In recent years heat storage using phase change materials has been also considered in the thermal control of electronic devices. In a recent work we presented some results for a parametric analysis of an energy storage system with a phase change material undergoing a two-levels steady-periodic heat boundary condition, as happens in certain electronic equipments. In particular, a hybrid system composed of a finned surface partially filled with a PCM, was analysed. This solution, which combines both passive (PCM) and active (fins and fans) cooling solutions, is of interest in high power amplifiers characterized by different levels of power dissipation, as is the case of the telecom base station power amplifiers, where the power is proportional to the traffic load. In the present paper we analyze some parameter previously not investigated, in particular the dimensionless transition temperature, for the role played by this parameter in the limitation of the operating temperature reached during the peaks of the power input. The study has provided further useful information for the design of these hybrid cooling systems.