Forum Post: RE: Turns ratio of flyback transformer calculation

Hi Son.

First of all, in order to have a little bit of dynamic, I find that D=0.47 is too high.

Usually, 0.4 is the selected value for the design @Vin_min.

After this you have to consider losses on your primary side (switch, current sense) and diode on secondary side.

For secondary side, in order to guarantee DCM also during transitory, usually D2=0.45 is selected.

So your turn ratio will be evaluated as:

[(Vin_min-Vsw-Vcs)*0.4]/[(Vo+Vf)*0.45]

Bye

Paolo