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Dave's Circuits
Circuits designed by David Johnson, P.E.
Master Category
List - Dave's Circuits
Last Updated on:
Tuesday, October 13, 2009 01:28 PM |
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Pot Controlled Variable LED Intensity
Circuit -- September 24, 2009 |
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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. |
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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. |
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| Rotary Pot |
Slide Pot |
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Click on Drawing Below
to view PDF version of Schematic |
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Master Schematic
Category List - David A. Johnson, P.E. |
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