GB781222A - Improvements in electric pulse circuits utilising transistors - Google Patents

Abstract

781,222. Transistor pulse generating, single and two stable state circuits. WESTERN ELECTRIC CO., Inc. June 24, 1955 [June 29, 1954], No. 18341/55. Class 40 (6). In a circuit employing a positive feedback path arranged to drive a transistor between cut-off and saturation, a device is connected between the output and a fixed potential, the device having a high-resistance characteristic for a certain voltage range and low resistance outside that range so that near saturation of the transistor the device passes to the low-resistance condition. Assuming the transistor 2 to be heavily conducting and transistor 1 nearly cutoff, the collector of transistor 2 is at a low potential while that of transistor 1 is at a relatively high potential so that breakdown diode 17 conducts in its forward direction while diode 18 is in the broken-down condition with a constant voltage established across it. A positive triggering pulse from source 20 decreases the current flow in diode 17, increasing that in diode 18 until the diode 17 passes to the off condition. Thereafter the positive pulse is fed over diode 18 and collector of transistor 2 to the base of transistor 1 to increase its state of conductivity. Due to the cross-couplings comprising constant voltage breakdown diodes 13, 14 shunted by capacitors 15, 16 between the collectors and bases of the opposite transistors the circuit rapidly changes over so that transistor 1 tends towards saturation while transistor 2 tends towards the cut-off condition. The collector potential of transistor 1 continues to fall and that of transistor 2 to rise until the breakdown potential of diode 17 is exceeded when a path is established through the forward resistance of diode 18 and the breakdown potential across diode 17. The charge on the memory capacitors 9, 10 now changes so that on the occurrence of the next triggering pulse the circuit is in a condition to be reset to its original state. The A.C. impedance between the two collectors is very low except for the period of the pulse when the changeover occurs. The diodes 17, 18 may be replaced by a diode in series with a battery, Fig. 3c (not shown). A stable circuit. A transistor 31, Fig. 4, is biased to be near cut-off while transistor 32 passes current. Positive triggering pulses applied over a normal diode 52 cause transistor 31 to conduct and due to the coupling between the collectors and bases of transistor 31, 32 transistor 32 is driven towards cut-off The capacitor 45 continues to charge until transistor 31 commences to decrease its state of conductivity. Due to the regenerative connection, the circuit reverts to its original state. The potential of the collector of transistor 31 is limited since either diode 47 or 48 conducts when the breakdown potential is exceeded. When saturation of transistor 31 is approached diode 47 breaks down whereas when the cut-off condition is approached diode 48 breaks down to prevent transistor 32 passing to its saturated state. In blocking oscillator the circuit of Fig. 5 which may be triggered from a source 65 or made free running the collector circuit is shunted by a breakdown diode 68 to prevent saturation occurring. The diode 68 also damps out unwanted disturbances by conducting subsequently in the forward direction.