Numbers used just to point out the total voltage doesn't matter, only the difference. Could be 50v, or 200v. As long as that spread between supply voltage and forward voltage is in a range the chip can deal with, it has no way of seeing the full supply voltage.
This question was posed to me by a few people last summer when I was playing with a similar notion: What about the excess voltage when the driver is low? The 7135’s in the drive circuit will see a much higher voltage then, right? I know what my answer was(don’t know if it was the right one), what’s yours?
Okay, well you’re using the chip in a matter it’s not explicitly rated for. As to whether it’s acceptable or not, I don’t know. It seems to me when the switch is off you have the potential for a voltage imbalance between the VDD and Out pins that the part may or may not be capable of dealing with.
'When the driver is low' meaning when it's 'off' by removing signal from the Vdd, or when it's in low mode via the MCU?
To make it even more complicated, I have a single mode 105C with the full 8.4v on the Vdd, and so far it's surviving just fine. It would not be fine with just a jumper from +Vin to Vdd using some of the extreme voltage examples I used earlier... :)
update: Made a 2x18650 body out of old 501b parts and copper tubing, the single mode 105c/MTG2 is still alive, somehow. Tested first with some sorta weak cells, did fine, so threw in two Panasonic 2900s... still alive. Makes a frightening amount of heat, don't know how much of it is coming from the poor little driver and how much from the LED, but it hasn't croaked yet.
A while back I ran a driver running two XM-Ls in series off a 8.4 volt power supply for a week straight and it survived.
So, this thing seems to work... I just picked parts off dead video cards & modems, then chose some from the resulting pile more or less at random.
100 ohm resistor in place of the diode, some unknown value zener on top of the capacitor on the other side.
Freshly charged Panasonic 2900mAh (NCR18650... C?) in series. This is a Frankendriver made of leftovers, I don't even know if these are 350 or 380mA chips, but there are 8 of them. MCU is from one of those 2-group drivers that never worked right, but the MCUs all seemed fine on other boards. Does a pretty wicked SQUEEEEEEEEEEEEEE on medium, but these MCUs did that even on their original boards, too.
low .08A
med .66A
high 1.65A
All modes work, group switching works, driver makes no finger-detectable heat on any mode.
8x7135 driver still going strong, I've run it thru about 4-5 discharge/charge cycles. The squealing noted above went away after it was installed in the light, on the bench test the + wire was just wedged between the coils of the spring, I think it was resonating and acting as a tiny speaker or something. It's quiet in actual use.
I'd love an explanation for the weird current readings though. I've connected the driver to a XML and powered by a single cell the output current is ~3A as it should be, but back on the MTG2 is does 1.6A again, so the driver isn't broken.
Would either of these drivers work for the mt-g2?
http://intl-outdoor.com/1a-2755v-buckboost-circuit-board-p-674.html
low current, but if it works…
http://intl-outdoor.com/boostbuck-318v-triple-xml-circuit-board-p-542.html
not quite designed for 6V led, but would it work or go wonky?
The first one is 1A. It’s a nice driver. I have one driving a Nichia in a 14500 clicky. You’d be seriously under driving your MT-G2 though. It kinda defeats the purpose of having an MT-G2.
The second one would be great with two cells and 5A. The only thing you have to look at is the drivers hight at 17mm, with a 24mm contact board. Your light would need a pretty big pill to accommodate it.
I’m going to try this one in a T10B.
The first one probably not. Most of those are meant to give moderate boost levels as the input V drops, but aren't able to nearly double the input voltage. Second one has been confirmed to work but it seems to have issues running from a single cell, something like it constantly trips the low voltage warning function - in boost mode with multiple cells and a bunch of series wired LEDs it might work OK, don't know if that's been tested or not though. On multiple cells it does work with the MTG2 (so buck mode = ok, boost mode = no).
edit: see what happens when you type too slow? xD
Lookee what I got today: boost/buck 3-18v right, and 9A(!) 5.5-12v left :evil:
This driver will work fine. As mentioned it will not run on one cell. It also has a pause between mode changes which may or may not annoy you.
Links please comfychair.
Large drivers. What are you planning on putting them in? I’d like to find a host that has a pill large enough to accommodate.
Don't know for sure yet, one will probably go in a 3D Mag, the 'pill' will have to be made from scratch anyway so driver size is ok as long as it fits in the tube.
The KD super output p7 driver would make a decent unit for 2x liion and has been cloned so many times I don’t know where it came from originally. That’s where I first saw it. 19mm Dia, ~2.8A on high, 3-modes, no blinkies. Sometimes sold with a post for B+, sometimes with a separate contact board. I used it with 5 nimhs in a flash light or 6 nimhs with remote packs for bike lights. It’s not the most efficient driver but it should work with up to 7 nimhs easily for an mtg2.
you should get about 800 lumens, a little less then an xm-l, so i agree not highly driven, but still no slouch
i can’t really find a single cell driver that can put out 2A for an mt-g2 (not that i am surprised to not find one)
Man, the 3-18v driver won't even run a single XML from 4.2v (even tried a 4P pack, so it's not voltage sag). Gives the two-blink low voltage warning.