Hello,
I am using UCC28600 for a flyback power supply whose main output is on the primary side of isolation barrier, so instead of opto coupler and TL431 I am using TL431 alone for regulation. Inductors and component values I have applied are exactly what the design spreadsheet generates. Current sense pin 3 is about 500mv Pk, but all my output voltages are below what I expect, the output voltage varies from 13.5 to 14.5 volts (for target of 15V) by changing input AC voltage, but when I check the reference voltage of the TL431, it is below 2.5 V (around 2.1-2.2v) so it seems something is regulating the output voltage at a lower level than the TL431 and as such my output voltage is lower than expected. my feedback voltage is around 1.6V on the entire range of input voltage and about 2.2V when the output is loaded to max and the frequency is about 60kHz. Any thought on what mechanism kicks in before output is regulated by voltage regulator?
Thanks
