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Circuits designed by David Johnson, P.E.
Last Updated on: Thursday, November 30, 2017 07:43 AM

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High Power Flashing LED   (February 27, 2010)
designed by David Johnson

 

 

The circuit converts an off-the-shelf solar powered LED path light from producing a steady state light to one that produces a flash.  This circuit includes a tiny dual Schmitt trigger inverter IC which form the pulse generator and the daylight sensor circuit. 

The circuit produces a positive pulse, which feeds the constant current LED driver circuit.  With each pulse, a heavy 1 Amp current pulse is sent through the infrared LED.  A second Schmitt trigger was used in the day/night sensor.  The voltage produced by the solar panel when illuminated by sunlight was used to suppress the pulser oscillator during daylight.

 

The LED driver circuit uses a quality n-channel MOSFET with a low channel resistance and a simple current regulator.  The regulator relies the voltage developed across a resistor.  When the voltage reaches about 0.6v it is enough to turn on a NPN transistor.  When turned on, the transistor reduces the drive voltage on the MOSFET gate. This negative feedback keeps the current set close to 1 Amp.  To aid in maintaining current regulation, by keeping the battery voltage from plunging, the circuits has a 4.7 farad supercapacitor across the battery.

Click on Drawing Below to view PDF version of Schematic

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DC Magazine, Issue 7, Page 7:  High Power Flashing LED


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