Video display protection circuit

Abstract

A grid kick circuit for applying beam cut-off bias to the grid of a kinescope to provide spot burn protection. The circuit includes a first switching circuit having an output coupled to a first electrode of a grid kick capacitor and a second switching circuit having an output coupled to a second electrode of the capacitor and the grid. When beam blanking is not desired, charging current is supplied to the capacitor through a first current path from a first voltage source while the second switching circuit regulates the voltage at a second electrode of the capacitor and the grid. Current for the second switching circuit is provided by a second current path which is coupled to the first voltage source and is independent of the first path. When beam cut-off is desired, the first switching circuit clamps the first electrode of the capacitor to ground, the second switching circuit decouples the second electrode of the capacitor from the second voltage source, and the cut-off voltage developed across the capacitor is applied to the grid of the kinescope. Advantageously, the first and second current paths provide improved capacitor charging efficiency, the active pull down of the capacitor voltage provides increased cut-off speed and the grid bias voltage is regulated during normal operation when cut-off is not desired.