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.
intermittently drop light output and blink on and off.
I think I recall someone here surmising that the bonding had failed due to thermal cycling - each time the bond heats, it disconnects and starts to cool. Something like that could happen to the chip, of course, but my money would be on the bond.
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.
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John Larkin Highland Technology, Inc
lunatic fringe electronics
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.
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Jeff Liebermann jeffl@cruzio.com
150 Felker St #D http://www.LearnByDestroying.com
** The OP is probably correct and I have seen the same symptoms with 3mm red LEDs. Over time, excess DC current damages the LED chips and they intermittently drop light output and blink on and off.
Caused havoc in a Mesa Boogie amplifier when most of the dropping resistors for the 20 odd LED/CdS cell opto-couplers were the wrong value, by a factor of 10, resulting in almost 100mA of drive current.
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.
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.
That's quite possible. I've seen something like that only once, but not at the claimed 0.5 second cycle time. With an old LED, it was like about 5-10 seconds ON and 0.5 seconds OFF. It takes a while for the heat from the LED to cause the wire bond to move, but less time for the leads to conduct the heat away.
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Jeff Liebermann jeffl@cruzio.com
150 Felker St #D http://www.LearnByDestroying.com
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.
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.
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Jeff Liebermann jeffl@cruzio.com
150 Felker St #D http://www.LearnByDestroying.com
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.
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.
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.
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.
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