Schematics > Motor, light and power control > Dome Lamp Dimmer
Dome Lamp DimmerThere are times when a little light inside the car would greatly assist one of
the passengers but the dome light is too bright for safe driving. The dimmer circuit
in fig. 1 may be added to an existing dome light or included with a new passenger
spot lamp. The upper op-amp generates a 700 Hz sawtooth waveform which is compared
to a setpoint voltage by the lower op-amp. When the sawtooth voltage is above the
setpoint, the transistors turn on supplying current to the bulb.
The setting of the potentiometer determines the width of the pulses sent to the
lamp and therefore the average voltage. The lamp is dim when the potentiometer is
set near the higher voltage. Since the TIP32 switches on and off instead of simply
dropping the voltage like a power rheostat, the power it dissipates remains low
and a heat sink is not necessary.
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Many autos run power to lamps with only one wire using the car body for the return
current path so the dimmer must interrupt the positive lead as shown. Simply cut
the wire leading to the lamp and connect the lamp end to the collector of the TIP32
and connect the battery end to the circuit power input. Run an additional ground
wire to the auto chassis from the circuit. This ground wire will not carry much
current and may be a smaller gauge.
Title: Dome Lamp Dimmer
Source: www.electronics-lab.com
Published on: 2005-02-03
Reads: 298
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