Switching regulated LED’s

[snowman]

Lets say I have 3 LuxIII's in series being driven by a constant current regulator and now I want to turn one LED off by shorting it out. Any negative effects to the regulator or the remaining ON LED's by doing so?

I assume the output voltage from the regulator will drop to maintain constant current but will the transient over voltage cause any LED's to let the smoke out?

Anyone try this before or have designs that do this?

 

[HarryN]

I assume that when you say "shorting it out" you mean some kind of switching that takes it out of the circuit on both the cathod and anode side.

When you do this switching, there can be a moment when the switch is "off" for all of the LEDs. At that moment, you effectively have an "open circuit", and some regulators will drive the voltage quite high and burn out.

If you are going to do it this way, you might want to make sure you either buy a driver circuit that can handle this, or put some kind of protection (such as a zener diode) across the driver Vout pins. I am not an EE, but I have seen this area discussed. (in the electronics section)

If you can find a variable output driver, it is actually more efficient to run 3 of the LEDs at a lower current than to turn one off.

 

[VidPro]

if he direct shorts one led, then there might be a burst for what miliseconds? untill the current control readjusts.

i would think that the driver would be the limitation.
the led can handle tiny short surges , as long as they arent to high.

and you certannly wouldnt want to OPEN when doing it (again dependant on the driver), just dead shorting the led.
and you would have to be sure that the driver then wouldnt go non-regulated , or was still in the range of the output voltage, vrses the input voltages.

efficiency and longevity says that it is better to drive the same leds at less current, than to run less leds.
that way you dont age the phosphors on one led over another. they love underdriven.