Being the design of a DC-DC, LLC resonant converter, difficult, because if FHA method is used the result may be inaccurate and if TDA methods are used the design algorithm can be difficult and not that straightforward, the idea of this work is to develop design method based on TDA that is the more straightforward possible. To do that a numerical solver has been developed, it is based on the standard TDA modeling and can analyze in a short time a big amount of possible configuration giving as output the most suitable configuration in term of the chosen figure of merit (that can be efficiency, volume, ...); in this case the chosen figure of merit is efficiency.