TLC5947 + Piranha RGB; How to deal with lower voltage for Red?

Other Hardware LEDs and Multiplexing
1

So, I have my 5947s running nicely with some plain old single colour LEDs.

Soon arriving is a bag of Piranha Super Flux RGB LEDs. Although the retailer documents them as being 3.2-3.6v on all three colours, I suspect that in reality (in common with all the other Piranhas out there), that the Red is in fact a lower range, say 1.8 - 2.2v.

With the 5947 being a constant current sink, I was really hoping to avoid a plethora of resistors. Am I basically saddled with feeding in, say, 3.5v, and then inlining a resistor to the Red to bring it down to say 2.0v?

I've seen a few people string Piranhas RGBs up to 5947s and have yet to see any reference to dealing with red as a special case. So I'm hoping there's a way round it. :slight_smile:

All ideas welcome. :slight_smile:

2

paulo999:
So, I have my 5947s running nicely with some plain old single colour LEDs.

Soon arriving is a bag of Piranha Super Flux RGB LEDs. Although the retailer documents them as being 3.2-3.6v on all three colours, I suspect that in reality (in common with all the other Piranhas out there), that the Red is in fact a lower range, say 1.8 - 2.2v.

With the 5947 being a constant current sink, I was really hoping to avoid a plethora of resistors. Am I basically saddled with feeding in, say, 3.5v, and then inlining a resistor to the Red to bring it down to say 2.0v?

Constant current means what it says.

paulo999:
All ideas welcome. :slight_smile:

Learn Ohms law.

Much more importantly, believe it.

3

Basically if you are driving LEDs with a constant current source, you do not have to concern yourself with what voltage is being applied to the LED ( or series chain of LEDS ) the constant current diver will take care of that and supply enough voltage to ensure 20mA or 1 amp ( or whatever you have chosen ) through its output pin.

4

Boffin1:
Basically if you are driving LEDs with a constant current source, you do not have to concern yourself with what voltage is being applied to the LED ( or series chain of LEDS ) the constant current diver will take care of that and supply enough voltage to ensure 20mA or 1 amp ( or whatever you have chosen ) through its output pin.

Thanks Boffin1... I had a feeling I was missing something plainly obvious.

And indeed I was. XD

5

paulo999:
Thanks Boffin1... I had a feeling I was missing something plainly obvious.

And indeed I was. XD

Ohm's famous equation has three values.

If you fix two of the values the third one has no choice about its value. It has to follow THE LAW!