Circuits designed by David Johnson, P.E.
Last Updated on:
Saturday, December 23, 2017 03:21 PM
List of Dave's Circuit Designs
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Blinkers & Flashers
HIGH INTENSITY LINE POWERED LED
FLASHER (Dec 8, 2008)
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.
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.
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.
on Drawing Below to view PDF version of Schematic