Circuits designed by David Johnson, P.E.
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List of Dave's Circuit Designs
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High Power Flashing LED
(February 27, 2010)
designed by David Johnson
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
DC Magazine, Issue 7, Page 7: High Power Flashing LED