GB1492593A - Electric control systems - Google Patents

Abstract

1492593 Control of D.C. motors DEFENCE SECRETARY OF STATE FOR 1 May 1975 [1 May 1974] 19134/74 Heading H2J [Also in Division G3] A D.C. control system for a load 3, e.g. a motor, comprises transistor switching means which is repetitively switched between a conductive state in which the load is connected to a D.C. power supply 2 and a non-conductive state in which the load is disconnected from the power supply, a clock pulse generator, a comparator 12, a bistable circuit 14 and a drive circuit 16, whereby clock pulses switch the bistable circuit into a first stable state in which it causes the drive circuit to drive the switching means into its conductive state, and whereby the comparator switches the bistable circuit into its second stable state, in which it causes the drive circuit to turn the switching means into its non-conductive state, upon an integrated feedback of the load voltage exceeding a predetermined level. The system shown in Fig. 1 comprises four transistor switching circuits 18, 20, 22, 24. The comparator 12 and bistable 14 receive pulses from the clock pulse generator (10), (not shown). When the comparator 12 receives a clock pulse, an integrating capacitor C4, which integrates the voltage across the load, is discharged, and when the bistable 14 receives a clock pulse it switches to a first stable state causing the drive circuit to make the switches 18-24 conduct. The bistable remains in this state until the comparator senses that the integrated voltage has reached the predetermined voltage when it reverts to its second state thereby causing the switches to go non-conductive. Details of the clock pulse generator 10, comparator 12, bistable 14, and driving circuit 16 are described with reference to Fig. 2 (not shown), and details of a switching circuit 18 and power supplies are described with reference to Fig. 3 (not shown). Particularly, each switching circuit is comprised of a plurality of transistors arranged in parallel in a Darlington type circuit with the emitter circuit of each transistor including equal resistance and with the lines connecting the collector of each transistor to the line connecting the circuit to the load being of equal length. The switching circuits may be arranged in pairs, each pair being controlled by a respective single transistor.