Analysis of Isolated DC-DC Converters for Medium Power Applications

DC-DC converters are widely used as power supplies in many applications of spacecraft subsystems such as dc motor drives, electronics packages, relay coil supplies etc. These dc-dc converters are required to step down or step up the raw bus voltage to the required output voltage. Based on the user requirement, a DC-DC converter is designed with a single or multiple output. For multiple outputs an isolated converter topology is must whereas for single output there is an option of using isolated topologies like Forward, Push-Pull, Flyback, Half bridge, Interleaved forward/ flyback, Full bridge etc. or simple non-isolated dc-dc converter topologies like buck or boost converter. Apart from considering complexity/ component count/ cost to finalize the topology, the requirement of ground isolation between power source and load end is very critical for some users to avoid ground noise induced problems, which may prompt the use of isolated topologies. In this paper, a detailed study & analysis, based on hardware results has been carried out for designing a single isolated output DC-DC converter for the output power requirement of 140W (28V/5A) operating at variable input voltage of 26V to 42V. Based on the literature survey, three isolated topologies, Half Bridge Converter, Push-Pull Converter and Interleaved Forward Converter have been shortlisted for hardware implementation & analysis. The advantages & disadvantages of all three topologies have been summarized and a comparison has been made based on hardware results. Parameters like efficiency, peak input current, maximum voltage stress on switch, switch power dissipation (both switching and conduction losses) and other important waveforms are analyzed in this paper for better understanding. Based on the comparison of three topologies, a conclusion has been made to decide the optimum topology for 28V/5A, 140W output power requirement for the input range of 26V–42V.