Conduction losses of conventional rectifiers are noticeable in low and medium voltage converters. To decrease the conduction losses, a synchronous rectifier (SR) which is basically a semiconductor switch is used instead of the freewheeling diode. However, a semiconductor switch can only be turned on and off by a proper gate drive signal. Also, the reverse recovery current of the SR body diode considerably increases both the switching losses and the electro-magnetic interference (EMI). A synchronous buck converter is usually the proper choice for low and medium voltage converters. By applying zero-voltage transition (ZVT) techniques, a time gap would be created between the conduction time of the main switch and the diode. Thus, the losses related to the reverse recovery time of the SR body diode are significantly reduced. Also, among the various SR driving techniques, the voltage-driven method is the proper choice for the ZVT synchronous buck converters. In this dissertation, a synchronous rectifier driving circuit based on voltage-driven method is adapted to ZVT synchronous buck converters. Also, a novel SR driving circuit with energy recovery is proposed. Both proposed SR drivers generate the driving signal according to the SR voltage polarity without using any external control signal. Also, these drivers can turn off the SR with delay and keep the SR on after its drain source voltage becomes positive. In this dissertation, a new ZVT synchronous buck converter is also introduced. The proposed ZVT converter is capable of operating at low and medium voltages. In this converter, soft switching conditions are provided for all switches and the reverse recovery losses associated with the SR body diode are eliminated. Also, the auxiliary switch does not require an isolated gate drive signal. The proposed driving circuits and the converter are introduced and the theoretical analyses are presented in the dissertation. Design considerations of each circuit and the simulation results are provided. Prototypes of the driving circuits and converters are implemented and the experimental results are presented to verify the theoretical analysis. Key Words Synchronous Buck Converter, Low Voltage Converter, Synchronous Rectifier (SR), Voltage-Driven Method, Zero-Voltage Switching (ZVS), Zero-Voltage Transition (ZVT) Technique.
