[WIP] 17mm DD+single-7135 driver / single sided / Dual-PWM

I manually solder by hand and have no issue using 0603 parts if it gets me the driver I’m after

Yes - 12K pulldown - it's what I had available and seems to work well. 0603 sizes are fine with me. I certainly would like Richard to chime in on this, but not sure if he's been spending much time on the 25/45/85's.

I haven't built any LDO based boards yet but am certainly interested because I have a couple of lights I'd like to use them in (e-switch multi-cell for 6V LED's).

I’ll get back to those comments, I’m just posting right now to point out that using a 2.5v LDO is a bad idea. (In other words I’m correcting myself.) I don’t think an LDO can be practical for single-cell since it won’t fully open the gate with most of the FETs we use. (The MCU will also drop some voltage, so there just won’t be enough to make the FET happy.)

Wight, I was about to comment on the low LDO voltage, and I agree with your correction. You really want a 4V+, preferably 5V LDO for two reasons: First, you want the gate voltage to be as high as possible to minimize RDS, and second you want to dissipate least amount of heat possible in the LDO, especially the smaller package ones if you are running 3S or 4S.

If you use an LDO with any clicky application you generally need to add a pulldown resistor to drain the capacitors so that you can switch modes fast enough with off-time memory.

As far as use of an LDO with 1S goes, I have found that most of the true LDO regulators will work with 1S and that the voltage drop across them isn't much worse than a normal schottky diode, but you do have to contend with the extra capacitor and the timing issue (see paragraph above).

I really think the FET makes a difference. I’ve used PSMN3R0-30YLD on wight’s FET+1, with t25 and bistro for a single XM-L2 without issues and used it on PD’s DoubleDown with t25 and bistro for a triple XP-L HI, no issues with just the standard components, both are power switch lights.

If people have to manually stack a second cap, that’s pretty crap for reflow IMO. Same thing with the 0.1uf that Tom E has been adding to fix ATtiny25 problems. I’ve publicly done several major reworks on the FET driver layouts + several more that never saw the light of day, so one more to get a better build process might be worth it.

As far as multi-cell applications: For me the first step is probably a board similar to these (DD+7135) with the addition of an LDO. That’s a much smaller leap than the leap to a buck driver - remember that I’ve never designed a successful buck driver. I tried pretty hard to design/build a QX5241 based on early on but couldn’t get it functioning. I learned a lot from that process and applied some of it when I did a much more handsome MAX16820 based board… which I never ended up building / testing. Since then RMM has gotten several sizes of buck driver working and all of us have learned a little here and there. I’m confident that I can design a buck driver which works now, especially with a few well placed tips from RMM. I just don’t plan to hop on that task first thing.

Sounds like the consensus is that we’ll take our lumps on 0603 where necessary. If I build something ‘unkind’ you have only yourselves to blame. :evil: :wink:

Thanks Tom E, that’s what I wanted to know. I’ve got some thoughts on reducing the quiescent draw of momentary lights a little bit more, we’ll see where they go.

Good points RMM.

Getting back in the saddle really has me dredging my mind for some stuff. I go back and forth forgetting important things - for example I’ve just been reminded that we normally depend on an internal 1.1v vRef for LVP with the ATtiny13a. There are tons of other equally important things that are slowly filtering back into my consciousness.

Is that what I’ve recommended / used in the past? Maybe I should do a build with the SiR800DP. I think I bought 1 or 2, but I don’t know that I’ve ever built anything with them. As I recall the SiR800DP is a bit different from many of the other FETs we run into.

Yes that’s the one you kinda recommended in your A17DD-SO8 / A20DD-SO8 / etc - thread. Seems like there has been a lot of discussion about the best performing FETs to use. Still haven’t read and more importanly understood all the info about FETs that was posted all over the forum. By the way, thanks, wight, for letting me see comfy’s scope images for the first time. :slight_smile: I’ve been clicking through that thread once or twice and wondered what the lacking images would look like. Most of this stuff is over my head but it’s quite entertaining.

The SiR800DP is a beast---it can handle more current than most of the other FETs I've tried---the difference is much more than the datasheet would suggest. If you try and run 4x XHP70 from a single PSMN3R0 you will find that it quickly desolders itself; with a single SiR800DP it is fine without making any other changes--and that's with a 5V gate drive (much higher than we usually get with 1S setups). So yeah, you can run crazy stuff through an SiR800DP. It seems to even run cooler than the 0R9 NXP FET I have in the same situation.

The SiR800DP does suffer from dV/dt induced turn on when you're switching from 100% quickly to moonlight (that's the little light blip you see). As Tom E. noted, a small pulldown resistor solves that issue.

I use 0603 exclusively in my drivers as I want to utilize the space as much as I can. I also bend pins on the MCU, put the MCU where the spring usually is (for space and easy access to flash the light without full disassemble) and cut of the tabs of the 7135s to make them shorter (custom Eagle library part). One of my drivers where I’ve done this: Mod: My take on the convoy S series with side switch mod.

I did a design with 0402 sized components but they where to annoyingly small for me to work with, so I’m sticking with 0603.

Btw, nice to see you back, if only for a while.

Has anyone built this driver with a second stacked 7135? Adjusted the modes to use the pair of 7135’s for more modes of non-FET power? (more efficiency)

Not physically stacked that I am aware of but with more 7135's. The single 7135 was basically a method to achieve a regulated "Lo" that many complained was either "to the moon Hi" or a "subterranean Lo".

Wight and PilotDog68 both have drivers with more than one 7135

Yep, I’ve done it multiple times. I got tired of stacking though so that’s when I made the DoubleDown driver boards.

I dunno. With 4 or 5 nice well spaced modes, only 1 mode (32%-40%) uses PWM's on the FET typically. The lowest 3 including moon use the single 7135. One full 7135 mode does like 120-170 lumens roughly with a good NW or CW LED, good AR lens, so that's like 10% typically.

4-5 modes are my favorite settings. Adding another 7135 has no advantage that I can see for a 4-5 mode set.

Am I missing it, but is a FET+1 OSHPark driver available anywhere, from anybody in 20 mm size? Anyone have an interest in making one if it's not around?

I really miss this wight FET+1 driver in a 20 mm size...

In most of my lights I just want three modes, and I like the middle mode to be regulated at ~1 or 1.5amps. That’s why I like the extra 7135’s.

You can use the 20mm DoubleDown for that too. If you just populate the top side it’s FET+1 with some other stuff thrown in.


Oh thanks PD68! I just looked at my OSHPark order history - did order these boards back on Nov 7th(silly me ).... I ordered 22's, 20's, and 17's. K, I know I need the 20's for a couple of projects, gotta get organized better..

your memory is getting almost as bad as Dale’s… :stuck_out_tongue:

I can totally relate to Dale. Wait, who's Dale?

You should add a second diode, and put it right next to the second resistor… so that the labels will say “R2D2”.


One of these drivers, loaded with the BLF A6 firmware, acts like it has next mode memory. Anytime I cut power, it moves forward. Does not appears to be related to time spent off.

So, in moon mode, click off for 10 seconds. Turn on, it is in mode 2. Click it off for a few minutes, click on, mode 3.


Suggestions on what to change? I have a stack of these that work. This one I reflashed, and replaced the OTC.

Sounds like the OTC is not discharging or at least that’s what the attiny thinks. Is it the same OTC cap as the other (working) drivers?