A selector sets respective phases of pulse driving signals in reverse when
a proportion signal or integration signal does not exceed a threshold.
Shifting the respective phases of the pulse driving signals from each
other lowers the ripple voltage. When the load current increases
drastically, the output voltage Vo tends to decrease remarkably because
of the shortage of capacity in the power supply. In this case, when the
proportion signal or integration signal exceeds its corresponding
threshold, a phase control unit causes the pulse driving signals to
synchronize their phases, i.e., the selector supplies the same ramp wave
to the comparators, so that respective output voltages supplied from the
DC voltage converter circuits attain the same phase, thereby restraining
the output voltage supplied to the load from decreasing remarkably.