The speed of DC motor can be control by usingSCRin AC circuit as shown in the below figure. The SCR A and B rectifier, the o/p voltage of transformer T1 and apply this pulsating DC voltages to the armature winding and rectifier “C” supplies similar voltages to the motor field winding. The o/p of SCR rectifier can be control by controlling the gate current of SCR. So, this way the SCR can operate at different levels of conduction and apply varies voltages to the motor armature, this way the speed of DC motor can control. If SCR conduct for long durations more voltages applied to the armature winding and speed of motor increases. For the next case the action, the operation will be vice versa to the pervious.