GB932174A - Improvements in apparatus for automatically controlling direct electric current at precise values - Google Patents

Abstract

932,174. Automatic current control. H. TINSLEY & CO. Ltd. Jan. 16, 1962 [Jan. 16, 1961], No. 1784/61. Class 38 (4). [Also in Group XL (c)] A highly stabilized direct current is supplied to a load from a battery through a series transistor which is controlled by a high-gain photoelectric amplifier. The battery 1 supplies the load 2 through a transistor 4 and a precision resistor 6. The voltage drop across the resistor 6 is opposed by the E.M.F. of a standard cell 12 and the resultant applied to a sensitive mirror galvanometer G1 over contacts A 1 , A 2 . (Assume all switch contacts to be in the opposite condition to that shown.) In the null position of galvanometer G1, two phototransistors 27, 28, mounted close together are equally illuminated. These photo-transistors form, with resistors 25, 26, a bridge having a battery 29 across one diagonal. Any deflection of the galvanometer G1 unbalances this bridge and so deflects a second mirror galvanometer G2 which is connected in series with resistors 18, 20 across the output diagonal of the bridge. Part of this output is fed back to galvanometer G1 through resistor 19 and capacitor 17. The galvanometer G2 proportionally illuminates a photo-transistor 8 which controls the transistor 4 and hence the current in the load 2. A capacitor 38 provides a rate feedback signal to the galvanometer G2. To protect the sensitive galvanometer G1 from overload, the circuit is initially set up manually to approximate balance by changing over all the switches to the positions shown so that the galvanometer G2 compares a portion of the voltage drop across resistor 6 with a voltage from a manually adjustable bridge 32 . . . 37.