Thanks. However, I have the following questions:
If the magentizing current really goes through the body diode of switch T1 or T2 (depends on the previous state) when both switches, T1 and T2, are off, it means there are voltage drop across the transformer primary side. The magnitude of the voltage acorss transformer equals to Vin (without accounting diode drop), and the time for this voltage to exist is D*T (D is duty ratio, T is the period of switching frequency), which is the time required to de-magnetizing the transformer
Since any voltage across one winding of a transformer, this voltage will reflect to the other windings acrroding to the turn ratio. Hence, the transformer secondary sees a voltage pulse with 2*D on-time rather than 1*D.
If what I guess is correct, it makes me confusing @_@
Scottie