UCC28781: Can UCC28781 support 200W application without PFC?

Hello Shaofeng,

Thank you for your interest in the UCC28781 ZVS-Flyback controller. 

I can say that is it not impossible but might be a challenge to deliver 200W with any flyback converter from 85V~264VAC.  Flybacks are normally chosen for low power off-line conversion up to ~150W, and 200W is "stretching" the capability.  The reason is that the peak switching currents at low bulk voltage become very high. 
Since the customer wishes a low-cost design, he will likely choose a lower-value bulk capacitance which means the lowest voltage of the bulk ripple may extend down to 50~70V.
Primary peak current (Ippk) may range up to 6~8Apk, for example.  By contrast, with PFC, Ippk can be <1Apk.  

While it is possible to design a 200W converter using UCC28781 without PFC, much of the anticipated cost savings may be expended on larger magnetics, semiconductors, and heatsinking, and larger EMI filter design.   It may be more beneficial to consider a forward-mode approach for 200W without PFC.  The UCC2897A active-clamp forward mode controller may be of interest.

Regards,

Ulrich