Optimizing 105C driver AMC7135

Never mind

Not the best picture but just add another 7135 chip by stacking on top of another one. These have two added.

Add another battery? It’s a linear driver - it can’t put out more voltage than it takes in.

Is it even possible for an XM-L to only register 3.03Vf at 2.8A? Maybe the emitter isn’t getting 2.8A?

Excuse me if I am off base. I am kind of a newb.

It is possible. 3.35 is “Typical”, but LEDs vary quite a bit from one to another in regards to Vf. I’ve seen them lower than that, in fact.

When driving an LED, you don’t try to maintain a voltage - you maintain a current. Voltage will take care of itself.

Unfortunately, if you don’t have a way to directly measure current at the tailcap, then there is no way to know if your emitter is a low Vf one that is getting 2.8A or if something is wrong (your battery can’t keep up with 2.8A draw, one or more of the AMC7135 chips is non-functional, etc). Measuring emitter voltage doesn’t tell you anything.

PPtk

Welcome to the club, YoSeKi!

If you measure the current and it’s 2.8A, then everything is fine and the LED gets exactly the voltage it wants. 3.03V s not unplausible for a hot XM-L.

If you want to optimize something, try to reduce contact resistance to the battery.

I have used IMR batteries where voltage sag at higher amp draw was an issue.

IMR or A123 cells are great when you need high current. 2.8Amps is hardly high-current for most of today’s cells though… With a 2900mAh cell, that’s not even 1C discharge.

You definitely need to read up on how an LED functions and how OHMS law relates to it. I’m sorry to say, but you don’t understand either of them at all. If your previous driver gave 3.5 or 4 A of current to the LED, then that is what the LED was taking. Period. No other possible scenario. Max suggested current is 3A, that doesn’t mean you couldn’t push 5A through it - it just means you’d be running outside of the specifications.

PPtk

It is due to the current.

LEDs do actually get a lot brighter with more current one member here tested one up to 5 amps and it got brighter with more current. Of course that was direct bonded to copper.

That Is not true, while they are less efficient with higher currents if properly heatsinked they will keep getting brighter until at least 5 amps. Iirc Match was able to get one to reach 1450 lumens which is actually more than Cree says they can.

Yeah scaru, but lets stay within realistic values for regular flashlights. :P

So are you suggesting that 3 amps is the best drive current even for something with a copper heatsink?

No. But there is something inbetween 3A and 5A. Talking about the usual hosts like P60, C8.. I'd say for limited use, 3.5A is the limit. For short "bursts", it might even be close to 4A.. but heat sag occurs rather fast. Most budget lights dont even have proper heatsinking so assuming a well built light with copper heatsink is a little unrealistic. :P

@Silicon: What I'm now telling you might be VERY wrong but it could also be more true than I expect it to be.. anyway, LEDs have a fordward voltage (Vf). They wont light up below that. Voltage determines the maximum current, so an XML wont pull 4A at 2.8V.. it might pull 6A at 4V but it doesnt have to. Thats where the AMC chips come in handy. They limit the current and also burn up some of the voltage but I dont really know if that matters..

You’re right, I don’t understand you. I don’t understand why you keep questioning the answers provided by people who understand the laws of physics. “Hmm, I don’t quite agree with the answers”

The key for an LED is I (Current) - Voltage is completely irrelevant. That is why, if you read the CREE datasheets, they will give you luminous intensity at a given current without even talking about voltage. An LED is an imperfect device - every single one of them is different, and this is why Vf in the datasheet is given as a “Typical” value and a “MAX” value, and they are pretty significantly different. A “MIN” isn’t even defined in the datasheet, because CREE doesn’t consider it a problem (and they’re right) if the Vf is lower than Typical. The “Goal” as you put it has NOTHING to do with 3.35V. With an LED, you either control current or you control voltage - the other value becomes what it needs to be all by itself. AMC7135s regulate current.

If it’s not as bright as your TN12, then any of these is possible:

  • Your TN12 is driven to higher than 3.4A (meaning there is nothing wrong with your driver)
  • Your TN12 has a much higher BIN Emitter than the one you’re working with (U2 compared to T4, for instance) (meaning there is nothing wrong with your driver)
  • Your TN12 has much better heat-sinking than whatever is currently heat-sinking your LED (meaning there is nothing wrong with your driver)
  • Your driver is broken and not actually supplying 3.4A
  • Your power source (battery?) can not provide 3.4A
  • Your power source (battery?) does not provide enough voltage for the LED to operate at 3.4A (measure your battery voltage while it’s running the LED)

If you can’t measure current, then you can not verify if a current regulator is working. To see if a current regulator is putting out its intended current, you’ll have to measure that value.

It depends on the heat-sinking of the LED and the efficiency of the optics. 700 Lumens OTF of an XM-L based flashlight is pretty normal.

Your being a newbie and having a lack of knowledge is no problem - there are lots of us here willing to help. That you continue to ignore the answers provided and replace fact with assumption and ill-knowledge is a bit more frustrating.

PPtk

I have just read some more docs about how do drive a led and I got it now.
Just relax, it is also frustrating for me to get answers like those :expressionless:
Subject is closed :o

“Never Mind” is the new Original Post? I wouldn’t count on getting a lot of help from the people here with that kind of attitude.

E1320, Dr Jones, willie, Vieplis, scaru, NightCrawl, and I all offered you answers, and you still continued to imply that our answers were wrong and that you needed to increase voltage but not current - which is impossible. If you’re uncomfortable being presented with answers that make sense, then I’m sorry about that.

Good luck with your mod.

PPtk

Dr. Jones (or anyone), could you maybe elaborate? I am getting some intermittent “flickering” (funny sounding word lol) with my SE-1 (Balder) and I pulled tail cap & it seems ok. The head is potted so can”t get at that. Bad tail cap switch? Chip? Any ideas? I need to find the prob before the send back window closes. Appreciate any help.

Keith (who don”t like no flickering)