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Re: [jallist] Re: Newby: How can i do this better?

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  • Eur van Andel
    On Tue, 26 Oct 2004 08:18:04 -0000, Vasile Surducan ... So you have motor and a TRIAC in series with the mains. The mains is at this
    Message 1 of 17 , Nov 1, 2004
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      On Tue, 26 Oct 2004 08:18:04 -0000, "Vasile Surducan" <vasile@...-cj.ro>
      wrote:

      >> You can't turn a TRIAC off. You will have to wait for a zero-
      >crossing before it
      >> turns off itself.
      >
      > A triac is turning off when the A1-A2 current is zero or is
      >changing his direction (is negative). This has nothing to do with the
      >main voltage. If it has, then you can't project static relays which
      >are turning off when you tell it to switch and not when the mains is
      >zerror crossing. There are many tehniques to switch OFF an triac when
      >you want to, no matter the mains. Even I can send you a book about
      >this, will be unusefull, is in romanian. I will search on my
      >database, maybe I'll found something in english.
      So you have motor and a TRIAC in series with the mains.
      The mains is at this moment about 100V and rising. The TRIAC is conducting a
      current of , say 1A.

      Do tell me how to shut the triac off in <100 us by applying voltage to the
      gate.


      --
      Ir. E.E. van Andel, Fine Wire Heat Exchangers, Fiwihex B.V. www.fiwihex.com
      Wierdensestraat 74, NL-7604 BK Almelo, The Netherlands eur@...
      phone +31-546-491106 fax +31-546-491107 mobile +31-653-286573
    • Wouter van Ooijen
      ... You can t, but you can turn it off by applying a pulse to the triac itself of the opposite polarity. IIRC this was a common way to do PWM with thyristors,
      Message 2 of 17 , Nov 1, 2004
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        > Do tell me how to shut the triac off in <100 us by applying
        > voltage to the gate.

        You can't, but you can turn it off by applying a pulse to the triac
        itself of the opposite polarity. IIRC this was a common way to do PWM
        with thyristors, long before power mosfets became dominant in this area.

        Wouter van Ooijen

        -- -------------------------------------------
        Van Ooijen Technische Informatica: www.voti.nl
        consultancy, development, PICmicro products
        docent Hogeschool van Utrecht: www.voti.nl/hvu
      • Vasile Surducan
        ... PWM ... area. Bingo ! Eur, you ll be then surprised to found that a triac may be switched OFF also in pure DC. The methode is highly used right now (and
        Message 3 of 17 , Nov 2, 2004
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          --- In jallist@yahoogroups.com, "Wouter van Ooijen" <wouter@v...>
          wrote:
          >
          > > Do tell me how to shut the triac off in <100 us by applying
          > > voltage to the gate.
          >
          > You can't, but you can turn it off by applying a pulse to the triac
          > itself of the opposite polarity. IIRC this was a common way to do
          PWM
          > with thyristors, long before power mosfets became dominant in this
          area.

          Bingo !

          Eur, you'll be then surprised to found that a triac may be switched
          OFF also in pure DC. The methode is highly used right now (and not
          only in the past like Wouter said)for high power DC-AC variable
          frequency converters. Usualy it use an auxiliary shut off thyristor
          (and a phase modifying circuit). There is another world which is
          dealing with this and is called "power electronics".

          best regards,
          Vasile
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