LED Driver for Alkalines

Hey guys, am figuring someone here can help me out. I am currently building a 4D Maglite and I need a driver that has modes and is designed to operate on alkalines or at least has an input voltage of 3 to 9V without a low voltage warning. The majority of drivers available have a low voltage warning below 5.8V which is exactly where 4D cells hit. This is what I'm using currently, it's great for every light except a 4D due to the low voltage warning.

http://kaidomain.com/BD39-17mm-2_2A...-6-Mode-Buck-Driver-Circuit-Board?search=bd39

I e-mailed KAI Domain but I don't believe there's any way to turn this off.

Just an edjumicated guess, but I'd bet you can disable the low-voltage warning by removing the 390K resistor. That's the small black component in the upper left marked "394".

If you're willing to experiment, it's so easy a cave-man could do it. All you have to do is crack it, and it's effectively removed. It's very brittle ceramic, and unsupported in the middle, so this is pretty easy to do, even without electronics tools, training, or experience. Repairing the damage, on the other hand, would be a different story.

I wouldn't expect KAI to be of any help, but please let us know if I'm wrong.

On the other hand, this driver specifies that it works down to 3V, so it can't do anything very drastic below 5.8V. Do you know that it does something bad?

Awesome, thanks so much! I will give it a shot tonight and let you know how I make out. This is the exact kind of info I am looking for!

KAI Domain was not much of a help but that's ok. I'm guessing they're not the ones who built the board they're just a distributor plus I'm sure there is some sort of liability with removing this feature.

I think the low voltage cutoff at 5.8V is to protect 2 Li-Ion cells from discharging too far but I'm using 4 D cells so that shouldn't affect anything on the cells. When the light enters this low voltage warning it dims and flashes so it basically makes it unsuable. It seems to happen below 3 V and between 4.5 and 5.8 V.

I want to use this for 4D and 5D Maglite mods so it would be nice to do away with this low voltage warning.

if that does not work, use 1 dummy cell, your driver has 2 low voltage warnings, 5,8v and 3v. 4,5v will be right between.
or you could get 1' pvc pipe, and use 5 C cells,
or you can use taskled b3flex driver.

Removing the resistor works 100%. Thanks so much!! If you're ever in Jersey lemme know and I owe ya a beer.

Just out of curiosity and if you have time, how does that resistor work? I'm guessing when the one side sees a certain current or voltage current it kicks the light into low voltage mode?

I really do like that b3flex driver but it's 1" diameter and my project can only accept a 17mm.

That resistor and the one next to it form a 'resistor divider' that scales down the battery voltage by a ratio determined by the resistor values. This brings it to a range where the chip can compare it to a fixed reference voltage.

If the scaled battery voltage is below the reference voltage, that's considered a 'low battery'. The designer gets to choose the low battery threshold by choosing the resistors.

By removing the proper resistor, you changed the ratio to 1:1. Now the full battery voltage is compared to the reference, and it never gets that low, so the low battery cutout never happens.

It's been many years since I've been in Jersey, but if you're ever in CT, LMK.