Smoothing modified sinewave Inverter

Discussion in 'The Projects Forum' started by simontay1984, May 21, 2009.

  1. simontay1984

    Thread Starter Member

    May 21, 2009
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    I have a Nikkai 12V to 230V 300W modified sinewave inverter. If possible, I want to modify it to output a purer sinewave (i'm not expecting perfect) similar to what the really expensive pure sinewave inverters produce.

    After spending ages searching Google about how to modify an inverter like mine to smooth the output, I found this page: http://bobmay.astronomy.net/misc/drivcorr.htm

    I've seen schematics for wien bridge oscillators that produce pure sinewaves with very low distortion and also sinewave generators using 555 timers.

    If it's possible, i'd probably use a wien bridge oscillator design as that produces a much smoother wave compared to a 555 and connect the output to the appropriate place on the inverters PCB.

    I also remember reading in a forum somewhere about whether adding a mains filter circuit (like on this page: http://www.conformity.com/artman/pu...inter_200.shtml) would improve the output.

    Any advice would be appreciated.

    Thanks for your time,
    Simon
     
  2. Wendy

    Moderator

    Mar 24, 2008
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  3. simontay1984

    Thread Starter Member

    May 21, 2009
    12
    0
    Thanks for your reply, Bill. Thats just what I was looking for!

    I read the PDF link about the National AN-263. Very interesting!
    Why use complicated digital circuits involing ADC's when some of the much simpler analogue designs would give similar (better?) results?

    After reading all six pages, it seems like you were designing a high frequency precision sinewave oscillator for a class D amplifier?
    Hope it all worked out well in the end!

    BTW, your oscilloscope looks ancient and in poor condition.
    Whats all that stuff around the edge of the screen?
    When I did computer science at uni, the oscilloscopes we used had many more controls and were in much better condition.

    Also, you don't happen to access to a service manual for a Panasonic SA-PM21?
    I've asked in this forum here: http://www.sharefx.net/audio-repair/panasonic-sa-pm21-service-manual/ but got no reply's.
    My friend has now given me said system and i'd like to have done the work by Tuesday evening

    Thanks,
    Simon
     
  4. Wendy

    Moderator

    Mar 24, 2008
    20,765
    2,536
    Can't help you with the manual, but this might be of some help...

    http://forum.allaboutcircuits.com/showthread.php?t=3246

    My oscilloscope IS ancient and in poor condition. Whatta ya expect for $10. The amature radio club was selling the dead ones for $5. And that was around 25 year ago. :D It works, if barely, good enough.

    I don't know what the grunge around the display is, maybe it's the grid decal decaying.

    Triangle waves are very useful, as are square waves and sine waves. If you go to my blog you will see a lot of articles I've written, if I get the function generator to an acceptable minimum it will become another one.

    Making a easy sinewave generator with simple parts has been a long term goal of mine, even in college. I might be getting there.
     
  5. Audioguru

    New Member

    Dec 20, 2007
    9,411
    896
    The idea about a modified sine-wave inverter is that its output transistors switch on and off so they stay fairly cool.
    If you try to filter the waves then the output transistors must operate linearily which will make them extremely hot.

    A pure sine-wave inverter uses Pulse-Width-Modulation at a high frequency to switch its Mosfets completely on and off so they stay fairly cool, then the high frequency is filtered out at the output.
     
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