Single-Stage Two-Flyback PFC Converter With Low Voltage Stress on a Switch

The proposed converter consists of two flyback ac-dc/dc-dc modules. Some power stored in a first coupled inductor is directly transferred to a load and the other is stored in two dc-link capacitors. Since a flyback ac-dc module operates in discontinuous conduction mode (DCM), line input current is in phase with the instantaneous line voltage and high power factor (PF) is achieved. In a next period, the energy stored in two capacitors is moved to a load by means of a second flyback dc-dc module. To achieve low voltage stress on a switch, two dc-blocking diodes are added so that the dc-link voltage is lower than a peak input voltage. The voltage stress on a switch is clamped to the double dc-link voltage. For a reduction of switching loss on a switch, the first flyback ac-dc module operates in DCM and the second flyback dc-dc module operates in critical conduction mode (CRM). The proposed converter features higher efficiency and higher PF than a conventional single-stage boost-flyback PFC converter. The performance of the proposed converter is verified from a 48 V and 100 W prototype, including its theoretical analyses and design procedures.