This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

LM3407: LED buck driver operation

Part Number: LM3407
I'm new to LED buck drivers. If I have an input voltage that is higher than the LED voltage, does the LM3407 drop the extra voltage internally? Or does it step down the LED driving voltage so that there is no extra voltage to drop at the LX pin?  
  • Hello Sara,

    This is a switching regulator so there is no drop in voltage like a linear regulator would do. The LM3407 charges the inductor when the MOSFET is on and when the MOSFET is off it discharges. Ignoring losses there are two V=L*(di/dt), one for charging the inductor where V=Vin-Vled and one for discharging the inductor V=Vled. The duty cycle of the MOSFET is determined by Vin and Vled and those equations.

    With a linear if Vled was 1/2 of Vin it would be 50% efficient. A switching regulator will be much higher but it depends on the design.

    Regards,