Awesome , thanks !
Added couple IR LEDs: new 4715AS-EA (upgraded AS), Luxeon IR 850nm 90deg and 150deg variants, all on 20mm mosX board:
Hows does the efficiency of the 1S LD-A4 driver compare to a common 7135 driver?
LD-A4 doesn't use PWM, so overall light efficiency is higher at lower currents.
On high mode driver efficiency is theoretically the same: Eff=Vled/Vbatt.
Average LD-A4/B4 efficiency (from full to empty battery) is around 85-90% for most LEDs.
Did you ever explain anywhere how it actually works? How do you use a FET to make a linear driver?
Variable linear regulator.
A FET can work as a variable linear regulator.
More expensive, but allows for higher efficiency since it is not using PWM.
That's probably ~100years (almost) old technology, FET works in linear mode (hence the name linear regulator) as variable resistor (from few MegaOhms to few miliOhms), analog electronics+ uC controls FET so that output current remains constant.
In theory it's simple, in practice not so much if you want wide output current range (from mA to 10-20A),low internal resistance,small size etc.
led4power, I so wish I could have Andruil with your driver….
That would be quite difficult to do, ad the LD A4 and B4 does not support e-switches if I remember well.
I will start with driver firmware/hardware upgrade soon, I was too busy with other stuff for quite a bit of time. But since change will not be cosmetic (pretty much complete redesign+e-sw+high power variants), this will take some time.
I got an impression that it wouldn’t be a quick job as it requires porting software to ATTiny1617 or to Pic16 or finding board space for ATTiny85. But nothing terrible either, especially that there’s good change someone would provide porting assistance.
Other than this I don’t think it would be hard. But then - I know very little about how it’s really done, so I may be very wrong.
That’s fantastic news! I am already excited thinking about a new Sofirn C8F with LD4 driver, triple XP-E2 red and side switch. 
I already use PIC16 on LD-x4 and always write my own firmware, so that's not problem, only problem currently is lack of time.
I was referring to how awesome it would be to run Andruil with your driver…and to be able to customize it to fit my needs perfectly.
Open source makes your hardware more valuable.
@led4power: I plan to mod an Astrolux S41 with Quad XP-E2 red (overcurrent up to 2.5A per LED if they sustain it). Do you think the LD4A driver would work in that flashlight. I’m not sure if the power dissipation might be too high for it. If it works, can you give me some recommendations what I should consider in terms of configurations, please? Thank you!
XP-E2? This test shows maximum at only 2A.
At 10Amps total LD-B4 is better option (in combination with mosled 4xp board) because its much larger heat dissipation capability.
It is fair enough that, having designed them from scratch and trying to make a small business out of his unique designs, l4p decided to not share his driver designs and just sell the drivers as is.
Looking at prices of other BLF drivers, I don't think someone can make and sell them for 10€ anyway. And in that price firmware development is included.
Much simpler FET+7135 costs about that, LD-x4 has much more expensive 4-layer PCB and 2x more components which are all very small, 0402 mostly.
I'm already hearing "what about China?", they even can't make BLF A6 work properly, plus LD-x4 is calibrated via precision external volt. reference, and tested before shipping, so I doubt even China can make it for 10€, definitely not in <1000pcs quantity.
I never said it was wrong. And never asked to open source his work (though that would be awesome). I just pointed out that IMO leveraging open source work of the community would make the LDx drivers better.
It did sound like some sort of request to make his work open source and that made me respond to it
I agree that open source developments are very much fun for hardcore modders, who want ultimate control of every single aspect of their flashlight. But for the type of modders that want or need a little bit more work taken out of their hands, led4power makes awesome quality components available.