Video display apparatus with kinescope spot burn protection circuit

摘要

A television receiver includes a kinescope spot burn protection circuit comprising a capacitor coupled between a source of blanking signal and a control grid of the kinescope for applying negative grid cut-off bias to the kinescope in response to the blanking signal. The amplifier is of the cascode type having a minimum output voltage for peak white levels of a video signal applied to the cathode. The protection circuit includes a potential divider for biasing the kinescope at a positive voltage level related to the minimum output voltage of the amplifier during normal operation of the receiver to maximize the brightness of displayed images. The protection circuit also includes a breakdown device in the potential divider for limiting the maximum grid bias voltage to a level less than the minimum output level of the amplifier but greater than the positive voltage level provided by the potential divider to thereby avoid forward biasing the grid of the kinescope upon termination of the blanking signal which otherwise could occur during recharging of the capacitor.