This paper presents a design methodology of a 50 lV isolated DC/DC converter serving as a power supply for aircraft equipment like a FADEC (Full Authority Digital Electronics Control). The particularity of this work is the design of a full converter regarding two antagonistic requirements which are a wide input voltage with an high efficiency. To fulfill those requirements an optimization regarding three different levels is done: 1- A suitable topology for wide input voltage range, 2- Proper technologies for high frequency operation and 3- A converter architecture to minimize the surface. A 50W, 18 - 80 V input voltage, 1MHz switching frequency converter is built using GaN transistors and a planar transformer. The proposed converter operates under optimized soft-switching conditions in order to minimize Switching losses and reached a peak efficiency of 95 %. This converter is compared with 2 other converters: an hard-switching 400 kHz Flyback topology which is the industrial standard equipment and an 1MHz soft-switching topology without the architecture optimization.