The Radar power supplies exhibit a complex electronics. The development of more and more compact systems makes that we must master the interaction between different parts of the power supply while reducing electrical (electronic circuits), magnetic (EMC) and thermal couplings from the internal circuitry of the power supply. The consideration of these phenomena is very difficult at the design of the power supply. We present in this paper two methods based on a circuitry model (quantification of sources of heat) and a finite element model (heat diffusion) that can help us in the design of prototype in the goal of improving the performance and thermal stability of radar.