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Basics of using the isolating transformer

  1. Sep 18, 2008 #1
    Hello, I have a differential signal going into an instrumentation amplifier (AD620).
    I would like to employ galvanic isolation on the inputs of AD620.
    Would anyone be so kind and tell me how it shall be wired?
    I dont know much about signal isolation. Shall 1:1 or 1:1:1 transformer be used?
    Can I also employ transils for protection - where to place them?

    Thanks in advance,
    regards Meereck
  2. jcsd
  3. Sep 18, 2008 #2


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    Science Advisor
    Gold Member

    We need to know a little more about what the input signal looks like. What's it amplitude and frequency, etc.
  4. Sep 19, 2008 #3
    hello, differentially, it is basically a sine wave in the range between 50-100kHz
    Amplitude about 0.5 Volts. I use AD620 for amplifying the signal.
    thanks, M.
    Last edited: Sep 19, 2008
  5. Sep 19, 2008 #4


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    Staff: Mentor

    50Hz-100kHz, or 50kHz-100kHz? It makes a big difference. If b), then you can use a 1:1 transformer designed to operate in that frequency band. If a), then you will not be able to use a transformer for such a wide range of frequencies. Instead, you would probably be better off isolating the full input amp & ADC circuit, and optically communicating with the ADC to get the data.
  6. Sep 19, 2008 #5
    How about a linear optoisolator?
  7. Sep 19, 2008 #6


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    Staff: Mentor

    Optos aren't linear, generally aren't used for analog coupling. Digitizing first and sending the digital date through an opto would be fairly common.

    There were some linear optos a while back (maybe from Linear Technology?), but I don't think they found any volume applications. Pretty pricey chips, as I recall.
  8. Sep 19, 2008 #7
    Agilent make some.

    http://dev.emcelettronica.com/voltage-conversions-galvanic-isolation [Broken]

    3.7 Euros in France..

    Last edited by a moderator: May 3, 2017
  9. Sep 20, 2008 #8
    thanks guys for ideas,
    the frequency will be 50kHz-100kHz.
    I read something about using 1:1:1 transformer for differential signals. Does it make any difference?
    Should some decoupling capacitors be used?
    have a nice weekend.
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