buck-boost circuit for flashlight

Discussion in 'The Projects Forum' started by Greg G, Feb 15, 2009.

  1. Greg G

    Thread Starter New Member

    Jan 25, 2009
    I've been modding lights for about a year and have the mechanics and machining behind it understood to a fashion (machinist by trade). I want to move up to building my own circuit so that I can have a better understanding of the electronics part of it.

    The first driver I'd like to build is for a Cree XR-E LED which has a Vf of ~3.7 @ 1.2 amps. The battery is a single Li-Ion which has 4.2 volts fresh off the charger, and about 3 volts when depleted.

    I was looking at the National LM5118 IC.


    Can anyone give me any pointers/advice on what I'm about to do?


    Last edited: Feb 15, 2009
  2. Bernard

    AAC Fanatic!

    Aug 7, 2008
    The specs. say it should work, go for it. Are you including a charging ckt?
    Missed the operating V of battery.
  3. Greg G

    Thread Starter New Member

    Jan 25, 2009
    Sorry, fixed it. It is an 18650 Li-Ion that is 4.2 volts when freshly charged. It is rated at 3.7 volts nominal. So it is above the Vf of the LED at the start and needs to be bucked, then drops below it and needs boosting towards the end.

    I charge these batteries out of the light.