Two-Transformer Current-Fed Converter With a Simple Auxiliary Circuit for a Wide Duty Range

Till now, various types of current-fed converters have been developed, and they exhibit good performance in isolated step-up applications. However, they have a common limitation in that the duty cycle must be larger than 0.5 for a proper operation, which guarantees a conducting path for the boost-inductor current. The limited duty cycle causes an inrush current at start-up and it makes it difficult to regulate the output voltage in a light-load condition. Although various auxiliary circuits have been developed that can be solutions for a duty cycle below 0.5, they increase the size and complexity of the total circuit. To relieve these problems, a new two-transformer current-fed (TTCF) converter, which can be operated along a wide duty cycle range with a simple structure, is proposed in this paper. In the TTCF converter, a magnetizing inductor of the transformer acts as a boost inductor, thus no additional boost inductor is needed. Moreover, only one auxiliary diode is employed for operation with a duty cycle below 0.5. Therefore, the proposed converter can be promising for isolated step-up applications with a simple structure.