公开(公告)号：GB2273425A

公开(公告)日：1994-06-15

申请号：GB9225835

申请日：1992-12-10

Applicant: IBM

Inventor： EAGLE DAVID JOHN ,  TAYLOR SIMON DAVID

IPC: H04N5/59

Abstract: A cathode ray tube display comprises a cathode ray display tube 80 having a cathode for emitting an electron beam and a control electrode 61 for controlling the intensity of the electron beam. A video amplifier 30 is connected to the cathode for modulating the electron beam as a function of an input video signal to generate a picture on the screen of the cathode ray display tube. A brightness control circuit 70 varies a voltage on the control electrode 61 to vary the brightness of the picture. A contrast control circuit 60 varies the gain of the video amplifier 30 to vary the contrast of the picture. A beam current limit circuit 50 has a first output TH1 connected to the contrast control circuit 60 for reducing the gain of the video amplifier 30 in response to the electron beam current exceeding a first threshold and a second output TH2 connected to the brightness control circuit 70 for reducing the voltage applied to control electrode in response to the beam current exceeding a second threshold greater than the first threshold. The second threshold prevents excessive beam currents from damaging the EHT generator when the voltage applied to the accelerating electrode of the cathode ray tube is incorrectly adjusted.