Abstract: An electrical circuit arrangement includes an inverter, a driver circuit and a protective circuit. The inverter includes a plurality of inverter switching elements each having a drive connection. The drive connection of at least one inverter switching element is connected to the driver circuit via a first switching element of the protective circuit (6). A drive connection of the first switching element is connected to a circuit node, which is connected to a first potential via a resistor and to a second potential via a second switching element.

Abstract: A screw (22) having the circumference of its head (23) toothed like a pinion firmly holds the cylindrical shank of a rotary tool in position in a slotted sleeve (17). A rack (25) on the front end of the hollow cylindrical spindle (24) meshes with the pinion or head (23) of the screw (22). The retraction or advance of the rack (25) is effected by a grooved ring (20) through screws (35,36) whose cylindrical heads are engaged in two helical guide slots provided in a nosepiece (19) and which are anchored in a pusher ring (28) indirectly applied against the rear face of the hollow cylindrical spindle (24).