GB1192921A - Ignition Warning Lamp Circuits for use in Road Vehicles - Google Patents

Abstract

1,192,921. Motor vehicle ignition circuits. JOSEPH LUCAS (INDUSTRIES) Ltd. 14 Aug., 1967 [15 Aug., 1966], No. 36413/66. Heading H2H. An ignition warning lamp circuit for a road vehicle includes an ignition switch 13 through which, in use, the warning lamp 27 is illuminated when the generator 15, which may be an alternator with associated full wave rectifier, is not charging the battery 12 of the vehicle; a capacitor, which is charged by the generator, and an amplifier having a high input impedance connected between the capacitor and the ignition switch so as to extinguish the warning lamp when the generator is producing an output. An output from the generator 15 is connected to the +ve side of battery 12 and to the anode of a diode 16, the cathode of which is connected to the capacitor 19 and to the base of a N-P-N transistor 17. The anode is also connected through a resistor 18 to an earthed return line 14. The emitter of transistor 17 is connected to the base of an N-P-N transistor 21, the collectors of transistors 17 and 21 being connected through a resistor 25 to a supply line 11. The emitter of transistor 21 is connected through a resistor 22 to the base of a transistor 23 which has its emitter connected to line 14 and its collector connected to line 11 through a resistor 26 and to the base of an N-P-N transistor 25 whose collector is connected to a warning lamp 27 and whose emitter is connected to the line 14. When the ignition circuit is closed, current flows through resistor 26 and the base emitter path of transistor 25 so that lamp 27 is illuminated. As soon as the generator 15 produces an output the capacitor 19 is charged and the voltage across capacitor 19 is amplified by the Darlington circuit constituted by the transistors 17, 21 which acts upon transistor 23 so that the base current is diverted from transistor 25 whereby the warning lamp 27 is extinguished.