In EV electronics, the Electrical Storage System (ESS) is typically isolated from the lower voltage system for lighting and accessories. In many installations this creates a need for isolated signal conditioning for ESS instrumentation when that instrumentation is powered by the low voltage system.  I found an off the shelf “Demo Board” for the Analog Devices AD7400A Isolated Sigma-Delta Modulator that made it quick and easy to build up an Isolator/Scaler module for monitoring the ESS with a 0-500V range.  The output is compatible with the 3.3v range of the custom control module on a prototype vehicle that is currently under test.

The HV input and 12v power source are fused for protection. The HV input is divided to yield a 0-320mv range at the input of the AD7400A. The output produces a fully isolated and scaled voltage of 1.65 to 3.3v that is linear (difficult to achieve with more common optical isolator circuits). The output is essentially an isolated and 5X amplified version of the 0 to 320mv input with a floor of 1.65v This equates to an ~1.65v range on the output (0.320 X 5).

For more detail on how the AD7400A and support circuits work on the Demo Board, see Analog Devices Circuit Note # CN0185.