Control circuit for vehicle courtesy light - provides time delay for lamp extinction after doors are closed

摘要

The control circuit is used to divert the lamp current from the controlling transistor, and also to limit the effects of any failure in the time delay circuit. The control unit (6) comprises a reservoir capacitor (C1), charge and discharge resistors (R1,R2,R3) and switching transistors (T1,T2,T3). The whole circuit is connected between the positive terminal (30) of the vehicle power supply and the door switch (TK). With the selector switch (5) in the normal position (2) closure of the door switch (TK), i.e. by opening a door, connects the lamp (3), and also the capacitor charge circuit (C1,R3) across the supply (30,31,7). The lamp current thus passes only through a routing diode (D2). When the capacitor is charged, the transistors turn on and the lamp current tends to flow through the last stage (T3). When the doors are closed, the lamp draws power from the capacitor until the latter has discharged (R1,R2) to the point where the transistors turn off, typically 12 seconds after door closure. Charging time is approximately 1 second.