High voltage protection circuit having predictable firing point

Claim 1

In a television receiver including a kinescope for generating at least one electron beam, deflection means for generating horizontal and vertical deflection signals for controlling the deflection of said electron beam, high voltage means for generating a relatively high operating potential in response to said horizontal deflection signals, and video processing means for controlling the modulation of said electron beam to provide a display, apparatus comprising: a transformer winding coupled to said deflection means for developing an alternating voltage in response to said horizontal deflecton signal; supply voltage means including at least a filter capacitor for developing a supply voltage for said deflection means and said video processing means; and an integrated circuit device having a first terminal coupled to said transformer winding and a second terminal coupled to said filter capacitor, said integrated circuit device including rectifying means coupled between said first terminal and said second terminal for charging said filter capacitor in response to said alternating voltage so that said supply voltage has a sufficient amplitude for a viewable display; switching means exhibiting the conduction characteristics of a silicon controlled rectifier coupled between said first terminal and said second terminal, said switching means including a control electrode for controlling the conduction thereof, said switching means being normally nonconductive; and voltage reference means including a Zener diode and a diode coupled in series relationship between said first terminal and said second terminal, said Zener diode and said diode also being directly connected in series between said second terminal and said control electrode of said switching means, said voltage reference means being normally nonconductive, said voltage reference means being rendered conductive and thereby coupling a conduction control current to said switching means to render it conductive in turn when the difference between said supply voltage and said alternating voltage exceeds a predetermined voltage, said diode being poled to inhibit the flow of current through said Zener diode except when said supply voltage exceeds said alternating voltage by said predetermined voltage, said predetermined voltage corresponding to the level of said relatively high operating potential for said kinescope at which the generation of potentially harmful X-radiation is likely, the amplitude of said supply voltage falling to a level at which the display is unviewable when said switching means is conductive.