper oscillator built with germanium transistors ( = not for
    production these days!) will run as low as 0.4V.

    There was an article in an old Electronics Now, by Fred Nachbaur, of such a
    circuit for single photocell use. I have it around here somewhere, and it
    might be referenced on Fred's website somewhere.

  8. Joerg

    Joerg Guest

    But watch out, IIRC it's 70uA quiescent, taken from the output cap. I
    wrote TI support a while ago about some tricks and whether they'd be
    kosher. Well, that was a couple months ago and I could not even get tech
    support to answer. Four (!) reminders, four promises to get back to me
    "soon", then zilch. That tells me something I'd have to keep in mind for
    future design decisions ...

    Hello TI, anyone listening?
  9. Phil Allison

    Phil Allison Guest

    ** The heading and the Q are in direct contradiction.

    ....... Phil
  10. Joerg

    Joerg Guest

    IMHO there isn't much of a market (yet). But there certainly won't be
    one developing if you can't obtain important info on available chips.
    Anyhow, most people in this field do that the old fashioned way. That
    would be a small helper circuit with a JFET and then a traditional
    switcher. If PHEMTs and stuff would be lower in cost we'd use them. But
    they cost a lot so mostly it's jelly-bean JFETs.
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