Welcome @dvramgir, to the community!
Classic PFCs, such as those typically set up with the somewhat older L6562A, generally have a problem with light-load conditions, which can have many causes. However, it is not possible to say exactly what you need to change without knowing all the parameters of your system. However, you can use your favourite search engine to search for terms such as ‘pfc light-load eficiency’ to find possible solution scenarios.
Regards
/Peter
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