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Pot Controlled Variable LED
Intensity Circuit -- September 24, 2009
The circuit below uses power from four rechargeable AA NiMH cells to drive 3 white
LEDs. A potentiometer varies the duty cycle of a pulse width modulator
circuit to vary the intensity of the LEDs from 0% to 100%. The beauty of the
circuit is that when the pot is all the way toward 0%, very little power is drawn
from the battery. Likewise, when the pot slider is moved toward the 100%
end, full power is fed to the LEDs. In effect, the pot becomes the on/off
switch.
A
dual low power voltage comparator TLV3702 from Texas Instruments forms a simple PWM
controller. The comparator IC draws very low current and has push-pull outputs.
This lowers the total number of parts needed. When the pot’s slider is in the
off position, the total current should be about 6 microamps. In the full on
position, the current increases to about 60ma, or about 20ma for each white LED.
If quality 2500ma-hour batteries are used, the lights should last a day and a half.
Rotary Pot
Slide Pot
Click on Drawing Below to view PDF version of Schematic
