Should I use an optocoupler?

Discussion in 'General Electronics Chat' started by drkblog, Jan 9, 2013.

  1. drkblog

    Thread Starter Member

    Oct 4, 2012
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    0
    Let's say I have a CMOS (5V) output connected through a resistor to the base pin of a transistor, working as a switch. And collector and emitter pins are working with 12V.

    This works but, should I use an optocoupler here?
     
  2. Meixner

    Member

    Sep 26, 2011
    116
    21
    No there is no need for one, The transistor and base resistor provide isolation between the 5V and the 12V.
     
  3. BReeves

    Member

    Nov 24, 2012
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    64
    I wouldn't.. Only time I use an optocouplers is if I'm going to be triggering a circuit from something far away like a sensor 50 or more feet from the circuit or in switching high voltage (AC line).
     
  4. JMac3108

    Active Member

    Aug 16, 2010
    349
    66
    No opto is needed. But make sure the base current into your transistor is withing the capability of your CMOS gate. If not, you might need a darlington transistor.
     
  5. drkblog

    Thread Starter Member

    Oct 4, 2012
    109
    0
    Thank you all!
     
  6. SPQR

    Member

    Nov 4, 2011
    379
    48
    This is very interesting.
    Are you using the coupler to "drive" a long wire?
    Can they "soup up" the output of a standard CMOS/TTL chip?
     
  7. BReeves

    Member

    Nov 24, 2012
    412
    64
    Other way around.. Usually have a 12 volt signal feeding the optoisolator from some distance. This isolates the electronics from the possibility of surges on the cable and adds a little noise immunity.
     
  8. SPQR

    Member

    Nov 4, 2011
    379
    48
    Ok, so it's not a "driver" but rather a pure "isolator".
    Thanks!
     
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