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LM3414: what limits the minimum LED current to 350 mA?

Christopher Richardson
Intellectual 360 points
Other Parts Discussed in Thread: LM3414

Dear LED Drivers Forum,

      If I size the inductance properly for a minimum average current of 250 mA, can I expect any problems beyond a widening of the tolerance of that current? If I want to use the LM3414 for an average LED current of 250 mA, would it be better to operate it at 350 mA or 500 mA and then dim with a PWM signal? I´d prefer not to add the PWM circuitry if I could avoid it.

     Thanks,

Chris

  • 0
    TI__Intellectual 2590 points

    As stated in the data sheet you should set your current for 350 mA and PWM to an average current of 250 mA. Because the amplifier is internally compensated and also has internal current sense controlled by  a current mirror may be related to the minimum current setting. I will check with the factory as to the actual reason for the minimum current setting

  • 0 in reply to Mike Kosteva
    Expert 1935 points

    BUMP!

    @Mike or someone from TI can you please answer this question?  I have a critical situation involving the same as the OP.

    Followup to OP would be, is there some fluctuation/instability that would occur at <350mA or is it just widened tolerance?  Any way to improve the tolerance at low currents?

    Thanks!

  • 0 in reply to bowerymarc
    Intellectual 360 points

    Hi Marc,

         I used to work at TI, and I know the apps engineers that developed the LM3414. They told me the only thing that will happen at lower currents is a widening of the tolerance of the average LED current. But there is no way I know of to improve that tolerance.

         To be honest, LEDs don´t need a very tight tolerance of drive current, unless it goes too high and they overheat. The tolerance of luminous flux is so much looser that a tightly controlled drive current isn´t really worth the trouble (in most cases.)

         Hope this helps,

    chris