Control for DC motor in bridge circuit - has digital logic circuits coupled to divider outputs giving zero motor current at zero speed

摘要

The dc motor function is determined by the mark-space ratio of control pulses. Identical trains of impulses with a 1:1 mark-space ratio at the inputs (a,b) give, together with the output of a summing amplifier (1)(c), either a positive or negative signal across the voltage dividers (2,4;3,5). Digital logic circuits (6,8;10,12) coupled to the divider outputs (d,e) then give signals through one or other of the channels (9,13;7,11) to connect either one pole or the other of the dc supply (f,g) to both ends of the motor (16). No motion results as there is no current flow. If the mark-space ratio departs from 1:1 then the logic channels do not operate simultaneously and complementary bridge transistors (19,20;17,22) turn on controlling the applied voltage and hence both speed and direction of the motor.