500V common mode voltage and current monitor circuit diagram

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Overview:
Circuit Function and Advantages The current in the circuit monitoring system shown in Figure 1 can operate at up to +500 V of positive high common mode DC voltage with an error of less than 0.2%. The load current is passed 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.

Figure 1: High Common Mode Voltage and Current Monitor (all connections and decoupling not shown)

When used with an external PNP transistor, the AD8212 can accurately amplify small differential input voltages with a positive high common-mode voltage greater than 500 V.

Galvanic isolation is provided by the four-channel isolator ADuM5402. This is not only to provide protection, but also to isolate downstream circuits from high common-mode voltages. In addition to isolating the output data, the digital isolator ADuM5402 provides +3.3 V isolated power to the circuit.

The measurement results of the AD7171 are provided in digital form via a simple two-wire SPI-compatible serial interface.

This device combination enables an accurate positive high voltage rail current sensing solution with low component count, low cost, and low power consumption.
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