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Optocoupler puzzle

Discussion in 'Electronic Basics' started by Randy Day, Nov 13, 2008.

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  1. Randy Day

    Randy Day Guest

    I dug an old 4N35 out of the junk box, and
    wired it up two ways (below).

    I put ~150us pulses on pin 2, and expected
    to see something similar at the output. What
    I get is a scope waveform that slowly ramps
    to about 2v over the 150us, before ramping
    back to rest in about 20us.

    I tried changing the 1k to 500ohm, and the
    10k to 1k, but it still showed a ramp.

    What the heck am I seeing, and why?

    +5v +5v
    | |
    .-. .-.
    | |1k | |10k
    | | | |
    '-' '-'
    | .-------. |
    |--|1 6|-- |
    | | |
    in --|2 5|----+-- out
    | |
    --|3 4|-----|
    | | |
    '-------' gnd

    +5v +5v
    | |
    .-. |
    | |1k |
    | | |
    '-' |
    | .-------. |
    |--|1 6|-- |
    | | |
    in --|2 5|----|
    | |
    --|3 4|----+-- out
    | | .-.
    '-------' | |10k
    | |
    '-'
    |gnd
    (created by AACircuit v1.28.6 beta 04/19/05 www.tech-
    chat.de)
     
  2. ehsjr

    ehsjr Guest

    Try this:
    Ground pins 2 and 4. Input to pin 1 through your resistor,
    and output from pin 5, with 100 ohms from pin 5 to +5V.

    Ed
     
  3. James Beck

    James Beck Guest

    Change the 10K to a 47K (or a 100K) and see what happens.
     
  4. Randy Day

    Randy Day Guest

    Tried your suggestion, and it helped a bit.
    What really made a difference was lowering
    the 1k to 200 ohms.

    Remind me not to use the 4N35 for any
    low-power projects. ;)

    Thanks, Ed.
     
  5. Ross Herbert

    Ross Herbert Guest

    :I dug an old 4N35 out of the junk box, and
    :wired it up two ways (below).
    :
    :I put ~150us pulses on pin 2, and expected
    :to see something similar at the output. What
    :I get is a scope waveform that slowly ramps
    :to about 2v over the 150us, before ramping
    :back to rest in about 20us.
    :
    :I tried changing the 1k to 500ohm, and the
    :10k to 1k, but it still showed a ramp.
    :
    :What the heck am I seeing, and why?
    :
    : +5v +5v
    : | |
    : .-. .-.
    : | |1k | |10k
    : | | | |
    : '-' '-'
    : | .-------. |
    : |--|1 6|-- |
    : | | |
    : in --|2 5|----+-- out
    : | |
    : --|3 4|-----|
    : | | |
    : '-------' gnd
    :
    : +5v +5v
    : | |
    : .-. |
    : | |1k |
    : | | |
    : '-' |
    : | .-------. |
    : |--|1 6|-- |
    : | | |
    : in --|2 5|----|
    : | |
    : --|3 4|----+-- out
    : | | .-.
    : '-------' | |10k
    : | |
    : '-'
    : |gnd
    :(created by AACircuit v1.28.6 beta 04/19/05 www.tech-
    :chat.de)


    First, try reading the data sheet.
    http://www.datasheetcatalog.org/datasheet2/1/03tgz200g5x4946jka7isojyj5wy.pdf
     
  6. Jasen Betts

    Jasen Betts Guest

    yeah I can see (with 20/20 hindsight) that it would.
    did you think to check the datasheet?
    that's what the datasheet is for
     
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