DC-reactor-less hybrid DC-DC converter with a core composed of four legs

Efficiency improvement and cost reduction are important requirements for the design of DC-DC converters. Zero voltage switching is one good solution for increasing efficiency, and an active clamp circuit is useful for implementing it effectively. A cost reduction could be achieved by devising a new transformer that functions not only as a conventional transformer but also as a DC reactor that reduces the switching device peak current. The magnetic core of the new transformer is composed of four legs. A novel hybrid DC-DC converter in which forward and fly-back converters are combined by using the transformer was developed. However, no design methodology for such a transformer has yet been established. Therefore, the modeling of the excitation circuit of the transformer is required. This paper proposes a novel method that simulates the operations of the DC-DC converter and estimates the magnetic flux distribution in the new transformer. The magnetic circuit of the transformer is transformed into its equivalent electric circuit with two ideal transformers. The performance of the DC-DC converter was examined by circuit simulations including the magnetic circuit of the transformer. Circuit simulation results agree fairly well with experimental ones.