[sdiy] LEDs and noise

Rutger Vlek rutgervlek at gmail.com
Mon May 18 11:21:42 CEST 2015

Hi all (and Roman),

It's probably a late reply from my side on this topic, but I recently got interested in LED drivers for a design I'm working on.

I like the idea of a current source for supplying the LED with power, and also found a nice example of a current source connector to a chain of transistor-switched LEDs in Douglas Self's book, but I was wondering how to deal with different current requirements of different LED's? Does each color of LED require it's own current source, or can different colors be fed from the same current source? Perhaps splitting the current source with limiting resistors over two LED chains (each with a different color) works?

I'd be interested to hear your solution(s).



On 8 mei 2015, at 08:53, Roman Sowa wrote:

> Supply the LED from + to GND and switch it on and off by shunting it to GND with a transistor. When transistor is off, LED is lit. When transistor conducts, the current flows via it and LED is dark. So for example if + is 12V, and resistor 10k, the current jump in power rail will be only about 170uA while LED current is 1mA.
> You can push it one step further and add a diode or 2 in series from collector to LED, to only make the LED-off voltage about 1V. LED will be dark anyway, but current jump is now about 70uA.
> Yet another step further, and supply the LED from current source. Then absolutely no current jumps in supply rail.
> I hope that's clear, if not, I'll draw ugly schematics.
> Roman
> W dniu 2015-05-08 o 01:32, David Moylan pisze:
>> If you're dealing with a lot of "blinkenlights" what's the best way to
>> handle them?  Is it better to power them between the + and - rails or
>> from one rail to ground?  Is it worth using a "dirty ground" scheme, or
>> is the noise induced on the supply rails itself?
>> Thanks.
>> Dave
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