Flyback converter - Vdc-min

Discussion in 'Physics' started by Skeebopstop, Mar 27, 2009.

  1. Skeebopstop

    Thread Starter Active Member

    Jan 9, 2009
    358
    3
    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
     
  2. Skeebopstop

    Thread Starter Active Member

    Jan 9, 2009
    358
    3
    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
     
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