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switchers -- input range

Discussion in 'Electronic Design' started by David Lesher, Dec 23, 2004.

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  1. David Lesher

    David Lesher Guest

    In another group; there's a discussion about PC switcher inputs
    ranges. This came up after a poster suffered from an open neutral,
    and lost a lot of equipment.


    A) Are their any switchers that automagicly sense the input and
    change ranges? Some older Mac's are labeled "110-130 or 220-250"
    vice the "110-250" of newer ones. Note I am NOT talking about units
    with a {manual} voltage selector switch.

    B) What's the gotcha on having a wider input range: More design
    effort, to be sure, but do you also lose in efficiency, watts/cc^3,
    power factor, etc? I've only read a little on switcher design &
    never soldered on one. I'd assume you need to worry about the ratings
    on the input L, C and other items, and the one limit is high-input
    voltage, low load, [vs low, high...] cases. Other things?
     
  2. legg

    legg Guest

    Yes. These will describe themselves as 'universal input' and list one
    wide input range of voltages. Sometimes this is achieved through an
    automatic switching between ranges (auto-ranging), sometimes through
    preregulation that may include power factor correction, and in some
    lower-powered applications simply by operating over the wider range
    (with the added stress absorbed by adequately rated parts).
    For your requirements (none stated), its just a matter of cost and
    availability. For consumer PCs the most likely parts available will be
    power-factor corrected supplies in PC form-factor, produced to comply
    to newer EN61000 harmonic limits. As they are not yet commodities,
    their pricing reflects the lower volume, rather that the component
    cost.

    For lower-powered projects or those not requiring PC clone
    form-factor, there are wide-range, pfc corrected or auto-ranging input
    supplies that are commodities reflecting the requirements of the
    marketplace listed in didtributor catalogs for your inspection (Power
    One, Condor and Kaga in the Digikey catalog, as examples).

    RL
     
  3. David Lesher

    David Lesher Guest


    Err, that's not what I am asking. I am contrasting units that state
    either of two input voltages vs those that have one WIDE (2-1)range.

    What do the 'either' units actually do? I know (as the other responder
    noted, perhaps a simple full-wave/half wave choice) such is possible
    -- my question is what is/was built/sold.

    (Or are the "either" units really just wide range ones with
    a different label?)
    Here my query is more theory-based. I know manufacturing costs
    predominate, and create the bias for the "Any Voltage" design;
    but I am curious where the piper gets paid when you do so....
    (TANSTAAFL.)
     
  4. I read in sci.electronics.design that David Lesher <>
    AIUI, they have/had a relay which opens its contacts very quickly if
    subjected to the higher voltage and puts the rectifier into the bridge
    mode (no voltage-doubling). A 120 V a.c. relay in series with a bridge
    rectifier with a 120 V zener string across the d.c terminals might be
    one way to do that.
     
  5. Rich Grise

    Rich Grise Guest

    In fact, I once worked for a guy who did exactly that - well, not
    exactly. He used a 220V relay, that pulled in and switched the dual
    primaries from parallel to series. I thought it was a really flaky
    design - kind of a klooge, actually - a diode and cap and resistor,
    and it depended on a "calibrated" pull-in voltage for the relay, but
    he sold a lot of them. But that wasn't a switcher - it was a 24V,
    40A ferroresonant battery charger. You might have one if you have
    a SkyJack scissors lift. :)

    Cheers!
    Rich
     
  6. legg

    legg Guest

    Your question was explicitly stated, and answered.
    Most dual range units work(ed) on the simple single-link-selection of
    full-wave or full-wave voltage doubler input rectification. Other
    topologies that switched points in the converter stage were also
    developed at various times.

    The opportunity of using more complicated mechanical switching (dp/dt)
    or manual plug/link assemblies, allowed the use of linear magnetics
    and simpler AC air movers, without further design. Some ingenuity was
    employed getting AC magnetics to move air and power housekeeping based
    on the single link method, including the use of tapped-winding fan
    motors being used as autotransformers.

    Automatic switchover is typically achieved using a triac in the single
    link position, or a relay in the complex switch situation. Sanken even
    manufactured a dedicated smart-power IC with an internal triac for the
    first technique (from memory the STK8900 and STK8901).

    What is/was built/sold? ..... Everything you might think of.

    RL
     
  7. legg

    legg Guest

    On Thu, 23 Dec 2004 19:02:22 +0000 (UTC), David Lesher

    Refreshed memory. Sanken part was STR80145, STR81145 and other
    variations.

    RL
     
  8. I always thought that the basic principle is very simple: the input
    voltage is double-wave rectified and charges a 500V cap; then, it is
    chopped up at 100 kHz or so, step-down transformed (high freq->smaller
    core) and rectified. Voltage control by PWM. In principle, such design
    doesn't care about voltage or even AC/DC (I'd swear I have seen a power
    supply rated something like 24-240V, DC/50Hz/60Hz).

    Nobody else seemed to suggest this approach---am I off-base here?
     
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