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Circuits designed by David Johnson, P.E.
Last Updated on:
Friday, March 23, 2012 06:20 AM
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More
LED's
Blinkers & Flashers |
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HIGH INTENSITY LINE POWERED LED
FLASHER (Dec 8, 2008)
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There are times when you would like to
generate an intensely bright flash of light using electrical power from the AC line.
The circuit below can drive a one to three watt power LED with about 350ma of peak
current. Since the circuit drives the LED with a constant current, any LED color
can be used. I have also shown how you could use an array of 7 LEDs, wired in
parallel. This array may not produce as much light as the single power LED but
the array would be cheaper to build. |
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circuit uses a classic Schmitt trigger oscillator, which drives a constant current switch
circuit. The components are selected so the circuit produces a short 20ms flash with
a flash rate of about 0.5Hz. A high voltage capacitor in series with a bridge
rectifier limits the current drawn from the power line to about 5ma. A 47 ohm metal
oxide resistor is used as a fuse. |
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the LED current pulse packs quite a bit of energy, a fairly large 2,200uF capacitor is
used to collect and store energy from the power line between flashes. The capacitor
voltage is limited by a zener diode to 7.5v. A diode and capacitor circuit isolates
the oscillator voltage from the main energy storage capacitor. This isolation
insures that the oscillator frequency and pulse width remain fairly constant. |
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Click
on Drawing Below to view PDF version of Schematic |
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