GB514004A - Improvements in and relating to electric valve circuits - Google Patents

Abstract

514,004. Switching systems for consumptionapparatus. BRITISH THOMSON-HOUSTON CO., Ltd. April 25, 1938, No. 12357. Convention date, April 24, 1937. [Class 38 (iv)] To enable current to flow to load 3 for a predetermined number of half cycles, the supply is controlled through push-pull valves 4, 5 fed from windings of trarsformer 11, the transformer having a third winding which is used to assure that the valve is conductive during each half cycle. The timing circuit 46 is described in Specification 416,374. When switch 61 is closed (condenser 51 being discharged) grid 39 of discharge device 36 becomes positive with respect to the cathode by an amount depending on the position of contact 49. Valve 36 becomes conductive and a number of pulses of peaked waveform, supplied by saturable transformer 20, pass through transformer 11. A voltage is thus generated in winding 16 which is applied to grid 39 to assure that device 36 is rendered conductive during such half cycle. Resistance 45 impresses a negative transient potential on anode 37 and so renders the valve non-conducting at the end of each half cycle of conduction. Valves 4, 5 are rendered conductive during the conducting period of valve 36. As condenser 51 charges through resistance 52 it will eventually reach a value which as it is applied to grid 39 blocks valve 36, the number of half cycles of conduction of valve 36 being determined by the setting of 49 and 52. Condenser 51 continues to charge and after a further time or number of non-conductive half cycles of the voltage of transformer 20, dependent on the setting of 50 and 52, valve 53 is rendered conductive by a voltage of peaked wave form over transformer 58 so that condenser 51 discharges and the cycle is repeated. The instant during a cycle at which valve 53 conducts, and the circuit to load 3 is switched on, is determined and adjustable by phase shifting device 60, whilst device 66 determines the point in each cycle at which valve 36 conducts and so controls the amount of energy transferred to load 3.