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Is the LM3402 Suitable for fast PWM dimming with a FET in parallel with the LEDs?

MagicMike
Prodigy 50 points
Other Parts Discussed in Thread: LM3402, LM3406

Hello,

When i look at the datasheet of the LM3406 i see that it is possible to dim the LEDs by connecting a FET in parallel with the LEDs. Is it safe to do the same with the LM3402 if you choose a big enough inductor? I see it doesnt have output voltage sensing like the LM3406 to control the off time.


Kind regards,

Michiel

  • 0
    TI__Expert 3495 points

    Michiel:

     

       Yes, you can do shunt FET dimming using LM3402. Unlike LM3406, the switching frequency of LM3402 inverse properotional to Vout. When the parallel FET is short, the switching frequency is very low. If the inductor is big enough, it can prevent it from going into discontinuous opration mode. So that is not going to be a problem.

       The purpose of LM3406 Vout sense is to keep the switching frequency constant.

     

    David Zhang

    Applications Engineer

    Lighting Power Products

    Texas Instruments