braking thyristor 13 and thyristors 10 at time t 5 for braking motor 11 in fig4 signal g 39 10 is shown at a level higher than signal g 10 for the sake of convenience to show that thyristors 10 are fired for the maximum ignition angle such an ignition angle temporarily increases current flowing through field coil 6 to make the motor brake more effective braking signal g 13 also fires thyristor 13 for a maximum ignition angle for the same purpose field coil 6 is thus strongly energized by the maximum ignition of thyristors 10 and 13 and on the other hand armature 5 is not supplied with current because it is short circuited by thyristor 13 when each of the ignition signals disappears at time t 6 thyristor 10 is cut off at a zero crossover point of ac power source 1 meanwhile thyristor 13 continues to discharge the electromagnetic energy stored in field coil 6 and simultaneously consumes current generated in armature 5 via a short circuit path through diode 14 across field coil 6 just after cutoff of thyristors 10 thus rotating energy of motor 11 is consumed by resistance of armature 5 and field coil 6 and the motor 11 is dynamically braked and is rapidly stopped thyristor 13 does not receive a braking signal g 13 during the braking period but the current generated during motor rotation holds the thyristor conductive until it disappears a diode 12 passes this current through field coil 6 and prevents this current from.