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More  Light Flasher Circuits   Micropower Circuits

Ultra Low Power LED Flasher
December 18, 2008
designed by David A. Johnson, P.E.

The efficiency of some newer LEDs is amazing.  Some of the latest green LEDs can launch blinding light with just one milliamp of current.  I take advantage of one of these newer devices in the circuit below.  The flashing circuit uses a classic multivibrator oscillator, made from a tiny National Semiconductor’s LMC7215 low power voltage comparator.

The circuit produces a short 10ms pulse every two seconds, drawing power from a 3v supply.  I suggest using a surface mounted green LED from Kingbright.  Although the LED peak current is restricted to just one milliamp, this part generates a very bright flash of light.  The circuit draws and average DC current of only 6 microamps from a 3v supply.  When powered by a small lithium coin cell with a 100ma-hour rating, it will flash for about two years.  This flasher might be a great add-on circuit for a flashlight, a key chain or even attached to a cell phone, so the thing can be found in the dark.  Another application might be for a fake car alarm indicator.  The circuit might also be used in conjunction with some other battery powered product, to let the user know when it is in operation.  The small 6uA current drain would not tax even the most stingy power budget.

Click on Drawing Below to view PDF version of Schematic

Circuit - Ultra Low Current LED Flasher - Dave Johnson

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