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

Flashlight Modding and DIY Parts
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For 20~22mm size we already have the LD-29 (about 21mm) which is capable to handle and deliver high current.

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Or you could plant this on a 22 mm contact board

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i need more than 3a though. 6a would be good. or more

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I wouldn't recommend using this with a contact board, as it relies on having a direct thermal path between the ground ring and the pill, either by use of a retaining ring or solder to transfer the heat from the driver. Any intermediate piece, especially another PCB, will limit the transfer to some extent.

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Looks great RMM. You know much more about this stuff than me. So I apologize if this is a dumb suggestion. I find that the fly back diode to be a limiting factor in some buck drivers. Maybe the inductor size you are limited to space wise is more of a bottleneck, but it looks like you have room to add a parallel to D1.

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Extreme high power isn't the point of this board. An extremely low profile along with programmability and reliability was the design goal; the other board (still to be released) is for higher power.

In a small SMD inductor there is a lot of resistance, and with that resistance comes a lot of heat at high currents. You also have to deal with core saturation on a small inductor like this, although it would tolerate 5A-6A. That is why there is two versions of the board: one for low-profile applications, and another that is for pills with a bit more room for an external inductor that can run more current due to its lower resistance and getting the heat away from the board (and also has a bigger diode). I didn't stick a huge diode on here because it simply isn't needed for what my design goal was (3.5A-4A), is smaller, and is less than half the price of a bigger diode.

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Would a copper ring soldered to the annular ring be ok?

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Would a copper ring soldered to the annular ring be ok?
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I'm sure it would be. That said, if you're patient you'll get a 20mm soon that can do 5A+ with a bigger inductor and diode on board. It will also be slightly more efficient due to the slightly bigger inductor, so if you want to do 20mm I'd wait.

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BTW, I am currently testing a few different 17mm revisions setup for more power, but I don't generally release anything that I haven't personally built and tested. I don't have time to support and post on many "WIP" types of threads. The general rule is that if I've shared it, it's actually been built and tested. It doesn't mean it will be perfect, but that if properly built it will work.

If you want maximum performance and efficiency you really need a Coilcraft inductor (XAL series). Their small inductors blow away everything else in similarly sized packages. They are almost three times the price of an Abracon or Bourns, but if you really want a 5A+ 17mm driver with an SMD inductor, I think it's the only way to go.

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I ordered from OshPark today so I threw three of these in my cart as well

Also placed an order with RMM today. Richard, please check my note and get back to me if there is a problem with the resistors I’m using.

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ill be waiting on a parts list so i no im ordering the right parts :)

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Hi Richard, as I read your OP I thought you’re working on a 17mm buck driver which can deliver 5A+ current (with bigger inductor), instead of 20mm isn’t it?

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I believe he’s doing both

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I believe he is designing 17mm low and high current drivers. It shouldn’t take much to extend the borders for the OshPark boards so he will probably release 20mm as well, but the goal is the 17mm boards as there is more of a need for them.

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A small, high-current buck has been a bit of an elusive holy grail for some time now. If anyone can pull it off, RMM will likely be the person.

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Your first mistake is believing that even I have any idea what I'm going to be working or releasing.

For 20mm/22mm there's enough room for a decent sized inductor, so there's no need for two boards with the 20mm and 22mm. My early attempts were to "have it all" in a single 17mm design, and those didn't work out very well.

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I wasn’t trying to put words in your mouth. The OP is about a low profile 17mm buck driver and you mentioned a taller 6a+ Version. I apologize if I wrongly guessed you would release a 20mm version once you were able to get the 17mm worked out. Ultimately, we are all just sitting back in anticipation of what you are able to come up with.

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Just to clarify, here's my current roadmap:

17mm, 2 boards:

i. MTN-MAXlp: 4A max, low-profile, small SMD inductor. [RELEASED]
ii. MTN-MAX: 6A+ max, larger external inductor. [IN TESTING]

20mm, 1 board: MTN-MAX: 6A+ max, either a larger SMD inductor or external inductor. [IN TESTING]

22mm, 1 board: MTN-MAX: 6A+ max, single sided, either larger SMD inductor or external inductor. [IN TESTING]

Plus some other larger boards down the line, with the same basic layout but improved efficiency due to the availability of space for a larger inductor.

36

Wow - this is great to have a true programmable buck driver! Thanx again Richard!

Question: I'm sure I missed this somewhere, but how do you program one of those MCU's in that form factor? Can it be programmed on-board?

I think I saw these listed on your site but didn't know what they went with. Can't navigate Mtn-E now to explore...