Understanding L4981A Application note.

Hello everybody,

                              I am trying to understand the calculations and derivations of L4981A average current mode PFC controller circuits from the application note, AN628 : DESIGNING A HIGH POWER FACTOR SWITCHING PREREGULATOR WITH THE L4981 CONTINUOUS MODE.

1) How was rms switch current found from O/P power and Peak inductor voltage?

2) Similarly how to find the RMS diode current?

How do the factors

3) The AC component of diode current flows into the output capacitor so

How to derive 

Ic?

4) RMS twice capacitor line frequency capacitor current

What is the difference between Total RMS-Capcitor Current and RMS twice line frequency capacitor current?

Does it refer to output bulk capacitor or input capacitor?

Why is 2f twice line frequency capacitor current important?

5) RMS high frequency capacitor current 

Does this refer to input capacitor or output bulk capacitor?

Please answer!

Thank you.