I am doing some research about using a LDO as a constant current LED driver and For this project, it is imperative that the LEDs remain as stable as possible. I also need to be able to easily adjust the brightness of the LEDs. I have a few clarification questions about the setup.
I would like to use an LT3085 as a constant current LED driver as described here and in the image below. The LEDs that I am planning on using are red Osram LRW5SM, which have a forward voltage of 2.0-2.6V and a forward current of 100-1000 mA. I am planning on using one LDO to control one LED.
My questions/clarifications:
To achieve a 2.2V voltage across the LED, I should place a 220k resistor at the SET pin, correct?- In order to adjust the current across the LED from 100mA to 500mA (max output of this LDO) with a 220k resistor at the SET pin, I would need a ~4.4-22 Ohm potentiometer (this seems pretty low) at the OUT pin, correct? [LED current = 10uA * (R1/R2)]
- What should I power this LDO with? Would a lab power supply work, or should I use a battery? What voltage?
- Is there a better LDO option altogether for what I'm trying to do?
Best Answer
A better idea would be to use the LT3085 in constant current mode, with a potentiometer it could be adjustable. At 50k this would give you the full 500mA, 10k would give you 100mA ect. Place the diode on the output after the 1 ohm resistor going to ground.