I have designed 30W led driver using DER 286 as ref.
I have followed fig 4 not fig 3 in DER 286.
everything works fine for 20 min. no heating stable voltage & current at output.
After 20 min latch activates for unknown reason.
I have checked layout many times and it mostly resembles the pcb given in der286.
If I check the the voltage at the base of Q2 it rises very slowly and when it reaches 600 mv latch activets.
Voltage across Vr3 is also within limit.
can you tell me where to look for such kind of fault.