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It's not really different from a boost PFC; the control scheme is pretty much the same. But a buck PFC will always perform worse than a boost PFC in almost every way. Why are you interested in a buck PFC?
I need to have regulated 230VDC for the half bridge stage for the 70W electronic ballast as a 70W HID lamp load but at the same time need high PF and THD < 10%. Currently I used the Boost PFC to get the regulated o/p 400VDC but the problem again I need to use some buck converter to achieve 230VDC .
So instead of that I can go for buck PFC converter. Please advice
I'm not sure if it's even possible to get 10% THD with a buck with that output voltage. Simulation would tell easily... But if possible, I would try to use a topology using a transformer, like a flyback, forward, or pushpull. I've seen Sepic used for PFC as well. Then you won't have a problem with dead conduction angle on the input and you can get good THD.
Sorry if it sounds like I'm dodging the question, but buck PFCs are really sort of awful so you should make sure you have no other choice.