Design, implementation and comparison of Si semiconductor MOSFET and GaN FET based SEPIC battery charge regulator

In this study, battery charge regulators are designed by using GaN FET and Silicon MOSFET as switching devices. The battery charge regulators are designed by utilizing Single Ended Primary-Inductor Converter, SEPIC, power conversion topology. The thesis study differs from similar literature studies both in terms of examining the switching characteristics of GaN FET and Silicon MOSFET and examining the advantages and disadvantages of SEPIC type converter compared to other DA-DA type converters. The input voltage range is determined as 40-55V and output voltage is determined as 26V for the battery charge regulator. The battery charge regulator has ability of working in both constant current and constant voltage modes. The power converter which utilizes Si MOSFET is driven under 100 and 300 kHz switching frequency and the one utilizes GaN FET is driven under 300 kHz switching frequency. The converter has ability to provide 100W output power under full load. In order to perform tests, two open loop, one for each switching device, and one close loop test board models are designed. The efficiency of the converter which uses Silicon MOSFET as switching device is measured as 90,15 % under 100kHz switching frequency; however the efficiency is measured as under 90% for 300kHz switching frequency. The efficiency of the converter which uses GaNFET as switching device is measured as 91,82% under full load. Performance tests has been performed on both Si MOSFET and GaN FET used battery charge regulators. The modes of battery charge regulator are validated for both simulations and tests. According to the test results, the advantages and disadvantages are discussed for both SEPIC converter and GaN FET.