which is known as u201c avalanche passage u201d for example this third state may arise when excess voltage occurs at the terminals of a transistor 13 during switching from a passage state to a blocked state when the voltage at the terminals of the transistor 13 exceeds a value of 45v for example the avalanche phenomenon occurs thus giving rise to a very rapid increase in the temperature of the transistor this temperature which is known as the junction temperature of the transistor 13 can reach a value close to 200 u00b0 c which is much higher than the maximum junction temperature of 175 u00b0 c in this case the switching function of the transistor 13 becomes inoperative and the functioning of the bridge is disrupted or blocked the ac dc converter 8 also comprises an element 15 for filtering the output voltage of the converter 8 in order to satisfy the requirements of electromagnetic compatibility this filtering element comprises a capacitor 15 with a low value for example 60 u03bcf such as to form a passive filter the power bus 9 comprises at least two conductors 22 22 u2032 comprising a parasitic line inductance 21 which must be as low as possible in order to optimise the energy transfers via the power bus 9 when the alternator starter 2 is functioning as an electric motor for example for starting the thermal engine the currents which circulate via the power bus 9 and the ac dc converter 8 are very high and can reach 1100 a fig3 shows a cross section according to the section of a first embodiment of the power bus 9 this power bus 9 comprises conductors 22 22 u2032 which are accommodated in a sheath 24 formed by.