Offline SMPS 16W: Post mains rectifier capacitor voltage fluctuation?

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treez

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Hello ,
I am doing a offline flyback (Pin=16W), (Vin=230VAC) (Post mains rectifier capacitor = 330nF.)

Page 7 (equn 2) of the following gives the voltage variation on the post mains rectifier capacitor.
https://www.mouser.com/pdfdocs/2-9.pdf

However, how do I calculate the "dch" value.
Since I only use 330nF, "DCH" will be large, but I don't know how to calculate it.
 

I assume that the voltage almost follows the fullwave rectified sine and drops to zero at zerocrossings, DCH = Vpeak. In detail, you need to know how the switcher reacts on input voltage variations.
 
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use 1000uf capacitor
 
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We would use such a low DC bus capacitor value if we implement a flyback switcher with PFC features. In this case, the secondary filter capacitor must store energy between the input voltage peaks to get a smooth output.
 
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We would use such a low DC bus capacitor value if we implement a flyback switcher with PFC features. In this case, the secondary filter capacitor must store energy between the input voltage peaks to get a smooth output
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..Yes indeed that's why we are doing it...its for a high volume light bulb, so we need a good degree of PFC
 

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