Confusion about inrush current with triac as AC switch

Discussion in 'Power Electronics' started by Xavier Pacheco Paulino, Dec 13, 2018.

  1. Xavier Pacheco Paulino

    Thread Starter Active Member

    Oct 21, 2015
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    I have read in many reliable sites that high inrush currents are avoided if you switch at zero crossing. But this App Note states the opposite. Am I misinterpreting something?

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  2. MaxHeadRoom

    Expert

    Jul 18, 2013
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    Difference seen with an inductive load, where the current waveform is out of phase with the voltage waveform, which is switched at the zero voltage point.
    Max.
     
  3. cmartinez

    AAC Fanatic!

    Jan 17, 2007
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    It depends on the type of load, such as resistive or inductive. But triggering a TRIAC at zero crossing minimizes EMI noise.
     
  4. Xavier Pacheco Paulino

    Thread Starter Active Member

    Oct 21, 2015
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    Thank you! I'm clear now. That's why I just read that zero crossing switches are not recommended for large inductive loads as also stated in this App Note. After all, I just mixed the loads, that's why my confusion.
     
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  5. cmartinez

    AAC Fanatic!

    Jan 17, 2007
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    Hey! Thanks for posting that. I too am learning something new out of this thread.

    As I side note, I strongly suggest you take a look at inrush current suppressors. Those devices present a certain amount of resistance at startup, but then almost go down to zero when the load stabilizes.

    Here's an example of what I'm saying.
     
  6. Xavier Pacheco Paulino

    Thread Starter Active Member

    Oct 21, 2015
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    Yeah, I'm using one of those at the input of the bridge rectifier for limiting the inrush into a bulk capacitor at startup. It works well.
     
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