Patent ID: 7235935

Claim:
A focus voltage generator in a video display apparatus having a cathode ray tube, comprising: a high voltage transformer including a first winding, a focus winding, a high voltage winding and a tracking winding, said tracking winding being disposed closer to said focus winding than to said high voltage winding to provide a tighter magnetic coupling to said focus winding than to said high voltage winding; a semiconductor switch responsive to a periodic signal and coupled to a resonant circuit that includes said first winding for generating resonant pulses in said first winding, said resonant pulses being transformer coupled to said high voltage winding to generate an ultor voltage at an ultor voltage electrode of said cathode ray tube and being transformer coupled to said focus winding to generate a focus voltage at a focus electrode of said cathode ray tube; and a capacitance coupled to said tracking winding to generate from said resonant pulses a current in said capacitance and in said tracking winding that selects a mode of tracking between said focus and ultor voltages, as a function of a beam current in said cathode ray tube.