Regulated Dual White LED Lamp

(C) G. Forrest Cook 2008

This project can be used with a CirKits solar circuit kit.

Regulated Dual White LED Lamp


Introduction

This is an ultra-simple LED lamp made with two white LEDs. It is suitable for use in both 12V solar powered and automotive applications. Only seven components are used in this circuit. It produces regulated light output from 11V to 20V. The circuit board can be potted in silicone to make the lamp completely water proof.

Specifications

Nominal Operating Voltage: 12V DC
Regulated Light Voltage Range: 11-20V
Operating Current: 20ma

Theory

The input power is filtered through a pi filter consisting of two 100nF capacitors and a 100 ohm resistor, this removes voltage spikes from the rest of the circuitry. The LM317L and 56 ohm resistor act as a current regulator that is set to 20ma. The current regulator is wired in series between the power source and the LEDs to provide a constant current.

Construction

A small circuit board was made using press-n-peel blue film, the board was sized to fit inside of a 1/2" PVC pipe connector. The parts were soldered into the circuit board and a length of two conductor speaker wire was soldered to the board for the power lead. A knot was tied in the power cable to act as a strain relief. The power cable was fed through a hole in the PVC connector. The entire assembly was filled with clear GE Silicone II caulk and left to dry. Be sure to allow the caulk to dry for several days in a warm place before applying power. Another brand of bathtub caulk was tried, but the caulk was electrically conductive and the circuit quickly failed.

Use

Connect this circuit to a 12V battery or power supply, be sure to observe the correct polarity. The LEDs should put out a bright white light. This light can be used for a night light, a flash light, automotive interior lights and background house lighting. The low current draw allows it to run for many hours on a battery.

Parts

2x white LEDs, T1-3/4 size
1x 56 ohm 1/4 W resistor
1x 100 ohm 1/4 W resistor
2x 0.1uF capacitors
1x LM317L adjustable voltage regulator
1x 1/2" Schedule 40 PVC pipe junction
GE Silicone II caulk
Two conductor speaker wire

CAD Files

EAGLE CAD schematic

EAGLE CAD board layout

PostScript file of PC Board

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