I trying to figure out when using Meanwell LDD driver, if I want to tailor the current to each series LED on the output to a specific current, should I use a series resistor in the chain?
Example: I have a 500mA output driver but I want to drive the LEDs at 400mA so I add a resistor in series to the LEDs...
Or, do I just Dim them with the driver's dimmer function?

 

Or, do I just Dim them with the driver's dimmer function?

Yes.
If that works, why would you want to fuss with adding a resistor?

 

Yes.
If that works, why would you want to fuss with adding a resistor?

Well if the driver is meant to work at 100% (no dimming) most of the time then it is more efficient. And the scale of the dimming would be able to work at 0-100% so it would have more resolution. (in my application dimming would be used 5-10% of the time)
I suppose that the resistor adds inefficiency as well though.

 

I suppose that the resistor adds inefficiency as well though.

If it's a constant-current driver then adding a resistor won't significantly affect the current.

 

It would once the driver reaches its voltage limit...but that is not such a good idea.

 

Yes, I see. Kind of. That is what i am trying to wrap my head around. So adding the resistor will simply make the driver up the voltage and not really limit the power to the LEDs then.

So in the case of the Meanwell drivers, The way that they achieve dimming is not by reducing current but instead applying a duty cycle to the max current. Is that correct? I believe that is what the data sheet is saying...

 

Yes, I see. Kind of. That is what i am trying to wrap my head around. So adding the resistor will simply make the driver up the voltage and not really limit the power to the LEDs then.

Correct

 

Thank you both. I understand. I can go design my circuit now. I will just get driver as close as I can to my target current without going under and then just limit the output through PWM.

 

In post #1 you say "if I want to tailor the current to each series LED on the output to a specific current" Do you mean that you want different currents through individual LEDs in the same series chain or are you running a number of series chains in parallel and want differen currents in each chain ? A schematic of how you plan to connect the LEDs to the constant current power supply would help us understand EXACTLY what you are trying to achieve. I have just tried to find a datasheet on you Meanwell LED driver but the company makes many different models. Can you provide a link to the datasheet on the MODEL THAT YOU HAVE ?

Les.

 

You can place resistors in parallel with each LED to shunt some of the current from the driver.

 

Thank you both. I understand. I can go design my circuit now. I will just get driver as close as I can to my target current without going under and then just limit the output through PWM.

Sounds like a good plan..
They do have a 350mA version of the LDD too.. Then you don't need to worry about PWM to adjust average current..

 

Some constant current drivers are sold as being adjustable. Is yours? Others might be adjustable with a bit of reverse engineering.

 

Some constant current drivers are sold as being adjustable. Is yours? Others might be adjustable with a bit of reverse engineering.

The LDD drivers are sealed/fixed at the factory with no adjustment..