Damn, it must a pretty good strain 
I am envious.
Single cell lights with driver space 17mm or less, no boost or buck driver known can match it. Big lights are more flexible with both voltage and driver space but still a very small driver selection. Taskled 6A drivers are over 30mm and cost $40. Great priducts and worth every penny but neither small enough, powerful enough, or cheap enough to compete with linear drivers.
Make an effort to use common hardware and open source firmware and if it works as he suggests then likely it will gain traction. Get it included in a GB light and it maybe will become mass produced. If it really is better and not much more expensive (good inductors cost more) then maybe it will compete. Some wonât care about smoothing pwm if it doubles the cost of a driver or doesnât have the latest ramping ui or canât be reflashed with a favorite ui. Dot all those iâs and cross the tâs or it will just be another nice driver with limited poularity. Even if itâs vastly better poor mcu selection could delay widespread use for a long time.
Iâd like to add that aside from other things, efficiency difference is typically overstated.
Typically a linear driver consumes 5-10% more power than equivalent buck or boost across full discharge. This can go up to about 12-13% in really extreme cases. Definitely nice to have. For some uses - important. But for others - not really.
Note that most 7135 based drivers add extra inefficiency in the form of running LEDs at higher currents and PWMing to get the desired output. Especially single-channel ones. FET-based linear drivers donât have it.
Does it do any harm to the Li-ion cell to take the highest current draw when it is at itâs lowest Voltage? I donât know if itâs bad or not, just feels that way to me. Is it?
Thatâs one thing I have concerns about in a Boost circuit. Currently testing a 12V Boost that creates a good bit of heat through the driver itself, pushing an XHP-35 from a single Samsung 30Q at around 2.3A emitter current. Draw on the cell gets rather high just before the cell dies⊠the driver is handling it though, albeit through a lot of ramping down and back up in maintaining the heat level. (averaging around 116Âș at the pill in a Convoy C8+)
With this light, Iâm beginning to see the value of at least having the option of full Turbo when the cell is low, configuration ability allows a wide range of options so itâs easy to use lesser levels on a regular basis and still have that option of a Turbo blast even right before the cellâs low Voltage forces a step down. So I do need to learn what effect all this has on the cell itselfâŠ
I was looking at 7135 driver and I always wonder why everyone use it also. It make sense to use low number like 4 in circuit, but I see people with 20x of those chip on pcb and it seems a little confusing to me. why not use bigger transistor? a simple big but cheap mosfet will have better thermal and be cheaper.
also I read the 7135 datasheet and I notice you can also use this chip which can do 1A, call the 5710, about 3x the 7135 current capability at 1A, so why nobody use this one? Can easy make 3A led driver with just 3 of this 5710.
http://www.consonance-elec.com/pdf/ææŻèŻŽæäčŠ/DSC-CN5710.pdf
I donât know. I guess that as long as the continuous discharge rating of the cell is not exceeded it wonât be too terrible. The discharge rating is stated for the whole discharge, not for a voltage range. I guess itâs between 12A and 15A depending on the step down voltage and driver efficiency, the 30Q is rated for 15A. If you are concerned you can always switch to a higher drain cell like the Molicel P26A.
What are the two legs beside the ground tab for? Those arenât on the usual 7135 chip.
Edit: Back about 4 or 5 years ago, before Comfychair started experimenting with the big 07N02 MOSFET on a Qlite, the only way we could gain power was by stacking 7135âs. We were all pretty tired of it, for sure, so we ran with the FET options and most of us didnât look back. Iâve recently stacked chips for use with the White Flat but other than that itâs been a while since Iâd put 32 chips on a Qlite. 
ggf, yes, of course⊠there are higher rated cells than the 30Q but thatâs what I had free when I got the driver to test.
I donât know electronics, other than all the mods Iâve done I wouldnât know jack about a flashlight. But I worked in a lumber yard for many years carrying building materials and I know that itâs far easier to carry a heavy load when youâre fresh than when youâre exhausted. Seems illogical to ask so much from something that has so little left to giveâŠ
As long as you donât exceed the specs (probably 15A), youâre fine. Usually thereâs also higher allowable current, as long as you donât exceed a certain cell temperature. Something like 20A, but donât exceed 75C. Burst currents can be even higher (for a few seconds).
Generally, theyâre trying to make sure the cell doesnât get too hot. If youâve got it wrapped in insulation, you might have to stay below the continuous current rating.
I agree it would be nice to have an easier way to get more linear regulated current. Some discussion of this 5710 chip here.
It regulates on the high side of the LED so itâs not a simple drop in for the 7135.
I agree for higher current the efficiency is usually not bad compared to a typical buck driver. But for low current the efficiency of linear regulation is worse. An extreme example is the 2mm white flat whose voltage is ~2.75V at 0.5A which equates to about 2.75/4.2= 65% efficient.
EXCEPT for the fact the no cell remains at 4.2V under load⊠so with sag considered efficiency will be something better than that 65%, not much but stillâŠ
Also, a lot of chargers terminate at 4.16V or so, in that case efficiency would take another step forwardâŠ
True, it was just a simple approximation for low current.
The efficiency improves as the voltage difference decreases, so as both the voltage drop from circuit resistance increases and the LED voltage increases with current. Linear driver efficiency approaches 100% at direct drive, when it doesnât drop any voltage.
Itâs putting a strain on the cell when it can least afford it. Cell-voltage for sure will drop like a rock, and current-draw from a boost circuit will almost certainly want to maintain output, drawing even more current from the cell.
Thatâs why at least with linears, theyâll saturate and pull out of regulation as cell voltage drops below Vf + 0.1V, drawing less current, dimming the LED, letting you know itâs on its way out.
Yeah, but that seems to be way too soon when youâre dealing with a lot of 7135âs in parallel. For example, on my Convoy C8âs that have 8 x 7135 chips, they drop about 25% of their output by the time the cell is about half-drained (3.75v). This is using 30Qâs, so they should not have much voltage sag at 2.8A current (about 0.1v sag).
I am unimpressed with using linear drivers in high-output lights. Boost-drivers are the way to go. Or FET (for cheap lights), and just accept the fact that itâs going to drop output quickly.
Bad? What is bad from your perspective? What is the maximum amount of cell stress you are willing to let be?
I do not see how drawing more current at the lowest voltage levels can be any more bad. As long as you aren't overheating the cell or going much above its rated discharge current there's nothing really bad involved. The slight increase in drawn current at the end also trips the low voltage warning/protection a tad sooner, this can be seen as a good thing. :-)
Let me say that charging the cell to 4.2V and letting it rest for hours (or more) before use is in fact more detrimental for it than some increase in current draw just before end of discharge. And let me also say that the increase in current draw is not just at the end, but a general phenomenon happening from start to end due to the more or less constant power output and corresponding more or less required constant power input. More or less because driver efficiency progression matters, of course.
Rating: no big deal. :-D
Actually, that might be because all that current is being pushed through thin pc board traces and vias, not actual wires, through 2 sides of the board, yet.
Kinda like the difference between an exhaust manifold and exhaust header. Lots backpressure in the manifold, not much in the header.
Ie,
vs
It seems like the OPâs question was answered pretty thoroughly in the first page of comments.
FET, FET+1, FET+N+1, and 7135-only drivers are popular because:
- Theyâre simple, easy, compact, cheap, and well-understood.
- Designs for them are openly published.
- Theyâre widely available.
- Theyâre supported by a bunch of open-source firmware.
- Theyâre easy to swap in to almost any light.
- They work well enough for most common purposes.
Other types of drivers offer a few benefits though. They increase efficiency, they enable higher-voltage or in-series LEDs, they improve output regulation if done well, they can reduce heat on medium-high modes, and they decrease the frequency of posts complaining about FETs, 7135 chips, and PWM.
Someone could make fancier drivers more popular, but it hasnât happened yet because:
- Theyâre harder to design, so fewer people are able to.
- Theyâre harder to fit inside small hosts.
- Hardware development costs money.
- The designs mostly arenât open-source.
- Aside from a couple common sizes, each light tends to need its own custom driver designed.
- Although some have been created, the good ones havenât really been widely available.
- Theyâre generally not compatible with open-source firmware, and the code for them has mostly remained closed.
This can change though, if a skilled electrical engineer is willing to publish a bunch of open designs for several different form factors, make them compatible with open-source code (or at least open up the code written for them), and work with a manufacturer to make them easy to obtain. Perhaps get in on some BLF community projects. Basically, donate a whole lot of time, effort, and money to the community. And BLF has a tendency to burn out the most skilled circuit designers, because their work is in such high demand and they donât really get paid for their work.
Iâm at least trying to make firmware ready for newer drivers, whenever those drivers come into existence. Like, creating a hardware abstraction layer and porting it to a variety of different MCUs and types of drivers. That way, new hardware can be immediately compatible with several interfaces, and new interfaces can be immediately compatible with several types of hardware, and users can mix and match as desired. But Iâm not doing the hardware side of that.
As mentioned, some of us (Mike C and myself, at least) are actively working with this chip.
And a few of my recent designs (not promised to be perfect, still in testing⊠please donât order unless you feel like gambling): 3A single sided, 17mm and 5A single sided for Emisar D1S
Interesting chip, but not a direct replacement for the 7135. More powerful and flexible, for sure. But it also has a slightly higher voltage drop. And if anyone knows of any chips similar to the 7135 / CN5710 / CN5711⊠feel free to share (or PM)!
Very nice, look like another fun project! Do you happen to have forum page you written about this drivers?