High-Efficiency Asymmetric Forward-Flyback Converter for Wide Output Power Range

This paper proposes an asymmetric forward-flyback dc-dc converter that has high power-conversion efficiency η
_e
over a wide output power range. To solve the problem of ringing in the voltage of the rectifier diodes and the problem of duty loss in the conventional asymmetric half-bridge (AHB) converter, the proposed converter uses a voltage doubler structure with a forward inductor L
_f
in the second stage, instead of using the transformer leakage inductance, to control output current. L
_f
resonates with the capacitors in the voltage doubler to achieve a zero-voltage turnon of switches and a zero-current turn-off of diodes for a wide output power range. The proposed converter could operate at a wider input voltage range than the other AHB converters. η
_e
was measured as 95.9% at output power P
_O
= 100 W and as 90% at P
_O
= 10 W, when the converter was operated at input voltage 390 V, output voltage 142 V, and switching frequency 100 kHz.