True dat. A single emitter, wide OP/TIR D4 non-hotrod would be a real Convoy S2+ killer.
A Nichia E21A D4 would be glorious.
I swapped in a Lexel TA 3 channel driver for my D3W1R. With the fet off its regulated around 550 lemons.
Linear FET drivers like that exist. For example, led4power makes some. They’re typically more efficient than a PWM FET driver, and slightly more efficient than a FET+N+1 driver… but less efficient than a boost or buck at most levels. Because instead of burning off extra voltage as heat, a buck driver converts the extra voltage into usable power.
what is so interesting on sst20 led? if we compare it with xpl……my another dilema which one to choose:)thanks
The SST-20 has more throw/lumen than the XP-L HI.
In lights like the D4, more throw is useful since you do not need to lessen battery life pushing + power to see far away.
And you can get the SST-20 in 95+CRI, which is nice.
thank you very much…bluesword…so now we can mix sst20 and floody optic…is it the best combination what do you think?
I agree.
At direct drive the FET isn’t burning off any voltage, you really can’t get any more efficient then that (at the same current level) with a buck boost because now you have an inductor in series with the LED in addition to a FET, (unless you have a bypass FET). I would like a buck boost, but peak power is kind of the selling point of an Emisar D4. My use case doesn’t require longer run time and I’ll take my zebra if I do require it. I’m not going to say that its worthless to develop a buck boost D4, and I would probably buy one, but I wonder what I would have to give up in size, brightness, etc.
The D4 driver is very flat and fits in a very shallow cavity in the D4. A buck/boost driver would certainly add at least 4mm to the length of the D4.
A single emitter D4 would also be longer because of the deeper optic. But there are a few exotic single emitter optics that are very shallow.
Yes, but at virtually every other output level, a buck/boost tends to be more efficient. And there’s no reason a buck driver couldn’t also have a FET for turbo. It could use whichever power channel is most appropriate for each level. The main drawback would be an inability to ramp smoothly all the way to turbo. Instead, it would have a gap in the ramp when it switches from the top of the buck circuit to the FET.
While trying to reassemble my D4 (after flashing Anduril) one of the e-switch solder pads got ripped off the driver 
. Is this repairable or do I need a new driver?
I did this on Lexel TA driver. With advice I hooked up E-switch to pin 2.
I am sure someone in the KNOW can tell you where to hook the E-switch.
Can you tell if its the one to MCU or ground?
Umm… Closest to pin 2 of the Attiny chip.
Looking at the photo of the driver in the 1st post of this thread, It sure looks like the switch goes to pin 2 on the MCU. You might be able to see the trace between the pad and the switch pin.
I can confirm the pad labeled SW+ is connected to pin 2 of the ATTiny85. The other goes to ground, which pin 4 is a convenient point to connect to ground. Or the adjacent pad of the closest resistor R?.
Thanks chadvone and sbslider, I soldered it to pin 2 and all’s good 
good news! 
I’m not an electrical engineer, but I would think eliminating the forward voltage of the FET would provide a significant improvement efficiency. For the D4, I see the number “09NE2LS5” on the FET. From the datasheet I found on that, it looks like it is 0.78V at 30A. This one, like most FETs, shows only minimal improvement in that Vf at lower currents - roughly 0.7V at 4A.
I’ve found the efficiency of the D4 generally fine for my needs though. I wouldn’t view improving further as a high priority.
Eliminating the forward voltage of the FET would definitely improve the efficiency, but the FET is the controlling element for lower light levels also.
A quick web search showed me a FET with 12milli ohm, 50A rating in the package used on the D4. FETs are like voltage controlled resistors, but once they are “on”, they are a fixed resistance. So 0.012V * 30A is 0.36V, and 0.012*4A is 0.048V. Not sure where the measurements above are measuring, but it seems like there is a fixed resistance in series with the FET being measured which is why the voltage does not change linearly with the current. Or, somehow at lower currents the FET is not being fully turned on at the 4A current. If the measurements include PWM and are being done with a digital volt meter, then all bets are off as to the accuracy of the voltage measurement.
Oh, and I am an electrical engineer, but I don’t get to play that role much these days, more of a project lead now. It’s fun to go back and frolic in the math now and then.
The white “grainy” one got really smooth within a week in my pocket. I could experience this again when I started using the short tube. But after 6 or 8 weeks of use, the D4 is just as smooth as my other lights. Just use and carry them.