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Using any Step-Down Regulator with adjustable current limit as a LED Driver

Is it possible to use any Step-Down Regulator with adjustable current limit as a LED Driver?  It seems that LED drivers are basically this, but I need something that is more than 1A (which is where TI stops it's portfolio).  Is this a good idea? or am I oversimplifying what a LED driver actually is? I don't need dimming, just a voltage controlled current source in a nice little monolithic package.

  • Generally you can do that, the shortcoming is that you will dissipate quite a bit of power in the current sense element unless it is specifically designed as an LED driver. I'm sure we have solutions for higher currents. Can you post your requirements? You can also post to the LED lighting forum.
  • I'm basically running a bunch of diodes with a total voltage drop around 2V and a requirement to adjust current between 3A and 6A. It's interesting because I see bucks from Linear that can do adjustable current limit (like the 8613) where output current is reduced to this limit. Similar TI parts don't seem to do this and their form of adjustable current limit is to hiccup and shutdown (?). LM3434 seems pretty close to what I'm looking for but it's not monolithic.

  • With a simple buck converter, you typically will set the current to your desired level by a resistor from the cathode side of the LED string to ground. R = Vfb / Iled. Now the output voltage of the regulator will vary to keep the LED constant. Pick a converter with the current limit less than the LED current. What type of LED requires 10A? That seems rather high.
  • That's a hard current limit though. I actually need to control what the current is -- i.e. a voltage controlled current source. I'm guessing TI doesn't have anything like this? TI parts are great value for what you get, though I just can't seem to find what I'm looking for this time around. Everything starts getting specialized. I even tried looking at battery chargers which is the same concept but too many fancy functions I don't need.

  • I think I have something. Thanks for the ideas! I can use any DC/DC and any sense resistor to an opamp + microcontroller to control feedback voltage as a means of controlling current.