Patent GB-787905-A (GB)
Title: Improvements relating to electronic selector stages
Inventor: BINDON DOUGLAS GEORGE
IPC: H03K17/54
Filed: 1954-10-12
Abstract: 787,905. Electric selective signalling systems. FERRANTI, Ltd. Sept. 29, 1955 [Oct. 12, 1954; Dec. 3, 1954], Nos. 29320/54 and 34991/54. Class 40 (1). The invention relates to electronic selector stages for pulse-energizing any selected one of a plurality of loads, and may be applied to the selective energizing of bi-stable magnetic core stores in which it is required to produce in any selected core two sequential pulses of opposite sense. As shown in Fig. 1, a plurality of transformers 1T1, 2T1, 3T1, &c., for energizing the corresponding loads 1L1, 2L1, 3L1, &c., are arranged in n columns N1, N2, N3, &c., and m rows M1, M2, M3, &c., the primary winding of each transformer being centre-tapped. Each column is provided with a column-selecting valve VI &c. whose anode is connected to the centre taps of the transformers T in that column, and the cathodes of valves V1 &c. are connected to a common cathode load resistor 21 which also forms the cathode load of a control valve 20. One end of the primary winding of transformer 1T1 is connected through a diode 1DA1 to a lead 11<SP>1</SP>, common to that row, the other side of the primary winding being connected through a diode 1DB1 to a lead 121, also common to the row. The remaining primary windings are similarly connected. The potentials of the pairs of leads 11<SP>1</SP>, 12<SP>1</SP>, &c., are respectively controlled by pairs of valves 131, 14<SP>1</SP>, etc;, which are individual to each row and determine the sense of each load-energizing pulse in it. In the quiescent condition the control grids of valves V1 ... V3, V12 are held at - 40 volts, the grids of valves 13<SP>1</SP>, 14<SP>1</SP>, &c., are held at - 40 volts, and the grid of valve 20 is held at + 25 volts. Valve 20 conducts and holds the potential of lead 10 at approximately +25 volts thereby maintaining valves V1 to Vn biased to cut-off. Valves 131, 14<SP>1</SP>, &c., are cut-off and the potentials of the leads 11<SP>1</SP>, 12<SP>1</SP> are +200 volts. To energize one of the loads, say 3L2, by two sequential pulses of opposite sense, two sequential negative-going pulses are applied to the valve 20 to drive the grid down to - 25 volts to ensure cutoff, the grid of the valve V2 is raised to earth potential, and the grid of the valve 14<SP>3</SP> is raised to earth potential. Valve 143 bottoms, its anode falling from + 200 to + 10 volts, and by autotransformer action of winding AT3 the anode of valve 133, and therefore lead 11<SP>3</SP>, rises to approximately 400 volts. When valve 20 is cutoff by the first pulse the potential of lead 10 is carried down to approximately earth level and at this point V2 conducts and holds lead 10 at this potential. The anode circuit of V2 is completed through the left-hand part of the primary of transformer 3T2 and diode 3DA2, diode 3DB2 remaining non-conducting. At the conclusion of the first pulse, valve 20 again conducts and valve V2 is cut off despite the raised bias on its control grid. The second negativegoing pulse applied to the valve 20 has a similar effect but this time valve 13<SP>3</SP> is biased to be conductive and the current path is through the right-hand part of the primary of transformer 3T2. Alternative arrangements for the driving valve 20 and the sense-determining valves 13, 14 are described.