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High Power LED Flasher
August 3, 2008
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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