Wednesday, November 27, 2013

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Regulated Dual White LED Lamp

This is an ultra-simple LED spot lamp that uses two white LEDs and a current regulator circuit. It is designed for use in 12V solar powered and automotive/boating applications, but can be used in many other applications. Only seven components are used in this circuit. It produces regulated light output across the 11V to 20V voltage range. The circuit board is potted in silicone to make the lamp completely waterproof.

Project Image

Regulated Dual White LED Lamp

I have built about ten of these lamps and they are all going strong after many years of daily operation. The lamps are part of several night-lighting systems that use a SCC3 charge controller to solar-charge a lead acid battery and a DAS1 Dark Activated Switch to turn on the lights at night.

Circuit Diagram

Regulated Dual White LED Lamp

The same circuit can be used with colored LEDs, it makes a great accent lamp if you use one emerald green and one ultra-bright blue LED. The circuit will also drive three LEDs on the red side of the spectrum since they run at a lower voltage than the blue, emerald green and white LEDs. An accent lamp made with deep red, orange and ultra-bright yellow LEDs complements the emerald green and blue lamp nicely.

  • Nominal Operating Voltage: 12V DC
  • Regulated Light Voltage Range: 11-20V
  • Operating Current: 20ma
The input power is filtered through an R-C 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 25ma. The current regulator is wired in series between the power source and the LEDs to provide a constant current.

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, the acetic acid that is released when the caulk cures is conductive. Another brand of bathtub caulk was tried, but the caulk stayed electrically conductive and the circuit quickly failed.

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 the lamp to run for many hours on battery power.

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

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