Circuit for regulating brightness and size of picture in display apparatus

摘要

A circuit for regulating the brightness and size of picture in a display apparatus is disclosed, in which a picture brightness regulating circuit and a picture size regulating circuit are organically coupled together, and the picture brightness and size are decided by utilizing composite adjusting signals of a microcomputer. The display apparatus receives and amplifies RGB signals from a computer main body to output them to a cathode ray tube, supplies a high voltage from a fly back transformer to the cathode ray tube, and carries out horizontal deflections by a horizontal deflecting circuit. The circuit for regulating the brightness and picture size in the display apparatus according to the present invention includes the following elements. A current sensing section senses the intensities of beam currents incoming into the cathode ray tube. A microcomputer decides the lower limit of a terminal voltage if the terminal voltage is lowered, the terminal voltage being anti-proportional to the beam current as sensed by the current sensing section. A brightness and picture size regulating circuit section decides the upper limit of the terminal voltage in relation to an internal power and an internal impedance of a video pre-amplifier. Further, it outputs brightness regulating signals to the video pre-amplifier to adjust a clamp level of RGB video signals if the terminal voltage departs from the lower limit of the microcomputer. Still further, it outputs horizontal/vertical size regulating signals to a deflecting circuit section to regulate the picture size. Therefore, the maximum brightness restriction line and the picture size regulating degree are decided by the composite adjusting signals of the microcomputer. As a result, the manufacturing time can be saved during the manufacture of the display apparatus, and therefore, the productivity can be improved. Further, the constitution of the brightness and picture size regulating circuit section is very simple, and therefore, the economy is improved during its designing.