I have designed a boost converter with a 400V output which uses a PFC IC For regulation, the IC measures the output via a potential divider which is fed into a pin on the IC
The IC is looking for approx 2.5V so with 400V output I use a divider with 3M and 19k
All is good in the world, very basic stuff
Now I am looking to protect the IC, I had a failure where I lost a ground and a voltage exceeding the 5V max was applied to the IC pin and the smoke was let out
To avoid this possibility I would like to clamp the maximum voltage to the pin and I thought lets drop a zener in there, in parallel with the 19k resistor so any misbehaviour will be clamped
When I actually sat down and thought about it I realised that 3M resistor is going to seriously limit the current and the zener wont be able to get past the knee point which typing this made me think it might not matter the voltage would still be limited. I dont want any regulation just protection
I plan on adding a TVS diode as well but thats just for spikes I dont think it can be expected to work with constant DC applied
Am I still ok to use a zener in this application?
Is there a better way?
Added schematic showing the zener in place, as you can see R2 and R8 come to approx 3M