Triggering a thyristor (SCR, triac). Is this good advice?

Discussion in 'General Electronics Chat' started by Alec_t, Jun 5, 2016.

  1. Alec_t

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    I was reading this ON Semiconductor publication about thyristors and noticed the following passage (page 2) :-
    "On the other hand, it is important to provide a trigger pulse large enough and fast enough to turn the gate on quickly and completely. Usually the gate trigger current should be at least 50 percent greater than the maximum rated gate trigger current."
    I totally agree with the first sentence, but am puzzled by the second sentence. Why have a rated maximum current if you then deliberately exceed it?
     
    Last edited: Jun 5, 2016
  2. MaxHeadRoom

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    I suspect that it should be 'greater than the Continuous Maximum rated gate current,
    With the operative work being 'Fast trigger pulse'.
    Max.
     
  3. Lestraveled

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    You will notice that there is an RMS gate current and then there is a peak gate current. I suspect they mean the trigger pulse current should be at least 1.5 time the RMS current.
     
  4. Alec_t

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    Thanks guys. That makes sense. It looks as though ON didn't say what they intended :rolleyes:.
     
  5. bertus

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    Hello,

    I have here a collection of application notes on triacs and thyristors.

    Bertus
     
  6. benta

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    Alec_t, your link leads to the datasheet of the ON Semi MCR08, which does not state anything that you quote.

    However, I suspect that you have an application note that is not very well written. This is not unusual.

    The statement:
    Usually the gate trigger current should be at least 50 percent greater than the maximum rated gate trigger current.
    is clumsily phrased and makes little sense.
    It should rather read
    Usually the gate trigger current should be at least 50 percent greater than the quaranteed turn-on IGT
    (in this case 200 μA, meaning you should provide at least 300 μA of gate current)

    Benta.
     
  7. Alec_t

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    Oops. Sorry. Link corrected.
     
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