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Vehicle Interior Lighting With Switch-Off Delay(BD318)

2014-12-10 14:40  
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This article briefly describes the Vehicle Interior Lighting With Switch-Off Delay (BD318). This principle is easy to understand, but also very practical. Depth understanding of circuit elements, can be more effective to grasp this principle. Do you know the circuit, for example, can understand and buy these components: BD318 , BD319, BD240 , BC557.

Nowadays, a switch-off delay for the vehicle interior lighting is a naturally a standard feature. However, with certain models having only spartan ?ttings, or older-model vehicles, you’re left sitting in the dark as soon as you climb in and close the door. That calls for an aftermarket accessory! The author built this circuit using ‘normal’ components (with leads), but in theSMDmanner, which means ?tting the components on the copper side. The only holes drilled in the circuit board were the four ?xing holes, and the entire assembly was ?rmly attached to the surface of the heatsink for power transistor T3 (the author used a finned heat sink rated at 7.2 °C/W). The heatsink is at ground potential.


Figure 1 

A value of 1 Ω was used for R3 with satisfactory operation of the darlington. The light goes on when the door is opened. After the door is closed, it continues to illuminate the interior of the car at full brightness for around 30 seconds,after which it slowly dims. Approximately 1 minute after the door is closed, the quiescent current drops to zero.



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