I think you are talking about reflected output voltage. It is used in flyback transformer. Why not go to find flyback transformer design method. Lots of articles in this forum.

所謂的折射電壓是根據電磁感應定論﹐電感電流不能突變﹐當toff 時﹐變壓器一次側的電壓就應該是兩者之和﹗