Opto Triac Driver question

Discussion in 'Electronics Resources' started by ghall426, Aug 31, 2012.

  1. ghall426

    Thread Starter Member

    Jul 22, 2009
    11
    0
    Why do the datasheets for an opto triac driver (like an MOC3012) show the LED trigger current IFT value 5mA as maximum value, but the note below it says:

    "All devices are guaranteed to trigger at an IF value less than or equal to max IFT. Therefore, recommended operating IF lies between max IFT (5mA for MOC3012M) and absolute max IF (60mA)."

    I would think the IFT of 5mA should be a MINIMUM, not a MAXIMUM. It's like this on several datasheets that I looked at.

    And a second question, if you can use any value between 5mA and 60mA, why do they make a MOC3010 with the IFT of 15mA? When would you need to use a MOC3010 instead of a MOC3012?
     
  2. panic mode

    Senior Member

    Oct 10, 2011
    1,321
    304
    you are not reading correctly...

    for example max forward current is 60mA
    rated forward current is 10mA
    and finally:
    "LED Trigger Current, Current Required to Latch Output" is max 5mA.

    i think the last one is that throws you off. you see electronic devices have wide tolerances. in a batch of MOC3012, there will be bunch of units with higher and lower sensitivity. the more sensitive ones will trigger output with smaller input current. less sensitive ones will do this with a bit more of forward current (If). but the datasheet tells that normaly MOC3012 will trigger at 3mA and no more than (max of) 5mA is needed to trigger any of them.

    you are welcome to use 15-20mA (you want to stay on middle ground). it is probably what most applications will use. 5mA will work too but if the current is bellow 5mA, only some units will work. you don't want to get close to 60mA as this is absolute maximum and borderline that device will tolerate. at or beyond that you are to expect damage to device.

    moc3010, 3011 and 3012 are likely same device made by same machine. then they get sorted and the more sensitive ones get label 3012, less sensitive ones get labeled 3010. printing label is last step in the manufacturing process before device is packaged. so if you get 30% or so units with a bit lower sensitivity, why throw it away? just sell it as another part. there is plenty of people who might choose it as suitable for their application (maybe because of more attractive price).
    same thing goes on in every industry. nobody throw away diamonds because they are not perfect clarity or are of smaller size, they will still sell even if the price is lower. chicken farms produce eggs which get sorted by size before packaging. they don't throw the eggs aways just because they are 5% smaller than the biggest ones. computer processors are all manufactured from same die then after they are packaged into familiar "chip" housings, they are tested. all working units are sold but ones that can run at higher speeds are sold for higher price. even if some of units show some flaws, affected parts are disabled and unit is still sold as lower grade (fewer cores, less cache...).
     
    Last edited: Sep 9, 2012
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