I'm trying to wrap my head around transient voltage protection and how to implement it when also trying to rectify a AC source to DC then step it down to 3.3V for a microcontroller. I understand that MOVs are great for high voltage and AC, where as Zener diodes are good for low power DC overvoltage protection.
My problem is that I have an 24V AC source which tends to be rather noisy and can spike due to solenoids and motors sharing the same rail. This is unfortunately out of my control. Obviously, surge protection is required, but how to implement it escapes me. I haven't been able to measure how high these surges get but I assume they are higher then the 40V max of the LM2596.
My current thinking, as illustrated by the diagram, is to take the 24V AC in then have a MOV to take any major spikes out. Once this is done then rectify the AC current to DC and have a second transient voltage suppressor in the form of a Zener diode. This diode has a reverse voltage of 39V which is lower then the max input of the LM2596 which is 40V. I have read that I might need to add a resistor to this Zener to reduce the load, but what load would be on the diode in a surge event? I know my max load on the 3.3V side of the regulator is 1A, however nominally around 400mA.
My real question is then, is my thinking correct or have I miss understood how to protect the circuit? If so, what do I need to look at/change to achieve my goal?