ES322523A1 - Improvements in spot suppression circuits in a cathode-ray tube - Google Patents

Abstract

The beam of a cathode-ray tube is suppressed during fly-back periods by the application to the control grid W (Fig. 5) of negative pulses derived in a circuit including a transistor T supplied with signals occurring in the line and frame scanning circuits BL, BT during flyback periods. Such signals are not of the ideal shape (rectangular) for correct suppression tending rather to approach a semi-sine curve and to be accompanied, particularly in the case of signals from the line scanning circuit, by parasitic (overshoot) pulses, the former resulting in only partial suppression during the fly-back and the latter resulting in unwanted blanking during the commencement of the trace period (Fig. 3, not shown). These defects are removed by adjustment of the ratio of the potential divider formed by resistors R 1 , R1 1 , and R 2 to make the amplitude of the parasitic pulses slightly lower than the cut-off voltage of the transistor so that the latter passes rapidly from cut-off to saturation on the occurrence of the true fly-back signal resulting in the production of rectangular suppression pulses of the correct width and substantially free from the parasitic pulses.