DETECTING HORIZONTAL BLANKING TIME IN CATHODE RAY TUBE DEVICES

摘要

Unlike previous methods for controlling functions in a video monitor where switching is timed and controlled by monitoring the retrace voltage level, the system of the present invention monitors the change in direction of current in the retrace tuning capacitor. The apparatus of the present invention comprises a small bead inductor (72) placed in the current path of a horizontal retrace capacitor (48) within the horizontal deflection circuit of the CRT device. Measuring the voltage across the bead inductor allows a very precise monitoring of the current through the retrace tuning capacitor. By designing the size of the bead inductor as disclosed, precise electrical pulses can be generated and detected during the retrace time of the CRT electron beam. The invention also minimizes left-side ringing due to the addition of the bead inductor to the horizontal deflection circuit, which lowers the stray resonant frequency within the horizontal deflection circuit.