GB1339231A - Motor control circuit - Google Patents

Abstract

1339231 Braking of D.C. motors BECKMAN INSTRUMENTS Inc 7 Jan 1972 [27 Jan 1971] 739/72 Heading H2J A drive and braking circuit for a series wound D.C. motor 4 adapted to be energized from an A.C. source 1 comprises a full wave rectifier 5 connected to the A.C. source and supplying direct current to the motor 4, switch means provided for connecting the rectifier 5, armature winding 16 and field winding 15 in series, said switch means normally being set in a first position such that the energizing current flows in the same direction in the armature and field windings to drive the motor and being actuatable to a second position in which the current flow through either the armature winding 16 or field winding 15 is reversed to brake the motor, and unidirectional current conducting means in parallel with the armature winding 16 and poled to conduct armature current when the circuit is in its braking mode. The full wave rectifier 5 includes two S.C.R's 8, 9 whose firing angles are controlled by pulses from a unijunction trigger circuit 10 to vary the magnitude of the direct current. The switch means comprises relay contacts 18 and 21 which in the drive mode of the motor co-operate with fixed contact pairs 19, 19<SP>1</SP> and 22, 22<SP>1</SP> respectively and in the braking mode co-operate with fixed contact pairs 20, 20<SP>1</SP> and 23, 23<SP>1</SP> respectively. A ripple reducing inductor 27 is connected in series with D.C. motor 4 and a limiting resistor 29 is provided in series with D.C. motor in the braking mode. The diode 30 is so poled that it conducts the armature current generated in the braking mode away from the field winding 15.