Abstract: A dynamic focus voltage generator includes a source of a flyback input signal at a horizontal deflection frequency. A double integrator is responsive to the input signal for generating a parabolic periodic signal. An amplitude detector is responsive to the parabolic periodic signal for generating a control signal that is indicative of an amplitude of the parabolic periodic signal. A comparator is responsive to a signal at a reference level and to the control signal and coupled to the double integrator for regulating an amplitude of the parabolic periodic signal in a gain control negative feedback manner. A non-linear network is responsive to the parabolic periodic signal for producing a bathtub shaped output signal that is coupled to a focus electrode of a cathode ray tube.

Abstract: A raster center control circuit for a CRT-type display device that automatically determines a correct horizontal center position of a raster, regardless of a horizontal sync frequency input from a video card. The raster center control circuit includes a horizontal deflection circuit, electrically connected to a horizontal deflection yoke, to supply the horizontal deflection yoke with a parabolic wave signal used to determine a horizontal center position of the raster. A memory device stores predetermined values for raster control according to horizontal sync signal frequencies. A microprocessor determines a frequency of a horizontal sync signal and generates a raster control signal by converting one of the predetermined values stored in the memory device into a raster control signal according to the predetermined frequency.

Abstract: A display apparatus including a CRT provided with an electron gun having a focusing electrode which is applied with a dynamic focusing voltage for focusing electrons drawn from a cathode of the CRT is disclosed. The display apparatus includes a dynamic focusing circuit for producing the dynamic focusing voltage by superimposing, on a dc voltage supplied from outside, an ac voltage which has a waveform varying in synchronization with horizontal and vertical deflections of an electron beam flowing to a fluorescent screen on the anode. The display apparatus further includes a compensator for lowering the dc voltage supplied to the dynamic focusing circuit by a predetermined value while a brightness signal indicative of brightness of a screen of the CRT exceeds a threshold value.