Noctigon KR1 and KR4 driver upgrading project

Many know by now that Noctigon/Emisar flashlights are available with boost driver if led configuration allows it.

Boost driver definitely brings many advantages, but it also has disadvantages such as high lowest mode. I wanted to alleviate this.

Luckily here in BLF we have people with many kind of skills and I have made friends with one particular individual that has interest in driver designing. He is of course our friendly neighborhood driver guru: TheFreeman.

He’s been refining his HDR driver-series, that combine low moonlight with good output and great efficiency.

He was willing to help me build one of his boost drivers, particularily BST21, that fits KR1/4 lights and has switch ring incorporated.

That’s it for now. To be continued…

First I ordered boards. I ordered them from Aisler this time. Next I ordered components from Mouser. Component shortage made things more difficult than they needed to be.

I searched many alternative parts and in the end TheFreeman sent me few low resistance mosfets from his personal stash with Attiny 1616 programmer.

When I had everything at hand it was time for assembly. I first build 6V 6A version for KR1. And here it is, straight from the hotplate:

To be continued…

Next phase was flashing the MCU. TheFreeman had modified the Anduril 2 code I think previously made for HDR linear driver.

I used AVRDudess and programmer TheFreeman also provided. I could have made one by myself, but this way it was easier.

First version of the firmware had some bugs, that were quickly smoothed out.

Next I did some testing.

I soldered wires to the ground ring and spring pad. I also added switch for ease of testing the driver and of course the led wires.

Notice that the driver has additional 5060 P-Fet capability on the backside for even better efficiency and pads for aux and switch lights. I plan to install that P-Fet next.

Bonus shot

To be continued…

I did some quick efficiency measurements.

Turbo output 6,15V; 5,9A
Turbo input 4V; 10,0A

Efficiency 90,8% without that bigger 5060 P-Fet.

Very good result.

Lower modes have even higher efficiency.

To be continued…

I did final tweaks to the driver. Added 5060 P-Fet, spring and bypass for it. I also changed R1 value to 180 kOhm for 6.3-6.4A output.

Next I need to disassemble KR1 and reflow XHP70.3 HI.

To be continued…

I dismantled KR1, added switch spring to the new driver. Then I decided to take some comparison photos of drivers.

And all together

Keen eyed viewers might have noticed that Noctigon/Emisar driver uses 50mOhm sense resistor. So it causes ~0.1V voltage loss in sensing stage. My earlier boost driver from Intl.Outdoor had 20mOhm one.
To be continued…

Next I reflowed XHP70.3 HI D2 M2 90cri on 20mm 7070 board. Then I added thermal paste and dropped it in flashlight head.

Next I mounted the driver and soldered the wires.

I assembled the head. I used Convoy M21B green AR coated lens for tint improvement.

Light is ready for use. I also added bypass to tail spring.

Next I’ll do some beamshots and Opple measurements.
To be continued…

Very nice! I hope to build one for my FW1A when components are available. Is the height of the inductor 3mm?


It can take 6*6mm and 7*7mm inductors.

Here I took some Opple readings.
First stepped mode stock step 4

Then turbo

This led has very neutral tint for whole output range. DUV 0.0029. Beam is very pure white. It seems to sustain top of the ramp easily. If checked from XHP70.3 datasheet it corresponds to about 1000 lumens after reflector and lens losses. Not bad for 90cri led in small flashlight(led bin: 2D M2 90cri). Turbo output corresponds to little over 4000 lumens after losses.
Here’s still one photo of the lowest mode.

Next I planned to took some beamshots and maybe compare moonlight modes of different flashlights.

To be continued…

Quick moonlight comparison between this KR1 and Convoy M21B. Both in lowest mode and both using a boost driver of similar max output. Both also have same led.

Can you guess which is which?

Some beamshots
2m distance



Some piping in darkish enviroment ~20m away.
Control photo


That’s it for now. I’m happy with this build. Only con of this light is the capacity of 18650. This driver will allow me to use every drop of it.

I suggest everyone to read TheFreeman’s driver thread. He’s closing the point of making these public. Still some UI things to solve. Anyone with skills in that regard is welcome to offer some help for him.

I will continue in near future with KR4 and 12V build.

Thanks for reading.

Outstanding design and execution!

I applaud your impressive skills.

Now if only Hank would adopt your modifications into the regular production line...

I'd love to have one exactly like it.

Enjoy your well earned success with this gem!

Thanks :slight_smile:

I am eager to see the final release. I’d love to put one in my Jaxman X2

That seems to be good looking flashlight, but not available anymore.

It would be good if Hank can make a KR series flashlight with 21700 battery!


Very nice to see the first of my HDR boost drivers assembled and used by someone other than me :smiley: , Haukkeli was very motivated to go through the whole process and he provided valuable feedback, he’s a great beta tester :+1: .

In this configuration (6.4A6V) the lowest mode is ~75uA, for comparison the lowest output (li-ion) Zebralight is the SC700D at 50uA (6V), with some tweaks it can go lower but I think this is low enough.

That light looks pretty good, what driver size is that though ? it looks very small for a 26650 light.