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Circuits designed by David Johnson, P.E.
Last Updated on:
Wednesday, December 20, 2017 06:09 AM
List of Dave's Circuit Designs
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Flameless LED Candle Power Boost
Designed by: Dave Johnson, November 2010
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| Problem: Make a battery powered flickering torch using a yellow LED candles with shone much brighter and was powered by a long lasting alkaline D cells.
Solution: Most flameless candles are now quite simple circuits consisting of nothing more than a power switch, a battery and a special flickering LED. To boost the power of this flickering device, you can insert into the circuit shown below.
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| This circuit
extracts the flickering signal from the special LED and uses the signal to drive
5 super bright yellow LEDs at a peak current of 20ma each. |
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Flameless Flickering LED
Candle Power Boost Circuit |
The
flickering effect is produced by a pulse width modulation (PWM) circuit,
internal to the special LED. Each time that LED circuit turns on, current
is drawn through the 560 ohm resistor R1. The voltage drop across the
resistor is enough to turn on the 2N3906 PNP transistor. That transistor
then produces an identical PMW signal at the collector, which swings over the
full 3v peak to peak voltage. The collector signal is then fed to the gate
of a ZVN4306 n-channel MOSFET. Acting as switch, the transistor routes
current through 5 super bright yellow LEDs. Each LED has a 47 ohm resistor to
limit the peak current to about 20ma. A fresh pair of 1.5v alkaline D
cells should be able to power the touch light for about 8 hours. |
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List of
Dave's
Circuits
List of Circuits from DC Magazine
eMail David A.
Johnson, P.E. about this circuit
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DC Magazine, Issue 13, Page 4:
Flameless LED Candle Power Boost |
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