Active Frame Flyback Circuit for CRT
Original Publication Date: 1984-Aug-01
Included in the Prior Art Database: 2005-Feb-04
To maximize the duty cycle and brightness of the image displayed by a raster-scanned CRT the vertical flyback time of the current in the deflection yoke is required to be decreased. A frame flyback circuit is described which switches in a higher voltage to the amplifier output stage during the flyback period to allow a faster rate of change during the flyback period. This switching is controlled by a pulse-shaping network which limits the instantaneous power dissipated in the amplifier and prevents fast switching transients which could disturb normal operation. The basic circuit with typical waveforms shown in Fig. 1 achieves the function of fast flyback. When the voltage at the output reaches a predetermined level, set by the Zener diode Z voltage, the transistor Q1 turns on, thus turning on the 'pull-up' transistor Q2.