Reading thyristor datasheet

Discussion in 'General Electronics Chat' started by #12, Dec 12, 2012.

  1. #12

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    Nov 30, 2010
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    They've changed the datasheets and I'm having difficulty reading this one, (and I never was good with triacs, anyway.) Can I apply a continuous positive DC current to the gate and make it run a 500 watt light bulb (on 120 V RMS) because it triggers both polarities of load from a DC gate current?

    Can you help me with a snubber for di/dt? I don't know if it needs an inductor in series to limit inrush current and I don't know if it needs a snubber for di/dt when it turns off..or you can name a different triac if this one's a PIB. (I need Igt below 20ma in both directions.)

    Thank you.
     
  2. Dodgydave

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    Jun 22, 2012
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    The gate has to be triggered with the same polarity as Mt2, so you can connect G and Mt2 together and your bulb will light up, it will trigger with 5 mA max.
     
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  3. tubeguy

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    Nov 3, 2012
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  4. #12

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    Dodgydave, I guess you just said a continuous DC current which has the same polarity at all times will not trigger this triac in one of the necessary conditions.

    True?

    tubeguy: Excellent idea. I think that will work because the opto uses the driving sinewave to apply the correct polarity.

    True?
     
  5. tubeguy

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    Yes, it automatically supplies the correct polarity with the added benefit of isolation.
     
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  6. #12

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    Excellent! A good excuse to use an opto in a circuit that doesn't absolutely have to have one.
     
  7. Dodgydave

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    Jun 22, 2012
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    No i said as long as the gate is the same polarity as MT2, it will work on both phases, an opto will work yes, so will a resistor capacitor divider ...like this
    http://www.google.co.uk/imgres?q=tr...88&start=23&ndsp=28&ved=1t:429,r:47,s:0,i:229

    PS. your title is wrong as its a Triac and not a Thyristor...
     
    Last edited: Dec 13, 2012
  8. #12

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    Thanks. I'll tell RCA to quit including triacs in their book labeled, "Thyristors". (Does RCA even exist now?)

    So, you say "as long as the gate is the same polarity as MT2". MT2 compared to what? There is only one terminal left, MT1. So, as long as the gate is the same polarity as MT2 is compared to MT1. and you also said that you didn't mean a constant DC current wouldn't work. Guess what...a constant DC current doesn't change polarity 100 times a second, so it can't be the same polarity as MT2 compared to MT1 during both halves of the power line.

    Just to be sure we're talking about the same thing, here are some drawings. I think one of the won't work.
     
  9. Dodgydave

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    Jun 22, 2012
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    If you notice the opto connects the gate to MT2, so as the polarity changes from + to - on mt2 it will still be the same on the gate + to -, the gate will still have the same polarity as mt2.


    So positive cycle Mt2 posative , Gate posative = triac on
    negative cycle Mt2 negative, Gate negative = triac on


    Understand, Verstehen, capiche !!!
     
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