Buck is the word your looking for.
A Buck driver can supply the required voltage of your emitter as long as there is sufficient overhead.
Huh, ok I actually have one of these ebay ones in hand, 131135364874
so your saying that will light the mk-r?
just to clear things up, how would that driver light my 3.5volt xm-l2 and a 12v mk-r?
Yes it will work with your MK-R.
on the page it say its suitable for a single xm-l2?
I corrected my previous post because I haven’t used that exact driver, there are many drivers like it that will blow a single XM-L2.
Ah ok I see.
I wonder why dont these drivers list the output voltage? Seems like that would be useful.
Obviously something major im missing. How does my current driver light my xm but not the mk-r,
but the ebay driver would light both?
Your current driver is designed for an emitter with a forward voltage requirement of around 3.2 volts, if you input a voltage higher than what the board is designed for it will blow the driver, emitter or both.
A buck driver can supply an emitter with whatever voltage is needed as long as the input voltage is sufficently higher than the output voltage.
Would the mk-r be dim if it was underpowered? or not turn on at all?
my xm-l2 will dim but not shut off.
the mk-r will not do anything, im wondering if its a bad emitter?
I just received it in the mail today.
What light are you putting the MK-R into?
Does it accept all 4 of your 26650’s in serial (front to back) connection?
Remember you must supply adequate overhead voltage to power a 12 volt emitter.
These are important questions which must be answered.
Vwarner, you’ve jumped in at the deep end here with no flotation aid. Many residents here on the forum have problems with these topics despite having experience. I don’t want to discourage you, but it seemed worthwhile to point out that if you’re having trouble swimming… that’s why!
vwarner, this may help you understand what different types of drivers are available, & what they can & can’t do.
Got my 5pcs 6V version today. Gonna put them into my 3T6 soon.
Guys, a question just occured to me. Theoretically, would an SK68 boost driver work to push single cell ~3.7V to the required ~5.8V MK-R voltage?
LOL, I actually tried this using a 3-mode sk68 and it actually lighted up! Go SK68! But no it won’t work as flashlight, it pushes out very low amp though. 
More like a low low.
Still I’m impressed sk68 can push voltage to light up MK-R.
Back to 3T6.
Sometimes boost drivers are artificially limited to ~5v.
PAM2805 is used in some “decent brand” AA/AAA boost drivers, such as DQG and Fenix. It features ~5.12v OVP as seen on page 5 of the datasheet: http://www.diodes.com/datasheets/PAM2803.pdf
Not all boost drivers necessarily have this limit. One driver to look at is DX SKU 7880. I suspect that 7880 may have no over voltage protection. http://www.dx.com/p/3w-5w-20-mode-regulated-circuit-board-for-flashlights-7880
Most or all boost drivers which are intended for use with 1xAA/AAA will also run the MCU from the boost output. If you boost much higher than 5.5v the MCU may be damaged.
TN30 suffering some vF Issues but is running!
Heh, does that lower left emitter have visibly dimmer dies? What configuration have you used?
One die does appear to have two areas of less brilliance on my screen too. Top and bottom of that left lower die.
They’re wired in 3p. What your seeing is actually the case with all 3, the die’s are noticeably arranged in matched [offset] pairs of slightly cooler / slightly more NW.
12v NW emitters on sinkPAD’s. The light runs great in modes 1-4, the vF issue rears its ugly head starting in mode 5 which is only about 5% brighter than 4 (and 6 is no brighter than 5 at all).
My plan is to go over the driver with all 24v cap’s and diodes then see how it runs on 4s, maybe I need to switch to 4s 16650 so the linear driver can handle it (from what I can figured the TN30 must not be buck, it’s 3s cells and 3s XM’s). My other option is to hack the driver replacing the driver portion with a FET driver and just retaining the factory control.
Edit to add: IRL I can not perceive a brightness difference between die’s, but again they are all the same in that half the die’s are slightly cooler than the other 2.
Gotcha. Can you post clear driver pictures? I have not seen the TN30 driver.
Alex, I dont currently have any pic’s but it’s obviously gonna be coming back apart soon, I’ll take some pic’s and post them here then.