An interleaved-series/parallel forward converter with wide input voltage range

A novel interleaved-series/parallel forward converter (ISP-FC) is proposed. The ISP-FC is composed of two low-voltage switching-legs and a high-voltage switching leg. The three switching-legs construct two forward cells. The voltage stress on the low-voltage switching-legs is only half of the input voltage while that on the high-voltage switching-leg is the input voltage. The maximum duty cycle of the ISP-FC can achieve 0.67, 1.33 times of that of the two-switch forward converter, which leads to wide input voltage range. The high-voltage leg switches can be soft-switched when duty cycle less than 0.5 while the low-voltage leg switches can be soft-switched when duty cycle larger than 0.5. As a result, high efficiency is achieved over a wide voltage range. The operation principles and characteristics of the ISP-FC proposed is analyzed in detail and verified with experimental results.