Xitanium current modification

[Garibaldi]

Does anybody know if it's possible to lower the current from a Xitanium LED driver so that different strings of LED's can be run at different currents?

Given the 1750mA model, it is possible to run one string at ~1A, one at ~700 and a couple at ~20. Is there a way to maintain the variable voltage of the Xitanium but change the current for a given string?

Is it possible to use one of the Supertex drivers, such as the CL2's I happen to have, in line with a string of 10mm LED's to drop its current to 20mA, while running high power LED's on other strings?

 

[Hero999]

Does anybody know if it's possible to lower the current from a Xitanium LED driver so that different strings of LED's can be run at different currents?

I doubt it.

Post the datasheet or at least the part number, for the drivers you're talking about.

~700 and a couple at ~20.

I take it you're talking about mA there.

Is there a way to maintain the variable voltage of the Xitanium but change the current for a given string?

What do you mean? LEDs always run from constant current, the voltage is varied automatically you provide the desired current.

Is it possible to use one of the Supertex drivers, such as the CL2's I happen to have, in line with a string of 10mm LED's to drop its current to 20mA, while running high power LED's on other strings?

Why not just use a current limiting resistor for the smaller LEDs?

 

[Garibaldi]

There's not a lot of documentation - here's the only link I can find http://www.advancetransformer.com/uploads/resources/Section_7.pdf. I will be using the LED120A0024V10F model.

The CL2's are temperature compensated so they are more reliable than resistors (and I have several of them) http://www.supertex.com/pdf/datasheets/CL2.pdf.

I also sent the question to Advance, so hopefully they can give me a definitive answer.

 

[Hero999]

I would recommend the current limiters for the 20mA LEDs and the switching power supply for the high powered LED.

I have a good idea of how these switching regulators work, it's not possible to set different current levels for different LEDs connected to the same converter.

 

[Mr RB]

You could use a LM317 on each string with one resistor to set the constant current for that string. The final string (the one with the highest current) just gets all the left over current that is not drawn by the other strings.

 

[Garibaldi]

That would be nice if that will work. The CL2's are easier because they just insert in series like another LED. My concern is using a constant current regulator to regulate the output of another constant current regulator. I don't know enough electronics to begin to guess if that will work or melt everything in the vicinity.

I have the Xitaniums on order, so I'll start playing with this some time next week. I just hate the idea of possibly frying the Xitanium or a high power LED. I've got plenty of 5mm LED's I can sacrifice, though

 

[Hero999]

The CL2s will rob current from the switching regulator so you need to account for this when setting the current.

The forward voltage of the strings plus the CL2s have to be less than the sting connected to the switching regulator or else they won't light.