We are using LNK420 in 75W design based in DER-291 single section. see schematic. After some days of working, one unit has a catastrophic failure, the IC has burned. The entire driver is polyurethane potted, but after disassembling we see the ic exploded. We see that many associated components are apparently well, lets say MOV RV1 ( a 275V, 20mm) , C9 470nF x 630V polipropilene, c13 100nF x 630V polipropilene, C14 10uF 450V, diodes D5, D7, VR1, bridge rectifier, D3, D6, D8, R19, C 15, C16. There are no evidence of PCB short circuits
Many times during bench tests, we had short circuits at output and open circuit and entirely design works very well
A little difference is that we need to put a 100nf connected at V pin and source pin to dont have shift in output current after potting.
We think the layout of PCB is good, based in layout of DER-291
We have many drivers working very well, but we are afraid and would like to know what happened. We are using the driver in a industrial application, and probably the failure happens at night. Next week we will monitor the power line to see if we have some over voltage, but the MOV rated to 275V was intact.
Could you please tell-us something, or some ideas about this failure ?