17mm & 20/26/27mm single-sided DD/FET driver release: A17DD-SO8 / A20DD-SO8 / etc

I definitely don’t see a problem with doing that.

While we’re on the topic… another option might be the “1500 Watt 12 Interval Heat Gun” from HF, Item#69343. It’s (constant) ‘sale’ price is $29.99, couple that with the standard 25%-off-on-a-single-item coupon and you’ve got $22.49. Features seem similar to the Wagner tool, but who knows.

Have you tested this with the Zener? Pull the standard diode and replace it with the 200ohm as usual, then do the math on the resistors for maintaining low voltage protection, right?

Realized I have an Olight M3X en-route, with an XM-L emitter and a 700 lumen rating. I also have an MT-G2 sitting around waiting for a home. 2 of em actually….

I have not tested this with a Zener. I have only tested 1s setups. You’re correct though, replace D1 with a 200ohm resistor and then do the LVP math and you should be golden.

Best place to solder a dedicated ground would be across the 3 ground pins of the FET since that’s where most if the juice flows.

wight, would be great to get your thoughts on two items.

First is regarding using your 26mm board to experiment with adding a thermistor circuit? These big multi-emitter lights need thermal protection more than pretty much every other light out three. ToyKeeper is building a program for garrybunk that should be able to use it to throttle power down when the thermistor gets too hot.


I thinking such a circuit should look just like a voltage divider you taught me about except for the following:

  • R2 will be a thermistor instead of a resistor.
  • There should be a capacitor parallel to thermistor. Probably can just be stacked on top of the thermistor if space is an issue.

It seems the power for the circuit should branch off the Vcc line. It would be good if the ground for the thermistor was directly linked to the ground ring for good thermal connection. I don't know what MCU pin pad to recommend. I would think any available one except PB3. I also don't know what thermistor or capacitor size to use.

Your 26mm board has some spare space. That and the fact that it will tend to be used in big high powered lights makes it seem like a great candidate. We will be get some insight with garrybunk's light, but that driver has a much different MCU Vcc circuit.


Secondly, what are your thoughts of paralleling a capacitor on R2 in a normal voltage divider circuit. I think it would smooth out the signal and might resolve the premature triggers that I think I may have been getting on my Crelant 7G10 build. I will be exploring this after I finish garrybunk's build.

EDIT: Clarified some wording.

ImA4Wheelr, you are correct that the circuit for using a thermistor should look like a voltage divider (because it is a voltage divider). I’m not certain which position will work best for us, I’ve seen diagrams with the thermistor in either position.

I don’t see what the point of the capacitor is (for either divider). I don’t expect for it to provide any smoothing.

Have you considered skipping the thermistor business and going with an all-in-one temp sensor? Microa has used LM45, RMM has been experimenting with MCP9700 (Post#625). MCP9700 sounds like a good one to me.

I did not include pads specifically for a temp sensing IC, but I did include pads. You may lay an MCP9700 across the pad attached to Pin3 and pickup GND right next to it. You’ll need an air wire to pickup Vcc but that’s it.

In response to your edit… the MCU Vcc circuit on both boards (when used for 2s+) is very similar AFAIK: it’s just a Zener and a limiting resistor.

Excellent info. Thanks wight. You're right, there is plenty of space on your 26mm to easily air wire in such a circuit. It wouldn't even have to be the air with the available open flat surface to run any wires needed. That will work just fine.

I see what you mean about the circuits actually being similar on the Vcc feed now.

Regarding the parallel caps. If they don't smooth, why do you think garrybunk's driver has them?

EDIT: I have no thoughts on the alternatives to thermistor. I don't have an working knowledge in this area.

Hope you don't mind this discussion here. Do you have a different thread you would prefer it in? I can move my posts there if you do. Here is a circuit diagram of some of garrybunk's driver:

I wouldn’t want to air-wire 0805 sized thermistors and resistors all the time, so if that turns out to be the thing to do I’d update the PCB. I doubt that it will be the thing to do though. Using a thermistor in a voltage divider is dependent on a known Vcc, so 1s use is impractical and 2s+ use requires the use of a known Zener value. The monolithic “sensor” IC is a much better route IMO.

As far as those caps go… good question. I don’t know the answer. I sometimes speculate that a fair number of the drivers we see have unnecessary components. I think that designers of lesser skill get a lot of “building block” circuits from datasheets and forums without a real understanding of what they do. They cobble these things together and get a functioning product and leave it at that. … that said, I could certainly be wrong in this case. I don’t have a very complete grasp of a lot of these concepts myself.

If your early LVP issues were happening in medium mode we could say that PWM might be causing something that needed to be smoothed. But early LVP with no PWM (HIGH/TURBO/whatever) on a linear light? I forgot that we were talking about a buck regulated light. Maybe we do need to smooth the divider. EDIT: I mean for your problem light, not over here.

This discussion is fine here; I don’t know of anywhere better to have it. I guess you posted the diagram to show how the thermistor and smoothing cap are wired?

I can (now) imagine that the smoothing cap could have an effect on low voltage stepdown and low voltage shutdown when in modes other than 255/255 on a linear or DD driver with PWM. I’m not aware of problems with it now though, so we’ll have to see. For buck drivers I think it makes more sense because of the spiky way current is drawn from the batteries.

Thanks again wight. Great info and thoughts as always. I think I understand what you're saying about buck having different issues regarding voltage dividing. I can see it will get real messy in here if we talk about your driver and buck. Sounds like we should discuss buck voltage dividing in garrybunk's mod thread (since that will be actively pursued soon).

I really like the idea of getting true thermal management in the DD environment and your 26mm driver seems like the best candidate for experimenting with it. When I get a chance do that, I will touch base with RMM so I don't reinvent the wheel.

More specifically, thinking about building a program… But I’m probably going to need actual hardware to test it on, or it’s very unlikely to work. Blind coding almost never goes well.

Regardless, I still doubt whether thermal protection is even relevant on a bike headlight. If the bike is moving, it’s unlikely to get hot enough to matter. I mean, unless it’s built really weird, like using a steel or plastic host… but IIRC this one is aluminum with heat fins and the intended use is to run it on medium or high (not maximum) during regular use. So, maybe 2.6 amps spread between two emitters. Doesn’t seem like it’s going to be an issue.

Would it be possible to fix a starting voltage with a Zener and use the thermistor to alter that in comparison to Vref? Then the cold voltage is constant for the entire battery cycle and goes down only with heat.

Sure, I think so. At that point you’ve got:

  • Zener
  • Limiting resistor
  • Thermistor
  • Other resistor for divider

Update on my Quad. I used a PH-08 from FastTech to put a quad in, with a solid copper pill and BLF17DD Ver 3.0. But I was having some flickering issues. So I pulled the V3 and put the A17DD-S08 with ToyKeepers newest Ramping firmware, bits commented out that didn’t apply to this light. Still flickered. So I pulled the tail cap apart and Voila! Dirty aluminum retaining ring and cheap pcb with dirty copper trace!

So, I cut a circle of copper from a bit of copper sheet Scott sent to me (Thanks again Scott! :wink: ) and soldered a spring on it, bypassed the spring with a 22ga wire. Then filed down the aluminum retaining ring so it’s flat and new metal.

This A17DD-S08 driver allows the freshly charged Efest 35A to run 15.2A through the Quad XP-L V6 2C emitters! Folks, this is a pretty small light, making over 3000 OTF lumens! :bigsmile:

I Truly Do Love It When A Plan Comes Together!!!

(it’s a given, I do NOT have cold hands…)

Um, the bad news is I only got about 7 seconds out of it on the lightbox at 4147 lumens, 3976 when it died, poof, just went out. So now I get to go back in and see just what happened. lol

Aww crap. :slight_smile:

Yeah, but dang it’s thrilling for a light this size to pass 4000 lumens! :bigsmile:

Light works fine, just won’t sustain the top end.

Just ran it 18 seconds at max level handheld, get’s REALLY hot, really quick! Still working, but shut it down.

It shut down when on the lightbox, headstanding, with all the heat rising into the copper right at the driver. :smiley: