TELEVISION APPARATUS HAVING KINESCOPE SPOT BURN PROTECTION CIRCUIT WITH EXTENDED GRID CUT-OFF TIME CONSTANT

摘要

A source of switched supply voltage is applied to apotential divider and coupled to an output terminal via acapacitor. An output tap of the potential divider is coupled to theoutput terminal via the conduction path of a grounded basetransistor. In operation the transistor (1) operates in an invertedmode for initially charging the capacitor, (2) operates in either anormal or an inverted mode for regulating a grid bias voltage atsaid output terminal for grid current flow of either directionrelative to the output terminal and (3) operates in an isolationmode upon removal of the switched supply voltage whereby thecapacitor applies a negative grid cut-off bias to the outputterminal, said transistor in said isolation mode preventingdischarge of the capacitor thereby providing a grid cut-off bias atsaid output terminal having an extended cut-off time constant dueto the lack of any discharge path for the capacitor other thanleakage.