GB858225A - Improvements in time-base circuits - Google Patents

Abstract

858,225. Valve sawtooth generating circuits. SYLVANIA-THORN COLOUR TELEVISION LABORATORIES Ltd. May 7, 1959 [May 7, 1958; Nov. 28, 1958], Nos. 14685/58 and 38522/58. Class 40(6). In a sawtooth current generator of the type in which a driver valve feeds the deflection coils through a transformer across which is connected a damper valve and capacitor in series, a further capacitor is connected in series with the damper valve and a circuit is provided which returns the capacitor voltage to a predetermined value during the flyback so causing the waveform of the capacitor voltage to have a parabolic component. In the Figure, the driver valve 10 feeds the deflection coils 14 through a transformer 11 across which is coupled a damper diode 13 in series with a boost capacitor 12. A further capacitor 17 is connected in series with the damper diode in parallel with a transistor 15 which is rendered conductive during the flyback to discharge the capacitor. The D.C. and sawtooth components of the damping diode current during the forward stroke build up voltages across capacitors 12 and 17 which compensate for non-linearity of the deflection due to the resistance of the coil circuit and the large radius of the cathode-ray tube face. When the voltage across the capacitor 17 is high the capacitor may be replaced by a number of larger capacitors connected in series each being provided with its own discharging transistors (Fig. 5, not shown). In an alternative embodiment (Fig. 6) the transistor is omitted and winding 18 is connected across the capacitor in series with a diode which is rendered conducting during the flyback so as to charge the capacitor 17 to a predetermined value (Fig. 6 not shown).