Television receiver with an automatic digital alignment system

Claim 1

Video display apparatus such as a television receiver or the like, comprising: a cathode ray tube having a focusing electrode and a high voltage terminal; an alignment computer; a memory coupled to said alignment computer for storing predetermined nominal focusing parameters; a cathode ray tube screen sensor coupled to said alignment computer; said alignment computer being responsive to information stored in said memory and to signals provided by said sensor for generating a digital focusing word; a converter circuit coupled to said alignment computer for forming at an output a pulse-duration modulated signal in response to said digital focusing word; a high voltage source coupled to said high voltage terminal; a network coupled to said high voltage source for deriving at a terminal a voltage equal to the focusing limit voltage corresponding to one of two focusing range limits; a blocking oscillator having a primary winding and a secondary winding; a rectifier circuit coupled between one end of said secondary winding and said focusing electrode; the other end of said secondary winding being coupled to said terminal; and a solid state switching means having a control electrode coupled to said converter circuit output, and a controlled path coupled between one end of said primary winding and ground, the other end of said primary winding being coupleable to a d.c. voltage; whereby the operating value of the focusing voltage at said focusing electrode differs from said focusing limit voltage in the direction of the voltage of the other of said two focusing range limits by the rectified voltage of said secondary winding.