In this paper a step-up/step-down isolated dc-dc converter referred to as a three-phase flyback push-pull dc-dc converter is presented. The power circuit is constituted by a pair of coupled inductors, a three-phase transformer, a capacitor, three switching transistors and three power diodes. The proposed converter offers the advantages of compact passive devices, low conduction power losses, full duty cycle range (0-100%), and inherent protection against transformer saturation. Furthermore, filter sizes are minimized to duty cycles of around 1/3 and 2/3. These characteristicsmakes this converter suitable formany applications, especially in low-voltage high-power applications such as telecommunications power supply, battery chargers, and renewable power systems. The operating principle and the idealized mathematical analysis in continuous conduction mode are presented. Experimental data were obtained from a laboratory prototype with an input voltage of 125 V, output voltage of 100 V, load power of 1000 W, and switching frequency of 42 kHz. The measured prototype efficiency was 94% for full load and 96% for 400W. © 2012 IEEE.