GB1287217A - Electrical device - Google Patents

Abstract

1287217 Supply systems for consuming apparatus TRW Inc 13 Feb 1970 [17 Feb 1969] 7069/69 Heading H2H [Also in Division H3] A circuit arrangement for energizing loads with a relatively heavy direct current is provided with means for timing the supply to the loads which means cut off the supply to the loads automatically at the end of a desired period of energization. Window heating elements 19 of a motor vehicle together with an indicator lamp 20 are energized over a contact 26 which closes when a relay 22 is energized by operation of a push-button switch 16 after closure of the ignition switch 17 which causes a coil 23 to be energized, which energization is then maintained by a circuit including resistor 30. Simultaneously with the energization of the loads 19, 20 a timing circuit comprising resistor 32 and capacitor 33 is energized and a voltage developed on the gate 35 of a programmable unijunction transistor 37. Capacitor 33 charges up and after a predetermined time the charge on the capacitor reaches a value at which the transistor 37 becomes forwardly biased whereupon the transistor fires and the capacitor 33 discharges through a second winding 24 of the relay 22. Winding 24 is arranged to buck winding 23 such that energization of winding 24 causes the contact 26 to open thus terminating the supply to the loads 19, 20. A thermistor 40 is connected in parallel with resistor 34 to provide over-compensation for the temperature characteristics of the capacitor 33. Thus the energization time of the loads 19, 20 is longer at lower temperatures than at higher temperatures.