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AMC1100 input protection #3

Vladimir Naumenkov
Expert 2970 points
Other Parts Discussed in Thread: AMC1100

Dear Mr. Jose Duenas Cuellar!

Sorry for persistence.

Please see the attach. I’d like to use single supply of AMC1100. If current flows in I2  direction, then voltage at R2 may cause current via Shottky diode VD2, but  this is not essential, as microcontroller “knows” in which direction flows current (microcontroller monitors zero crossing of 230V AC) and performs the measurement, when current flows in I1 direction. Resistor R10 is needed for prevent VD3 from damage in the overcurrent moment.  I installed VD3 as the voltage at the R2 may be 30-40V at the overcurrent moment.    Will this circuit work? Please, answer why the resistors at the AMC1100 inputs must be no more 20 Ohm? What would happen, if they is 30-40 Ohm? We are satisfied with the measurement error of 20% at the input voltage 20 mV and error of 7 - 10% at the input voltage 200-250 mV.

TIA

Vladimir Naumenkov www.agat.by

Figure 7_07.04.2014.docx
  • 0
    TI__Genius 9975 points

    Hello Vladimir,

    Not a problem, your question is quite welcomed!

    I think the circuit you attached in this point will work to protect the AMC1100 provided the overcurrent is not excessive.

    The PTV3.9B seems to have enough margin although I would feel more comfortable if it had a bit larger reverse current capabilities.

    The value of the input resistors connected to the AMC1100 determine the time constant for charging the AMC1100 input sampling capacitor. The larger the series resistance is the longer it takes for the sampling capacitor to charge. We recommend using small resistances (20 ohm or less) to ensure the sampling capacitor has plenty of time to fully settle.


    If you can tolerate a large error in the current measurement, then it is OK to use larger than 20 ohm input resistors.

    Hope this helps.

    Best regards,

    Jose

  • 0 in reply to Jose Duenas
    Expert 2970 points

    Dear Mr. Jose Duenas Cuellar

    Thank you.  You have reported, that  "circuit you attached in this point will work to protect the AMC1100 provided the overcurrent is not excessive". Please, answer, what current value, in your opinion, is "excessive" for this circuit? 

    Sincerely

    Vladimir Naumenkov