Abstract: The very fast circuit breaker assisted by semiconductor electronics. A piston 21 slides in an insulating housing 20 and along a center shaft 22. The piston 21 has of an exciting winding 25 and a magnetic yoke 26, which by cooperating with an armature 28, join the piston 21 to the center shaft 22, a shoulder of which renders possible the holding of a repulsion disk 34. The repulsion disk carries the moving contacts 35 and 36, which cooperate with the stationary contacts 37 and 38, when the piston is in its high position under the effect of a locking spring 24. Upon the injection of a current into the repulsion coil 45, the repulsion disk 34 is violently repulsed in the downward direction, while jumping the electromagnetic lock established between the magnetic yoke 26 and the armature 28. An admission of compressed air through an orifice 27 permits the descent of the piston 21.