Front/back porch voltage-regulator of vertical focus control signal

摘要

A voltage control circuit to control a focus exactly by controlling a front/back porch voltage level of a vertical focus control signal regardless of a slight error in an upper and a lower part of a cathode-ray tube. In order to control the front/back porch level of the vertical focus control signal, a certain level of a DC voltage put out by a level controller is added to a saw tooth wave generated by integrating a DC voltage put out by a microcomputer in a first integrator. In a second integrator, a parabola wave is generated by secondly integrating the DC voltage. The level of the DC voltage added to the saw tooth wave is controlled by putting out the generated parabola wave as the vertical focus control signal according to a slight error generated in the upper and the lower part of a cathode-ray tube, and this enables to control the front/back porch voltage level of the vertical focus control signal and the focus exactly in the upper and the lower part of the screen.