GB978805A - Improvements in or relating to sawtooth current wave generating circuit arrangements - Google Patents

Abstract

978,805. Valve sawtooth circuits. PHILIPS ELECTRONIC & ASSOCIATED INDUSTRIES Ltd. Feb. 14, 1961 [Feb. 17, 1960], No. 5453/61. Heading H3P. In a deflection circuit for a television display tube, the H.T. boosting capacitor is divided into two series-connected parts, the voltage across one part being used to control the deflection current amplitude. As shown in Fig. 3, a sawtooth current is generated in deflection coils 13 by valve 1 under control of waveform 2. The efficiency diode 11 provides a boosted H.T. voltage across capacitor 39 which, with capacitor 40, forms the flyback energy recovery circuit. Capacitors 39, 40 have comparatively low value so that parabolic voltages 41, 42 are provided by integration of the sawtooth current. Waveforms 41, 42 are added to the sawtooth current through the deflection coils 13 to provide the S-shaped waveform required for wide-angle cathode-ray tubes. The flyback voltage at point 21 is rectified by valve 19 to provide a negative bias for valve 1. Increase in sawtooth current amplitude will result in an increase in the amplitude of waveform 42 fed to the grid of valve 19 so that the rectified flyback voltage at the grid of valve 1 will become more negative thus correcting the increased amplitude. The E H.T. supply, obtained by rectifying the flyback voltage by means of a diode 30, is similarly stabilized. Valve 19 cathode voltage is stabilized by a neon tube 44. The capacitor 20 may alternatively be connected to point 14. In Fig. 5 (not shown) the neon tube 44 is replaced by a voltage-dependent resistor and the grid of valve 19 is fed via a blocking capacitor. Reducing radiation.-Windings 37, 38 form a push-pull circuit to minimize radiation from the deflection circuit. Winding 38 may be omitted if this feature is not required. Specifications 849,980 and 898,625 are referred to.