PWM switch model resonant capacitor?

[cupoftea]

Hi,
On page 233 of Basso's book "switch mode power supplies", he refers to a "resonant capacitor" (as attached) calculated with the CC-PWM switch model.
I have the book, though cannot find details of how this capacitor should be calculated.
(it doesnt help that my copy has fallen to pieces so i cant "strum" though it any more)
The index sheds no light either.

Do you know how to calculate it?

This capacitor is part of the Buckboost power stage feedback loop transfer function.

 

[Easy peasy]

It looks like an error of some sort, the C should really be the output C

if it is correct the Cs would be the capacitance seen by the pri wdg of the flyback - ( unlikely as other things on the output swamp this effect )

 

[D.A.(Tony)Stewart]

if you write to Christophe , I guarantee he will answer you.

 

[cupoftea]

OK thanks, ive finally sorted the books pages into order, shuffled them back together, slated myself bitterly for not buying the eBook, and on page 158, (Basso Book "switch mode power supplies") it describes what is "Cs"....

It is a so called "resonating capacitor".
It is a figment of the "PWM switch model".

Its capacitance is the kind of pulse to pulse memory that a CCM Current mode converter has in that it causes the sub harmonic oscillation.
So it is given by Cs = 4/(L.ws^2)
where ws is the switching frequency in radians.

This is the final missing key to unlock the buckboost power stage transfer function of page 233 , equn 2A_24

--- Updated Mar 4, 2024 ---

...And when this value of capacitor Cs is inserted into the calcs, the troublesome poles due to the Sub-harmonic osc go back below the 0dB line.