So, I melted some solder on the iron tip, applied it to the side of the cap while holding the cap with a tweezers, and it came right off, quick and easy. Now that it's off the board, measured it on my old Fluke DMM, and it showed 4.6 µF, which is typical - the readings I get are always lower than the rating, so probably a 4.7 µF.
This is really interesting... Think'n further back, maybe the 10 µF value was more common... comfy or maybe RMM might know more?
Unfortunately I realized after setting this up that it’s a pretty terrible setup, so these scope images are somewhat worthless. My test LED was an old XP-G, probably with some damage, which only pulled around 2.5A from a high-drain cell. That said, they aren’t entirely worthless so see below. Scope probes are placed with (1) on FET gate, (2) clipped through the center via onto the BAT+ pad, and (3) clipped onto C1 right next to MCU VCC. I’ve got about 60mm total of 26AWG LED wiring and about 600mm of 18AWG battery wiring. I need to swap the LED out for something which will pull more current and use a bit heavier LED wiring.
The build here is using a v030 PCB with these parts:
C1 - 1uF (X7R - #C2012X7R1E105K125AB)
OTC - n/a
R1 - 19.1k
R2 - 4.7k
R3 - bypassed (0-ohm)
R4 - n/a
R5 - n/a
R6 - n/a
D1 - stolen from Nanjg (~0.2v drop)
Z1 - 4.3v SOD-123 Zener w/ legs bent to fit on SOD-323 pads (#MMSZ5229B)
I think they are functional enough for an advanced builder like you to make something out of them. As I mentioned above, my first test was a crappy one!
Definitely don’t forget that you’ll need SOD-323 and 0603 components. For the build above I populated R1/R2 with 0805 size and it was beyond “tight”: one had to lie down on it’s side. The SOD-123 w/ bent pins was also a very poor fit and very close to the resistor pad next to it. (The 0805 on C1 was no problem though, even w/ the Pomona clip.) You might want to make yourself a note about R1/R2 being reversed in case you forget before they come in (sorry about that, I’ll correct it in the next revision).
I wouldn’t be surprised if a limiting resistor was needed for the Zener. If we use a 5.1v Zener maybe something in the range of 10 to 50 ohms would be good? We’ll know more after I do a higher current test.
You know the drill… no guarantees… you’re the official test pilot!
Uh… I was given the 10uF number by someone who claimed that checking capacitor with a multimeter wasn’t accurate enough, and that he had measured the 105C part properly with whatever super-technical lab grade stuff and that it was a 10uF. Not saying any of that is fact, just that that’s where the number came from. I’m pretty sure I remember who it was but haven’t gone looking for the exact post, so I don’t want to name names.
comfy - no sweat really, like wight said. Just interesting in pt of history - could be they used 10 uF caps early on. 10 uF caps are so well proven, I’d feel it would be risky to experiment with lower values, unless it’s a major re-design as wight is doing, of course.
Just fyi, I’ve measured 10’s, 1’s, and 0.1’s uF caps with 2 different DMM’s (Fluke and advanced model UNI-T) and they all measure slightly lower, but pretty consistent in the range, clearly identifiable.
I had no intention to point a finger at someone and I always saw it as minor details - which it probably still is.
The reason I brought it up now and here is that you all thankfully invest a lot of time and effort and I wanted to avoid that you - unknowingly - might use different components and have strange results, be it at the FET, at the OTC or while adapting firmware. I can’t help otherwise with these drivers but I follow with interest.
Alex - didn't look carefully at your v030 til now. Wow, impressive all that fits! Ohhh - is that a MCU pin #3 pad connected, but covered up? I'm really not lik'n soldering a thin wire to pin #3 directly on the v009's for a locator /LVP LED. Looks like I could just scrape off the covering of the pad?
Edit: Debating whether I should order these 030's now or wait til some testing is done. Not sure I followed everything, but have you been able to breadboard/proto/test this out somehow?
FWIW, Dale has parts for a few v030s on the way and we’re going to try to experiment to figure out what value resistors and such work best. I assume the OTC resistor, at least, will need some tweaking. Maybe other parts too.
However, feel free to do your own experimenting. It’ll probably be faster if you do it since the hardware and software parts of your brain don’t have to use email to talk to each other.
Hhmmmm. I can probably get most parts from here @work, but not sure yet. I looked more carefully at Alex's tests in port #352 (thanks David, my bad!).
K, I'm a little confused, got some Q's:
this should handle high PWM rates, like 15K?
looks like there's ringing on the (2) line. Is that because of long LED wires or something else? Is that a bad thing or good/ok?
I'll just go ahead and order boards - $2.20 is no problem at all - feel like I'm ripping them off anyways... I'll be testing on an 85 and not interesting in OTC.
Oops, sorry I didn’t reply Tom E - I saw your post earlier and meant to. :-x
As far as PWM, this is no different from earlier revisions. Were there any particular changes or comments that brought on the question?
The ringing is on BAT+. I suppose that it’s due to inductance in the battery/LED wires?
I agree, every time I order a 17mm or less board I feel like I’m getting a steal from OSH Park. Hopefully we serve some useful function for them!
OK, apparently what I have on hand isn’t that powerful! I hooked up the only triple PCB I have, which is a triple XP-G2. I used it with the highest drain cell I have, a heavily used Samsung INR18650-15M. This setup was only good for 10.3 amps as measured with a clamp meter.
That said, I produced a couple of scope images and played around a bit. These shots are in a low mode, I failed to take pictures of medium modes.
This is the same driver build from post #352 but with some wiring changes (in addition to the LED change):
I changed the battery wiring to ~200mm total of 18awg.
I changed the LED wiring to the 22awg included with the triple.
I soldered on new test points for the scope probes.
Channel order is
BAT+ from spring side of driver.
MCU VCC measured at C1.
FET Gate measured at gate pin.
We can see that MCU VCC reached a safe-for-the-MCU 5v which is nonetheless very high considering that it’s attached to a 4.3v zener with no load resistor! I speculate that the Zener may die an early death like this. We’ll have to try and figure out the peak and average current it’s seeing. Gate looks pretty clean to me, with a bit of badness on the turn-off that we can probably clear up with the pulldown resistor. BAT+ reaches crazy high voltages. The second shot is on a 2v/div scale and shows a crazy high B+ spike of 8v from a single cell! This spike did get a volt or two worse in medium modes.
I’ll see about adding a gate pulldown resistor and testing with that.
When I’ve done realtime voltage monitoring on a FET-only board (Ferrero Rocher), I’ve gotten pretty big variability on voltage depending on the exact timing of the ADC reading. For a realtime display it’s actually not such a bad thing, since it makes the indicator flicker at a varying rate according to voltage. So, it actually provides more of a fine-grained indicator due to the spikes being out of phase with the measurements.
This also affects LVP, but it’s not usually an issue because LVP uses a heavy lowpass filter and because the spikes aren’t very big at low voltage.
For non-realtime displays it works well to shut off the emitter, wait a short while, then take and average some measurements.
I think the only worrisome impact of the spikes is whether it might damage or reset driver components. The MCU actually does pretty well dealing with the spikes as long as they’re not high enough to cause a reset.
If we go with Halo’s idea to eliminate the voltage measurement pin (and voltage divider parts) in favor of the VCC/Vref method, the VCC spikes may become more meaningful to the MCU. I give it only a 50/50 chance of mattering though, for the same reasons the non-fatal spikes don’t matter much on current designs.
The BAT+ spike looks a little scary. I wonder if that could damage the emitters over time. Dale has mentioned that some of his lights don’t measure up to their original performance any more, and this might explain why.
While the B+ spikes may certainly be doing something bad to the LED, I’d say that other factors probably weigh in more heavily. Dale’s shown that things such as batteries, bypasses, clean lenses, etc can have big effects. With all that ruled out my vote is on the heavy currents put into the LED: the LED has thermal resistance between the die and the thermal pad and there’s no getting away from it. More heat will result in an elevated die temp which I suspect will degrade the LED much more quickly than at Cree’s maximum currents. That said, I certainly don’t know. I’d love to eliminate as much bad behavior as possible, including the voltage spike on B+.
This PCB (v030) is not compatible with Halo’s idea. Click through and take a close look at the first graph since it’s easier to read. Each division is 1 volt and zero is 1 division above the bottom (where the little yellow/orange tags are). In post #365 the MCU trace is aqua colored. Note that Halo’s idea is to determine MCU VCC, but as we can see MCU VCC is never similar to B+ voltage. Instead, VCC starts at ~4v and then bounces up to 5v and tapers back off.
I’m impressed with DEL’s results from post #648 here and plan to try out an RC snubber.
I implemented an RC snubber using 10nF and 4.7ohms and got similar results to those DEL showed: ringing was removed but the peak voltage on B+ remained pretty similar.
Try the two-10uF setup, one before & one after D1. That helps with the bounce at B, and also allows a tiny bit of boosting at Vcc (but with B flatter, the boosting is kept below critical levels).
Well, I built a v009 today to install into a light I need to get rid of… and sure enough I ran into the “bright flash” issue you’ve been talking about Tom E. I didn’t do any measurements - I just installed a 0803 12k resistor as a gate pulldown (as you suggested). Problem solved. Thanks!
