White level limiter for colour TV CRT - has white limit dependent on signal derived from brightness control knobs setting

摘要

The white level limiting circuit for a colour television cathode-ray tube has the video signal supplied to the cathode-ray tube via a limiter circuit whose limit level is dependent on the setting of the brightness control knob on the front of the receiver. The limiting circuitry itself consists of a transistor stage in emitter-base connection whose bases are supplied with the video signal and whose collectors are coupled over a reverse biased diode to the brightness control potentiometer and to the bases of the emitter followers that feed the colour channels output amplifiers. The reverse biased diode may be coupled to a transistor collector electrode whose collector-emitter path becomes conductive on specified conditions.