GB1272218A - Improvements in or relating to alternator regulator systems - Google Patents

Abstract

1,272,218. Automatic voltage control. MULLARD Ltd. May 12, 1969 [May 30, 1968], No.25967/68. Heading G3R. An automatic voltage regulator for a vehicle having an alternator A, rectifier A1, A2, A3, battery 26, ignition switch 5, a separate wire SW to sense the battery voltage and warning lamp WL, comprises a transistor T13 which intermittently energizes the field winding F of the alternator in accordance with the condition of a bi-stable circuit formed of a long tailed pair of transistors T2, T3, to whose bases are respectively applied signals representative of the battery voltage and a desired value thereof, the regulator being designed to exhibit hysteresis with respect to the battery voltage between turning on and off the field current to the alternator. The battery voltage signal is obtained from resistors 2, 3 through a transistor T1, whilst the desired value signal is obtained from a reference voltage derived from the emitter-base breakdown characteristic of a transistor T11, this voltage being applied to transistor T3 through the base-emitter of a transistor T9 or the emittercollector of a transistor T10 according to the state of the bi-stable circuit T2, T3. The operation of the circuit including members T1---T4, T9, T10 is analysed to show that the hysteresis voltage at the terminal B, which voltage corresponds to the two states of the bi-stable circuit (and hence to the ON and OFF conditions of the transistor T13), is independent of the values of the resistors 5, 6 and dependent only on the ratio resistors 2, 3. This feature obviates the need for close tolerance resistors and thus enables the regulator to be of solid state integrated circuit form. For this reason transistors T5, T7 are respectively combined with transistors T6, T8 to provide sufficient amplification of the signals transmitted thereto. Transistor T1 is chosen to provide voltage temperature coefficient compensation for that of the transistor T11 and may consist of a transistor with one or more diodes in series with the base-emitter path. Transistor T11 may have its collector or base left open-circuited, transistors T2, T3 may have compensating voltage-temperature coefficients and resistors 11, 14 are chosen to provide further temperature stability. Transistors T5, T6 control the Darlington-connected transistors T12, T13 and transistors T7, T8 compare the alternator and battery voltages to control an ignition warning lamp WL in the usual way. If the wire SW sensing the battery voltage should become disconnected, transistors T12, T13 are turned off to open circuit the field winding and so prevent build-up of the alternator voltage. Feedback in the regulator is provided by transistors T14, T15 and resistors 12, 13.