Standby relay board
This device needs to power two loads from two universal input (85-265V) sources with a standby capability where if one source fails, the other immediately takes over the load with minimal disruption.
Having two distinct sources meant that isolation was key. The power for the relay coils was drawn from both the lines such that either of the lines could power the entire system. Non-isolated topology was used to keep the footprint small.
Analog logic was developed for this which would ensure that change over happened at the right time without any phase-neutral or phase to phase short. The logic had delay were added to ensure that safe operation.