problem of linear optocoupler

Discussion in 'General Electronics Chat' started by shoka, Jun 11, 2010.

  1. shoka

    Thread Starter Active Member

    Mar 12, 2009
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    hello,
    i want to measure a voltage of 700 v max and feed it to the ADC of microcontroller so , i want to isolate the circuit with a linear optocoupler.
    i want to use LIA120 but i can't understand how to design the circuit?
    if any one help me to design that one or recommend another type of linear optocoupler which he had used before

    thanks in advance
     
  2. beenthere

    Retired Moderator

    Apr 20, 2004
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  3. shoka

    Thread Starter Active Member

    Mar 12, 2009
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    thanks beenthere,
    but the input diffrential voltage is very small about 200 mV to guarantee linearity.
    do u think it'll be accurate to measure 700 volt. and it malny designed for sensing current
    thanks again for your reply
     
  4. t_n_k

    AAC Fanatic!

    Mar 6, 2009
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    Presumably you've also considered a Hall Effect voltage transducer. Simple & robust - but may not meet your economic constraints, if any.
     
  5. hgmjr

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    Jan 28, 2005
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    Another technique for achieveing opto-isolation is to use a Voltage-to-Frequency converter the output of which you pass through an opto-isolator. The output of the opto-isolator can then be fed to a Frequency-to-Voltage converter to recover a facsimile of the original DC signal.

    hgmjr
     
  6. shoka

    Thread Starter Active Member

    Mar 12, 2009
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    thanks t_n_k
    do u recommend me certain model ?
    thanks hgmjr
    does Voltage-to-Frequency deal with the harmonics of the signal and also can i isolate ac using it ?
     
  7. hgmjr

    Moderator

    Jan 28, 2005
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    What frequency components do you expect to encounter in the 700 volt AC signal?

    Yes opto-isolation is achievable. The V-to-F feeds a corresponding F-to-V. These two stages are separated by an opto-isolator. It is the opto-isolator that provides the isolation.

    Of course to accomplish full isolation, the v-to-f stage will need its own independent power source.

    hgmjr
     
  8. R!f@@

    AAC Fanatic!

    Apr 2, 2009
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    An observation.....

    700V ....High voltage.........where are we?
    do you know the OP?
     
  9. hgmjr

    Moderator

    Jan 28, 2005
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    Greetings shoka,

    Can you provide us with more details about what you are trying to accomplish with this measurement scheme? 700Vac is a very high voltage to be working around.

    hgmjr
     
  10. shoka

    Thread Starter Active Member

    Mar 12, 2009
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    i have an induction generator which is driven by motor emulated wind turbine , the voltage out of the the generator is rectifier ans then inverted to give 380v, 50 Hz as the induction generator works with variable speed (means variable voltage and variable frequency) i need the linear optocoupler for isolation purposes
     
  11. retched

    AAC Fanatic!

    Dec 5, 2009
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    You are trying to pass 380v through an opto?

    It will be a VERY VERY large custom made opto. (house size)

    Why use optical isolation? How about a transformer?
     
  12. bertus

    Administrator

    Apr 5, 2008
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    Hello,

    You could also take a look at an isolation amplifier.
    These have an input of ± 10 Volts so a 1:100 attenuator will give you a ± 1000 Volts range.

    Bertus
     
  13. t_n_k

    AAC Fanatic!

    Mar 6, 2009
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    Try Google with the search term "700V voltage transducer" and you'll get a few hits.
     
  14. hgmjr

    Moderator

    Jan 28, 2005
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    Perhaps the easiest and the safest way to deal with the 700Vac source is to use a stepdown transformer. A 100:1 stepdown would get you in the ballpark and then all you would need is a resistor voltage divider to get you the rest of the way to your target voltage.

    hgmjr
     
  15. shoka

    Thread Starter Active Member

    Mar 12, 2009
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    plz any one tell me how to design a circuit for hcnr200 linear optocoupler ??

    thanks in adance
     
  16. retched

    AAC Fanatic!

    Dec 5, 2009
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    Thats not enough information.

    Do you want a circuit for a hcnr200 linear opto that handles 700 volts?

    Here is the datasheet, it has many circuits using the hcnr200:
    http://www.datasheetcatalog.org/datasheet/hp/HCNR200.pdf

    READ the datasheet to be sure you are using the opto within its operational specs.
     
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