Simple speed regulation circuit of DC motor

Circuit working principle: The regulated voltage generated at both terminals A and A is supplied to the armature winding of the motor after full-wave rectification
, and RP is adjusted to achieve the purpose of speed regulation. It is worth pointing
out that although the full-bridge diode has a freewheeling effect, the motor will still
beat when the speed is very low. This is because the conduction time of the bidirectional thyristor
is quite short at this time, and under the influence of the motor's back electromotive force, It is already in an unstable critical state of on and off. The solution
is to try to reduce the influence of the back electromotive force load of the bidirectional thyristor, and
connect false load resistors in parallel to both ends of the armature, so that the thyristor can work normally even when the conduction angle is small. The selection of this resistor
should be based on eliminating low-speed beating of the motor . For example, connecting a 1 kfl resistor in parallel to a 70 W motor used in machine tools
can eliminate bounce.