Tool/software:
Hello,
I want to replace a FAN6602 with a UCC287502 on a 300W 24Vdc flyback power supply. The primary voltage is supplied by a PFC, and the controller supply voltage is provided by another small auxiliary flyback. I've done the first tests and the results are pretty good: the regulation stability is correct whatever the load, and there's no overshoot at start-up.
However, I'm having problems detecting overtemperature on the FLT input. It seems to activate between 15 and 20°C below the theoretical threshold. After some investigation, I noticed low-frequency ripples on this input. I increased the filtering (C50 to 100nF), which lowered the amplitude of the ripple. 100nF seems to be the limit, beyond which the power supply won't start... I haven't seen any similar instability on the other inputs of the circuit. I enclose part of the schematic and a view of the voltage on FLT.
Do you have any idea of the origin of this problem and how to solve it?
Thanks in advance
Thierry
