Hi all,

I am looking into a flyback converter design. I am following http://www.fairchildsemi.com/an/AN/AN-4137.pdf

My concerns at the moment are with the DC capacitor after rectification. The conditions are the following:

Pin = 62.5W
fl = 50Hz
Cdc = 100uF
Vlin-min = 100Vac
Dch = assume 0.2

With this information, from equation 3 in the AN, I get Vdc-min = 100V.

When I re-arrange equation 3 logically, I do the following:

Pin = delta-Energy/time

time = (1-Dch)/50Hz = 0.016s

delta-Energy = 0.5CVdc-max^2 - 0.5CVdc-min^2 = 0.5C(1.404*Vline-min)^2 - 0.5Vdc-min^2

delta-Energy*time = Pin*(1-Dch)/(Cdc*fL)

so I substitute this back in and re-arrange and I get

Vdc-min = 1.404 Vline-min, which must be wrong because that is Vdc-max!

What am I missing here?

Thanks in adavance

 

Was my post confusing? Should I try to reword it better?

If it made no sense I can throw it into word with my derivation as proper equations.

I am very confused on this and hate to just 'follow formulas' I don't understand.

Cheers