Optoisolator?

Discussion in 'General Electronics Chat' started by RRITESH KAKKAR, Jul 29, 2010.

  1. RRITESH KAKKAR

    Thread Starter Senior Member

    Jun 29, 2010
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    Plz can u tell me what is optisolator....?
     
  2. beenthere

    Retired Moderator

    Apr 20, 2004
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  3. Papabravo

    Expert

    Feb 24, 2006
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    It is an LED and a Photo-transistor. When the LED is illuminated the photo-transistor goes from cutoff to saturation. When the LED is dark the photo-transistor returns to cutoff. The photo-transistor can be configured as a common emitter switch or as an emitter follower depending on weather you want the output to be inverting or non-inverting. The chief reason for using one is to provide isolation between the input circuit and the output circuit.

    Does that answer your question?
     
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  4. mikeysela

    Member

    Jul 24, 2010
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    have a look at phot-traics too. they can isolate DC lines from AC lines and seem to be quite useful
     
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  5. Nik

    Well-Known Member

    May 20, 2006
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    "It is an LED and a Photo-transistor"

    It may be an LED driving a photo-diode with one or two transistor stages to follow. These tend to be faster than photo-transitors. 6n136 & 6n139 are classic examples, the latter a de-facto standard for MIDI interfaces.

    One gotcha is the Current Transfer Ratio (CTR) from LED to photo-diode is typically ~0.0015 (~0.15%) meaning it takes a lot of amplification. You can trade speed for bandwidth by using a resistor to draw down open base if available.

    FWIW, Avago (TM) have a spice model for the 6n136. There's currently nothing available for 6n139.
     
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  6. bertus

    Administrator

    Apr 5, 2008
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