UCC28180: UCC28180 Bulk cap issue

Hello Hsu cheng,
Do you really mean the L4981A since there is no L4891A ?
Yes you can use the UCC28180 instead of the L4981A since both parts are fixed frequency average current CCM type pfc controllers.
If you operate the UCC28180 at the same switching frequency then you will be able to use the same output capacitance.

Regards
John

Hello Hsu

I couldn't find a data sheet or any information on the L4891A device

Given that the L4891A and the UCC28180 are both single phase CCM Boost PFC controllers and are operating at the same switching frequency then the output capacitor ripple will be the same.

The most important factors governing the low frequency (100Hz/120Hz) output ripple voltage on a boost PFC

The amount of capacitance - more capacitance gives less ripple voltage
The line frequency - you will have more voltage ripple when running off 50Hz than you will when running off 60Hz
The load current - higher load currents give higher voltage ripple

There will also be a high frequency current in the output capacitor but this won't cause a significant voltage ripple because the capacitor impedance will be lower at the switching frequency than at line frequency. The high frequency current is a function of the switching frequency, the PFC inductor, Input Voltage, Output voltage and load current.

Regards
Colin

Hello Hsu cheng,
Please open another post for this new question.
I am marking this post as closed since you have received all relevant information for your initial issue.
Regards
John