GB1181397A - Improvements in or relating to Voltage Stabilising Circuits - Google Patents

Abstract

1,181,397. Rectifying. TELEFUNKEN PATENTVERWERTUNGS G.m.b.H. 20 March, 1967 [5 April, 1966], No. 12917/67. Heading H2F. [Also in Division G3] The EHT voltage supplied to a television tube 10 is automatically stabilized with variations of beam current by passing the latter through the control winding 11 of a transductor 25 whose working winding 12 is series-connected between a winding 4 of the output transformer 1 and an impedance 13 so that the pulsating voltage appearing at the junction of members 12, 13 varies with the variation of current through the winding 11. This pulsating voltage is passed via a rectifier 14 and a potentiometer 19 to the control grid of a power valve 5 whose gain is thus automatically varied with beam current variation to maintain the EHT voltage constant. The basic bias voltage for the valve 5 is obtained from the circuit comprising members 15, 16, 20 ... 23, the resistor 16 being voltage dependent and being adjusted so that the positive biasing voltage existing by virtue of the transductor when the beam current is zero is compensated. A failure of the voltage applied to the winding 12 or of the rectifier 14 thus does not give rise to a control of the valve 5 which would produce a rise in EHT voltage. In a modification, Fig. 2 (not shown), in which the VDR16 is used to produce the control voltage for valve 5, members 14, 19, 27 are omitted, the signal from the junction of members 12, 13 is fed to the VDR16 and resistor 23 is connected to the grid of valve 5. Winding 4 is centre tapped to earth to form two push-pull windings which form a bridge circuit with the members 12, 13 having zero output when the beam current is zero. The regulating action may be limited at a predetermined point by suitable choice of the characteristic of inductance of winding 12 against control winding current, Fig. 3 (not shown). Other ways of varying the control range of the characteristic comprise connecting an inductor in shunt with the winding 12, adjusting the potentiometer 19, connecting a resistor in parallel with the winding 11, and effecting electrical or permanent magnet type pre-magnetization of the transductor. The transductor may have another control winding responsive to the mains supply voltage. Instead of being supplied by the winding 4, the pulsating voltage may be obtained from other sources of varying voltage.