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

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

Here’s a driver I’ve been wanting to do for a long time and never did. It’s based on the Chinese QX5241 buck controller, same controller used in the old DX SKU 20330 and the new-version DRY driver. As far as I know it’s also the same one used for a bunch of other drivers such as one IOS previously carried and this 5A one from LCK-LED as well as a few others.

All of the above drivers other than the DX one seem to employ a second FET wired in a way that I do not understand. It must be there for a reason, but I don’t know what. Here is where I describe the way the second FET is connected.

A Nanjg 105c and a new-version DRY driver together will contain nearly all the needed components to assemble this driver. It requires the torroid from the new-version DRY driver, so that makes this driver quite tall, the top of the torroid is about 11mm above the bottom of the PCB. This driver requires a 5mm diameter by >2.4mm tall spring or spacer due to the large diode on the bottom. As you can see, the combined height of the board may be 14-15mm thick overall. I haven’t calculated sense resistors, but since I only put a single 1206-sized pad you’ll probably need to pick that out for a special order.

LED+ connects to one leg of the torroid, the other leg attaches to the via next to the Q1 marking. LED – connects to the body of the FET. I forgot to add some 1μF capacitors on the VIN and VCC lines for the two microchips respectively. I’ll need to go back and add those. We may be able to cram in a second 1206-sized sense resistor.

Update: Current progress is in post #26.
Update: Current 17mm design progress is in post #42 and post #59. Since that wasn’t working I’ve switched to a 20mm design for now as a sanity check, see posts #76 / 77 / 78. TLDR: 20mm buck section works.

Still fine, still on a break. One day I’ll catch up with you folks! previous wight catchup Wink
list of my drivers & variants (A17DD, FET+1 stuff, WIP stuff, etc)

Edited by: wight on 10/05/2014 - 00:08
wight
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Still fine, still on a break. One day I’ll catch up with you folks! previous wight catchup Wink
list of my drivers & variants (A17DD, FET+1 stuff, WIP stuff, etc)

Microa
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You have omitted a 1uF which is connected to the pin 4 of QX5241 and the ground.

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

Still fine, still on a break. One day I’ll catch up with you folks! previous wight catchup Wink
list of my drivers & variants (A17DD, FET+1 stuff, WIP stuff, etc)

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

WarHawk-AVG
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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

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

WarHawk-AVG wrote:
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?

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.

Still fine, still on a break. One day I’ll catch up with you folks! previous wight catchup Wink
list of my drivers & variants (A17DD, FET+1 stuff, WIP stuff, etc)

WarHawk-AVG
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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 Big Smile

wight
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WarHawk-AVG wrote:
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 Big Smile

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.

Still fine, still on a break. One day I’ll catch up with you folks! previous wight catchup Wink
list of my drivers & variants (A17DD, FET+1 stuff, WIP stuff, etc)

Microa
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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.

wight
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Microa wrote:
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.

Still fine, still on a break. One day I’ll catch up with you folks! previous wight catchup Wink
list of my drivers & variants (A17DD, FET+1 stuff, WIP stuff, etc)

wight
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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.



Still fine, still on a break. One day I’ll catch up with you folks! previous wight catchup Wink
list of my drivers & variants (A17DD, FET+1 stuff, WIP stuff, etc)

wight
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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.

Still fine, still on a break. One day I’ll catch up with you folks! previous wight catchup Wink
list of my drivers & variants (A17DD, FET+1 stuff, WIP stuff, etc)

Helios-
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WarHawk wrote:
Not sure if they just look really close together to me or not.

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.


Counterfeit 18650s, 2,<a href=“http://

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wight wrote:
WarHawk-AVG wrote:
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 Big Smile

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.

Oh so this isn’t a single emitter driver but a multiple in series driver…k gotcha
ImA4Wheelr
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Cool project. Thanks for starting and sharing this.

wight
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Helios- wrote:
WarHawk wrote:
Not sure if they just look really close together to me or not.

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

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.

ImA4Wheelr wrote:
Cool project. Thanks for starting and sharing this.

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.

Still fine, still on a break. One day I’ll catch up with you folks! previous wight catchup Wink
list of my drivers & variants (A17DD, FET+1 stuff, WIP stuff, etc)

WarHawk-AVG
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Yup..I shoulda read…thanks wight

wight
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I realize that I post a lot of links. Wink

Still fine, still on a break. One day I’ll catch up with you folks! previous wight catchup Wink
list of my drivers & variants (A17DD, FET+1 stuff, WIP stuff, etc)

wight
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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 (so plus shipping twice, once to your buying agent and once to you & plus commission to the buying agent) 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.

Still fine, still on a break. One day I’ll catch up with you folks! previous wight catchup Wink
list of my drivers & variants (A17DD, FET+1 stuff, WIP stuff, etc)

wight
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Helios- wrote:
WarHawk wrote:
Not sure if they just look really close together to me or not.

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.

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.

Still fine, still on a break. One day I’ll catch up with you folks! previous wight catchup Wink
list of my drivers & variants (A17DD, FET+1 stuff, WIP stuff, etc)

WarHawk-AVG
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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

wight
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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. 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.

Still fine, still on a break. One day I’ll catch up with you folks! previous wight catchup Wink
list of my drivers & variants (A17DD, FET+1 stuff, WIP stuff, etc)

wight
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Just realized that I’ve been developing this driver on a 16mm PCB, not 17mm.

Still fine, still on a break. One day I’ll catch up with you folks! previous wight catchup Wink
list of my drivers & variants (A17DD, FET+1 stuff, WIP stuff, etc)

Rufusbduck
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FWIW the lfpak56 is about half the size of the larger fets and is rated for 100A if you find board space tight. There’s an even smaller “33” rated for 60A. The design is only a few years old so it might not go out of production soon like the Vishay did.

Three Tanna leaves to give him life, nine to give him movement. But what if he eats the whole bag?

Scott

wight
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Thanks RBD. I’m going to look into that package, space is tight if I try to put an SMD inductor on the board.

The particular DPAK Vishay product we were buying on eBay was no doubt out of production long before we started buying it. Powerful DPAK/TO252 FETs will probably be produced until after we are dead. There should really be no fear of the supply of DPAK FETs drying up.

Still fine, still on a break. One day I’ll catch up with you folks! previous wight catchup Wink
list of my drivers & variants (A17DD, FET+1 stuff, WIP stuff, etc)

wight
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Well, thanks again RBD. That was a great suggestion, and together with making my work area an actual 17mm circle instead of 16mm (!), that freed up a lot of space. The pin configuration is also different, in a good way. I’ve done a total rework on the board.

  • SMD inductor. There is space for approximately an 8×8mm inductor. I will rework the pads to better accommodate various landing patterns.
  • ~1.1mm uncovered via to add a big wire-wound toroid inductor instead of the SMD one. This is just an option in case that makes sense for a build.
  • Large +/- LED pads on more or less opposite sides of the board.
  • Swapped diode to top of the board. Lots of space for the diode. You should be able to fit various ~5A diodes on those pads
  • Moved MCU to the bottom
  • LFPAK56 / SOT-669 / Power-SO8 style FET – there should be many options for this
  • Three 1206 sized sense resistors, still on bottom.
  • The bottom now has a smaller component height. You should be able to use a standard Nanjg 105c spring (5mm x whatever) or a standard 5×2mm brass peg. I’ve removed the wings from the 5mm BAT+ pad though, so in order to install it you need to put it on before the sense resistors. There is a large copper pour between them, just heat the pad using the sense resistor pads.
  • I kept the offtime cap, but I also brought out PB2 on top of the board. It’s available with a covered trace between inductor and FET – just scrape off the resist. This can be used for an e-switch, but like I said before this driver will have a really high parasitic drain and is a bad choice for an e-switch. I’ll probably remove most or all of this trace when I rework the inductor pad area anyway.


Still fine, still on a break. One day I’ll catch up with you folks! previous wight catchup Wink
list of my drivers & variants (A17DD, FET+1 stuff, WIP stuff, etc)

wight
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So here are the gotchas:

  • While the new-version DRY board has been run up to >7Amps by zeremefico, the diode will probably generate a lot of heat and could fail. AFAIK diodes in this style of package are only available up to around 5A, other packages such as DPAK are used for larger diodes. Therefore the current revision of this board is intended for ~5A or less operation.
  • I don’t have a complete grasp on inductor selection. The QX5241 does not have a fixed operating freq, the freq varies due to various factors: Vin to Vout ratio, drive current, inductance, maybe other stuff. The maximum the QX5241 can handle is 2Mhz. With the space limitations of a 17mm board, I think the highest inductance we can hope to achieve is 6.2uH with what I assume is a relatively expensive Coilcraft inductor. For cheap options we are limited to 4.7uH or less. Those inductors are readily available in the $0.65 to $2.00 USD range in values that can handle >5A without burning a lot off as heat.

Not a gotcha, but the overall size of v020 is similar to that of a Nanjg 105c – this board is about 1.0-1.5mm taller depending on inductor selection.

Still fine, still on a break. One day I’ll catch up with you folks! previous wight catchup Wink
list of my drivers & variants (A17DD, FET+1 stuff, WIP stuff, etc)

Rufusbduck
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On the FET’s that I have the drain is the big tab and bottom plate, the gate is the single pin you have as the gate, and the source(ground) is what you have connected to the diode.

Three Tanna leaves to give him life, nine to give him movement. But what if he eats the whole bag?

Scott

wight
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Well that’s bad. Let me go back and look.

Still fine, still on a break. One day I’ll catch up with you folks! previous wight catchup Wink
list of my drivers & variants (A17DD, FET+1 stuff, WIP stuff, etc)

wight
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I had the part right, it’s as you say. I got those backwards when I hooked it up in the schematic. Grr.

Still fine, still on a break. One day I’ll catch up with you folks! previous wight catchup Wink
list of my drivers & variants (A17DD, FET+1 stuff, WIP stuff, etc)

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