Determining Peak Secondary Current

Mathematical Method of determining Peak Secondary Current in Flyback Converters

This text describes how to determine the peak secondary current in a flyback converter working on the boundary between continuous and discontinuous mode. For a more intuitive method, please see Flyback Converter Design

Energy in the inductor can be represented by:


and


Also


(where Ls is the secondary winding inductance)

Therefore



Therefore



Where T is the period of the switching waveform

So


is equal to (1 – Duty Cycle) (i.e. the discharge time of the secondary winding)

So



and



So


Now, from


i.e. the change in secondary current

So


So to find the peak secondary inductor current, we take the average output current, multiply by 2 and divide by (1-DC)

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