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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 Hobby CircuitDavid Johnson, P.E.

More  Drivers    Lamp Control     LED Circuits
White LEDs     Potentiometers

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