selection of opamp for high side shunt

Discussion in 'General Electronics Chat' started by ak52, May 11, 2016.

  1. ak52

    Thread Starter Member

    Oct 15, 2014
    145
    4
    Hello Everyone,
    I am trying to implement a shunt resistor on the high side.
    I am finding it difficult to select the differential amplifier/opamp which amplifies the the voltage across the shunt.
    Here are my requirements.
    Input voltage : 150v DC.
    Range of current to be measured : 0 to 50A
    Vcc of opamp cannot be more than 5v

    I searched many places but my main issue is the Commom mode input voltage range,
    I couldn't find any opamp that can handle the high voltage.
    If anybody knows of such an amplifier please share the part number.
    Many thanks,
    AK
     
  2. AnalogKid

    Distinguished Member

    Aug 1, 2013
    4,546
    1,252
    Linear Tech makes special purpose diff amps for this application. They might be under "power management" on their website (instead of "instrumentation amps"). A common trick is to attenuate the two signals by something like 50:1 so the DC value falls within the diff amp CM range, the crank up the diff amp gain to get the current signal back without the DC.

    Another methoc is a transconductance amp that floats on the high DC voltage with an open collector PNP output stage. A scaling resistor to GND sets the output voltage / input current transfer function.

    ak
     
  3. crutschow

    Expert

    Mar 14, 2008
    13,056
    3,245
    Google high voltage difference amplifier.
     
  4. Lestraveled

    Well-Known Member

    May 19, 2014
    1,957
    1,215
    The T.I. INA138 or INA168 are high side current sensors and there is an app note that shows how to use them at very high input voltages.
     
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