Help with decision re final stage of PWM output

Discussion in 'The Projects Forum' started by Denesius, Feb 17, 2015.

  1. Denesius

    Thread Starter Member

    Feb 5, 2014
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    14
    I have a 3-phase PWM circuit, with a pulse freq of 20kHz and a sine wave modulation of 400Hz. Each phase output stage feeds an IR2110 driving MOSFETs in an H-bridge configuration. System/input power is 12VDC, and the final output needs to be 120v, 400Hz, 3-phase with about 500mA capacity each phase. I haven't put together the low-pass filter yet.
    Question:
    Is there an advantage to using a 75VA transformer for each phase to kick up the filtered output from 12V to 120V, versus using a flyback switcher with a 350VA transformer to bump up the 12VDC supply to 170VDC, and then using this as the feed into the MOSFETs?

    (the assumption is that the former would use need small transformers in each phase as part of the filter, while the latter would need a single larger transformer as well as some sort of inductor for the output of each phase)
    Parts count, weight & size are the driving factors. Thanks for any input
     
  2. Kermit2

    AAC Fanatic!

    Feb 5, 2010
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    951
    three 75 VA xformers

    they will be used at near full capacity and therefore be more efficient loss wise. the amount of ferrous metal used will be almost the same. sounds like the single xformer would be more massive based on the VA ratings
     
    Denesius likes this.
  3. Denesius

    Thread Starter Member

    Feb 5, 2014
    89
    14
    The formula for the filter (with the notch at 800Hz) comes out to (approx) 2.5mH. Since the primary on the transformer is about 1400mH, I assume the capacitance is reduced proportionately?
     
  4. Kermit2

    AAC Fanatic!

    Feb 5, 2010
    3,795
    951
    yes. use the values you have to calculate the values you need.
     
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