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

I’ll post my question and the answer from wight here if someone is interested :

… and I don’t use stars any more either. It seems to have become an obsolete carry-over from nanjg days. But I sure could use a convenient pad to solder other stuff to, like an e-switch.

The tiny25/85 efforts have really expanded options, and reduced the need to actually open up the light to make changes.

Another option is to choose a FET with higher on resistance. You will reduce peak current, get rid of turbo-to-moon blink, and save several dimes.

This might not be a great idea. I plead the fifth.

  • This is a Zener+resistor setup placed behind a polarity protection diode. Normally the polarity protection diode might cause our infamous boost problem, but with a 5v zener in place this should not occur. I expect that this should allow for a much smaller decoupling cap for the MCU… but I’ve been wrong before. At this moment I’m not actually certain whether this setup presents a quiescent current problem for single-cell momentary lights.
  • 17mm layout… which is a mess of course.
  • 0603 and SOD-323 sized passives.
  • 2mm via for positive.
  • This passes DRC.
  • Physical component keepout is 0.8mm rather than 1.0mm. Electrical keepout remains at 0.5mm.
  • LED- is smaller than I’d like.
  • GND vias are all placeholders.

BTW, any ideas on how to enable a bleeder to leak power to a lighted tailcap while off, without interfering with OTC drain? Or how to influence the rate of OTC drain?

Also, any thoughts on how to reduce power fluctuations at the MCU when the main FET power circuit is repeatedly going from zero to a zillion amps? It seems to have sort of a splash effect, and the tiny25/45/85 chips aren’t as splash-resistant as the tiny13.

RE: point #2 - that’s what post #300 is really about. Tom E has combated that effect by adding a ton of capacitance (20uH total), but I feel like that’s a bandaid type solution. I’m very interested in comments on what I’ve drawn up and shown in post #300.

RE: point #1 - crap, I felt like I was forgetting something as I worked on this board. Adding a that tailcap-led-setup was on the to-do list. I just looked it up… apparently pilotdog68 has just been putting a 560 ohm resistor across BAT+/BAT- on the driver.

EDIT: also, my thoughts on influencing the rate of OTC drain are still what they were a few days ago in the A17DD-SO8 thread. What I said over there was that it might be better to increase the capacity of the OTC by an order of magnitude or so and then use a bleeder resistor of our choosing. Clearly this PCB is going to get crowded with all that stuff (especially because a good 10uF cap for the application will be 0805 or larger). I also haven’t thought this idea all the way through at all, it may not really make sense once I put it on paper. I suspect that I’d better think some more and look at the datasheet. In the meantime if someone wants to play around with it they are welcome to do so. It would be a straightforward thing to experiment with.

Ohh btw, I pulled the C1 cap off of a SS/Cu X5 (based on this FET+1 design) using a ATTin25, and tested it - best I can tell it's a 12 uF cap. On my DMM, 10 uF caps tests at ~9.6 uF, 22 uF caps also tested a little lower, so the cap off the SS/Cu X5 board tested at 11.5 uF.

Sorry, but I'm not sure I understand enuf to comment on your proposal. But also I would like to make it clear I don't care about 13A's any longer - only interested in 25's and 85's. I consider 13A's obsolete now - all I've been working on over the last few months is 85's (e-switch based) and 25's clicky based. I don't mind the 13A footprint because the bent pin setup for the 85 works well, but I do want an 85 to work reliably in a high powered setup, preferably with the SIR800DP FET. Raising the value of the cap seems to fix the problems - I've had these problems on pretty much every 25 and 85 board I've built (maybe 15-20), seems like. It may be a bandaid, true, but it's the only bandaid that works reliably. I didn't do this on my own - it was recommended by EE's, both here on BLF and at work here. I was just the one trying it, testing it.

Edit: wait... from what I recall, it was recommended the cap be as close to the MCU Vcc pin as possible, and this is what you did here. Also a big cap after the diode could be trouble, but the smaller cap you are using is a good thing for sure. Hhmmm. This may address issues the EE's raised - you might be good goin in this direction, but I dunno much bout these things, but dang - looks pretty good!

One of my other "fixes" that worked was adding a 0.1 uF cap across the MCU pins of grnd to Vcc. I literally have the cap sitting on top of the MCU wired that way, and actually can still clip the MCU and re-program it. This was my typcial "fix" for my e-switch Narsil based 85 FET+1 v009 drivers, and seemed to work, accept for the last one over the weekend -- had to double up the 10 uF cap to get it working.

Thanks for the [unquoted] info Tom E. As for the quoted bit… I’m pretty sure that it’s the wrong analysis. The issue w/ a cap after the diode in previous FET/DD setups was that there was enough inductance in the circuit to get an unwanted boost circuit with the diode followed by a cap. I think that a smaller cap would actually tend to make this worse if everything else was left the same. In this case everything else is not left the same, I’ve added the Zener/resistor combo to hopefully get rid of the extra voltage from the [unwanted] boost circuit. The boost circuit is certainly still there, the extra volts are just getting dumped by the Zener. At least that’s the plan.

Using big caps to get rid of unwanted voltage spikes isn’t inherently bad AFAIK, but in our case it’s not something that we necessarily have a lot of space for. Replacing 1 extra 0805 cap with 2 extra 0603/SOD-123 sized components isn’t necessarily the greatest achievement in the world (heh), it’s just something to chew on. Without putting an oscilloscope on the circuit and checking things, I suspect that if this circuit works as intended it may also clamp the voltage better and tolerate bigger spikes. And of course it adds pads for a Zener.

Yep, I'm clueless with this stuff - I kind of/sort of understand you -- just forget bout my attempt analysis .

In one of my lights with this driver the voltage indicator only works when the light is hot. Probably a bad solder connection. Since I can’t find a circuit diagram - could someone point me to the most suspect components?
Thanks
Michael

Meh, I still listen anyway. :wink:

I’d say to check R1/R2 and all the pins Pin 7 on the MCU.

Thanks!
Finally I resoldered all pins of all components. Everything ok now, got even 2 more amps. 14 amps in total now with my triple Convoy S2+. Of course I could use this light as a soldering iron after 30 seconds …
Great driver!

That’s great. 14 amps is impressive. What emitters are you using?

3x XP-L HI U6. With full LG HE4 battery. I use this battery in this light only for tests, it gets too hot. Protected Keeppower 2900 for daily use give a max of 9 amps, 18350 efest purple even 10 amps. Still plenty …

BTW, I’ve heard a few times not to use a zener on an e-switch light since it drains power in standby mode. Would the same apply to a clicky with lighted tail, or is it pretty much irrelevant since the standby power should mostly be going through a bleeder instead of the rest of the circuit?

I’d think you’ll have a different problem: How will you reconcile the voltage of the series cells to the Vf of the tailcap lights? Are you using 6v tailcap LEDs or putting two (or more) in series to get the forward voltage up?

Here is the latest iteration on the A17DD-L. This version uses mostly 0603 sized passives and has a lot of stuff…

  • The new, proposed, Zener for 1s setup.
  • 0805 OTC + 0603 pulldown
  • 0603 bleeder for PD’s tailcap LEDs
  • Pin 3 pad as requested by Tom E
  • Maintains 1mm physical keepout for components and 0.5mm non-GND keepout.
  • 2mm BAT+ passthrough

Of course it’s still looking a little rough, but DRC seems to be OK. (Yes, I’m aware that the 7135 needs to be attached to LED-)

For a 1s e-switch application the intention is to use a zener with a higher breakdown voltage than battery voltage. (5v) This should prevent the problem you are thinking of for an e-switch. For multicell applications an e-switch with a zener is still a mistake!

The tail LEDs are a huge drain,they don’t need much help to flatten your battery… But yes, double trouble if a person did both a zener e-switch and a tail LED setup.

For multi-cell clicky applications with a zener and tail LEDs… Yes, the Zener will play a roll. I’m not certain, but I believe that the Zener’s roll will be small in comparison to the drain from the tail LEDs.

Just put them in series as necessary with an appropriate current limiting resistor.

1. Well, it depends on your definition of “huge” and how bright you like your tail led’s. They can be taken down as low as 0.1ma and still be useful with dark-adjusted eyes. I have seen some e-switch lights have much higher vampire drain.
2. Tail led’s are normally used on clicky lights, not e-switches, but even so I’m not sure on this. I would think the tail led’s could just use the leakage from the Zener, and not have to bleed off any more current than was already leaking.

Finally, BLF is back online. Yay!

@wight, very cool to have you back! Looks like a nice board, although I don’t understand why you did this and that, but that’s simply because I don’t know much about electronics.

I like that you kept the OTC in 0805 size, so we could go to a higher value OTC, if needed, without loosing X7R,10%, 25 VDC ratings, right?

(edit: that’s what you mentioned in comment #303)

With the recent drivers I thought about stacking four 0.22µF C0G rated caps as an OTC, you think this might work (/ makes sense)?

(edit: that’s stupid, hard to find and way too expensive in 0805 size.)

The additional zener is not meant for a 2s setup. Of course that’s what most of us are thinking when reading “zener”… Is it some kind of what they call flyback-diode?

What’s the purpose of a OTC pull-down resistor?

Sorry for asking so many (dumb?) questions…

@PD, I think with your new smart (MCU controlled) tailcap, we could reach power consumptions an order of magnitude lower than that, at least, if everything optimized for that.

For the record I think TK measured the Attiny by itself taking more than 0.1ma, but we’ll see. Those boards were shipped to me yesterday.