18 LED dimmable LED lamp

(C) 2007 G. Forrest Cook

Power this project from sunlight with a CirKits solar power circuit board kit.

18 LED Lamp Photo

18 LED Lamp Schematic

18 LED dimmable LED lamp


This circuit is a dimmable white LED lamp array with 18 LEDs. The lamp brightness is regulated as long as the input voltage is above 10.5V. A low-dropout analog voltage regulator is used for a simple and relatively efficient design. The lamp produces enough light to use as a a reading lamp or a small work lamp.


Power Requirements:
Input Voltage: 10.5-16V DC
Input Current: 11-150mA at 12VDC


The 12V DC input voltage is routed through the 1A fuse and the on/off switch. The 1N4001 diode acts as a crowbar device. If reverse polarity is applied, the fuse will blow and the rest of the circuitry will be protected. Power is sent to the LM2941CT voltage regulator IC. The regulator is wired to produce a voltage range from 5.5V (dim) to 8.3V (bright).

The 4.7K resistor across the 1K brightness adjustment potentiometer produces a non-linear brightness adjustment to compensate for the eye's logarithmic brightness perception response. The LEDs are organized in six series groups of three with a 24 ohm current limiting resistor on each group. This arrangement limits the maximum current through each LED group to around 20mA.


Connect the DC input terminals to a 12V source, such as a 12V lead acid battery. Be sure to observe the correct polarity. Turn the power switch on and adjust the brightness adjustment for the desired brightness.


Here are the Eagle CAD files for the printed circuit board:

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