Hello,
I have made a flyback design with a UCC28811. The design is based on the SLVR574 reference design. The MOSFET controlled by the UCC28811 directly charges the transformer.
I added a dimming option to the design. The output current is regulated by an external 1-10V signal. This means that there are many different operating values. The output current can vary from 5-100% and the input voltage can be 100-240VAC.
The problem I am having is that I cannot seem to get the feedback loop stable under all conditions. Either it will oscillate, or there wil be overshoot at startup.
Is there a way to calculate the correct using rule of thumb calculations? There is actually two compensations in the loop. One is at the UCC28811 and the other is at the secondary side. I would think that one of the compensations should set the total loop speed where the other is mainly proportional. But which one needs to do what?