Wight, I'll admit that I don't understand what's going on with it but it seems to work. I am feeding through the EN. I didn't even know that we had a datasheet on this thing!
It probably got buried in the thread somewhere (#104), but I’m pretty confident we are looking at the QX9920 controller. http://www.yuketek.com/pdf/QX9920.pdf
Actually while getting ready to link you to it I re-read the introduction in the datasheet (through an online translation) and I see that they clearly specify using the EN pin for PWM. Whoops! I’m glad I already suspected myself, softens the blow ;-). Anyway I really want to know about that TOFF pin in this case. Maybe that pin is useless, or maybe tweaking that pin could soften the spikes. Currently I really fail to understand it’s purpose.
Will you please post screenshots from your scope showing the output from this driver? That would be really useful to me. Especially a detail shot of the spike. Thanks in advance.
Ouchyfoot wrote:I'm building a light and plan to use this driver (7A) stock with an MT-G2. Do you forsee any problems?
I would go with what ever RMM advises, but I can say that I've been driving one at about 11.5 amps sporadically with this driver using 3S King Kongs with no issues. I say sporadically because I don't use High mode much. For all I know, I may be slowly beating the emitter to death, but it hasn't shown any signs of distress yet.
The voltage spike should be a poof situation, either it poofs or it doesn’t. So I think you should be good to go.
I don't have any screenshots but when I'm testing the new inductors I will take some. All I know is that 0.9V+ output ripple is A TON! The issue we run into with buck drivers is that there really isn't very much space inside of a flashlight to fit big components. The only way that I know of to downsize components is to switch at a higher frequency which allows for smaller capacitors and inductors, otherwise if we want high current we've got to have large components.
Sounds good. You’re correct about switching at a higher freq. This is also undesirable due to increased switching losses.
I still suspect that high current is doable with a small inductor. IIRC in my LD-29 thread I said I measured the freq the buck circuit was operating at as around 400-500kHz (I posted a more specific number over there). That driver puts out 3A in stock form. It gets >80% efficiency and the output is absolutely smooth. HKJ’s review shows almost no ripple, I saw the same thing in my own testing. If we can generate a smooth 3-4A output at that freq with small 7.4 x 6.6 x 3.0mm SMD inductor it seems that it should be possible (maybe not with the QX9920) to generate two or three times as much current with similar ripple using an inductor which is two or three times as large.
RMM,
Since you have an oscilloscope, you may be interested in this idea. When I first worked on this driver, I mistakenly replaced the large diode with a 70N02 FET. I was driving a MT-G2 around 11.5 amps and the driver behaved nicely and did not generate heat on that area of the board. The heat generated only in the area around the voltage sense resister bank. Wight noticed the error I had made. When I replaced the FET, the driver became considerable hotter due to the large diode generating heat too.
I have no idea what was happening in the driver with the FET for a diode. Maybe it just blocked current flow through the inductor. I've been meaning to look at the traces to consider what was happening. The big tab pad for the diode connects to the toroidal inductor which is connected to the positive LED pad. The Ground and Gate pads share a pad that connects to the big tab pad of the FET pad. I have know idea how an N-channel would behave with positive power applied to a FET's Ground and Gate pins and Negative to the large tab. That is something I should check with a DMM.
Who Who knows what it was doing to the emitter as that the MT-G2 is one tough hombre. That is something you have the equipment to measure should it sound like something worth exploring.
That’s something I might try with my Y3. RMM said he put two 25v 22uF capacitors on the output to absorb the spike when you turn it on. 
And then he said that it didn’t work. Keep reading.
Couldn’t hurt though… It seems it was a minor success anyway. Maybe a bigger capacity cap. Or mess with a resistor to let it fill slower. Like 1-2 secs till it reaches voltage. I used to do a lot of that with relays, to add a delay to relays. Also had 1 farad cap storage (huge bank of caps back in the 90s) to keep the draw from the alternator consistent. This stuff is all coming back to me. But the big cap remember really helped smooth things out in the voltage department and kept the voltage stable from the regulator. It might work if it was just a bigger cap- I’m not sure if they make ceramic caps that big though, or if there’s enough room. I might try it though, like with a regular japanese cap to test and see if the spike is there on the lower end before and after.
I mean it can’t hurt to put it in there. The cap would make it kind of cool too cause the light would fade out
You might learn something from doing it. It won’t do any of the things you think it will, although it won’t do much bad either.
Among other important points, understand that this driver (like other buck drivers) probably operates somewhere in the range of 1,000 to 1,000,000 cycles per second. RMM was attempting to smooth out the “turn on” spike during each of those cycles. Not some spike when the light itself is turned on.
The cap will certainly not cause any fade in or out.
As far as resistors - I cannot think of any configuration of caps and resistors that makes sense on the output side.
Just to further clarify - anything that you do which takes 1 second to take effect will not help with an LED that gets blown in under 0.001 seconds.
Unfortunately I think the truth of the matter is that the effect of adding an output cap will be so minuscule as to be undetectable without an oscilloscope. So you probably won’t learn from doing it unless you have and use a scope.
If you’re really interested in getting back on your feet with electronics and relating that to flashlights, I’d recommend figuring out current sensing. It doesn’t seem like you have a handle on that yet, and that’s a pretty basic concept. It revolves around applying Ohm’s Law. It’s hard for me to see how you’re going to either achieve or learn anything just by throwing parts at a problem which you don’t have.
Yeah your right though- never really got into power supplies. More plc programming and cooling components was my thing, and programming, wifi, car stereo… I’m just throwing stuff out there, doesn’t mean I’m right. It’s good to have other people’s experience, even in other fields cause then someone like you who understands it better might look at a different angle.
I mean if I posted half the stuff I’ve made over the years you’d sheet your pants. I don’t study basic electronics but I know enough to get it working. I’m a welder, machinist, pretty much jack of all trades. Trying my hand at flashlights- which to tell you the truth is a bit deeper than I expected But that’s awesome
From my experience the cap will keep the lights on till it drained. But were talking 1 farad so I was thinking if you add a resistor, that would give the cap time to put a drain on the emitter current till it filled. But if your saying the driver cycled and the spikes happen each cycle- then that makes sense, doesn’t work.
I’ve never used this driver with MT-G before, so is this normal behavior?
I tested with new fully charged 18650B. Perhaps my test was flawed.
The MTG was from a newly ordered batch.
I can’t repeat the test per say, as the driver is now installed in a light, and the emitter is in a box. I could test again using the same emitter and a different new HX1175B.
Anyone else driving MT-G2 with two cells with this driver?
I don't recall ever trying to measure the driver with 2S cells. I will do my best to measure a new stock driver with 2S and then 3S tonight.
I just received the buck converter wight recommended to me in another thread. I will also try to get around to swapping the buck converter on my broken diver and hope it does the trick.
That would be great. After I tested with two cells, all I did was add a magnet and a third cell, so I think my test was true.
The driver I used came out of another light (the same one relic is driving 3xMT-G2 with) I do have some brand new ones on hand.
Some odd test results of HX1175B and MT-G2
I tested three different HX1175B with MT-G2. Here are my results.
With 2 x 18650
Driver A - 3.5A
Driver B - 4.2A
Driver C - 4.8A
With 3 x 18650
Driver A - 7A
Driver B - 13A
Driver C - 6.8A
These are my results. I can't explain them, especially the 13A. All the modes were functioning, and I could feel it heating up fast. It kind of scared me.
Please check the markings on the sense resistors of each driver (A/B/C) and post your results.
B and C have R068 resistors. A is already wired into my Boxer, but probably the same.