INPUT DC Link Capacitor of Flyback Converter

[khatus]

Hello guys , currently I am searching for documents to design a smps using flyback converter. I have found a document which uses the following formula to calculate the INPUT DC Link Capacitor of Flyback Converter. Here is the picture of their design



And here is the formula they used





My question is from where they derive the formula??

[T3sl4co1l]

The diagram basically gives it away... do some geometry and prove it.

What would you need, what are you missing, to do the proof?  Inputs?  Methods?  How much can you infer from what you know about the circuit's operation, and the laws of circuits and components?

I don't know offhand, but suspect that, the equation is approximate -- conduction angle factors into it, as does the discharge curve (which in general, is not going to be a linear ramp as in the diagram).  In general, I think the true solutions will be transcendental -- that is, involving a relation of the form x = sin(x), which cannot be solved, only approximated.  So they chose to assume conduction angle (letting you make your own error on that parameter ), and the rest follows from a basic power balance and a constant current assumption.  That's my guess.

Tim