Probably not a lot, but we’ll see. The inductor isn’t too bad I think. The FET is good. The diode is the primary suspect. It might be the one heating up, it’s really hard for me to tell. I don’t have the appropriate equipment to measure component temps.
I thought the scope image of the output looked OK at 4A. I went ahead and tried to run 6A but ran into problems. My little CC/CV buck PSU couldn’t supply enough current to deal with the buck driver’s input spikes (3A limit) at 15v which was as high as I wanted to take the driver with these components. I switched to the 5V line on an old computer PSU, which was a cross-load since I had no load on the 12v line. I have no idea how the 5v line behaved, but I definitely insta-poofed the emitter. I doubt that the cross-loaded PSU had anything to do with it, but now I wish I’d just hooked up a known-OK 12v PSU to the driver instead of a questionable 5v supply.
There’s little doubt that the emitter damage is from over-voltage, so I think I need to re-examine the scope trace at 4A and see how high that’s actually getting.
I’ll order some better parts ASAP.
EDIT: Regardless of what better parts do for efficiency, I expect that higher in/out voltages will improve efficiency. So driving an MT-G2 or a string of XM-L2’s should show better efficiency. Also, reducing switching freq will probably improve efficiency, so a higher value inductor would help but I don’t think we can fit a higher value inductor w/ a high current rating.
I briefly had a 17mm board functioning at 0.5A, regulated. (!!!)
Something I’m doing is killing… something. Not really certain what’s up, but it’s encouraging that the 17mm layout may be OK after all. I think I’m damaging either QX5241 chips, FETs, or both. I should have taken notes, I forgot exactly when it started working or when it stopped working. The important part is that it worked with the board populated in a fairly normal way. I tested it multiple times in the working configuration with from 6 to 12v inputs feeding an XM-L2, regulated pretty much rock solid at 0.5A using an R400 current sense resistor.
No real updates on this, but I did play around a small amount over the weekend.
I had two 3.3uH SMD inductors. One was a Bourns SRP7030-3R3FM, I already installed that one on a 20mm board. The other was a Wurth Electronics 74437349033. When I reflowed the Wurth everything looked fine, but then I grabbed it and waggled it to make sure that it felt secure…and it broke in half. The encapsulating material just felt… clay-ey and crummy. The Bourns one looks and feels much harder. Anyway 74437349033 still works as far as I can tell (it’s on a driver that doesn’t function yet). The windings are still hooked up and look fine. That said, I doubt I’ll order any more of that particular one. Now that I check the datasheets again, Trise is much higher on the Wurth model. It’s also way taller and the top on mine was smudged!
In other non-news, I’ve had a Mouser cart open on a home computer for a couple of weeks, building up an order… that computer died, and the cart was tied to the session on that web browser. Crap!
I broke a buck converter on one of my HX=1175b's. So I ordered some QX5241 chips in the hope that they will be compatible with the circuit and have the same pin out. I'll report back on what happens.
I added a 22uF cap to the output and made things worse! (I installed the cap using an airwire between the positive and negative LED leads)
I'm using a 20mm driver w/ two R100 for a set current of 4.1 Amps. With no output cap I get a peak voltage of about 6.5v according to my scope. With the cap it looks like over 7v! The entire waveform seems to be at a slightly higher voltage with the cap installed and the ringing or whatever is definitely bigger. (both taller and longer)
I picked up a cheapy LCF meter from eBay. The one I purchased (which I don’t actually recommend so far) is http://www.ebay.com/itm/121228917349 from xinyangshi. Identifying markings both on the PCB and in the firmware’s splash screen are:
2011.05.27
XLDZ
The screw terminals seem to be a problem, so I’m hardwiring the inductors now. I pulled two pins from a 2.54mm pin header and soldered them onto the bottom of the LCR meter PCB, then soldered each inductor onto the ends of those pins.
I measured:
~4.5uH - Bourns SRP7030-3R3FM
~3.65uH - physically damaged Wurth Electronics 74437349033 when I hold it together! - when I don’t hold it the values range from 4uH to 8uH depending on the crack width (4uH is the smallest crack width I can get to stay put).
I’ve decided that I really don’t like the Power-SO8 footprint I’m using here. Somehow I ended up using a footprint that’s 8mm long - that’s huge compared to a ~6mm long Power-SO8 package, including the LFPAK56 descendant. When you reflow the FET tries to pull away from the end where the gate pin is and just barely hangs on. The recommended footprint for LFPAK56 is 6.8mm long, I could go even shorter here I’m sure. Also less wide. This would increase the density of the board and make building it more of a sure thing.
I still think I’m damaging these controllers somehow - maybe just with sloppy work, I’m not sure. I’m going to do a little more testing today at ~3-4A and see where it gets me. If nothing else I’d like to release the 20mm board soon so people can play around with it.
I have some of These
They don’t look like the same larger board but I wonder if it has the same buck ic on a different layout and could tell us anything. The second pic in the link shows a large cap that might be 47microf. If you want one to look at or for parts or simply want me to open one up for pics let me know. I don’t like them as they have the 5-mode program I eschew.
It would be interesting to see pics of the larger board. The smaller board is just an FET PWM modes board, you should be able to remove it and still operate the driver as a dumb single mode driver. It seems that 9 times out of 10 (figuratively speaking) the controller will be either QX5241 or QX9920. If there is a sanded SOT23-6 on the board compare it with the pinouts I noted in post #104 in the HX-1175b thread. They are easy to differentiate: one controller uses a middle pin to control the FET (DRV pin) and a corner pin next to that for GND. The other controller uses a corner pin for DRV and the middle pin next to it for GND.
I’m almost beginning to think building some breakout boards for these components and putting on a prototyping peg board might save ALOT of frustration…once R&D with the breakout boards is done and working good, then build up the actual driver board in one shot…this way at least you can build multiple components and mix/match w/o all the daggum soldering and worrying about overheating/damaging the components.
Like this but OSHPark
You guys are kicking so much butt, but it bothers me that you guys are getting so close and stupid stuff like soldering and re-soldering sensitive components just seems to be tripping you up.
Would a slew of very simple breakout boards w/ header pins and/or solder points help at all?
I’m hope you guys don’t think I am trying to poopoo your work…but maybe peg boarding it up might help with the R&D aspect of building an experimental driver
This guy built a high current motor controller for a skateboard…his prototyp e
It’s a good suggestion, and a valid point similar to what RBD has indicated a couple of times with the “start with a larger PCB” thing. Also maybe flawed in some similar ways :-(. As I’ve pointed out before, we have a functioning schematic. That is the schematic from the datasheet. We do not need to develop a schematic. Component values may need to be adjusted, etc, but I’ll be very surprised if the schematic actually changes.
Motor controllers have some fancy stuff, but they are also very much just high current PWM drivers (no step down).
Unfortunately I think that there are a couple of things that prevent us from using a breadboard for this:
low current testing of this schematic has already been done in the form of the DX SKU I mentioned in the OP. We could probably assemble a low-current QX5241 driver implementation on a breadboard, but I don’t know what it would show us that we don’t already know?
breadboards have both resistance and impedance issues
this is a high current driver, breadboards do not generally get along super well with high current?
the 20mm board works I think. What will breadboarding the same schematic (the only change was deleting one sense resistor IIRC) show us about the 17mm?
So that’s what I think about that. I think you look over a lot more material concerning development of projects like this in forums and videos than I do. If you see other people doing this kind of thing (step up or step down driver development where the driver operates on the order of several amps) please do let me know. I’m definitely willing to be wrong about this.
OTOH here is the current news:
I’ve ordered some parts from Mouser in order to allow construction of several of the 20mm boards.
I’ve ordered a new scope (Rigol DS1074Z) since the trigger on my scope has a problem and it was never trusted to begin with.
I think I will revise the 20mm board very slightly before many/any more are built.
After multiple forum members brought up attempting to make HX-1175b smaller I said no thanks since we didn’t know what the controller was. Now I know what the controller is (QXMD’s QX9920). Seeing SolarForce’s QX9920 driver specifically as well as many others <span class=“etc with, working been has ohaya driver “16.5mm” the think], [I variants driver T6 the all HX-1175b,”> has changed my mind. I am thinking that I will soon start development of a two board solution for that. A high-current QX9920 solution will not fit in 17mm without using two boards. Development of that driver will be in parallel with development of this one, we’ll see which one turns out “better.” The buck section will be on the suspended daughter board, MCU and a vreg will be on the 17mm PCB.
I’ve got new supplies and tools in hand, but have not yet done anything with them. I’ll get motivated soon.
In the meantime I just noticed that this driver also uses the QX5241a: 9A 3-Mode 5.5-12V Circuit board. HKJ wasn’t super impressed with the efficiency, but hopefully better component selection will keep us around 80%. RMM comments that most XM-L2’s seem to die around 4.15v over here (post #110), so we can see from HKJ’s scope traces that depending on the input voltage this thing would totally zap XM-L2’s. HKJ didn’t specifically mention the input voltages, only that the two traces were at different voltages.
EDIT: I forgot to mention that those scope traces (the pictures with green lines that look like wiggly square waves) look exactly like what I’ve been seeing.
Thanks VOB, I’ve been taking a break from FL projects and focusing on other things. I expect the 20mm stuff will be forthcoming as soon as I get back to this, then we’ll re-attack 17mm! The layout issues shouldn’t have much affect on component selection - therefore I expect 4A to be a non-issue. Those could be my famous last words though ;-).
Cleaned off my work area. Realized that the only thing I’m really short on is PCBs. I’ve got one 20mm blank left, so that’s what I’ll start with. After that it’s recycling the ones I had problems with.
… crap, now I gotta remember what all these parts are for and where they go!
Turns out that after all this time, these are still the right parts! ;~~)
I sat down and checked my numbers, for 4A I needed two R100’s. I picked out enough of each component and laid it out on the driver to make sure I had everything, then went back and checked on the computer since I didn’t put an orientation mark on the board for the QX5241. I put everything in my little parts bowl, squoze out about the right amount of solder paste onto the appropriate pads, then placed everything for the top side of the board. I reflowed using my 1500W heat gun on the High/950° setting, let it cool, then flipped it over and installed both 0805 caps by hand, then a jumper to pull the DIM pin high since I wasn’t installing the Attiny13A. I hooked it up to a PSU at 10v / 3A and it worked, drawing approximately 1.54A and outputting just under 4A to the LED.
Next I’m going to ignore the urge to fiddle with the buck section and jump straight to installing an MCU.
e
I think you look over a lot more material concerning development of projects like this in forums and videos than I do. If you see other people doing this kind of thing (step up or step down driver development where the driver operates on the order of several amps) please do let me know. I’m definitely willing to be wrong about this.
