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Last Updated on: Tuesday, October 14, 2014 06:34 AM

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More  Drivers    Lamp Control     LED Circuits
White LEDs     Potentiometers

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 potís 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
Rotary Pot Slide Pot

Click on Drawing Below to view PDF version of Schematic

Pot Controlled Variable LED Intensity Circuit - David Johnson, P.E.

More  Drivers    Lamp Control     LED Circuits
White LEDs     Potentiometers

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