TV frame sweep DC voltage generator - feeds vertical sweep circuit and video amplifier supply from common winding

摘要

Energy to drive current through the vertical diverter (DV) is drawn exclusively from a generator (2) supplied with line flyback pulses from the sec. winding (S1) of the line output transformer (TL). A capacitor (CL) and resistors (Rm,Rn) together with the divertor (DV) form a load impedance for this generator such that the voltage at its terminals is of constant sign, irrespective of the direction of divertor current. The DC voltage is produced by a rectifying circuit (D2,C2) connected to the same winding. For transistorised colour TV receivers the line transformer needing only one sec. winding is less bulky and costly. The generator (2) incorporates an active switch, bidirectional in current and unidirectional in voltage, comprising a thyristor (TH1) and inverse diode (D1) in series with the sec. winding. The thyristor gate (G) is pulsed by a negative-feedback control circuit (3) connected to a sawtooth generator (5) so that conduction time during each line is a function of the line number. The electrolytic capacitor (CL) is chosen so that the average positive voltage between its terminals is high enough to ensure a positive output to the thyristor control circuit.