Definitely do your follow-up testing please, that resistor should make cutoff voltage way too low.
… is it possible that you don’t actually have nlite on that MCU?
I’m sure you’ll be much happier with the ability to flash.
I don't know it's n lite but it is a 3 mode, no disco with solder selectable moon mode, memory, and mode order. I'll update with test results.
Wight,
I tested low voltage stepdown with the 19.1k resistor installed. Stepdown occurred reliably at 2.8 volts.
Brian
My opinion is that as long as you discontinue use as soon as stepdown starts you’ll have no issues. Looking back at the NLITE section on DrJones’ site it appears that there is no low voltage cut-off, only a single stepdown. (Whereas STAR repeatedly steps down in an effort to do a ‘battery stretch’.) Understand that your battery has exceptionally little capacity left at 2.8v, so you will have no significant early warning.
So after acknowledging these important limitations, this sounds fine within the scope of what you can currently do for yourself. Clearly my recommendation would be different if you could flash.
Further thought leads me to believe I got the MCU discussed above off a q-lite from IOS. Actual investigation confirms the presence of solder select disco modes. My bad.
To actually test NLITE on this driver I built a second driver with a different MCU. This one came from RMM about a month ago on a 4x 7135 driver and I had him flash nlite onto it. I built the driver with 22k resistor first and got the first stepdown at 3.21 volts. There were several steps noted to progressively lower light levels but there was no associated flashing. I substituted a 19.1k resistor and didn't get a stepdown until 2.7 volts. That's a long way of saying NLITE works fine.
Cool, thanks for the additional info. Definitely useful stuff!
Your measurements appear to show a variance from the specified value on either the 22k or the 19.1k resistor. No big surprise there. For example, 1% tolerance on a 19.1k allows for the wide range of 18909 to 19291 ohms.
To knock the 22k resistor down you could piggyback a high value resistor such as 220k to 330k. Ideally that might net a 2.96v, 3.01v, or 3.04v stepdown respectively for 220k, 270k, or 330k. (this is based off of your 22k stepdown measurement, not your 19.1k stepdown measurement)
I scrounged a 330k resistor and piggybacked on the 22k. Stepdown voltage was 2.95v. I'm putting the light back together now!
Any thoughts on a piggyback resistor value that might reduce the stepdown voltage from the 3.47v I was getting with the 22k and q-lite combo? The 2.8v I'm getting with the 19.1k is a bit low for comfort.
I’m glad the 330k did something decent.
As far as a value to piggyback for the qlite’s R1, sure. All I’m doing is using a handful of calculators. I understand how this stuff works, but just punching stuff into calculators is easiest for me.
- Determine target voltage. For that I use a voltage divider calculator, such as this one from Raltron. Simply input your Input voltage (stepdown voltage) R1, and R2.
- Determine target R1 value. Change the input voltage to the desired stepdown voltage. Delete R1 and recalculate.
- Determine piggyback value for 22k R1. Use a parallel resistor calculator (solver!) such as this one from sengpielaudio. Input our starting resistor value (R1) into R1. Input the target value into Rtotal.
- Choose nearby standard resistor values. http://ecee.colorado.edu/~mcclurel/resistorsandcaps.pdf
- If necessary do your calculations in reverse now, calculate the Rtotal for a piggybacked resistor (say 330k on 22k), then punch that into your voltage divider calc along with the 4700 ohm R2 and the output voltage you calculated earlier. This will allow you to produce/check the stepdown voltage.
That was an interesting process, thanks for the education. If I did it right, the gate voltage calculator comes up with an R1 value of around 18.4k for a stepdown voltage 0f 3.0v. The issue of course is that we already know that an R1 value of 19.1k gives a stepdown voltage of 2.8v so going lower won't help. What troubles me some is that the entering the stepdown measurement of 3.47v and the 22k/4.7k resistor values gives a gate voltage of 0.611, somewhat higher than your expectation. Some seat of the pants stacking (assuming we needed a total R1 value between 19.1k and 22k) gave me a tested stepdown voltage of 3.1v at a total R1 value of 20.5k by stacking a 300k resistor. I might try an 800k next if I can find one.
Which direction are you trying to go from 3.1v?
It would likely help if you measured your resistors. You did use a 1% 22k part, right? I’d measure all 3: the 19.1k, the 22k, and the 4.7k.
Has anyone tested this FET yet? RBD? DBCstm?
Thanks.
I have a few of them, but haven't gotten around to testing one yet. It was super expensive, so I really want it to do something! 
Me too… on both counts.
Being close to Mouser it won’t take but a couple 2 or 3 days for them to show up.
I won’t sit on em. 
I’m interested in putting this driver in my Convoy C8. Currently, it’s just an XM-L2 with 7135*8 but I want to take it to the next level. What all would I need for the conversion? Would I need additional heatsinking to make it work? Looking forward to hearing back!
- With a good cell and a low-Vf emitter this driver will provide extremely high currents. Most XM-L2 don’t have a low enough Vf to get the craziest currents, but you could easily see something like ~6A, which is a lot. You’ll need to ensure that you are using a DTP MCPCB such as the ones from SinkPAD, Noctigon, or Maxtoch. A regular non-DTP MCPCB (copper, aluminum, whatever) can be expected to destroy your emitter at 6A. Look at MTN Electronics or INTL Outdoor for those parts, although I think there are plenty of other places that carry SinkPADs.
- Of course you must ensure that the (DTP) MCPCB is adequately seated against the head and transmitting heat out to the flashlight body properly. Normally this involves having a thin layer of TIM (CPU heatsink grease) under the MCPCB. This high-current situation is very hard on the LED, so heat management (cooling the LED) is critical.
- No heatsinking at all should be necessary for the driver. It produces very little heat (only “switching losses”).
- Mouser and DigiKey partslists to build the driver are on Page 2 of this thread.
- You’ll also want a driver spring, probably (again, MTN or IOS are good places to look). You’ll definitely want to bypass both springs. (Unless you don’t use a spring on the driver. In that case you’ll only need to bypass one spring of course!) The quality of the spring doesn’t matter much once it’s bypassed, you don’t need a high end spring. Here are two threads which show bypasses:
Mod: Convoy L4, a good mod host? Is it even necessary to mod? (look in the OP)
I'm only achieving 2.25A from a 3.04A driver (look at post #55)
Much more involved than I thought it’d be, and that’s ok. I’ll probably just wait for this A6 GB to happen!
It’s not really involved. The only crucial thing is to heatsink the LED properly.
In general doing spring bypasses is only necessary to improve performance. All high current lights benefit from doing this. (If you won the Vf lottery and have an XM-L2 emitter with a really crazy low Vf it’s possible that you could damage a spring. I’ve only done that with an oldschool XM-L @ 8-9A, the XM-L2 will not likely pull enough current for that to happen.)
Which diameter MCPCB would I need for a Convoy C8?
Would this driver work in lieu of building my own from scratch? Pros? Cons?
I don’t have a C8, but I imagine it’s 20mm. There are many different C8’s, so I recommend that you take yours apart and check for yourself to be sure. I think older or less nice C8’s may have used 16mm.
Nothing wrong with that driver! The layout is inspired by this driver (v024). I think that my driver (v024, v031, v043) is considerably more attractive in appearance than the ones from MTN. Performance should be in the same class.
I’d still recommend building your own: you’ll learn more, become more comfortable with the parts, and save money. RMM charges a very fair price for his assembled and programmed drivers… but you can still build your own for a fraction of the cost. You can purchase PCBs and parts for 3 of these for the price of one pre-built driver. (Much) Better price breaks happen at 10x though, so I’d order 3x PCBs (the minimum) for $2.20 and at least 10x of all the parts from Mouser, just like the cart in post #38 shows. You may want to pickup 100x of the 1uf capacitor and the two resistors, as the price breaks are huge on those once you hit 100 pcs. It’s $4.00 extra total for an extra 270pcs (90 extra of each). The 1uf capacitors are especially useful for converting Nanjg-105c drivers to offtime.
Take a look and form your own opinion. IMO the parts are cheap enough compared to built drivers that you can afford to destroy… well… a LOT of them in the learning process if necessary.