Interleaved ZVS Flyback-Forward converter with reduced output voltage stress on secondary rectifier diodes

In this paper, a novel active clamp Flyback-Forward converter is proposed for large voltage gain and high power applications. The interleaved configuration on the primary side is employed to handle the large input current. An improved voltage doubler configuration is adopted on the secondary side to make the output diodes sustain only half of the high output voltage. Furthermore, the output diode voltage stress can be auto-balanced due to the inherent series structure of the coupled inductors. Therefore, the low voltage stress diodes can be used to enhance the circuit performance. Moreover, the active clamp circuits can be employed to recycle the leakage energy and absorb the possible turn-off voltage spikes on the primary power devices. In addition, zero-voltage-switching (ZVS) soft switching operation is achieved for all the active switches during the switching transition. The output diode reverse-recovery problem is alleviated due to the leakage inductance, leading to a great reduction of switching losses. Finally, a 40 V-input 380 V-output 1 kW prototype is built to demonstrate the effectiveness of the theoretical analysis.