17mm QX5241 5Amp 1-4 LED 2-4s Li-Ion Buck driver, WIP - I'm back in the saddle.

Thanks Microa, I am working on that now :wink: I also left out the 1uF connected to pin 3 and ground.

The Cin at the pin 3 (Vin) should be at least 47uF. The smallest size X7R MLCC I can find is 0805 47uF25V.

are those standard 0603 or 0805 solder pads for the resistors or capacitors? Not sure if they just look really close together to me or not. Most cool though, is this a buck type setup? ATtiny driven?

P.S. Whip up a 20mm when you make the 17 as well :wink:

Really? Why? Only the SM5241 datasheet shows 47uF, the QX5241 shows 1uF and the LY5241 datasheet doesn’t seem to mention it. To me it doesn’t seem like you’d need that much capacitance just to smooth out the 5mA the chip draws.

They are 0805 pads. It’s a buck setup. I used the standard pin configuration for the ATtiny13a w/ one of our normal firmwares. This is for clicky only. It’s going to look at little more packed in a minute or two here.

What is the voltage range of that driver? If it can buck 3x in series down to run a single emitter…I have a home depot defiant I can upgrade to a 26650 rather than C cell :smiley:

I expect this driver to perform like a less-efficient new-version DRY driver. The voltage range should be something like 2-3s or 2-4s. Remember, this thing will be huge with the torroid on top.

Don’t be confused. Cin is 47uF which is connected to pin 3 (Vin) and the 1uF which is connected to pin 4 (Vcc) which is 5V regulated output.

QX5241 application circuit shows 1uF for pin3 (Vin). I don’t know if that’s correct.

I have revised the driver to add 0805 caps for both Vin on the QX5241 and Vcc on the ATtiny. I also added a second sense resistor in parallel. I did not do a very clean job and I will probably improve the layout in the C1/R4/R1 area at least, as well as some unattractive traces.



OK, past bedtime. I cleaned up the sense resistor area and moved the offtime cap to the top of the board (it was right above the sense resistors).

This does pass DRC w/ 6mil spacing.

Yea, I think they look off too. 0805 should have a pad separation around 0.7mm. Oshpark renders boards using tStop for the copper areas instead of Top for some reason. Makes all pads look 3mil larger in the renders.
Are you using the oshpark DRC? The default eagle DRC has 4mil mask instead of 3.
I don’t know, even if its the eagle default 4mil, pads look off. Course I didn’t sleep last night so my eyes might be off.

Oh so this isn’t a single emitter driver but a multiple in series driver…k gotcha

Cool project. Thanks for starting and sharing this.

I didn’t realize that I could adjust that - I see it now. Thanks. I had it set to the default, 4mil. I’m using the Eagle R0805 package for the divider resistors and C0805 for the caps.

WarHawk-AVG, please read the thread. It’s a buck driver and will go at least low enough for a single white emitter. Results are posted in the short thread I linked. The driver will not operate on a single lithium ion cell. The links in the OP were meant to answer this question.

Thanks, let’s hope we get something useful out of this thing. I’m feeling pretty good based on the lineage (all the other successful drivers based on this controller). The only thing that I’m concerned about is how big an efficiency hit we take from eliminating the weird dual-FET setup I mention in the OP. It’s not a synchronous buck configuration, so I really don’t understand what those other designs are doing with the second FET.

Yup…I shoulda read…thanks wight

I realize that I post a lot of links. :wink:

While searching for boards to rob components from in order to populate this driver, I came across this:

http://item.taobao.com/item.htm?id=17981669490

At ~$2.50/each in China I figure that’s not much better than the new-version DRY driver. Has anyone seen these drivers around on AliExpress or eBay for a better shipped price? I see them on eBay for crazy prices (>$10!!), but no decent prices.

I’ve just taken a closer look. I’m seeing about a 0.16in / 0.4064mm spacing. Are you guys using the stock Eagle libraries or something else? Thanks.

EDIT:
Well, I made some mild placement adjustments, cleaned some things up, and fixed a couple of DRC issues. v014 is ordered for testing. I don’t have a lot of parts to test with, so let’s hope it doesn’t fry stuff.

I have quite a few custom .lbr

I also use 0603 pads, my 0805 components fit just fine on the pads when I use hot air to reflow the components

Might just give you a bit more space on your placement

Custom Eagle parts makes sense. I’ll have to take a look at these PCBs when they arrive (since I know exactly what Eagle parts I used) and compare with real life 0805 components.

While looking at other drivers I recently realized that there’s no reason for me to fret over the need for a big inductor. I’ve been looking for wrapped toroids like we find on the DRY driver and original SRK driver, but I wasn’t able to figure out where to shop parametrically to find high-current toroids at the desired inductance. Turns out there’s no reason not to plop a (phsyically smaller!) SMD inductor right on top of all the other parts. It’s big enough to easily hookup with an air-wire.

This solves half of the crisis I was running into… the parts on the new-version DRY driver are probably spec’ed for 3-5A, it’s hard to say. zeremefico showed the driver running at 7A, but he did not discuss heat. I assume that at that current the diode and inductor are putting off some heat due to being under-spec’ed. I know people are going to want more current. A bigger diode is possible with a redesign and easy to source. We’ve already got the FET bit mostly figured out, that’s old news. So the missing link was the inductor. :slight_smile:

Big inductors still cost a few bucks and the corners start to poke out past 16mm or so, but I think this is doable.