4) 4th stage (t3, t4) – Fig. 9(c)
When S3 is turned off, the energy stored in L3 is transferred to the load through D3, D4 and D5. Currents iD4(t) and iD5(t) are added to switch currents iS1(t) and iS2(t), respectively. This stage finishes at instant t4 when S3 is turned on again.
5) 5th stage (t4, t5) – Fig. 9(a)
At instant t4, S3 is turned on and the first stage is repeated. This stage finishes at instant t5 when S1 is turned off.