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Thread: ST Response to bad traics

  1. #1
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    Default ST Response to bad traics

    I received an answer from STMicroelectronics to my inquiry about the traic failures, I don't think this will solve our problems but it may be worth checking. I don't have a scope but if someone can check their ssr's and post what they find maybe we can eliminate at least one thing. I did send 10 traics (BTA04-700T CHN 912) to Mouser for failure analysis. I will keep everyone posted as to the results.

    PS Had another BTA04-700T go bad tonight.

    Gary,

    It appears as though the problem occurred when you switched from a triac that requires 50mA of gate current to one that requires 5mA. I believe there is noise in your system triggering the 5mA triac.


    The solution is to

    1) Use a less sensitive triac.

    2) Measure the triac gate current with an oscilloscope to determine is a current
    transient is present.

    3) Find the source of noise and eliminate it.



    You can measure the gate current with a current probe or make a differential measurement of the voltage drop across the 180R series gate resistor.

    If you think the triac is defective, you can return it for a failure analysis through the source from which it was purchased.

    Sincerely,

    Ed Friedman
    =====================
    Ed Friedman
    Product Marketing
    STMicroelectronics
    Phone: 781-402-8529
    Cell: 781-929-3064
    Fax: 781-861-2669
    Last edited by JP90; 12-13-2010 at 12:24 AM.

  2. #2
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    Default Re: ST Response to bad traics

    I'm not sure I understand this response - - is he saying that the TRIAC is still good but that you (and others) have so much noise on their gate inputs (>5mA) that the TRIAC always triggers?
    Brian

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  3. #3
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    Default Re: ST Response to bad traics

    Quote Originally Posted by budude View Post
    I'm not sure I understand this response - - is he saying that the TRIAC is still good but that you (and others) have so much noise on their gate inputs (>5mA) that the TRIAC always triggers?
    That's how I'd take it. Interesting... but it actually makes some sense.
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  4. #4
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    Default Re: ST Response to bad traics

    Unless the noise could cause the traic to fail ?????? I am not buying this answer just yet. We all can't have noise on our AC lines.
    Last edited by JP90; 12-13-2010 at 12:39 AM.

  5. #5
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    Default Re: ST Response to bad traics

    It might not take very much noise if the triac is super-sensitive. Hmmmm...
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    Default Re: ST Response to bad traics

    I don't buy it yet either.

    In any case, a 5 mA triac may very well trigger at less than 5 mA, although it is not guaranteed to do so. If I recall right, there is some gate current spec below which it will not trigger, but this quite a bit smaller than 5mA.

    Also, there are additional trigger mechanisms for a triac besides just putting the appropriate amount of current through the gate, but I'm too tired to look into it now. There are some appnotes out there which discuss this, perhaps an1001.pdf (use google).
    Phil

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    Default Re: ST Response to bad traics

    I believe he thinks that its always a problem and not something that worked and now it doesn't.

    If it was noise, sometimes it would work again. We're using the same circuit that's common in the industry.

    Besides, there are other sensitive gate TRIAC's that are in use and they're not failing.
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  8. #8
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    Default Re: ST Response to bad traics

    I find it strange that so many people are having problems with the BTA04-700T triacs, especially when STMicroelectronics now shows them as discontinued on their website.

    I wonder if they were having problems with them, or they just didn't have enough demand for them to keep them in their lineup.

    Just my .02

  9. #9
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    Default Re: ST Response to bad traics

    I cant use a BTA04-700T to control any 240v lights here in sydney due to noise on my ac line. With just just the line side (ie triac, gate resistor and moc) connected and no control side connected or even soldered on an ssrez i get my lights flickering so gave up on it and switched to dc

  10. #10
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    Default Re: ST Response to bad traics

    Maybe the issue of TRIACs false triggering is simply the result of the poor device selection choice or circuit design. Using snubberless TRIACs or adding an R/C snubber to a standard type may be prudent given some of the loads the Christmas crowd use.
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