Pulse Width Modulated (PWM) Forward DC-DC converter is a buck-derived isolated power converter which is used extensively in low power to medium power applications. Satisfactory operation of the transformer utilized in forward converter plays
a crucial role in the overall operation of the forward converter. Hence detailed analysis
pertaining to design of forward transformer is important. The forward transformer
is unique as the magnetizing inductance is not required to store magnetic energy.
Additionally, the forward transformer has a tertiary winding, which is required to
reset the core and to prevent core saturation. This adds to the complexity of design and analysis as compared to a flyback transformer. The effect of winding losses
due to High-Frequency (HF) eddy currents caused by harmonics is also considered
in this work. Dowell's equation was extended to determine the winding resistances
for forward transformer in Continuous Conduction Mode (CCM). The Fourier series
of the transformer winding current waveforms are derived. The winding resistances
derived based on the Dowell's expression and the current expressions derived based
on spectral analysis are employed in evaluating the winding losses. The procedure to
design a HF forward transformer in CCM is presented. The effect of harmonics was
computed using MATLAB, and verified by circuit simulation with Saber Sketch. The
results were found to be in good agreement.