Abstract: A Closed loop Boost dc-dc converter with novel capabilities of fuzzy logic controller is proposed, which mainly meant for constant power loads. The fuzzy logic controller controls the system to achieve constant output as per the requirement of the load. Due to the variation of input voltage and load current, a two stage ZVT boost converter with series resonant convertor is used to give supply to the load. The selected converter has the advantage of No duty cycle loss, wide zero voltage switching (ZVS) range, No ringing problem of the rectifier. The closed loop system is developed in such a way that, it provides necessary corrections for any slight variation in system output. The advantage of fuzzy logic improved the system efficiency in terms of accuracy compared to other conventional controllers. The system suits for electrolyzer.