JPS57199155A - Electromagnetic focusing device for cathode-ray tube - Google Patents

Abstract

PURPOSE:To provide an electromagnetic focusing device for a cathode-ray tube which can easily focus an electron beam on every point of a picture surface, the circuit regulation of which is simple, and in which the adverse effect or mutual interference on a deflecting part of magnetic fields can be widely reduced. CONSTITUTION:The intensity of the magnetic fields and the positions of the z- axis direction of permanent magnets 11 and 12, which are fixed to an electromagnetic focusing part 10, are preset so that an electron beam deflected toward the peripheral part of the picture surface of a CRT are focused on the fluorescent screen. When the electron beam is deflected toward the center of the picture surface of the CRT, that is to say, as the deflection amount becomes smaller, focusing correction coils 13 and 14 of the part 10 have an increased correction current so that the static electromagnetic focusing caused by the magnets 11 and 12 is corrected. Here, a current with parabolic wavy form should be supplied to terminals 15 and 16 of the coils 13 and 14. By the means mentioned above, since the polarities of the magnetic fields of the permanent magnet and the focusing correction coil (dynamic focusing coil) work in reverse directions, any generation of cross talk can be prevented.