Optimization of the input and output stages in high efficiency power supplies

Switched mode power supplies are found in all applications e.g. telecom-cabinets, PCs, monitors and fan motor drives. In most cases of medium and high power applications such supplies consist in three conversion stages. The first power stage is a so called PFC frontend, which reduces the harmonic currents. The second stage transforms the PFC-output voltage to an ac-voltage, which is adjusted to the requirements of the equipment. The third stage rectifies the ac-voltage of the previous inverter. To increase the efficiency of the power supply, each of these stages must be as efficient as possible. The paper describes methods to increase the efficiency of the first power conversion stage (PFC) by using modern semiconductor devices and by a new topology, which eliminates one PFC-rectification stage. Also, optimization criteria for the rectifier output stage will be given.