To effectively suppress the electric field formed by the radiation from the front and the whole of a CRT not by shielding but by previously cancelling electric field components.
A high-tension voltage obtained by rectifying the high-tension coil pulse voltage of a fly-back transformer 22 is divided by a splitting resistor and, based on this detection voltage, the power source voltage supplied to the primary coil of the fly-back transformer 22 is controlled by a power source voltage control circuit to make the high voltage constant. After being controlled in polarity, phase and amplitude, the parabolic voltage in the vertical and horizontal periods are inputted into this circuit through a horizontal parabolic waveform input terminal 14 and a vertical parabolic waveform input terminal 15 to be added and mixed. Through this, no dynamic focussing parabolic voltage is caused to appear in the high-tension coil voltage of the fly-back transformer 22. since the phase and amplitude are easily controlled in a comparatively low frequency region, a frequency range of 5Hz to 400Hz, the cancelling effect for electric field components is large.
KOYAMA MASAYUKI
NONAKA YASUSHI
HITACHI VIDEO IND INF SYST INC