Patent GB-1032671-A (GB)
Title: A pulse former having low power drain during quiescent conditions
IPC: H03K3/30
Filed: 1963-03-18
Abstract: 1,032,671. Transistor monostable circuits. GENERAL TIME CORPORATION. March 18, 1963 [March 26, 1962], No. 10653/63. Heading H3T. A monostable pulse-generating circuit comprises two normally non-conducting reciprocally coupled transistors of opposite conductivity types, the output of each being cross-coupled to the input of the other, and a transformer wound upon a saturable core and having three windings, a first one of which is connected in series in the collector-emitter path of one of said transistors to permit the output of said one transistor to be developed thereacross and the second and third of which are connected respectively between emitter and base and in series in the collector-emitter path of a third transistor, so that, on the application of a suitable trigger pulse to one of the reciprocallycoupled transistors, both are rendered con - ducting and current commences to flow in said first transformer winding, said current continuing until the transformer core saturates in one direction whereupon the positive feedback provided by the reciprocal coupling becomes insufficient to maintain the reciprocally-coupled transistors conducting and the current in said first winding ceases, the decay in current inducing a voltage in the second winding of the transformer in such a direction as to render the third transistor conducting, so that current flows through the third winding which is so coupled to the second winding and to the core that it provides positive feedback via said second winding to maintain the third transistor conducting and it effects the resetting of the saturable core to its other state of saturation whereupon the positive feedback ceases and the circuit reverts to the quiescent state. In the circuit illustrated, trigger pulses for the reciprocally coupled pair of transistors of opposite conductivity types T3, T4 are derived from a Schmitt trigger circuit comprising transistors T1, T2 to which input pulses are applied at terminal 11. Capacitor 40 serves to differentiate the rectangular pulse appearing at the collector of transistor T1 to derive the trigger pulse applied to the base of transistor T3. Alternatively the trigger pulse may be obtained by differentiating the rectangular pulse at the collector of transistor T2; in this ease the circuit is triggered in coincidence with the trailing edge of the input pulse. The application of a negative-going triggering pulse to the base of transistor T3 causes both transistors T3. T4 to conduct and current to commence flowing in winding 51 of saturable-core transformer 50. Upon the core saturating, the feedback provided by winding 51 falls to a very low value so that transistors T3, T4 are switched off and the current in winding 51 falls to zero, inducing a voltage in winding 52 in such a direction as to make transistor T5 conduct. Current consequently flows in such a direction in winding 53 as to maintain transistor T5 conducting and also to reverse the saturation in the transformer core. When saturation in the reverse sense is attained feedback via winding 52 ceases and transistor T5 is switched off. The circuit then remains in this condition until the application of a further input pulse at terminal 11. During the conduction of transistor T5 a voltage is developed in winding 51 in such a direction as to charge capacitor 70 positively. This prevents the brief negative pulse which is generated by winding 51 when transistor T5 switches off from triggering transistor T3, so inhibiting any tendency for the circuit to become free-running. Output pulses comprising a rectangular negative-going portion followed by a rectangular positive-going portion may be taken from the emitter of transistor T5 or from an additional winding 75 of the transformer. A rectifier may be incorporated in the output circuit to select either the negativegoing or positive-going portion of the output waveform.