PFC buck converter

Hello Monil

The only Buck PFC controller in the TI portfolio is the UCC29910A. It was developed to produce a 84V output from universal line input of 85V to 264V and it is not possible to change the input/output RATIO. If you use this device you will have to scale the output accordingly and I estimate that Vo would be about 150V. This could then be fed into the LLC second stage.
Be aware that the BUCK PFC works well but has the disadvantage of being more susceptible to input surges (lightening strikes) than the more usual Flyback.
A 'normal' boost PFC will have an output voltage above 650V if you wish to operate it at 460Vac in.

I assume that you are using 50/60Hz inputs ?

Regards
Colin

Hello Monil

The input surge problem is still present in the boost topology BUT it is much less severe than in the buck topology. The reason is that there is a direct path from the input L/N connections to the bulk capacitor, this path is not present in the buck topology. In a surge event a lot of the surge energy goes to charging this bulk capacitor and this limits the voltage that the surge can generate in the system. You may still need some surge limiting components (Varistors for example) across the line but overall the boost topology has much better surge behaviour than the buck.

The output voltage of a boost PFC must be higher than its input voltage- At 460Vac in that means Vout > 650V - normally Vout is about 5% higher than this so about 680V in your case.

TI has a wide range of PFC controllers but at this power level - about 960W - the best choice is a single phase CCM boost controlled by a UCC28180  http://www.ti.com/lit/ds/symlink/ucc28180.pdf . Have a look at our reference design for a 900W PFC stage at http://www.ti.com/tool/TIDA-00443?keyMatch=tida-00443&tisearch=tidesigns   it's rated for 264Vac input so you would have to re-scale it for a 420V input but it would be a good starting place.

Regards

Colin