TV receiver automatic picture control - works independently of line flyback using shaped pulse derived from sinusoidal line oscillator

摘要

The television receiver circuit has automatic picture control independent of the line flyback to avoid risk of damage to semiconductors in the video amplifier stages caused by spikes in the line scan and flyback stage. A special pulse shaping circuit produces pulses to control the line flyback. - The pulse-forming circuit is a transistor whose base is connected via a capacitor to the output of the sinusoidal line oscillator. It is biassed so that its base-emitter circuit acts as a peak detector for the sine waveform and the squared off pulse at the collector has narrow pulse-width. This pulse controls the video stage gain.