Mode4 [t3-t4]; Fig. 5(d): Current of the magnetizing inductor becomes zero in this mode and diode D3 gets reverse biased. Other components remain at their previous states.
Mode5 [t4-t5]; Fig. 5(e): This mode starts when the current of magnetizing inductor becomes zero. Secondary side current of the coupled inductor becomes zero and D5 gets reverse biased. Only D1 is conducting, but other diodes and S are turned off.