GB791236A - Improvements relating to bridge circuits particularly for stabilising a.c. voltages - Google Patents

Abstract

791,236. Automatic voltage control systems. GENERAL ELECTRIC CO. Dec. 30, 1954 [Dec. 30, 1953], No. 37680/54. Class 38 (4). [Also in Group XXXVI] In an automatic A.C. voltage control system of the kind in which a controlled self-saturating magnetic amplifier is connected in series between the input and output terminals, the output voltage error is detected by a demodulator bridge. In one embodiment, the bridge consists of tungsten filament lamps 11 in two arms, and, in the other arms, linear resistors 12 in series with transformer secondaries 14 which produce a circulating alternating current round the bridge proportional to the system output voltage (from terminal 5). A D.C. bias obtained by rectifying at 17 a portion of the output voltage tapped off the output transformer at 8 is applied to the bridge across diagonal 18. The circulating current due to transformers 14 does not produce any signal across diagonal 25 because of the symmetry of the circuit, but it does control the effective resistance of the lamps 11. The D.C. bias at 18 is adjusted so that for a desired value of output voltage (and corresponding circulating current) the total current both A.C. and D.C. through the lamps 11 causes the bridge to balance. Then any change in output voltage changes the A.C. circulating current (changes in D.C. bias are neglected) thereby changing the effective resistance of the lamps so that the bridge is unbalanced and produces a D.C. output signal across diagonal 25. This voltage controls the main magnetic amplifier 44 which is in series between the input 1 and the output auto-transformer 6 via magnetic amplifiers 28, 29. In a modification, Fig. 2 (not shown), the A.C. control voltage is applied to all bridge elements in parallel via blocking condensers.