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??

 

Try read papers about rectifiers
http://cbasso.pagesperso-orange.fr/Downloads/Papers/bulk capacitor calculations.pdf
https://www.bwcelectronics.com/articles/WP10A190.PDF
http://snet.elth.pub.ro/snet2004/Cd/circ/circ_P7.pdf

 

Don't know about the formula, but most of the psus i've worked on use 150uF to 330uf smoothing capacitor. The Larger wattage types use 470uF.

 

If longevity and reliability are important, capacitors are often much higher in value than required based on simple calculations in order to bring operating temperature rise due to ESR to an acceptable level. The ratio of RMS to average current in the input and output of flyback converters is often very high since both input and output current is "chopped." For example, the peak current in the output caps of a flyback delivering 5 A average DC can easily be 20 to 25 A. High performance types like "polymer" types are becoming more viable as choices for output capacitors, especially at lower voltages, but not for input capacitors because the required voltage ratings are not available.