Finally, the two-inductor, two-switch circuit shown in Fig. 1
that is described in [6]–[10] exhibits some interesting properties.
Specifically, the main feature of this circuit is that the voltage
stress of each switch is one half the voltage stress of the switches
in the single-inductor implementation in [5]. In addition, the
input current is distributed evenly through the two boost inductors
so that the current ripple in the output capacitor is smaller
than in the single-inductor implementation. However, the major
limitation of the two-inductor circuit in Fig. 1 is its inability to
regulate the load in a wide range with constant-frequency control.
To facilitate the explanation of this limitation, Fig. 2 shows
key waveforms of the circuit in Fig. 1. As can be seen from
Fig. 2, current in inductor increases during the entire
on time of switch and decreases during the entire off time of
switch . Similarly, current in inductor increases during
the on time of switch and decreases during its off time. As
a result, even when the effective converter duty cycle D, which
is defined as the ratio of the overlapping conduction time of the
two switches to half of their switching period, is reduced to zero,
the inductors continue to store energy since switches and
are conducting for half of switching period . To reduce the
stored energy and extend the load regulation range, it is necessary
to shorten the conduction time of the switches. This can
be accomplished by increasing the switching frequency. Therefore,
the circuit in Fig. 1 requires variable-frequency control to
maintain the output voltage regulation in a wide load range.
In this paper, a new two-inductor, two-switch boost converter
topology that can achieve output-voltage regulation from full
load to no load in a wide input-voltage range using constant-frequency
control is introduced. This topology employs an auxiliary
transformer with a unity turns ratio to couple the current
paths of the two boost inductors so that both inductors conduct
identical currents. Due to this current-mirror effect of the auxiliary
transformer, no energy is stored in the inductors when there
is no overlapping of conduction times of the two switches, i.e.,