Patent GB-808434-A (GB)
Title: Improvements in or relating to transistor circuits
Inventor: SHARPE CLIFFORD
IPC: H03K29/00
Filed: 1956-03-01
Abstract: 808,434. Transistor single stable state circuits. UNITED KINGDOM ATOMIC ENERGY AUTHORITY. Feb. 27, 1957 [March 1, 1956; Jan. 18, 1957], Nos. 6421/56 and 1885/57. Class 40 (6). In a triggered blocking oscillator wherein feedback is provided by a transformer having one winding connected to the collector and a second winding to another electrode alternate negative pulses are supplied by a further winding to the two guide electrode systems of a dekatron. The transistor S, Fig. 1 (Comp. Spec.) is maintained cut-off by a connection over resistor R1 to a high positive potential. A negative-going input pulse is applied over capacitor C to lower the base potential of the transistor which passes collector current through the primary L1 of the feedback transformer T. The increase in collector current causes the collector potential to approach earth with the result that a similar potential charge appears across the secondary L2 due to the unity ratio and is applied to the anode of diode D which ceases to conduct. The current previously flowing through resistor R2 is thus switched to the base circuit to maintain the transistor conducting. The cathode potential of diode D1 falls as the capacitor C2 charges negatively and continues until the potential falls below that of the anode when the diode D1 conducts, base current ceases and the circuit restores to the offstate. The collector potential falls until the diode D4 conducts to prevent an over-swing, after which it is returned to the normal supply potential. The width of the generated pulse may be varied by adjusting the resistor R2 and capacitor C2. In the normal condition diode D7 conducts so that the guide electrodes G1, G2 are maintained near earth potential by diodes D5, D6 conducting. When the transistor S passes to the on condition a large pulse is fed out to guide electrode G1 and capacitor C3 charges negatively since diode D6 maintains the further end of winding L3 near earth potential. When the transistor S goes off electrode G1 remains at the pulse potential and electrode G2 is carried to a negative potential of twice that value. Subsequently the guide currents discharge the capacitor C3 which is then returned to earth potential as the collector voltage recovers. In this manner the discharge is stepped around the tube E. The capacitor C3 also provided positive feedback during the pulse. The circuit is reset by opening the switch SW1 when the discharge passes to the cathode K1 and when the switch re-closed is restored to cathode K2 and a negative pulse is fed through diode D5 and capacitor C3 to the base of transistor S which causes the discharge to step round to the first electrode. In a modification, Fig. 3 (Comp. Spec.) the feedback circuit from the winding L2 to the base of the transistor is made over the diode D2 and when the transistor passes to the on stage a negative potential is established at the junction of diode D2 and inductor L4. A current builds up through the inductor until it equals the current in resistor R8 when the base current is cut off and the circuit restores to the normal off condition. The pulse width is determined by the value of the inductor L4, and the circuit R7, D8 provides damping. The triggering potentials may be in the form of positive pulses applied to the emitter. The first Provisional Specification describes a blocking oscillator circuit in which the triggering pulses are fed to the collector and the base circuit comprises a winding of the transformer with a capacitor and resistor in series connected to the base, which determine the duration of conduction. In an alternative arrangement, the input pulses are applied over a transformer to the emitter of the transistor. It is stated that point contact transistors may be used. In a modification, described in the second Provisional Specification, the base of the transistor is connected over a resistor and diode to the transformer winding, the duration of the conducting state being determined by the inductance of the winding and the resistor. Alternatively feedback may be taken to the emitter.