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Sine filter working

  1. Aug 17, 2011 #1

    Could someone please explain how EXACTLY a sine wave is produced using an LC filter from a PWM waveform generated by an inverter.

  2. jcsd
  3. Aug 17, 2011 #2
    Hi raikko

    In order to create a sine wave, the duty cycle of the pwm signal should be varied in a

    sinusoidal manner, this can be done using micro controller, and each pwm period an interrupt is

    generated, and the duty cycle takes a new value in the interrupt service routine. (Note that

    the values that the duty cycle should take are saved in an array; say up to 200 elements).

    This will generate a sine wave which has also the carrier frequency part of its harmonic

    components, so we put a low pass filter (LC filter) in order to eliminate the switching

  4. Sep 21, 2011 #3
    Thanks for the reply.
    However what I wanted to know is how the LC filter works in eliminating the carrier frequency of the generated PWM signal.
  5. Sep 21, 2011 #4


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    Kind of the same way FM demodulation works on your radio, I would imagine? :wink:
  6. Oct 31, 2011 #5
    hello how is everyone. Could someone kindly send me a link for a pure sinewave imverter circuit/ Thank you
    Last edited by a moderator: Nov 8, 2011
  7. Nov 1, 2011 #6

    jim hardy

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    for an intro to one technique
    try a google on

    magic sinewave tinaja

    the series L is high impedance at carrier frequency so attenuates carrier by voltage divider action
    the paralllel C is low impedance at carrier frequency so shunts carrier attenuating it further.

    you can also shape a square wave into a pretty decent sinewave with tuned filters that attenuate the harmonics
    Last edited: Nov 1, 2011
  8. Nov 1, 2011 #7
    Thank you for your support but I went to the magic sinwave site but I did not see a circuit please help me on this . thank you
    Last edited by a moderator: Nov 8, 2011
  9. Nov 8, 2011 #8
    @olivermsun and @jim hardy - Thanks for the answers
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