GB650790A - Improvements in or relating to circuits for producing and controlling pulsating unidirectional currents - Google Patents

Abstract

650,790. Rectifying. ASKANIA REGULATOR CO. Aug. 8, 1947, No. 22103. Convention date, Dec. 2, 1942. [Class 38 (ii)] [Also in Group XXXVII] A circuit for producing and controlling a pulsating unidirectional current comprises a gaseous discharge tube having an anode circuit including a source of A.C., circuit means for applying to the grid of the tube a biassing interrupted voltage wave and/or a signal alternating voltage wave of the same frequency as the anode voltage wave but in phase quadrature therewith, circuit means for applying to the grid a control alternating voltage of the same frequency as the anode voltage wave and normally sufficient to prevent firing of the tube when in opposite phase to the anode voltage, and means for varying the amplitude and/or phase with respect to the anode voltage of the control voltage wave so as to control the frequency of firing of the tube in accordance with the amplitude and/or phase variation. The voltage applied to the grid 3 has a number of components, viz. an alternating voltage across the points 12, 13 obtained over a phaseshifting circuit 18, and which has an amplitude so that when it is in phase opposition to the anode voltage it is sufficient to prevent the discharge tube 1 firing, and a D.C. component tending to make the grid negative derived from a condenser 15 and another D.C. component tending to drive the grid positive derived from a condenser 11. The condenser 15 is charged during the conductive periods of the discharge tube and is discharged during non- conductive periods while the condenser 11 is charged almost instantaneously at the beginning of a conductive period. Unidirectional halfwave current pulses will thus be supplied to the load circuit 8 during each positive half-cycle of anode voltage until the condenser 15 is charged sufficiently to drive the grid negative and so prevent the tube from firing, in which condition the tube will remain until the condenser has discharged. The function of the condenser 11 is to build up a positive charge at the beginning of a conductive period to ensure the firing of the tube. Pulses of unidirectional current are thus delivered to the load-circuit in groups separated by periods of non-conduction. Adjustment of the length of the conductive periods, or of the non-conductive periods, or both, may be effected by altering the amplitude or phase of the voltage derived from the phase-shifting circuit 18 and by the variable resistor 24 and the potentiometer 22, the overall range of the circuit being controlled by variable resistor 9 and potentiometer 17. In another embodiment a further alternating control voltage, of the same frequency as the voltage at points 12, 13, but displaced 90 degrees therefrom, is injected into the grid circuit between condenser 11 and resistor 10 so that any change in the amplitude of this voltage will control the operation of the tube. A pair of tubes feeding a device such as an A.C. series commutator motor is described in which the motor is controlled in accordance with the value of the injected A.C. control voltage; or alternatively the circuit may be utilized in a Selsyn system.