GB916630A - Improvements in or relating to transistor timing circuits - Google Patents

Abstract

916,630. Transistor pulse circuits. NATIONAL RESEARCH DEVELOPMENT CORPORATION. April 1, 1960 [March 13, 1959], No. 8864/69. Class 40 (6). A transistor circuit comprises two transistors having a reactive impedance coupling the emitter circuits, a direct current coupling between the collector circuit of one transistor and the base of the other, whereby the circuit has two operating conditions with one or the other transistor conductive respectively, constant current feed circuits for each emitter and means responsive to an output of the circuit for clamping the circuit in one of its states. Fig. 4 shows a monostable circuit based on a free-running multivibrator described with a reference to Figs. 1-3 (not shown). The basic multivibrator comprises two transistors T1, T2 having their emitters supplied through constant current circuits comprising transistor T6 and T7 and connected by a capacitor C, while the collector of transistor T1 is coupled to the base of transistor T2. When transistor T1 is conducting, the current from the two constant current supplies flows through the transistor T1, the current from T7 charging a capacitor c and the combined current flowing through resistor R, so biasing transistor T2 to cut-off. This continues until the charging of condenser C causes the emitter of transistor T2 to become positive with respect to the base so that transistor T2 conducts and by regenerative action T1 is cut-off. The combined constant currents now pass through T2 until the condenser has so charged that the emitter of transistor T1 becomes positive with respect to the base, whereupon the circuit reverts to its initial condition. This basic free-running multivibrator circuit is adapted to form part of a pulse-delay system in which there is provided a further transistor T3 connected to the emitter of transistor T2 so as to maintain the transistor normally non-conducting. A trigger pulse applied to terminal 7 will change the state of a bi-stable circuit T4, T5 so applying a voltage to the base of transistor T3 to render it conducting and permit the circuits T1, T2 to commence to operate. After one cycle of the circuit T1, T2 a pulse is produced in output transformer 9 which resets the bi-stable circuit to its original condition terminating the operation of circuits T1, T2 and providing a delayed output pulse at V. High valued resistors may be used in place of the constant current transistors T6 and T7 and the output pulse may alternatively be taken from a resistor in the collector circuit of T2. Greatest stability is obtained in the circuit if the two constant current supplies are equal and if the leakage currents of transistors T6 and T7 are equal. The operating period of the circuit may be varied by varying the value of capacitor C or of the load resistance R and the delay in restoration of the circuit may be diminished if the collector of the clamping transistor T3 is returned to the natural potential for that point in the circuit. According to the Provisional Specification, the multivibrator circuits T1, T2 could alternatively be used as a frequency divider by applying synchronizing pulses of harmonic frequency via terminal 10 or 10A (Fig. 6), to the base of transistor T1. These pulses may be of either polarity. The natural frequency of the circuit may be suitably varied by means of RV1.