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

Is your firmware set up for that 223 at R1 or is it still thinking there’s a 1912 there? That might well be why.

That’s not why. In that case the stepdown would happen at too low a voltage, not too high. EDIT: I was wrong about that. Sorry DBCstm! :frowning:

That said, nlite is a hex from DrJones. It’s precompiled for the reverse polarity protection diode to be in series with the 19.1k/4.7k divider. The 22k/4.7k combo is specifically intended to mitigate the effect of removing the diode from in front of the voltage divider. That’s what this driver does.

Reducing the value of R1 is still the way to go, but if kyfishguy’s numbers are accurate it appears that DrJones setup the stepdown to happen at a much higher voltage than STAR for example.

That is the voltage under load?

(Because if so, this really doesn’t add up to me. DrJones’s standard nlite firmware should be looking for something like approximately 0.55v to start stepping down. The 22k / 4.7k combo should not give such a low voltage until around 3.1v at the battery.)

Yes,

That is the voltage at the battery under load. I'm thinking I'll just start over with new components and a different MCU and see what happens.

I made a mistake in my post above. Now edited w/ strike through and some follow up text.

If you are unable to flash the MCU you should just drop R1 until you get the cutoff you want. I’d try 19.1k based on your measurements so far. If your measurements are not accurate then my suggestion will also not be accurate.

As these guys have noted, you have another problem if you have the R1: 22K and R2: 4.7K resistors in there and it is stepping down at only 3.47v. For a sanity check, it is good to measure what the MCU pin is seeing, as that will rule out all variables except for the MCU itself. As wight noted, it shouldn't start stepping down until around 0.55v on pin 7.

The 22K R1 instead of the 19.1K was to compensate for the different driver layout so that the standard firmware ADC values could still be used.

Ok, I tried the 19.1k resistor and it runs fine. I ran the voltage down to 3.28 which amounted to a couple minutes run time. I had to stop there because the pill was outside of the host and getting very hot. I'll do some further testing tomorrow to see how low the voltage will go before stepdown. It has become a certainty that I've got to gear up to flash firmware if I'm going to continue playing with this stuff.

Thanks guys,

Brian

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.

  1. 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.
  2. Determine target R1 value. Change the input voltage to the desired stepdown voltage. Delete R1 and recalculate.
  3. 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.
  4. Choose nearby standard resistor values. http://ecee.colorado.edu/~mcclurel/resistorsandcaps.pdf
  5. 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. :wink: