Buck driver design - component selection example

I checked on that for you:

Tterev3, thanks a lot for sharing. With all your shared knowledge you even helped ck to start his own business...!! You should have some shares in it :)

Great work you are doing!!!

Tterev3 you make it seem so easy, this is great stuff, I almost understand it :slight_smile:

What size board will this be on?

Thank you for explaining this for the masses.

Nice :beer:

Lol thx :8)

Hop the initial driver I’m putting together will be a drop in replacement for a courui (plenty of room to work). The board will also take care of the series cell conversion (will need mods to factory tail board and a power cycle clicky switch is highly recommended).

After it’s running I will start work on hopefully fitting this in a ~20mm driver (maybe 26mm, that fits a lot of the multi-emitter plunger lights), that is unless someone else wants to take my .sch and do a board… Tterev3 may have pointed this out in the OP but it’s recommended this buck chip be used in lights that have a mechanical clicky (which is why on the ones I plan to build I’ll be doing the tail clicky mod, tho it will fully utilize the side e-switch) hints the 26mm version for things like the tr-j18/9xt6, 3xt6 and so on.

I’ll be doing the courui in PIC however it’ll be an SOIC8 PIC so should be almost no work to move a few traces for ATTiny13’s.

All ears!

And hoping for a 17mm board version

Me to buddy, seriously doubt that tho, plus it will be a taller than a typical BLF driver by a good amount too. Especially with that big 2512 sense resistor (the size that comes on SRK’s) I just don’t see it happening in 17mm. Maybe with 2 1206’s stacked like my RGBW drivers but IDK about that even.

Thanks for this. In my reading, I’ve seen a lot of people saying that switch mode power supplies (SMPS), like a buck driver, need a fair amount of empirical testing. Does using a commercial buck controller help much with that, or is it still important to do careful testing?

I hope this gets enough play to get stickied.

Once you have a proven and functional circuit I'll be happy to have a crack at designing a 17mm version.

Thanks for a great plain English explanation, will be following this with great interest.

Cheers David, _who has just seen his big head Courui cowering in the corner_ J)

This is awesome. Thanks for the writeup!

Love your contributions towards the community.

It’s always important to do testing, even on non-SMPS designs, but yes, using a chip like this makes it much easier to get to something that works very quickly. There’s always a lot of opportunities for optimizing the design after the initial attempt if you have the means to do detailed tests.

For example, in this design, I chose a big inductor because of Maxim’s test circuit, but after a crude saturation analysis, it appears that we could use a much smaller one. If space isn’t an issue, you could just stick with 33uH and have very low ripple, but if we’re short on space, I’d order a few smaller inductors and then measure the frequency that the converter decides to run at - if it doesn’t approach the 2MHz limit, it will work just fine.

This is way beyond my realm of expertise and totally fascinating. Subscribed.

tterev - any chance you’re in the Triangle area? I’d like to buy you a beer sometime (and/or check out some of the lights you’ve made).

On the design of the board, you Can use 0603 pads for space, and still be able to use 0805 components, it is a “high density ” pad footprint, but you already knew that :wink:

Awesome thread, let’s get this sukka started :smiley:

Both mattaus and wight had good designs but haven’t heard much about them late

To save board safe would the Atmel ATtiny10 be sufficient, I found a PCB based ZIF socket, might work for programming, just need a good code writer to whip up an awesome UI ; )

For a power cycle only, more simple UI yes it’s probably enough, plus with the attiny10 a 10f322 is a direct swap, same pinout between AVR & PIC. One thing tho is no voltage divider input so no voltage monitoring on the attiny10

With the initial design being for a dual switch light (courui is side switch only but I’ll be installing a tail clicky) it’ll have to be something bigger to run momentary FW.

Ok looking at the Vishay SL42 datasheet (covers the SL43 also) I see that the IF (AV) rating is different from Al to FR4 and that on FR4 its only 4A, is this still safe to use at 8A output on an oshpark board (albeit with a large Cu pour) considering that?

I didn’t notice that, good catch. Probably best to find a different one

Allright here's my parts list, look good?

1 MAX12820

2, 3, 9 1uf 16v 0805 (I have a reel of these)

4 Vishay Dale 2515 .025ohm 2W 1%

5 Inductor in OP

6 Diodes inc Schottky 10A 40V PowerDI™ 5 (I choose this slightly more expensive and higher rated diode for a few reasons, one being this package is smaller than the more common DPAK and also because while its more expensive individually it offers a better bulk discount)

7 AOD510 (exceeds all requirements, has great low RDS(on) and I have a hundred of them)

8 For my use a 12F617 but probably make an ATTiny13A version at the same time for everyone else

10 470ohm 0603's cause again thats what I already have on hand

hopefully links work, digikey is strange...

Tiny10’s can have issues being programmed in C. Like very easy to run out of RAM and stack space.