Electromagnetic focus apparatus

摘要

The focus coil 14 adjusts the focal point of electron beam which forms raster. The electromagnetic focus apparatus controls the ON/OFF-combinations of the respective switches 42 to 45 in synchronization with the horizontal synchronization signal S1. By this ON/OFF-controlling, the current waveform is formed, which is supplied into the focus coil 14. The microcomputer 55 adjusts the timing of the ON/OFF-controlling of the respective switches 42 to 45 in compliance with the horizontal amplitude value of the electron beam.