Dc dc conversion by using transformer for isolation

hi,
i am planning to design a dc-dc converter with transformer for isolation an i all i need a +15 and -15 on the output side of the transformer and my frequency is 50khz and so decided to go for a ferrite core for transformer and it is a circular type. can any one help me in selecting a proper core and the bridge rectifier ic to be used to get my required output

and also please can you say the ic for inverting my dc to ac for giving input to transformer. I selected the EL7104 and it is half bridge and i need a full bridge to get an ac output


than Q