5 Watt KL3 mod

I finally suceeded in my mod of a KL3 to a 5Watt LS. I have had no luck in a previous post soliciting if anyone knew anything about the KL3 driver. After several hours of research, I figured out what they are doing (what some call magic). It's fairly straightforward circuit using a buck converter and it appears to be VOLTAGE REGULATED. I need to investigate this further as I still can't identify a SOT-23-5 IC that goes between the sense resistor and the voltage feedback of the buck converter .

Anyways,I lowered the sense resistor value and replaced the emitter with a white 5W LS (The 5W LS's that Arc Flashlights is selling are from a very nice batch of U and V rank flux). The 5W is now biased at about 550mA and Vf=6.23V. Though underdriven at 3.4Watts, it puts out a very impressive flood of light My digital camera is out of service so I can't post any pics right now but I'm working on showing off my handiwork. Wow! This is my first high quality mod and boy was I glad I took the risk in disassemblying the KL3. It suffered very little cosmetic damage through the surgery. This KL3 was begging to be modded to a 5W due to its large mass.

Just thought this might be of interest to any modders out there.

Cheers

Quote from someone here at CPF: I wish I didn't have to go to work tomorrow so I could do more mods, or something to that effect.

You certainly have my interest, though I am hardly a modder.
John

Arc is selling 5 watt LSs?

Yes, Peter made a post in the Arc flashlights section a few days ago. I bought three so far since they are at least U rank though he still has a few V rank flux. As far as I know, Peter handsorted these to eliminate the greenies. The two that I have in lights are very white with a very slight bias towards the blue, very nice for my preference. Go get some of these before they run out. They are not cheap at $45 a pop but where else can you get hand sorted 5W LS's? Arc is doing us modders a big favor IMO by making these available to us. I'm very happy with the results of this mod though I doubt I'll EDC this beast any day soon. I'm hanging on to my Arc LS with the clickie for everyday use.

CM

CM,

That's REAL surgery! Great job! We await pics!

- Don

Wow, I'm honored. McGizmo replies to my KL3 mod post!!

Don, I'll try to get some beamshots as well as shots of the KL3.

CM

The only way i'll buy one is if you mod it for me

^me too

Where shall we erect the mounument your excellancy?

But really you do need some pics, or if possible send a working prototype to the LED Museum so Craig can evaluate it properly, he is most fair and unduly precise.

Sounds like you did a good mod!

Aw shucks. Thanks guys. I know what I did means little unless I can show some evidence so I'm gonna get some pictures and beamshots here soon.

Originally posted by CM:
... After several hours of research, I figured out what they are doing (what some call magic). It's fairly straightforward circuit using a buck converter and it appears to be VOLTAGE REGULATED. I need to investigate this further as I still can't identify a SOT-23-5 IC that goes between the sense resistor and the voltage feedback of the buck converter

.....

Click to expand...

<font size="2" face="Verdana, Arial">Great mod! As far as the circuit - nearly all switch mode controller IC's operate using voltage regulation (as opposed to current regulation). Modders and Mfg'ers here wishing to create a current regulated light take those parts and devise crafty methods to fool the IC's into regulating current. It's tricky to do this and maintain high efficiency since current regulation usually involves a current sense resistor - which must be extremely low in value (ohms) so as not to waste valuable battery power.

If I were to guess at the purpose of the 5 pin SOT-23, I'd say it's a high speed Op-Amp. Given your excellent sleuthing and circuit description - I'll bet I'm right. The Op-Amp is amplifying the voltage developed across the sense resistor to a more appropriate level for the voltage feedback pin of the regulator. The one lousy thing about small SMT parts is the lack of space on the package for a real part number!!

Again - great job, and excellent description....

php_44

I looked at the circuit again last night and determined that it is in fact current regulated. They are sensing the voltage through a small sense resistor, multiplying that and feeding it back into the Vfb input of the switcher. You are absolutely right in that many people use novel schemes to trick the IC into regulating current, that is exactly what the KL3 circuit is doing.

The sense resistor is 0.47ohms which translate to 58mW of wasted power assuming 350mA bias to a 1W LED. You're right about the 5 pin sot-23 also (boy you really know your stuff!!!). What was giving me the fits was the non-standard pinout of the op-amp that Surefire was using--the layout did not correspond to standard SOT-23-5 op amp pinouts. I knew it had to be a non-inverting topology so I kept on looking if the part they're using does indeed exist. I found a Microchip SOT-23-5 that matches what I originally suspected was the op amp so now the problem is completely solved. I finally went to sleep at about 3AM. Whew!!

Thanks for confirming my findings, it always helps to have a second set of (good) eyes.

CM

Hooboy, to me you guys are talking Greek but the results always speak for themselves. CM, you are indeed a Mod God!

Wow@CM - just ordered a KL3 just because of your work

Two questions - what voltage you need to drive the 5W KL3 - 3 cells - I suspect 2 won´t do as the KL3 circuit is only regulating down not up ?

How did you modified the sense resistor - just swapped against another value ?

TIA

Klaus

Klaus,

3 cells are required as the regulator is a buck converter. The sense resistor is originally .47 ohms. I used a 1.2ohm resistor in parallel with that to get the ~550mA LED drive. There is also a 0.1 ohm resistor that senses the input current and if you want to drive the LED full force at 700mA, you need to reduce the 0.1 by an appropriate amount. See the data sheet on the Linear Tech LTC1772 for a complete description of the switcher or if you want, I can calculate a value for you. You can probably reduce the 0.1 to half it's value and be fine though as the ultimate regulation comes from the 0.47ohm sense resistor. Good Luck with the mod. If you get stuck, just ask me and I'll be happy to walk you through It's possible to do this mod with almost no cosmetic damage to the KL3 so take it slow and easy.

Cheers

Was it hard to get the centering of the emitter correct?

-YC

yclo,

I either got very lucky eyeballing the LED centering or it was very easy. The trick is to lay it in there with the thermal goop holding it in place before soldering it in. Hold the KL3 head as far away from you as you can while you guestimate the centering. I picked an imaginary X-Y axis (you can even mark it on the head) and try to hit the bulls eye with the emitter. It wasn't 100% perfect but it was good enough that you can't tell unless you're looking for it. The 5W isn't as sensitive to centering IMO as much as the 1W High Dome is (that's a real PITA to center).

Oh, so you're using the the standard collimator then?

Did I mention that this is one cool mod?

-YC

yclo,

Thanks, everything is stock except the LED and the extra 1.2ohm resistor. If Surefire can get a steady supply of 5W whites, this is a no-brainer for them. The KL3 can handle the power due to its size.

CM