17mm/22mm MTN-MAXlp - Low-Profile 1A-4A Programmable Buck Driver + 22mm MTN-MAX

^Cool stuff. No wonder you’re such a busy guy :wink:

From what little research I have done the zener mods are inefficent at low power, thus I have been waiting on a (less then 4 amp is fine) 6V buck to run the 6V emitters but with out spilling the difference into heat. I am no expert and I might have gotten somting reversed but it seems that for other then DD way hot short run lights a more sophisticated driver is needed.

How are you controlling the amperage of these drivers? I see 4 amp and 6 amp listed. Is it a function of what the battery has available? If it is then other than the components used, isn’t it DD?

Look up “buck converter”.

Yea, well that is beyond me. I don’t get it. I’m reading more…
I really wish I could understand what exactly different size inductors do. I’m going to start studying it…
BTW, I need another M6, when are you opening back up? :bigsmile:

Richard. Be a nice boy now and get back in that nursery and look after the good wife before I come around and spank you. This forum will survive without you for a few days. Saying that, will you survive without us for a few days?

This may be less efficient running an MT-G2 off of two 18350s, depending on what current level you set it at. I suspect that at 3A or more the 7135 driver will be on average more efficient over the full discharge of the batteries. If you wanted to run an MT-G2 at something silly like 1.5A or 2A the buck driver would probably be more efficient.

Linear regulators, like the AMC7135, are pretty efficient where the input voltage is close to where the output voltage is needed to maintain a certain output, with all extra being turned into heat. With 18350s at 3A and above there is enough voltage sag that you're not staying very far above what is needed for very long.

With a buck regulator, you generally have more switching losses, and you are also always running all of the LED current through a sense resistor, which burns off power, and through an inductor, which also burns off some power (especially smaller inductors). So, when input and output drop to the even, or almost even point, the efficiency of the small buck driver will be worse than what you would have gotten out of a 7135 based driver.

Now, remember that this may not hold true for 2x26650 or 2x18650 running an MT-G2 at lower amps, but an MT-G2 with 2x18350s at 3A+ I think that the 7135s are actually doing a pretty good job efficiency-wise.

Has anyone received their boards yet? Anyone built one yet? I've built several of these now in different configurations and have them in different lights, and I feel very confident that they work and work well.

A few more thoughts and tips:

1. Absolutely do not try to solder this by hand. You need to reflow to get these done right, especially since the thermal pad under the buck IC is critical to proper performance.

2. Make sure you get enough solder underneath the Buck IC's thermal pad. The thermal vias tend to wick up some of the solder, so you need a bit more than you would think.

3. Space your low and critical levels a bit farther apart than you normally would. For example, if you normally use 160 and 145 for your low and critical values, use 170 and 145 instead. The way that the buck driver loads the batteries is different than with a DD or linear driver single-cell setup, because the current draw actually increases on each cell as they drain instead of decreasing, so having values that are too close together leads to an immediate shutoff after the LVP is activated with no or very little "in between" time.

OshPark expects my boards to be back around 4-19. The OP was 4-5 and I ordered 4-7. That being said I don’t even have all the stuff to attempt this build yet, nor am I confident enough that I won’t screw it up.

Sometimes part of learning is failing, although I try to avoid that part if possible!

Oh I’m well aware of that. Like you, I just hate failing.

Parts kit coming at mtn?

Is there interest? You're the first one who's asked for one. If there's a few more I'll put one up.

Oh… I just assumed. I don’t plan on making enough of these to make a larger order from mouser worth it. How many parts will be shared between this one and the 20mm?

Preliminarily it is all the same except for the flyback diode and sense resistor, although maybe I’ll end up with two different 20mm boards so that those who have parts for the 17mm and don’t need more than 3.5A-4A can use the same parts.

I’m actually interested in complete driver, do you offer them now or in the near future?

I probably won't be offering them complete for a while because I just don't have time to build them right now. I have built a few for a customer who asked about them a few months ago, but besides that I've only built them for myself.

That said, I have two of them complete right now that I've built that are just sitting on the shelf I could sell. I will list them on the garage sale page.

I will get a parts kit up tomorrow.

Richard, do you already have enough spares for a parts kit now or would you have to order? Reason I ask is I already have a order with you that I’m sure you haven’t had time to complete. If you already have the stuff then I’d like to purchase a couple kits and have it shipped with the other order. If you would have to order it, I’d probably just place another order with mouser. I can always find more stuff to buy I don’t really need, just like shipping with you! I have a 2S UF-1405 that I had planned on putting an E2 Torch in and using a low current buck, but I’d rather push a G2 at 4a.

The Mouser parts list is putting me off a little. DigiKey I've found cheaper in the past when comparing qty 1 or 10 for example, so I've only ordered parts from DigiKey up til now. Also trying to figure qty of boards to make in this size, what lights best fit, etc. I'd probably want to use it in 1 or 2 e-switch lights, or lights with a wider driver, so, bigger board options (and higher power) of your next generation may be better for me, or take the chance with a contact board setup which you are not recommending. Dunno yet.

I shop at Mouser based on price, and price alone. For me Mouser has almost always been cheaper than Digikey.

For e-switch, you've either got to be OK with some quiescent current drain, or go to a bigger driver layout with more parts.

Hold out a little longer for the bigger boards. You have to think of the thermal path of one of these like you do with a high-powered LED---it will fry itself if pushed hard without a sufficient thermal path. We are pushing it already by making everything so small.