Regulation of the scan width of a raster scanned CRT deflection system

DETAILED DESCRIPTION According to one aspect of this invention there is provided in combination with a horizontal scanning system for a CRT, said system being of the resonant shunt efficiency type and including a damper diode, a tuning capacitor, a decoupling capacitor, switching means and a horizontal deflection coil; means for supplying a variable frequency valve signal to said scanning system to produce a horizontal scan of variable frequency; a variable output voltage power supply for supplying a variable power supply voltage to said horizontal scanning system; means for deriving an error signal indicative of a change in magnitude of the peak to peak deflection current in said coil from a predetermined magnitude; and means for supplying said error signal to said variable output voltage power supply to decrease said magnitude of said peak to peak voltage in response to an increase in said deflection current and to increase said voltage in response to a decrease in said magnitude of said peak to peak deflection current, thereby to maintain said magnitude of said peak to peak deflection current substantially constant regardless of changes in frequency of the horizontal scan.