LD-2 : 6Amps pwm-less linear driver - info and FAQ thread

That's pretty rare and potentially dangerous, but it seems battery protection circuit still works ok.

That sounds like low voltage warning.Check battery voltage.

Are you saying that is the battery protection? Is it checking for low voltage? Or current?

This is happening with several of my (different) batteries, including the Eagletac (which is protected) and several Efest batteries. Some of these havenā€™t been used in awhile so Iā€™m charging them up now and will try them again.

Make sure you file or sand off the pcb tabs where it was connected to the wafer. I read of one member who was having trouble with the led wires shorting to a retainer ring and this would be likely to happen if the driver was in cocked because of the tabs since even with the relatively thick retainer of the X6 there is still gnd ring showing all around the inside of the retainer.

Finally I did a proper torture test of LD-2 with external MOSFET.

Since LD-1 beginning some members wanted to use this tiny driver(designed for small/med size high power lights) for driving big setups,from XM-L2 or XPL triples,and these days triple XHP50s or 70s,or MTG2s isn't unusual.So we're talking about potentially hundreds of watts of input/output power,and in extreme cases, 10+Watts of power dissipated in driver,and that's a lot of heat for common "float in the air" drivers; this is amount of heat generated by XM-L2 at 3+A!

"Expander boards" (under LD-1 info thread) were potential solution;idea was to put MOSFET(main source of heat in linear driver) and other necessary components on separate PCB with good thermal path to flashlight body,so that heat from mosfet could be dissipated more easily.In reality "expander boards" did offer higher heat dissipation,but they were too complicated to use/connect,and since bottom side was connected to mosfet's drain,additional insulating layer between board and flashlight was necessary,overall just too complicated.

After LD-2 announcement,again similar questions about high power setups appeared.

Only choice was again some soft of "external" mosfet mounting,but this time for LD-2 only mosfet needs to be on external PCB,which simplifies things a lot. I didn't like FR-4 vith vias solution on expander boards;they don't have great conductivity, and as I mentioned they must be further insulated from flashlight with kapton/mica sheet+themal grease/paste.

Another solution is custom designed MCPCB(metal core pcb),just like for leds,but I figured out,I can use existing XM-L MCPCBs with a little modification (remove copper trace under Gate pin):

Only three wires are needed(two thick wires and one thin wire for gate) for complete connection,and MCPCB bottom side is already electrically insulated so this pcb can be mounted/glued directly to heatsink/flashlight body,just like typical led star mounting.

I used XP-G2 triple (parallel) for my torture test(s),mosfet board was glued with Arctic Alumina adhesive on test heatsink. LD-2 is in old convoy C8 pill for testing purpose. Thermal probe+UT-71C is used for mosfet case temperature monitoring.

Wiring is simple: mosfet's drain(red wire) is connected to leds cathode(-), mosfet source(black wire) is connected to mosfet source on LD-2 board,mosfet gate(thin black wire) is also connected to mosfet gate on LD-2 board,driver GND remains connected to Battery GND,leds anode are connected directly to Batt + via thick wire,driver Vcc-spring pad is connected via thin wire to Batt +.

First test: XP-G2 x3,1xTF32650,1s setup,6A high

Since dissipation on high is only~1W no problems there,even stock driver without cooling can handle that.

Second test: XHP70,2xTF32650,2s setup,6A high

Voltage drop over mosfet: 1.25V

Power dissipated in Mosfet: ~7.5W

Mosfet case temperature: ~90C

Heatsink temperature: ~30C

Calculated thermal resistance mosfet-heatsink: ~8C/W

~8C/W was higher than expected,that means mcpcb has around 6.5C/W thermal resistance,which is little bit higher than expected(but those are cheap Chinese mcpcbs,so no surprise there).

Max. allowed mosfet temperature according to datasheet is 175C,so 7.5Watts is no problem.

Third test:XP-G2 x3,2x18650,2s setup,6A high

In third test parallel xp-g2 x3 is driven from two partially discharged LG D1 in series(yes,1s leds to 2s cells),this way I could easily generate much more heat in mosfet,since voltage drop is very high (~2.5V).

Voltage drop over mosfet: 2.5V

Power dissipated in Mosfet: ~15W

Mosfet case temperature: ~135C

Heatsink temperature: ~30C

Calculated thermal resistance mosfet-heatsink: ~7C/W

Similar result like in 2nd test,mosfet was preety hot at 15Watts of dissipation,and this was with heatsink at 30C.

In flashlight max. case temperature would be ~60C,so 15Watts would cause ~165C mosfet temperature,I wouldn't go any more that that,so conclusion is that maximum allowed power dissipation with mosfet mounted on cree mcpcb is ~15W. This should cover 95% of builds.

I expect results to be better with branded mcpcbs,like Berquist,because they use thinner dielectric with a little bit higher thermal conductivity:

http://www.digikey.com/product-search/en?FV=fff40008,fff80475,fffc00d3&chp=0

Also tested 20mm version of mcpcb,and results are identical,as expected.

Last test was with mosfet mounted on noctigon;test was identical to 3rd one,except cells were two fresh TF32650:

Voltage drop over mosfet: 4.2V

Power dissipated in Mosfet: ~25W

Mosfet case temperature: ~65C

Heatsink temperature: ~30C

Calculated thermal resistance mosfet-heatsink: ~1.4C/W

Since noctigon is direct thermal path,resistance of mcpcb is really negligible,and thermal resistance is much lower,only 1.4C/W which is basically datasheet number for tested mosfet thermal resistance. Even at 25Watts of dissipation mosfet is only ~35C warmer than heatsink,so theoretically it could take much more.

But in this case noctigon's lack of dielectric layer is disadvantage,because mosfet drain is connected to whole noctigon body,and must be insulated from flashlight.This might be useful for very high power setups,but for most of the builds common al mcpcb will be good enough.

I'll post schematic later.

Good job :slight_smile:

Using a mcpcb as the heatsink/thermal path to the flashlight for the FET is a very good idea.

I look forward to see future mods incorporate this, it really change what is possible with your linear driver :slight_smile:

Upadated/removed OPA172IDCKR from DIY parts list under "3s and 4s Li-ion cell operation" ,since it isn't pin compatible with MCP6H01 (kinda weird,sot23 package and sc-70 pacakge have different pinouts for OPA172).


I am going to order a couple of LD2 ā€™s soon so I was wondering if any of their components are worth exchanging for the originals on the LD1,and if they are available as extras.I am particularily thinking of the thermal stepdown thyristors.Slim chance,but I thought Iā€™d ask :wink:

No,LD-1 doesn't have hardware or input for ntc resistor.

Thanks for the reply. i will be ordering in the week.

Just read your test of post 121 with interest, it looks like a thorough job and gives a good insight in the possibilities of this FET/friver ! :-)

Hi

Do I understand correctly, that both of these resistors (marked with red arrows in picture) should be 750kOhm for 2S operation?

I plan to order some soon & i wonder if anyone have any information on how hard we can run them in the X6? I want to use it for my triple instead of the DD FET driver, with as much amp the driver can take i guess it is the 12A option right? Or is there a 10-11A option, i donā€™t know if the X6 XP-L triple even gets to as much as 12A but maybe the 12A really mean in that case, direct drive but with regulated modes?

If i would stuff the driver compartment with as much silicon cubes as would fit would that be enough? I donā€™t want to use the termistor on the mcpcb because i want it to run as hot as it can, and leave the drivers internal temp protection be enough to save the driver from overheating but not more.

Yes, two resistors of the same value but different values for each voltage level.

I think 12A with triple xp-l and DD driver was reported by some members,and since LD-2 has similar parasitic resistance, 12A sounds fine if you really want max. lumen.

Nice :slight_smile: Thanks

I have the driver set up for 6V with moon parts installed and activated in a heavily modified 502B (extra length for 2x 18650 and 10 copper fins). The driver and ntc are fully potted and ground is bridged to the host pill(also copper)with copper wire and solder. All 4 modes work(moon is just a lower low since I didnā€™t change the moon R) but switching is a bit inconsistent, sometimes more than one half press and has to be brief. After the light heats up in high mode half press no longer changes modes. It stays in high until I turn it off and let it cool, then it functions as before. It does not go into overheat shut down or even ntc step down and this occurs before the fins get uncomfortably warm. Itā€™s not a floating P60 design anymore, the new copper pill screws into threads cut into the copper fins. Is this an issue with an off-time capacitor that has been stressed?

That sounds like ntc isn't connected the right way(are you sure you connected it to correct pads?) and/or even more possible is that there is a short between ntc +pad and off-time capacitor, which is right next to the ntc +pad.That probably happened during ntc +wire soldering. If this is the case,then off-time cap has ~200kOhm parasitic resistance when cold,which would explain why tap must be pretty fast to change mode;when flashlight gets hot that parasitic resistance drops to ~115kOhm,and explains why you cannot change modes anymore - parasitic resistance causes off-time capacitor to discharge much faster than usual, so driver sees that as turn off.

But since driver and ntc are potted,I'm not sure if it's possible to fix that problem.

It is a good idea to check if everything works OK before permanent seal.

I soldered both ntc and led wires from the spring side so bridging should not have occurred but nothingā€™s certain when I solder. The potting is somewhat removable and not bonded to the pill only the driver so Iā€™ll check that. I presume the cap is between the mcu and gnd at the top of the board in your picture(trace running straight up to board edge right of led-). Thanks for giving me some things to check.

Heat and a fancy UI do not like each other, so it appears again.