Circuit Solutions, Pump Motor Monitor by David Johnson P.E.


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Circuit Solutions Notebook
Last Updated On: Monday August 18, 2008

Latest Technical Challenge Previous Circuits Solutions Circuit Solutions in Progress

30 LED Night-Light

Challenge:

Design an efficient long life night-light, using up to 30 white LEDs

Solution:

The circuit solution below uses capacitor to limit the current through a series-parallel string of 30 LEDs. 15 LEDs are wired in series in one direction and 15 more in the other direction. The capacitor limits the average current to about 20ma. The 100 ohm metal oxide resistor acts as a fuse. As the sketch below depicts, perhaps the final product would have three clusters of 10 LEDs on three sides of plastic block, which would plug into the 120vac outlet. They might be angled slightly inward toward the wall, so light would spill onto the wall behind the device. With quality white LEDs the device should last for 10 or more years.