Freewheeling current in push-pull forward converter

The push-pull forward (PPF) converter is similar to the push-pull converter in topology. But the PPF can eliminate the problems in conventional push-pull converter, including the high switching losses and the high voltage spike of the switches, also with the additional advantage of reducing input current ripple and thus reducing the size of input filter greatly. The previous work has revealed some of them. The freewheeling current in the off duty is an important parameter in the push-pull forward converter. However, the mechanism of freewheeling current and its influence on the performance of the PPF converter has not been deeply researched. Based on the analysis of the PPF's operation principles, the freewheeling current is detailed from the point of energy conversion in the paper and its analytical expression is given. The input current of the PPF is continuous, and the undesired harmonics of the input current is smaller than conventional buck type converters, these features aid in reducing the requirement for input filter. Simulation and experimental results verify the analysis.