nichia use in car

[flownosaj]

I'm looking for help here guys. I'm planning on wiring 3 nichia warm white leds off of my car's 12v accessory wire. I want to set up a switch to illuminate the interior of the cavernous center console storage bin when the lid is open.

My question is since these have a Vf of around 3V and an If of 30mA, can I use a 15W 22ohm resistor and the LM317 just like the luxeons as discussed in the luxeons in the car thread?

Question 2: What kind of small pot can I use to dim or brighten the lights without risk of blowing the nichias?

Question 3: If I decide to switch to amber LEDs, what would I have to change since the Vf drops to 2V?

I appreciate any help /ubbthreads/images/graemlins/bowdown.gif

-Jason

 

[evan9162]

1)
Yep, and you don't need a 15W resistor. Since the voltage across the current set resistor for the LM317 circuit is 1.25V, with the 22 ohms, you will get 56mA of current (very high for a 5mm LED). Anyways, at that current level, the resistor will only be dissipating 70mW - so a normal, 1/4W resistor would work fine. For nominal 30mA, you would need ~40 ohms, but use a 47 ohm resistor to be safe (will give you 27mA).

2) Put a pot in series with the current set resistor (still between the Adj and Out pins). When the pot is at 0 ohms, then the full current will flow (set by the resistor). As you crank up the resistance on the pot, less current will flow. Make sure the pot can dissipate 1/4 W of power.

3) Nothing - the LM317 will regulate the current, so as long as the current into the amber LED is the same, you won't have to change a thing.

 

[flownosaj]

Thanks--now I just need to get a day off to rip apart my console /ubbthreads/images/graemlins/smile.gif
/ubbthreads/images/graemlins/thumbsup.gif

-Jason