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  1. #16
    Prolific Poster charliecoultas's Avatar
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    Default Re: Current transformer AC - DC

    If the input goes negative, which it does, then I'm afraid you will need a neg rail fo the op-amp.
    Glad it seems to be coming together well.

    Charlie

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    Prolific Poster joesaliba's Avatar
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    Default Re: Current transformer AC - DC

    Quote Originally Posted by charliecoultas View Post
    If the input goes negative, which it does, then I'm afraid you will need a neg rail fo the op-amp.
    Even if I am sampling only the positive side?
    Regards

    Joseph

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    Fanatical Contributor top204's Avatar
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    Default Re: Current transformer AC - DC

    The circuit's actions means the signal has a DC offset, so the middle of the signal is 2.5 Volts, the low is 0 Volts and the high is 5 Volts, so a standard ADC will work perfectly.

    I uses to use a similar circuit to get the negative readings from an LM35 temperature gauge many years ago, where it had a DC offset for 0 degrees.

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    Default Re: Current transformer AC - DC

    Quote Originally Posted by joesaliba View Post
    Even if I am sampling only the positive side?
    It doesn't need an op-amp although you can use one. A comparator is quite adequate and many PICs have them for just such a job. An op-amp or comparator than has a common mode voltage than includes ground should be ok without the need for a -ve supply rail.

    Cheers,
    David

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    Default Re: Current transformer AC - DC

    Sorry - that was supposed to read -
    An op-amp or comparator that has a common mode voltage that includes ground should be ok without the need for a -ve supply rail. (than - that)
    Any comparator that uses PNP inputs like all the LM339 variants will have a common mode that includes ground and the comparators in the PCs are very similar in this respect.

    David

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    Prolific Poster joesaliba's Avatar
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    Default Re: Current transformer AC - DC

    Thanks all for your time and feedback. Will use just an ADC for now as results are very stable.
    Regards

    Joseph

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