GB617566A - Improvements in or relating to circuit-arrangements for interrupting electric currents by means of a gas- or vapour-filled discharge tube - Google Patents

Abstract

617,566. Switching systems for consumption apparatus; converting. PHILIPS LAMPS, Ltd. Oct. 7, 1946, No. 29886. Convention date, Jan. 26, 1943. [Classes 38 (ii) and 38 (iv)] To prevent re-ignition, due to residual ionization, after extinction of a gas- or vapourfilled discharge tube for interrupting a high voltage and high power circuit, as for instance an inverter circuit, the current passed by the tube is transferred at the moment of extinction to a hard valve in parallel with the tube and which after short period, sufficient for the filling of the tube to de-ionize. under the relatively low anode-cathode voltage then obtaining, is rendered non-conducting to interrupt the circuit. As shown in Fig. 1, a load 2 is supplied from a high voltage D.C. source 1 through a mercury cathode discharge tube 3 having an ignition electrode 6. In parallel with the tube 3 is a hand triode 7 and an extinguishing circuit for the tube comprising in series a condenser 12 charged from a source 11, a smaller condenser 14 and an auxiliary discharge tube 13 having an igniter 17. To interrupt the load current, triode 7 is rendered ready for conduction by removal of a blocking grid bias; igniter 17 is then energized to discharge the condensers 12, 14, thereby bringing about a momentary reduction, or reversal, of voltage across the tube 3 which consequently extinguishes. The triode then takes over the load current and limits the anode voltage rise of tube 3 to a value, say, 500 to 1000 volts, insufficient to cause re-ignition during deionization. The grid blocking voltage is subsequently re-applied to triode 7 to interrupt the load circuit. The full source voltage then appearing across the extinguishing circuit is absorbed mainly by the small condenser 14. The hand valve may have magnetic, instead of grid, control. Two sets of tubes and valves may be used back-to-back for the cyclic switching of alternating current.