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

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led4power
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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&c...

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.

cajampa
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Good job 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 Smile

led4power
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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).


Billy X
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I am going to order a couple of LD2 ‘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 I’d ask Wink

led4power
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No,LD-1 doesn't have hardware or input for ntc resistor.

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

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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 ! Smile

zipelgas
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Hi

Do I understand correctly, that both of these resistors (marked with red arrows in picture) should be 750kOhm for 2S operation?
2j18kqs.jpg

Overkill is just about enough!

cajampa
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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 don’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 don’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.

Rufusbduck
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zipelgas wrote:
Hi

Do I understand correctly, that both of these resistors (marked with red arrows in picture) should be 750kOhm for 2S operation?
2j18kqs.jpg


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

Three Tanna leaves to give him life, nine to give him movement. But what if he eats the whole bag?

Scott

led4power
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cajampa wrote:
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 don'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 don'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 n lookot more.

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.

cajampa
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Nice Smile Thanks

Rufusbduck
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I have the driver set up for 6V with moon parts installed and activated in a heavily modified 502B (extra length for 2× 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 didn’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. It’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?

Three Tanna leaves to give him life, nine to give him movement. But what if he eats the whole bag?

Scott

led4power
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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.Frown

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

 

 

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I soldered both ntc and led wires from the spring side so bridging should not have occurred but nothing’s certain when I solder. The potting is somewhat removable and not bonded to the pill only the driver so I’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.

Three Tanna leaves to give him life, nine to give him movement. But what if he eats the whole bag?

Scott

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

led4power
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Rufusbduck wrote:
I soldered both ntc and led wires from the spring side so bridging should not have occurred but nothing's certain when I solder. The potting is somewhat removable and not bonded to the pill only the driver so I'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.

Well,maybe some solder leaked through the pad hole and cause a short,I'm pretty much 100% sure that there is a short between that pad and off-time cap. Capacitor you're describing is the off-time cap. 

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djozz wrote:

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

I assume you're talking about off-time memory issues on various blf DD/7135 drivers when they got hot,but this doesn't happen with LD-2,and LD-2 runs much hotter than DDs in some cases,becasue it's linear driver.After all,you did a real torture test on LD-2 prototype, in which driver shtuted down due driver overtemp. several times (which means whole driver was hotter than 100C,much hotter and any DD driver could be),and I din't remember you report any off-time memory issues.

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led4power wrote:

djozz wrote:

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

I assume you're talking about off-time memory issues on various blf DD/7135 drivers when they got hot,but this doesn't happen with LD-2,and LD-2 runs much hotter than DDs in some cases,becasue it's linear driver.After all,you did a real torture test on LD-2 prototype, in which driver shtuted down due driver overtemp. several times (which means whole driver was hotter than 100C,much hotter and any DD driver could be),and I din't remember you report any off-time memory issues.

Yes, I was referring to the BLF-A6 driver, and was a bit quick to extend it here, I admit. I now read it might be a soldering problem.

I did have some erratic behaviour on the LD2 prototype (as reported) but that was not UI related, looked like something with the FET, it was not repeated inside a flashlight.

led4power
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djozz wrote:

I did have some erratic behaviour on the LD2 prototype (as reported) but that was not UI related, looked like something with the FET, it was not repeated inside a flashlight.

If I remember correctly, extreme power dissipation (6-7W I think) without cooling was the cause.

Anyway,I'm sure Rufusbduck's problem is ntc-offtime cap short,because symptoms match theory perfectly.

Rufusbduck
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You nailed it. Not a solder short but a single strand of the ntc didn’t go in the hole. You can see it here sticking up from the base of the black wire like the boner that it is. Couldn’t see it with a naked eye. Fixed that and then toasted the op amp trying to test it with a 6V battery and test leads. I’ve got a new op amp on it now and it seems to be behaving but I can’t run it full power for long without the led in the light and that means re potting, re installing, and re crossing my fingers.

Three Tanna leaves to give him life, nine to give him movement. But what if he eats the whole bag?

Scott

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Nice find and fix RBD. Fingers crossed.

 

djozz quotes, "it came with chinese lettering that is chinese to me".

                      "My man mousehole needs one too"

old4570 said "I'm not an expert , so don't suffer from any such technical restrictions".

Old-Lumens. Highly admired and cherished member of Budget Light Forum. 11.5.2011 - 20.12.16. RIP.

 

Rufusbduck
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All 9 of ‘em. Wink I’m lovin/hatin this light more each day. Like bad hair, it grows on you.

Three Tanna leaves to give him life, nine to give him movement. But what if he eats the whole bag?

Scott

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@led4power – Bravo! Those are some excellent deductive reasoning skills. You certainly know your product well.

itsonlyme
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Any idea why the light flashes approx 5 secs after switching on high? It flashes 4 or 5 times then steps down to low.
Xhp70, 6 amps. The other driver worked fine but for the fact I messed up the soldering and it only had one mode so I changed it.

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itsonlyme wrote:
Any idea why the light flashes approx 5 secs after switching on high? It flashes 4 or 5 times then steps down to low. Xhp70, 6 amps. The other driver worked fine but for the fact I messed up the soldering and it only had one mode so I changed it.

I had a similar problem Here

Possibly a short with the NTC
But got it working fine after cleaning each solder joint up

Custom builds | Modifications | Powder Coating 
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Sounds like lvp kicking in. Enough contact to work but drops enough voltage to register too little charge. Could be marginal contact in switch or tube/brass retainer contact. Maybe shim the switch 1/2 mm so it’s retainer makes better contact with the battery tube. Also, 6A is a lot of current and pushes Vf up high so any cell not high drain will both sag quickly and not run long. Even a high drain cell won’t run for long on high either.

Three Tanna leaves to give him life, nine to give him movement. But what if he eats the whole bag?

Scott

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itsonlyme wrote:
Any idea why the light flashes approx 5 secs after switching on high? It flashes 4 or 5 times then steps down to low. Xhp70, 6 amps. The other driver worked fine but for the fact I messed up the soldering and it only had one mode so I changed it.

5 blinks is low voltage warning,stage 1(<3V,or <6V for 2S);that usually means you have bad connection somewhere,ground path is mostly source of problems.

itsonlyme
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It was lvp, thanks for the suggestions guys.
Funny thing is that it was flashing in two modes but the third mode didnt. Then the third mode started flashing also so I thought it was a heat issue.

led4power
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Flashing probably didn't occur in the lowest mode,because voltage drop/sag was lower than on mid/high mode,so driver was at 3+ volts.As battery discharged, voltage dropped low enough,so that LVP activated also on low mode. All this is completely normal behavior.

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