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Square wave to sine wave converter

Discussion in 'Electronic Projects Design/Ideas/Reviews' started by ghauri, Jun 17, 2006.

  1. Mikebits

    Mikebits Well-Known Member

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    ONLINE
  2. SMUGangsta

    SMUGangsta New Member

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    im quite sure if there was a simple one it would have been posted in this thread already as its over a year old, mabey try some of the ideas suggested earlier
     
  3. audioguru

    audioguru Well-Known Member Most Helpful Member

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    The lousy old LM324 has full output up to only 2kHz. It is low power without enough bias current in its output transistors so it has up to 3% crossover distortion.

    Better opamps go up to at least 100kHz at full output without any measurable crossover distortion.
     
  4. dave

    Dave New Member

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  5. MrAl

    MrAl Well-Known Member Most Helpful Member

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    Hi Mike,

    Ok, i did, and found that the design equations and even philosophy
    isnt quite right. Let me explain...

    First, a fixed frequency sine wave generator made from a square
    wave generator followed by a filter (as that article is about) to
    smooth the square wave into a sine wave is best by making
    the filter a bandpass filter rather than a low pass filter. That
    design uses a low pass filter so it's not as good as one that uses
    a band pass filter, and since both designs use about the same
    number of components, why not use a band pass instead?
    The low pass does not produce as good a sine wave, with the
    tops bent to the left somewhat instead of an almost pure sine.
    It's not too bad i guess, but with the same components a
    bandpass would be better.

    Second, the design formula for the filter provides for a very
    high output which allows too much of the original square
    wave to reach the output. This leads me to believe that
    the second formula:

    R5=1/(8.8856*F*C1)
    R6=R5

    is also incorrect.
    A better formula would be:

    R5=2/(8.8856*F*C1)
    R6=R5

    which effectively doubles R5 and R6.


    Third, the design formula for the center frequency of the
    square wave oscillator is totally incorrect. This would result
    in the calculation of components that dont provide the
    correct operating frequency.
    The formula given is:

    R1=(0.5*F)/(0.693*C1)

    but it's obvious with that oscillator that as frequency increases R1 has to
    decrease, so the corrected formula is:

    R1=(0.5)/(0.693*C1*F)


    These formula changes make a better sine wave oscillator,
    but again if the output filter was a BP type it would be
    even better.
     
  6. vino.p

    vino.p New Member

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    thank you mike bits. your circuit works very well. any do you any one have LEAD ACID BATTERY CHARGER WITH AUTO CUT OFF circuit.
     
  7. ARCon

    ARCon New Member

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    where would i be able to find a schematic for a 220v 50hz true sine wave inverter?
    I am looking for something large to use as a backup for my whole house....

    Why are true sinewave inverters so scarce?
     
  8. audioguru

    audioguru Well-Known Member Most Helpful Member

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    A true sinewave inverter has a very complicated circuit.
    Use a gasoline-engine powered generator.
     
  9. marcbarker

    marcbarker New Member

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    A gasoline-powered generator sounds the easiest solution. Be careful, power companies call this "back feeding", they can get nasty if they think there's a risk of power finding its way onto their network. Linesman have be killed this way.

    probably because the power density of storage batteries is so low, compared to that of a fossil fuel powered generator. Also the capital outlay and maintenence for the equivalent energy in the form of storage batteries is a lot more expensive than a tank of diesel/gas.



    While I'm here, I'll answer the orig posting of 2 years ago.....
    1. Make the opamp into a sine wave oscillator. e.g. a "phase shift", "twin-T" or "wein bridge".

    2. When you close the feeback loop, don't provide enough feedback for it to freely oscillate (just increase an R if it's a wein bridge).

    3. Choose enough feedback for it to "ring" at the oscillator centre frequency.

    4. Couple the square wave, to this 'oscillator'. Tight if you want a wider range of frequency, looser if you want lower distortion. The output will be in phase with the sq wave. You'll probably need AGC.

    PS. Instead of opamp, if you used just a single transistor (eg as a 'phase-shift-oscillator'), the circuit will be lower parts count, and you'll probably get away without needing AGC (e.g. thermistor). Because a simple common emitter BJT circuit is non-linear and what is "nasty distortion" in audio design, is here a nice 'compression' function to stabilise the sine amplitude.
    Hope this helps, I'd done this trick before and it worked for me. I used several of these to clean up a group of sinewave tones received over a radio link.
     
    Last edited: Jul 6, 2009
  10. Mahtab Saikia

    Mahtab Saikia New Member

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    Hallow!
    Would any one can provide a circuit that can be installed at output side of square wave inverter(500 watts) to convert it to sine wave output without losing its performances.
    Thanks
     
  11. mneary

    mneary New Member

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    Sorry, no can do. That's the reason a square wave inverter is efficient and cheap.

    The best circuit to convert a square wave inverter output to sine wave would look much like a sine wave inverter.
     
  12. Hero999

    Hero999 Banned

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    Add a huge big and heavy LC fliter.
     
  13. Mahtab Saikia

    Mahtab Saikia New Member

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    squre wave to sine wave converter( In inverter)

    Would you provide circuit just to convert a square wave inverter's output to sine wave, either at any point with existing circuit & transformer ?
     
  14. audioguru

    audioguru Well-Known Member Most Helpful Member

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    The peak voltage of the square-wave is the same as its average voltage. But the peak voltage of a sine-wave with the same average voltage as a square-wave is much higher (1.414 times higher). Then you need a voltage boosting circuit which also increases the current from the square-wave.

    If you use a huge, heavy and expensive filter to smooth the square-wave into a sine-wave then its resistance will cause poor voltage regulation where the voltage will be too high when the load current is low and the voltage will be too low when the load current is high.

    Throw away the old-fashioned square-wave inverter and buy a modern PWM pure sine-wave one that is small, lightweight, inexpensive and has good voltage regulation.
     
  15. mneary

    mneary New Member

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    It's really simple. Take the 230V square wave and put it into a transformer 230V to 18VAC. This will have approximately 16V square wave. Put this 16V square wave through a full wave rectifier and filter and get 14VDC. Put 14VDC into sine wave inverter.

    done and good.
     
  16. adeel.hasan

    adeel.hasan New Member

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    Is there any one who can HELP please
    How to convert the square waves in sinusoidal waves when the input is 30 volts?
     
  17. magnatro

    magnatro New Member

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    Lol.................!
     
  18. ll4m14

    ll4m14 New Member

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    anyone who thinks there is a way to convert the square wave output from an inverter to sine wave
     
  19. audioguru

    audioguru Well-Known Member Most Helpful Member

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    If an inverter has a square-wave output then it is extremely cheap and simple.
    The peak-to-peak amplitude of the square-wave is the same amplitude as the RMS amplitude of a sine-wave inverter.
    The peak-to-peak amplitude of a sine-wave inverter is 2.828 times higher than for a square-wave inverter.

    You cannot simply filter the harmonics away from the square-wave because the filter parts will be huge and cause the output voltage to be too low. The wrong p-p output swing will also cause the output voltage to be too low.

    You cannot use a linear audio amplifier because it would waste a lot of power making heat.
     
  20. mneary

    mneary New Member

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    Rectify the square wave and send it to a sine wave inverter.
     
  21. cbenham

    cbenham New Member

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    An easy plug-and-play way to convert the output of a square wave power inverter to a sinewave is to use a sinosoidal type constant voltage transformer like those made by Sola and many other power conditioner manufacturers.

    However, nothing is for free. There are a few drawbacks and rules which must be followed...

    If the inverter is rated at 1000 watts CONTINUOUS square wave power out, get a CVS type Sola transformer rated at 500 to 750 VA output and connect a load of no more than 350 to 600 VA with reference to the capacity of the CVS you are using.
    These transformers are available sometimes inexpensively on a certain auction website we all love to hate.

    Make sure the CVS transformer is rated at the same frequency, i.e. 50 or 60 HZ as the inverter outputs. They have a ferro-resonant capacitor circuit and only work at the nameplate frequency, i.e. 50 or 60Hz.

    These transformers have lots of iron and are therefore heavy. Since they run saturated they produce lots of heat.

    This scheme really does work. I am currently using a 60VA Sola CVS transformer to make a sinewave output at 60 Hz from a Heathkit square wave inverter model MP-10. The sinewave 120VAC output is used to power a CD player that will not work with a squarewave because the 60 Hz is plainly audible in the speakers. The CVS transformer kills the noise.

    Hope this information if of use to somebody even if it a couple or years late.
    Cliff
     
    Last edited: Jul 10, 2010

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