Wight’s Linear fet driver with an opamp flourish
This time a cleaner reflow build with less carpet fluff and flux residue, hope it still works as well as the prototype
Two 0.01Ohm sense resistors should net 10A. Though I may be persuaded to up that to 12-13A if initial tests go well and led temps are reasonably safe looking.
The fet will be mounted to the base of the copper pill with a strip of thermal tape. That should hopefully transfer enough heat away to keep the fet comfy and also isolate the fet drain from the rest of the light electrically. The little ram heatsink I had laying around and it gave me a good place to mount the fet and add some thermal mass to it at the same time.
The low vF of this emitter and the high drive current means there should be a fair amount of heat generated at the fet, but I’d think this setup should do a good enough job of keeping temps in check.
I settled on the T06N02 fet for it’s nice fast behaviour when used in conjunction with the 7136 and opamp, but I have better options on hand in terms of thermal and Rds On performance. I’ll see how this one fares and may upgrade it to something better later.
Finally I beefed up the tailcap section a bit to minimize spring resistance.
I like this external wire approach, keeps full compression on the spring or springs in my case and still gives a solid low resistance bypass.
The straight build of Wight’s driver runs the SBT-70 very well and will run it at the amperage you’re looking for with no problem, so why all the work-arounds?
And why so much concern about the FET getting hot, you’ll be pulling 10A through a MOSFET designed for 150A, running 3.5V when 30V is it’s max. Baby stuff compared to what it’s designed for. In normal set-up it doesn’t get hot at all.
I’ve built dozens of those, use em exclusively with triples and such.
The one powering my SBT-70 is one of the very first, the one that didn’t even have outer ground rings on the battery side. I just pulled 8.72A from a rested old 20R in that one. The Courui, with 3 parallel cells, can run that light with no effort. You might easily see 12A. That’s what modes are for, right?
Oops! Maybe not! That one has the 7136 chip on it, I see the outline now…thought you rigged that on there. Sorry, carry on.
Edit: Now I’m really confused. The A17DD-S08 +LDO is a variant of the board I’ve built lots of. Does the addition of the LDO cause the fet to run hot? I was looking at that driver when Wight announced it, I see it doesn’t seem to have taken off, is there a problem? I meant to switch over to this instead of Zener mods but totally forgot about it. (as if that’s not an everyday occurrence)
I know what you mean. If you read it all the way through you’ll see half of that thread is me asking dumb questions trying to understand it. I ended up using one in my Supfire L5 build. I believe that light and this one are the only working copies of that driver currently.
It’s quite simple, just look at is as a 7135 driver with only one chip
The beauty of using this driver is that I don’t have to stack 26 7135s to get 10Amps and I can mount the single hot part (this being a linear regulator the fet WILL get hot) neatly somewhere where it can be kept cool. And again, I haven’t worked it out exactly, but because of the low vF of that sbt-70 and a 10A drive current. I except there to be a fair amount of heat burned off in the driver.
The bigger the difference between vF of the Led and vBatt and the higher the driver current, the more energy is dumped in a linear driver to keep things regulated at a constant current.
The opamp mod is just a workaround to enable the 7136 chip to properly accept a higher frequency PWM input. It has some kind of soft start behaviour on the output which doesn’t agree with a lot of fets when PWM is too fast.
That’s a really small spot! I measured my uniquefire 1405 (dedomed) and sbt-70 aspheric at 12 metres and got roughly 3 and 4 times (respectively) the size. I’m curious to know what the lux will be?
Oh you have an sbt-70 aspheric? Cool.
What kind of lens did you use in your one?
It’s definitely a small spot, but don’t quote me on the exact size just yet.
Don’t have the focus dialed in right for maximum throw yet, just did a quick test getting the die roughly in focus at that range.
So I suspect this isn’t ideal for longer ranges and that may have a knock on effect on the close range spot size as well.
The Courui is actually a great host for dialing in focus, since you can fine tune the distance between the die and the lens just by unscrewing the “head” a little bit to verify if you’ve got it right.
I don’t recall exactly where I got the lens from. It was the first lens I ever bought, I was using it in a different light previously. I have bought about 3-4 lens’ since then but they were all rubbish so I’ve given up looking for another lens.
After posting that last post I was laying in bed and i thought ‘why didn’t I compare the deft-x?’ Oh well, I can do that tonight maybe.
I’d be interested in hearing a spot size description for the deft-x as well.
—
Good news and not so good news.
The good…
Driver is finished and working great, I dug through my parts box and switched to a different fet with a lower Rdson and added a second one in parallel to reduce that resistance even further. Should be around 2.5mOhm now. My lowest resistance fets, some vishay ones, unfortunately didn’t play nice with the op-amp output. They were the first that didn’t work and produced some nasty oscillations that totally killed the mode range.
Annoying, but I’m not doing anything to clamp down on oscillations on the opamp feedback circuit so it’s bound to happen with some components.
Every other fet I’ve tested on this driver has worked great and with the currently installed units it’s even compatible with 17khz fast PWM while maintaining a full mode range. No flicker or audible whine, so it’s just like a 7135 driver but without the headache of stacking 35 chips! Sweet
Current sense resistors are 2x 0.01Ohm and 2x 0.05Ohm all in parallel which gives me a regulated 13Amps to the led.
I was too caught up wrangling all those wires into place to take more pictures. But you can make out the two fets soldered to the copper heatsink piece and the black tape wrapped driver. Yellow wire is gate signal and the driver is powered through a reverse clicky.
The ground connection is through a brass bolt and copper tab screwed into the body of the light. I didn’t trust the contact board to make good ground contact, it’s a poor design aspect of the Courui that the driver board relies on an bad interference fit and pressure from the batteries to make ground contact.
-
Now for the not so great news.
The light is very impressive indoors and the lovely round hotspot with pencil thin beam is delightful. But in terms of throw figures and outdoor wow factor it’s kinda underwhelming. Of course I knew this wasn’t ever going to be a throw champ but still, the combination of very narrow beam and sorta weak maximum brightness makes it surprisingly dull outside at night.
Bearing in mind I live in a heavily light polluted spot and the moon was pretty bright last night.
But still, I had my standard reflector-ed Courui with me for comparison and subjectively it blew the mega lenser away in terms of perceived/useful throw and of course also in total output.
Even though the standard Courui is reading at less than half the candela of the Lenser I didn’t really spot any targets (100-200m range) where the Lenser illuminated it visibly better than the Courui. Of course the high CRI of the sbt-70 definitely showed much better definition of reds and browns of tree bark for example. But because the spot is so small and the area illuminated so narrow its hardly a very useful feature.
I don’t think it would need to be all that much brighter to be impressive, I was just hoping to be awed a little more.
So a pretty disappointing first field test tbh…pointing the light up into the sky is still awesome though. It’s a true white laser beam in that regard, and if there’s fog…well… J)
Initial readings at 5meters
Courui Lenser: 257,500cd (SBT70 - 13Amps) Dirty lens, focus not dialed in perfect etc but should give a good first impression
Courui Reflector: 97,000cd (XML2 - 5-6Amps) partially discharged cells, possible grounding issue/flicker Edit: Grounding ring improved and reading now shot up to 165,000cd
—
I need to take some proper measurements and verify the throw figures for both lights, and I need to verify if current draw is actually reaching 13A on the fully assembled sbt-70 light. But I think it’s pretty much doing fine at the driver level.
So I’m thinking I will have to try some light recycling to try and boost the lux to acceptable levels, the real problem with having a lens so far away from the led is that the vast majority of the light output is not hitting the lens at all.
I also have a 95mm PCX lens that I could try. It has a much shorter focal length, and while that produces a far larger spot (2.5x wider at 10 meters) it may be more impressive/useable outside at night. I will also give that a go and see if I like it better.
Frankly my favourite use of this light right now is as a true mule, so I can admire the gorgeous high cri output of the led. I’m tempted just to hang it from the ceiling like this and use it as a worklight
I’m working on an aspheric light for a friend and am finding similar boring results. This one too has the aspheric quite far from the emitter, an opposite of yours in that it’s a de-domed XP-G2. Very disappointing end results though.
Like you, I really like this as a mule. It’s just that pretty an emitter and makes up for it’s lackluster performance. I actually ordered a second one and will most likely use it in this configuration in a smaller light, just to look good.
Yeah, I guess it’s also my lukewarm feelings towards aspheric/lenser lights in general that are tainting my expectations. The circular spot fools me into thinking it’s directly comparable to a reflector light when it really isn’t.
I took the light out again tonight without the regular Courui and I had more fun, I suspect I should have gone with the cool white variant of the emitter though. Just to get that extra cool white brightness pop off distant targets, not to mention the extra output would have been welcome.
Anyone in Europe have a Wavien collar they’d like to sell?
I’d love to play around with one of those things.
I would also love to play with an Wavien collar but they are just crazy expensive
But you looks to be a handy guy & you can design stuff in 3D, maybe you can get something fabricated that works just as good. Check out borg’s post #51 in this thread
And comfychair made one also, unfortunately he seems missing from BLF for quite a while & all his pictures is off line, from this thread from post #6
Thanks for the links, I’d seen Comfy playing around with diy collars before but Borgs cool machined aluminium piece looks great.
Am I mad or would something like this be a great starting point for making a collar?
Polished up on the inside (I think it’s aluminium, hopefully it can be mirror polished) and ground top and bottom to get the right dimensions for the openings.
Hopefully they are actually nice and spherical as that would seem to be the most critical aspect to it’s effectiveness as a collar.
Yeah maybe it could work, i could be willing to take a stab at testing if i just could find some good starting point, where did you found those?
I really hope we can get some more discussions & modding on collars going here on BLF, because that looks to be an massive potential booster for aspheric lights. The problem is Wavien collars are anything but budget, it would be great if we could find a easy way to do them our self, so it is not an question if we can afford it, but it is just one more thing we always do when we want to to max out our lights.
Sorry, I forgot all about it as I’ve been busy lately.
I measured the deft at 12m. It was out of focus at such close range but measured it anyway and got around 32cm across the square die image.
As far as cheap collars, the mag reflector is hard to beat. I have a wavien on the sbt-70 aspheric but if I were to do another recycled light mod I would be using the mag reflector. It is marginally less effective than the wavien, based on my own dodgy foolings, but not enough difference to justify the price.
Also the sbt-70 light is more practical than the deft. I went camping the weekend just gone and a portion of my lights are throwers which weren’t really any good for the area we were in (hills and tall trees) a floody multi emitter would’ve been more practical. Of course, I know these things get built for the fun of it 8)
