According to the disclosure, a power sub-assembly (3) for a micro-hybrid system (1) in an automobile includes an AC-DC converter (8) with a transistor bridge (13), an energy storage device (10) and a power bus (9) including at least two cylindrical conductors (22, 22′). According to the disclosure, conductors (22, 22′) include respective coaxial cylindrical surfaces (23, 23′). The power bus integrated in the power subassembly allows for a parasitic inductance that is by far lower than that of the standard cables in power subassemblies of the prior art, particularly in order to avoid overvoltage at the terminals of the transistors in the AC-DC converter.