I have a PCB layout that I need to modify in order to protect the mosfet from a transient voltage when the user connects the power supply. Occasionally the mosfet gets damaged due to transient voltages. Will I be able to get away by just using a TVS diode connected from Source to Gate and without using a resistor on the Gate? The gate is directly connected to a via on the board and I cant mod it that easily.
simulate this circuit – Schematic created using CircuitLab
I am not sure that 1N4733 is fast enough to protect the MOSFET. I wasn't able to find any figures regarding it's speed - so it's probably not tested nor controlled. These transients are in nanosecond range - and it's really hard to do anything with them, other than have a resistor in series.
One possibility in current circuit to keep MOSFET safer without resistor is to pick part with higher Vgs in the same package, it should be at least double source voltage without resistor : signal reflection doubles voltage, parasitic inductance can drive it even higher.
You can dampen the transients of connecting up the power source by adding a large capacitor in parallel with the power input. A large capacitor on the input will counter-act the inductive spike you may get when connecting power -- especially connecting long leads. If you want belt and suspenders, add a 220 uF 50V aluminum electrolytic, a 47 uF 35V tantalum and a 10 uF 35V ceramic. (Although I'm totally just guessing here -- for real engineering, you need to make measurements and run the numbers.)
Additionally, a very fast TVS intended for ESD protection will quite possibly protect these devices. Just make sure you have sufficient leeway -- a TVS I'm currently using is for example rated for a 17V normal operating/standoff voltage, and have a max clamping voltage of 27V.
Aluminum electrolytic + TVS is supposed to be "good protection" from what I've learned.
