I would to identify the cause of a problem affecting a faulty board based on an existing design based on the TOP270EG (see attached schematic).
Characteristics of the supply: mains ~240V, output ~27.5V 3A
- applying the full load causes an overheating of the 200V surge suppressor D7.
- holding the full load results in braking the following components: D7, R10,R108 and U1
- the switching frequency on the faulty board seems to be lower than on an healthy board (~58KHz vs ~122KHz)
- the drain of the TOPSWITCH is driven for longer on the faulty board (~2.5us vs 1.5us)
Could you help me to identify why the TOPSWITCH is not operating at the expected frequency?
Thanks for your support