This unique circuit makes your dome light look cool.
Usually when the car door is closed, the dome light
just goes OFF. With this circuit, you can have our dome
light fade slowly in brightness and finally go OFF.
This slow dimming of the light gives a very good feeling
at night. It looks very romantic!
The circuit can
be explained as follows: When the car door is open,
the push to off switch of the door is ON and hence it
charges the 22uF capacitor fully. The opamp is acting
as a voltage follower and its output is same as the
voltage across the capacitor, which is 12V when the
capacitor is fully charged. Due to a high voltage at
the output of the IC, the transistor saturates, turning
ON the bulb to full brightness.
Now when
the door is closed, the door switch is pushed in and
hence the switch goes OFF. When the switch is OFF, the
capacitor starts discharging slowly through VR1 and
the 10K resistor and the voltage across it decreases
slowly. Hence at the output of IC 741 also the voltage
decreases gradually, hence decreasing the base current
to the transistor. This produces a slowly decreasing
current through the bulb and the bulb fades out and
finally when the capacitor is fully discharged, the
bulb goes OFF.
After building the circuit,
with the push-to-off switch in ON position (not pushed
in) i.e. the car door open, adjust the preset VR2 to
the required initial brightness of the bulb. Then push
the switch in to turn it OFF(or close the door) and
adjust VR1 for the time to bring the bulb from full
brightness to OFF.
I would suggest you set VR1 and
VR2 to their maximum values.
Note:
2N3055 power transistor needs proper heat sink.
Designed by Naveen
P N
webmaster@electronic-circuits-diagrams.com
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