A novel and simple hybrid DC-DC converter of resonant forward and PWM flyback

A novel single switch, hybrid DC-DC converter is proposed in this paper, where an unregulated resonant forward converter is cascoded with a PWM regulated flyback converter. The converter output is formed by resonant forward circuit utilizing transformer leakage inductance and a resonant capacitor. It transfers the energy fully to the output and is only dependent with transformer turns ratio. Zero current turn off is realized at secondary forward diode without reverse recovery loss. Both forward part and flyback part share the same primary transformer winding. The output of the flyback part, instead of delivering magnetizing flux energy to the load directly, is moved to the primary side and connected in series with input source. With fixed transformer turns ratio, a PWM regulated flyback part is employed to regulate the output voltage. The proposed topology maximizes the capability of energy delivering and is able to ensure both high efficiency and simple control methodology with a wide operating range and high output current. To verify the concept, a high frequency 400V to 20V/65W DC-DC converter for adapter power supply at 200 KHz switching frequency is designed and tested with the proposed architecture.