Replacement LED?

The LED in my flashlight is blinking (2/sec). It?s not the support
circuitry (constant current): the voltage across the LED is constant 4v. I
presume it?s a failure mode of the LED. It happens immediately upon
power-on.
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The form-factor is close to a 5x5mm (h x diam). Standard through-hole leads.
But it?s a pretty high-intensity one. Don?t know what makes it so, but I
classify anything with a yellow square visible in the center as
?high-intensity?. Maybe not technically accurate, but there you are.
What I?ve found so far is either a standard 5mm LED but not very bright, or
SMD types requiring heat sinks.
It?s a great little light, and I?ve not found anything as small,
long-lasting, with single AA that I like as much. And this is a learning
experience, so there?s that.
Any pointers to a suitable replacement LED would be appreciated.
Thanks.
Reply to
DaveC
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So it has a boost SMPS?
Reply to
Bob Engelhardt
That's probably a downconversion phosphor. White LEDs are really blue LEDs with a blob of epoxy on top, loaded with yag powder that converts some of the blue to yellow.
Reply to
John Larkin
I beg to differ with your diagnosis. Unless the LED has magically turned into a thermostat controlled flasher, it's not going to do that. More likely, the LED driver circuit is doing the flashing. Based on zero detail about the actual flashlight, my wild guess(tm) would be the big electrolytic that usually goes across the battery. Broken or badly soldered connections on the driver PCB are also likely.
If it's not too much trouble, could you disclose the maker and model number of your flashlight? Extra credit for providing a link to the manufactures web site or China source link. If there are no numbers or sources, perhaps a photo of the assembled flashlight?
Yep. You're looking at the wrong stuff. Maybe something by Cree: Nope. Ok, I give up. What the photo looks like is a common dome shaped LED (as in the Cree URL above) with a lens over it. I did some Googling looking for the lens and couldn't find it.
I have one that meets your requirements. L3 Illumination L10: Single cell, very bright, tolerably priced, small, adjustable brightness, etc. However, there's a catch. It has 4 brightness levels set by twisting the two sections of the body. No problem except that it makes it a two handed operation. I would have preferred a push button at the back end. I've also measured the brightness (using my highly creative and non-standard procedure) at about 90-110 lumens (varies with temperature).
Again, I don't think it's the LED. The driver board is a more likely culprit. Put it under a magnifier and see if you can find the broken trace. Put a light behind the PCB to make it easier to see the break. If desperate, trace out the schematic and try to identify the LED controller chip. If it uses an MLCC capacitor, use a hot air gun to reflow, not a soldering iron tip.
You might also get some help in CandlePowerForums:
Good luck.
Reply to
Jeff Liebermann
Nebo NU15J:
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I like this model for its good trade-off between brightness and battery life. Might be ?better?, but this fits my needs. (And it ft fits in my pocket along with my micro Swiss army knife...)
No controller chip. Looks like a boost converter (inductor, BJT, schottky diode, ceramic cap).
I scoped the voltage across the LED: it's constant 4v (with a very small--20mv?--rise and fall as it switches on and off). Haven?t yet measured current. Surely if there was a bad solder joint or other failure it would show up here.
Thanks for the referrals of other lights, but I?m not buying a replacement. I?m doing this for fun and to learn.
Cheers.
Reply to
DaveC
Thermostat controlled flasher is probably the exact description. It happens when LEDs are driven straight from batteries too, and is probably the bond wire heating and cooling making intermittent contact at a few Hz.
I have a cheap LED torch which uses nine parallel connected white LEDs running directly from 3 AAs. After a battery replacement, one is out, four flash at different rates, and four are on.
Cheers
Reply to
Syd Rumpo
Desolder the original LED, carefully , as balance of probability it will be fine. Jumper in any old high power LED and see if that flashes too.
Reply to
N_Cook
Circuit:
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which is identical to the application note in the datasheet (scroll down to the ME2108A diagrams):
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(easily translated via Google, but a bit more confusing...)
Measured current at the battery terminals is 275 mA (due to meter insertion loss it?s difficult to get an accurate current reading at the LED?s terminals--the LED dims). Voltage across the LED is a pretty-constant 4v. Estimating the efficiency of the converter at (roughly) 75 percent the LED is using 825 mW.
I guess I?m looking for a 1W replacement?
How?s my math?
Thanks.
Reply to
DaveC
Looks like the flashing LED is a common problem:
Some day, someone will design a flashlight with an automatic PWM light dimmer. Shine the light at something bright, and the flashlight runs at full brightness. Shine it at something in the dark, and it goes to fairly dim.
Yep, that's about it. No controller.
Ok, I'm wrong. The flashing is not caused by the non-existent controller chip.
Like I mumbled previously, see if there's a dome type LED under a plastic lens. You'll probably need to unsolder the LED leads to do this. If they really are two parts, it should be possible to find a replacement LED.
If you can't identify the LED by the power output, try measuring the current drain with a new battery. Multiply the current with your measured 4V, and you should get the power in watts. That should tell you if you should be looking for a 1/2, 1, or 1.5v LED.
Reply to
Jeff Liebermann
Jeff Liebermann sez:
That?s my post on canblepowerforums.com. (c:
lens. You'll probably need to unsolder the LED leads to do this. If they really are two parts, it should be possible to find a replacement LED.
Will do.
You mean 1/2, 1, or 1.5 *watt* LED, yes?
Thanks.
Reply to
DaveC
Oops(tm).
Oops 2.0(tm). I was in a rush to get out of door. Sorry. Also, I just noticed that there is no such thing as an individual 1.5w LED.
Reply to
Jeff Liebermann
Didn't you say it used a *single* 1.5 volt AA cell? I think that would make it 412 milliwatts not counting the conversion efficiency, so more likely a 1/2 watt LED.
Reply to
rickman
I think this is an under-used(?) 1W LED.
unit. That way can dissipate some W.
But that presents its own set of problems. Optics will need to be matched to the new LED.
Hmm...
Reply to
DaveC
On 22 Mar 2016, rickman wrote (in article ):
1.5v boosted to 4v (measured) output from the converter. 275 mA (measured) at the battery terminals. I make that to be 1100 mW. If presume 75 percent efficiency, 825 mW.
No?
Reply to
DaveC
Perhaps I am missing something. The battery terminals will be at the battery voltage, no? So why would you use 4 volts which is at the output? It would be 4 volts times the LED current or the battery voltage times the input current.
Reply to
rickman
Rick
Yikes! Of course you?re right.
Thanks.
Reply to
DaveC
From what small ammount of playing with the voltage converters, they are almost like a transformer in action. If you go to a higher voltage, the low voltage current will be a lot more than is used by the load, and if going to a lower voltage , the current from the battery will be less than the actual current used by the load. That keeps the total power drawn the same minus the efficency of the converter.
Reply to
Ralph Mowery
Sounds about right. If you can light it up, just measure the battery current drain, and calculate or estimate the power dissipation.
If you can remove what I believe to be a lens, I think you'll find that the actual LED is rather conventional and can be found in the Cree catalog. If you sort the above list by power output, there are only 3ea 1w LED's listed. Just find the right die size and good luck soldering the tiny chip. You can also dig throught the current flashlight offerings and see which 1w chips are popular.
Learn by Destroying.... then buy a new flashlight.
Reply to
Jeff Liebermann
On 22 Mar 2016, DaveC wrote (in article):
Just measured working light of same model: using power supply @1.5v (measured at flashlight battery terminals), the current from the ps is 400 mA. Estimating 75 percent efficiency that makes about 450 mW.
So a 1/2W replacement LED might be what I?m looking for.
Thanks.
Reply to
DaveC
[Jeff Lieberman]
I found these:
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Looks good, no?
Reply to
DaveC

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