The forward converter is basically a buck converter with
a transformer and a second diode added to allow energy to be delivered
directly to the output through the inductor during the transistor on-time.
Fig. 1 shows the schematic and waveforms for the forward converter. In
this figure, note that the transistor is connected in series with the
primary of the additional transformer. The second transformer provides
a phase shift that causes the polarity of its voltage to be such that
it will flow to the output while the transistor is in conduction. This
allows a better flow of energy to the output through the transistor. This
means that the output current is continuous with the result that the ripple
will be minimal. This also means that the filtering capacitors can be
smaller, which makes the entire power supply smaller.
Above: Fig. 1: Schematic of a forward converter and waveforms.