GB1361301A - Control circuit - Google Patents

Abstract

1361301 Control of D.C. motors CKD PRAHA OBOROVY PODNIK 7 Feb 1972 [8 Feb 1971] 5572/72 Heading H2J [Also in Division G3] A control circuit for a D.C. motor 13, 14 comprises a chopper having main and commutating thyristors 6, 7 in series with an inductor 4 and the motor, the thyristors being triggered by respective pulse generators 20, 21 controlled by a unit 22 which has inputs connected to a required current signal (from potentiometer 24), an actual current signal (from 15) and the output of a comparator 23 which compares the motor current with the charge on a commutating capacitor 8. The unit 22 comprises a flip-flop responsive to the difference between the inputs from 24 and 15, which are both connected to the base of an input transistor, the output of the flip-flop being connected, together with the signal from comparator 23 (which has a Schmitt trigger and so is on/off in nature), to a monostable circuit which controls the pulse generator. The generator 20 for the main thryristor 6 produces a train of triggering pulses and comprises a transformer coupled blocking oscillator while that for the thyristor 7 produces a single pulse from a transistor circuit. The arrangement is such that when the current is below the desired value a train of pulses from 20 triggers on thyristor 6 until the current reaches the desired value or the value set by the voltage on the commutating capacitor, whereupon generator 21 produces its pulse to turn on 7 and hence turn off 6. The object is to ensure that the current does not rise to such a value that the commutating capacitor would be ineffective to turn off 6. The circuits are illustrated in detail (Fig. 2, not shown). The thyristors are protected by RC circuits 16 ... 19.