An accurate current monitor circuit diagram

The figure below shows an accurate current monitor circuit diagram. This circuit can operate at positive high common-mode DC voltages up to +500 V with an error of less than 0.2%. The load current passes through a shunt resistor external to the circuit. The shunt resistor value should be chosen so that the shunt voltage is approximately 500 mV at maximum load current.

When used with external PNP transistors, the AD8212 can accurately amplify small differential input voltages with high positive common-mode voltages greater than 500 V. Galvanic isolation is provided by the ADuM5402 quad-channel isolator. This is not only for protection, but also to isolate downstream circuitry from high common-mode voltages. In addition to isolating the output data, the ADuM5402 digital isolator provides +3.3 V isolated power to the circuit. AD7171 measurement results are provided as digital codes through a simple two-wire SPI-compatible serial interface. This combination of devices enables an accurate positive high-voltage supply rail current sensing solution with low component count, low cost, and low power consumption.