Main > Main Forum

LED Wiz - RGB LEDs 3.3v/2v bank select

Pages: << < (2/3) > >>

drventure:

Hey Franco

Thanks for the confirmation. I was planning on following the dirs  :) , just curious why that's the way it is.

But yeah, I definitely know they work work if you get em backwards, and I had no idea about the common anode in the rgb LEDs, but I just happened to get lucky I guess and I picked up the right kind!

I was hoping I could control some ELWire directly via the LEDWiz, but, after some emails with Randy, looks like that won't happen. I'll have to drive them through a relay of some sort.

But I was kind of expecting that so no big deal.

Dudeman:


--- Quote from: Franco B on August 11, 2009, 10:46:23 am ---Are you sure Dudeman? It didn't work for me.

--- End quote ---
Positive. I've done it... on purpose and by accident.

Here's one way:
http://www.theledlight.com/ledcircuits.html

Here's the other:
http://www.nycresistor.com/2008/05/04/handy-dandy-led-resistor-calculator/


With RGB LEDs, I "assume" (we know where that leads) that you need to use seperate resistors for each cathode because each color requires a different voltage. I say assume because I've never used one.

Red 1.63 < ΔV < 2.03
Green 2.18 < ΔV < 4.0
Blue 2.48 < ΔV < 3.7


RandyT:


--- Quote from: Dudeman on August 11, 2009, 03:25:50 pm ---With RGB LEDs, I "assume" (we know where that leads) that you need to use seperate resistors for each cathode because each color requires a different voltage. I say assume because I've never used one.

Red 1.63 < ΔV < 2.03
Green 2.18 < ΔV < 4.0
Blue 2.48 < ΔV < 3.7

--- End quote ---

This is true.  If a resistor could not be placed on either side of the LED, then at least one type of RGB LED could not exist.  But they do, in fact, come in both common cathode and common anode configurations.

RandyT

Franco B:

Could you confirm this Randy?:

Would there be any problems with using the 3.3v from the PSU (to the LED Wiz banks) for the blue and green cathodes (using no resistors)?


--- Quote from: BobA on August 11, 2009, 08:46:13 am ---AFAIK there are slight differences in the internal resistance of the LEDs when in operation.  This makes the resistor in series with them a necessity to properly provide voltage to the LED.   I do not think that providing voltage to the 2 colors without a resistor is a safe solution.

--- End quote ---


RandyT:


--- Quote from: Franco B on August 13, 2009, 12:43:52 pm ---Could you confirm this Randy?:

Would there be any problems with using the 3.3v from the PSU (to the LED Wiz banks) for the blue and green cathodes (using no resistors)?


--- End quote ---

Everything I have ever read has stated that one should use some sort of resistor to limit current, even if the voltage is the same as required by the LED.  The thing is, the calculations show a 0 ohm resistor when using these numbers, so that is essentially a jumper, not a resistor.  Therefore, I think that you would be safe omitting the resistor, so long as the supply is well regulated, and the LED's are operating within the stated spec. 

One way to look at this is (apologies in advance to the EE folks):  If the LED is rated for 4v which, with an appropriate resistor in circuit, causes it to glow brightly, and you are feeding it less voltage without a resistor (3.3v), which you can see causes it to glow less brightly, then you probably are going to get longer than rated life from the LED, not shorter.

RandyT

Pages: << < (2/3) > >>

Go to full version