I am working on a high-side current sensor, where the high-side is around 3kV. I have come to the conclusion, with some help from you kind folks, that it is best that I float the majority of my circuit up at that 3kV level. However, I need to get the signal out to ground level, so that it can be input to a microcontroller. I am having a hard time finding any isolation devices who isolate at such a high working voltage, rather than transient voltage. Does anyone have any suggestions of such a device? I guess I also need an isolated DC/DC converter, that will let me power the 3kV floated circuit from a power supply at the ground level…I also am struggling to find such a thing.
Any help or suggestions would be greatly appreciated.
Thank you so much.
Best Answer
Specialty optoisolators that can handle 50KV working voltage are available off-the-shelf, if you don't mind doing a little more work to properly isolate the I2C signal:
Yeah, that's an optoisolator. That's what you need for 50 KV isolation.
Slightly lower isolation rating parts (10 KV) are also available for considerably less money:
Note that these are all discrete optoisolators. If you can switch to a SPI ADC, it would make the isolator considerably easier to design, though you can isolate I2C with discrete isolators:
Here is a whitepaper about I2C isolation topologies.
Depending on the I2C data-rates you want to achieve, it may be fairly involved.
Further follow-up:
Here is an excellent white-paper about safety concerns in power-supply designs.