On my board there is a 4-pin connector as follow:
- +24V DC (up to 6A)
On the system there is no real earth, because there are no metallic parts (chassis, case, structure, etc...).
I'm going to protect the board as follow:
- SM712 between I/O lines and the "virtual" earth (see below)
- unidirectional TVS with 24V stand-off voltage between power and "virtual" earth
- two Schottky in antiparallel between GND and "virtual" earth
The "virtual" earth is nothing but a large PCB trace that runs along the board edge (where the connectors are placed) and is connected to the actual GND at the power input connector through an inductor.
The idea is to provide an easier way for the spike's current to flow instead of enter inside board.
Here a schematic that summarize:
What do you think about?