PURPOSE: To ensure an optimum focus state in front of a screen for a CRT receiver by applying the optimum focus voltage despite change of the horizontal and vertical amplitudes of a screen display part.
CONSTITUTION: A focus controller consists of a CRT 1 which displays the images, a dynamic focus voltage generating circuit 3 which generates the dynamic focus voltage synchronously with a deflecting circuit 8, a flyback transformer 4 which superposes the dynamic focus voltage on the high DC voltage, a focus electrode 5 which receives the output of the transformer 4 and converges an electron beam, a display part detecting means 6 which detects the horizontal and vertical amplitudes of a screen display part projected on the CRT 1, and a waveform control circuit 7 which controls the amplitude of the dynamic focus voltage based on the output of the means 6. In such a constitution, an optimum focus state is secured through the control carried out in accordance with changes of the horizontal and vertical amplitudes of the screen display part.
YOSHIDA MASAHIRO
TAGAMI TOMOHISA
OZAWA KENJI
Next Patent: DYNAMIC FOCUS CIRCUIT