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Modified Sine Wave Inverter

Discussion in 'General Electronics Discussion' started by Fritz Mulder, Apr 27, 2015.

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  1. Fritz Mulder

    Fritz Mulder

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    Apr 27, 2015
    Hi Guys. I'm busy building a modified sine wave inverter based on a schematic I found on the internet. I'm using a Pic18f452 for my controller and IRFZ44 mosfets. Currently I'm testing the inverter using a very small centre tap transformer to switch 12vdc to 220V AC at 50hz. The problem is the primary input voltage is bad looking due to the transformer primary being switched causing back emf and there is nothing in the circuit to absorb the voltage spikes. I need help with a snubber circuit of something to clamp down these voltage spikes. I have included pictures of the circuit diagram, unloaded Mosfet output waveforms and the transformer Primary voltage waveform. Any help would be appreciated. Thanks
     

    Attached Files:

  2. BobK

    BobK

    7,682
    1,686
    Jan 5, 2010
    Do you have a load on the secondary? If not, try putting an appropriate load in the way of a small light bulb.

    Bob
     
  3. Fritz Mulder

    Fritz Mulder

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    Apr 27, 2015
    I'm getting my transformer soon. Its an old microwave transformer thats being rewound to 12-0-12 on the secondary and then I will try to put a 100watt light bulb on.
     
  4. ramussons

    ramussons

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    71
    Jun 10, 2014
    Connect a small value, say 1.0 uF non polarised capacitor across the primary and check.
     
  5. Fritz Mulder

    Fritz Mulder

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    0
    Apr 27, 2015
    Thanks. I will give it a try
     
  6. Fritz Mulder

    Fritz Mulder

    4
    0
    Apr 27, 2015
    I found this article on the internet http://www.homemade-circuits.com/2013/10/modified-sine-wave-inverter-circuit.html?m=1

    My unloaded waveforms compare with their's and when I load my transformer the voltage spikes seem to clear out a bit . I'm going experiment and modify my code to produce sine wave pwm output and then use LC filter on the primary to try and get better results. Will put up some waveform when I done.
     
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