GB1068307A - Circuit arrangement for the generation of a periodically fluctuating unidirectional current in an inductive load - Google Patents

Abstract

1,068,307. Waveform generation circuits; cathode-ray tube circuits. FERNSEH G.m.b.H. Sept. 17, 1965 [Sept. 19, 1964; Nov. 25, 1964; Aug. 25, 1965], No. 39764/65. Headings H3T and H4T. A parabolic waveform is produced in an inductive load by connecting it in parallel with a capacitor and inpulsing it unidirectionally at twice the resonant frequency of the parallel circuit. In Fig. 4 (not shown), a circuit using a transistor switch and a series phase shift-coil (3) generates parabolic (or semi-sinusoidal) current waves in a focusing coil (1) of a cathoderay tube to maintain focus during the scan. In Fig. 6 a similar circuit using S.C.R's. adds a line frequency modulation to the framescanning current (as in waveform C) to ensure registry of the raster of a shadow mask tube. The circuit comprises two generators, each comprising a load inductor 1 tuned to about half the line frequency by a capacitor 2 and connected in series with a small inductor 3 and an S.C.R. to a D.C. voltage source U. When the S.C.R. is fired, capacitor 2 is charged resonantly through inductor 3 until after half-acycle, when the voltage across the capacitor reaches a reverse peak and the S.C.R. automatically extinguishes. The capacitor then discharges into the inductive load and the circuit rings for half-a-cycle producing a half sine wave current in the load if the tuning is exactly to half the line frequency and a parabolic current if the ratio of frequencies is greater than 2. The load inductors are coupled to the deflection coils through a capacitor 8 which blocks frame deflection currents and an inductor 10 is provided to block the parabolic waves for the frame output transformer secondary winding S. Inductor 3 is chosen to provide a desired phase shaft between the input pulses and the parabolic wave. Components 11, 12 prevent self-oscillation in inductor 3. The two circuits provide parabolic waves in opposite sense and these are differentially modulated by the frame saw-tooth applied at A so that at the mid-point they are equal and opposite. The two S.C.R's. may each be replaced by two complementaty transistors which may be connected to series with rectifiers to prevent reverse conduction or by valves.