ES336712A1 - Convergence apparatus for nullifying unwanted induced deflection currents - Google Patents

Abstract

A convergence control circuit for a multibeam colour reproducing cathode-ray display tube includes means for nullifying unwanted currents induced in the convergence means from the beam deflection means. Such currents produce adverse effects at the vertical deflection frequency, mainly in the blue-gun convergence means and the described embodiment is directed to the correction of such effects. Thus, as shown in Fig. 3, the vertical winding 34B of the blue convergence magnet 32, which is supplied with a voltage wave 45b, generally of parabolic shape and derived via a shaping circuit 44 from the wave 42 produced across cathode resistor 39 of the vertical output tube 35, to effect the normal convergence correction, is further supplied via potentiometer 59 with opposite polarity pulse type voltage waveforms 50, 51 derived from the vertical output transformer 37. These waveforms are modified by the shunt arrangement of diode 61, which may be replaced by a capacitor (Fig. 13, not shown) and resistor 62, as explained with reference to equivalent circuits (Figs. 4 and 5, not shown) and voltage waveforms (Figs. 6a to 9, not shown) to produce a resultant voltage waveform having the shape shown in Fig. 10. This produces a current waveform in winding 34B having the shape shown in Fig. 12 which opposes the current waveform (Fig. 11) induced by the beam deflection means due to the proximity of the latter to the convergence windings on the neck portion of the display tube (Fig. 1, not shown). The vertical windings 34G and 34R of the red and green convergence magnets are supplied with the parabolic voltage waveform 45 and tilt control is effected by means of a master tilt control potentiometer 48 which introduces a saw-tooth current wave 52 as a result of application of the voltage waveforms 50, 51. Differential tilt control is effected by potentiometer 56 and a differential amplitude control potentiometer 53 varies the distribution of the parabolic current through the windings 34G, 34R. The circuitry for the horizontal convergence winding 33G, 33R, 33B may be of known type.