The power conversion circuit can be operated at the
continuous conduction mode (CCM) or the discontinuous
conduction mode (DCM), depending on the continuity of the
inductor current. The circuit operation can be described by
three stages in accordance with the statuses of the two power
switches, the active switch S and the diode D, as shown in Fig.
2. At the CCM, the circuit is operated between Stages I and II
alternately. Stage III occurs only when the inductor current
falls off to zero at the DCM. At a lower output voltage during
the starting transient, the converter may draw currents from
two dc voltage sources simultaneously. As the output voltage
goes up, the two sources supply the currents to the inductor and
the load alternately. The steady state operation is described in
the followings.
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