A New Soft-switched Flyback Converter with a Minimum Number of Elements and High Efficiency

Background: This paper proposes a new soft-switching flyback converter with a simple structure and high efficiency. The proposed converter has zero current switching conditions for the turning-on distance and zero voltage switching conditions for the turning-off distance of the switch. Objective: With a minimum number of elements, a soft switching condition is created for all semiconductor devices, and high efficiency is obtained. Methods: To create the ZCS condition, an inductor is used, and when the switch is turned on, the current due to the existence of this inductor increases slowly. But when the switch is turned off, this inductor has an energy that suddenly discharge on the switch, which is then controlled by a capacitor and discharged in capacitor. Then when the energy is discharge in capacitor, this capacitor is connected to the switch, which increases the voltage of the switch slowly and ZVS condition is stablished. Also the energy of leakage inductance in this state is discharged in that same capacitor which eliminates destructive effect of this inductor. Results: A prototype of the proposed converter is implemented and tested in 60 W power. The experimental results verified theoretical analysis and shown that soft switching condition is established. Also 92% efficiency at full load is obtained, which shows the efficiency has increased. The current of the diodes in experimental results shows that when the diodes are turned off, ZCS condition is created, therefore reverse recovery problem of the diodes does not exist. Conclusion: Therefore, the proposed converter has high efficiency and simple structure, which is suitable to convert AC voltage to DC voltage for the devices power supply.