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.
Microa has experience with the QX5241 from past efforts and he did mention something about it’s internal LDO PSU not being up to snuff once Vin (battery voltage) was high enough. That’s what the MCU runs off of in this design. I’m pretty sure that the buck section will be fine with what you want to do. Powering the MCU is the only dicey part based on what Microa was saying. We’ll have to see about it!
Yes, but I will not be confident in how accurate they are. The QX5241 is known to have pretty nasty output and there seems to be some trickyness with measurements.
IIRC I’ve compared the readings from my crappy PSU and my short-thick-lead-modded HF DMM and feel confident that the voltage and current readings they provide are accurate.
But when I hookup a DMM to measure output voltage, current falls immediately. Also it seems that something bad is happening with the buck controller, because the PSU starts indicating CC with a flickering CC light - meaning there are input spikes from the buck driver.
My new ’scope will do measurements and doesn’t seem to make the buck driver wig out, but output current does still fall around 0.1A or a little less when I have the ’scope hooked up.
Here’s what I see with a “hot” test bench (heatsink was around 40-50°+):
Vin = 10v
Iin = 1.5A
Vout AVG = 3.43v
Vout RMS = 3.8v
Iout = 3.52A
Without the HF DMM in place RMS voltage is very close to AVG voltage.
I don’t think we are getting true average current from the HF DMM, so I’m not sure how accurate the efficiency calculation can be.
It seems that efficiency may be beyond >80% at 3.5A-4A output. I think it’s hard to draw a lot more from that data.
It’s also worth noting that the scope sees super high voltage spikes. I clearly see full 10v spikes. The XM-L2 LED survives. Maybe this is a sign that the L value of my inductor is much too low for this controller to deal with.
As a sanity check I put my “new DRY” driver back together and tested that. It doesn’t get along with my PSU super-well in “high” modes, but max output voltage was not equal to input voltage. More like 5.4v.
Next I’ll swap the higher value inductor from that driver over onto one of my 20mm ones.
Maximum output voltage behaves properly with the larger inductor in place. Also with the larger inductor in place I noticed an operating frequency just shy of 1Mhz. I didn’t think to check that when I had the smaller inductor installed.
I think it’s fair to say that the 3.3uH inductor is just too small for the QX5241, regardless of one of the datasheets claiming 2Mhz operation. Depending on your usage scenario of course. That’s a big factor… we might have to do some charts!
I put two of the Bourns SRP7030-3R3FM inductors in series and that seems to keep peak voltage down to 6.4v (from 10v with only one) on 10v input.
Also it looks like I need to learn how to properly use that freq counter. I can get it to show a variety of things, so instead I counted myself. It’s 4.5 divisions at 1uS/div. So it seems like “High” with this driver and the two inductors in series is operating at ~220Khz.
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.
