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Circuits designed by David Johnson, P.E.
Last Updated on:
Friday, March 12, 2010 12:08 PM
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Flasher
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High Power LED Flasher
August 3, 2008
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| Power LEDs
are becoming more popular these days. The DC input power to these devices ranges
from 1 watt to 5 watts. Normal LEDs only receive about 0.05 watts. At this
higher power, these devices can emit a lot of light. You can buy them in just about
any color in the rainbow but white seems to be the most popular. One application for
these devices is a flashing light. If the flash duration and flash rate is kept low,
the average current can be low enough that even a small battery can last quite a while. |
| The circuit
below is designed to power any 1 to 5 watt power LED. It is designed to run from a
+3v supply, which includes two standard alkaline or NiMH AA cells. It uses a charge
pump method to provide the higher voltage needed by white and blue LEDs. It also has
an active current liming circuit, set for 250ma. This is sufficient current to
produce an intense light flash. |
| The circuit
uses a classic two transistor oscillator to produce the pulse train. With the
components shown, the circuit generates a 20ms pulse at a frequency of about 0.5Hz.
The 2.7 ohm resistor sets the LED pulse current at about 250ma. The average battery
current is only 1.3ma, so a pair of standard AA cells should power the flasher for about
one month. This intensely bright flasher might find uses in warning lights and might
be great for those who ride their bicycle at night. The intense bright flashes are
impossible to miss at night. |
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Click on Drawing Below to view PDF version of Schematic |
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