Patent GB-992536-A (GB)
Title: Motor control circuit
IPC: H02P8/12
Filed: 1964-01-22
Abstract: 992,536. Control of A.C. motors. MOTOROLA Inc. Jan. 22, 1964 [Feb. 18, 1963], No. 2819/64. Heading H2J. A synchronous motor 140 is controlled by bi-stable and mono-stable multivibrators 12, 14, receiving triggering pulses from terminal 16, one output of circuit 12 being coupled to one input of AND-gate 22. The phaseinverted output of circuit 12 is coupled to one input of AND-gate 24, the second inputs of gates 22, 24, being coupled to a single output of circuit 14. The outputs of gates 22, 24 are coupled by driver stages 26, 28 to a bridge circuit 30, comprising transistors 30a-30d, and with a pair of opposite corners connected across a motor winding at terminals 33, 35. When a triggering pulse is received from either driver stage, the corresponding transistor 30a or 30b is rendered conductive to complete a connection between a D.C. source and the respective terminal 33 or 35. Transistors 30d, 30c are respectively rendered conductive with the transistors 30a, 30b, so that the opposite terminal 35 or 33 is connected to earth. The motor is thus energized with pulses in opposite directions, the period between pulses being increased from zero as the triggering frequency at terminal 16 is reduced, whereby the average pulse voltage amplitude supplied to the motor is reduced with frequency whilst the instantaneous amplitude remains fixed at the level of the D.C. supply. Since the impedance of the motor also changes with frequency, the average current drawn by the motor remains substantially constant over a wide frequency-range. As shown, the triggering pulses at terminal 16 are amplified and shaped by transistor 50, circuit 12 comprising transistors 52, 54 connected as a bi-stable multivibrator. Signals appearing on the leads 23, 25 are supplied to the gates 22, 24. Circuit 14 comprises transistors 60, 62, the timing period being adjusted by capacitor 63 and resistors 65-67 to be approximately equal to one-half cycle of the highest frequency to be used for the motor drive. The output of circuit 14 is coupled by leads 27 to gates 22, 24, which comprise transistors 82, 92. In the absence of coincidence of positive-going signals applied to their inputs, transistors 82, 92 are maintained conductive to maintain driver stages 26, 28, cut off. The driver stages 26, 28 comprise transistors 116, 118, connected as cathode followers. The motor 140 may be of the single phase hysteresis type with capacitor starting. The collector potential for the bridge, gate, and driver transistors is derived from a common unregulated supply, the circuits 12, 14 having a regulated collector supply. Transistor 102 prevents the gates being triggered by random pulses. For a two-phase motor, an additional bi-stable multivibrator is connected to a common triggering source, with the phase-inverted outputs of the multivibrator providing triggering for a pair of control circuits of the type described, to supply pulses to the motor windings in phase quadrature, Fig. 4 (not shown). For a single phase motor with capacitor start, the control circuit is triggered at twice the motor frequency, and, for a two phase motor, the triggering frequency is four times the motor frequency.