GB1178383A - Improvements relating to Control Circuit Arrangements. - Google Patents

Abstract

1,178,383. Vehicle power supply systems. MULLARD Ltd. 20 Feb., 1967 [27 April, 1966], No. 18430/66. Heading H2H. [Also in Division G3] An alternator 1 such as may be used in the electrical system of a motor vehicle is associated with a circuit arrangement including a device, e.g. a lamp 19, for indicating when the alternator output exceeds a predetermined level, a control quantity derived from the alternator output being applied to control a transistor switch which when closed provides a short-circuit across the device. As shown, the switch is constituted by a transistor 18 which also forms part of a voltage regulator 10 to 13, 15 to 17, connected to control, in known manner, the excitation current supplied to the field winding 2 of the alternator, the collector/emitter path of transistor 18 being connected, together with a further switch 14 which may be combined with the ignition switch of a vehicle, in parallel with the lamp 19. When the switch 14 is closed and the alternator 1 first started up, the voltage from a battery 8 connected to be charged from the alternator renders transistor 17 conductive, and field current flows by way of transistor 17, lamp 19 and switch 14, the lamp 19 thus being energized as transistor 18 is non-conductive under these conditions. As the alternator output builds up, a control signal derived from the alternator output windings is applied to the base of transistor 18 by way of resistors 21, 22, 23 connected as shown; when the output reaches the predetermined level transistor 18 conducts to short-circuit lamp 18 which is thus extinguished. A resistor 20 may be connected in parallel with the lamp 19, which could be replaced by a buzzer. The arrangement may be applied to a negative-earth system (Fig. 2, not shown), and the voltage regulator may include a positive feedback circuit to aid its switching action (Fig. 3, not shown). The switch 14 may be actually constituted by the ignition switch of a vehicle instead of being associated therewith.