Automatic CRT Heater Control
Original Publication Date: 1987-Feb-01
Included in the Prior Art Database: 2005-Jan-31
To extend CRT life, a cathode heater is initially run at a low voltage and increased as cathode emission decays. Screen brightness or beam current is sensed to provide an input to a digital controller to automatically control the heater voltage supplied by a voltage regulator. An adaptive algorithm operates at intervals to determine the optimum heater voltage to minimize cathode decay. The maximum brightness of all cathode ray tubes reduces with life. The primary reason for this is the decay in emission capability of the cathodes. If a cathode is run within its normal limits of current density, then the life is determined primarily by the cathode temperature. This is because the most important constituent of the universal oxide cathode is free barium, which is volatile.