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Square to Sine Wave

Discussion in 'Electronic Design' started by west, Jul 9, 2006.

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  1. west

    west Guest

    I have an inverter that puts out a nice 120v square wave. The inverters that
    put out a pure sine wave are expensive. Does anyone know where I can obtain
    schematics to build a square to sine wave converter fo my inverter? Thanks
    in advance.
  2. Luhan

    Luhan Guest

    You can't get there from here.

  3. Joel Kolstad

    Joel Kolstad Guest

    If you have a somewhat fixed load at lowish (<100W or so) power levels, you
    can use a rather large inductor and capacitor to build a low-pass filter and
    knock down the non-60Hz (or 50Hz) harmonics. Add more inductors and
    capacitors to make the result as sine-ish as you're willing to pay for...

    In the general case of high power/widely varying loads, this approach
    quickly becomes more expensive than just buying a sine wave converter in the
    first place and hence isn't practical... unless you're looking for an
    educational in winding your own high power inductors, which actually is
    rather fun...
  4. The Phantom

    The Phantom Guest

    As a matter of curiosity, if a device (black box) were available to connect to
    the output of your inverter and provide a sine wave from the inverter's square
    wave, what would you be willing to pay for it? And how much power are we
    talking about here?
  5. Guest

    I read that series resonant converters are good for upto 20 kW at epanorama.
    But they are intended for the dc/ac conversion not as an after the
    fact solution.
  6. Fred Bloggs

    Fred Bloggs Guest

    Anything at all can be done by finding the right schematic? Make sure it
    contains a transformer because by the time you attenuate all the high
    frequency components, your output will be at brown-out level.
  7. J.A. Legris

    J.A. Legris Guest

  8. Tim Williams

    Tim Williams Guest

    Poppycock. A steep (couple pole) low-pass filter will do it.

    Delivering a reasonable amount of power through it, at a variety of loads
    and power factors, and having the inverter appreciate it, is another story
    completely. ;-)

  9. Ken Smith

    Ken Smith Guest

    If the filter is steep because of notches and the notches are at the odd
    harmonics, and implemented buy parallel tuned circuits, it may not be so

    Prehaps more stages
    180Hz 300Hz V
    -----+--))))))---+---)))))---+---)))))---+------+--- Load
    ! ! ! ! !
    ----!!-----+----!!----- --- )
    --- )
    ! )
    GND !

    It works at higher frequencies.

    By time you pay for the extra parts, a sine wave inverter may look better.
  10. Ken Smith

    Ken Smith Guest

    Or, the load regulation will be bad.

    XL = 1
    ---)))))-----+---- Load
    --- XC = 1

    If you try to unplug the load, the connector will flash over.
  11. Luhan

    Luhan Guest

    I believe my original post was essentially correct. Commercial sine
    wave inverters use variable pulse width modulation to closely
    approximate a sinewave. A minimul amount of filtering is needed after

    Starting with a square wave at some considerable power level, leaves
    only expensive and impractical options.

    In other words, to get there, you need to start from someplace else.

  12. Carl Ijames

    Carl Ijames Guest

    How about the simplistic idea of just using a commercial line filter?
    The original poster did not specify his power level, but Belkin and
    Schaffner and Curtis (among many others) make one and two stage filters
    up to 12-15A at 120V for under $50. Doesn't solve the voltage droop, of
    course, but sure is easy.
  13. Luhan

    Luhan Guest

    Interesting idea, but I thought those filters only removed fairly high
    frequencies? That in itself may get rid of some of the 'noise' that
    square wave inverters are notorious for.

  14. Jamie

    Jamie Guest

    but you can get there from other there.
  15. joseph2k

    joseph2k Guest

    I guess you are younger at heart than me, somewhere in the past decade i
    ceased to consider winding high power inductors fun.
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