Testing a Cree XHP50.2 J4 3A led

TA, congrats on 8k posts! :partying_face:

LOL, I didn’t even realize I had posted that much.

It seems to be for sale!

Check out this thread for details.

I will have 100pc here in a couple days :slight_smile:

Thanks for the heads up, now to find a 5000k version

For those of you that want some I have the 3 volt XHP50s in stock now.
https://asflashlights.com/home/130-cree-xhp-70-n4-5700k.html

Those are bare LEDs. When I get back on Monday if there are any left I will reflow some to mcpcbs.

Hi All,

I'm new to this forum and to Cree LEDs. I have a project in mind using the XHP50.2, however I can see that I'm at the bottom of a steep learning curve.

I intend powering the 6/12V version from a 3 cell LiPo

a Few questions if I may:

  • I note that people mention reflectors. Were do I find these? I assume that they are a can of worms in their own right.
  • Do you use propriety drivers, or do you manufacture these? i.e. do you use custom driver chips? Can I simply ise a mosFET driven from my processor?
  • I was hoping to find built-in temperature sensors to manage heat - what do you guys do?

I anticipated seeing details of drivers and best practice in the Cree data sheets, but sadly no!

  • Is there a 'must read' resource that you can recommend?

Kind regards

A

Welcome to BLF! :slight_smile:

You are on a flashlight forum, so the solutions that many of us have for driving leds may be a bit different from what you need for your application. The electronics that we use to drive the leds are often small and simple and are low-voltage to have them run from batteries. Also we like to drive leds hard and do not care a lot about led life. Many flashlights do have thermo regulation though, not to keep them longterm happy but to prevent shortterm frying.

That said, we may have some help for you. There is not a short manual here on BLF, but there are some resources for leds and stuff, mainly this one may be of help: LEDs & Other Stuff - (Reference Guide) .

There are a few vendors that sell flashlight related parts, like leds, drivers, reflectors etc. Since you are in the UK, the US sources (mtnelectronics.com, illumn.com, Mouser, Digikey) are often too expensive because of shipping cost, others sources are kaidomain.com, banggood.com, led4power.com.

Nice, I have a few of these on order looks like they will be pretty good with a bit of drive, looking at your chart i may even swap out the Xhp70.2 in the L6 for one of these

Thanks for the quick reply.
That’s quite a reference, I’ll check it out!

Regards
A

I’ve got a question about driving the 6V XHP50.2.

I’m planning to run four 6V XHP50.2 in parallel on a 5050 Q8 MCPCB with a direct drive TA driver. I have read that the XHP50.2 6V is sensitive to overcurrent and gets dark dies fast. To limit the current in direct drive I would not bypass the tail spring, use 22 AWG wire and use only 10 or 20A max discharge cells. They would run on two 26350, 18350 or 26650 batteries in a Haikelite SC04.

I would also cut some traces on the Q8 MCPCB and add some sense resistors. Do you think it is enough if I add one R010 resistor for all four leds or would it be better to have one resistor for each led?

I would use two 5000K 90CRI H2 and two 2700K 90CRI G2. I don’t know if they have a different Vf so maybe I should use one resistor for the 5000K and one for the 2700K? Before I start the build I’m seeking advice from anyone who has experience with the XHP50.2 6V so that my leds will survive and run safely in this flashlight.

My understanding of the XHP50.2 reliability issue is that it is a quality control problem at Cree that affects the quality/strength of the bonding of each die to the package. Then differential thermal expansion cycling during use causes the bond(s) to fail and those dies go dark.

My guess is that, while very high current would probably make it more likely for a bond to fail, the quality of the bonds in the specific batch of LEDs you’re using probably has a larger impact on whether your LED will fail. Maybe (hopefully) this was only a problem in some earlier batches of the XHP50.2. I haven’t heard of any of the 3V XHP50.2s failing. Although those use a slightly different package layout I would think the die bonding process is similar.

So, unfortunately, at this point it seems like a gamble to use these LEDs. Maybe you get some good ones or maybe not. Maybe others have some more recent experience with these LEDs. I would go ahead and use the XHP50.2s. If some of them fail, maybe replace two of them with 2 3V LEDs (like XML2) in series? That will at least give you a little insurance to salvage the light if you get a couple failures.

As far as adding resistance to lower the current, I’m not sure what you should do. With some decent 26650 cells and everything bypassed you should pull around 20-24A (5-6A each LED). With the best high drain 26650s it would be closer to 30A. With 26350 cells you might get more like 12A. Leaving the tailspring unbypassed might not be a good option if it will overheat the spring. Adding one R010 for each LED would be putting the resistors in parallel so it would be like adding only 2.5 mOhms of resistance. Very approximately, adding 40 mOhms of resistance would reduce the current by about 4A for the case of the decent 26650 cells.

XHP50.2 6V can easily handle about 7-8A, as you got four you can say like 30A are fine, to get this much out of any XX350 cells is impossible, 2S/4P 18650 could bee too much
usually even between different bins the voltage difference should not be big, if you got like 20mOhms thats totally fine to balance them out, which could be achieved by one having a longer smaller gauge

Thank you for the explanation, EasyB. I think it was actually one of your builds where you reported 7 XHP50.2 failing one after another. Maybe I will try to add two R082 resistors in parallel to limit the current.

Thank you, Lexel. I will definitely use long and thin wires. Are you sure that the XHP50 can handle 7-8 A without getting dark dies? Is the XHP50 more likely to fail in multiple emitter setups?

I also wanted to build a flashlight with four 26650 in series and 12 XHP50. I planned to use 3V XHP50 5000K but it seems at the moment they are hardly available anywhere. The advantage of 6V XHP50’s is being available in 4000K and high cri.

So if I would use 12 XHP50 6V in direct drive with 4 26650 do you think it would be too much and cause some leds to fail? Of course I would use copper MCPCBs and the emitters in 2S6P configuration.

Problem with parallel LEDs in common are thats possible the current does not split up evenly
XHP50.2 can be likely driven as a single LED with 8A
XHP50 Gen 1 not
parallel with 41mOhms would limit the current a bit and helps even out different LED forward voltages a bit

lets say you target 5A per Emitter one LED has 6.5V the other 6.4V forward voltage
the current would not split up evenly for the XHP50.2 you got about 0.75A difference between both LEDs so 6.5V gets only 4.625A the 6.4V gets 5.375A
so if you plan 12V you are better off pair each series string to get as close together with the other,
as its like a chain the LED with the lowest forward voltage takes most current and if it dies the others get also more current

if you add 50mOhms in front of the LED you limit the current as it needs 0.25V more to get 5A flowing,
but in this case also 1.25W heat are generated on the resistor so you need ones that can handle high power
also if an LED with 0.1V difference wants to draw 0.375A more it lowers it to about 0.3A more, not enough to be seen as a solution

But you can even out strings with different resistor values adjusting them to the same overall forward voltage,
but then you need a bench power supply and open up the strings on the MCPCB and got some work

Easiest way to limit current in a DD light such as this in my experience, is to simply use lower drain cells.

If 30Q’s are too much, generally dropping down to GA’s get me into safe current ranges and is way easier then messing with other options.

If that is not enough, second best option I have found is to simply use longer and/or thinner gauge wire to limit current some. Just don’t go too thin or the wire will melt, you can go longer though.

for a customer I made once a MCPCB with driver circuitry on it
I used 2 0.47 Ohms in parallel for an XPL-Hi that pretty muh nailed the current to 3A tops from two high drain 18650 in parallel

Surprizingly the resistors stayed very very cool, I could have probably gone with lower than 2 0.75W ones
the main criteria limiting them is heat and they are usually rated on x mm² of PCB to dissipate the rated power

in general driving those LEDs close to their physical limits in parallel is not a good idea

Oh yeah, I forgot that mounting the resistors to the mcpcb helps dissipate heat much better than if they were mounted on a driver. Duh.

Actually Ohms law says amps times resistance equals voltage…It is watts law that says volts times amps equals watts. I know it is nit picky, but a guy named Georg Ohm came up with Ohms law, and Watts law is named after James Watt, an inventor. Though similar, it is 2 separate laws.

Fixed. :+1: