Isolation using optocoupler

Discussion in 'General Electronics Chat' started by happyfpga, Oct 4, 2008.

  1. happyfpga

    Thread Starter New Member

    Oct 4, 2008
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    0
    Hi, I have a design transfering 8 bit parallel data between two I/O ports of MCUs. The data path needs to be able of withstanding 30+Vdc, therefore I need isolation at both TX and RX sides. I plan to use two optocouplers for each data line, one optocoupler's output connects to another optocoupler's input, i.e. the 2nd optocoupler's diode Anode will be one end of the data path, the 1st optocoupler emitter will be another end of the data path.

    Is there any potential problem or better solution? I appreciate your help!
     
  2. hgmjr

    Moderator

    Jan 28, 2005
    9,030
    214
    Have you taken a first cut at the isolation interface of the circuit you need? If so, can you post it so that we can see how to improve what you have so far?

    hgmjr
     
  3. happyfpga

    Thread Starter New Member

    Oct 4, 2008
    7
    0
    hgmjr, thanks for the post. Here is the schematic. When there is no data transferring between two ports (another working mode), the data line will have +35VDC from another device.

    I have not picked up the specific optocoupler yet. What I am currently concern is the Vec of the 1st optocoupler will be very large (35-12). The current through the 2nd diode will be very large too if R2 is selected for normal working mode.

    Any suggestion? Thanks a lot
     
  4. beenthere

    Retired Moderator

    Apr 20, 2004
    15,815
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    Why must that line have 35 volts placed on it?
     
  5. happyfpga

    Thread Starter New Member

    Oct 4, 2008
    7
    0
    Ok, I need to clarify the suitation more, there are two working modes required.

    1. For working mode 1, I need to test the connection of 8 lines to make sure there is no open on each line and no short between each other. So I use two I/O ports of MCU, one for TX transmiting HEX data to another RX port for comparing. Any better idea on it? Simple LED circuit can not detect short.

    2. With mode 2, these 8 lines will be used to transmit 35VDC and some logic signals.

    I know the application case is strange, but it is actaully required. Thanks.
     
  6. beenthere

    Retired Moderator

    Apr 20, 2004
    15,815
    282
    There must be more than just the one line involved. We might be able to suggest some solution with a full schematic posted. Otherwise, we're just making guesses.
     
  7. happyfpga

    Thread Starter New Member

    Oct 4, 2008
    7
    0
    All ciruits for other 7 data lines are exactly same as the attached one.

    I got a suggestion from other people that replace the 1st optocoupler with a line driver. This way looks like workable.

    Anyway, thanks for the attention! I like this forum.
     
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