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I am working on a project in which I am required to sense current in micro ampere range from a 2 kV power supply. Here is a link of an article which I am referring.

https://www.analog.com/en/technical-articles/optocoupler-extends-high-side-current-sensor-1kv.html

High Voltage micro current sensing

While searching on Google I found that in high side current sensing the common mode voltage range should include the supply voltage (that i am providing to the load) within its range. The common mode voltage range of the MAX4172 IC used in the circuit is +2 to +32 V. Will it support my 2 kV supply. If not, could anyone please suggest an alternative solution to this problem.

*Also I am confused about the 9 V battery and 1000 V. Why their positive side is connected to the same node?

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  • \$\begingroup\$ What is you goal - overcurrent protection or precise measurement? Defining the exact current range would help too. \$\endgroup\$
    – Todor Simeonov
    May 27, 2017 at 10:11
  • \$\begingroup\$ My goal is precise measurement of current within a range of 0 to 830 micro amps \$\endgroup\$
    – Sabheeh Ali
    May 28, 2017 at 6:53

1 Answer 1

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The common mode range of the MAX4172 is measured with respect to its supply. As you see, it is powered by a floating 9v battery, which provides rails of Vin and Vin-9v.

If you duplicate the circuit you have presented, then it will have a rail of 2kV, and a ground of 1993V. This puts the 2kV input's common mode of 9v squarely in the 2V to 32V range required.

If you don't want to use a 9v battery, then you will need to provide a similar high-side supply arrangement possibly from your input voltage, or some other isolated converter. There are other ways, depending on the duty cycle of your supply.

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  • \$\begingroup\$ i am confused about the 9v battery and 1000v. Why their positive side is connected to the same node? \$\endgroup\$
    – Sabheeh Ali
    May 28, 2017 at 6:59
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    \$\begingroup\$ Consider the 4172 rails. If batt-ve went to 1000+ve, then you have 1000 and 1009, and the sense resistor is outside the CMR. If batt-ve went to GND, then you have 0 and 9, and the sense reisstoor is outside the CMR. If batt+ve went to GND, then you have -9 and 0v, and the sense resistor is outside the CMR. Only by connectign batt+ve to 1000+ does the sense reistor end up with the CMR of the 4172. \$\endgroup\$
    – Neil_UK
    May 28, 2017 at 7:18

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