Thomson Consumer Electronics Inc.

Marvin N Norman

Lawrence E Smith

Walter Truskalo

Robert Joseph Gries

Peter Ronald Knight

An active amplifier is responsive to a vertical parabola voltage developed across a trace or S-shaping capacitor for developing a DC voltage at an increased voltage level than can be obtained by rectifying the parabola voltage. The increased voltage level is developed in a capacitor, during part of the period of each scan. The capacitor is discharged through a parallel resistor. During normal scanning, the capacitor voltage, alternately, increases and decreases, but remains above a threshold level as detected by a comparator. Upon scan loss, the capacitor discharges below the threshold and the comparator triggers blanking of the kinescope driver. In this way, the phosphors of a cathode ray tube of a television, especially a projection television, are protected from burning due to a loss of electron beam deflection.

Scan loss detector for cathode ray tube

A boost capacitor has a first terminal that is coupled to a retrace capacitor of a horizontal deflection circuit. A diode couples a trace voltage in an S-shaping capacitor to the boost capacitor to charge the boost capacitor during trace. A second diode rectifies a voltage that is equal to the sum of the boost capacitor voltage and a retrace voltage developed in the retrace capacitor for generating a screen grid voltage for a cathode ray tube.

Voltage booster for CRT electrode supply

A voltage at a control grid of a cathode ray tube is generated at a blanking level to provide beam current blanking when horizontal deflection loss occurs. The control grid voltage at the blanking level is developed in a capacitor prior to an instant in which the horizontal deflection loss occurs. When the capacitor voltage is applied to the control grid to provide the blanking level, the capacitor is discharged slowly. To maintain the capacitor charged, prior to such instant when horizontal deflection is lost, the capacitor voltage is not applied to the control grid as long as the horizontal deflection is normal, regardless of whether vertical deflection loss occurs. Either horizontal deflection loss or vertical deflection loss will disable a video driver stage that controls the cathode of the cathode ray tube for providing additional beam current blanking capability.

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Noblesville, IN, United States of America

Marvin N Norman