GB940784A - Improvements in or relating to voltage regulator circuits - Google Patents

Abstract

940,784. Automatic voltage control systems. WESTINGHOUSE BRAKE & SIGNAL CO. Ltd. May 8,1961 [May 9, 1960], No. 16250/60. Heading G3R. A D.C. voltage regulator circuit having input and output terminals 12,13 has its output voltage held constant by a series regulating transistor 11 whose conductivity is altered by a control transistor 15 biased by a potential divider 17, a Zener diode 18 providing a reference voltage. A second control transistor 16 protects the transistor 11 against overload and is normally inoperative when the volt drop across the portion of the divider 21 between the emitter of transistor 16 and the resistor 20 is greater than the volt drop across the resistor 20. When the output voltage falls slightly below its regulated level on reaching the current limit of transistor 11, the diode 18 ceases to conduct and the voltage on divider 21 is then derived from the divider formed by resistances 19, 22. Further fall in output voltage causes the volt drop between the emitter of transistor 16 and the resistor 20 to fall below that across the resistor 20, with the result that the output current is limited by the action of transistor 16 on transistor 11. To minimise current flow when the terminals 13 are short-circuited, the resistor 20 may be replaced by a non-linear element such as a rectifier poled forwardly. Transistor 11 may be replaced by a plurality of transistors arranged in parallel, series,or series-parallel relationship.