Patent GB-763960-A (GB)
Title: Improvements in or relating to circuit arrangements for electric discharge tubes
Inventor: CROWTHER GERALD OFFLY
IPC: H03K17/52
Filed: 1954-12-21
Abstract: 763,960. Electric discharge-tube circuits. MULLARD RADIO VALVE CO., Ltd. Dec. 21, 1954, No. 36910/54. Class 40(6) In a circuit comprising a gas-filled cold cathode electric discharge tube having a trigger electrode, part or all of the load for the tube is provided in the cathode circuit so that at the instant preceding the extinction of a discharge the trigger elecrode is held by the cathode at the voltage desired prior to re-ignition so that the speed at which the tube may be triggered is increased; the time constant of the cathode circuit is much less than that of the trigger circuit. Fig. 1 shows a circuit comprising a cold-cathode gas tube 1 of the type described in Specification 763,959 [Group XL(a)] in which the values of components are such that the tube is selfquenching and the cathode in the quiescent condition is at earth potential. When a positive pulse is applied at terminal 12 to the trigger electrode a discharge is set up between trigger and cathode and spreads to the main anode/cathode discharge path, capacitor 9 partially discharging, until the trigger/cathode burn voltage exists between these two electrodes. Capacitor 8 is charged by the main discharge in the tube and the voltage of the trigger electrode is thus held at a voltage equal to the voltage drop across capacitor 8 plus the trigger/cathode burn voltage, which total voltage is approximately that which the trigger normally is required to attain on the quiescent condition prior to a discharge being set-up. When the discharge ceases the cathode voltage falls rapidly due to the short time constant of the cathode circuit so that the upper frequency of operation of the tube is set by its de-ionization time and not by the long time-constant of the trigger circuit. In a modification .shown in Fig. 2 the cold-cathode gas discharge tube 20 is of the type described in Specification 763,959 which comprises in addition to the anode and cathode a firing electrode 22, a triggei electrode 24 and an apertured deionizing screen 23, a negative trigger pulse being applied to terminal 32 as described in Specification 723,892. The trigger 24 is prevented from rising above the voltage Vc of terminal 33 by rectifier 34 and screen 23 is supplied with a voltage equal to the equipotential surface on which the screen lies or the mean voltage of such surface. In the absence of pulses at electrode 22 a small priming discharge exists between trigger 24 and firing electrode 22. On arrival of a negative pulse at 22 capacitor 36 discharges and the main anode/cathode discharge occurs the cathode voltage rises, due to capacitor 27 charging, to a value equal to or more positive than that of screen 23. Due to the burning voltage existing between cathode 21 and trigger 24 the. trigger rises rapidly to the desired pre-ignition voltage as described in connection with Fig. 1 above. At the instant of extinction of the discharge, screen 23 collects positive ions and a positive ion cloud thus collects near the anode so that rapid de-ionization of the tube results and the speed of operation of the circuit is increased.