GB767727A - Improvements in or relating to transistor rectangular-wave generator circuits and the like - Google Patents

Abstract

767,727. Transistor pulse generating, single and two stable state circuits. MULLARD RADIO VALVE CO., Ltd. Feb. 1, 1955 [March 29, 1954; June 11, 1954], Nos. 9123/54 and 17224/54. Class 40(6) In a circuit with loads RC, RE in the collector and emitter leads of junction transistor T1, Fig. 1, the collector is connected over a D.C. coupling to the base of junction transistor T2, a further impedance RX being connected between the emitters. If the impedance includes a D.C. path the circuit may be listable, a monostable or astable circuit resulting from the employment of a capacitor without D.C. path. In one of the two stable states, transistor T1 is fully conducting and all the electrodes are near earth potential. Due to the further potential drop across resistor RX the effective emitter-base potential of transistor T2 is very small and the transistor is nearly cutoff. In the other state, transistor T2 is fully conducting, the emitter current being sufficiently great to bias the emitter of transistor T1 , below earth potential so that the transistor is cut-off. Assuming transistor T1 to be on, the circuit may be triggered by negative pulses in the loop T1, T2, RX or by a positive pulse applied over the resistor Rb, the circuit being reset by pulses of the opposite sign A square wave may be derived from the emitter of transistor T2 and a wave of opposite sign from a load in the collator circuit. A capacitor Ce may be included to speed up the response of the circuit and an impedance having a D.C. resistance may be included between the collector of T1 and the base of T2. The emitter of transistor T2 may be returned to earth over resistor Rg, Fig. 2, and resistor RX omitted. If resistor RC is so great that transistor T1 is saturated then the circuit is mono-stable with transistor T1 in the on condition, while if transistor T1 is not saturated, the circuit is astable. The collector of transistor T1 may be connected over a diode to a potential intermediate earth and -EC to prevent the storage of holes, and a load may be included in the collector lead of transistor T2. In a modification, Fig. 3 a single source of positive pulses is applied over capacitors Cl, C2 and a steering network of diode D1, D2 to trigger and reset the circuit. With transistor T1 conducting, diode D2 is biased off and a negligible bias exists across diode D1 so that the circuit is triggered to the opposite state. With transistor T2 on, the emitter potential is low so that diode D1 is biased off, only a small bias existing across diode D2. The next input pulse is effective over diode D2 to reset the circuit to its original condition.