Hi Tiers
i use the UCC256302 in my AC/DC project, there are some waveform as below(Figure 1):
Yellow channel is the current of the resonant inductor
Blue channel is the FB voltage.
Green channel is the output voltage
Q1: Why does the current of resonant inductor have such a big spike? What causes possibly, how to solve?
Figure 1
Q2(Figure 2):
FB voltage is not stable in no load mode. Is there any solution to solve it, thx
Figure 2
Hello Jack,
Oscillation could be due loop stability and opto coupler TL431 feedback circuit is not setup correctly.
The following application brief gives some design guide lines to help make your design more stable.
You can find it at this web address 
There is also and excel software design tool that you can use to check your design. You can find it at this web address.
There is also an evaluation module that you can order and evaluate to help with your design. It can be found at the following web address.
Regards,
