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### Topic: Driving a 1W star with a L317 (Read 1 time)previous topic - next topic

#### bugz650

##### Jan 18, 2013, 06:29 am
Hey guys,

I've been using Arduino for a bit now and LOVE screwing around with flashing lights

***i need to run a 1W star on a dimmer, and was thinking of using the L317 adjustable voltage regulator and a (X)ohm pot.***

I will generaly use PWM and a TIP122 to drive each channel of a 3W star LED   ( using 10K pull down resistor at the gate,  100ohm current limit for the MCU,  and a 2W-10ohm current limit for the led {5v > 3v@350 ma(ish) right?}  )

BUT i want somthing CHEEP & EASY for a single LED

I would like to regulate AND adjust both voltage and current with the L317 but i can't find the right fomula ( or maby make sence of it  lol)

OR

will i have to regulate it @ 5V, use a curent limiting resistor, and adjust the voltage with a pot?

Any reasonably simple solutions i overlooked would allso be apreciated.

#### cmagagna

#1
##### Jan 18, 2013, 07:30 am
Does it have to be a L317? How about something like a TLC5916?

#### majenko

#2
##### Jan 18, 2013, 12:51 pm
If you must use an LM317, then I would say run it just in constant current mode, and adjust the current.  As long as you limit the maximum current to the maximum of the LED (using a static resistance), you should be fine.  The voltage is irrelevant as it will always be the set by the LED.

#### Erni

#3
##### Jan 18, 2013, 01:27 pm
Take a look at this schematic by BillO

http://arduino.cc/forum/index.php/topic,102101.msg767419.html#msg767419

You can use this LM317 calculator to calculate the resistor

http://www.reuk.co.uk/LM317-Current-Calculator.htm

#### dhenry

#4
##### Jan 19, 2013, 12:40 am
Quote
Take a look at this schematic by BillO

Something like that generates a fixed output current.

If you put a pot over the resistor and put the adj pin on the wiper, you get to vary the output current.

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