Timing circuit for car parking lights - turns out lights after period determined by RC-network, if engine is idle and doors closed

摘要

The circuit comprises a switch, an RC time delay setting network and two amplifiers with feedbacks from the output of the second to the RC circuit. The switch connects the input to ground via a resistor (R1). The input is connected to the base input of a Darlington pair comprises two PNP transistors whose collector output is connected to a resistor (R4) and thence to the base of a third transistor (T3) which is a NPN type. The latter has a grounded emitter and the collector is connected to a lamp. The lamp is connected to positive supply via a resistor (R5) and also back to the input via a capacitor (C1). The positive supply is also connected to the input via a resistor (R2) and the emitter of the Darlington pair. For switching off lights powered when car is parked, saving car battery loading.