I am designing a circuit that will gate single phase 120V AC through back-to-back N-channel MOSFETs connected as shown below. When passing AC, one MOSFET is on and the body diode in the other is forward biased. The active MOSFET changes for the positive and negative half cycles. When blocking AC, both MOSFETs are off.
I am considering putting transient voltage suppression across the drains on the MOSFETs to protect them from breakdown caused by high voltage spikes. I would use 200V breakdown MOSFETs with a 150V breakdown TVS.
Is using a TVS across the MOSFETs a reasonable design decision?
Are the above component voltages reasonable for a 120V circuit?
Is there any reliability/survivability advantage to using MOSFETs with a drain-source breakdown voltage significantly higher than the TVS breakdown voltage, versus just slightly higher?