N channel MOSFET (part NO STP28N65M2)

[MShar.0]

HI, I am using ST mosfet (part NO STP28N65M2) in High input AC voltage limiting circuit (as per AN2652) where Q2 MOSFET is STP28N65M2. and D3 diode is 6.8V zener.

The product was operative from 2 month. and After that i found that MOSFET was open.

on Debugging it, i found that Gate and source are showing 1V in multimeter ( on fresh sample it is open, probabbly one of the protection diode between gate and source is short)

I could not able to figure the root cause why this has happe.

Can you please let me know the reason for Gate to source diode getting short.

Regards

Manish