I didn’t mention this earlier because I wasn’t paying much attention to it, but I had a clamp meter on the emitter lead when I was testing, and it was in the same range current-wise. What I mean to say is when I was increasing the voltage at the power supply (and watching the current drop at the power supply), the emitter current was kind of going the same way (i.e., it wasn’t increasing).
Can you tell which resistors might those be? I’m assuming that that was why you all were asking to pull the toroid, but I’m not sure when I’ll have time to do that, so I don’t mind doing some random resistor shorting in the meantime to see if I can get the current bump :)!!
I always discourage people from shorting resistors. When I say resistor mod, I mean changing resistor values or stacking resistors, not shorting resistors. I understand that other people may have a different perspective and that that’s confusing. Shorting sense resistors on either buck or boost setups normally fries stuff. Only certain specific drivers have extra limits which prevent that.
The sense resistor(s) is under the toroid. I see one right next to the 1165c silkscreen. You’ll definitely need to pull the toroid order to do the mod. Pulling the toroid shouldn’t take you more time than shorting resistors would have? In order to work on the driver more efficiently I’d recommend removing the toroid, attaching LED+ to one leg of the toroid, and attaching the other leg using a short wire of appropriate thickness to BAT+ (or wherever it was connected to start with). This will let you do work without moving the toroid on and off of the driver.
There are other things under the toroid we want to see as well 
As you increased Vin the emitter current was
- Staying constant?
- Dropping?
I’ll let you know tomorrow…
It looks like the emitter current gets to about 1.25-1.3V, then stays pretty much constant as I increase Vin.
Good work. That describes proper behavior for this thing. Next step is to reduce the sense resistance.
Can you explain what you said? Are you saying that because you believe that this is a buck driver at this point, and the behavior I’m seeing matches that of a buck driver?
I’ll take a look at pulling the toroid off this weekend.
Thanks,
Jim
It’s definitely a buck driver. Your earlier description left the possibility of a malfunctioning buck driver. We now know that it’s a properly functioning buck driver.
A “properly functioning, but incorrectly-spec’ed buck driver” (the 3 amp part) :)…
Here’s a link to the resistor mod thread for the other driver. What’s unknown is the resulting emitter current.
Hi,
This’ll be a bit of cross-posting, but I just noticed that the driver in the Cofly KX-T21 is apparently this smaller driver:
Jim
I’m curious about something?
On the other thread about the Cofly light which appears to use the same driver, nofearek9 reported 1.4 amps at the tailcap with 2xLi-ion. So I guess that’d be like 1.4 x 8V = 11.2 watts, right?
On the emitter side, let’s say the Vf was about 4V, so if the power-out was ~11.2 watts, then emitter current should be about 2.8 amps?
But, from the testing I did initially with the bench power supply, even though I didn’t go more than say 5.5V, current at the emitter didn’t increase to that level (seemed to go down instead)?
Shouldn’t I have seen, say, 3 amps at the emitter?
I’ll need to test with the single XM-L again, but this time, bump the Vin to the driver to maybe 8V (yes, I’m willing to lose that emitter)…
EDIT: I just tested again, both with a single XM-L U2 (I think) and a new XM-L2, and am seeing the same behavior I saw before. With Vin up to 8V, the current both at Iin and Iemitter were dropping to about 0.7 - 0.8 amps. I also measured Vemitter (just in case) and was about 3V with the XM-L2 (I didn’t make a note of it for the XM-L, but I think that Vemitter was about the same, i.e., about 3V).
So I’m still puzzled!
I understand this is a buck driver, but where the heck is that power/watts disappearing to? Is the driver soaking up all the extra power/current?
I SHOULD be seeing about 2+ amps Iemitter, correct :(?
EDIT:
Although this is not the right chip, just to get an idea, I found this:
http://andrewpearson.org/?p=643
So, assuming that this driver is using a similar chip, I am guessing that the answer to my question about where the excess power is going is to the sense resistors in the R1/R2 voltage divider (fig. 11 in the above page), and probably the reason I’m seeing lower than 3 amps is that the sense resistors’ values are controlling that.
So that’s why you all are looking for the board without the toroid, to try to figure out which resistors could be/need to be changed to try to bump the driver output current?
Your description of whether emitter current (Iout) stays constant keeps changing! I asked for clarification earlier and you clarified by giving an example where it did not change. 
Iout should stay the same once Vin is above a certain voltage. Your most recent description of Iout dropping shows a problem of some sort.
Let’s really make sure we are on the same page now. Are you saying that Iout stays constant with 2*XM-L but changes with only 1*XM-L?
In the most recent scenario you described [With Vin up to 8V, the current both at Iin and Iemitter were dropping to about 0.7 - 0.8 amps. I also measured Vemitter (just in case) and was about 3V with the XM-L2] all your losses are in the driver.
After your good find in nofearek9’s COFLY KX-T21 review we are left with 2 or 3 possibilities (that I can think of):
- You got a bad batch of HX-1163c drivers, nofearek9 got a good one in the COFLY light.
- The version you got is on the same PCB but uses different components to support higher Vf than the one in the COFLY light. And it’s just a crappy driver after those modifications.
- The version you got is on the same PCB but uses different components to support higher Vf than the one in the COFLY light. And the particular items you got are defective.
Without component values from a working board it’s going to be difficult if #2 or #3 are the case. I could not find specifications for this driver on Lightmalls, they don’t even list that it’s a buck driver, the input range, or anything.
I think your interpretation of where the extra power is going is probably wrong. If the sense resistor(s) was burning off 3.5W you’d know it ;-). One or more things should be getting fairly hot though. Once you move the inductor out of the way we can check.
Basically this board is nothing but a (broken, non-functioning) mystery right now. Werner and I asked to see clear pictures of the board without the inductor because of that. We don’t know the parts in use, their configuration, or anything. I doubt that there is a magic button under there, so there’s only so much good to be had by guessing what we want to see under there… if taking the inductor off and showing pictures on the forum generates results you’ll learn from that! A list of all legible component markings would also be useful - sometimes those chips are very hard to read even in good pictures.
Oops. As a follow up, I took a slightly closer look at the blog post you linked to. Figure 11 is… not relevant. It shows a constant voltage configuration, not a constant current configuration. I’m no guru, but I strongly doubt that the modifications Andrew Pearson suggested to Fig11 work correctly. I would hesitate to use his blog post about a probably failed project as a learning resource. (no offense to AP, I encourage everyone to try and make high current drivers!)
Note that there’s no followup post with a success story. I’d say it’s a safe bet that this project was abandoned because it did not actually function.
Hi,
Sorry, I was running to do some Sunday stuff earlier, and just got back.
Re. the AP page and Fig. 11, I was just pointing to that for some info.
I think that we may be working at different purposes, or maybe more accurately, for the same purposes but doing different things towards that.
What I’m (still) hoping is to get this driver pushing 3 amps to the emitter, if it can do that. I suspect you (all) might also want that.
I’m assuming that the driver should be able to do that (yes, I know what A-S-S-U-M-E stands for), so I keep thinking that I must have something “incorrect”, i.e., maybe a wrong emitter with a wrong Vf, or whatever, so I’ve been doing a lot of switching things around here, using different emitters and number of emitters, different wires, etc.
At the same time, I don’t have (easy) access to what I’d need to pull the coil off the drive… or more precisely, I’m not very good with solder wick or with the solder suckers, so I’ve been putting off doing something that would potententially destroy the driver.
I think I understand the more methodical approach that you and Werner are taking, though, so I’ll give that a try at this point, since I have some time with what’s left of this weekend. I’m actually thinking of just cutting that sucker off of the board, because that’d definitely be the fastest way to get it off. I’ll post back if I can get some pics of the bare toroid-less board.
Later, and thanks,
Jim
No - Wait - Stop - Don’t Cut. …just melt the solder at the joint and pull it loose from the board with needle nose. (just lurking here, waiting to see what this board is doing…)
LowLumen is right. Cutting is fine, but I was not suggesting cutting, sucking, or wicking. There is plenty of slack available to remove one leg of the inductor at a time. Just heat them up and pull them out, one at a time.
I see nothing to indicate that you’ve got anything wrong unless it’s wire placement, and that sounded fine. You’ve already tried several different LED setups and you’ve tried a range of input voltages. Continuing to plug at it in that way is a waste of time IMO.
I don’t know why I missed this, but I found that I can re-position the toroid well enough to get some pics that might be good enough, so I’ll post those in a bit, then, if it’s still not good enough to help, I’ll do what I need to get the darn thing off.
Some new, hopefully better info:
I used some new heavier leads from the driver to the emitter (an XM-L2 on Noctigon) and re-tested and I think that this is the behavior I am seeing (and I tried it several times):
- As I increased Vbat (Vin to the driver) when it gets to somewhere around 4.5 - 5V, the current to the driver (Iin/Ibat) starts dropping, and basically continued to drop as I increased Vbat/Vin.
- I have my clamp meter on the emitter lead, and watched Iemitter more carefully this time (sorry about earlier), and also measured Vemitter. I did these Iemitter and Vemitter measurements at Vbat/Vin at 5V - 9V at 1V increments. For all of these measurements, Vemitter stayed almost exactly 3.00V, and Iemitter stayed at 0.89 - 0.90 amps.
In other words, it looks like above a certain Vbat/Vin:
- Iemitter stays at 0.89 - 0.90 amps and Vemitter stays at 3.00V, but
- As Vbat/Vin increases, Ibat/Iin decreases.
I’ll post the pics that I can get in a bit…