Patent GB-730061-A (GB)
Title: Improvements in or relating to electric trigger circuits
Inventor: GRAYSON HARRY
IPC: H03B19/14
Filed: 1952-12-23
Abstract: 730,061. Transistor multi-stable-state circuits. STANDARD TELEPHONES & CABLES, Ltd. May 8, 1953 [Dec. 23, 1952], No. 32603/52. Class 40 (6). In an electric-trigger circuit employing at least one transistor and having two stable states in one of which the transistor is conductive and in the other of which it is substantially non- conductive, an alternating current is applied to the circuit so that when the transistor is conductive it delivers an alternating-current output which is rectified to derive a direct-current bias voltage which is applied to the same or another transistor to maintain the first transistor in its conducting state. In a first embodiment, Fig. 1, the output from an A.C. source 13 is applied via a transformer 10 to the emitter electrode 3 of a transistor 1. The emitter electrode is so biased that the transistor is normally non- conductive ; however, on the application of a positive pulse to the emitter from terminal 12 collector current flows through a circuit including the primary winding of a transformer 5. An alternating current is consequently induced in the secondary winding of the transformer 5; this is rectified by the rectifier 14 to produce a positive emitter bias voltage across the condenser 15, this bias voltage maintaining the transistor conductive after the cessation of the initiating pulse applied to the terminal 12. The subsequent application of a negative-pulse to the terminal 12 renders the transistor non- conductive once more. As shown, output pulses, consisting of a train of oscillations, are taken from terminal 16, though by the selection of other output points, pulses derived solely from the D.C. component of the collector current may be obtained. The circuit of Fig. 1 also includes a limiting arrangement, comprising rectifier 18 and condenser 19, which prevents the transistor becoming conductive, when in its non-conductive state, in the event of an increase in the amplitude of the alternating-current output of the source 13. In a modification, Fig. 2 (not shown), the rectifier 14 is replaced by a full-wave-rectifying bridge. In a second embodiment, Fig. 3, the transistor 1 is normally biased so as to be non-conducting. However, upon the application of a positive pulse to the terminal 12 oscillations commence due to the coupling between the collector and emitter electrodes provided by the coupled coils 21, 24, and a positive bias voltage is developed across the condenser 23 due to the action of the rectifier 25. Oscillations are consequently maintained until such time as a negative pulse of sufficient amplitude is applied to the terminal 12. A D.C. pulse output is taken from across the decoupled resistor 7 in the collector circuit. In the modification of Fig. 4, which shows part of the circuit only, the condenser 23 in the emitter circuit is connected to a tapping-point on the coil 21. In a third embodiment, Fig. 5, employing two transistors, one transistor is conductive and the other non-conductive. An A.C. source is coupled to the emitter electrodes 3A, 3B through transformer 27 having two separate secondary windings. Assuming that transistor 1A is conductive, current having an A.C. component-flows in the collector circuit of the transistor and a negative bias is applied to the emitter 3B of transistor 1B due to the action of transformer 31A, rectifier 35A and condenser 36A, this negative bias maintaining the transistor 1B in a non-conductive condition despite the positive bias applied from battery 30 via resistor 29B. Upon the application of a positive pulse to terminal 38B, the transistor 1B is rendered conductive and a negative bias voltage is developed across condenser 36B, thus cutting off the transistor 1A and removing the negative bias from the transistor 1B. Thus the transistor 1B remains conductive and the transistor 1A remains non-conductive after the cessation of the positive pulse applied to terminal 38B. A further positive pulse applied to terminal 38A will restore the circuit to its original condition. Output D.C. pulses are obtained at the terminals 39A, 39B. In a modification, Fig. 6 (not shown), the bias potentials derived from each transistor when in its conductive condition is of reversed polarity and is applied to the base electrode of the other transistor to maintain that transistor non-conductive.