In an embedded power supply using INN2604, sometimes we see a problem that seem related to the auto restart state machine that doesn't work well. The problem causes the damage of the electronic board because the INN2604 doesn't regulate the output voltage during the power up (the outputs voltage run up 10volt over the nominal value) and the auto restart state machine runs for an undefined time loop.
The power supply has three outputs voltage. The 5V and 12V on one winding of flyback transformer are cross regulated, the 17V on auxiliary winding is not regulated. At power up there isn't load on 12V, on 5V around 50mA, and on 17V around 20mA.
Attached you can find:
- An oscilloscope screenshot of 12V and 17V outputs during the problem.
- The circuit schematic of the power supply block.
This issue seems occur more often at low input line voltage (around 180Vac), could it be related to UV sensing?
A solution that seems mitigate the problem is to increase C85 (the capacitance of the feedback network) from 470pF to 10nF. Could it be related to the feedback regulation network?
Thank you in advance for support.