Selecting the right DC/DC Led Driver - Page 1
Forum section: electronics / projects

author: LLee
author_rank: Newbie
timestamp: October 29, 2023, 08:36:42 am
content: Hello I need to select a dc/dc led driver, probably a boost. My battery voltage can be from 5V to 9V. My Leds are 4 times 5W (Imax = 1000mA, Vf total= 5,6 x4 = 22,4V)Now I want to have them dimmable with esp32, But I am not sure about selecting a led driver because there are so many of them can someone help me in the right direction many thanks!I will probably also use a buck led driver because im deciding to also have a different Led with 2,2Vf (Imax = 1000mA) thats also dimmable with the same esp32. But I can't seem to find buck led drivers that go from 5V input to as low as 2,2V output. Or is this just a wrong way of doing? I am pretty new.

author: mariush
author_rank: Super Contributor
timestamp: October 29, 2023, 09:13:28 am
content: Your battery must also be capable of supplying that much power ... if you have 22.4v x 1A = 22 watts , with the conversion losses of the driver you would have around 24 watts. At 5v input from battery that would mean around 5A of current pulled from the battery.If you have 4 independent leds, each with a forward voltage of 5.6v, you could arrange them as 2 separate strings of 2 leds in series, to get a forward voltage of around 12v - you may get better conversion efficiency and 2 led drivers may be cheaper than a single powerful one. It may also be convenient as you could turn off one of them completely if you need lower brightness.

author: LLee
author_rank: Newbie
timestamp: October 29, 2023, 09:39:11 am
content: Thank for that mariush, what if I don't use the leds on max current.I am using 2 Li-ions in series, (5V to 8V) with 3000mAh. The Imax of the leds is 1A but if I just use 65% procent of the max so 650mA.So around 15Watts on the driver. Means around 3A pulled from the battery so they will be in use for around 1 hour. I don't know if li-ions can handle that.So maybe I should consider more batteries in series? Or less leds maybe 2 max...

author: Marco
author_rank: Super Contributor
timestamp: October 29, 2023, 04:06:55 pm
content: Battery tool 18650s get discharged significantly faster than 1C.I just searched digikey for led drivers, 1 output, dc dc, boost, current 3A and up, sorted by stock and looked down the list ... TPS61500 and MIC3223 look good.Didn't bother to look at dimming, cause they nearly always have a dimming input.For buck I searched led drivers for 1 output, dc dc, buck, current 1A and up, sorted by stock. Spoiled for choice unlike the boost one (because that one needed high power, which with internal switches limits options). Just pick based on preferred brand and package. AL8861 has a cute SOT89-5 package.

author: mariush
author_rank: Super Contributor
timestamp: October 29, 2023, 05:14:10 pm
content: AL8861 is step-downI'd suggest something like MP24833 for example :https://www.digikey.com/en/products/detail/monolithic-power-systems-inc/MP24833-AGN-Z/7361434It's a bit low frequency (210kHz) so inductors may be a bit big, but may not matter in your application. It can do 3A of current.TPS61500 also looks ok :https://www.digikey.com/en/products/detail/texas-instruments/TPS61500PWPR/1985029...RT8511 looks like it would work to me :https://www.digikey.com/en/products/detail/richtek-usa-inc/RT8511BGQW/6676723It's got a 2.2-2.6A switch current limit, so if you have 6-8.5v in, 11-12A, you can probably get more than 500mA of current.

author: Marco
author_rank: Super Contributor
timestamp: October 29, 2023, 06:01:53 pm
content: He asked for a step down too for a separate LED.MP24833 and RT8511 will be hard to cool. TPS61500 and MIC3223 have a little more meat on their bottom.