Zenith Electronics Corporation

James R Oates

Gregory J Beaumont

Richard J Steinmetz

In a horizontal drive circuit for a video display, means are provided for sensing the horizontal output pulse used to energize the high voltage sweep transformer and, in turn, the electrodes and deflection coils in a cathode ray tube (CRT). Horizontal output pulse height which represents not only the voltage applied to the CRT, but also retrace pulse duration is detected and utilized to terminate the video output when the horizontal pulse voltage level exceeds a predetermined value. Because this approach uses the collector pulse output of the horizontal output transistor to detect high voltage conditions, video shutdown during unsafe CRT operation is available not only for excessive peak voltage conditions, but also for improper retrace time operation due, for example, to sweep transformer malfunction.

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Wheeling, IL, United States of America

James R Oates