As the switch-mode power supply has evolved, additional
adjustments to the original circuits have been made to get more power
from smaller components. This means that the efficiency for the system
must be increased. One simple way to do this is to use a center-tapped
transformer that utilizes both the top and bottom half-cycles. Fig. 1
shows a schematic of the push-pull converter in which the push-pull converter
utilizes a center-tapped transformer for both the primary and secondary
windings. The primary winding is controlled by two transistors, which
allow one of them to conduct during each half-cycle, so the output is
receiving voltage directly through one of them at all times. This means
that the efficiency of this configuration is approximately 90%. This allows
the overall size for the power supply to be smaller for a comparable power
supply whose efficiency is 75% to 80%.
Above: Fig. 1: Schematic of a push-pull converter.