Abstract: A brightness adjustment device for a display device including a microprocessor for outputting a brightness control signal according to a synchronizing signal provided from a display signal source; a parabolic wave generator for generating a parabolic wave according to the brightness control signal supplied from said microprocessor; a video pre-amplifier for summing a video signal provided from the display signal source and the parabolic wave supplied from the parabolic generator and amplifying the summed signal; and a video main amplifier for amplifying the video signal supplied from the video pre-amplifier and outputting the amplified video signal to a cathode ray tube.

Abstract: A spot is prevented from occurring on the center portion of a cathode ray tube when electric power is turned off by using a voltage charged in a capacitor which are used for outputting a vertical blanking signal in a vertical blanking signal generating circuit of an image display device for displaying an image in use of the cathode ray tube. The present invention is provided with a discharge cut-off element between a negative electric power source and the capacitor for outputting a vertical blanking signal and a discharging element for discharging a charged voltage of the capacitor to the ground. The present invention prevents a charged voltage ofthe capacitor from being discharged until thermoelectrons are not emitted from the cathode so as to supply a negative charged voltage to the first grid of the cathode ray tube continuously, so that a spot is prevented from occurring.

Abstract: An initial drive voltage supply control circuit for an SMPS, comprising a rectifier for rectifying and smoothing an AC voltage inputted by an AC input unit to convert it into a DC voltage, a switching transformer having a primary coil for receiving the DC voltage from the rectifier and secondary and tertiary coils for inducing desired voltages in response to the DC voltage received by the primary coil, an output power controller for supplying or blocking the DC voltage from the rectifier to the primary coil of the switching transformer, an initial drive voltage controller for supplying an initial drive voltage to the output power controller and blocking the initial drive voltage to the output power controller when a normal drive voltage is supplied to the output power controller after the lapse of a predetermined time, a load output unit for rectifying and smoothing the voltage induced in the secondary coil of the switching transformer to output an operating voltage to a load, a drive voltage supply unit for