GB689993A - Improved load current control circuit including an electric discharge device - Google Patents

Abstract

689,993. Rectifying. BRITISH THOMSONHOUSTON CO., Ltd., and LUDBROOK, L. C. Nov. 30, 1950, No. 29364/50. Class 38 (ii). In a supply circuit wherein a discharge device 10 serially connected with a load 16 across A.C. supply terminals 15 provides a control for the unidirectional current pulses in such load, the range of control of the device 10 is extended by an excitation circuit which renders the device conductive at a point nearer, than would otherwise be the case, the beginning and end of each positive half-cycle, e.g. when the anode 11 of the device is at a potential only a few volts above that of its cathode 12. This excitation circuit comprises the connection of a condenser 21 in series with a rectifier 19 between the anode 11 and cathode 12 of the device, the junction of these components 19, 21 being connected to the control electrode 13 of the device and the rectifier being so poled that the condenser is charged during each half-cycle when the anode is negative so as to provide a current pulse to initiate the discharge in the device when desired during the following half-cycles when the anode is positive. As shown, Fig. 1, applied to a pentode thyratron the condenser and rectifier are shunted across one limb 17 of a potentiometer 17, 18 shunting the device 10, and the discharge therein is initiated when desired by the reduction, such as by the superposition of a peaky waveform voltage, upon a bias potential applied to an auxiliary electrode 14. Applied to an ignitron, Fig. 2. the ignition instant is determined by a further discharge device 23 connected between the condenser 21 and the ignition electrode 13 of the ignition. A number of basic half-wave circuits shown may be embodied in known polyphase and bridge arrangements.